Racemization and resolution in the organic solid state

Wilson, Keith Rainier

doi:10.14288/1.0060105

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Racemization and resolution in the organic solid state Wilson, Keith Rainier 1972

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Title	Racemization and resolution in the organic solid state
Creator	Wilson, Keith Rainier
Publisher	University of British Columbia
Date Issued	1972
Description	Two examples of the simplest type of organic solid-state reaction - the thermal interconversion of optical isomers - have been extensively studied by means of polarimetry, differential scanning calorimetry, and X-ray powder diffraction. The first reaction investigated was the reverse Diels-Alder reaction and recombination of the cyclopentadiene-fumaric acid adduct. Polycrystalline samples of (+)-enantiomer (m.p. 176°) racemize completely in the solid state from 130° to 165°. First-order kinetics (ΔH = 40.0 kcal mole⁻¹, ΔS = 14 cal deg⁻¹mole⁻¹) are strictly obeyed; the racemization rate is insensitive to variations in crystal size and optical purity. The reaction, which is only five times slower than the melt rate extrapolated to these temperatures (for the melt from 176° to 194°, ΔH = 29.7 kcal mole⁻¹, ΔS = -6.9 cal deg⁻¹mole⁻¹) occurs throughout the polycrystalline sample rather than at crystallite boundaries, dislocations, or other preferred sites. Phase studies show that the product separates as a racemic compound (m.p. 186°) which forms a eutectic (at 165°) with the resolved enantiomers. From 165° to 176°, the racemization shows autoacceleration and sigmoid-shaped kinetic curves characteristic of concurrent reactions in the solid and melt phases. The second system studied was that formed between R-(-)- and S-(+)-1,1'-binaphthyl, and surprisingly, resolution, rather than racemization, was observed to occur from 76° to 158°. This unprecedented solid-state resolution is made possible by a solid-solid phase change from a racemic compound (m.p. 145°) to a. eutectic mixture (m.p. 158°) of crystals of pure enantiomers, at temperatures where interconversion occurs in the reactant-product interface. Polycrystalline 1,1’-binaphthyl samples of very low optical activity having the correct phase content (racemate plus crystals of only one enantiomer) for a controlled resolution can be easily and reproducibly prepared. These samples resolve from [α][sub D] = 2° to [α][sub D] = ca. 210° (in either (+) or (-) directions) in less than one hour at 150°. The limit of resolution ([α][sub D] = ±245°) is attained simply by recrystallization of the resolved sample from acetone. The resolution therefore involves the conversion of all of a racemic material to only one enantiomer. Kinetic studies of the solid-state resolution show a smooth development of optical activity with time. A Prout-Tompkins analysis indicates that crystallites of growing enantiomer spread throughout the racemic sample, requiring 62 kcal mole⁻¹ activation energy. Crystallization of completely racemic 1,1'-binaphthyl melt in a closed system gives rise to optical activity. The probability distribution of 200 individual crystallizations is symmetric about [α][sub D] = 0° and proves that optically active samples can be created under absolutely spontaneous conditions (i.e., in the complete absence of external dissymmetric influences).
Genre	Thesis/Dissertation
Type	Text
Language	eng
Date Available	2011-03-29
Provider	Vancouver : University of British Columbia Library
Rights	For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
DOI	10.14288/1.0060105
URI	http://hdl.handle.net/2429/33027
Degree	Doctor of Philosophy - PhD
Program	Chemistry
Affiliation	Science, Faculty of Chemistry, Department of
Degree Grantor	University of British Columbia
Campus	UBCV
Scholarly Level	Graduate
Aggregated Source Repository	DSpace

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RACEMIZATION AND RESOLUTION IN THE ORGANIC SOLID STATE  by  KEITH RAINIER WILSON B.Sc.  ( H o n s . ) , U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1967  A THESIS SUBMITTED^IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n t h e Department of CHEMISTRY  We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e required standard  THE UNIVERSITY OF BRITISH COLUMBIA J a n u a r y , 1972  In presenting  this thesis i n p a r t i a l fulfilment of the requirements for  an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference  and study.  I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may by his representatives.  be granted by the Head of my Department or  It i s understood that copying or publication  of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission.  Department of  CHe^CST^V  The University of B r i t i s h Columbia Vancouver 8, Canada  Date  F£&G.Oflrg.-\  -2,7-.  t^TT^  ii  ABSTRACT Supervisor: Two  Dr.  R.E.  Pincock  examples of the s i m p l e s t  type of o r g a n i c  solid-state reaction  - the t h e r m a l i n t e r c o n v e r s i o n of o p t i c a l i s o m e r s - have been e x t e n s i v e l y s t u d i e d by means of p o l a r i m e t r y , d i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y ,  and  X-ray powder d i f f r a c t i o n . The and  f i r s t r e a c t i o n i n v e s t i g a t e d was  the r e v e r s e D i e l s - A l d e r r e a c t i o n  r e c o m b i n a t i o n of the c y c l o p e n t a d i e n e - f u m a r i c  samples of (+)-enantiomer (m.p. from 130° 14 c a l deg  t o 165°.  176°)  a c i d adduct. P o l y c r y s t a l l i n e  racemize completely  F i r s t - o r d e r k i n e t i c s (AH  "'"mole "*") are s t r i c t l y obeyed;  s i t i v e t o v a r i a t i o n s i n c r y s t a l s i z e and  *  = 40.0  i n the s o l i d  k c a l mole  the r a c e m i z a t i o n optical purity.  -1  , AS  The  reaction, to these  *  AS*  = -6.9  c a l deg  t o 194°,  AH'  -1 = 29.7  k c a l mole  (m.p.  ,  "Snole "*") o c c u r s throughout the p o l y c r y s t a l l i n e sample  r a t h e r than at c r y s t a l l i t e b o u n d a r i e s , d i s l o c a t i o n s , o r o t h e r sites.  =  rate i s insen-  w h i c h i s o n l y f i v e times s l o w e r t h a n the m e l t r a t e e x t r a p o l a t e d  t e m p e r a t u r e s ( f o r t h e m e l t from 176°  +  state  preferred  Phase s t u d i e s show t h a t the p r o d u c t s e p a r a t e s as a r a c e m i c compound 186°)  From 165°  w h i c h forms a e u t e c t i c ( a t 165°) t o 176°,  the r a c e m i z a t i o n  w i t h the r e s o l v e d  shows a u t o a c c e l e r a t i o n and  enantiomers. sigmoid-  shaped k i n e t i c c u r v e s c h a r a c t e r i s t i c of c o n c u r r e n t r e a c t i o n s i n the  solid  and m e l t phases. The  second system s t u d i e d was  1,1'-binaphthyl,  and  t h a t formed between R - ( - ) - and  S-(+)-  s u r p r i s i n g l y , r e s o l u t i o n , r a t h e r than r a c e m i z a t i o n ,  o b s e r v e d t o o c c u r from 76°  t o 158°.  was  This unprecedented s o l i d - s t a t e reso-  l u t i o n i s made p o s s i b l e by a s o l i d - s o l i d phase change from a r a c e m i c compound  iii  (m.p.  145°)  to a. e u t e c t i c m i x t u r e (m.p.  158°)  o f c r y s t a l s o f pure e n a n t i o -  mers, a t t e m p e r a t u r e s where i n t e r c o n v e r s i o n o c c u r s i n the r e a c t a n t - p r o d u c t interface.  P o l y c r y s t a l l i n e 1 , 1 - b i n a p h t h y l samples o f v e r y low o p t i c a l 1  a c t i v i t y h a v i n g t h e c o r r e c t phase c o n t e n t (racemate p l u s c r y s t a l s o f o n l y one enantiomer) f o r a c o n t r o l l e d r e s o l u t i o n can be e a s i l y and prepared.  These samples r e s o l v e from [ c t ]  e i t h e r (+) o r (-)  D  reproducibly  = 2° t o [ a ] = .ca.. 210° ( i n D  d i r e c t i o n s ) i n l e s s t h a n one hour a t 150°.  The l i m i t o f  r e s o l u t i o n ( [ a j ^ = i245°) i s a t t a i n e d s i m p l y by r e c r y s t a l l i z a t i o n o f t h e r e s o l v e d sample from a c e t o n e .  The r e s o l u t i o n t h e r e f o r e i n v o l v e s t h e con-  v e r s i o n o f a l l o f a r a c e m i c m a t e r i a l t o o n l y one e n a n t i o m e r . o f t h e s o l i d - s t a t e r e s o l u t i o n show a smooth development w i t h time.  A Prout-Tompkins  Kinetic  of o p t i c a l  studies  activity  a n a l y s i s i n d i c a t e s t h a t c r y s t a l l i t e s o f growing  enantiomer s p r e a d throughout t h e r a c e m i c sample, r e q u i r i n g 62 k c a l mole activation  1  energy.  C r y s t a l l i z a t i o n o f c o m p l e t e l y r a c e m i c 1 , 1 ' - b i n a p h t h y l melt i n a c l o s e d system g i v e s r i s e t o o p t i c a l a c t i v i t y .  The p r o b a b i l i t y d i s t r i b u t i o n o f  i n d i v i d u a l c r y s t a l l i z a t i o n s i s symmetric about o p t i c a l l y a c t i v e samples  [ct]  D  200  = 0° and p r o v e s t h a t  can be c r e a t e d under a b s o l u t e l y spontaneous  condi-  t i o n s ( i . e . , i n the complete absence o f e x t e r n a l d i s s y m m e t r i c i n f l u e n c e s ) .  iv  TABLE OF CONTENTS  1  Introduction  2  R a c e m i z a t i o n o f (+) - B i c y c l o [ 2.2.1 ]hept-5-ene-trans_-2 ,3d i c a r b o x y l i c A c i d i n t h e L i q u i d and S o l i d S t a t e s  17  2.1  Racemization i n the L i q u i d S t a t e  18  2.2  Racemization i n the S o l i d S t a t e  23  2.3  The Phase Diagram  27  2.4  Mechanism i n t h e S o l i d S t a t e  35  2.5  Conclusion  43  3  R e s o l u t i o n o f Racemic 1 , 1 ' - B i n a p h t h y l i n t h e S o l i d S t a t e  45  3.1  The P r e p a r a t i o n o f 1 , 1 ' - B i n a p h t h y l  46  3.2  D i s c o v e r y o f the S o l i d - S t a t e R e s o l u t i o n  49  3.3  Phase Diagram o f t h e System R- and S - 1 , 1 ' - B i n a p h t h y l  55  3.4  P e r f e c t i o n of the S o l i d - S t a t e R e s o l u t i o n  83  3.5  K i n e t i c Study o f t h e S o l i d - S t a t e R e s o l u t i o n  103  3.6  The Spontaneous G e n e r a t i o n o f O p t i c a l l y 1,1'-Binaphthyl  139  3.7 4  1  Active  Conclusion  147  Experimental  150  Bibliography  172  Appendix A:  The Phase L i m i t o f R e s o l u t i o n  Appendix B:  C a l c u l a t i o n o f AG  178  L~*H as a F u n c t i o n o f Temperature  184  V  LIST OF TABLES  I  II  Ill IV V VI  F i r s t - O r d e r Rate C o n s t a n t s f o r R a c e m i z a t i o n o f (+)-29 i n S o l i d , M e l t , and S o l u t i o n .  20  A c t i v a t i o n P a r a m e t e r s f o r R a c e m i z a t i o n o f (+)-29 i n S o l i d , M e l t , and S o l u t i o n .  21  Summary o f I n i t i a l I n v e s t i g a t i o n s o f t h e Development o f O p t i c a l A c t i v i t y i n Neat, P o l y c r y s t a l l i n e 1,1'-Binaphthyl.  51  Examples o f t h e C y c l i n g o f Racemic 1 , 1 ' - B i n a p h t h y l t o High S p e c i f i c R o t a t i o n s .  54  X-Ray Powder D i f f r a c t i o n P a t t e r n s f o r L o w - M e l t i n g (Racemate) 58 and H i g h - M e l t i n g ( E u t e c t i c ) Forms o f 1 , 1 ' - B i n a p h t h y l . S p e c i f i c R o t a t i o n s o f S i n g l e C r y s t a l s O b t a i n e d from t h e R e c r y s t a l l i z a t i o n o f Racemic 1 , 1 ' - B i n a p h t h y l .  61  VII  E n t h a l p y o f F u s i o n o f t h e H i g h - M e l t i n g Form o f 1,1'Binaphthyl at Various S p e c i f i c R o t a t i o n s .  76  VIII  The Development o f O p t i c a l A c t i v i t y on H e a t i n g P o l y c r y s t a l l i n e , Racemic 1 , 1 ' - B i n a p h t h y l .  85  The Development o f O p t i c a l A c t i v i t y on H e a t i n g P o l y c r y s t a l l i n e , Racemic 1 , 1 ' - B i n a p h t h y l Under a S o l v e n t .  90  The I n f l u e n c e o f Added Seed C r y s t a l s o f O p t i c a l l y A c t i v e 1 , 1 ' - B i n a p h t h y l on t h e S o l i d - S t a t e R e s o l u t i o n o f P o l y c r y s t a l l i n e , Racemic 1 , 1 ' - B i n a p h t h y l .  92  The I n f l u e n c e o f O p t i c a l l y A c t i v e 1 , 1 ' - B i n a p h t h y l Seed C r y s t a l s on t h e R e s o l u t i o n by C r y s t a l l i z a t i o n from a S u p e r c o o l e d , Racemic 1 , 1 ' - B i n a p h t h y l M e l t .  93  IX X  XI  XII XIII XIV XV XVI  F i n a l S p e c i f i c R o t a t i o n s i n the S o l i d - S t a t e R e s o l u t i o n o f 1,1'-Binaphthyl ( K i n e t i c Batches).  109  Low Temperature S o l i d - S t a t e R e s o l u t i o n o f 1 , 1 ' - B i n a p h t h y l . I l l A v r a m i - E r o f e e v Exponents f o r the S o l i d - S t a t e R e s o l u t i o n of 1,1'-Binaphthyl.  131  Prout-Tompkins Rate C o n s t a n t s ( k ) f o r t h e S o l i d - S t a t e Resolution of 1,1'-Binaphthyl.  135  Low Temperature R e c r y s t a l l i z a t i o n o f R- and S-1,1'Binaphthyl.  179  ?  vi  LIST OF TABLES  XVII  (continued)  Heat C a p a c i t i e s a t C o n s t a n t P r e s s u r e f o r L o w - M e l t i n g (Racemate) and H i g h - M e l t i n g ( E u t e c t i c ) Forms o f 1,1'Binaphthyl.  190  vii LIST OF FIGURES  1.  F i r s t - o r d e r k i n e t i c p l o t s f o r r a c e m i z a t i o n o f neat (+)d i a c i d 2_9 i n the m e l t phase.  19  2.  R e l a t i o n of l o g  22  ^ /T) t o r e c i p r o c a l t e m p e r a t u r e f o r  r a c e m i z a t i o n o f (+)-enantiomer 29. i n m e l t , s o l i d , s o l u t i o n ( i n t e t r a l i n ) phases.  and  3.  F i r s t - o r d e r k i n e t i c p l o t s f o r racemization of neat, polyc r y s t a l l i n e (+)-29 i n t h e s o l i d phase.  24  4.  F i r s t - o r d e r k i n e t i c p l o t s f o r r a c e m i z a t i o n of neat, p o l y c r y s t a l l i n e (+)-29 a t 152° i n the s o l i d phase and a t 161° where m e l t solid.  25  5.  K i n e t i c d a t a f o r r a c e m i z a t i o n of n e a t samples o f (+)-29 i n t h e s o l i d (155°), i n t h e b i p h a s e m e l t + s o l i d system (166°), and i n a c o m p l e t e l y m e l t e d system ( a t 176°).  26  6.  D i f f e r e n t i a l s c a n n i n g c a l o r i m e t e r t r a c e s (programming  29  rate:  10 deg min ^) f o r t h e d i a c i d 29_ a t v a r i o u s c o m p o s i t i o n s : (a) 0%, (b) 24.8%, (c) 45.2% and (d) 50% ( - ) - e n a n t i o m e r . 7.  Phase r e l a t i o n s h i p o f m i x t u r e s o f (+)- and (-)-enantiomer o f compound 29_. V e r t i c a l b a r s i n d i c a t e the u n c e r t a i n t i e s i n t r a n s i t i o n t e m p e r a t u r e s ( t a k e n a t the b e g i n n i n g o f d . s . c . endotherms). Undetermined phase b o u n d a r i e s ( d o t t e d l i n e s ) are estimated f o r completeness.  31  8.  (a) Schematic f r e e e n e r g y - c o m p o s i t i o n p l o t i n the phase system (+)- and (-)-29, a t c o n s t a n t p r e s s u r e ( a t m o s p h e r i c ) and t e m p e r a t u r e (150°). The d o t t e d l i n e s show the l o w e s t f r e e energy s u r f a c e s f o r the two-phase r e g i o n s . (b) Schematic f r e e e n e r g y - r e a c t i o n c o o r d i n a t e p l o t f o r the s o l i d - s t a t e r a c e m i z a t i o n of (+)-29 (shown as A ( y ) ) a t 150°.  39  9.  I n f r a r e d spectrum o f 1 , 1 ' - b i n a p h t h y l ( n u j o l m u l l ) . (a) Low-melting form. (b) H i g h - m e l t i n g form.  56  S k e t c h o f the h a b i t o f a s i n g l e c r y s t a l o f pure R- o r S1 , 1 ' - b i n a p h t h y l , showing t h o s e f a c e s w h i c h were apparent under the m i c r o s c o p e , (a) View of a, b, and c f a c e s . (b) View normal t o c f a c e , (c) View normal t o d f a c e .  62  10.  viii  LIST OF FIGURES ( c o n t i n u e d )  11.  Schematic f r e e e n e r g y - t e m p e r a t u r e p l o t s f o r r a c e m i c 1,1'b i n a p h t h y l , showing l o w - m e l t i n g form ( L ) , h i g h - m e l t i n g form (H) and m e l t (M) s u r f a c e s . (a) M o n o t r o p i c r e l a t i o n ship, (b) E n a n t i o t r o p i c r e l a t i o n s h i p . (c) Phase d i a g r a m w h i c h would r e s u l t from the m o n o t r o p i c r e l a t i o n s h i p , (d) Phase diagram w h i c h would r e s u l t from the e n a n t i o tropic relationship.  67  12.  D i f f e r e n t i a l scanning c a l o r i m e t e r traces f o r racemic 1 , 1 ' - b i n a p h t h y l , as a f u n c t i o n o f programming r a t e .  69  (a) 2.5 deg min ^.  (b) 10 deg min  (c) 40 deg min  ^.  13.  Schematic e n t h a l p y - and e n t r o p y - t e m p e r a t u r e p l o t s f o r r a c e m i c 1 , 1 ' - b i n a p h t h y l . (a) O r d e r i n g o f l o w - m e l t i n g form ( L ) , h i g h - m e l t i n g form (H) and m e l t (M) e n t h a l p i e s . (b) O r d e r i n g o f e n t r o p i e s of the same phases.  74  14.  (a) Phase diagram f o r t h e R- and S - l , 1 ' - b i n a p h t h y l system, showing m e t a s t a b l e e x t e n s i o n s ( d o t t e d l i n e s ) of t h e phase boundaries. (b) Schematic f r e e e n e r g y - c o m p o s i t i o n p l o t a t 130°, showing t h e l o w e s t (dashed l i n e ) and the n e x t - l o w e s t ( d o t t e d l i n e s ) f r e e energy s u r f a c e s . (c) As f o r ( b ) , but a t 150°.  80  15.  S p e c i f i c r o t a t i o n as a f u n c t i o n o f t i m e f o r t h e s o l i d s t a t e r e s o l u t i o n o f r a c e m i c 1 , 1 ' - b i n a p h t h y l (L B a t c h ) a t  86 135°.  16.  Schematic phase diagram between r a c e m i c 1 , 1 ' - b i n a p h t h y l and a s o l v e n t w i t h b.p. > 160°. D o t t e d l i n e s a r e metas t a b l e e x t r a p o l a t i o n s o f phase b o u n d a r i e s , and show t h e h i g h e r s o l u b i l i t y o f the l e s s s t a b l e forms.  89  17.  Schematic r e p r e s e n t a t i o n o f t h e t e r n a r y system formed between s o l v e n t , R- and S - l , 1 ' - b i n a p h t h y l . M e t a s t a b l e e x t r a p o l a t i o n s o f phase b o u n d a r i e s ( s o l u b i l i t y c u r v e s ) a r e shown as d o t t e d l i n e s . (a) Temperature: -78°, (b) Temperature: +25°.  102  18.  K i n e t i c d a t a f o r t h e s o l i d - s t a t e r e s o l u t i o n of n e a t , p b l y c r y s t a l l i n e 1 , 1 ' - b i n a p h t h y l , S - l K i n e t i c B a t c h a t 135°. E f f e c t of g r i n d i n g and o f s t o r a g e a t 25° f o r s i x weeks.  104  19.  K i n e t i c d a t a f o r the s o l i d s t a t e r e s o l u t i o n of n e a t , p o l y c r y s t a l l i n e 1 , 1 ' - b i n a p h t h y l , S-2 K i n e t i c B a t c h at 125°. E f f e c t o f s t o r a g e of samples a t 0° f o r f o u r months.  105  ix  LIST OF FIGURES ( c o n t i n u e d )  20.  K i n e t i c d a t a f o r the s o l i d - s t a t e r e s o l u t i o n o f n e a t , p o l y c r y s t a l l i n e 1 , 1 ' - b i n a p h t h y l , S-2 and R - l K i n e t i c B a t c h e s a t 135°.  106  21.  K i n e t i c data f o r the s o l i d - s t a t e r e s o l u t i o n of neat, p o l y c r y s t a l l i n e 1 , 1 ' - b i n a p h t h y l , S-2 and R - l K i n e t i c B a t c h e s a t 115°.  107  22.  K i n e t i c data f o r the s o l i d - s t a t e r e s o l u t i o n of neat, p o l y c r y s t a l l i n e 1 , 1 - b i n a p h t h y l , S-3 K i n e t i c B a t c h a t (a) 135 and (b) 115°.  108.  23.  C a l i b r a t i o n curve f o r q u a n t i t a t i v e powder photography.  by X-ray  121  24.  Development o f s p e c i f i c r o t a t i o n w i t h e x t e n t o f phase t r a n s f o r m a t i o n ( X y ) , S-2 K i n e t i c B a t c h a t 125° ( a f t e r f o u r months' s t o r a g e a t 0°). D i a g o n a l r e p r e s e n t s t h e c o n d i t i o n [a]/[o] = %.  123  25.  Avrami-Erofeev p l o t s f o r the s o l i d - s t a t e r e s o l u t i o n of neat, p o l y c r y s t a l l i n e 1 , 1 ' - b i n a p h t h y l , S - l K i n e t i c B a t c h a t 135° and 105°. The sample s t o r e d s i x weeks a t 25° i s p l o t t e d a g a i n s t l o g ( t i m e , seconds) + 1.  126  26.  Avrami-Erofeev p l o t s f o r the s o l i d - s t a t e r e s o l u t i o n of neat, p o l y c r y s t a l l i n e 1 , 1 ' - b i n a p h t h y l , S-2 K i n e t i c B a t c h a t 135°, 125° ( o r i g i n a l r u n ) , 115°, and 105°.  127  27.  Prout-Tompkins p l o t s f o r t h e s o l i d - s t a t e r e s o l u t i o n o f n e a t , p o l y c r y s t a l l i n e 1 , 1 ' - b i n a p h t h y l , S - l K i n e t i c B a t c h a t 135°. E f f e c t o f g r i n d i n g and of s t o r a g e a t 25° f o r s i x weeks.  128  28.  Prout-Tompkins p l o t s f o r t h e s o l i d - s t a t e r e s o l u t i o n o f n e a t , p o l y c r y s t a l l i n e 1 , 1 ' - b i n a p h t h y l , S-2, S-3 and R - l K i n e t i c Batches a t 115°.  129  29.  R e l a t i o n o f l o g (ky) (from Prout-Tompkins p l o t s ) t o r e c i p r o - 134 c a l temperature f o r the s o l i d - s t a t e r e s o l u t i o n of n e a t , p o l y c r y s t a l l i n e 1,1'-binaphthyl, a l l four k i n e t i c batches. S t r a i g h t l i n e s a r e l e a s t - s q u a r e s f i t s t o d a t a f o r each b a t c h .  30.  P e r c e n t a g e of l , l ' - b i n a p h t h y l samples g i v i n g s p e c i f i c r o t a t i o n s between +240°. The c u r v e shows the G a u s s i a n normal d i s t r i b u t i o n c a l c u l a t e d f o r the mean o f +0.14° and t h e s t a n d a r d d e v i a t i o n o f 86.4°.  1  phase a n a l y s i s  F  141  X  LIST OF FIGURES ( c o n t i n u e d )  31.  R a t i o o f samples h a v i n g p o s i t i v e r o t a t i o n s t o t h e t o t a l number o f samples o f 1 , 1 ' - b i n a p h t h y l c r y s t a l l i z e d a t 150°. The 200 samples a r e t r e a t e d as two s e t s o f 100 each. The c u r v e s a r e c o n f i d e n c e l i m i t s c a l c u l a t e d f o r a 0.99 degree o f c o n f i d e n c e and a p r o b a b i l i t y o f 50% p o s i t i v e and 50% n e g a t i v e f o r each sample.  142  32.  S c h e m a t i c r e p r e s e n t a t i o n o f t h e two p o s s i b l e t e r n a r y systems formed between s o l v e n t , R- and S - 1 , 1 ' - b i n a p h t h y l a t -78°. (a) R- and S-enantiomers form a e u t e c t i c m i x t u r e , (b) R- and S-enantiomers form a racemate. A l t h o u g h (b) i s more s t a b l e , (a) can e x i s t f o r i n d e f i n i t e p e r i o d s o f t i m e at -78°.  181  33.  R e l a t i o n o f t h e f r e e energy d i f f e r e n c e between racemate 187 and r a c e m i c e u t e c t i c forms o f 1 , 1 ' - b i n a p h t h y l t o t e m p e r a t u r e . L H F i r s t a p p r o x i m a t i o n , assuming C^ = 0 (see t e x t ) . L~*ft D o t t e d l i n e s a r e u n c e r t a i n t i e s i n AG^  ^423 ^ ^423' ^ individually. R e l a t i o n o f t h e f r e e energy d i f f e r e n c e between racemate 189 and r a c e m i c e u t e c t i c forms o f 1 , 1 ' - b i n a p h t h y l t o t e m p e r a t u r e . L H Second a p p r o x i m a t i o n , assuming = constant (see t e x t ) . L~*H D o t t e d l i n e s a r e u n c e r t a i n t i e s i n AG^ caused by e r r o r s i n a n  34.  caused by e r r o r s i n  AH^ ^ 423  t a  e n  AsV^?, and C^ - C^, taken 423  p  p  individually.  xi  ACKNOWLEDGEMENT  I remain most g r a t e f u l t o P r o f e s s o r R i c h a r d E. P i n c o c k , who more than any o t h e r p e r s o n was r e s p o n s i b l e f o r t e a c h i n g me t h e methods and meaning o f c h e m i c a l continuous  research.  I v e r y much a p p r e c i a t e h i s g u i d a n c e and  encouragement o v e r t h e p a s t f o u r y e a r s .  I would l i k e t o thank my w i f e f o r h e r l o v e and u n d e r s t a n d i n g , e s p e c i a l l y d u r i n g t h e w r i t i n g o f t h i s t h e s i s , f o r h e r h e l p w i t h some o f the t i n y , t r o u b l e s o m e d e t a i l s d u r i n g i t s p r e p a r a t i o n , and f o r t u r n i n g a deaf e a r t o t h e words emanating from t h e a u t h o r w h i l e bent o v e r t h e typewriter. I would a l s o l i k e t o thank P r o f e s s o r s H a r r i s o n , S t e w a r t , T r o t t e r , B r e e and S c h e f f e r and t h e i r r e s e a r c h groups f o r d i s c u s s i n g s e v e r a l  aspects  o f t h i s p r o j e c t w i t h me, and f o r a l l o w i n g me t h e l i b e r a l use o f t h e i r instruments  and equipment.  Thanks a r e a l s o due t o Mr. F. Slawson and Mr.  G. S n i d e r f o r h e l p w i t h i l l u s t r a t i o n s and t o M i s s D. Johnson f o r p a r t i a l l y typing this  thesis.  I s h o u l d a l s o l i k e t o e x p r e s s my a p p r e c i a t i o n t o t h e H.R.  MacMillan  F a m i l y Fund ( U n i v e r s i t y o f B.C.) f o r a f e l l o w s h i p , and t o t h e N a t i o n a l R e s e a r c h C o u n c i l and t h e Graduate S t u d e n t F e l l o w s h i p Fund f o r f i n a n c i a l assistance.  1  1  INTRODUCTION  Modern knowledge o f the o r g a n i c information  on t h e s t r u c t u r e and p h y s i c a l p r o p e r t i e s o f a g r e a t  of m a t e r i a l s . standing  s o l i d state largely consists of variety  Not n e a r l y so w e l l - d e v e l o p e d , however, i s o u r under-  of chemical r e a c t i v i t y i n organic  which are chemically  unstable  solids.  have been a v o i d e d .  U s u a l l y , systems F o r example,  many o f the t e c h n i q u e s used f o r t h e p h y s i c a l i n v e s t i g a t i o n s o f o r g a n i c s o l i d s - from u l t r a v i o l e t s p e c t r o s c o p y t o s t a b l e c r y s t a l s of high p u r i t y .  causing  - require  Any c h e m i c a l r e a c t i o n c o m p l i c a t e s t h e  i n v e s t i g a t i o n , c a u s i n g measured p r o p e r t i e s eventually  semiconductor physics  t o change w i t h t i m e , and  the breakdown o f c a r e f u l l y grown s i n g l e c r y s t a l s .  Even i n o r g a n i c  c h e m i s t r y , where s o l i d r e a g e n t s a r e e n c o u n t e r e d  d a i l y , the s o l u t i o n phase has been t h e medium p r e f e r r e d  for investigations.  Here, the v i e w i s g e n e r a l l y h e l d t h a t r e a c t i o n s i n o r g a n i c  s o l i d s are  too s l u g g i s h t o be o f s y n t h e t i c u t i l i t y , o r too complex t o be amenable to common p h y s i c a l o r g a n i c  analysis.  There a r e , however, some w e l l - e s t a b l i s h e d areas o f endeavour where the r e a c t i v i t y o f t h e o r g a n i c  s o l i d s t a t e has been o f g r e a t i n t e r e s t .  The d e c o m p o s i t i o n o f s o l i d o r g a n i c to organic  compounds, e s p e c i a l l y those r e l a t e d  e x p l o s i v e s , have u n t i l f a i r l y r e c e n t l y a c c o u n t e d f o r most  of the research  with r e a c t i n g organic  solids.  1  I n s e v e r a l r e v i e w s from  1963-1966, Morawetz  c o n s i d e r e d the r e p o r t e d examples o f r e a c t i o n s i n  o r g a n i c s o l i d s , and drew a t t e n t i o n t o the surge o f i n t e r e s t i n s o l i d s t a t e p o l y m e r i z a t i o n s , now b e i n g w i d e l y e x p l o r e d . One f a s c i n a t i n g a s p e c t o f r e a c t i o n s i n o r g a n i c s o l i d s , w h i c h has r e c e i v e d t h e a t t e n t i o n o f s e v e r a l groups,  i s the p o s s i b i l i t y of s t e r e o -  c h e m i c a l c o n t r o l by the c r y s t a l l a t t i c e .  The v e r y e l e g a n t and d e t a i l e d  3 4 i n v e s t i g a t i o n s o f Schmidt and Cohen ' c r y s t a l l i n e monomers a r e w e l l known.  i n t o the photodimerizations of These w o r k e r s demonstrated how  the g e o m e t r i c a l o r i e n t a t i o n and s p a c i n g o f r e a c t i n g m o l e c u l e s l a t t i c e determines  product stereochemistry.  e x p l a i n s the observed  i n the  Such " t o p o c h e m i c a l  control"  p r o d u c t s i n most p h o t o r e a c t i o n s o f o r g a n i c s o l i d s .  More r e c e n t i n v e s t i g a t i o n s ^ have shown t h a t even some o f the e x c e p t i o n s may s t i l l be s u b j e c t t o c o n t r o l s , b u t o f a d i f f e r e n t n a t u r e .  A case i n  p o i n t i s 9 - c y a n o a n t h r a c e n e w h i c h e x i s t s i n a "head-to-head" arrangement i n the c r y s t a l l a t t i c e , but g i v e s a " h e a d - t o - t a i l " photodimer. apparent  f a i l u r e o f l a t t i c e c o n t r o l was understood  This  w i t h the d i s c o v e r y  of s u i t a b l e d i s l o c a t i o n s i n t h e c r y s t a l a c r o s s w h i c h t h e r e a r e " h e a d - t o - t a i l " p a i r s of molecules. forms t h e observed  stereoisomer.  Reaction across the d i s l o c a t i o n This r e s u l t underscores  then  the i n f l u e n c e  of c r y s t a l l i n e o r d e r , b o t h i n t h e r e g u l a r l a t t i c e and a t some d i s l o c a t i o n s , on t h e c o u r s e o f s o l i d - s t a t e r e a c t i o n s . O t h e r accounts  o f t h e c o n t r o l e x e r c i s e d by the s o l i d s t a t e on  p r o d u c t d i s t r i b u t i o n and s t e r e o c h e m i s t r y have been g i v e n .  Some r e c e n t  r e p o r t s demonstrate t h e wide v a r i e t y o f o r g a n i c r e a c t i o n s w h i c h a r e susceptible to s o l i d - s t a t e p e r t u r b a t i o n . examined the t h e r m a l d e c o m p o s i t i o n epimers 1_ and 2_:  A l l r e d and Smith*' have  o f the h e t e r o - s u b s t i t u t e d norbornene  3  1  3  4  CH„0  T h e r m o l y s i s of the exo epimer 1_ i n t h e gas phase o r p h o t o l y s i s i n s o l u t i o n gave the b i c y c l o p e n t a n e s _3 and 4_, w i t h t h e t r a n s isomer 3^ i n s l i g h t e x c e s s ; however, p h o t o l y s i s of c r y s t a l l i n e 1 produced t o t a l l y the c i s isomer 4_.  almost  Analogous r e a c t i o n s of the endo epimer _2 showed  p r e f e r e n t i a l f o r m a t i o n of h_ i n f l u i d media b u t an e x c e s s o f _3 i n the crystalline state.  T h i s r e v e r s a l o f s t e r e o s p e c i f i c i t y was e x p l a i n e d  by f o r m a t i o n o f a s h o r t - l i v e d d i r a d i c a l w h i c h was  inverted i n f l u i d  media but r e t a i n e d i t s c o n f o r m a t i o n i n the r e s t r i c t e d environment the s o l i d s t a t e .  of  L i k e w i s e , S i t e , ^ i n a s t u d y o f t h e d e c o m p o s i t i o n o f the  q u a t e r n a r y ammonium s a l t 5_ i n the m e l t e d and s o l i d s t a t e s , n o t i c e d t h a t  5  3  4  reaction i n the s o l i d gives a higher than r e a c t i o n i n t h e m e l t .  proportion  of ortho-substitution  A s t r i k i n g i l l u s t r a t i o n of c r y s t a l l a t t i c e  8 c o n t r o l has been g i v e n by P e n z i e n and Schmidt,  who i n v e s t i g a t e d t h e  r e a c t i o n o f bromine v a p o r w i t h s i n g l e c r y s t a l s o f 4 , 4 ' - d i m e t h y l c h a l c o n e ( 6 ) , an a c h i r a l compound w h i c h c r y s t a l l i z e s i n an e n a n t i o m o r p h i c space group.  The r e s u l t i n g d i b r o m i d e was o b t a i n e d  w i t h one e n a n t i o m e r i n  6  excess.  Hence, t h i s p r o c e s s c o n s t i t u t e s an a b s o l u t e  synthesis. develops.  asymmetric  When t h e r e a c t i o n i s performed i n s o l u t i o n , no a c t i v i t y A n o t h e r g a s - s o l i d r e a c t i o n , t h e a i r o x i d a t i o n o f some 9  s t e r o i d s , was r e p o r t e d heating  by B r e n n e r e_t aJL.  R e a c t i o n o c c u r r e d on  o r on i r r a d i a t i o n , b u t depended s t r o n g l y on t h e p o l y m o r p h i c  form o f each compound.  Some s t e r o i d s were v e r y s u s c e p t i b l e t o o x i d a t i o n  i n one c r y s t a l m o d i f i c a t i o n , and t o t a l l y u n r e a c t i v e  i n another.  S o l i d - s t a t e c o n t r o l s have been demonstrated w i t h f r e e r a d i c a l s generated e i t h e r t h e r m a l l y ^ ' ^ materials.  o r under i o n i z i n g r a d i a t i o n ^ i n o r g a n i c  Evidence o f the expected greater  p r e s e n t e d b o t h i n t h e form o f i n c r e a s e d to hydrogen a b s t r a c t i o n o u t s i d e selectivity''"''" i n an o r g a n i c  cage e f f e c t has been  r a t i o s of recombination  the c a g e , ^ and as i n c r e a s e d 1  glass over that i n s o l u t i o n .  r a d i c a l addition polymerizations  reactions  stereo-  In free  i n t h e s o l i d s t a t e , w h i c h have r e c e n t l y  5  been r e v i e w e d ,  the polymer  o f t e n b e a r s some o r i e n t a t i o n a l ( " t o p o t a c t i c " )  r e l a t i o n s h i p t o the monomer l a t t i c e . ^ > ^ c  o f p r o d u c i n g polymer those produced  j_  n  f a c t , the v e r y p r o s p e c t  c h a i n s w h i c h are more r e g u l a r l y o r i e n t e d  than  i n s o l u t i o n has been a major r e a s o n f o r t h e renewed  interest i n reactions i n organic s o l i d s . From r e v i e w i n g the r e p o r t e d examples o f o r g a n i c s o l i d - s t a t e r e a c t i v i t y , i t seems t h a t most are e i t h e r chance o b s e r v a t i o n s o r e l s e d e t a i l e d e x a m i n a t i o n s o f systems w h i c h t e n d to be r a t h e r complex.  If  a good u n d e r s t a n d i n g o f the mechanisms of r e a c t i o n s i n o r g a n i c s o l i d s i s t o be a c h i e v e d , t h e n the v e r y s i m p l e s t of r e a c t i o n s s h o u l d be investigated.  These s h o u l d p r o v i d e i n s i g h t i n t o t h e most  p r o c e s s e s o c c u r r i n g i n the r e a c t i n g o r g a n i c s o l i d .  elementary  In t h i s thesis  the  " s i m p l e r e a c t i o n " w i l l be r e g a r d e d as a t h e r m a l ( o r g a n i c ) s o l i d - s t a t e r e a c t i o n w h i c h always c o n s i s t s o f two components.  The  t y p e s of r e a c t i o n s  t h i s d e f i n i t i o n i n c l u d e s and e x c l u d e s can be c o n s i d e r e d as F i r s t of a l l ,  the o r g a n i c s o l i d - s t a t e r e a c t i o n s w h i c h  proceed under i r r a d i a t i o n o r a r e r a d i a t i o n - i n d u c e d and then t h e r m a l l y are r e l a t i v e l y complex p r o c e s s e s .  follows. either proceed  I n the case of u l t r a v i o l e t  r a d i a t i o n , the e l e c t r o n i c energy l e v e l s of the m o l e c u l a r s o l i d must be t a k e n i n t o a c c o u n t , as w e l l as the mechanism of energy w i t h i n the s o l i d .  transfer  R e l e v a n t t o t h i s i s the d i s c u s s i o n by S a r t i - F a n t o n i  13 1 '  i n c o n n e c t i o n w i t h the p h o t o c h e m i c a l r e a c t i o n s of 9 - s u b s t i t u t e d anthracenes. b r e a k i n g may structure. The  I f i o n i z i n g r a d i a t i o n i s u s e d , r a t h e r i n d i s c r i m i n a n t bond r e s u l t , and t h e r e can be c o n s i d e r a b l e damage to the  crystal  2  d e f i n i t i o n a l s o r e s t r i c t s the p o s s i b l e systems to those o f  6  two components.  T h i s l i m i t a t i o n f o l l o w s from the f a c t t h a t systems  o f t h r e e or more components can p o s s e s s e x c e e d i n g l y complex phase relationships.  The  t a s k of i d e n t i f y i n g the r e a c t i v e phases c o u l d  become v e r y d i f f i c u l t i n such systems.  Therefore, r e a c t i o n s of a simple  compound t o g i v e a t l e a s t two d i f f e r e n t p r o d u c t s decompositions)  (such as  a r e e x c l u d e d , as a r e r e a c t i o n s o f two  m o l e c u l e s t o g i v e one o r s e v e r a l p r o d u c t s .  thermal  ( o r more) d i f f e r e n t  I n t h e l a t t e r c a s e , i f the  two r e a c t a n t s are i n s e p a r a t e phases (two s o l i d s , s o l i d and l i q u i d ,  etc.),  any m e c h a n i s t i c d e s c r i p t i o n must a l s o i n c l u d e the p r o c e s s o f d i f f u s i o n i n s o l i d s i f r e a c t i o n i s to p r o c e e d beyond a monolayer o f p r o d u c t molecules a t the i n t e r f a c e between t h e r e a c t a n t s . The  " s i m p l e r e a c t i o n s " a r e t h e r e f o r e t h o s e w h i c h have o n l y a s i n g l e  r e a c t a n t and a s i n g l e p r o d u c t .  The  r e a c t a n t must be e i t h e r neat  c o n t a i n o n l y the p r o d u c t as an i m p u r i t y .  R e a c t i o n s performed  or  i n inert  s o l i d media ( e . g . g l a s s , h o s t c r y s t a l o r polymer m a t r i x ) a r e n o t " s i m p l e " because the i n e r t medium c o n s t i t u t e s a t h i r d component.  The  "simple  r e a c t i o n " can t h e r e f o r e be r e p r e s e n t e d a s :  A  where n i s a s m a l l i n t e g e r .  **  When n e q u a l s one, the s o l i d r e a c t i o n i s  an i s o m e r i z a t i o n .  When n i s two,  dimer c o n v e r s i o n .  One  isocyanates i n  nB  the r e a c t i o n i s a t h e r m a l monomer-  i l l u s t a t i o n of t h i s i s the d i m e r i z a t i o n o f a r y l  the s o l i d s t a t e . ^  The  r e v e r s e p r o c e s s , the s i m p l e  d e c o m p o s i t i o n of a dimer i n t o i t s monomer f r a g m e n t s , i s e x e m p l i f i e d by the t h e r m a l r e a c t i o n o f 9-cyanoanthracene  14  dimer.  P r o c e s s e s where  7  n i s t h r e e or g r e a t e r a r e found i n the f o r m a t i o n o f o l i g o m e r s , b u t the r e s t r i c t i o n s o f " s i m p l i c i t y " makes examples  rare.  That i s , i f a monomer •>  t r i m e r r e a c t i o n proceeds v i a a dimer w i t h a d i s c r e t e e x i s t e n c e , t h e t o t a l s y s t e m becomes one of t h r e e components. Examples  of t h e r m a l s o l i d - s t a t e i s o m e r i z a t i o n s a r e somewhat more  common t h a n t h o s e o f t h e r m a l monomer-dimer r e a c t i o n s . r e p o r t e d examples  Some o f the  a r e i n need o f more e x p e r i m e n t a l work, b u t a few have  been i n v e s t i g a t e d i n c o n s i d e r a b l e  detail.  There a r e a few i l l u s t r a t i o n s o f t h e r m a l s o l i d - s t a t e  tautomerism.  16 Pope and coworkers  o b s e r v e d t h a t a n t h r o n e (7) r e a d i l y t a u t o m e r i z e s  t o a n t h r a n o l (8) i n the s o l i d - s t a t e from  84° t o 158°.  In fact,  a n t h r a n o l i s e a s i l y p r e p a r e d by h e a t i n g anthrone a t i t s m e l t i n g p o i n t  0  OH  then quenching q u i c k l y t o room t e m p e r a t u r e .  No k i n e t i c s were r u n , but  the h a l f - l i f e a t room t e m p e r a t u r e i n benzene s o l u t i o n i s about 2 h o u r s . The n i t r o s o p h e n o l 9_, w h i c h c r y s t a l l i z e s from benzene i n a "green form", undergoes a s o l i d - s t a t e c o n v e r s i o n a t 129°  t o a " r e d f o r m " (m.p.  154°)  17 w h i c h has been shown by c r y s t a l l o g r a p h i c s t u d i e s monoxime s t r u c t u r e 10.  t o have the o_-quinone  The same t a u t o m e r i s m e x i s t s i n s o l u t i o n , and  b o t h forms have i n t r a m o l e c u l a r hydrogen b o n d i n g .  I f the p a l e y e l l o w  8  10  9  c r y s t a l s o f the d i n i t r o b e n z y l p y r i d i n e  .11 are i r r a d i a t e d w i t h l i g h t o f  o  w a v e l e n g t h 4000 A, deep b l u e c r y s t a l s are produced.  When the p h o t o -  p r o d u c t i s k e p t i n t h e d a r k , t h e r m a l r e c o n v e r s i o n t o L l o c c u r s i n a few  H 11  hours.  12  A c r y s t a l s t r u c t u r e d e t e r m i n a t i o n of 11  t o suggest t a u t o m e r i s n s t r u c t u r e s 1_1 and 12.  l e d S e f f and T r u e b l o o d  ( v i a t h e oxygen of the o - n i t r o group) between Another thermal-photochemical i n t e r c o n v e r s i o n i n 19  the s o l i d s t a t e was photoisomer  r e v e a l e d by a c r y s t a l l o g r a p h i c s t u d y  ( s t r u c t u r e 13) of b i ( a n t h r a c e n e - 9 , 1 0 - d i m e t h y l e n e ) ( 1 4 ) .  The p h o t o i s o m e r  L3, w h i c h c o u l d be produced by s o l i d - s t a t e  of _14_ or s i m p l y by c r y s t a l l i z a t i o n from c h l o r o f o r m i n the undergoes a dark r e c o n v e r s i o n t o i t s v a l e n c e tautomer state.  of the  irradiation light,  14_ i n the s o l i d  9  An i n t e r e s t i n g case o f s t e r e o i s o m e r i s m a t an oxygen-carbon bond due  to hydrogen bonding i n the s o l i d s t a t e was  p u b l i s h e d r e c e n t l y by  20 CurtLn and B y r n .  The  compound d i m e t h y 1 - 3 , 6 - d i c h l o r o - 2 , 5 - d i h y d r o x y -  t e r e p h t h a l a t e e x i s t s i n b o t h a y e l l o w form (m.p. (m.p.  140°)  and a w h i t e  c a . 185°). S t u d i e s w i t h d e u t e r a t e d p h e n o l i c g r o u p s , and  and n u c l e a r q u a d r u p o l e  resonance  infrared  i n v e s t i g a t i o n s are c o n s i s t e n t w i t h  s t r u c t u r e 15a and 15b, r e p r e s e n t i n g the y e l l o w and w h i t e  15a  respectively.  form  forms,  15b  A t h e r m a l s o l i d - s t a t e c o n v e r s i o n from the y e l l o w t o the  w h i t e form o c c u r s at  125°.  A k i n e t i c s t u d y o f the i s o m e r i z a t i o n of s o l i d c i s - a z o b e n z e n e 21 has been performed by Tsuda and K u r a t a n i .  (16)  The c i s - t r a n s c o n v e r s i o n  10  was  i n v e s t i g a t e d i n samples w h i c h were powdered and compressed  i n KBr  N=N^  N=N 16  discs.  The r e a c t i o n o c c u r s i n the s o l i d s t a t e , g i v i n g r i s e t o s i g m o i d - ,  shaped k i n e t i c c u r v e s , w h i c h were s e n s i t i v e t o the method o f sample p r e p a r a t i o n , a n d the e x t e n t of g r i n d i n g . One  case o f a s o l i d - s t a t e r e a c t i o n between c o n f o r m a t i o n a l i s o m e r s 22  has been r e p o r t e d .  S e v e r a l y e a r s ago Brown and S u j i s h i  what they p o s t u l a t e d as t h e c o n v e r s i o n on  observed  h e a t i n g o f an u n s y m m e t r i c a l  isomer 17a t o a s y m m e t r i c a l i s o m e r 17b o f a t r i - a - n a p h t h y l adduct.  The s o l i d - s t a t e c o n v e r s i o n was  borine-ammonia  d i s c o v e r e d by n o t i n g t h a t the  140°C  • NH,  NH,  17a  17b  p r e s s u r e of d i s s o c i a t e d ammonia was q u i t e d i f f e r e n t f o r each m a t e r i a l , and t h a t the h i g h l y  d i s s o c i a t e d adduct c o n v e r t e d t o the more s t a b l e  adduct on h e a t i n g t o  140°.  Some i l l u s t r a t i o n s of t h e r m a l i s o m e r i z a t i o n v i a group m i g r a t i o n s i n the s o l i d s t a t e e x i s t .  Almost twenty y e a r s ago, S l u y t e r m a n and  23 coworkers  examined the t h e r m a l r e a c t i o n s o f t e t r a g l y d n e m e t h y l  e s t e r (18) i n the s o l i d s t a t e .  H e a t i n g n e a t 1_8 a t 100°  produced  sarcosyl  11  H.N-CH.-C-(-N-CH.-C-)--OCH 2 2 |f | 2 || 3 O H 0  triglycine  +  *• CH -NH -CH -C-(-N-CH -C).-0 3 2 2 || , 2 || 3 O H 0 0  0  ( 1 9 ) , t h e r e s u l t of a m e t h y l m i g r a t i o n , w h i c h i s perhaps  most f e a s i b l y e x p l a i n e d by an i n t e r m o l e c u l a r s h i f t from t h e e s t e r end o f one m o l e c u l e  t o t h e amino end o f a n e i g h b o u r .  A t h i g h e r tempera-  t u r e s (185°) and i n s o l u t i o n a t 100° p o l y c o n d e n s a t i o n reaction.  i s t h e main  A k i n e t i c r u n a t 100° showed S-shaped c h a r a c t e r ; t h e  i n d u c t i o n p e r i o d was s h o r t e n e d somewhat by g r i n d i n g t h e sample. A n o t h e r rearrangement i n t h e s o l i d s t a t e has been s t u d i e d i n d e t a i l 24 25 by C u r t i n and c o l l a b o r a t o r s .  '  Two d i f f e r e n t  arylazotribenzoylmethanes,  20 and 2 1 , undergo m i g r a t i o n o f a b e n z o y l group b o t h t o oxygen ( f o r m i n g the e n o l benzoate 22) and t o n i t r o g e n ( f o r m i n g t h e hydrazone 2 3 ) .  The  0  22 N=N  20  X = H  21  X = Br  0 II  (C H C-) C=N-N  0 23  study was backed by an x-ray c r y s t a l s t r u c t u r e a n a l y s i s o f the bromod e r i v a t i v e 21_, by d i f f e r e n t i a l t h e r m a l a n a l y s i s , and by o b s e r v a t i o n o f  12  the r e a c t i o n b o t h i n s i n g l e c r y s t a l s on a m i c r o s c o p e h o t s t a g e and i n a p o l y c r y s t a l l i n e sample by powder d i f f r a c t o m e t r y .  F o r example, when  20 i s h e a t e d a t 5°/min, m e l t i n g o c c u r s a t c a . 124°, i m m e d i a t e l y by rearrangement accompanied  and i s f o l l o w e d  t o an e q u i m o l a r m i x t u r e o f 22_ and  by the e v o l u t i o n o f h e a t .  23,  F u r t h e r h e a t i n g converts the  i s o m e r 22_ t o 23_ o v e r a temperature range of 40°, and f i n a l l y the pure hydrazone m e l t s a t 200°.  E x a m i n a t i o n o f m i x t u r e s o f the t h r e e  compounds 20_, 2_2_ and 2_3 s u g g e s t e d a e u t e c t i c t e m p e r a t u r e above The r e a c t i o n proceeds i n the s o l i d s t a t e i n the temperature 70-105°.  110°.  range  A l t h o u g h t h e system i s v a s t l y s i m p l e r t h a n most d e c o m p o s i t i o n s ,  i t u n f o r t u n a t e l y i n v o l v e s t h r e e components, and a more d e t a i l e d d e s c r i p t i o n o f phase r e a c t i v i t i e s and r e l a t i o n s h i p s would be  rather  difficult. 26 An i n i t i a l r e p o r t by L e f f l e r  of the s o l i d - s t a t e  isomerization  of 2 , 2 ' - d i i o d o d i b e n z o y l p e r o x i d e (24) has r e c e i v e d f u r t h e r a t t e n t i o n  0  0  from a c r y s t a l l o g r a p h i c s t a n d p o i n t by Gougoutas.  The r e a c t i o n o c c u r s  i n s e v e r a l weeks i n t h e c r y s t a l l i n e s t a t e a t room t e m p e r a t u r e , and o v e r n i g h t a t 110°.  The p r o d u c t b e n z i o d o x o l e 25_ produced  i n single  c r y s t a l s of _24 i s r e m a r k a b l y w e l l - o r d e r e d and b e a r s a t o p o t a c t i c r e l a t i o n s h i p to the r e a c t a n t l a t t i c e .  T h i s g e o m e t r i c a l correspondence  13  suggests that h a l f of the phenyl r i n g s f l i p  through 180° d u r i n g  reaction,  a m o l e c u l a r movement w h i c h i s s u r p r i s i n g l y l a r g e i n terms o f t h e s p a c i n g allowed  i n the l a t t i c e .  A study of the r e l a t e d peroxides  X = hydrogen, 2-bromo, 2 - c h l o r o ,  2_6^ where  2 - f l u o r o , 3 - c h l o r o and 4 - n i t r o showed  0—0  26  2 7b  28  that a l l react i n the s o l i d s t a t e ,  and some  single c r y s t a l topotactic transformations  undergo s i n g l e c r y s t a l -  s i m i l a r to the diiodo  compound 24. 29-33 Some s i m p l e  i s o m e r i z a t i o n s , w h i c h o c c u r e a s i l y on m e l t i n g ,  may a l s o p r o c e e d i n t h e s o l i d s t a t e . t h e s e systems below  R e i n v e s t i g a t i o n of reactions i n  the m e l t i n g p o i n t s concerned may r e v e a l some  unusual s o l i d - s t a t e behaviour. I n t e r e s t i n c h e m i c a l r e a c t i o n s i n o r g a n i c s o l i d s began i n t h i s 34 35 l a b o r a t o r y w i t h t h e work o f P i n c o c k and K i o v s k y frozen solutions.  I t was d i s c o v e r e d  occurring i n organic  '  on r e a c t i o n s i n  t h a t common c h e m i c a l r e a c t i o n s  and aqueous s o l v e n t s showed s u r p r i s i n g f e a t u r e s  below t h e f r e e z i n g p o i n t o f t h e s o l v e n t .  A detailed kinetic  proved t h a t these observed changes i n k i n e t i c o r d e r and l a r g e a c c e l e r a t i o n s c o u l d be c o m p l e t e l y concentration  study rate  accounted f o r s i m p l y by t h e i n c r e a s e d  of reactants i n l i q u i d regions  I t was u n n e c e s s a r y t o i n v o k e any n o v e l  of the frozen  solid-state effects.  solvent. These  14  l i q u i d r e g i o n s n e c e s s a r i l y e x i s t above the e u t e c t i c t e m p e r a t u r e of s o l v e n t - s o l u t e phase system.  I t was  t h e r e f o r e emphasized t h a t i n a l l  r a t e s t u d i e s i n f r o z e n s y s t e m s , even those as f a r as 70° m e l t i n g p o i n t s c o n c e r n e d , any q u a n t i t a t i v e l y separated  the  below the  r e a c t i o n i n a l i q u i d phase must be  out b e f o r e v a l i d c o n c l u s i o n s  regarding  solid-  s t a t e phenomena can be drawn. A l o g i c a l e x t e n s i o n of the i d e a s d e v e l o p e d d u r i n g the work on r e a c t i o n s i n f r o z e n , i n e r t s o l v e n t s was  to consider  p o i n t thermal r e a c t i o n i n a neat s o l i d r e a c t a n t . product w i l l  above the e u t e c t i c of the system. o n l y two  In general  l o w e r the m e l t i n g p o i n t of the r e a c t a n t , and  p o t e n t i a l l y o c c u r i n b o t h the s o l i d and  has  from a k i n e t i c  stand-  the  r e a c t i o n can  the l i q u i d phases a t t e m p e r a t u r e s  I f the system i s " s i m p l e " , i . e . ,  components, the i m p o r t a n t  phase r e l a t i o n s h i p s may  be  easy  to e s t a b l i s h . For t h i s r e a s o n ,  the f i r s t  system s t u d i e d was 3A  r o t a t i o n of p o l y c r y s t a l l i n e a - D - g l u c o s e .  the t h e r m a l  muta-  36 Isothermal  kinetic  runs below the m e l t i n g p o i n t of pure a-D-glucose (146°) p o s s e s s e d  an  S-shaped c h a r a c t e r .  sample,  R e a c t i o n began s l o w l y i n the i n i t i a l l y s o l i d  but as the p r o d u c t g-D-glucose d e v e l o p e d , the r e a c t i o n a c c e l e r a t e d the sample began to m e l t ; maximum r a t e was whereafter nature  o b s e r v e d on complete m e l t i n g ,  the r a t e d e c r e a s e d as e q u i l i b r i u m was  approached.  of the k i n e t i c c u r v e s c o u l d be e x p l a i n e d by n e g l e c t i n g  r e a c t i o n i n the s o l i d phase, and l i q u i d phase.  The  and  c o n s i d e r i n g o n l y t h a t i n the  The  sigmoid  any developing  r e a c t i o n a c c e l e r a t e s because the r e a c t i n g l i q u i d  phase i n c r e a s e s i n volume a t the expense o f the u n r e a c t i v e s o l i d phase. 37 A second s t u d y ,  t h a t of the t h e r m a l  endo- and e x o - 5 - n o r b o r n e n e - 2 , 3 - d i c a r b o x y l i c  i s o m e r i z a t i o n of p o l y c r y s t a l l i n e a n h y d r i d e s (27 and  28,  15  r e s p e c t i v e l y ) above and below t h e i r m e l t i n g p o i n t s , demonstrated the  27 (m.p.  164°)  28 (m.p.  143°)  type o f k i n e t i c s w h i c h can a r i s e from r e a c t i o n o c c u r r i n g s i m u l t a n e o u s l y i n b o t h s o l i d and l i q u i d phases.  C h e m i c a l e q u i l i b r i u m i n the two-  component systems o c c u r s a t an e q u i m o l a r m i x t u r e o f i s o m e r s , and can be approached from e i t h e r s i d e .  S o l i d endo i s o m e r , h e a t e d a t 120-164°,  e v e n t u a l l y m e l t e d , b u t u n l i k e a - D - g l u c o s e , the form o f the k i n e t i c c u r v e s was not s i g m o i d , but f i r s t o r d e r . if  That i s , r e a c t i o n o c c u r r e d as  the system were t o t a l l y m e l t e d , even though the s o l i d phase  present.  Phase s t u d i e s showed t h a t s o l i d endo i s o m e r was  was  a "crystalline  37 liquid"  above 94°, and t h a t m o l e c u l e s i n t h i s phase p o s s e s s e d  m o b i l i t y and c o u l d i s o m e r i z e e q u a l l y as f a s t as t h o s e i n the l i q u i d phase.  S o l i d exo a n h y d r i d e c o u l d n o t i s o m e r i z e as r e a d i l y as t h e  endo a d d u c t , and t h i s f a c t was curves.  r e f l e c t e d i n the shape o f the k i n e t i c  Rate e q u a t i o n s f o r b o t h r e a c t i o n s were d e v e l o p e d by  t h a t the r e a c t i o n i n the s o l i d phase i s f i r s t o r d e r .  assuming  The r a t e e q u a t i o n  c o u l d be i n t e g r a t e d , and by a s s i g n i n g d i f f e r e n t v a l u e s t o the s o l i d s t a t e r a t e c o n s t a n t , t h e form of b o t h the endo and exo k i n e t i c c u r v e s c o u l d be g e n e r a t e d .  A s e p a r a t i o n of the k i n e t i c c o n t r i b u t i o n s of  b o t h s o l i d and m e l t phase r e a c t i o n s was In v i e w of the f a c i l i t y  therefore accomplished.  w i t h w h i c h r e a c t i o n proceeds i n s o l i d endo  16  and exo a n h y d r i d e s , we d e c i d e d t o examine the p o s s i b i l i t y o f s o l i d - s t a t e r a c e m i z a t i o n i n two o p t i c a l l y a c t i v e systems. Diels-Alder  b i n a p h t h y l (30).  The  second was  S i n c e the two  a  enantiomers,  a simple hydrocarbon,  (+)-l,l'-  components i n each o f t h e s e systems are  29  30  the phase r e l a t i o n s h i p s are s i m p l i f i e d .  s t a t e r e a c t i o n , i f i t occurs at a l l ,  The  f i r s t , also  a d d u c t , was ( + ) - b i c y c l o [ 2 . 2 . l ] h e p t - 5 - e n e - t r a n s - 2 , 3 -  d i c a r b o x y l i c a c i d (29).  hopefully,  The  Any  true s o l i d -  s h o u l d be e a s i l y r e c o g n i z e d  and,  examined more c l o s e l y .  r e s u l t s o f our s t u d y o f the c y c l o p e n t a d i e n e - f u m a r i c a c i d  adduct (29) a r e p r e s e n t e d i n S e c t i o n 2 o f the t h e s i s . (and unexpected i n S e c t i o n 3.  Our  f i n d i n g s ! ) w i t h the 1 , 1 ' - b i n a p h t h y l system  investigations are r e p o r t e d  17  2  RACEMIZATION  OF  (+)-BICYCLO[2.2.1]HEPT-5-ENE-TRANS-2,3-DICARBOXYLIC 38  ACID (29) IN THE LIQUID AND SOLID STATES T h i s m o l e c u l e , w h i c h owes i t s dissymmetry t o two c h i r a l carbon atoms, can c o n c e i v a b l y i n t e r c o n v e r t w i t h i t s enantiomer i n t h e m e l t and i n s o l u t i o n , and p o s s i b l y a l s o i n t h e s o l i d C  °2  H  A  state.  C0 H 2  C0 H 2  29, (+)-enantiomer (m.p. 176°), ( i ) - r a c e m a t e  The r a c e m i c compound 29_ was p r e p a r e d  (m.p.  186°)  3.  from t h e addends ( c y c l o 39 p e n t a d i e n e and f u m a r i c a c i d ) u s i n g the method o f Koch. Resolution 40 t o t h e (+)-enantiomer was e f f e c t e d v i a t h e b r u c i n e s a l t , m u l t i p l e r e c r y s t a l l i z a t i o n s from a c e t o n e - w a t e r .  using  The p u r i f i e d (+)-  d i a c i d 29, was more h i g h l y r e s o l v e d ( d i f f e r e n t p r e p a r a t i o n s gave 26 s p e c i f i c r o t a t i o n s o f [ c t ] ^ = +137° and +147° i n acetone) and p o s s e s s e d 40 a h i g h e r m e l t i n g p o i n t (177-179°) than t h a t o r i g i n a l l y  reported  on ( [ a ] p = +89°, m.p. 166-168°). A l t h o u g h the o p t i c a l p u r i t y o f the The p r e p a r a t i o n and t h e r e s o l u t i o n o f ( + ) - d i a c i d _29 was p e r f o r m e d r e s oi ln v et dh i sd i al ca ibdo r remains t h eb ek fi on re et i cthe r e work s u l t s r pe rp eo sr etnetde di nbelow a t o r y by unknown, M.M. Tong, this t h e s i s was begun. 3.  18  d i d not depend, even i n the s o l i d s t a t e , on the e x t e n t of r e s o l u t i o n .  2.1  R a c e m i z a t i o n i n the L i q u i d S t a t e  2.1.1  The  M e l t Phase  K i n e t i c runs i n the m e l t phase were p e r f o r m e d from 176- 194°. method i n v o l v e d h e a t i n g i n d i v i d u a l s e a l e d ampules c o n t a i n i n g C+)-29 i n a c o n s t a n t occurred, was  temperature bath.  and a l t h o u g h  t h e r e was  not s i g n i f i c a n t b e f o r e  The  purified  R a c e m i z a t i o n to [ c t j ^ =  0°  a s l i g h t y e l l o w i n g of s a m p l e s , t h i s  the m a t e r i a l was  essentially  racemic.  P r o d u c t s t u d i e s showed t h a t a t l o n g r e a c t i o n times ( g r e a t e r than 15 h a l f - l i v e s ) , some p o l y m e r i z a t i o n o c c u r r e d , but was  the i n i t i a l  reaction  s i m p l y an i n t e r c o n v e r s i o n of e n a n t i o m e r s . When the r e s u l t s were p l o t t e d as f i r s t - o r d e r r e a c t i o n s ( l o g [a] / [CX]Q b  v s . t i m e ) , s t r a i g h t l i n e s were o b t a i n e d  t o o v e r 90% r e a c t i o n ( F i g u r e 1 ) .  The  are l i s t e d i n T a b l e  observed f i r s t - o r d e r r a t e constants  H a l f - l i v e s f o r r a c e m i z a t i o n v a r i e d from 3 min 176°.  The  a t 194°  I.  t o 12 min  at  ease o f r e a c t i o n a t the m e l t i n g p o i n t of (+)-29 s u g g e s t s  t h a t any s o l i d - s t a t e r e a c t i o n , even i f s l o w e r by one  or two  orders  of  magnitude, might s t i l l be m e a s u r a b l e . 2.1.2  The The  S o l u t i o n Phase  racemization  of (+)-29 was  also studied i n t e t r a l i n s o l u t i o n ,  a t t e m p e r a t u r e s where the pure d i a c i d 2_9_ would be s o l i d Again,  f i r s t - o r d e r p l o t s were s t r a i g h t l i n e s , and  constants k  (131-152°).  the o b s e r v e d r a t e  are shown i n T a b l e I.  A l l of our s p e c i f i c r o t a t i o n s [a] were measured at the sodium D The s u b s c r i p t D w i l l h e r e a f t e r be o m i t t e d f o r s i m p l i c i t y .  line.  19  TIME MINUTES  F i g u r e 1.  F i r s t - o r d e r k i n e t i c p l o t s f o r r a c e m i z a t i o n o f neat  29 i n t h e m e l t phase.  (+)-diacid  20  Table I First-Order  Rate C o n s t a n t s f o r R a c e m i z a t i o n o f (+)-29 i n S o l i d , M e l t and  Temperature, °C  k  obs  Solution  Phase  x 10"*, s e c ^  194.3  380  melt  189.1  248  II  181.8  147  II  176.6  103  II  melt + s o l i d  166.2  8.3  161.2  7.09  155.4  4.23  solid  152.4  2.76  II  140.2  0.654  II  130.9  0.227  II  152.4  6.98  143.7  2.93  II  131.3  0.834  II  a  ti  II  a  solution  I n i t i a l rate constant.  The a c t i v a t i o n parameters  f o r r a c e m i z a t i o n i n t h e m e l t and i n  s o l u t i o n were o b t a i n e d from a p l o t o f l o g k ^ /T by t h e E y r i n g e q u a t i o n :  v s  *  1/1  a s  required  21  where K and h a r e Boltzmann's and P l a n c k ' s c o n s t a n t s , r e s p e c t i v e l y , t T i s the a b s o l u t e t e m p e r a t u r e , and AS enthalpy of a c t i v a t i o n .  f and AH  a r e the e n t r o p y and  The f r e e energy o f a c t i v a t i o n , AG^,  i s obtained  from the r e l a t i o n : [2]  AG*  =  AH*  -  TAS*  and the temperature chosen f o r comparison of the r e a c t i o n i n d i f f e r e n t phases was  150°.  The r e s u l t s a r e l i s t e d i n T a b l e I I and p l o t t e d i n  F i g u r e 2.  The r a t e i n t e t r a l i n s o l u t i o n i s seen t o be some 2.0-2.5 t i m e s  Table I I A c t i v a t i o n Parameters f o r R a c e m i z a t i o n o f (+)-29 i n S o l i d , M e l t , and Solution  k  (150°),  Q b g  sec  1  AG*  (150°),  k c a l mole  melt  11.3 x I O  - 5  solid  2.05 x 1 0  - 5  solution  5.14  x 10~  5  a  32.6  1  AH*  AS*  k c a l mole  1  c a l mole "'"deg  29.7  -6.9  34.0  40.0  +14  33.2  33.6  1  +0.8  E x t r a p o l a t e d from the t e m p e r a t u r e range 176-194'  s l o w e r than t h a t i n the m e l t ( e x t r a p o l a t e d ) .  This small difference i s  r e f l e c t e d i n a m a r g i n a l l y h i g h e r f r e e energy o f a c t i v a t i o n i n t e t r a l i n solution.  Such a s m a l l s o l v e n t e f f e c t i s t y p i c a l o f r e v e r s e D i e l s - A l d e r  I90°  180°  170°  2.20  160° 2.30  150° i  I40 •  c  ~2AO  '/ xlCT T  F i g u r e 2.  R e l a t i o n of l o g  ^ /T)  t o  r e c i p r o c a l temperature f o  r a c e m i z a t i o n of (+)-enantiomer 2_9_ i n m e l t , s o l i d , and s o l u t i o n (in tetralin)  phases.  23  r e a c t i o n s and r e c o m b i n a t i o n s .  A l s o , t h e magnitude o f t h e a b s o l u t e  r a t e c o n s t a n t s i n b o t h l i q u i d media i s c l o s e t o t h a t o f s i m i l a r nD i e l1 s - AA lU d e r  2.2  reactions.  Racemization The  4  2  »  4  reverse  3  i n the S o l i d  State  r a c e m i z a t i o n o f t h e ( + ) - d i a c i d .29 was e x p l o r e d below i t s  m e l t i n g p o i n t (176°).  P o l y c r y s t a l l i n e samples o f r e s o l v e d 29 were  s e a l e d i n ampules and h e l d a t v a r i o u s t e m p e r a t u r e s below 176°. I t was found t h a t r a c e m i z a t i o n c o u l d i n d e e d o c c u r as low as 130°. M o r e o v e r , t h e k i n e t i c form o f t h e r e a c t i o n from 130° t o 155° was first-order.  P l o t s o f l o g [ a ] / [ a ] Q v s . time were a g a i n l i n e a r t o a t  l e a s t 90% r a c e m i z a t i o n ( s e e F i g u r e s 3 and 4 ) .  There were no i n h i b i t i o n  p e r i o d s as have been v i r t u a l l y always o b s e r v e d  for solid-state  1 organic  44a and i n o r g a n i c  decompositions.  The k i n e t i c r e s u l t s were i n -  s e n s i t i v e t o g r i n d i n g , d i f f e r e n t b a t c h p r e p a r a t i o n s o r sample h i s t o r y . A l s o absent was any dependence on t h e e x t e n t o f r e s o l u t i o n o f t h e samples. The k i n e t i c s i m p l i c i t y o f the r e a c t i o n from 130° t o 155° p e r m i t t e d treatment  o f t h e observed  rate constants  ( T a b l e I ) i n t h e same manner  as those f o r r e a c t i o n i n t h e m e l t and i n s o l u t i o n .  The p l o t o f l o g  k ^ /T a g a i n s t r e c i p r o c a l t e m p e r a t u r e i s shown i n F i g u r e 2.  Activation  parameters (Table I I ) were o b t a i n e d from t h e r e s u l t i n g s t r a i g h t The  r a t e c o n s t a n t a t 150° i s seen t o be o n l y about 5 times  line.  smaller  than t h a t o b t a i n e d from the m e l t e x t r a p o l a t e d t o 150°. I n the t e m p e r a t u r e range 161°to 166°, a d e p a r t u r e f i r s t - o r d e r k i n e t i c s was observed  ( F i g u r e s 4 and 5 ) .  from  simple  A sigmoid  shape  24  1  2000  1  4000  I  6000  i  8000  I IO.OOO i  TIME MINUTES  F i g u r e 3.  F i r s t - o r d e r k i n e t i c p l o t s f o r racemization of neat, poly-  crystalline  (+)-29 i n the s o l i d phase.  25  <  O  '  200  1  400  1  600  i  800  i  i  IOOO  1200  i  1400  TIME MINUTES  F i g u r e 4.  F i r s t - o r d e r k i n e t i c p l o t s f o r racemization of neat, p o l y -  crystalline  (+)-2_9 a t 152° i n t h e s o l i d phase and a t 161° where  melt „ * i s o l i d .  26  20  40  60  80  IOO  120  TIME M I N U T E S  F i g u r e 5. the  solid  K i n e t i c d a t a f o r r a c e m i z a t i o n o f neat samples o f (+)-29 i n (155°), i n t h e b i p h a s e m e l t + s o l i d system (166°), and i n a  c o m p l e t e l y m e l t e d system ( a t 176°) .  27  was  q u i t e e v i d e n t i n the f r a c t i o n u n r a c e m i z e d v s . time p l o t s a t t h e s e  two t e m p e r a t u r e s ( F i g u r e 5 a t 166°). linearity  ( F i g . 4 a t 161°).  The l o g p l o t s d e v i a t e d from  Rate c o n s t a n t s w e r e , however, o b t a i n e d  from the i n i t i a l s l o p e s of the l o g p l o t s ( T a b l e I ) f o r comparison t o the o b s e r v e d f i r s t - o r d e r c o n s t a n t s from l o w e r t e m p e r a t u r e r u n s . S i g n i f i c a n t y e l l o w i n g o f the samples o c c u r r e d , much more r a p i d l y t h a n w i t h the m e l t r e a c t i o n a t t e m p e r a t u r e s as h i g h as 194°.  Some  sintering indicated p a r t i a l melting.  2.3  The Phase  2.3.1  Diagram  The D e t e r m i n a t i o n of the Phase  Diagram  I n o r d e r t o i n t e r p r e t c o r r e c t l y the k i n e t i c r e s u l t s below the m e l t i n g p o i n t , i t was n e c e s s a r y t o a s c e r t a i n the t e m p e r a t u r e below w h i c h the system of e n a n t i o m e r s i s t o t a l l y s o l i d . b i n a r y phase diagram was  To t h i s end, the  determined using d i f f e r e n t i a l scanning  c a l o r i m e t r y and X-ray powder d i f f r a c t i o n . I n g e n e r a l t h e r e a r e o n l y t h r e e t y p e s of b i n a r y phase  diagrams  45a 46 formed between e n a n t i o m e r s .  '  These a r e the s i m p l e e u t e c t i c , the  f o r m a t i o n of a "phase r u l e " compound, and f o r m a t i o n of a s o l i d at a l l compositions.  solution  I n the s i m p l e e u t e c t i c the c r y s t a l form of one  enantiomer does not accommodate the o t h e r  and the r a c e m i c m o d i f i c a t i o n  i s a two-phase m i x t u r e o f i n d i v i d u a l c r y s t a l s o f pure e n a n t i o m e r s . The "phase r u l e " compound d i a g r a m i s s i m i l a r i n t h a t c r y s t a l l i n e  forms  a r e i m m i s c i b l e , b u t the r a c e m i c m o d i f i c a t i o n i s a s i n g l e phase ( t h e racemate) c o n t a i n i n g b o t h e n a n t i o m e r s i n a 1:1 r a t i o . c e x c e p t a t t h e extreme edges of the diagram.  I n the s o l i d  28  s o l u t i o n t y p e of d i a g r a m , t h e c r y s t a l l a t t i c e o f one e n a n t i o m e r can c o n t a i n t h e o t h e r i n a l l p r o p o r t i o n s , and a s i n g l e s o l i d phase e x i s t s at a l l c o m p o s i t i o n s . The  s i n g l e o b s e r v a t i o n t h a t t h e r a c e m i c d i a c i d 29_ m e l t s h i g h e r  than  the r e s o l v e d m a t e r i a l i m m e d i a t e l y r e s t r i c t s t h e c h o i c e s o f diagrams t o two:  (a) f o r m a t i o n  o f a phase r u l e compound o r (b) f o r m a t i o n  of a  s o l i d s o l u t i o n m e l t i n g h i g h e r when r a c e m i c than when r e s o l v e d . The  c h o i c e between t h e s e two i s e a s i l y made w i t h t h e d i f f e r e n t i a l  47 scanning and  c a l o r i m e t e r ( d . s . c ) . The method  i s a n o n e q u i l i b r i u m one,  can be used t o measure phase changes w h i c h a r e r a p i d , s u c h as  melting or fast s o l i d - s o l i d transitions.  The p r o c e d u r e i n v o l v e s  h e a t i n g a s m a l l amount o f sample i n a pan and an empty r e f e r e n c e pan at a constant  rate.  Any energy r e l e a s e o r a b s o r p t i o n i n the sample i s  compensated by t h e c a l o r i m e t e r so t h a t t h e a r e a o f t h e r e c o r d e d i s d i r e c t l y p r o p o r t i o n a l to the enthalpy  of the t r a n s i t i o n .  peak  Transition  t e m p e r a t u r e s a r e e a s i l y d e t e r m i n e d once t h e d . s . c . i s c a l i b r a t e d . Samples o f t h e d i a c i d 29_ r a n g i n g  i n s p e c i f i c r o t a t i o n from +137°  t o 0° were h e a t e d on t h e d s . c .  and t h e t e m p e r a t u r e s and e n t h a l p i e s  of t r a n s i t i o n were d e t e r m i n e d .  Some r e p r e s e n t a t i v e d.s.c. t r a c e s a r e  shown i n F i g u r e 6.  The r e s o l v e d and r a c e m i c d i a c i d 29_ gave no peaks  from room temperature up t o t h e r e s p e c t i v e m e l t i n g p o i n t s  (176°  and 186°) , where sharp endotherms were r e c o r d e d . The e n t h a l p i e s o f fusion (AH ) were 5.38+ 0.16 k c a l m o l e " (29.5 ± 0.9 c a l g ) fusion 1  _ 1  J  f o r t h e (+) e n a n t i o m e r 29_ and 7.13 ± 0.24 k c a l m o l e " f o r the racemic m a t e r i a l . calculated  from:  The c o r r e s p o n d i n g  1  (39 ± 1 . 3 c a l g  e n t r o p i e s o f f u s i o n were  _ 1  )  29  F i g u r e 6. 10 deg min (b) 24.8%,  D i f f e r e n t i a l scanning f o r the d i a c i d (c) 45.2%, and  c a l o r i m e t e r t r a c e s (programming  2_9_ a t v a r i o u s c o m p o s i t i o n s : (d) 50%  (-)-enantiomer.  (a) 0%,  rate:  30  AS.  [3]  .  fusion  AH. ^  =  . U S 1  °  n  T m.p.  w h i c h h o l d s o n l y a t t h e m e l t i n g p o i n t where t h e f r e e e n e r g i e s o f s o l i d and m e l t a r e i d e n t i c a l .  The AS,, . f o r the r e s o l v e d d i a c i d 29 was fusion —  12.0 ± 0.3 c a l deg "'"mole "*" and f o r t h e r a c e m i c d i a c i d , 15.5 ± 0.5 c a l deg "'"mole  \  Samples i n t e r m e d i a t e i n a c t i v i t y , however, gave a s i n g l e at 165°, sometimes f o l l o w e d by a second endotherm temperatures.  The endotherm  endotherm  at s l i g h t l y higher  a t 165° i n samples h a v i n g a range o f  compositions s t r o n g l y i m p l i e s that t h i s i s a e u t e c t i c temperature. endotherm  The  i s l a r g e s t f o r a sample h a v i n g a s p e c i f i c r o t a t i o n o f +68°.  These o b s e r v a t i o n s a r e t h o s e e x p e c t e d f o r a phase system w i t h r a c e m i c compound f o r m a t i o n . A e u t e c t i c p o i n t ( t e m p e r a t u r e : 165°, c o m p o s i t i o n : h a l f r e s o l v e d ) e x i s t s between t h e r e s o l v e d and r a c e m i c d i a c i d 29. The t e m p e r a t u r e s a t w h i c h t h e d.s.c. peaks appeared a r e p l o t t e d i n F i g u r e 7.  The appearance o f a second endotherm 48 49a  c o n s i s t e n t w i t h t h e phase system.  '  f o r some samples i s  At appropriate compositions,  t h e s e samples w i l l p a r t l y m e l t a t t h e i n v a r i a n t e u t e c t i c t e m p e r a t u r e , then f i n i s h m e l t i n g o v e r a range o f t e m p e r a t u r e s from t h e e u t e c t i c t o the l i q u i d u s c u r v e .  The appearance o f a second peak i n d i c a t e s the  maximum r a t e o f t h i s s e c o n d a r y m e l t i n g .  The p o i n t a t w h i c h t h e  second peak r e t u r n s t o t h e base l i n e i s sometimes t a k e n as t h e p o s i t i o n 48 of the l i q u i d u s c u r v e ,  b u t i n o u r samples t h e m e l t was t o o v o l a t i l e  to a l l o w a p r e c i s e d e t e r m i n a t i o n o f t h i s p o i n t . l i q u i d u s c u r v e s have been  For completeness, the  s k e t c h e d i n t h e phase diagram  (dotted  lines)  31  \  180  MELT  \  \  PHASE  1 / /  170  \ \ \ \  /  PHASE  /  \  * / \ /  1  V—1^-  u o  MELT  x  /  /\ ''  w  ai  160  SOLID SOLUTION (y) PHASE  H  RACEMATE  PHASE  150  140 j  I  J  20  L  _L  _L  J  40  60  80  L  100  PERCENTAGE (-)-ENANTIOMER Figure 7.  Phase relationship of mixtures of (+)- and (-)-enantiomers of  compound 29_.  V e r t i c a l bars indicate the uncertainties  in transition  temperatures (taken at the beginning of d.s.c. endotherms).  Undetermined  phase boundaries (dotted lines) are estimated f o r completeness.  A l s o drawn i n i s a t e r m i n a l s o l i d s o l u t i o n , y> w h i c h must e x i s t , but may  have a c o m p o s i t i o n range w h i c h i s s m a l l and d i f f i c u l t  determine w i t h the d.s.c.  '  to  The second h a l f o f the diagram ( ( - ) - s i d e )  i s a m i r r o r image of the (+) s i d e , and i s shown i n F i g u r e 7 f o r completeness.  The  (-)-enantiomer 29 was not  isolated.  The d . s . c . r e s u l t s were v e r i f i e d by X-ray powder p h o t o g r a p h y . Photographs o f the r e s o l v e d a c i d were d i f f e r e n t from those o f the racemate.  A sample w h i c h had been h a l f r a c e m i z e d showed b o t h s e t s o f  c h a r a c t e r i s t i c d i f f r a c t i o n r i n g s , and no o t h e r s . two s o l i d phases a t t h i s c o m p o s i t i o n .  No  There a r e t h e r e f o r e  metastable intermediate  phases a r e formed d u r i n g the r e a c t i o n .  2.3.2  The I d e n t i f i c a t i o n and S t a b i l i t y o f R e a c t i v e Knowing the phase diagram ( F i g u r e 7 ) , we a r e now  the phases i n w h i c h r a c e m i z a t i o n o c c u r s .  From 130°  Phases able to consider  t o 155°,  s o l i d phases a r e i n v o l v e d i n the f i r s t - o r d e r r e a c t i o n . p r o c e e d s , an u n r e a c t i v e racemate s e p a r a t e s  only  As r a c e m i z a t i o n  from t h e r e a c t i v e s o l i d  (+)-enantiomer. Between the e u t e c t i c t e m p e r a t u r e and the m e l t i n g p o i n t s c o n c e r n e d , the m e l t and s o l i d c o e x i s t , and r e a c t i o n o c c u r s s i m u l t a n e o u s l y i n b o t h phases.  S o l i d samples w i l l  t u r e s i n t h i s range.  e v e n t u a l l y m e l t when h e l d a t  As r a c e m i z a t i o n p r o c e e d s , the l i q u i d  tempera-  phase 37  grows i n volume a t t h e expense of the s o l i d phase.  I t can be shown  t h a t a f i r s t o r d e r r e a c t i o n i n a d i s a p p e a r i n g s o l i d phase  combined  w i t h a f a s t e r r e a c t i o n i n a g r o w i n g m e l t e d phase, w i l l g i v e r i s e t o  33  an S-shaped k i n e t i c c u r v e . and 166°  ( F i g u r e 4,5).  Such c u r v e s a r e o b s e r v e d i n runs a t  The i n d i v i d u a l c o n t r i b u t i o n s of s o l i d  161°  and  37 m e l t e d phase r e a c t i o n s can, i n p r i n c i p l e , be s e p a r a t e d .  However,  i n t h i s case the a v a i l a b i l i t y o f k i n e t i c d a t a a t t e m p e r a t u r e s where the system i s t o t a l l y m e l t e d o r t o t a l l y s o l i d makes such a s e p a r a t i o n unnecessary. Our use o f the phase diagram to c h a r t the c o u r s e of a c h e m i c a l r e a c t i o n s h o u l d perhaps be e x p l a i n e d more f u l l y .  The meaning o f  such a diagram i s not e n t i r e l y c l e a r from the d i s c u s s i o n t h i s f a r , s i n c e the phases d e s c r i b e d a r e n o t i n c h e m i c a l e q u i l i b r i u m . Systems of d y n a m i c a l l y i n t e r c o n v e r t i n g i s o m e r s such as t h e e n a n t i o m e r i c d i a c i d s 29_ a r e t r e a t e d i n s t a n d a r d t e x t s on phase e q u i l i b r i a as " p s e u d o b i n a r y s y s t e m s " . ' T h i s  term means t h a t s t r i c t l y  under  e q u i l i b r i u m c o n d i t i o n s , the system would behave as a s i n g l e component. However, under n o n e q u i l i b r i u m c o n d i t i o n s ( s u c h as w i t h a d.s.c.) i t i s p o s s i b l e t o d e t e r m i n e a b i n a r y phase diagram.  The n e c e s s a r y c o n d i t i o n  h e r e i s t h a t the c o m p o s i t i o n o f t h e sample s h o u l d n o t change d u r i n g the time t a k e n f o r the e x p e r i m e n t .  I n t h i s c a s e , a t the  u s u a l d.s.c. h e a t i n g r a t e s (10°/min), the m e l t i n g r e g i o n i s c o v e r e d i n l e s s than two m i n u t e s , d u r i n g w h i c h time v e r y l i t t l e r a c e m i z a t i o n occurs (Figure 5). The methods f o r d e t e r m i n i n g such " n o n e q u i l i b r i u m " phase  diagrams  52 seem w e l l u n d e r s t o o d , but the meaning of such diagrams becomes c l e a r e r from the p o i n t of v i e w of free energy. Consider f i r s t of a l l a A l t h o u g h 161 i s below the b i n a r y e u t e c t i c , the r e l a t i v e l y r a p i d d a r k e n i n g o f samples i n d i c a t e s t h a t o t h e r components are formed. These can l o w e r the b i n a r y e u t e c t i c temperature,53 c a u s i n g the appearance o f a l i q u i d phase.  34  two-component system o f i s o m e r s , w i t h no p o s s i b l e i s o m e r i z a t i o n At c o n s t a n t p r e s s u r e , o f t e m p e r a t u r e and  the f r e e energy of each phase w i l l be a  composition.  temperature - c o m p o s i t i o n - f r e e  reaction.  function  A t h r e e - d i m e n s i o n a l p l o t of  energy w i l l t h e r e f o r e  i n d i v i d u a l f r e e energy s u r f a c e s  - one  consist  of  f o r each phase - suspended o v e r  the t e m p e r a t u r e - c o m p o s i t i o n p l a n e ( i . e . the phase d i a g r a m ) .  The  stable  phase ( o r phases) a t each p o i n t on the d i a g r a m i s d e t e r m i n e d by l o w e s t f r e e energy s u r f a c e point.  the  ( o r c o m b i n a t i o n of s u r f a c e s ) - ^ ' ^ above t h a t  Hence the e q u i l i b r i u m phase diagram i s g e n e r a t e d .  If  the  phases a t e v e r y p o i n t are always the most s t a b l e ones ( i . e . a l l phase changes a r e r a p i d ) , then a l l p o i n t s on the phase d i a g r a m are  attainable  experimentally. Now  l e t us a l l o w f o r the i n t e r c o n v e r s i o n  of components.  Even  though the phases are r e a c t i v e , a l l w i l l have i n d i v i d u a l f r e e energy surfaces  as b e f o r e .  It s t i l l ,  t h e r e f o r e , makes sense t o speak of  the l o w e s t - l y i n g f r e e energy s u r f a c e s , but t h e s e d e t e r m i n e i s not  the phase diagram w h i c h  an e q u i l i b r i u m d i a g r a m .  For example,  the  e melting  p o i n t o f a pure isomer  can be d e f i n e d  as the t e m p e r a t u r e a t  w h i c h the f r e e e n e r g i e s o f the pure s o l i d and pure l i q u i d i s o m e r e q u a l , but such a p o i n t i s not i t s f r e e energy f u r t h e r by  i n equilibrium.  system can  changing i t s c o m p o s i t i o n u n t i l  chemical e q u i l i b r i u m i s reached. t e m p e r a t u r e and  The  are  lower  final  I f the phases e x i s t i n g a t  any  c o m p o s i t i o n are always those h a v i n g the l o w e s t f r e e  e n e r g i e s at t h a t p o i n t , then the phase changes are f a s t .  The  diagram  can then be d e t e r m i n e d e x p e r i m e n t a l l y , p r o v i d e d the i s o m e r i z a t i o n r e a c t i o n Such a p o i n t has been c a l l e d an " i d e a l c o n s t a n t " and the p s e u d o b i n a r y system has been r e f e r r e d t o as a system i n " f a l s e e q u i l i b r i u m " 4 5 b b t. the r e l a t i o n s h i p to f r e e energy s u r f a c e s , a l t h o u g h i m p l i e d , s h o u l d be e x p l i c i t l y s t a t e d .  e  u  35  i s s u f f i c i e n t l y slow.  I f the r e a c t i o n i s t o o f a s t , some p o i n t s , such  as t h e pure isomer m e l t i n g p o i n t s , may be i m p o s s i b l e t o a t t a i n (see S e c t i o n 3.3.2.1). I n t h i s manner, by assuming t h a t phase changes a r e more r a p i d t h a n t h e i s o m e r i z a t i o n , t h e course o f a r e a c t i o n may be mapped on a phase diagram.  F o r example, when a r e a c t i o n i s " p a s s i n g t h r o u g h "  two-phase s o l i d + m e l t r e g i o n a t c o n s t a n t the c o m p o s i t i o n  to our treatment  2.4  t e m p e r a t u r e and p r e s s u r e ,  o f t h e s o l i d and m e l t phases w i l l be c o n s t a n t  to t h e s o l i d u s and l i q u i d u s c o m p o s i t i o n s .  a  and e q u a l  Such an approach i s b a s i c  of r e a c t i o n s i n n e a t o r g a n i c m a t e r i a l s .  Mechanism i n t h e S o l i d  State  I n v i e w of t h e many c o m p l e x i t i e s a s s o c i a t e d w i t h r e a c t i o n s i n f the s o l i d s t a t e surprising.  the k i n e t i c s i m p l i c i t y o f t h i s r a c e m i z a t i o n i s  Reactions  i n o r g a n i c s o l i d s commonly show i n d u c t i o n  p e r i o d s , a u t o c a t a l y t i c e f f e c t s , " ^ o r a dependence on a g i n g and on particle size."^  A l l o f these f e a t u r e s are conspicuously  absent  below t h e e u t e c t i c of t h e system o f e n a n t i o m e r s w h i c h we have s t u d i e d . The  f i r s t - o r d e r k i n e t i c s mean t h a t t h e r a t e - d e t e r m i n i n g  step i n  the s o l i d - s t a t e r a c e m i z a t i o n can o c c u r w i t h e q u a l p r o b a b i l i t y a t any p o i n t i n the p o l y c r y s t a l l i n e s o l i d .  That i s , t h e l o c a t i o n o f t h e  d i a c i d m o l e c u l e s 2_9_ (whether they a r e a t t h e edges o f c r y s t a l l i t e s , a t defects o r d i s l o c a t i o n s , o r deeply  imbedded i n a r e g i o n o f p e r f e c t l a t t i c e )  makes no d i f f e r e n c e t o t h e i r r e a c t i v i t y . Consistent w i t h t h i s i s the ^ A c o l l e c t i o n of papers d e a l i n g g e n e r a l l y w i t h r e a c t i o n s i n s o l i d s may be found i n the p u b l i s h e d symposia on t h e R e a c t i v i t y o f S o l i d s .  36  o b s e r v a t i o n t h a t g r i n d i n g o r use o f d i f f e r e n t b a t c h p r e p a r a t i o n s no e f f e c t on the k i n e t i c r e s u l t s .  has  I n t h e s e d i f f e r e n t samples t h e r e  w i l l be a w i d e l y d i f f e r e n t p o l y c r y s t a l l i n e g r a i n s i z e and d e f e c t o r d i s l o c a t i o n d e n s i t y i n the r e a c t a n t . The  r e a c t i o n i s a l s o not c a t a l y z e d by the p r e s e n c e of the  ( r a c e m i c compound).  As the p r o d u c t  phase grows, the  i n t e r f a c e w i l l i n c r e a s e , pass through reactant disappears. product  at due  reactant-product  a maximum, then d e c r e a s e as  I n some o r g a n i c d e c o m p o s i t i o n s t h e  s u r f a c e causes a c c e l e r a t i o n o f the r e a c t i o n and  of sigmoid-shaped k i n e t i c curves.  product  the  developing  the  production  I n our s y s t e m , maximum r a t e o c c u r s  the b e g i n n i n g of the s o l i d r e a c t i o n .  Such a r a t e maximum i s not  t o a v e r y s h o r t a c c e l e r a t i o n p e r i o d and the p r e s e n c e o f  product  phase, because X - r a y r e s u l t s c l e a r l y show o n l y the pure e n a n t i o m e r at  the s t a r t o f the r e a c t i o n . T h e r e f o r e , the n e c e s s i t y o f h a v i n g t o grow a p r o d u c t  a r e a c t a n t cannot c o n t r o l the r a c e m i z a t i o n r e a c t i o n .  The  phase from change o f  phase a s s o c i a t e d w i t h the r e a c t i o n must be f a s t compared t o the r a t e g determining  step.  C o n s i d e r a t i o n w i l l now step.  be g i v e n t o the n a t u r e o f the  rate-determining  I n the m e l t , the r a c e m i z a t i o n w i l l c o n s i s t o f a r e v e r s i b l e  first-order reaction: o  °  There i s one s p e c i a l i z e d case of f i r s t - o r d e r k i n e t i c s i n a r e a c t i o n c o n t r o l l e d by a phase change. Some i n o r g a n i c d e c o m p o s i t i o n s show f i r s t - o r d e r b e h a v i o u r because of a v e r y f i n e p a r t i c l e s i z e . 5 8 However, the s o l i d - s t a t e r e a c t i o n o f the d i a c i d 2_9_ i s independent of the s t a t e of s u b d i v i s i o n of the s o l i d , so t h a t our o b s e r v e d f i r s t o r d e r k i n e t i c s are not due to t h i s e f f e c t .  37  k  A (melt)  l  „  B (melt) k  2  where A and B a r e the e n a n t i o m e r i c adducts proceeds  29_-  to 0° s p e c i f i c r o t a t i o n , k^ = k^.  S i n c e the r a c e m i z a t i o n  The o b s e r v e d  first-order  r a t e c o n s t a n t w i l l , as i s u s u a l i n such e q u i l i b r i a , c o n s i s t o f the sum o f t h e f o r w a r d and r e v e r s e r a t e c o n s t a n t s , o r :  k  obs  (melt)  k  =  1  n  + k„ 2  =  2k, 1  In  the a c t i v a t i o n p l o t ( F i g u r e 2 ) , k k  of  k ^ Q  s  s  ( m e l t ) = 2k^ i n E q u a t i o n 1 (p  (melt) was used.  Substitution  20 ) w i l l make no d i f f e r e n c e t o  ± the e n t h a l p y o f a c t i v a t i o n , AH , b u t w i l l a f f e c t the i n t e r c e p t and hence A s  i n a s m a l l way.  To c o r r e c t f o r t h i s , t h e e n t r o p y o f  a c t i v a t i o n s h o u l d be augmented by 2.303R l o g 2  }  o r 1.4 c a l deg "'"mole "'".  T h i s c o r r e c t i o n i s s m a l l compared t o the l a r g e e n t r o p y between r e a c t i o n i n t h e m e l t and i n t h e s o l i d In  difference  (21 c a l deg "'"mole "'") .  t h e s o l i d , t h e mechanism cannot be t h i s s i m p l e , i n v i e w o f  t h e phase r e l a t i o n s h i p s between e n a n t i o m e r s .  However, any mechanism  must i n c o r p o r a t e t h e o b s e r v a t i o n o f f i r s t - o r d e r k i n e t i c s . sequence o f events c o n s i s t s o f the f o l l o w i n g : k  3  k  4 5  A(y)  B( ) Y  k  A(y)  +  B( ) Y  C(Y)  C( ) Y  • C ( s e p a r a t e phase)  A reasonable  38  C r e p r e s e n t s the p r o d u c t compound, w h i c h i s c o n s i d e r e d as a hydrogen bonded p a i r o f e n a n t i o m e r s .  A l l species are f i r s t contained i n the  Y phase ( F i g u r e 7 ) . A t low c o n v e r s i o n s , t h e f i r s t p r o d u c t s  formed  from a f i r s t - o r d e r p r o c e s s i n a s i n g l e r e a c t a n t phase w o u l d e x i s t i n s o l i d s o l u t i o n w i t h the r e a c t a n t , s i n c e a s u f f i c i e n t l y s m a l l number of product molecules  randomly s c a t t e r e d throughout  the r e a c t a n t m a t r i x  h c o u l d n o t form a s e p a r a t e phase.  As r e a c t i o n p r o c e e d s ,  the reactant  phase would e v e n t u a l l y become s u p e r s a t u r a t e d i n p r o d u c t , and u n s t a b l e w i t h r e s p e c t t o a two-phase r e a c t a n t - p r o d u c t system.  The l a s t r e a c t i o n  t h e r e f o r e shows t h e compound C s e p a r a t i n g ( r e l a t i v e l y q u i c k l y , as d i s c u s s e d above) from t h e y phase. The r e v e r s i b l e i n t e r c o n v e r s i o n o f enantiomers rate constants ( i . e . , m e l t phase.  w i l l n o t have e q u a l  k^ ^ k^) i n t h e y phase as i s the case i n t h e  The y c r y s t a l s w i l l p r e s e n t a d i s s y m m e t r i c  environment t o  the enantiomer B, c a u s i n g a d i f f e r e n c e i n t h e f r e e e n e r g i e s o f A and B i n t h e y phase.  The a d d i t i o n o f B e n a n t i o m e r t o pure A w i l l  first  lower^^'^''" then r a i s e t h e t o t a l f r e e energy o f t h e y phase (see Figure 8 ( a ) ) .  The f r e e e n e r g i e s o f t h e s p e c i e s B and C r e l a t i v e t o A  are shown s c h e m a t i c a l l y i n F i g u r e 8 ( b ) .  B and C a r e a t a h i g h e r  energy than A because they a r e n o t e x p e c t e d  to f i t i n t o the y l a t t i c e  as e a s i l y as A. The f i r s t p a i r of r a t e c o n s t a n t s w i l l t h e r e f o r e l i k e l y be o r d e r e d k. < k.. Once a B m o l e c u l e i s formed, i t w i l l be surrounded 3 4 w i t h A m o l e c u l e s , and w i l l p r o b a b l y be e a s i l y a b l e t o move i n t o p o s i t i o n to  form hydrogen bonds w i t h A, t h e r e b y c r e a t i n g compound C.  I f this  k  I n some p h o t o d i m e r i z a t i o n s , t h e p r o d u c t i s c o n s i d e r a b l y s o l u b l e i n the r e a c t a n t l a t t i c e . ' *  TEMPERATURE: 150°  RACEMATE PHASE  o  w •z w W W  MIRROR IMAGE OF (y) PHASE'  100  50 PERCENTAGE (-)-ENANTIOMER  O W Z  w w w  Pi  REACTION COORDINATE F i g u r e 8.  (a)  Schematic f r e e e n e r g y - c o m p o s i t i o n  system ( + ) - and (-)-29, a t c o n s t a n t e r a t u r e (150°) .  pressure  p l o t i n t h e phase  (atmospheric)  The d o t t e d l i n e s show t h e l o w e s t  and temp-  f r e e energy  s u r f a c e s f o r t h e two-phase r e g i o n s . (b)  Schematic f r e e e n e r g y - r e a c t i o n  coordinate plot f o r  the s o l i d - s t a t e r a c e m i z a t i o n o f (+)-29 (shown as A ( y ) ) a t 150°.  40  r e a c t i o n i s f a s t , then perhaps k^ << k,. A(y) throughout  w i l l be s u f f i c i e n t l y l a r g e to a l l o w  most o f the r e a c t i o n .  f r a c t i o n of t o t a l d i a c i d w h i c h i s A and i n y. at  This quantity i s unity  the b e g i n n i n g o f the r a c e m i z a t i o n , and z e r o a t t h e end.)  e q u a t i o n f o r the d i s a p p e a r a n c e  [ 4 ]  (A(y) i s the mole  _ dA£r)_  =  ^  k  rate  o f A(y) i s :  _ k^B (y)  A ( y )  The  +  k A(y)B(y) 5  and i f k^ < k^ << k ^ A ( y ) , B(y) i s a s h o r t - l i v e d r e a c t i v e i n t e r m e d i a t e i n t h e y phase. A s t e a d y - s t a t e t r e a t m e n t  [5]  = 0 = k A(y) - k B(y) 3  =  4  + k A(y)  -  ~  5  S u b s t i t u t i o n of [5] i n t o  5  k  J  k  k A(y)B(y)  4  k A(y) B(y)  [6]  on B(y) g i v e s :  J  k  5  [4] y i e l d s :  = k A(y) - ^ 3  +  k A(y) = 3  2k A(y)  I n t e g r a t i o n w i l l g i v e the r e s u l t k ^ g ( s o l i d ) = 2k^.  3  Therefore,  the  above assumptions about t h e r e l a t i v e magnitudes o f the r a t e c o n s t a n t s l e a d t o t h e c o n c l u s i o n t h a t as soon as one A c o n v e r t s t o B, immediately  d i s a p p e a r s i n the f o r m a t i o n of  another  C.  As w i t h the m e l t r e a c t i o n , the s u b s t i t u t i o n of k . ( s o l i d ) = obs 2k^ i n E q u a t i o n 1 (p 20 ) does n o t a l t e r AH' f o r the s o l i d , and changes the c a l c u l a t e d AS  ±  o n l y by a s m a l l amount (1.4 c a l deg  -1  mole  -1  )  41  The  a c t i v a t i o n parameters d e s c r i b e  i n the s o l i d - the reverse  t h e same p r o c e s s i n t h e m e l t as  D i e l s - A l d e r r e a c t i o n and r e c o m b i n a t i o n t o  form the enantiomer - and can be compared f o r t h e two phases. the f r e e e n e r g i e s o f a c t i v a t i o n a r e c l o s e J.  AH  Although  (Table I I ) , the c a l c u l a t e d  4.  and AS  T  a r e markedly d i f f e r e n t .  Passage o f t h e adduct from t h e  ground s t a t e t o t h e t r a n s i t i o n s t a t e a p p a r e n t l y increase  i n v o l v e s an e n t r o p y  (a l o c a l d i s r u p t i o n i n the h i g h l y ordered c r y s t a l l a t t i c e ) ,  at t h e c o s t o f a h i g h e r  energy o f a c t i v a t i o n than i n t h e m e l t .  The  s i m i l a r i t y o f r a t e c o n s t a n t s i n t h e s o l i d and m e l t (k , ( m e l t ) / obs k k ( s o l i d ) = 5 a t 150°C) i s r a t h e r s u r p r i s i n g c o n s i d e r i n g t h a t t h e Q  g  few examples i n w h i c h t h i s comparison can be made show much l a r g e r 3 4 2a r a t i o s ( c a . 10 -10 ) . However, t h e endo c y c l o p e n t a d i e n e - m a l e i c a n h y d r i d e adduct 27 (p 15 ) a l s o has a f a c i l e s o l i d - s t a t e i s o m e r i z a t i o n but  t h i s r e a c t i v i t y can be a t t r i b u t e d t o a p l a s t i c c r y s t a l l i n e  solid  37 state.  Such m o b i l e s o l i d s a r e c h a r a c t e r i z e d by a low e n t r o p y o f -1 -1 59a  f u s i o n ( c a . 5 c a l deg  mole  ),  much s m a l l e r  than t h e e n t r o p y o f  f u s i o n o b s e r v e d (12 c a l deg "'"mole "'") f o r the ( + ) - c y c l o p e n t a d i e n e f u m a r i c a c i d adduct 29_, r e p o r t e d there  here.  U n l i k e t h e endo a n h y d r i d e 27,  i s t h e r e f o r e a d i s t i n c t energy d i f f e r e n c e between the ( + ) -  d i a c i d 29_ i n t h e m e l t and i n the s o l i d  state.  S e v e r a l y e a r s ago H i n s h e l w o o d ^ c o n s i d e r e d  t h i s energy  i n r e l a t i o n to the rate constants i n both s t a t e s .  difference  Assuming t h a t t h e  t r a n s i t i o n s t a t e i s t h e same i n b o t h s o l i d and m e l t , he s u g g e s t e d  that  the r a t e d i f f e r e n c e might be r e l a t e d q u a n t i t a t i v e l y t o t h e e n t h a l p y o f fusion:  AH.  w  f7i 1  n  J  k(melt) k(solid)  _ ~  .  fusion RT  However, s u b s t i t u t i o n o f our determined AH^ . (5.38 k c a l mole ^) fusion  2 l e a d s t o a r a t i o of k ( m e l t ) / k ( s o l i d ) o f 6 x 10 a t 150°, considerably g r e a t e r than the o b s e r v e d f a c t o r o f 5. An improved r e l a t i o n s h i p 37 c o n s i d e r s the f r e e energy d i f f e r e n c e i n the ground s t a t e  (i.e.,  a c c o u n t s f o r b o t h e n t h a l p y and e n t r o p y d i f f e r e n c e s ) : r o  ,  [ 8 ]  „ £ n  k(melt) k(solid)  G(melt) RT  =  G(solid)  Near the m e l t i n g p o i n t , t h e f r e e energy d i f f e r e n c e between the phases can be approximated by the e n t h a l p y and e n t r o p y o f f u s i o n : ^  roi 1  J  o l n  . . k(melt) k(solid)  _  w  AH  . fusion RT ~ fusion R  AS. , fusion R ,1_ 1_ . ^T ~ T m.p. }  where t h e r e l a t i o n A s . . = AH. . /T „ fusion f u s i o n m.p, been t a k e n i n t o t h e e q u a t i o n . S u b s t i t u t i n g n  y i e l d s k ( m e l t ) / k ( s o l i d ) = 1.5  1  e  a t 150°,  ( E q u a t i o n 3, p 30) has ^ » ^ . = 5 . 3 8 k c a l mole fusion  v  considerably  c l o s e r t o the  observed r a t i o of 5. I n t h e above d i s c u s s i o n , the r a t e d i f f e r e n c e was  t a k e n as a  r e f l e c t i o n of the d i f f e r e n c e i n ground s t a t e f r e e e n e r g i e s o n l y .  In  g e n e r a l , however, b o t h the t r a n s i t i o n and ground s t a t e s i n the s o l i d r e a c t i o n may  be d i f f e r e n t from t h o s e i n the l i q u i d s t a t e .  The  r e s t r i c t i o n s imposed on the r e a c t i n g m o l e c u l e i n t h e s o l i d s t a t e can  A3  be l i k e n e d to a cage e f f e c t .  The  a c i d ) produced as i n t e r m e d i a t e s w i l l be h e l d i n p o s i t i o n by d i f f u s i n g apart.  addends ( c y c l o p e n t a d i e n e  i n the r e v e r s e  Diels-Alder  the s u r r o u n d i n g l a t t i c e r a t h e r  fumaric  reaction than  I f the r e s t r i c t i o n i s s e v e r e enough, such a cage  e f f e c t c o u l d be s t e r e o s p e c i f i c ; i n t h i s be r e v e a l e d  and  case s t e r e o s p e c i f i c i t y would  i n a reduced r a t e of r a c e m i z a t i o n  i n the s o l i d ,  the d i s s o c i a t e d addends would r e t a i n o r i e n t a t i o n .  since  Since rate  retardation  i s o n l y s l i g h t , such a mechanism i s e s s e n t i a l l y i n o p e r a t i v e .  Rather,  the addends a r e f r e e t o r o t a t e q u i c k l y and  the  enantiomer  2.5  recombine, forming  29.  Conclusion This s o l i d - s t a t e r e a c t i o n i n d i c a t e s that c e r t a i n thermal  t i o n r e a c t i o n s may solid state.  The  not be a p p r e c i a b l y higher  reorganiz-  k i n e t i c a l l y hindered i n  the  energy needed t o approach a t r a n s i t i o n s t a t e  i n a c r y s t a l l a t t i c e can be o f f s e t p a r t i a l l y by a f a v o u r a b l e  entropy  of a c t i v a t i o n , f a c i l i t a t i n g the s o l i d - s t a t e r e a c t i o n . R e a c t i o n s i n s o l i d s can be k i n e t i c a l l y s i m p l e even though a phase change o c c u r s d u r i n g 37 i n neat organic  solids  reaction.  Examples of f i r s t - o r d e r r e a c t i o n s  62 '  a r e r a r e , but  t h i s i s perhaps o n l y  a  r e f l e c t i o n on the s m a l l number of systems t h a t have been s t u d i e d a kinetic  from  standpoint.  O b s e r v a t i o n i n s i n g l e c r y s t a l s of a p r o d u c t phase a p p e a r i n g a t  2 A 63 d e f e c t s , d i s l o c a t i o n s or i n t e r f a c e s  '  t h a t r e a c t i o n o c c u r s a t such s i t e s .  Instead,  p r o d u c t has  does not n e c e s s a r i l y i n d i c a t e i t may  mean t h a t  a l r e a d y been formed by a s i m p l e p r o c e s s i n s i d e the  the reactant  crystal,  and i s o n l y s e p a r a t i n g out a t such i r r e g u l a r i t i e s .  studies with polycrystalline between the two  Kineti  samples can be used t o d i f f e r e n t i a t e  possibilities.  3  RESOLUTION OF RACEMIC 1,1'-BINAPHTHYL IN THE SOLID STATE  The  compound 1 , 1 ' - b i n a p h t h y l i s one o f t h e s i m p l e s t  carbons.  I t s dissymmetry i s m o l e c u l a r i n n a t u r e ,  c h i r a l hydro-  and enantiomer  i n t e r c o n v e r s i o n i s p o s s i b l e s i m p l y by r o t a t i o n about t h e i n t e r a n n u l a r bond, r a t h e r than by any b o n d - b r e a k i n g p r o c e s s .  The r o t a t i o n i s  s u f f i c i e n t l y r e s t r i c t e d t o a l l o w i s o l a t i o n o f e i t h e r enantiomer.  First  r e s o l v e d i n 1961, S - ( + ) - 1 , 1 ' - b i n a p h t h y l has been used i n s o l u t i o n racemization  studies.^ ^  The h a l f - l i f e f o r r a c e m i z a t i o n  s o l v e n t s i s c a , 15 min a t 50°.  Recently,  i n several  R-(-)-1,1'-binaphthyl  was  67 a l s o r e s o l v e d and s t u d i e d i n s o l u t i o n .  The a b s o l u t e  configuration 68  of 1 , 1 ' - b i n a p h t h y l was deduced from a c r y s t a l l o g r a p h i c s t u d y i n 1968.  46  3.1  The P r e p a r a t i o n o f  3.1.1  1,1'-Binaphthyl  S-(+)-1,1'-Binaphthyl Racemic  from the D i a s t e r e o m e r i c R e s o l u t i o n o f  Naphthidine  S-(+)-1,1'-Binaphthyl  has been s u c c e s s f u l l y r e s o l v e d v i a the (+•)-  naphthidine p r e c u r s o r . ^ ' ^  We  t h e r e f o r e began our p r e p a r a t i o n o f  o p t i c a l l y a c t i v e 1 , 1 ' - b i n a p h t h y l by s y n t h e s i z i n g r a c e m i c n a p h t h i d i n e The  f i r s t p r e p a r a t i o n o f n a p h t h i d i n e w h i c h we attempted  was  (31).  that  69 g i v e n by Sah and Y u i n . naphthalene  by f e r r i c  I t i n v o l v e d the o x i d a t i v e c o u p l i n g o f 1-aminooxide:  NH  2  31 The  r e p o r t e d y i e l d o f p u r i f i e d n a p h t h i d i n e was  hands t h e method gave poor y i e l d s was  60%.  However, i n our  (<10%) o f n a p h t h i d i n e , and the  procedure  abandoned i n f a v o u r o f a n o t h e r w h i c h seemed more p r o m i s i n g . T h i s second p r e p a r a t i v e r o u t e was  1-Aminonaphthalene was azonaphthalene naphthalene  was  developed  by Cohen and  d i a z o t i z e d then r e d u c t i v e l y c o u p l e d t o form  ( 3 2 ) , w h i c h was  i s o l a t e d i n a crude form.  The  azo-  suspended i n b o i l i n g e t h a n o l and reduced w i t h stannous  c h l o r i d e i n h y d r o c h l o r i c a c i d to hydrazonaphthalene, rearranged  Oesper.^  to naphthidine h y d r o c h l o r i d e .  hydroxide regenerates  the f r e e base.  The  which  immediately  Treatment w i t h sodium y i e l d of  recrystallized  47  naphthidine was  stated as 33.5%.  The procedure worked w e l l , and we were  32 able to prepare 45 g of pure naphthidine (m.p. the sequence eight times. was  201-202°) by repeating  Average y i e l d of the l a s t f i v e preparations  26%.  Racemic naphthidine was  then resolved by forming the s a l t with  (+)-ammonium a-bromo-D-camphor—iT-sulfonate. performed  this r e s o l u t i o n .  Theilacker and Hopp^ have 1  Use of two moles of resolving agent for each  mole of naphthidine gave 65% material a f t e r r e c r y s t a l l i z a t i o n  from  ethanol-water.  33,  We carried this resolution as far as the s a l t  obtaining the material i n somewhat lower y i e l d s but comparable s p e c i f i c rotations ([a] = +80°).  48  The  ( + ) - n a p h t h i d i n e a-bromo-D-camphor-ir-sulf onate s a l t  (33) can be  d i r e c t l y deaminated t o S - ( + ) - l , l ' - b i n a p h t h y l , w i t h o u t h a v i n g t o i s o l a t e  33 free (+)-naphthidine.  T h i s p r o c e d u r e was d e v i s e d by C o l t e r and Clemens,  and gave ( + ) - 1 , 1 ' - b i n a p h t h y l ( [ a ] = +145-165°) i n 40-55% y i e l d . adopted  t h i s method, w i t h a s l i g h t l y m o d i f i e d p u r i f i c a t i o n p r o c e d u r e , and  were a b l e t o o b t a i n S - ( + ) - 1 , 1 ' - b i n a p h t h y l  3.1.2  We  Racemic 1 , 1 ' - B i n a p h t h v l  ( [ a ] = +97°) i n 55% y i e l d .  from O p t i c a l l y I n a c t i v e Reagents  I n o r d e r t o c h a r a c t e r i z e f u l l y t h e phase system  formed between  r e s o l v e d and racemic b i n a p h t h y l ( o r , more c o r r e c t l y , between R- and S - l , 1 ' - b i n a p h t h y l e n a n t i o m e r s ) , some r a c e m i c 1 , 1 ' - b i n a p h t h y l was p r e p a r e d . 72 The p r e p a r a t i o n f o l l o w e d was t h a t o f S a k e l l a r i o s and K y r i m i s . The G r i g n a r d reagent from 1-bromonaphthalene was c o u p l e d by c u p r i c c h l o r i d e , forming  1,1'-binaphthyl:  49  The reaction proceeded easily, and starting materials were readily available, so that large quantities of racemic 1,1'-binaphthyl could be obtained (our yield of purified binaphthyl was 20%).  3.2  Discovery of the Solid-State R e s o l u t i o n  111  Having obtained some 1,1'-binaphthyl which was optically active, we then prepared to look for any racemization below the melting point 73 (158°) of the solid.  Since there was good evidence  for the existence  of two crystalline forms of 1,1'-binaphthyl (m.p. 145° and 158°), i t was of interest to check for racemization in both forms.  These  "low-melting" and "high-melting" forms could be obtained by slow and fast recrystallizations, respectively, from petroleum ether (b.p. 73 30-60°).  Accordingly, half of the prepared  optically active 1,1'-  binaphthyl ([a] = +97°) was recrystallized rapidly (giving crystals of [a]= +99°), and half slowly (giving material with [a] = +79°) from pentane.  At the boiling point of pentane (36°) a l i t t l e racemization of  the dissolved 1,1'-binaphthyl w i l l occur.^ Our i n i t i a l check for the presence of any solid-state racemization was to heat 20 mg of the polycrystalline 1,1'-binaphthyl sample with activity [a] = +99° for one hour at 120°.  When the sealed ampule was  opened and analyzed, the specific rotation was [a] = +108°.  Racemization  had not occurred, and the apparent increase in rotation caused us to check the precision of the polarimetric method of analysis. learned that the figure should be correct to within ±2°. therefore seemed genuine, but needed verification.  It was  The increase  A second sample of  the same material was therefore heated, along with a sample of [a] = +79°  50  m a t e r i a l , f o r 36 h a t 120°. changed  A n a l y s i s showed t h a t t h e l a t t e r had n o t  a t a l l from [a] = +79°, b u t t h e o r i g i n a l m a t e r i a l had i n c r e a s e d  from [ a ] = +99° t o +114°.  Even a f t e r such p r o l o n g e d h e a t i n g t h e sample  remained a w h i t e , c r y s t a l l i n e s o l i d and gave t h e s i n g l e 1 , 1 ' - b i n a p h t h y l peak when a n a l y z e d by g a s - l i q u i d chromatography.  The b i n a p h t h y l was  e v i d e n t l y r e s o l v i n g , not r a c e m i z i n g , i n the s o l i d  state.  T h i s i n c r e d i b l e r e s u l t was soon v e r i f i e d r a t h e r d r a m a t i c a l l y .  In  o r d e r t o f i n d t h e range o f t e m p e r a t u r e s i n w h i c h t h i s phenomenon might o c c u r , t h e second t e m p e r a t u r e chosen was 150°, n e a r e r t h e h i g h e r m e l t i n g p o i n t o f 158°.  Samples o f b o t h b a t c h e s o f o p t i c a l l y  active  1 , 1 ' - b i n a p h t h y l , a l o n g w i t h some c o n t r o l samples o f r a c e m i c 1 , 1 ' - b i n a p h t h y l (which had a l s o been r e c r y s t a l l i z e d r a p i d l y and s l o w l y from were h e a t e d f o r v a r i o u s l e n g t h s o f t i m e ( T a b l e I I I ) .  pentane)  The o r i g i n a l  ( f a s t r e c r y s t a l l i z e d ) sample o f a c t i v e 1 , 1 ' - b i n a p h t h y l i n c r e a s e d s t e a d i l y from [ a ] = +99° t o +163° o v e r a p e r i o d o f 2.5 days.  Samples from  t h e s l o w l y r e c r y s t a l l i z e d b a t c h , w h i c h had remained a t [ a ] = +79° a t 120°,  i n c r e a s e d t o [ a ] = +205° w i t h i n two hours and remained a t t h i s  r o t a t i o n f o r 2.5 days.  The r a c e m i c sample which had been r e c r y s t a l l i z e d  q u i c k l y remained a t [ a ] = 0° t h r o u g h o u t .  However, t h e s l o w l y  l i z e d r a c e m i c sample, s u r p r i s i n g l y , d e v e l o p e d o p t i c a l  activity.  R o t a t i o n s were somewhat s c a t t e r e d , b u t a l l e l e v e n i n d i v i d u a l were p o s i t i v e .  recrystal-  samples  T h i s s e l f - r e s o l u t i o n o f l , l ' - b i n a p h t h y l can a p p a r e n t l y  o c c u r even i n m a t e r i a l w h i c h i s r a c e m i c ( [ a ] = 0.0 JT 0.5°). T h i s u n u s u a l b e h a v i o u r o f s o l i d 1 , 1 ' - b i n a p h t h y l prompted  a search  f o r a method o f p r e p a r i n g b a t c h e s o f b i n a p h t h y l w h i c h would r e s o l v e t o a h i g h r o t a t i o n from a low i n i t i a l r o t a t i o n s i m p l y on h e a t i n g .  Since a l l  51  Table I I I Summary o f I n i t i a l I n v e s t i g a t i o n s  o f t h e Development  of Optical  Activity  i n Neat, P o l y c r y s t a l l i n e 1,1'-Binaphthyl  1 , 1 ' - B i n a p h t h y l Used  M a t e r i a l o f [ a ] = +99° II  it  b  Temperature, °C  120 it  149.6  Time, hours  [ a ] , degrees  1  +108  36  +114  1  +126  II  tt  2  +130,  it  II  5  +135, +133°  it  II  24  +157, + 1 5 2  "  II  63.5  M a t e r i a l o f [ a ] = +79° II  120 149.6  +129°  c  +163  36  +79  1  +105  "  it  2  +193,  II  it  5  +208, +206°  II  it  24  +208, +210°  II  II  63.5  +207  12.5  0,  0°  0,  o  c  Racemic Batch A  149.6  II  II  37.5  II  it  63.5  ^Racemic B a t c h B  149.6  +205°  0  0.017  +4  II  it  0.083  +41,  +47  C  II  "  0.5  +98,  +90  C  II  it  1.0  +79  52  (Table I I I ,  continued)  Racemic B a t c h B, c o n t i n u e d  149.6  12.5  II  II  37.5  II  II  63.5  +119,  +79  +93,  C  +83  +97  From a f a s t r e c r y s t a l l i z a t i o n ( p e n t a n e ) . k  From a s l o w r e c r y s t a l l i z a t i o n ( p e n t a n e ) . S p e c i f i c r o t a t i o n s o f two i n d i v i d u a l samples h e a t e d f o r t h e same l e n g t h o f t i m e a t t h e same t e m p e r a t u r e .  s o l i d samples o f 1 , 1 ' - b i n a p h t h y l had been r e c r y s t a l l i z e d , t h e n e x t s e v e r a l weeks were devoted t o t r y i n g t o d e v e l o p a method o f r e c r y s t a l l i z i n g racemic or p a r t i a l l y a c t i v e 1,1'-binaphthyl " s u c c e s s f u l l y " pentane.  from  V a r i a t i o n s were made i n t h e r a t e o f r e c r y s t a l l i z a t i o n , t h e  c o n c e n t r a t i o n o f 1 , 1 ' - b i n a p h t h y l i n t h e pentane s o l v e n t , and t h e method of  seeding.  No d e l i b e r a t e attempt was made t o add seeds o f f o r e i g n  d i s s y m m e t r i c m a t e r i a l ; i t was d e s i r a b l e t o r e s t r i c t t h e system to R- and S - l , 1 ' - b i n a p h t h y l .  entirely  Once a r e s o l v a b l e b a t c h ( i . e . , one w h i c h  would i n c r e a s e s i g n i f i c a n t l y i n s p e c i f i c r o t a t i o n on h e a t i n g ) was o b t a i n e d , however, c a r e f u l r e p e t i t i o n o f t h e c r y s t a l l i z a t i o n  procedure  would n o t produce a second b a t c h w h i c h was e q u a l l y as s u c c e s s f u l . From t h i s e x p e r i m e n t a t i o n t h e f o l l o w i n g i m p o r t a n t f a c t was l e a r n e d . A l l samples o f 1 , 1 - b i n a p h t h y l , r e g a r d l e s s o f t h e p a r t i c u l a r method o f 1  p r e p a r a t i o n , e i t h e r r e t a i n e d o r i n c r e a s e d s p e c i f i c r o t a t i o n when h e a t e d i n t h e s o l i d s t a t e below 158°. No r a c e m i z a t i o n e v e r o c c u r r e d on h e a t i n g p u r e , a c t i v e 1 , 1 ' - b i n a p h t h y l below i t s m e l t i n g p o i n t .  Also,  we o b s e r v e d t h a t c o o l i n g a sample t o room t e m p e r a t u r e o r below  then  r e h e a t i n g d i d not produce any a d d i t i o n a l i n c r e m e n t i n r o t a t i o n .  Re-  53  c r y s t a l l i z a t i o n from pentane d i d n o t cause a p p r e c i a b l e l o s s o f a c t i v i t y . Combining t h e s e o b s e r v a t i o n s , we d e v i s e d a c y c l i n g p r o c e d u r e w h i c h was c a p a b l e  of producing  l a r g e r q u a n t i t i e s of w e l l - r e s o l v e d  S t a r t i n g w i t h e i t h e r s l i g h t l y resolved 1,1'-binaphthyl m a t e r i a l which gained  1,1'binaphthyl.  or a racemic  some o p t i c a l a c t i v i t y on h e a t i n g , a s p e c i f i c r o -  t a t i o n a t l e a s t as g r e a t as [a] = +190° c o u l d e v e n t u a l l y be o b t a i n e d . (The is  l i m i t o f r e s o l u t i o n , as we l a t e r d i s c o v e r e d  [ct]p = i245°,)  1  (Appendix A, p 1 7 8 ) ,  F i r s t , t h e sample ( u s u a l l y ca_. 1 g i n s i z e ) was  r e c r y s t a l l i z e d from pentane.  To c o n s e r v e m a t e r i a l , t h e pentane was  removed i n vacuo a f t e r t h e r e c r y s t a l l i z a t i o n was c o m p l e t e .  The s o l i d  was t h e n h e a t e d a t 150°, and an i n c r e m e n t i n r o t a t i o n a l m o s t always occurred.  A second r e c r y s t a l l i z a t i o n o f t h i s more a c t i v e m a t e r i a l  a g a i n produced c r y s t a l s w h i c h c o u l d r e s o l v e even f u r t h e r on h e a t i n g . By c y c l i n g i n t h i s manner, t h e o p t i c a l a c t i v i t y o f any sample o f 1,1'b i n a p h t h y l c o u l d be s y s t e m a t i c a l l y enhanced.  Racemic s t a r t i n g m a t e r i a l  w h i c h d i d n o t change on h e a t i n g c o u l d be made t o r e s o l v e by d i s s o l v i n g i n some a c t i v e m a t e r i a l a t t h e r e c r y s t a l l i z a t i o n s t a g e .  An example o f  an e x p e r i m e n t t h a t produced a s p e c i f i c r o t a t i o n o f [a] = +194° i n f o u r c y c l e s , and one g i v i n g [a] = -194° a f t e r t h r e e c y c l e s a r e shown i n i' Table IV. One s h o r t c o m i n g o f t h i s p r o c e d u r e was t h a t a l t h o u g h  some i n c r e m e n t  i n r o t a t i o n was a s s u r e d , we were u n a b l e t o p r e d i c t how l a r g e i t would be. i  Some samples would i n c r e a s e o n l y a few degrees on h e a t i n g ;  others  ° The h i g h e s t s p e c i f i c r o t a t i o n a t t h e sodium D l i n e , 5893 A, r e p o r t e d f o r samples o f o p t i c a l l y a c t i v e l , l ' - b i n a p h t h y l o b t a i n e d by t h e c l a s s i c a l r e s o l u t i o n p r o c e d u r e i s [O]D +192°.65 Other v a l u e s a r e [a] = +245° at 5791 X and [a] = -250°at 4360 A . T h i s c o n v e r s i o n o f e s s e n t i a l l y a l l o f a r a c e m i c m a t e r i a l t o o n l y one ^ e n a n t i o m e r i s sometimes r e f e r r e d t o as an "asymmetric t r a n s f o r m a t i o n , " but we p r e f e r t h e more g e n e r a l term, " r e s o l u t i o n . " =  6 4  6 7  54  T a b l e IV Examples o f t h e C y c l i n g o f Racemic 1 , 1 ' - B i n a p h t h y l t o H i g h  Specific  Rotations  [a] A f t e r  Recrystallization,  [a] A f t e r H e a t i n g a t 150°  C y c l e Number degrees  degrees  ( +41,  0  1  +44)  +44)  2  ( +42,  (+109, + 1 1 6 )  3  3  (+110, + 1 1 2 )  a  (+186, + 1 8 5 )  3  4  (+175, + 1 7 9 )  a  (+197, + 1 9 0 )  3  1  0  ( -52, - 4 5 )  2  -34  -79  3  -49  3  b  a  a  -194  Duplicate analyses of the batch being cycled. T h i s l o s s i n a c t i v i t y on r e c r y s t a l l i z a t i o n o c c u r r e d because dec o l o u r i z i n g carbon was used i n t h e pentane s o l u t i o n . 1,1'-Binaphthyl r a c e m i z a t i o n i n pentane i s c a t a l y z e d by c e r t a i n c a r b o n b l a c k s .  jumped some 150° i n r o t a t i o n .  T h e r e f o r e , t h e number o f c y c l e s  required  t o a c h i e v e [ a ] = ±190-220° v a r i e d from one t o g r e a t e r than f o u r i n t h e experiments  attempted.  T h i s r e m a r k a b l e a b i l i t y o f l , l ' - b i n a p h t h y l t o r e s o l v e s i m p l y on h e a t i n g r e f l e c t s an u n u s u a l s t e r e o s p e c i f i c i t y i n t h e s o l i d s t a t e . thorough knowledge o f t h e phase r e l a t i o n s h i p s o f t h e R- and S-1,1'b i n a p h t h y l system i s an e s s e n t i a l p a r t o f any e x p l a n a t i o n o f t h e  A  55  phenomenon.  Our attempts to establish the nature and r e l a t i v e s t a b i l i t y  of the phases are reported i n the following section.  3.3 3.3.1  Phase Diagram of the System R- and S-l,1'-Binaphthyl Nature of the Phases The low- and high-melting forms of l , l ' - b i n a p h t h y l reported by 73  Badar ejt a l  were also obtained i n our r e c r y s t a l l i z a t i o n s of racemic  and p a r t i a l l y active material.  Contrary to t h e i r observations with  racemic 1,1'-binaphthyl, we found no good c o r r e l a t i o n between the r a p i d i t y of r e c r y s t a l l i z a t i o n and the form obtained."'  Both low- and  high-melting forms resulted from both slow and rapid r e c r y s t a l l i z a t i o n s . Most often, mixtures of the two forms were obtained.  That i s , perhaps  half of a sample would melt at 145°, the rest melting at 158°. Occasionally, r e c r y s t a l l i z a t i o n would y i e l d one form with very l i t t l e , i f any, of the other, and these batches allowed a study of both forms. 73 In agreement with Badar and coworkers,  each form had a character-  i s t i c infrared spectrum when taken i n a nujol mull (Figure 9).  The  s t r i k i n g difference at 769 cm ^ and also the smaller differences from 940-980 cm ^ reported by these investigators are quite apparent.  When 73  either form i s taken into solution, these differences disappear. The fact that the most marked difference was  i n the C-H out-of-plane  v i b r a t i o n region of the spectrum led these authors to suggest that within each R or S configuration, a c i s (30a) conformation might exist i n one c r y s t a l l i n e modification, and a trans (30b) conformation i n the other. ^ or, as just presented, any r e l a t i o n to the speed of r e c r y s t a l l i z a t i o n and the a b i l i t y of the material to resolve on heating.  Figure (a)  9.  I n f r a r e d spectrum of 1 , 1 - b i n a p h t h y l ( n u j o l m u l l ) ,  L o w - m e l t i n g form.  1  (b)  H i g h - m e l t i n g form.  57  30b  30a R-C-)-1,1'-Binaphthyl,  R-(-)-1,1'-Binaphthyl,  c i s conformation  trans conformation  X-Ray powder d i f f r a c t i o n also d i f f e r e n t i a t e s between the two forms.  Table V l i s t s the two patterns we obtained for the low- and  high-melting forms on a Debye-Scherrer  powder camera, alongside a pattern  for 1,1'-binaphthyl determined by Hofer e_t a l .  For each interplanar  d spacing i s l i s t e d the i n t e n s i t y of the l i n e r e l a t i v e to the most i n tense l i n e i n the photograph.(designated l i n e s are indicated.  100).  The three strongest  This format i s that of the American Society for  76a Testing Materials  and allows a comparison between our r e s u l t s  (obtained with Cu Ka r a d i a t i o n , wavelength  1.54178 X) and those of  Hofer (obtained with Fe Ka r a d i a t i o n , wavelength of his reported melting point (159.5-160°),  1.93728 X ) .  there i s l i t t l e  In s p i t e correspondence  between our pattern for the high-melting form and the 1,1'-binaphthyl pattern of Hofer.  Rather, the four strongest l i n e s on his pattern and  on ours for the low-melting form are i n close agreement.  Similarities  among the weaker l i n e s are d i f f i c u l t to f i n d , but at these low intens i t i e s comparison  i s d i f f i c u l t because our figures represent integrated  i n t e n s i t i e s whereas his are v i s u a l estimates.  58  Table V X-Ray Powder D i f f r a c t i o n P a t t e r n s f o r L o w - M e l t i n g (Racemate) and H i g h M e l t i n g ( E u t e c t i c ) Forms of 1,1' - B i n a p h t h y l  L o w - M e l t i n g Form  High-Melting  Form  d, A  I/I,  d, X  u  25  6.9  3rd  45  6.4  2nd  80  5.6  4.65  5  5.0  4.07  5  4.74  3.94  20  4.39  100  3.14  10.1 5.3 5.0  3  Literature  75  d, £  h  10  10.2  50  2nd  70  6.0  25  3rd  55  5.4  3rd  75  5  5.0  2nd  80  50  4.66  25  100  4.39  10  4.07  5  4.11  50  5  3.72  70  3.98  50  2.97  20  3.46  10  3.69  2.92  5  3.33  10  3.52  5  2.79  5  3.20  10  3.20  25  2.54  5  3.11  10  3.00  50  2.48  5  3.00  5  2.95  25  2.34  5  2.91  5  2.81  35  2.28  5  2.84  5  2.68  10  2.16  5  2.78  30  2.56  35  2.08  5  2.21  5  2.49  35  2.03  5  2.35  25  2.29  25  2.25  25  2.18  25  2.14  25  2.08  35  2.04  10  3.67  1st  Unresolved  doublet.  3  1st  1st  100  59  The for  f a c t w h i c h i s most apparent  from T a b l e V i s t h a t the p a t t e r n s  t h e low- and h i g h - m e l t i n g forms a r e c o n s i d e r a b l y d i f f e r e n t .  t o t a l absence o f t h e s t r o n g e r l i n e s o f one  The  form o f 1 , 1 - b i n a p h t h y l  in  1  the p a t t e r n of the o t h e r a t t e s t s t o t h e h i g h "phase p u r i t y " o f our samples.  The  l o w - m e l t i n g form a n a l y z e d was  r a c e m i c , but the h i g h -  m e l t i n g form, w h i c h we c o u l d o b t a i n i n a l l a c t i v i t i e s  (from [a] = 0 to  +245°) , gave t h e same p a t t e r n r e g a r d l e s s of t h e s p e c i f i c r o t a t i o n o f  the  sample a n a l y z e d . F o r t u n a t e l y , a f u l l c r y s t a l l o g r a p h i c s t u d y o f the  low-melting  form has r e c e n t l y been performed by K e r r and R o b e r t s o n . ^ m o d i f i c a t i o n belongs  to a m o n o c l i n i c , centrosymmetric  8 = 105.7°.  There a r e f o u r m o l e c u l e s  u n i t s i n b o t h R and  S molecules  The  The  S molecules  c = 10.13  two  two  1 of  naphthalene  a r e c i s d i s p o s e d , w i t h an a n g l e o f  68° between them, and a r e v e r y c l o s e t o the dimensions itself.  X,  t o each u n i t c e l l ,  w h i c h have the R c o n f o r m a t i o n , the o t h e r s b e i n g S.  crystal  space group  ( C 2 / c ) , w i t h l a t t i c e parameters a = 20.98 X, b = 6.35 and  This  of  naphthalene  e x i s t e n c e o f an o r d e r e d a r r a y o f e q u a l numbers of R  and  e s t a b l i s h e s the l o w - m e l t i n g form as a "phase r u l e " compound  (see S e c t i o n 2.3.1, p 27) i n the b i n a r y system R- and S - l , 1 ' - b i n a p h t h y l . L e t us now  c o n s i d e r t h e n a t u r e o f the h i g h - m e l t i n g form.  The  fact  t h a t the X-ray powder photographs o f t h i s form a r e the same a t a l l s p e c i f i c r o t a t i o n s e l i m i n a t e s a "phase r u l e " compound (which would have been a polymorph of the l o w - m e l t i n g form) as a p o s s i b i l i t y . ^ '  ^  T h i s l e a v e s a c h o i c e of e i t h e r a e u t e c t i c m i x t u r e o f i n d i v i d u a l R and S c r y s t a l s o r a s o l i d s o l u t i o n c a p a b l e o f c o n t a i n i n g b o t h enantiomers a l l proportions.  in  I f the l a t t e r i s t r u e , then the s o l i d s o l u t i o n must  60  be c l o s e t o i d e a l s i n c e t h e d s p a c i n g s remain unchanged as a f u n c t i o n o f composition.  I n a n o n i d e a l s o l u t i o n one would  expect a m o l a r volume  change (and hence a change i n d s p a c i n g s ) as t h e c o m p o s i t i o n i s v a r i e d . The c h o i c e between t h e r e two a l t e r n a t i v e s was means o f a r a t h e r f o r t u i t o u s r e s u l t .  e a s i l y made by  One b a t c h o f r a c e m i c  l,l'-binaphthyl  happened t o c r y s t a l l i z e from acetone o v e r a few days i n e s p e c i a l l y large crystals  (2-4 mm  i n d i a m e t e r ) which were shown by i n f r a r e d  t o be the h i g h - m e l t i n g form.  analysis  We were t h e r e f o r e g i v e n the o p p o r t u n i t y  o f h a n d - p i c k i n g the w e l l - f o r m e d c r y s t a l s f o r p o l a r i m e t r i c  analysis.  I f the h i g h - m e l t i n g form i s a e u t e c t i c m i x t u r e of i n d i v i d u a l R and S c r y s t a l s , then each s i n g l e c r y s t a l s h o u l d p o s s e s s a h i g h o p t i c a l in either direction.  I f i t i s an i d e a l s o l i d s o l u t i o n , then the l a t t i c e  can accommodate e i t h e r a n t i p o d e w i t h e q u a l ease. would  rotation  then grow by s e l e c t i n g randomly  r a c e m i c s o l u t i o n , and would  The s i n g l e  crystals  e i t h e r R o r S m o l e c u l e s from a  t h e r e f o r e p o s s e s s , most p r o b a b l y , a r o t a t i o n  of zero. The c r y s t a l s were examined under t h e p o l a r i z i n g m i c r o s c o p e . h e m i h e d r a l f a c e s were d i s t i n g u i s h a b l e .  A l t h o u g h such  No  enantiomorphous  f a c e s a r e always p r e s e n t i n e u t e c t i c m i x t u r e s o f e n a n t i o m e r s , they a r e 46 not always s u f f i c i e n t l y w e l l d e v e l o p e d t o be e a s i l y o b s e r v e d .  How-  e v e r , the s i n g l e c r y s t a l s were r e a d i l y r e c o g n i z e d under the m i c r o s c o p e The p i c k i n g a p a r t o f s i n g l e c r y s t a l s , t h e o l d e s t method of r e s o l v i n g r a c e m i c m a t e r i a l s , ^ has n e v e r been w i d e l y used and remains somewhat o f a n o v e l t y . However t h i s p r o c e d u r e , which i s not s y n t h e t i c a l l y u s e f u l because o f the s m a l l q u a n t i t i e s i n v o l v e d , can g i v e v a l u a b l e i n f o r m a t i o n about the n a t u r e o f the r a c e m i c m o d i f i c a t i o n , o r even the v e r y e x i s t e n c e of o p t i c a l a c t i v i t y i n a g i v e n m a t e r i a l . Very r e c e n t l y Wynberg79 has used t h i s method to r e s o l v e s e v e r a l h e t e r o helicenes.  61  by l o o k i n g  f o r t o t a l e x t i n c t i o n on r o t a t i o n o f t h e m i c r o s c o p e s t a g e  between c r o s s e d p o l a r s . shown i n F i g u r e 10.  A sketch of the habit  of these c r y s t a l s i s  The c r y s t a l would e x t i n g u i s h  p o s i t i o n o t h e r than normal t o t h e c and d f a c e s . extinguish  when viewed i n any Such a f a i l u r e t o  w i l l a r i s e when an o p t i c a l l y a c t i v e c r y s t a l i s b e i n g viewed 80  a l o n g an o p t i c a x i s ,  a preliminary  i n d i c a t i o n t h a t each c r y s t a l b e i n g  examined c o n t a i n s m o l e c u l e s o f o n l y one e n a n t i o m e r . Ten  w e l l formed s i n g l e c r y s t a l s were c a r e f u l l y s e p a r a t e d from t h e  mixture, dissolved  i n benzene, and a n a l y z e d f o r a c t i v i t y .  ( T a b l e V I ) show t h a t each c r y s t a l was h i g h l y  The r e s u l t s  r e s o l v e d ( n i n e out o f t e n  Table VI Specific Rotations of Single  Crystals  O b t a i n e d from t h e R e c r y s t a l l i z a t i o n  of Racemic 1 , 1 ' - B i n a p h t h y l  C r y s t a l Number  W e i g h t , mg  [ a ] , degrees  1  2.45  +222  2  6.20  +208  3  6.45  +203  4  6.25  +207  5  11.10  -199  6  11.30  +212  7  7.85  -164  8  8.55  -204  9  5.30  +222  9.55  +197  10  62  Figure  10.  Sketch of the h a b i t of a s i n g l e c r y s t a l o f pure R- or  S - l , 1 ' b i n a p h t h y l , showing those f a c e s which were apparent under the microscope. to c f a c e .  (a) (c)  View o f a, b, and c f a c e s . View normal to d f a c e .  (b)  View normal  63  were a t l e a s t 80% r e s o l v e d ) , a n d ' t h a t b o t h R and S c r y s t a l s were present i n the mixture.  The h i g h - m e l t i n g form i s t h e r e f o r e a e u t e c t i c  m i x t u r e o f i n d i v i d u a l R and S c r y s t a l s . I n t h i s t h e s i s , the words " e u t e c t i c form" w i l l be synonymous w i t h " h i g h - m e l t i n g form," and w i l l a p p l y t o m i x t u r e s of R and S c r y s t a l s i n any r a t i o , from 100% R, through the racemic c o m p o s i t i o n (where an e q u i m o l a r m i x t u r e o f R and S c r y s t a l s e x i s t ) , to 100% S.  The  eutectic  form i s n o t a s i n g l e s o l i d phase l i k e t h e racemate ( l o w - m e l t i n g f o r m ) , but c o n s i s t s i n s t e a d o f two s o l i d phases,  an R phase and as S phase.  The h i g h - m e l t i n g form i s not c o n s i d e r e d a p o l y m o r p h ^ * melting  3  o f the  low-  form.  A l t h o u g h the n a t u r e of b o t h the low- and h i g h - m e l t i n g m o d i f i c a t i o n s o f c r y s t a l l i n e 1 , 1 ' - b i n a p h t h y l a r e now diagram cannot y e t be c o n s t r u c t e d . e r a t u r e ranges problem  known, the phase  Some i n f o r m a t i o n as to the temp-  over which each form i s s t a b l e , must be o b t a i n e d .  and i t s c o n n e c t i o n to the s o l i d - s t a t e r e s o l u t i o n w i l l  This  be  considered next.  3.3.2  R e l a t i v e S t a b i l i t y o f t h e Phases The  s i m p l e s t way  i n f r e e energy  to d e t e r m i n e which o f two phases l i e s  a t a g i v e n temperature  and c o m p o s i t i o n ( i . e . , a t a  g i v e n p o i n t on the phase diagram) i s t o observe t o a n o t h e r a t the p o i n t i n q u e s t i o n .  lowest  the c o n v e r s i o n o f  one  W i t h f a s t t r a n s f o r m a t i o n s (such  as m e l t i n g ) t h i s o b s e r v a t i o n i s e a s i l y made. slow the problem becomes more d i f f i c u l t .  I f the phase changes a r e  I n the c o u r s e o f t h i s work,  s e v e r a l approaches were n e c e s s a r y i n d e t e r m i n i n g the r e l a t i v e  stability  64  of a l l 1 , 1 ' - b i n a p h t h y l phases.  3.3.2.1  Melting P o i n t Observations  The o r i g i n a l d i s t i n c t i o n between the two c r y s t a l l i n e m o d i f i c a t i o n s 73 of 1 , 1 ' - b i n a p h t h y l was based on m e l t i n g p o i n t s .  We  c o n f i r m e d t h a t the  l o w - m e l t i n g form (a racemate) m e l t s a t 144-145°, and t h a t the h i g h m e l t i n g form (a e u t e c t i c m i x t u r e ) m e l t s a t 157-158°.  In fact, a l l  samples o f h i g h - m e l t i n g form, from [a] = 0 t o ±245°, m e l t e d a t 157-158°. T h i s o b s e r v a t i o n a t f i r s t appears t o c o n t r a d i c t our e a r l i e r s i n c e e u t e c t i c m i x t u r e s o f enantiomers  findings,  c h a r a c t e r i s t i c a l l y melt  at the r a c e m i c than a t the r e s o l v e d c o m p o s i t i o n .  lower  However, s i n c e a  mechanism e x i s t s f o r the i n t e r c o n v e r s i o n o f e n a n t i o m e r s , the R- and S - l , 1 ' - b i n a p h t h y l i s a p s e u d o b i n a r y system  system  ( S e c t i o n 2.3.2, p 3 2 ) .  I f r a c e m i z a t i o n i n the melt i s r a p i d , the m e l t i n g p o i n t s may  be  observed  to o c c u r f a r below the i d e a l v a l u e s . The p r e s e n c e o f f a c i l e r a c e m i z a t i o n i n the m e l t was verified.  A 20 mg  easily  sample o f 1 , 1 ' - b i n a p h t h y l ( [ a ] = +234°) was s e a l e d  i n an ampule and immersed i n a b a t h t h e r m o s t a t t e d a t 160.3°. t h r e e minutes  the sample a t t a i n e d t h i s t e m p e r a t u r e and c o m p l e t e l y  m e l t e d , and a f t e r a t o t a l o f f i v e minutes i t was temperature.  In  A n a l y s i s gave  [cx]= 0.0 ± 0.5°.  r a c e m i z a t i o n of 1 , 1 ' - b i n a p h t h y l ^ ^ a t u r e , the h a l f - l i f e i s l e s s than 0.5  quenched t o room  I f s o l u t i o n r a t e s of  are e x t r a p o l a t e d to t h i s sec.  temper-  Racemization i s v i r t u a l l y  i n s t a n t a n e o u s , and a r e l a t i v e l y s l o w r a t e of h e a t i n g (1 deg min c a p i l l a r y m e l t i n g p o i n t a p p a r a t u s , o r even 40 deg min d i f f e r e n t i a l s c a n n i n g c a l o r i m e t e r , as mentioned  1  1  in a  with a  i n the f o l l o w i n g s e c t i o n )  65  would account f o r the o b s e r v a t i o n o f a m e l t i n g p o i n t w h i c h i s i n d e pentent of composition.  The i d e a l m e l t i n g p o i n t of pure R- o r S-  1 , 1 ' - b i n a p h t h y l i s t h e r e f o r e i m p o s s i b l e t o determine."'" 1 , 1 ' - B i n a p h t h y l w h i c h has been m e l t e d above 158° a great extent.  Some m e l t e d samples can be h e l d a t 125°  without c r y s t a l l i z a t i o n .  indefinitely  However, t h e a d d i t i o n o f seed c r y s t a l s o f  h i g h - m e l t i n g form t o t h e m e l t j u s t below 158° lization.  supercools to  r e a d i l y causes  S i m i l a r o b s e r v a t i o n s o f the m e t a s t a b i l i t y o f t h e  crystal1,1'-  82 b i n a p h t h y l m e l t have been made by B i n n s and S q u i r e ,  who  reported  that  samples c o u l d be c o o l e d as low as 120° w i t h o u t c r y s t a l l i z a t i o n . Samples o f l o w - m e l t i n g form c o n t a i n i n g v e r y l i t t l e o f the e u t e c t i c m o d i f i c a t i o n m e l t e d e s s e n t i a l l y c o m p l e t e l y a t 144-145°.  However, i f  the samples c a n t a i n e d l a r g e r q u a n t i t i e s o f the h i g h e r m e l t i n g  eutectic,  t h e l a t t e r r e a d i l y c r y s t a l l i z e d from t h e m e l t o f t h e former i n t h e t e m p e r a t u r e range 145-158°.  I f c r y s t a l l i z a t i o n of t h i s form was  e s p e c i a l l y e f f i c i e n t , the sample d i d not appear t o m e l t a t a l l a t 145°.  I n such c a s e s , some m e l t i n g c o u l d be o b s e r v e d i f the sample  was  r a p i d l y immersed i n a t e m p e r a t u r e b a t h between 145-158°. From t h e s e o b s e r v e d t r a n s i t i o n s ( e u t e c t i c form ->- m e l t a t 157-158°, racemate -*• m e l t -*• e u t e c t i c form from 145°  t o 158°, and m e l t -*-eutectic  form below 158°), some o r d e r i n g of the f r e e energy s u r f a c e s a s s o c i a t e d w i t h each phase can be deduced. 1  The two p o s s i b l e f r e e energy  situations  The b e h a v i o u r of 1 , 1 - b i n a p h t h y l on m e l t i n g emphasizes the dangers i n u s i n g m e l t i n g p o i n t as a means of d e d u c i n g phase systems between o p t i c a l i s o m e r s . A l t h o u g h commonly used,^6 the m e l t i n g p o i n t diagram can l e a d t o e r r o n e o u s c o n c l u s i o n s i f the e n a n t i o m e r s a r e o p t i c a l l y unstable. 1  66  a r e i l l u s t r a t e d s c h e m a t i c a l l y i n F i g u r e 11 (a) and ( b ) .  The f r e e energy-  t e m p e r a t u r e diagrams a r e t a k e n a t the r a c e m i c c o m p o s i t i o n and a t c o n s t a n t p r e s s u r e ( a t m o s p h e r i c ) . These c u r v e s resemble t h o s e f o r t h e two ways i n w h i c h the phases of a s i n g l e component e x h i b i t i n g dimorphism can be r e l a t e d : t h e m o n o t r o p i c ( F i g u r e 11 ( a ) ) and t h e e n a n t i o t r o p i c 11 ( b ) ) r e l a t i o n s h i p . ^ * ' ^ ' ^ k 3  in h t  e  first,  (Figure  the l o w - m e l t i n g form (L)  i s u n s t a b l e r e l a t i v e t o the h i g h - m e l t i n g form (H) a t a l l t e m p e r a t u r e s below 158°.  At 145°,  L i n t e r s e c t s the m e l t s u r f a c e (M) and m e l t s  metastably.  Between 145°  and 158°, any h i g h - m e l t i n g form i n the sample  causes c r y s t a l l i z a t i o n o f t h i s m e l t and a l o w e r i n g of t h e f r e e energy o f the system.  At 158°,  i b r i u m w i t h the m e l t .  the h i g h - m e l t i n g form can e x i s t i n s t a b l e  equil-  I n the second r e l a t i o n s h i p ( F i g u r e 11 ( b ) ) , the  l o w - m e l t i n g form i s s t a b l e below a t r a n s i t i o n t e m p e r a t u r e ( x ) , b u t e x h i b i t s the same m e l t i n g b e h a v i o u r as i n the m o n o t r o p i c c a s e .  The c h o i c e  between the two p o s s i b i l i t i e s l i e s i n e s t a b l i s h i n g the p r e s e n c e o r absence o f t h e s o l i d - s o l i d t r a n s i t i o n p o i n t x. We now have enough i n f o r m a t i o n t o p o s t u l a t e a mechanism f o r t h e resolution reaction.  At 150°,  the i n c r e a s e i n o p t i c a l r o t a t i o n  evi-  d e n t l y o c c u r s because the racemate phase m e l t s , l e a v i n g c r y s t a l s o f R- and S - l , l ' b i n a p h t h y l ( e u t e c t i c form) b e h i n d t o a c t as seeds f o r the e n s u i n g m e l t -* e u t e c t i c form t r a n s f o r m a t i o n .  I f t h e e u t e c t i c form i n  the o r i g i n a l sample c o n s i s t s o n l y of S c r y s t a l s , then the p r e f e r e n t i a l c r y s t a l l i z a t i o n o n l y of S - l , 1 ' - b i n a p h t h y l can o c c u r , the s u p p l y o f S m o l e c u l e s b e i n g m a i n t a i n e d by the r a p i d enantiomer i n t e r c o n v e r s i o n i n the m e l t phase.  C o n v e r s i o n o f the e n t i r e sample t o pure S - l , 1 ' b i n a p h t h y l  i s t h e r e f o r e p o s s i b l e , p r o v i d e d the unwanted R c r y s t a l s have been  67  Pi  PS W  w w w  W  w  145 158  (a)  145 158  T  TEMPERATURE (°C)  (b)  TEMPERATURE (°C)  158  u o  o  145  H  0 (c)  F i g u r e 11.  50  100  0  PERCENTAGE S-ENANTIOMER  (d)  50  PERCENTAGE S-ENANTIOMER  Schematic f r e e e n e r g y - t e m p e r a t u r e p l o t s f o r r a c e m i c  1 , 1 ' - b i n a p h t h y l , showing l o w - m e l t i n g form ( L ) , h i g h - m e l t i n g form (H) and m e l t (M) s u r f a c e s . (b)  Enantiotropic  (a) M o n o t r o p i c r e l a t i o n s h i p ,  relationship.  ( c ) Phase diagram w h i c h would  r e s u l t from t h e m o n o t r o p i c r e l a t i o n s h i p . w h i c h would r e s u l t from t h e e n a n t i o t r o p i c  100  (d) Phase diagram relationship.  68  eliminated. From s t u d y i n g the p o s s i b l e phase diagrams a r i s i n g from the monot r o p i c and important  e n a n t i o t r o p i c r e l a t i o n s h i p s ( F i g u r e 11 c o n c l u s i o n can be drawn.  (c) and  I f the system i s e n a n t i o t r o p i c ,  then a p a r t i a l l y a c t i v e sample of 1 , 1 ' - b i n a p h t h y l c o n t a i n s o n l y S c r y s t a l s and state.  (d).) , an  h e l d at point p  racemate c r y s t a l s when i n i t s most s t a b l e  Such a sample, on h e a t i n g t o 150°,  should t h e r e f o r e  r e s o l v e to S - l , 1 ' - b i n a p h t h y l because o f the absence o f R  totally  crystals.  Thermodynamics would t h e r e f o r e be o p e r a t i n g so as to f a v o u r the d u c t i o n o f a h i g h l y s t e r e o s p e c i f i c sample o f s o l i d  pro-  1,1'-binaphthyl.  I t i s v e r y d e s i r a b l e , t h e n , t o know w h i c h phase d i a g r a m d e s c r i b e s R- and S - l , 1 ' - b i n a p h t h y l  3.3.2.2  system.  D i f f e r e n t i a l Scanning C a l o r i m e t r y - Q u a l i t a t i v e  The mining  d i f f e r e n t i a l scanning  calorimeter i s very h e l p f u l i n deter-  phase diagrams ( S e c t i o n 2.3.1, p 2 7 ) .  I n the c o u r s e o f  s t u d i e s , many hundreds of samples o f 1 , 1 ' - b i n a p h t h y l d.s.c.  I n none o f the samples was  apparent.  The  o n l y peaks o c c u r r e d  from 145°  t o 158°.  Two  endotherms and  A t y p i c a l d.s.c.  (racemate) and  an exotherm a r e  This i s f o l l o w e d immediately  c r y s t a l l i z a t i o n of the  pro-  melting  by the e x o t h e r m i c  e u t e c t i c form from the m e l t ,  ( e n d o t h e r m i c ) m e l t i n g of the e u t e c t i c form.  high-  discernible.  f i r s t endotherm, at 144-145°, c o r r e s p o n d s to the m e t a s t a b l e  o f the racemate.  the  transition  ( e u t e c t i c ) forms i s shown i n F i g u r e 12 as a f u n c t i o n o f  gramming ( h e a t i n g ) r a t e . The  our  were run on  any s i g n o f a s o l i d - s o l i d  t r a c e o f a sample c o n t a i n i n g b o t h the l o w - m e l t i n g melting  the  The  then f i n a l l y by  the  f i n a l endotherm t h e r e -  69  144-145  157-158  144-145  157-158  (a)  w sa H o X w  (b)  w H  o Q z w  (c)  TEMPERATURE (°C)  Figure 12.  D i f f e r e n t i a l scanning calorimeter traces f o r racemic  1,1'-binaphthyl, as a function of programming rate. (b)  10 deg min *  (c) 40 deg min *  (a) 2.5 deg min  -1  70  f o r e c o m p r i s e s b o t h t h e e u t e c t i c form o r i g i n a l l y p r e s e n t i n t h e sample p l u s t h a t w h i c h c r y s t a l l i z e d from t h e m e l t o f t h e racemate.  At f a s t e r  programming r a t e s , t h e d i m i n i s h e d s i z e o f t h e f i n a l endotherm  and o f t h e  exotherm mean t h a t t h e o r i g i n a l sample d i d n o t c o n t a i n much e u t e c t i c form.  R a t h e r , most o f i t c r y s t a l l i z e d from t h e m e l t a t s l o w e r h e a t i n g  rates. Pure h i g h - m e l t i n g form ( o b t a i n e d by h o l d i n g any sample o f 1,1'b i n a p h t h y l a t 150°) shows a s i n g l e endotherm t h e s p e c i f i c r o t a t i o n o f t h e sample. e r a t u r e o f t h e endotherm  a t 157-158° r e g a r d l e s s o f  Even a t 40 deg min \  t h e temp-  ( a p p a r e n t l y s l i g h t l y h i g h e r because o f t h e  t h e r m a l r e s i s t a n c e o f t h e i n s t r u m e n t ) i s t h e same whether t h e sample i s resolved or racemic.  As j u s t e x p l a i n e d ( S e c t i o n 3.3.2.1), c o n s t a n c y  o f m e l t i n g p o i n t w i t h c o m p o s i t i o n w i l l o c c u r when e x t r e m e l y r a p i d enantiomer i n t e r c o n v e r s i o n t a k e s p l a c e on m e l t i n g . S i n c e i t i s i m p o s s i b l e t o c r y s t a l l i z e t h e h i g h - m e l t i n g form from t h e m e l t a t 150° w i t h o u t t h e use o f seed c r y s t a l s , t h e appearance o f t h e h i g h e r t e m p e r a t u r e endotherm  on d . s . c . a n a l y s i s o f 1 , 1 ' - b i n a p h t h y l  i m p l i e s t h a t t h i s form must have been p r e s e n t i n t h e o r i g i n a l i n a t l e a s t t r a c e ("seed") q u a n t i t i e s .  sample  Thermal a n a l y s e s o f dozens o f  d i f f e r e n t samples o f 1 , 1 ' - b i n a p h t h y l p r e p a r e d i n v a r i o u s ways showed t h a t i t was i m p o s s i b l e t o produce w o r k a b l e q u a n t i t i e s o f l o w - m e l t i n g form c o n t a i n i n g a b s o l u t e l y no seed c r y s t a l s o f t h e h i g h - m e l t i n g form. A l l showed endotherms a t 157-158°.  Some samples were e s p e c i a l l y low i n  t h i s e u t e c t i c c o n t e n t , s i n c e no h i g h - m e l t i n g endotherm was o b s e r v e d a t the u s u a l h e a t i n g r a t e o f 10 deg min ^. t o 2.5 deg rain \  However, on r e d u c i n g the r a t e  some e u t e c t i c form c r y s t a l l i z e d then m e l t e d , i n d i c a t i n g  71 traces of this form i n the sample-  This method i s therefore a sensitive  check of the "phase purity" of low-melting samples. One single procedure did, however, produce absolutely pure lowmelting form i n small quantities.  When pure 1,1'-binaphthyl, regardless  of i t s phase content or activity, was melted above 160° on the d.s.c, then program cooled (at rates up to 20 deg min ^) to 50-60°, the sample solidified.  On reheating at any programming rate, only the racemate  endotherm was observed; no eutectic form crystallized from the melt above 145°«  In contrast, i f the same sample i s melted above 160° and  cooled very quickly by removing the sample planchette and placing i t on a metal surface at room temperature, a glass forms; i f the sample i s replaced i n the holder then reheated, i t solidifies at about 90-100°, then melts at 157-158°, with no indication of any low-melting form. This micro (<5 mg) method of preparing the pure high- and low-melting forms i s surprisingly reproducible - the same sample can be converted back and forth indefinitely to either form, simply by varying the rate of cooling. What do these qualitative d.s.c. observations t e l l us about the relative stability of the two crystalline modifications?  First of a l l ,  they verify the ordering of the free energies of racemic 1,1'-binaphthyl in the region of the melting points (145° to 158°).  Secondly, the  manner in which the low- and high-melting form can be reproducibly obtained 81c with the d.s.c. i s revealing.  In the experience of McCrone,  i f two  polymorphs are obtained by cooling the melt in different ways, the least stable form i s that which crystallizes -from the most highly supercooled melt.  Melts can be highly supercooled when a small amount i s cooled very  72  r a p i d l y , l i k e the way d.s.c. p l a n c h e t t e .  i n which t h e h i g h - m e l t i n g form was  produced  i n the  The s u g g e s t i o n i s t h e r e f o r e t h a t a t l o w e r temper-  a t u r e s the l o w - m e l t i n g form i s the more s t a b l e m o d i f i c a t i o n . These o b s e r v a t i o n s w i t h a s u p e r c o o l e d m e l t s h o u l d a l s o o b t a i n 81c with a supersaturated solution.  That i s , the more h i g h l y  s a t u r a t e d s o l u t i o n s h o u l d y i e l d t h e l e s s s t a b l e o f t h e two  super-  forms.  A c c o r d i n g l y , we p r e p a r e d f i l t e r e d s o l u t i o n s o f r a c e m i c 1 , 1 ' - b i n a p h t h y l i n e t h e r , a c e t o n e , and benzene.  These were a l l o w e d to. e v a p o r a t e ' s l o w l y  at room t e m p e r a t u r e o v e r s e v e r a l days. c r y s t a l s were racemate  I n each case the r e s u l t i n g  form w i t h v e r y few seeds o f e u t e c t i c form, as  r e v e a l e d by d.s.c. a n a l y s i s .  S i m i l a r l y p r e p a r e d s o l u t i o n s were  o r a t e d q u i c k l y ( i n l e s s than f i v e minutes)  evap-  i n a stream of dry a i r at  room t e m p e r a t u r e .  The e u t e c t i c form was  (X-ray a n a l y s i s ) .  I f i t i s t r u e t h a t the more s u p e r s a t u r a t e d c o n d i t i o n s  produce  o b t a i n e d i n h i g h phase p u r i t y  t h e l e s s s t a b l e form, then a g a i n t h e i m p l i c a t i o n i s t h a t t h e  racemate  i s s t a b l e a t room t e m p e r a t u r e .  F o l l o w i n g t h i s e m p i r i c a l p r i n c i p l e to i t s l i m i t , we d e c i d e d t o s e a r c h f o r any o t h e r c r y s t a l m o d i f i c a t i o n s ( l e s s s t a b l e than the lowand h i g h - m e l t i n g forms) by c r e a t i n g an e x t r e m e l y s u p e r c o o l e d m e l t . To t h i s end, some r a c e m i c 1 , 1 ' - b i n a p h t h y l was c a p i l l a r y then m e l t e d i n a 175°  bath.  posed  The c a p i l l a r y was  to X-rays f o r 20 h.  i n an X-ray powder  The c a p i l l a r y was  immersed i n t o a b a t h o f l i q u i d n i t r o g e n . the tube.  packed  then i m m e d i a t e l y  A g l a s s y s u b s t a n c e formed i n  then mounted i n the powder camera and  W i t h i n f o u r hours the sample s o l i d i f i e d .  d i f f r a c t i o n p a t t e r n showed l i n e s due o n l y t o the racemate e u t e c t i c form, and no o t h e r c r y s t a l m o d i f i c a t i o n .  and  the  exThe  73  3.3.2.3  D i f f e r e n t i a l Scanning C a l o r i m e t r y - Q u a n t i t a t i v e  A l t h o u g h t h e above o b s e r v a t i o n s suggest an e n a n t i o t r o p i c s h i p , a more q u a n t i t a t i v e approach would be v e r y h e l p f u l .  relation-  Specifically,  i f t h e a c t u a l f r e e energy d i f f e r e n c e between t h e racemate and t h e e u t e c t i c forms c o u l d be c a l c u l a t e d as a f u n c t i o n o f t e m p e r a t u r e a t c o n s t a n t p r e s s u r e and c o m p o s i t i o n ( t h e r a c e m i c c o m p o s i t i o n ) , then t h e s t a b l e ranges o f each c o u l d be d e t e r m i n e d .  I n other organic s o l i d s , 83 84  f r e e energy c a l c u l a t i o n s have been used f o r j u s t t h i s purpose.  '  S u f f i c i e n t information i n the m e l t i n g region of 1,1'-binaphthyl i s a v a i l a b l e t o a l l o w c a l c u l a t i o n o f t h e f r e e energy d i f f e r e n c e between the two c r y s t a l m o d i f i c a t i o n s a t 150°C (423°K).  T h i s can be seen  from  the f r e e energy p l o t s ( F i g u r e 11 (a) and ( b ) ) and t h e s c h e m a t i c e n t h a l p y and e n t r o p y p l o t s o f F i g u r e 13.  The e n t h a l p y d i f f e r e n c e i n g o i n g from  the l o w - m e l t i n g (racemate) form t o t h e m e l t (L->M) can be c a l c u l a t e d t h e a r e a o f t h e d.s.c. endotherm a t 145°C (418°K). e n t h a l p y change h i g h - m e l t i n g ( e u t e c t i c ) form (431°K) can be d e t e r m i n e d .  from  S i m i l a r l y , the  m e l t (H-*M) a t 158°C  S i n c e t h e f r e e energy change a t t h e s e two  p o i n t s i s z e r o , t h e e n t r o p y change on m e l t i n g can be c a l c u l a t e d f o r b o t h forms:  [10]  AS  418  L->M = 0 AG '418  ,L-*-M AH' 418  L->*i (418)AS 418  ,H->M = 0 AG '431  H->M AH 431  H--M (431)AS 431  and  AS  H->M 431  (431)  I  (a)  1  ]_  145  158  TEMPERATURE (°C)  I  I  145 (b) F i g u r e 13. racemic  1  I  158  TEMPERATURE (°C) Schematic  e n t h a l p y - and e n t r o p y - t e m p e r a t u r e  1,1'-binaphthyl.  plots f o r  (a) O r d e r i n g o f l o w - m e l t i n g form ( L ) ,  h i g h - m e l t i n g form (H) and m e l t e n t r o p i e s o f t h e same phases.  (M) e n t h a l p i e s .  (b) O r d e r i n g o f  75  where the subscript  refers to the absolute temperature  of the t r a n s i t i o n .  Since 150°C i s close to the melting points of both forms (145°C and 158°C), we may  assume to a good approximation that the enthalpy and  entropy changes on melting are i d e n t i c a l to the corresponding changes at 150°C (423°K).  AH  That i s ,  61  L->M  AH  418  L->M  H-*M  423  AH  H-*M  431 =  423  fiH  and  [11] AS  L-»M  AS  418  L->M  A<;  423  Ab  H-»M  431  =  H-*M  A9  Ab  423  This approximation allows us to calculate the enthalpy, entropy, and free energy difference between the two c r y s t a l l i n e forms ( L and H ) at 150°C ( A H ^ j , AS^? 423  AH ~*  [12]  and AG^J,  423  L  4  2  3  423  A  H  423  "  A  A  S  4 2 3  "  A  = A H ^ 423  -  H  respectively).  H->M  _  423  *  L->M A  H  . H-^M  "  L-*M  C  [13]  418  A  H  431  A S ^ 4 3 1 H  A  S  4 2 3  AG ^ 423  [14]  L  A  H  G  "  L  A  H  S  4 2 3  =  (423)  A  as a f u n c t i o n  4 1 8  "  A  B  AS™  B e f o r e p r o c e e d i n g to show how determined  S  t h i s f r e e energy  of temperature,  we  difference  s h a l l p r e s e n t our  can  be  results  L-*-M  thus f a r .  The  e n t h a l p y of m e l t i n g f o r the racemate ( A H ^ g ) was  mined w i t h a sample which c o n t a i n e d n e g l i g i b l e e u t e c t i c not c r y s t a l l i z e any The  endotherm was  eutectic  form  the melt  form and d i d  above 1 4 5 ° C  (418°K).  a s i n g l e , sharp peak, from which an e n t h a l p y of  7 . 2 9 i 0 . 1 5 k c a l mole ^ ( 2 8 . 6 change, c a l c u l a t e d  from  deter-  0 . 6 c a l g "*") was  obtained.  The  entropy  from E q u a t i o n 1 0 , i s AS^'J = 1 7 . 4 8 t. 0 . 4 0 c a l deg ''"mole  76  Endotherms c o r r e s p o n d i n g  t o t h e m e l t i n g o f t h e e u t e c t i c form H+M  were s i m i l a r l y used t o c a l c u l a t e ^H^^^.  However, t h e e u t e c t i c i s c a p a b l e  o f h a v i n g any s p e c i f i c r o t a t i o n , depending on t h e r e l a t i v e amounts o f R and S c r y s t a l s i n t h e m i x t u r e .  T h e r e f o r e , e n t h a l p i e s o f f u s i o n were  determined  f o r s e v e r a l samples o f e u t e c t i c form p o s s e s s i n g d i f f e r e n t  activities  (Table V I I ) .  S e v e r a l d e t e r m i n a t i o n s were made f o r each sample, TABLE V I I  E n t h a l p y o f F u s i o n o f t h e H i g h - M e l t i n g Form o f 1 , 1 ' - B i n a p h t h y l  at Various  Specific Rotations  „H-»M . , , -1 AH,„,, k c a l mole , 431  * H-»M -1 AH,,..,, k c a l mole , 431  m u l t i p l e analyses  mean v a l u e  A  , [ocj, degrees  r  n  U  -245  5.11,  4.70  4.91  -205  5.12,  5.28,  5.13,  5.36  5.22  -8  5.68,  5.61,  5.72,  5.65  5.67  +137  5.85,  5.43,  5.85,  5.43  5.64  +154  5.72,  5.68  +223  4.51,  4.95,  +238  4.39,  4.60  5.70 4.68,  5.07  4.80 4.50  because a l l gave endotherms w i t h a s l i g h t l e a d i n g  edge, which can produce  47 e r r o r s when the peaks a r e i n t e g r a t e d . samples h a v i n g h i g h r o t a t i o n s possess  Comparing t h e mean v a l u e s , t h e H-*M somewhat lower v a l u e s o f A H ^ ^ .  S i n c e t h e f i n a l s t a t e i n m e l t i n g e u t e c t i c form o f any a c t i v i t y i s t h e  77  r a c e m i c m e l t , the lower e n t h a l p i e s between r e s o l v e d  and  could r e f l e c t a d i f f e r e n c e i n enthalpy  r a c e m i c e u t e c t i c form.  However the d i f f e r e n c e s  perhaps too c l o s e t o the s c a t t e r i n i n d i v i d u a l a n a l y s e s t o be seriously.  For t h i s purpose the e n t h a l p y of f u s i o n of  -1 used.  The  considered  Moreover, our g o a l i s to d e t e r m i n e r e l a t i v e f r e e e n e r g i e s of  the r a c e m i c system. [a] = -8°  are  sample (5.67  ± 0.08  i  k c a l mole  o r 22.3 H~*M c o r r e s p o n d i n g e n t r o p y change i s A S ^ . ^  I 0.3 13.15  =  the  - l cal g ) w i l l ± 0.22  cal  be  deg  —1  , -1 mole The  magnitudes o f the d e t e r m i n e d e n t h a l p y and  f o r b o t h the low-  and h i g h - m e l t i n g  s c h e m a t i c e n t h a l p y and  fusion  forms j u s t i f i e s the o r d e r i n g  entropy surfaces  i n Figure  A p p l i c a t i o n of E q u a t i o n s 12, 13 and and  entropy of  of  the  13.  14 g i v e s  the e n t h a l p y , e n t r o p y  f r e e energy d i f f e r e n c e s between the racemate and  the e u t e c t i c forms  at 150°C (423°K):  AH  L->H 423  (7.29  AS  L+H 423  (17.48 - 13.15) c a l d e g ^ m o l e "  AG  L-»H 423  [1620  The  - 5.67)  k c a l mole"  1  = 1.62  - (423)(4.33)] c a l m o l e  ± 0.23  k c a l mole"  1  = 4.33  ± 0.62  - 1  = -212  ± 490  cal deg mole - 1  c a l mole"  - 1  1  r a t h e r l a r g e e r r o r l i m i t s i n these v a l u e s i s d i s a p p o i n t i n g .  A l t h o u g h the e n t h a l p i e s  and  entropies  of f u s i o n f o r the racemate  e u t e c t i c forms have been measured to l e s s than 2.3% L_*H  d i f f e r e n c e s AH,__ 423 two  1  and  measured v a l u e s ,  XJ->H  A S . „ _ are r e l a t i v e l y s m a l l and 423 • r e s u l t i n g i n a 14%  uncertainty, involve  and the  subtracting  relative uncertainty.  Finally,  L-*H  p e r f o r m i n g a second s u b t r a c t i o n to o b t a i n A G , _ 9  produces a v e r y  large  78  uncertainty.  Even the a l g e b r a i c s i g n o f the f r e e energy d i f f e r e n c e , the  i m p o r t a n t c r i t e r i o n f o r r e l a t i v e s t a b i l i t y , i s i n some doubt. L~*H n u m e r i c a l r e s u l t AG^-j  =  -212  c a l mole  —1  The  r e p r e s e n t s t h e most p r o b a b l e  v a l u e o f the f r e e energy d i f f e r e n c e a t 150°C.  The f a c t t h a t  this  d i f f e r e n c e i s most p r o b a b l y n e g a t i v e i s i n a c c o r d w i t h our e x p e r i m e n t a l r e s u l t s - the e u t e c t i c form i s i n d e e d produced from the m e l t o f the racemate a t 150°C (see F i g u r e 11 (a) and Any f u r t h e r d i s c u s s i o n o f how  ( b ) , p 67).  the f r e e energy d i f f e r e n c e might  change w i t h t e m p e r a t u r e t h e r e f o r e i n v o l v e s most p r o b a b l e v a l u e s . There i s s t i l l  some advantage  w i t h t h e hope t h a t i t may  i n p r o c e e d i n g w i t h such a t r e a t m e n t ,  s u p p o r t the e x i s t e n c e of a s o l i d - s o l i d  t r a n s i t i o n t e m p e r a t u r e x, even i f a p r e c i s e v a l u e i s not o b t a i n a b l e . Because o f the r a t h e r l e n g t h y development i s p r e s e n t e d i n Appendix B, p L e t us now  necessary, t h i s treatment  184.  summarize the e v i d e n c e f o r the e n a n t i o t r o p i c  of racemic m o d i f i c a t i o n s .  F i r s t of a l l ,  ordering  slow and r a p i d c o o l i n g o f the  m e l t on the d.s.c. g i v e s racemate and e u t e c t i c form, r e s p e c t i v e l y . Slow and r a p i d e v a p o r a t i o n o f s o l u t i o n s a t room t e m p e r a t u r e g i v e t h e same r e s u l t s .  These o b s e r v a t i o n s a r e c o n s i s t e n t w i t h the  b e i n g t h e more s t a b l e form a t room t e m p e r a t u r e .  racemate  S i n c e the l e s s  stable  o f two forms " r a r e l y , i f e v e r " can be produced above the t e m p e r a t u r e 81c at w h i c h b o t h have e q u a l f r e e e n e r g i e s ,  the f a c t t h a t b o t h can be  o b t a i n e d at a l l by r e c r y s t a l l i z a t i o n a t room t e m p e r a t u r e i m p l i e s x i s above room t e m p e r a t u r e . S e c t i o n 3.5.1  that  A n t i c i p a t i n g a r e s u l t presented i n  ( p L L 2 ) , we have found t h a t the l o w e s t t e m p e r a t u r e a t w h i c h  the racemate -*• e u t e c t i c form t r a n s f o r m a t i o n can be o b s e r v e d i s 76°C,  79  so that T must be lower than this temperature.  The treatment i n Appendix  B supports the enantiotropic r e l a t i o n s h i p , with a most probable t r a n s i t i o n temperature of 86°C. These independent observations together are consistent with the system R- and S-l,1'-binaphthyl possessing an enantiotropic phase r e l a t i o n ship at the racemic composition, and a phase diagram l i k e that i n Figure 11 (d), p 67, with the t r a n s i t i o n temperature x between 25 and 76°C. Because the higher temperature l i m i t i s closer to the calculated most probable t r a n s i t i o n temperature, the value of T w i l l be taken as ca. 70°C for the remainder of this t h e s i s .  3.3.3  The Stable and Metastable Phase Diagram The phase diagram for the R- and S-l,1'-binaphthyl system i s redrawn  in Figure 14 (a). The s o l i d l i n e s represent phase boundaries r e f l e c t i n g the lowest free energy surfaces i n a temperature-composition-free energy plot (Section 2.3.2, p 32).  This type of phase diagram (two racemic  modifications, where a racemate i s the low temperature form and a eutectic mixture i s the high temperature form) has also been observed with (+)-  rv> rum™ CH„CHCONH„  I o2 CH C O  H  ^  2  f CO" 2  CH CHCONH  0H  34  3  2  NH. 4  +  35  |92~ CHOH  C 0  R  u  +  H CO " Ru 2 H  36  +  TEMPERATURE: 130°  >i pi  158 150 145 u  o  (b)  w w w  130 -  TEMPERATURE: 150°  H  Ed H  ca. 70 (c)  erf w w w  25 (a) 50  100  PERCENTAGE (-)-ENANTIOMER Figure 14.  _L  50  PERCENTAGE (-)-ENANTIOMER  (a) Phase diagram for the R- and S-l,1'-binaphthyl system, showing metastable ex-  tensions (dotted lines) of the phase boundaries.  (b) Schematic free energy-composition plot  at 130°, showing the lowest (dashed line) and next-lowest (dotted lines) free energy surfaces, (c)  As for (b), but at 150°.  100  81  and  (-)-ammonium hydrogen m a l a t e  ( 3 4 ) , where x = 73°;  w i t h (+)- and  85 ( - ) - d i l a c t y l d i a m i d e ( 3 5 ) , where x = 35°; w i t h (+)- and ( - ) - r u b i d i u m 45d t a r t r a t e ( 3 6 ) , where x = 40°; and w i t h the complex s a l t (+)- and Q  ( - ) - [ C o ( C 0 ) ] K - 3 . 5 H 0 , where x = 2  4  3  3  2  C  13°.  The phase diagram ' r e p r e s e n t i n g the l o w e s t f r e e energy s u r f a c e s w i l l not show any s t r u c t u r e f o r the m e l t i n g of the 1 , 1 ' - b i n a p h t h y l racemate a t 145°,  s i n c e t h i s t r a n s f o r m a t i o n i s m e t a s t a b l e and  between phases which a r e a t h i g h e r f r e e e n e r g i e s a t t h i s  occurs  temperature.  However the t r a n s f o r m a t i o n i s v e r y r e a l and f o r t h i s r e a s o n we have deduced the m e t a s t a b l e phase b o u n d a r i e s and superimposed F i g u r e 14 (a) ( d o t t e d l i n e s ) .  them on  The a r e a s e n c l o s e d by the d o t t e d l i n e s  have no s i g n i f i c a n c e i n the phase r u l e sense; they m e r e l y r e p r e s e n t m e t a s t a b l e e x t r a p o l a t i o n s o f t h e s t a b l e a r e a s , and must be c o n s i d e r e d individually.  The o r i g i n of the d o t t e d l i n e s can be seen i n the  f r e e e n e r g y - c o m p o s i t i o n p l o t a t c o n s t a n t p r e s s u r e and a t 130° 14 ( b ) ) and a t 150°  ( F i g u r e 14 ( c ) ) . The most s t a b l e f r e e  arrangement at b o t h of t h e s e t e m p e r a t u r e s  experimentally.  (Figure  energy  i s shown by t h e dashed  and i s seen to be a e u t e c t i c m i x t u r e o f R and S c r y s t a l s ,  schematic  as  line,  determined  The n e x t most s t a b l e arrangement i s shown by the d o t t e d  l i n e s i n F i g u r e 14 (b) and  ( c ) . At 130°,  t h e s e connect s o l i d R w i t h  racemate on one s i d e o f t h e diagram, and s o l i d S w i t h racemate on the o t h e r , i n the same manner as they do s t a b l y below c a . 70°. s i m i l a r d o t t e d l i n e s connect R and S c r y s t a l s  individually  At  t o the m e l t  phase, an arrangement which i s l o w e s t i n f r e e energy above 158°. g o i n g t o h i g h e r t e m p e r a t u r e s , the r a c e m i c m e l t d e c r e a s e s  150°,  i n free  In energy  82  r e l a t i v e t o t h e racemate and.the e u t e c t i c m i x t u r e , becoming l o w e r than the racemate a t 145° and lower than the e u t e c t i c m i x t u r e a t 158° ( s e e a l s o F i g u r e 11 ( b ) , p 6 7 ) . If a p a r t i a l l y resolved  sample o f S - l , 1 ' - b i n a p h t h y l a t t a i n s i t s  most s t a b l e s t a t e a t 25° ( p o i n t p, F i g u r e 14 ( a ) ) , i t w i l l c o n s i s t of S c r y s t a l s and racemate c r y s t a l s .  only  When t h e sample i s h e a t e d t o  150° ( o r , f o r t h a t m a t t e r , any t e m p e r a t u r e between 145° and 158°), t h e racemate w i l l melt i n t h e p r e s e n c e o f t h e more s t a b l e S c r y s t a l s . these c r y s t a l s exercise  complete c o n t r o l o v e r t h e e n s u i n g  If  crystallization,  then t h e e n t i r e sample w i l l become S - ( + ) - l , 1 ' - b i n a p h t h y l i n a d r i v e toward lower f r e e energy. (discussed  i n Section  Preparation  3.4, which f o l l o w s )  complete r e s o l u t i o n i n a s i n g l e Likewise,  of the correct  initial  should therefore  material  result i n  step.  between c a . 70° and 145°, a d i r e c t racemate -*• e u t e c t i c  t r a n s f o r m a t i o n would l o w e r t h e f r e e energy o f t h e system.  Preliminary  o b s e r v a t i o n s a t 120° ( T a b l e I I I , p 51) i n d i c a t e t h a t even w i t h o u t t h e i n t e r m e d i a c y o f t h e m e l t , enantiomer i n t e r c o n v e r s i o n  i s possible,  m i t t i n g a r e s o l u t i o n of 1,1'-binaphthyl completely i n the s o l i d Our  extensive k i n e t i c investigations  reported i n Section  perstate.  m  i n t h i s t e m p e r a t u r e range a r e  3.5.  We r e f e r t o t h i s g e n e r a l phenomenon as a s o l i d - s t a t e r e s o l u t i o n . At a l l t e m p e r a t u r e s , from 70° t o 158°, i t i s a r e s o l u t i o n by t h e s o l i d s t a t e - that i s , the r e s o l v i n g "agent" i s the d i s c r i m i n a t i n g s u r f a c e of t h e growing c r y s t a l s o f pure e n a n t i o m e r . Below 145°, the r e s o l u t i o n i s o c c u r r i n g t o t a l l y i n t h e s o l i d s t a t e , by means o f a s o l i d s o l i d phase transformation.  83  3.4  P e r f e c t i o n of t h e S o l i d - S t a t e R e s o l u t i o n Our i n i t i a l attempts  to r e s o l v e neat, p o l y c r y s t a l l i n e  1,1 -binaphthyl 1  ( S e c t i o n 3.2, p 4 9 ) , a l t h o u g h s u c c e s s f u l , s u f f e r e d from a l a c k o f r e p r o ducibility.  The b e s t method we d e v i s e d was a c y c l i n g p r o c e d u r e ,  which  e v e n t u a l l y a c h i e v e d a h i g h r e s o l u t i o n , but d i d so i n an u n p r e d i c t a b l e fashion.  Much o f our r e s e a r c h e f f o r t w i t h t h e 1 , 1 ' - b i n a p h t h y l  was d i r e c t e d toward  system  t r y i n g t o a c h i e v e some c o n t r o l over t h e r e s o l u t i o n .  The d e t e r m i n a t i o n o f t h e phase diagram was a major s t e p i n u n d e r s t a n d i n g what o r i g i n a l l y seemed a v e r y u n u s u a l r e a c t i o n .  Perhaps now we c o u l d  use t h i s knowledge t o p r e p a r e r e p r o d u c i b l y t h e e l u s i v e b a t c h o f s o l i d 1 , 1 ' - b i n a p h t h y l h a v i n g o r i g i n a l l y l i t t l e o r no o p t i c a l r o t a t i o n b u t p o s s e s s i n g t h e a b i l i t y t o r e s o l v e t o t a l l y s i m p l y on h e a t i n g t h e s o l i d material.  Once t h i s i s a c c o m p l i s h e d ,  such a h i g h l y s t e r e o s p e c i f i c  s o l i d c o u l d be used t o s t u d y t h e k i n e t i c s o f t h e r e s o l u t i o n e n a b l i n g , h o p e f u l l y , a more d e t a i l e d m e c h a n i s t i c  process,  description.  Our s e v e r a l approaches t o t h e problem o f r e p r o d u c i b i l i t y a r e 79a treated i n this section. h i s attempted  with  h e t e r o h e l i c e n e r e s o l u t i o n s , "both e x c i t i n g and f r u s t r a t i n g , "  and i n t h e end, v e r y 3.4.1  We found t h i s t a s k , as d i d Wynberg  The B e h a v i o u r  rewarding. o f S o l i d Racemic  1,1'-Binaphthyl  B e f o r e t h e more e l a b o r a t e schemes a r e d i s c u s s e d , t h e b e h a v i o u r o f racemic  1 , 1 ' - b i n a p h t h y l , i s o l a t e d d i r e c t l y from t h e G r i g n a r d c o u p l i n g  r e a c t i o n ( S e c t i o n 3.1.2, p 48) s h o u l d be e s t a b l i s h e d . 1,1'-binaphthyl  was used as a c o n t r o l , and heated  Initially,  alongside  a c t i v e samples w h i c h i n c r e a s e d i n r o t a t i o n a t 150°.  racemic  partially  I n t h i s way, i t was  84  d i s c o v e r e d t h a t even r a c e m i c m a t e r i a l c o u l d d e v e l o p o p t i c a l a c t i v i t y on heating.  Of t h e two b a t c h e s (A and B) o f r a c e m i c 1 , 1 ' - b i n a p h t h y l o r i g i n -  a l l y s t u d i e d ( T a b l e I I I , p 5 1 ) , one (A) d i d n o t r e s o l v e a t a l l , b u t t h e o t h e r (B) gave s c a t t e r e d a c t i v i t i e s , w h i c h were a l l p o s i t i v e . Throughout  t h e c o u r s e o f t h i s work, s e v e r a l G r i g n a r d p r e p a r a t i o n s  were performed when s t o c k s o f r a c e m i c 1 , 1 ' - b i n a p h t h y l r a n l o w , and i t became r a t h e r r o u t i n e t o c h a r a c t e r i z e each b a t c h by h e a t i n g a few samples a t 150°and c h e c k i n g f o r any r e s o l u t i o n .  Table V I I I compiles the r e s u l t s  o f samples o f t h e r a c e m i c m a t e r i a l w h i c h were h e a t e d f o r v a r i o u s r e a s o n s . A d i f f e r e n t " b a t c h " i s p r e p a r e d each time a g i v e n p r e p a r a t i o n was r e c r y s t a l l i z e d , so t h a t a l l m a t e r i a l w i t h i n each b a t c h has t h e same phase c o n t e n t and average c r y s t a l s i z e and p e r f e c t i o n .  A l t h o u g h some were  r e c r y s t a l l i z e d i n the presence of racemic 1,1'-binaphthyl seeds, t h e r e was no d e l i b e r a t e a d d i t i o n o f any a c t i v e  crystals.  Racemic 1 , 1 ' - b i n a p h t h y l shows some v e r y i n t e r e s t i n g b e h a v i o u r on heating.  Most o f t h e r a c e m i c b a t c h e s ( e x c e p t A, E, G, and 0) d e v e l o p e d  o p t i c a l a c t i v i t y when heated a t t e m p e r a t u r e s from 100° t o 150°.  The f a c t  t h a t t h i s r e s o l u t i o n o c c u r s below 145° f i r m l y e s t a b l i s h e s t h a t t h e m e l t i s n o t n e c e s s a r y t o t h e r e s o l u t i o n p r o c e s s - t h e d i r e c t phase t r a n s f o r m a t i o n racemate -* e u t e c t i c form i s s u f f i c i e n t t o c r e a t e o p t i c a l  activity.  A l t h o u g h t h e b e h a v i o u r o f some b a t c h e s i s n o t w e l l d e f i n e d because o f t h e few samples h e a t e d , o t h e r s ( e . g . , B and L) were i n v e s t i g a t e d w i t h many samples and r e v e a l e d a v e r y s u r p r i s i n g tendency t o d e v e l o p o p t i c a l i n one d i r e c t i o n o n l y .  F o r example,  t h e 37 samples  activity  taken from Racemic  B a t c h L a r e p l o t t e d i n F i g u r e 15 as a f u n c t i o n o f t i m e .  A l l samples a r e  p o s i t i v e and w i d e l y s c a t t e r e d i n o p t i c a l r o t a t i o n ; no k i n e t i c t r e n d s a r e  85  Table V I I I The Development o f O p t i c a l A c t i v i t y on H e a t i n g P o l y c r y s t a l l i n e ,  Racemic  1,1'-Binaphthyl  Racemic B a t c h  Time, hours  [a] , degrees  1  +25  D  1  +65  E  1  0  F  1  G  1  I  15.5  -63  13  -77  C  Temperature,  °C  149.6  0  b  -45  b  2  -78, - 1 4 0  b  16  -87, - 1 2 9  b  19  K  +24, 0  -52,  5  -124  120  46  -108  100  120  L  135  0 t o 50  M  135  15  N  149.6  -5 see F i g u r e 15 -8,  -9  1  -22  5  +3  2  0,  o  b  b  F o r Racemic Batches A and B, see T a b l e I I I , p 51. S p e c i f i c r o t a t i o n s o f two i n d i v i d u a l o f time a t t h e same t e m p e r a t u r e .  samples h e a t e d f o r t h e same l e n g t h  TEMPERATURE:  135°  +250 on  3  o w p  +200  o o o  S3  O H < H O  1—I  +150  o  pi U o w 00  O  oo  o o  o o  +100  o  o o  +50  o o o  &o-Q  o  o 1 —  10  J 30  20 TIME  F i g u r e 15.  S p e c i f i c r o t a t i o n as a f u n c t i o n  b i n a p h t h y l (L Batch) a t 135°.  L 40  50  (HOURS)  o f time f o r t h e s o l i d - s t a t e r e s o l u t i o n o f racemic 1,1  87  discernible.  An e q u a l l y r e m a r k a b l e r e s u l t , as a l r e a d y n o t e d , was  o b t a i n e d w i t h Racemic B a t c h B, where a l l 11 samples r e s o l v e d i n a p o s i t i v e direction.  Some b a t c h e s ( I and J , f o r example), a l t h o u g h i n v e s t i g a t e d  l e s s e x t e n s i v e l y , develop only n e g a t i v e r o t a t i o n s . 1 , 1 ' - B i n a p h t h y l p r e p a r e d from o p t i c a l l y i n a c t i v e r e a g e n t s seems to are  possess a b u i l t - i n s t e r e o s p e c i f i c i t y .  Some d i s s y m m e t r i c i n f l u e n c e s  p r e s e n t i n t h e b a t c h e s , w h i c h d e f i n i t e l y appear r a c e m i c when a n a l y z e d  by p o l a r i m e t r y . As w i l l be proven i n S e c t i o n 3.6, r a c e m i c 1 , 1 ' - b i n a p h t h y l does n o t p o s s e s s any f o r e i g n d i s s y m m e t r i c i m p u r i t y w h i c h can i n f l u e n c e the d i r e c t i o n of r e s o l u t i o n .  R a t h e r , t h e i n f l u e n c e s must a r i s e from t h e  1 , 1 ' - b i n a p h t h y l system i t s e l f ,  i n t h e form o f s m a l l , i m p e r c e p t i b l e 46  e x c e s s e s o f one enantiomer.  I t i s generally recognized  that  racemic  p r e p a r a t i o n s c o n t a i n t i n y e x c e s s e s o f one enantiomer due t o random s t a t i s t i c a l f l u c t u a t i o n s alone.  However, o u r r a c e m i c p r e p a r a t i o n s were  performed  a f t e r t h e f i r s t o p t i c a l l y a c t i v e l , l ' - b i n a p h t h y l samples were  obtained.  I t i s p o s s i b l e t h e r e f o r e t h a t t h e s m a l l e x c e s s e s c o u l d have  a r i s e n from r e s o l v e d 1 , 1 ' - b i n a p h t h y l d u s t i n o u r l a b o r a t o r y , which may overshadow any random f l u c t u a t i o n s . Whatever t h e r e a s o n f o r t h e i r e x i s t e n c e , t h e s e u n o b s e r v a b l e e x c e s s e s o f one enantiomer  can be a m p l i f i e d t h r o u g h t h e phase i n t e r -  a c t i o n s i n t h e R- and S - l , 1 ' - b i n a p h t h y l system.  As r e v e a l e d by t h e  q u a l i t a t i v e d.s.c. r e s u l t s i n S e c t i o n 3.3.2.2 (p 68), e v e r y r a c e m i c b a t c h c o n t a i n s some e u t e c t i c form, even i f t h i s i s p r e s e n t o n l y i n trace quantities.  S i n c e any enantiomer  excess must be c o n t a i n e d i n t h e  e u t e c t i c form (as a g r e a t e r number o f , s a y , R than S c r y s t a l s ) , then i f t h i s form i s o n l y a s m a l l p a r t o f t h e t o t a l sample,  the r a t i o of R to  S c r y s t a l s w i l l be f a r g r e a t e r than t h e r a t i o o f R t o S m o l e c u l e s i n t h e  88  whole sample.  On h e a t i n g , t h e enantiomer i n excess r e v e a l s i t s i d e n t i t y  by c a u s i n g t h e c r y s t a l l i z a t i o n o f m o l e c u l e s o f i t s own c o n f i g u r a t i o n . The 1 , 1 ' - b i n a p h t h y l system i l l u s t r a t e s a n o v e l method o f c h e c k i n g f o r t r a c e enantiomer e x c e s s e s , f a r s i m p l e r than t h e hundreds  of r e c r y s t a l -  l i z a t i o n s on k i l o g r a m q u a n t i t i e s o f " r a c e m i c " m a t e r i a l w h i c h a r e sometimes n e c e s s a r y t o make such e x c e s s e s o b s e r v a b l e . ^ W h i l e t h e manner i n w h i c h r a c e m i c 1 , 1 ' - b i n a p h t h y l can produce o p t i c a l a c t i v i t y on h e a t i n g i s v e r y i n t e r e s t i n g i n i t s e l f ,  the s p e c i f i c  r o t a t i o n s f a l l c o n s i d e r a b l y s h o r t o f complete r e s o l u t i o n ( [ a ] = ±245°). Perhaps c h a n g i n g t h e method o f r e s o l u t i o n might make some improvement. The phase changes accompanying  the r e s o l u t i o n of racemic 1,1'-binaphthyl  a r e racemate ->• melt -»• e u t e c t i c form a t 150° and racemate -*• e u t e c t i c below 145°.  form  An i n t e r e s t i n g a l t e r n a t i v e i s racemate ->- s o l u t i o n -*• e u t e c t i c  form, w h i c h i s p o s s i b l e when t h e s o l i d r a c e m i c samples a r e h e a t e d i n t h e p r e s e n c e o f a s a t u r a t e d s o l u t i o n o f 1 , 1 ' - b i n a p h t h y l i n an o p t i c a l l y inactive solvent.  Such a phase change i s c a l l e d a s o l u t i o n phase t r a n s -  8 ld formation,  and o c c u r s because t h e more s t a b l e o f two c r y s t a l l i n e  m o d i f i c a t i o n s i s always t h e l e s s s o l u b l e o f t h e two ( F i g u r e 1 6 ) .  I n the  t e m p e r a t u r e range 70-145° t h e racemate, b e i n g t h e more s o l u b l e (and l e s s s t a b l e ) form, m a i n t a i n s a s o l u t i o n o f 1 , 1 ' - b i n a p h t h y l w h i c h i s s u p e r s a t u r a t e d w i t h r e s p e c t t o the e u t e c t i c form, and t h e growth o f c r y s t a l s o f pure enantiomer can o c c u r from s o l u t i o n .  Such a change i n growth  environment may f a v o u r a b l y a f f e c t t h e r e s o l u t i o n . We t h e r e f o r e performed some s o l u t i o n phase t r a n s f o r m a t i o n s i n a tube s e a l e d a t b o t h ends and d i v i d e d i n t o two chambers by a f r i t t e d  disc.  The c r y s t a l s and s o l v e n t were l o c a t e d i n one end o f the tube which was  89  PERCENTAGE SOLVENT  F i g u r e 16.  Schematic  phase diagram between racemic  and a s o l v e n t w i t h b.p.> 160°.  1,1'-binaphthyl  Dotted l i n e s are metastable e x t r a p o l a t i o n s  o f phase b o u n d a r i e s , and show t h e h i g h e r s o l u b i l i t y o f t h e l e s s stable  forms.  90  t o t a l l y immersed i n a b a t h h e l d a t the t e m p e r a t u r e o f i n t e r e s t .  After  a p e r i o d o f time the s o l u t i o n c o u l d be f i l t e r e d from the c r y s t a l s the s i n t e r e d g l a s s d i s c w i t h o u t removing bath.  the sample from the  through  temperature  The t r a n s f o r m e d c r y s t a l s c o u l d then be a n a l y z e d f o r o p t i c a l  activity.  The r e s u l t s of n i n e such e x p e r i m e n t s from 110°  to 150°  using  2 - p r o p a n o l and e t h y l e n e g l y c o l as s o l v e n t s a r e l i s t e d i n T a b l e IX. Racemic B a t c h I ( w h i c h , as shown i n T a b l e V I I I , r e s o l v e s p o o r l y i n the absence o f a s o l v e n t ) was  used i n the e x p e r i m e n t s .  A l t h o u g h somewhat  h i g h e r r o t a t i o n s a r e were observed w i t h 2 - p r o p a n o l a t 120°, r o t a t i o n s c o u l d not be c o n s i s t e n t l y produced.  the b e s t  R a t h e r , the a c t i v i t i e s  were s c a t t e r e d , but a l l were, c h a r a c t e r i s t i c a l l y , i n one  direction  (negative). Table IX The Development o f O p t i c a l A c t i v i t y on H e a t i n g P o l y c r y s t a l l i n e , Racemic 1,1'-Binaphthyl  Solvent  Temperature,  Ethylene g l y c o l "  "  2-Propanol 11  3  Under a S o l v e n t  °C  Time, hours  [ a ] , degrees  110  17  0  130  24  -84  149.6  43  90  15  0  120  17  -158  "  43  -198  65  -186  19  -180  43  -144  A l l samples were t a k e n from Racemic Batch I .  -2.5  91  3.4.2  P h y s i c a l A d d i t i o n o f Seed C r y s t a l s of A c t i v e 1 , 1 ' - B i n a p h t h y l I t appears t h a t the few c r y s t a l s o f R and/or  S-l,l'-binaphthyl  w h i c h happen to e x i s t i n the r a c e m i c samples, w h i l e e f f i c i e n t l y g o v e r n i n g the d i r e c t i o n of the development the magnitude  of the r o t a t i o n .  T h i s may  o f a c t i v i t y , cannot  o c c u r because  control  these c r y s t a l s  a r e too few and too w i d e l y s c a t t e r e d t o be f u l l y e f f e c t i v e as seeds. At t h i s p o i n t we d e c i d e d t o abandon the r a c e m i c system and t o i n t r o d u c e m e c h a n i c a l l y some seed c r y s t a l s o f h i g h l y r e s o l v e d 1,1.'-binaphthyl t o the p o l y c r y s t a l l i n e m a t e r i a l , h o p i n g t o "swamp o u t " the e f f e c t of the o r i g i n a l seeds and t o c o n t r o l the r e s o l u t i o n a r t i f i c i a l l y .  This physical  s e e d i n g was done w i t h f i v e b a t c h e s o f r a c e m i c 1 , 1 ' - b i n a p h t h y l , w i t h t h e r e s u l t s i n T a b l e X.  U s u a l l y , the added seed comprised l e s s t h a n 3% o f  the t o t a l w e i g h t o f the sample, a c c o u n t i n g i t s e l f f o r l e s s than specific rotation.  6°  The seed c r y s t a l s were added i n powdered form t o  t h e r a c e m i c m a t e r i a l , c o n t a i n e d i n a g l a s s ampule.  The ampule was  then  s e a l e d , shaken v i g o r o u s l y f o r f i v e minutes t o d i s t r i b u t e the added s e e d s , and then h e a t e d .  I n two cases (F and G) the r e s o l v a b i l i t y o f the r a c e m i c  m a t e r i a l ( T a b l e V I I I , p 85) was  improved.  However, r o t a t i o n s were n e v e r  v e r y h i g h , and w i t h B a t c h I , seeds of b o t h p o s i t i v e and n e g a t i v e r o t a t i o n s s i m p l y d e c r e a s e d the n e g a t i v e a c t i v i t i e s d e v e l o p e d i n the racemic m a t e r i a l .  unseeded,  T h i s f a i l u r e o f the p h y s i c a l a d d i t i o n of seeds i s  p r o b a b l y a r e f l e c t i o n of the d i f f i c u l t y i n m i x i n g two s o l i d s  (i.e.,  seed  c r y s t a l s and r a c e m i c m a t e r i a l ) m e c h a n i c a l l y . Perhaps  the a d d i t i o n of seed c r y s t a l s t o the r a c e m i c , s u p e r c o o l e d  1 , 1 ' - b i n a p h t h y l melt might be more e f f e c t i v e than the m e c h a n i c a l m i x i n g of s o l i d s .  A s e r i e s o f e x p e r i m e n t s were performed to t e s t t h i s s u g g e s t i o n ,  92  Table X The I n f l u e n c e o f Added Seed C r y s t a l s o f O p t i c a l l y A c t i v e on the S o l i d - S t a t e R e s o l u t i o n o f P o l y c r y s t a l l i n e , Racemic  [a] o f Seeds,  Percent of T o t a l  1,1'-Binaphthyl 1,1'-Binaphthyl  [a] P r o d u c e d ,  Racemic B a t c h degrees  B  +99  F  +200  M a t e r i a l Due t o Seeds  10 3  degrees  +55 +112  tt  0.9  +53  II  ti  0.9  +91  II  ti  0.7  +42  H  II  0.05  +62  1.2  -20  1.6  -28  3.4  -15  G  -212  I  II  II  +204  II  The t o t a l w e i g h t o f each sample ( e x c e p t H) was between 10 and 20 mg. The sample t a k e n from P.acemic B a t c h H weighed 2.0 g. I t s b e h a v i o u r i n the absence o f a r t i f i c i a l s e e d i n g was not checked. A f t e r h e a t i n g a t 150° f o r a t l e a s t one hour.  and the r e s u l t s a r e l i s t e d i n T a b l e X I , i n the o r d e r i n which t h e y were obtained.  E i g h t d i f f e r e n t samples o f h i g h l y a c t i v e 1,1'-binaphthyl were  used as seeds.  The s u p e r c o o l e d m e l t s were p r e p a r e d by h e a t i n g 0.2 g o f  r a c e m i c 1,1'-binaphthyl i n a s t o p p e r e d t e s t tube a t 170-190° f o r t h r e e minutes t o d e s t r o y a l l s o l i d forms o f 1 , 1 ' - b i n a p h t h y l , then q u i c k l y  0  93  Table XI The I n f l u e n c e o f O p t i c a l l y A c t i v e l , l ' - B i n a p h t h y l Seed C r y s t a l s on t h e R e s o l u t i o n by C r y s t a l l i z a t i o n from a S u p e r c o o l e d , Racemic 1 , 1 ' - B i n a p h t h y l  [a] o f Seeds,  Number and  Temperature o f  degrees  C o n d i t i o n o f Seeds  S u p e r c o o l e d M e l t , °C  ca. 1 mg c o a r s e powder  149.6  1  +200  2  ti  II  3  0  3  -7  a few c o a r s e g r a n u l e s II  4  none  6  +200  7  +204  8  -212  tt  II  14  -212  15  +204  II  16  -212  II  17  +204  18  -212  19  +204  20  it  II  it  one  granule it it II  -7 +52  -6 +22  +172  135  it  11  +149  +176  +204  13  +126  it  II  a few c o a r s e g r a n u l e s  +205 +203  +214  ti  +204  B  A  -21Q  0  none  degrees  ti  it  11 12  it  it  9 10  a few c o a r s e g r a n u l e s  II  [a],  Melt  0 0 +1  140  0  tt  -9  145  +3  149.6  +144  155  -183  -10  -194  +76  +73  it  -1  +51  it  +81  +77  +25  +40  149.6  II  145 II  +5 -18  b  94  (Table X I ,  continued) 149.6  cne g r a n u l e  -73  -22  21  +194  22  +204  "  "  +139  23  +200  a few c o a r s e g r a n u l e s  "  +196  +158  24  -212  c a . 1 mg f i n e powder  "  -42  -35  25  +200  145  +95  26  -212  one g r a n u l e  0  D u p l i c a t e a n a l y s e s on t h e same sample a r e l i s t e d under A and B.  immersing  most o f t h e tube i n a t h e r m o s t a t t e d s i l i c o n e o i l b a t h  h e l d a t 150°).  (usually  The s e e d i n g c r y s t a l s o f l , l ' - b i n a p h t h y l , which v a r i e d  from  a s i n g l e p a r t i c l e t o a f i n e powder, were then added t o t h e s u p e r c o o l e d melt.  The tubes were s t o p p e r e d w h i l e t h e s o l i d l , l ' - b i n a p h t h y l grew  ( u s u a l l y , o v e r n i g h t ) , to t r y to eliminate laboratory dust. Some e x p e r i m e n t s having  [ a ] > 200°.  experiments  were v e r y s u c c e s s f u l i n p r o d u c i n g  However, attempts  usually failed.  t o reproduce  1,1'-binaphthyl  these s u c c e s s f u l  The d u p l i c a t e a n a l y s e s show t h a t some  i n d i v i d u a l samples were q u i t e inhomogeneous i n a c t i v i t y , i m p l y i n g t h a t the added seeds c o u l d n o t always e n t i r e melt.  c o n t r o l the c r y s t a l l i z a t i o n of the  U n i n t e n t i o n a l seeding probably accounts  f o r the lack of  r e p r o d u c e a b i l i t y , s i n c e even "unseeded" samples e v e n t u a l l y c r y s t a l l i z e d . I n a d v e r t e n t s e e d i n g can be e l i m i n a t e d by p e r f o r m i n g t h e c r y s t a l l i z a t i o n s i n s e a l e d ampules.  I n f a c t , using a s p e c i a l procedure, a l l  1 , 1 ' - b i n a p h t h y l seeds can be e l i m i n a t e d , and t h e r e s o l u t i o n by c r y s t a l l i z a t i o n can be performed  spontaneously.  Because o f t h e i r  special  95  i n t e r e s t , the r e s u l t s of these extensive experiments are reported i n S e c t i o n 3.6.  F o r t h e p r e s e n t d i s c u s s i o n , we s h a l l s i m p l y s t a t e t h a t  this  method does n o t c o n s i s t e n t l y produce h i g h l y a c t i v e 1 , 1 ' - b i n a p h t h y l . Because s e v e r a l o t h e r systems have been s u c c e s s f u l l y r e s o l v e d by  85 seeding a supersaturated s o l u t i o n , t r i e d w i t h 1,1'-binaphthyl.  t h i s a d d i t i o n a l method was a l s o  By means o f a s p e c i a l e x p e r i m e n t a l p r o c e d u r e  w h i c h we d e v e l o p e d , a s i n g l e seed h a v i n g [ a ] = -212° was p l a c e d i n c o n t a c t w i t h a f i l t e r e d , s u p e r s a t u r a t e d s o l u t i o n o f 1,1'-binaphthyl i n at 120° ( s e a l e d t u b e ) . i n d e e d a poor r e s u l t .  2-propanol  C r y s t a l s d e v e l o p e d , b u t a n a l y s i s gave [ a ] = -2°, A second attempt was made, t h i s time u s i n g a  h i g h - s p e e d s t i r r e r t o d i s p e r s e f i n e l y ground seed c r y s t a l s ( [ a ] = -194°) i n a supersaturated solution with ethylene g l y c o l .  The r e s u l t i n g  activity  o f t h e p r e c i p i t a t e d m a t e r i a l was, however, o n l y [ a ] = -38°. No f u r t h e r a t t e m p t s t o seed out o p t i c a l l y a c t i v e 1,1'-binaphthyl from s o l u t i o n were made. 3.4.3  The B e h a v i o u r o f P a r t i a l l y A c t i v e S o l i d  1,1'-Binaphthyl  E v i d e n t l y , t h e m e c h a n i c a l a d d i t i o n o f seed c r y s t a l s t o r a c e m i c 1,1 -binaphthyl 1  ( i n s o l i d , l i q u i d and s o l u t i o n phases) i s a poor method  of r e p r o d u c i b l y p r e p a r i n g h i g h l y o p t i c a l l y a c t i v e m a t e r i a l .  This i s  p r o b a b l y due t o t h e f a c t t h a t i n t h e s e e x p e r i m e n t s , t h e e f f e c t o f t h e seeds i s n o t " f e l t " by t h e b u l k o f t h e sample, i n s p i t e o f e f f o r t s t o o b t a i n (manually) a good d i s t r i b u t i o n o f t h e seed c r y s t a l s .  A f a r more i n t i m a t e  mixture i s apparently required. The b e s t method o f m i x i n g o p t i c a l l y a c t i v e and r a c e m i c  1,1'-  b i n a p h t h y l i s t o d i s s o l v e b o t h i n a s u i t a b l e s o l v e n t then r e c r y s t a l l i z e  96  the p a r t i a l l y a c t i v e m a t e r i a l .  I n e f f e c t , t h i s was  o r i g i n a l c y c l i n g e x p e r i m e n t s ( S e c t i o n 3.2,  performed i n the  p 4 9 ) , but not a l l o f  r e c r y s t a l l i z e d b a t c h e s would r e s o l v e w e l l on h e a t i n g . have been due  This f a i l u r e  p l u s c r y s t a l s of o n l y one We now  s t a t e , and  may  to the f a c t t h a t not a l l of the p a r t i a l l y a c t i v e samples  were i n t h e i r most s t a b l e s t a t e at room t e m p e r a t u r e ( i . e . ,  (p 6 4 ) .  the  enantiomer),  racemate  as d i s c u s s e d i n S e c t i o n 3.3.2.1  t u r n our a t t e n t i o n t o the achievement o f t h i s most s t a b l e  the p o s s i b i l i t y of r e p r o d u c i b l y p r e p a r i n g t h a t h i g h l y s t e r e o -  s p e c i f i c batch of 1,1'-binaphthyl  which w i l l r e s o l v e completely  in a  single heating. A sample w h i c h i s not i n i t s most s t a b l e s t a t e would be t o have too h i g h a e u t e c t i c phase c o n t e n t , and  expected  the approach t o t h i s s t a t e  i s i d e n t i c a l w i t h the c o n v e r s i o n o f a l l r a c e m i c m a t e r i a l i n the sample t o the racemate, l e a v i n g o n l y racemate and enantiomer.  c r y s t a l s o f the d e s i r e d  Such a s o l i d - s t a t e c o n v e r s i o n , i f i t o c c u r s  at a l l , i s  c e r t a i n l y v e r y s l u g g i s h at room t e m p e r a t u r e . Slow s o l i d - s o l i d t r a n s f o r m a t i o n s  can be speeded up t h r o u g h the  use  8 ld o f s o l u t i o n phase t r a n s f o r m a t i o n s . t r a n s f o r m a t i o n racemate 70°,  s o l u t i o n -*• e u t e c t i c form, w h i c h o c c u r s  have a l r e a d y been r e p o r t e d  periments,  R e s u l t s of the s o l u t i o n phase  ( S e c t i o n 3.4.1, p 8 3 ) .  In these  above ex-  we had hoped t h a t the p r e s e n c e of a s o l u t i o n might improve  the a c t u a l r e s o l u t i o n p r o c e s s .  I f the r e v e r s e t r a n s f o r m a t i o n  (racemic  e u t e c t i c -> s o l u t i o n -* racemate) can be e f f e c t e d at room t e m p e r a t u r e (see F i g u r e 16, p 8 9 ) , i t might be p o s s i b l e t o p r e p a r e good s t a r t i n g m a t e r i a l f o r the s o l i d - s t a t e r e s o l u t i o n s . To t e s t the p o s s i b i l i t y of such a t r a n s f o r m a t i o n , we attempted t o  97  produce racemate  from b o t h p a r t i a l l y a c t i v e and almost r a c e m i c e u t e c t i c  form i n two s e p a r a t e e x p e r i m e n t s .  However, even a f t e r v i g o r o u s s t i r r i n g  of t h e p u l v e r i z e d e u t e c t i c samples  i n c o n t a c t w i t h pentane a t room  t e m p e r a t u r e f o r up t o t h r e e days, and a f t e r s e e d i n g t h e m i x t u r e w i t h c r y s t a l s o f racemate, no t r a n s f o r m a t i o n was o b s e r v e d .  C o o l i n g the  r a p i d l y - s t i r r i n g m i x t u r e t o -78° and changing s o l v e n t s t o methanol  also  has a b s o l u t e l y no e f f e c t . The f a i l u r e o f t h i s s o l u t i o n phase t r a n s f o r m a t i o n may c a s t some doubt on t h e c o n c l u s i o n from phase s t u d i e s t h a t the racemate  i s the  s t a b l e form o f r a c e m i c 1 , 1 ' - b i n a p h t h y l a t room t e m p e r a t u r e and below. However t h i s n e g a t i v e e v i d e n c e i s n o t e n l i g h t e n i n g , s i n c e even  solution  phase t r a n s f o r m a t i o n s may be s l o w , e s p e c i a l l y i f t h e d i f f e r e n c e i n 8 Id s o l u b i l i t i e s o f t h e two forms i s s l i g h t . The b e s t method o f p r o d u c i n g t h e racemate, i n s p i t e o f i t s unp r e d i c t a b l e r e s u l t s , i s r e c r y s t a l l i z a t i o n from s o l u t i o n . a l l y r e c r y s t a l l i z e d from b o i l i n g pentane at t h i s t e m p e r a t u r e were s l i g h t .  We had o r i g i n -  (36°), s i n c e l o s s e s i n r o t a t i o n  Low t e m p e r t u r e r e c r y s t a l l i z a t i o n s (-78°)  from a c e t o n e , used i n t h e l i m i t o f r e s o l u t i o n s t u d i e s (Appendix A, p 1 7 8 ) , can be c a r r i e d out w i t h v i r t u a l l y no l o s s e s i n a c t i v i t y by s o l u t i o n r a c e m i z a t i o n , and we n e x t e x p l o r e d t h i s as a method o f p r e p a r i n g 1,1'b i n a p h t h y l w h i c h might r e s o l v e w e l l on h e a t i n g . The p r o c e d u r e we f o l l o w e d i n v o l v e d making an almost  saturated  s o l u t i o n o f p a r t i a l l y a c t i v e ( [ a ] = ±10°) 1 , 1 ' - b i n a p h t h y l i n acetone a t room t e m p e r a t u r e .  T h i s s o l u t i o n was c a r e f u l l y f i l t e r e d then p l a c e d i n  a Dry I c e - a c e t o n e b a t h , where f i n e c r y s t a l s appeared i n about t e n m i n u t e s . A f t e r 30 minutes to one hour, c r y s t a l l i z a t i o n seemed c o m p l e t e , and r a p i d  98 f i l t r a t i o n w h i l e c o l d gave c a . 80% m a t e r i a l .  The f i r s t such  recrystalliz-  a t i o n we t r i e d was p e r f e c t l y s u c c e s s f u l ; c r y s t a l s h a v i n g an a c t i v i t y o f [a]  = +0.8° r e s o l v e d , on h e a t i n g a t 150° o v e r n i g h t , t o [a] = +209°.  This  r e p r e s e n t e d t h e l a r g e s t i n c r e m e n t i n o p t i c a l r o t a t i o n we had y e t o b s e r v e d . A second e x p e r i m e n t , r e p e a t i n g e x a c t l y t h e p r o c e d u r e o f t h e f i r s t ,  was  a l s o s u c c e s s f u l ; m a t e r i a l o f a c t i v i t y [a] = +0.3° gave [a] = +205° on heating.  The p r o c e d u r e seemed r e p r o d u c i b l e .  A t h i r d experiment was  performed on a l a r g e r amount (4 g) o f 1 , 1 ' - b i n a p h t h y l and i t , t o o , p r o duced 80% m a t e r i a l , [a] = +1.4°, w h i c h c o u l d i n c r e a s e t o [a] = +211° on h e a t i n g a t 150°.  T h i s l a r g e b a t c h o f r e s o l v a b l e 1 , 1 ' - b i n a p h t h y l was  used i n a k i n e t i c s t u d y (as K i n e t i c B a t c h S - l ,  S e c t i o n 3 . 5 ) , from w h i c h  i t was l e a r n e d t h a t even a t 105°, r e s o l u t i o n t o [a] = +221° was  possible.  A f o u r t h low t e m p e r a t u r e r e c r y s t a l l i z a t i o n was an attempt t o o b t a i n 1 , 1 ' - b i n a p h t h y l w h i c h would g i v e h i g h n e g a t i v e r o t a t i o n s on h e a t i n g . Much to our d i s a p p o i n t m e n t , t h e attempt f a i l e d , and o n l y [a] = -31° was a t t a i n e d on h e a t i n g a t 135° o v e r n i g h t .  A p p a r e n t l y we had unknowingly  changed some parameter t o w h i c h t h e r e c r y s t a l l i z a t i o n p r o c e d u r e i s r a t h e r sensitive.  We then s e t out t o d e t e r m i n e t h e e x t e n t t o w h i c h our o r i g i n a l  s u c c e s s f u l p r o c e d u r e c o u l d be a l t e r e d . S i x t e e n more r e c r y s t a l l i z a t i o n s were performed and s e v e r a l f a c t o r s were v a r i e d : the a c t i v i t y o f the s o l u t i o n o f 1 , 1 ' - b i n a p h t h y l from w h i c h r e c r y s t a l l i z a t i o n o c c u r r e d , from [a]  = 0 t o [ a ] = 71°; the c o n c e n t r a t i o n o f 1 , 1 ' - b i n a p h t h y l i n t h i s  solution,  from 1.43 g / 100 ml acetone ( s a t u r a t e d ) t o 0.67 g / 100 ml a c e t o n e ; and the  time a l l o w e d f o r r e c r y s t a l l i z a t i o n a t -78°, from 15 min t o 12 h.  v a r i e d were such q u a l i t a t i v e f a c t o r s as a g i t a t i o n w h i l e  Also  recrystallization  o c c u r r e d , methods o f f i l t r a t i o n , p u r i t y o f acetone s o l v e n t ( d i s t i l l e d o r  99  u n d i s t i l l e d ) , and s e e d i n g w i t h v a r i o u s forms o f 1 , 1 ' - b i n a p h t h y l ( b o t h a c t i v e and r a c e m i c ) . obtained. failed.  I n a l l o f t h e s e e x p e r i m e n t s , poor r e s u l t s were  Even v e r y c a r e f u l a t t e m p t s t o r e p r o d u c e t h e o r i g i n a l p r o c e d u r e We can o f f e r no e x p l a n a t i o n as t o why t h e f i r s t  three r e c r y s t a l -  l i z a t i o n s worked p e r f e c t l y , and t h e e n s u i n g s i x t e e n d i d not s u c c e e d . Perhaps t h e p r e p a r a t i o n o f r e s o l v a b l e 1 , 1 ' - b i n a p h t h y l by t h i s method i s governed by d e l i c a t e k i n e t i c f a c t o r s , w h i c h a r e d i f f i c u l t  to control  experimentally. At t h i s time we d i s c o v e r e d , somewhat by a c c i d e n t , a method w h i c h has produced h i g h l y r e s o l v a b l e 1 , 1 ' - b i n a p h t h y l e v e r y t i m e . of  In the course  c y c l i n g a q u a n t i t y o f 1 , 1 ' - b i n a p h t h y l t o h i g h r o t a t i o n s , we r e c r y s t a l -  l i z e d an a c e t o n e s o l u t i o n o f [ a ] = +10° m a t e r i a l a t -78° ( h o p i n g t o o b t a i n c r y s t a l s w h i c h would produce a t l e a s t some a c t i v i t y on h e a t i n g ) , t h e n , to  c o n s e r v e m a t e r i a l , we d i d n o t f i l t e r  t h e c r y s t a l s from t h e s o l u t i o n ,  but i n s t e a d d i s t i l l e d o f f t h e acetone under reduced p r e s s u r e a t 25°. The m a t e r i a l o b t a i n e d ( [ a ] = -9.5°) r e s o l v e d t o [ a ] = -216° on h e a t i n g at  150° f o r 16 h.  An e x t e n s i v e i n v e s t i g a t i o n o f t h i s  e v a p o r a t i o n p r o c e d u r e was c o n d u c t e d .  recrystallization-  Twenty-seven e x p e r i m e n t s were p e r -  formed, s i x t e e n o f w h i c h were r e p r o d u c i b i l i t y checks and p r e p a r a t i o n s o f h i g h l y r e s o l v a b l e 1 , 1 ' - b i n a p h t h y l , and e l e v e n o f w h i c h were v a r i a t i o n s on t h i s s u c c e s s f u l p r o c e d u r e .  Of t h e s i x t e e n r e p e t i t i o n s , f i f t e e n gave  m a t e r i a l which would r e s o l v e t o g r e a t e r than [ct] = 190° (78% r e s o l u t i o n ) on h e a t i n g a t 150°. The s u c c e s s f u l r e c r y s t a l l i z a t i o n - e v a p o r a t i o n p r o c e d u r e , summarized h e r e f o r d i s c u s s i o n and g i v e n i n d e t a i l i n S e c t i o n 4.3.2.3 ( b ) , p 1 5 8 ) , i s easy t o p e r f o r m .  The method i n v o l v e s d i s s o l v i n g 1 , 1 ' - b i n a p h t h y l o f  100  [a] = 2° t o 15° i n d i s t i l l e d acetone  (1.2 g / 100 m l ) , f i l t e r i n g t h e  s o l u t i o n , then s w i r l i n g i t i n a Dry I c e - a c e t o n e b a t h u n t i l appear (about 15 m i n ) .  crystals  The c o l d f l a s k i s then p l a c e d on t h e r o t a r y  e v a p o r a t o r and t h e vacuum (water a s p i r a t o r ) a p p l i e d .  When t h e g r e a t e s t  vacuum i s a t t a i n e d , t h e c o l d f l a s k i s l o w e r e d i n t o a b a t h a t 20-25°. As t h e f l a s k warms, t h e c r y s t a l s b e g i n t o d i s s o l v e and t h e acetone to d i s t i l l o f f .  begins  These two p r o c e s s e s (warming and l o s s o f s o l v e n t ) oppo-  s i t e l y a f f e c t t h e amount o f 1 , 1 ' - b i n a p h t h y l i n s o l u t i o n , and most ( b u t not a l l ) o f t h e c r y s t a l s d i s s o l v e a t one p o i n t , w h e r e a f t e r they come back o u t o f s o l u t i o n as t h e l o s s o f s o l v e n t c o n t i n u e s .  Eventually  ( i n about 30 m i n ) , a l l t h e s o l v e n t d i s a p p e a r s , and t h e r e m a i n i n g  crystals  w i l l r e s o l v e w e l l on h e a t i n g . S t r a i g h t e v a p o r a t i o n o f a s o l u t i o n o f 1 , 1 ' - b i n a p h t h y l g i v e s poor results.  A l s o , f o r t h e p r o c e d u r e t o s u c c e e d , t h e c r y s t a l s must n o t  t o t a l l y d i s s o l v e during the evaporation.  P a r t i a l evaporation of solvent  f o l l o w e d by f i l t r a t i o n g i v e s u n p r e d i c t a b l e r e s u l t s . The s u c c e s s o f t h i s p r o c e d u r e e v i d e n t l y depends on t h e p r e s e n c e , during the evaporation of a s l i g h t l y a c t i v e s o l u t i o n of b i n a p h t h y l , of s u i t a b l e seed c r y s t a l s .  These " c o r r e c t " seeds a r e g e n e r a t e d d u r i n g t h e  warming o f a c o l d m i x t u r e o f s o l i d m a t e r i a l p l u s s o l u t i o n t o room temperature.  The f a c t t h a t almost a l l c r y s t a l s d i s a p p e a r d u r i n g t h e  e v a p o r a t i o n i m p l i e s t h a t those which d i s s o l v e a r e " u n d e s i r e d " seeds, t h e " c o r r e c t " seed c r y s t a l s r e m a i n i n g b e h i n d t o i n d u c e t h e f u r t h e r growth o f resolvable 1,1'-binaphthyl. A p o s s i b l e e x p l a n a t i o n f o r t h i s phenomenon l i e s i n a c o n s i d e r a t i o n o f t h e t e r n a r y system i n v o l v e d . racemate,  When a p a i r o f enantiomers  forms a  t h e t e r n a r y phase diagram between R, S and o p t i c a l l y  inactive  101  s o l v e n t appears as i n F i g u r e 17 a t any  constant  t e m p e r a t u r e which i s  above t h e m e l t i n g p o i n t of t h e s o l v e n t and below t h a t of the mers. 5d,53,85 4  system a t -78°,  F  ig  u  r  11  e  () a  i s  and F i g u r e 17  s c h e m a t i c r e p r e s e n t a t i o n of the  a  (b) r e p r e s e n t s  l i n e s a r e t h e s t a b l e phase b o u n d a r i e s . and  enantio-  three-phase regions are l a b e l l e d .  the same at 25°.  I n F i g u r e 17  ternary  The  solid  (b) the one-  two-  I n b o t h d i a g r a m s , the d o t t e d  lines  r e p r e s e n t m e t a s t a b l e e x t r a p o l a t i o n s of the s o l u b i l i t y c u r v e s of s o l i d racemate, and s o l i d  S.  Point y represents  ( s c h e m a t i c a l l y ) the o v e r a l l c o m p o s i t i o n  s l i g h t l y a c t i v e S - l , I - b i n a p h t h y l s o l u t i o n a t the b e g i n n i n g c r y s t a l l i z a t i o n - e v a p o r a t i o n procedure.  At 25°,  d i s s o l v e s at  however, i t l i e s f o r m a l l y i n the  S + racemate + s o l u t i o n r e g i o n , so t h a t t h e s e two a r a t e from t h e s o l u t i o n .  the  i t i s seen t o l i e i n the  one-phase s o l u t i o n r e g i o n , s i n c e a l l s o l i d 1 , 1 ' b i n a p h t h y l At -78°,  of  of the r e -  1  t h i s temperature.  R,  three-phase  s o l i d phases can  In a d d i t i o n , i t probably  l i e s behind  sep-  the  s o l u b i l i t y c u r v e s o f a l l t h r e e s o l i d p h a s e s , and the m a t e r i a l w h i c h crystallizes t o 25°  l i k e l y c o n t a i n s R,  S, and  (on the r o t a r y e v a p o r a t o r ) ,  racemate t o g e t h e r .  (b).  However, s i n c e  l i e s f a r t h e s t from the R s o l u b i l i t y c u r v e , t h i s  d i s s o l v e f i r s t and  f a s t e s t , l e a v i n g b e h i n d o n l y S and  out the 1 , 1 ' - b i n a p h t h y l  i n s o l u t i o n as t h e e v a p o r a t i o n  s o l i d m a t e r i a l thus obtained  probably  temperatures.  form  the can  racemate t o seed proceeds.  c o n s i s t s o n l y of racemate  S c r y s t a l s , the l o n g - s o u g h t phase m i x t u r e which i s i d e a l l y r e s o l u t i o n at h i g h e r  rewarming  a l l t h r e e phases w i l l b e g i n t o d i s s o l v e  as the system approaches t h a t i n F i g u r e 17 p o i n t y now  On  The and  suited for  102 S  SOLVENT  F i g u r e 17.  Schematic r e p r e s e n t a t i o n o f t h e t e r n a r y system formed  between s o l v e n t , R- and S - l , 1 ' - b i n a p h t h y l .  Metastable extrapolations  of phase b o u n d a r i e s ( s o l u b i l i t y c u r v e s ) a r e shown as d o t t e d (a)  Temperature: -78°,  (b)  Temperature: +25°.  lines,  103  3.5  K i n e t i c Study of the S o l i d - S t a t e R e s o l u t i o n Once a method of p r e p a r i n g s o l i d 1 , 1 ' - b i n a p h t h y l which would  r e s o l v e c o n s i s t e n t l y to a h i g h s p e c i f i c r o t a t i o n had been found, a k i n e t i c i n v e s t i g a t i o n of the r e s o l u t i o n p r o c e s s became p o s s i b l e .  Four  d i f f e r e n t b a t c h e s o f r e s o l v a b l e 1 , 1 - b i n a p h t h y l were used i n the k i n e t i c 1  s t u d y - t h r e e p r o d u c i n g S - ( + ) - 1 , 1 ' - b i n a p h t h y l and one g i v i n g R - ( - ) - l , l ' b i n a p h t h y l on h e a t i n g .  The f i r s t k i n e t i c b a t c h , S - l , c o n s i s t e d o f  g o f m a t e r i a l a c q u i r e d by a s i m p l e low temperature from acetone (p 98).  The o t h e r s (S-2, 4.0  3.0  recrystallization  g; S-3, 5.7  g; and R - l , 3.8  were p r e p a r e d from the s u c c e s s f u l r e c r y s t a l l i z a t i o n - e v a p o r a t i o n  g)  procedure  (p 9 9 ) .  3.5.1  The Development of O p t i c a l A c t i v i t y w i t h Time The r e s o l u t i o n r e a c t i o n of each b a t c h was  f o l l o w e d by h e a t i n g  i n d i v i d u a l s e a l e d ampules c o n t a i n i n g a c a r e f u l l y weighed amount (15-20 of  the p o l y c r y s t a l l i n e 1 , 1 ' - b i n a p h t h y l a t a g i v e n temperature f o r v a r i o u s  l e n g t h s of t i m e .  Some r e p r e s e n t a t i v e s p e c i f i c r o t a t i o n - t i m e p l o t s a r e  shown i n F i g u r e s 18-22. - 135°, was of  mg)  125°,  115°,  K i n e t i c runs were performed a t f o u r  and 105°  e x p l o r e d o n l y a t 135°  - f o r a l l k i n e t i c b a t c h e s except S - l , w h i c h  and 105°.  The f i n a l s p e c i f i c r o t a t i o n s , [a] , F  each o f t h e s e runs a r e l i s t e d i n T a b l e X I I .  A l l b a t c h e s r e s o l v e d to  g r e a t e r than [a] = ±200° a t 150°, but w i t h a h a l f - l i f e accurate k i n e t i c  temperatures  too s h o r t f o r an  description.  S e v e r a l comments s h o u l d be made r e g a r d i n g the form of the k i n e t i c curves.  What i s i m m e d i a t e l y o b v i o u s i s the smoothness to the k i n e t i c  p o i n t s - much more s a t i s f a c t o r y f o r k i n e t i c a n a l y s i s than the s c a t t e r  TEMPERATURE: 135° +250 CO  w o w  +200  53 O r-l H  +150  Q  <  H O Pi O r-l U-i r-l O  • O r i g i n a l k i n e t i c run Run performed a f t e r s i x weeks' s t o r a g e a t 25°  +100  Li]  CU  CO  A Run u s i n g ground +50  Run u s i n g more h i g h l y ground samples  20  40  E f f e c t of grinding  100  120  (MINUTES)  K i n e t i c data f o r the s o l i d - s t a t e r e s o l u t i o n  K i n e t i c Batch a t 135°.  80  60 TIME  F i g u r e 18.  samples  of neat, p o l y c r y s t a l l i n e 1,1'-binaphthyl, S - l  and o f s t o r a g e a t 25° f o r s i x weeks. o  J  1  1  I  I  1  I  I  I  I  1  2  4  6  8  10  12  14  16  18  20  22  TIME  F i g u r e 19.  L  24  (HOURS)  K i n e t i c d a t a f o r the s o l i d - s t a t e r e s o l u t i o n of n e a t , p o l y c r y s t a l l i n e 1 , 1 ' - b i n a p h t h y l , S  K i n e t i c Batch at 125°.  E f f e c t of s t o r a g e of samples a t 0° f o r f o u r months.  106  +150  TEMPERATURE: 135°  +125  +100 +75 S-2 K i n e t i c Batch 00  +50  w  Qi O W  +25  a 53 o i—i  20  H <! H O  Pi  c_> M PK rH U W P-i  -25  40  30 TIME  50  60  (MINUTES)  -50  00 -75 -100  -125  G  O  -OR-l K i n e t i c Batch  •150  Figure 20.  K i n e t i c data for the s o l i d - s t a t e resolution of neat,  p o l y c r y s t a l l i n e 1,1'-binaphthyl, S-2 and R-l K i n e t i c Batches at 135°.  107  F i g u r e 21.  K i n e t i c d a t a f o r the s o l i d - s t a t e r e s o l u t i o n of n e a t ,  p o l y c r y s t a l l i n e 1 , 1 ' - b i n a p h t h y l , S-2  and R - l K i n e t i c Batches a t  115°.  108  +250 h  00 w w PS o O  +200  z o  M H <: H  + 150  h  u  +100  h  o  r-l  u W 00  +50 h  10 (a)  20 TIME  30 (MINUTES)  +250 h  oo  w w Pi o w o  +200 h  z o  l-l H < H O Pi  +150  u  +100  h  00  +50  h  r-l CJ K  10 (b) F i g u r e 22.  TIME  15 (HOURS)  K i n e t i c data f o r the s o l i d - s t a t e r e s o l u t i o n of neat,  p o l y c r y s t a l l i n e 1 , 1 ' - b i n a p h t h y l , S-3 K i n e t i c B a t c h a t (a) 135° and (b) 115°.  109  Table X I I F i n a l S p e c i f i c Rotations i n the S o l i d - S t a t e R e s o l u t i o n of 1,1'-Binaphthyl ( K i n e t i c Batches)  K i n e t i c Batch  Temperature, °C  t  S-l  149.6  +211  25  min  135.0  +201  37  min  0  ^ ' degrees  Half-Life  135.0  b  +201  53  min  135.0  d  +182  13  min  135.0  e  +61  3  min  105.1  +221  149.6  +226  <1  min  135.0  +84  14  min  »  124.9  +67  »  124.9°  +136  4  h  114.9  +110  17  h  105.1  +123  149.6  +200  <1  min  135.0  +201  5  min  124.9  +214  38  min  114.9  +223  5  105.1  +229  1.1 days  149.6  -233  <1  min  135.0  -123  13  min  124.9  -71  1.2 h  114.9  -69  6  105.1  -79  1.7 days  S-2  S-3  »  R-l  6.6 days  1.7 h  4.3 days  h  h  110  Time taken to a c h i e v e [a]  /2. r  Run performed a f t e r s i x weeks' s t o r a g e a t  25°.  Run performed a f t e r f o u r months' s t o r a g e a t 0°. Run  u s i n g ground samples.  Run u s i n g more h i g h l y ground samples.  o b t a i n e d when r a c e m i c 1 , 1 ' - b i n a p h t h y l Although  the a c t i v i t y d e v e l o p s  i s t i c shape to the c u r v e s .  i s heated  smoothly,  ( F i g u r e 15, p 8 6 ) .  t h e r e appears t o be no c h a r a c t e r -  Some a r e s i g m o i d  ( a l t h o u g h none have  prolonged  i n d u c t i o n p e r i o d s ) , and o t h e r s appear to i n c r e a s e l i n e a r l y w i t h time o r even show a r a t e maximum a t t h e s t a r t o f the r u n . lution also varies. 150°,  t h e S-2  at lower  The  extent of r e s o -  C o n t r a r y t o the v e r y h i g h r o t a t i o n s a c h i e v e d  and R - l K i n e t i c Batches  suffer a loss i n resolving  at ability  temperatures.  The k i n e t i c runs a r e a l s o s e n s i t i v e to g r i n d i n g o r to s t o r a g e f o r any g r e a t l e n g t h o f t i m e .  As demonstrated w i t h the S - l sample a t  135°,  the a c t o f g r i n d i n g the s t a r t i n g m a t e r i a l causes a f a s t e r r e s o l u t i o n to a lower s p e c i f i c r o t a t i o n ( F i g u r e 18).  A l s o , the S - l K i n e t i c B a t c h d i d  not show the same k i n e t i c s b e f o r e and a f t e r s t o r a g e f o r s i x weeks a t room temperature  (25°).  I n s t e a d , the r e s o l u t i o n was  a l t h o u g h t h e e x t e n t of r e s o l u t i o n was  preserved.  k i n e t i c s o f t h i s b a t c h ware not e x p l o r e d a t 115°  slowed  somewhat,  For t h i s r e a s o n o r 125°.  The  others  were s t o r e d a t 0° w h i l e the k i n e t i c runs were performed ( w i t h i n weeks). A r e p r o d u c e a b i l i t y check of the S-2 a f t e r f o u r months' s t o r a g e a t 0°  K i n e t i c B a t c h was  the  five  performed  ( F i g u r e 1 9 ) , and showed an unchanged  r a t e of r e s o l u t i o n but an enhanced e x t e n t of r e s o l u t i o n ( o r i g i n a l l y , to  Ill  [a]  = +67°; a f t e r f o u r months, to [a] = 136°).  T h e r e f o r e , the v a l u e of  [a]_, w i l l have a l t e r e d t o some e x t e n t d u r i n g the f i v e weeks taken f o r the F k i n e t i c r u n s , but any changes i n the r a t e of r e s o l u t i o n a r e p r o b a b l y small.  There i s some v a l u e i n n e g l e c t i n g t h e s e changes to a l l o w an  a n a l y s i s i n terms o f known r a t e e q u a t i o n s f o r s o l i d - s t a t e  reactions.  T h i s w i l l be done i n S e c t i o n 3.5.2. Some samples o f t h e f a s t e s t - r e s o l v i n g b a t c h (S-3) were ground a c c e l e r a t e the r e a c t i o n even f u r t h e r ) and heated a t temperatures 105°,  below  to e s t a b l i s h the l o w e s t t e m p e r a t u r e a t which the r e s o l u t i o n  proceed.  The r e s u l t s a r e o r g a n i z e d i n T a b l e X I I I .  Even a t 98°,  (to  can samples  Table X I I I Low  Temperature S o l i d - S t a t e R e s o l u t i o n o f  Temperature, °C  97.7  93.0  87.6  Time, weeks  [ot], degrees  0  +1.4  2.6  +9  11.2  +156  24.9  +227  0  +1.8  1.0  +67  3.7  +114  4.0  +125  0  +1.8  1.0  +33  3.7  +64  4.0  +77  1,1'-Binaphthyl  Kinetic  Batch  S-l  S-3,  'round  112  (Table X I I I ,  continued)  83.3  76.9  64.2  0  +1.8  1.0  +16  4.0  +26  0  +1.8  1.0  +5.8  4.0  +11  25.5  +22  0  +1.8  1.0  +1.9  4.0  +1.2  25.5  S-3,  ground  0  are capable of r e s o l v i n g t o h i g h r o t a t i o n s , but c o n s i d e r a b l e l e n g t h s of time a r e r e q u i r e d .  The l o w e s t t e m p e r a t u r e a t which an i n c r e a s e i n  s p e c i f i c r o t a t i o n i s o b s e r v a b l e i s 76°, where [ a ] = +22° was a c h i e v e d a f t e r s i x months.  No r e a c t i o n was d i s c e r n a b l e a t 64°, even a f t e r h a l f  a year. The absence o f r e s o l u t i o n a t 64° c o u l d i m p l y t h a t t h i s  temperature  i s l o w e r than t h e s o l i d - s o l i d t r a n s i t i o n t e m p e r a t u r e T ( F i g u r e 11 ( d ) , p 67).  However, c a u t i o n s h o u l d be used i n making such a c o n c l u s i o n , i n  v i e w o f t h e slowness o f t h e r e s o l u t i o n a t 76°.  I t i s best simply to  s t a t e t h a t t h e low temperature k i n e t i c r e s u l t s i n d i c a t e t h a t x i s l o w e r than 76°. From t h e r e s u l t s g i v e n above i t i s o b v i o u s t h a t t h e k i n e t i c b e h a v i o u r o f t h e s o l i d - s t a t e r e s o l u t i o n of 1 , 1 ' - b i n a p h t h y l i s c o n s i d e r a b l y more  113  complex than the s i m p l e f i r s t - o r d e r s o l i d - s t a t e r a c e m i z a t i o n o f the d i a c i d _29_ r e p o r t e d i n S e c t i o n 2 o f t h i s t h e s i s .  Such a k i n e t i c c o m p l e x i t y  i s t o be e x p e c t e d , c o n s i d e r i n g the n a t u r e of t h e p r o c e s s e s i n v o l v e d i n the r e a c t i o n .  The r e s o l u t i o n i s caused by the s t e r e o s p e c i f i c growth o f  c r y s t a l s of one enantiomer a t the expense o f the racemate phase. p r o c e s s would be h i g h l y dependent  Such a  on the a r e a o f the i n t e r f a c e between  t h e s o l i d r e a c t a n t phase and t h e s o l i d p r o d u c t phase.  Any p r o c e d u r e w h i c h  can change the a r e a of t h i s i n t e r f a c e i n the s t a r t i n g m a t e r i a l  will  58 g r e a t l y a f f e c t the observed r a t e o f r e a c t i o n . The f a c t t h a t an e n t i r e sample o f a l m o s t - r a c e m i c 1 , 1 - b i n a p h t h y l 1  can c o n v e r t t o e s s e n t i a l l y o n l y one enantiomer means, o f c o u r s e , t h a t enantiomer i n t e r c o n v e r s i o n must o c c u r somewhere i n t h e sample. where the racemate m e l t s , l e a v i n g b e h i n d c r y s t a l s of o n l y one  At  enantiomer,  r a c e m i z a t i o n o c c u r s v e r y r a p i d l y ( w i t h a h a l f - l i f e o f l e s s than sec i n the m e l t ) .  150°,  0.5  Growing S c r y s t a l s ( f o r example) can s e l e c t S m o l e c u l e s  from a m e l t which i s e s s e n t i a l l y always r a c e m i c ( w h i l e i t l a s t s ) . t h e t e m p e r a t u r e range 76° t o 135°, where the sample i s e n t i r e l y  In  solid,  enantiomer i n t e r c o n v e r s i o n (a s i m p l e c o n f o r m a t i o n a l change) can c o n c e i v a b l y o c c u r i n the i n t e r f a c e between growing S c r y s t a l s and the d i s a p p e a r i n g racemate c r y s t a l s . very extensive.  I n a p o l y c r y s t a l l i n e sample, t h i s i n t e r f a c e w i l l  be  S i n c e the r e a c t a n t - p r o d u c t i n t e r f a c e r e p r e s e n t s an a r e a  o f c o n t a c t between c e n t r o s y m m e t r i c (racemate) and n o n c e n t r o s y m m e t r i c (pure enantiomer) c r y s t a l s , i t w i l l be q u i t e d i s o r g a n i z e d ( " i n c o h e r e n t " ) ^ The h i g h e r ( s u r f a c e ) f r e e energy  a s s o c i a t e d w i t h t h i s p a r t o f the s o l i d  s t a t e c o u l d w e l l f a c i l i t a t e enantiomer i n t e r c o n v e r s i o n , making the s o l i d - s t a t e  resolution.  possible  3  114  If  the i n t e r c o n v e r s i o n of enantiomers i n the r e a c t a n t - p r o d u c t  inter-  f a c e i s v e r y f a s t compared t o t h e r a t e o f growth o f c r y s t a l s o f pure e n a n t i o m e r , then t h e r e a c t i o n i s e s s e n t i a l l y o n l y a phase change.  Phase 61  changes a r e almost always governed by n u c l e a t i o n - a n d - g r o w t h  processes.  That i s , n o t o n l y can a phase t r a n s f o r m a t i o n o c c u r v i a growth o f s m a l l c r y s t a l l i t e s of product  which e x i s t i n i t i a l l y i n the r e a c t a n t phase, but  new c r y s t a l l i t e s can form ( n u c l e a t e ) d u r i n g t h e phase change. t h i s p o i n t , we have c o n s i d e r e d enantiomer p r e s e n t  Up t o  o n l y t h e growth o f " s e e d " c r y s t a l s o f pure  i n i t i a l l y i n t h e s o l i d sample o f  1,1'-binaphthyl.  Indeed, t h e e l i m i n a t i o n o f c r y s t a l s o f "unwanted" enantiomer was t h e prime o b j e c t i v e i n t h e d e s i g n i n g o f e x p e r i m e n t s t o produce r e s o l v a b l e 1,1'binaphthyl.  However, as w i l l be seen, t h e k i n e t i c r e s u l t s r e q u i r e a  c o n s i d e r a t i o n o f t h e n u c l e a t i o n o f new e u t e c t i c c r y s t a l s from t h e r e a c t i n g racemate phase. The  prospect  o f n u c l e a t i o n i n t h e R , S - l , l ' - b i n a p h t h y l phase  system c a r r i e s w i t h i t some i n t e r e s t i n g s t e r e o c h e m i c a l According  consequences.  t o t h e c l a s s i c a l t h e o r y o f n u c l e a t i o n , ^ ' ^ ^ new c r y s t a l s a r e  formed from l o c a l s t a t i s t i c a l  f l u c t u a t i o n s i n energy, c o n c e n t r a t i o n , and  o r i e n t a t i o n o f m o l e c u l e s i n t h e r e a c t a n t phase.  But i n t h e 1 , 1 ' - b i n a p h t h y l  system, t h e r e a c t a n t phase i s a r a c e m i c c r y s t a l below 145° o r a r a c e m i c melt between 145° and 158°. j u s t as l i k e l y  T h i s means t h a t t h e l o c a l f l u c t u a t i o n s a r e  t o i n v o l v e R m o l e c u l e s as S m o l e c u l e s .  I n o t h e r words,  n u c l e a t i o n i n t h e r a c e m i c phase i s e x p e c t e d t o c r e a t e b o t h R and S c r y s t a l l i t e s with equal p r o b a b i l i t y .  T h i s w i l l be t r u e r e g a r d l e s s o f t h e  s i t e s o f n u c l e a t i o n i n the r e a c t a n t c r y s t a l .  Whether n u c l e a t i o n i s  homogeneous - o c c u r r i n g a t a l l p o i n t s i n t h e r e a c t a n t c r y s t a l w i t h  equal  115  l i k e l i h o o d - o r whether i t o c c u r s o n l y a t d e f e c t s , d i s l o c a t i o n s o r boundaries  between r e a c t a n t c r y s t a l l i t e s , t h e o v e r a l l p r o d u c t s o f  n u c l e a t i o n s h o u l d be a r a c e m i c , e u t e c t i c m i x t u r e o f i n d i v i d u a l R and S crystallites.  A racemic r e a c t a n t phase w i l l show no p r e f e r e n c e f o r  the f o r m a t i o n o f any one The to  reasons  enantiomer.  f o r t h e f a i l u r e o f some batches  of 1,1'-binaphthyl  r e s o l v e w e l l on h e a t i n g a r e t h e r e f o r e : (a) t h e presence  lites  o f b o t h enantiomers  of c r y s t a l -  i n the i n i t i a l m a t e r i a l before heating,  (b) t h e n u c l e a t i o n o f racemic m a t e r i a l d u r i n g t h e r e a c t i o n , o r (c) b o t h .  for  The k i n e t i c r e s u l t s p r o v i d e an o p p o r t u n i t y t o t e s t t h e s e  reasons  f a i l u r e , s i n c e we know t h e c o n d i t i o n s under w h i c h t h e h i g h  resolv-  a b i l i t y of the batches S-l  can be d e s t r o y e d .  F o r example, g r i n d i n g t h e  K i n e t i c B a t c h causes a f a s t e r r e s o l u t i o n , but t o a l o w e r  rotation.  C e r t a i n l y , g r i n d i n g w i l l break apart the S c r y s t a l l i t e s present  initially  i n t h e m a t e r i a l (and i m p a r t i n g a s m a l l s p e c i f i c r o t a t i o n o f [ a ] = +1.4°), c r e a t i n g a g r e a t e r r e a c t a n t - p r o d u c t i n t e r f a c e and c a u s i n g a more r a p i d reaction.  I n a d d i t i o n , R c r y s t a l l i t e s a r e e i t h e r formed d u r i n g t h e  g r i n d i n g p r o c e s s o r n u c l e a t e d ( a l o n g w i t h an e q u a l number o f S c r y s t a l l i t e s ) when t h e ground sample was h e a t e d .  The f a c t t h a t t h e racemate has a  l o w e r m o l a r volume (196.2 ml mole "*") than t h e e u t e c t i c form (214-216 ml n  mole ^)° i m p l i e s t h a t t h e p r e s s u r e o f g r i n d i n g c o u l d n o t cause a phase n  C a l c u l a t e d from t h e c r y s t a l l o g r a p h i c d a t a o f K e r r and R o b e r t s o n ^ f o r the l o w - m e l t i n g form o f l , l ' - b i n a p h t h y l , 82 E x t r a p o l a t e d t o 25° from t h e d i l a t o m e t r i c d a t a o f B i n n s and S q u i r e f o r t h e h i g h - m e l t i n g form o f l , l ' - b i n a p h t h y l between 120° and 158°.  116  change from t h e racemate  t o an e q u i m o l a r m i x t u r e o f R and S c r y s t a l s .  Hence t h e sample, b o t h b e f o r e and a f t e r g r i n d i n g , v e r y l i k e l y c o n t a i n e d e s s e n t i a l l y o n l y S c r y s t a l s and racemate  c r y s t a l s , t h e R form b e i n g  n u c l e a t e d ( a l o n g w i t h S) more r e a d i l y from t h e ground sample.  The  reason f o r t h e decreased e x t e n t o f r e s o l u t i o n i n ground samples may then be t h a t g r i n d i n g c r e a t e s s t r e s s e s , d i s l o c a t i o n s , and o t h e r i m p e r f e c t i o n s i n t h e r e a c t a n t l a t t i c e , and t h e s e can a c t as s i t e s f o r t h e n u c l e a t i o n of racemic m a t e r i a l . A l s o , t h e S-2 and R - l K i n e t i c Batches r e s o l v e d r a t h e r p o o r l y i n the t e m p e r a t u r e range 105-135° (where t h e r e a c t a n t phase i s t h e racemate) and e x c e l l e n t l y a t 150° (where t h e r e a c t a n t phase i s t h e m e l t ) .  I f the  poor r e s o l v a b i l i t y a t 105-135° i s due t o t h e i n i t i a l p r e s e n c e o f b o t h R and S c r y s t a l l i t e s , then one would a t 150°, which i s n o t t h e c a s e .  expect t h e growth o f b o t h forms  also  A more t e n a b l e e x p l a n a t i o n i n v o l v e s t h e  n u c l e a t i o n o f r a c e m i c m a t e r i a l from t h e racemate phase, b u t n o t from t h e m e l t phase.  As mentioned  e a r l i e r , t h e 1,1'-binaphthyl  melt s u p e r c o o l s  to a g r e a t e x t e n t , and c o m p l e t e l y m e l t e d samples w i l l remain a t 150° i n d e f i n i t e l y without c r y s t a l l i z a t i o n , unless c r y s t a l s are i n t e n t i o n a l l y added.  A l t h o u g h growth on seed c r y s t a l s o c c u r s r e a d i l y a t 150°, n u c l e -  a t i o n o f new c r y s t a l s does n o t . T h e r e f o r e a h i g h degree o f r e s o l u t i o n may o c c u r a t 150° b u t n o t a t 105-135°. The S - l and S-3 K i n e t i c B a t c h e s r e s o l v e t o g r e a t e r than 82% r e s o l u t i o n a t a l l temperatures s t u d i e d .  The f a i l u r e t o a t t a i n  total  r e s o l u t i o n ( [ a ] = i245°) i n t h e s e b a t c h e s i s p r o b a b l y due t o c r y s t a l s o f unwanted R enantiomer  p r e s e n t i n i t i a l l y , r a t h e r than t o n u c l e a t i o n , s i n c e  t h e r e i s no improvement i n r e s o l u t i o n w i t h these samples a t 150°, where  117  n u c l e a t i o n i s absent. The  changes on s t o r a g e o f the S-2  K i n e t i c B a t c h over s e v e r a l months  i s c o n s i s t e n t both w i t h n u c l e a t i o n and w i t h the presence enantiomer.  On one hand, the improved e x t e n t o f r e s o l u t i o n o f the  m a t e r i a l on s t o r a g e c o u l d be due  causing n u c l e a t i o n of  A n n e a l i n g i s made p o s s i b l e  racemic  by the r e l i e f o f s u r f a c e and  s t r a i n f r e e e n e r g i e s i n the p o l y c r y s t a l l i n e sample. the presence  S-2  to the p a r t i a l a n n e a l i n g out of the  c r y s t a l i m p e r f e c t i o n s and b o u n d a r i e s material.  o f unwanted  On t h e o t h e r hand,  o f unwanted enantiomer c o u l d be d i m i n i s h e d by a v e r y  phase t r a n s f o r m a t i o n a t 0°, c o n v e r t i n g r a c e m i c  slow  e u t e c t i c form back t o  the racemate. The  s e c r e t to preparing 1,1'-binaphthyl which w i l l r e s o l v e w e l l  h e a t i n g a t a l l temperatures  e v i d e n t l y i n v o l v e s m i n i m i z i n g not o n l y the  c r y s t a l s o f unwanted enantiomer,  but a l s o the tendency o f the racemate  t o n u c l e a t e r a c e m i c , e u t e c t i c form. is d i f f i c u l t  Although  the l a t t e r  requirement  to c o n t r o l , i t can be a v o i d e d s i m p l y by p e r f o r m i n g  r e s o l u t i o n a t 150°,  on  where t h e racemate m e l t s , and a l l b a t c h e s  of  b i n a p h t h y l p r e p a r e d by the s p e c i a l r e c r y s t a l l i z a t i o n - e v a p o r a t i o n  the 1,1'pro-  cedure (p 99) a t t a i n a v e r y h i g h degree o f r e s o l u t i o n .  3.5.2  Treatment o f R e s u l t s i n Terms of Rate Laws f o r S o l i d - S t a t e R e a c t i o n s Although  some q u a l i t a t i v e c o n c l u s i o n s can be drawn from the k i n e t i c •  r e s u l t s ( S e c t i o n 3.5.1), a more q u a n t i t a t i v e t r e a t m e n t  can  potentially  p r o v i d e i n s i g h t i n t o the mechanism and e n e r g i e s i n v o l v e d i n the resolution.  solid-state  118  As w i l l be seen, the r a t e e q u a t i o n s w h i c h have been developed s o l i d - s t a t e r e a c t i o n s i n v o l v e an e x p r e s s i o n o f y, the f r a c t i o n as a f u n c t i o n of t i m e .  for  transformed,  I n t h i s r e s o l u t i o n r e a c t i o n , the f r a c t i o n t r a n s -  formed i s c o n v e n i e n t l y t a k e n as the e x t e n t o f the phase t r a n s f o r m a t i o n racemate ->• e u t e c t i c form, r e g a r d l e s s of the f i n a l r o t a t i o n That i s , y = X^, where  achieved.  i s the mole f r a c t i o n o f 1 , 1 ' - b i n a p h t h y l  the e u t e c t i c ( h i g h - m e l t i n g ) form.  in  A l t h o u g h X^ = 1 a t the end o f the  t r a n s f o r m a t i o n , i t i s c l o s e t o but not e x a c t l y z e r o a t the b e g i n n i n g , s i n c e some s m a l l seed c r y s t a l s o f e u t e c t i c form e x i s t i n the material.  initial  Hence, b e f o r e the r e a c t i o n , the m a t e r i a l i s c o n s i d e r e d  already s l i g h t l y  as  transformed.  D u r i n g the r e s o l u t i o n , [a] was a f i n a l r o t a t i o n , [ a ] _ , was  measured as a f u n c t i o n o f t i m e ,  attained.  until  I n t u i t i v e l y , i t would seem t h a t  r  [ a ] / [ a ] y = X^,  but the c o n d i t i o n s under w h i c h t h i s e q u a l i t y w i l l h o l d  s h o u l d be examined more c l o s e l y . I n any b a t c h of 1 , 1 - b i n a p h t h y l , 1  the o n l y phases p r e s e n t  t h e racemate, c r y s t a l s o f R, and c r y s t a l s o f S. t h e e u t e c t i c form.  (or  \-  -H •L  *R- -F  The  [15]  (or  V W  (or (or  I t i s convenient  The  to d e f i n e the  = mole f r a c t i o n o f R ( o r S) i n a l l  are  l a s t two c o n s t i t u t e following:  phases  = mole f r a c t i o n o f R ( o r S) i n e u t e c t i c ( h i g h - m e l t i n g ) form = mole f r a c t i o n of R ( o r S) i n racemate ( l o w - m e l t i n g )  X  S-F>  = mole f r a c t i o n o f R ( o r S) a t end of t r a n s f o r m a t i o n  s p e c i f i c r o t a t i o n o f the sample a t a l l times i s :  [ a ]  =  [ a ]  S  ( X  S " V  =  C a ]  R  ( X  R "  V  form  119  where [ct] = +245°, and [o]„ = -245°, the s p e c i f i c rotations of S R  completely  c  resolved S and R-l,1'-binaphthyl, respectively. But since the racemate contains an equimolar , and since X  quantity of S and R-l, 1'-binaphthyl, i . e . ,  =  g  + X_ g  and X^ = X^ ^ +  L  =  then the difference  i n mole fractions of S- and R-l,1'-binaphthyl i n a l l phases i s i d e n t i c a l to that only i n the eutectic form (Xg - X^ =  -  ^) and so i t i s  always true that:  [16]  []  = [a]g(X _  a  s  -  H  X^)  At the end of the transformation, X  = X b—ri  [17]  [ ] a  F  - [a] (X _ s  s  -  p  and X^ b-r  Ul  l»l  Consider now perfectly.  - " -" " "*S  X F  S  , so that: K—r  X_) R  p  Therefore, i n a l l batches of p o l y c r y s t a l l i n e  [18)  = X  K—n  1,1'-binaphthyl,  H  - F " *R-F  a hypothetical sample of 1,1'-binaphthyl  which resolves  I f the resolution i s to pure S-enantiomer, then [a]  = [a] . r  b  In such a r e s o l u t i o n , no nucleation of racemic material would occur, and the eutectic form would always consist only of growing S c r y s t a l s . Therefore, X _ g  rioi  H  = X^,  M  - Lsl  = X_ R  X  F  = 0, X _  S-H "  g  = 1, and Equation 18 becomes:  F  „  120  T h e r e f o r e , i n t h e p e r f e c t r e s o l u t i o n , w h i c h i s approached by t h e S - l ' and S-3 K i n e t i c Batches a t a l l t e m p e r a t u r e s s t u d i e d , and by t h e S-2 and R - l K i n e t i c Batches a t 150°, the e x t e n t o f t r a n s f o r m a t i o n , y, e q u a l s  [a]/[a] . p  I n t h e k i n e t i c runs where [a]., i s f a r from [ a ] o r [a]„, i t may c  not be a c c u r a t e t o equate  and [ c t ] / [ a ] p .  I n t h e s e samples, (S-2 and  R - l from 105-135°) where n u c l e a t i o n o f r a c e m i c m a t e r i a l can o c c u r t o a c o n s i d e r a b l e e x t e n t , s i t u a t i o n s can c o n c e i v a b l y a r i s e where X^. advances more r a p i d l y than [a]/[a]„.  F o r example, e x t e n s i v e n u c l e a t i o n o f  r  r a c e m i c e u t e c t i c form o c c u r r i n g a t t h e b e g i n n i n g o f t h e t r a n s f o r m a t i o n would n o t i n c r e a s e [ a ] / [ a ] p but would i n c r e a s e X^.  I n k i n e t i c runs  where [ctjj, << [ a ] g , t h e r e f o r e , t h e e x t e n t t o w h i c h X^ i s a p p r o x i m a t e d by measured r o t a t i o n s s h o u l d be i n d e p e n d e n t l y d e t e r m i n e d . An independent measurement o f X^ can be performed by f o l l o w i n g t h e r e s o l u t i o n r e a c t i o n by X-ray powder d i f f r a c t i o n .  We t h e r e f o r e m o n i t o r e d  t h e r e s o l u t i o n o f t h e S-2 K i n e t i c B a t c h a t 125° ( F i g u r e 19, p 105, k i n e t i c r u n a f t e r f o u r months a t 0°) u s i n g q u a n t i t a t i v e X-ray powder photography.  The method we used was s i m i l a r t o t h e " d i r e c t comparison 76a method" d e s c r i b e d by C u l l i t y . By c h o o s i n g one l i n e i n t h e d i f f r a c t i o n o  p a t t e r n o f t h e racemate  (d = 10.1 A) and one i n t h e p a t t e r n o f t h e o  e u t e c t i c form (d = 6.4 A) w h i c h would be d i s t i n c t i n a m i x t u r e o f t h e two forms, t h e d i s a p p e a r a n c e o f racemate and t h e appearance o f e u t e c t i c c o u l d be q u a n t i t a t i v e l y f o l l o w e d .  A standard procedure f o r the develop-  ment o f t h e powder photographs was d e v i s e d , so t h a t when the d e v e l o p e d photographs were a n a l y z e d on a m i c r o d e n s i t o m e t e r , t h e r e s u l t i n g peak a r e a s were r e p r o d u c i b l e .  A c a l i b r a t i o n c u r v e ( F i g u r e 23) r e l a t i n g t h e  121  WEIGHT FRACTION  F i g u r e 23.  H (.. ... )  C a l i b r a t i o n c u r v e f o r q u a n t i t a t i v e phase a n a l y s i s by X - r a y  powder photography.  122  peak "area fraction" of eutectic (high-melting) form (A^/A^tA^) to the weight fraction of eutectic form (W„/W„+W ) was constructed by analyzing T  H  known mixtures of the two forms.  n  L  In several cases (e.g. at a weight  fraction of 0.435) more than one sample was taken from the known phase mixture, to check the reproducability of the method.  These multiple  analyses agreed to within 2%. Samples of the S-2 Kinetic Batch were held at 125°for various lengths of time, then cooled to room temperature and analyzed for specific rotation as well as for phase content. Figure 24, which shows how  The results are plotted in  [ot]/[a]p depends on X^.  The straight diagonal  represents the case where [a]/[a]p = X^. As shown by the results given ±h the Figure, the development of optical activity, even in samples of 1,1'-binaphthyl which do not resolve well, is rather closely parallelled by the phase change racemate eutectic form.  The i n i t i a l S-2 material contains some eutectic form, as  expected from i t s i n i t i a l activity of [a] = +11.8°.  However, the extent  of phase transformation i s rather small considering the i n i t i a l rotation, implying that the eutectic form in the sample is pure S.  For i f no R  crystals were present, X^ = Xg_^ and from Equation 19, X^ = Xg_ [a]/[a] = 11.8/245 = 0.0482. c  H  =  If R crystals existed in the i n i t i a l  sample, X^ would be even larger. This result verifies the conclusion in Section 3.5.1  that the S-2 sample resolves poorly because of nu-  cleation of racemic material rather than the presence of R crystals in the i n i t i a l sample. To a good approximation, then, the extent of transformation is given by [a]/[a]„. r  One would expect that the approximation would improve  F i g u r e 24.  Development o f s p e c i f i c r o t a t i o n w i t h e x t e n t o f phase  transformation at 0°).  ( X ^ ) , S-2 K i n e t i c B a t c h a t 125°  Diagonal  represents  the c o n d i t i o n  ( a f t e r f o u r months'  [a]/[ct]  =  storage  124  as [a]  F  approached [a]  o  (or [a] ) , u n t i l i n the perfect r e s o l u t i o n , as K  discussed above, [ a ] / [ a ] ^ must equal X^.  With this assurance, an  analysis of the k i n e t i c r e s u l t s according  to rate laws can now  be conducted.  The k i n e t i c s of reactions i n s o l i d s consisting i n i t i a l l y of a single component have been considered  i n some d e t a i l i n two major f i e l d s  of research.  The k i n e t i c s of phase transformations have received con87 88 siderable i n t e r e s t i n metallurgy, ' and the k i n e t i c behaviour of 89 1  decomposition reactions (more inorganic explored  rather widely i n chemistry.  than organic ) has been  However, from a l l of these i n -  vestigations one must conclude that there exists no universal rate equation which describes the k i n e t i c s of a l l reactions i n s i n g l e s o l i d components.  The t h e o r e t i c a l approaches to such s o l i d - s t a t e reactions  find i l l u s t r a t i o n i n a l i m i t e d number of systems, and often describe 89 only the i n i t i a l or f i n a l part of a reaction. On the other hand, empirical rate equations known to apply to a larger number of systems 90 are d i f f i c u l t to interpret exactly i n terms of reaction mechanisms. The  complexities  of many s o l i d - s t a t e reactions have even led to the  development of methods of treating k i n e t i c results i n the absence of A „. 88,91,92 any assumed rate equation. 88 Of the empirical rate equations that have been developed, two are most widely used.  The  f i r s t of these, usually called the Avrami-  90 93 Erofeev Equation i n inorganic chemistry ' or the Johnson-Mehl92 Avrami Equation i n metallurgy appears, i n d i f f e r e n t i a l form, as:  [20]  g  = k" t " "  1  (1-y)  125  and i n i n t e g r a t e d form, as:  [21]  y = 1 - exp(-  -f  t ) n  or:  l o g logC^T")  [22]  =  n  log(t)  + n log(k ) 6  Agreement w i t h t h i s r a t e e x p r e s s i o n w i l l  - l o g ( 2 . 3 0 3 n)  t h e r e f o r e be r e v e a l e d  l i n e a r i t y o f a p l o t of l o g l o g ( ^ ') v s . l o g ( t ) . done f o r a l l f o u r k i n e t i c b a t c h e s , F i g u r e s 25 and  by  Such an a n a l y s i s was  two o f w h i c h a r e i l l u s t r a t e d i n  26. 89  The second commonly used r a t e law i s the Prout-Tompkins E q u a t i o n , w h i c h i n d i f f e r e n t i a l form i s :  &  [23]  = k  7  y (1-y)  and w h i c h i n t e g r a t e s t o :  logC^O  [24]  = k  7  t  +  constant  The r e s o l u t i o n k i n e t i c s of a l l b a t c h e s were t r e a t e d a c c o r d i n g equation,  to t h i s  and some r e p r e s e n t a t i v e l o g ( j ^ - ) v s . time p l o t s a r e shown i n  F i g u r e s 27 and 28. 58 90 93 I n t h e r e c e n t a c c o u n t s of s o l i d - s t a t e r e a c t i o n k i n e t i c s ,  '  '  i t has been emphasized t h a t c a u t i o n s h o u l d be used i n i n t e r p r e t i n g any apparent f i t of e m p i r i c a l r e s u l t s t o s o l i d - s t a t e r a t e e q u a t i o n s .  Kinetic  '  2.5  3.0  3.5  4.0 LOG  F i g u r e 25. binaphthyl,  4.5  5.0  5.5  6.0  6.5  (TIME, SECONDS)  Avrami-Erofeev p l o t s f o r the s o l i d - s t a t e r e s o l u t i o n o f n e a t , p o l y c r y s t a l l i n e , 1,1'S - l K i n e t i c Batch at 135° and 105°.  a g a i n s t l o g ( t i m e , seconds) + 1 .  The sample s t o r e d  s i x weeks a t 25° i s p l o t t e d ^  2.5  3.0  3.5  4.0 LOG  26.  4.5  5.0  5.5  6.0  6.5  (TIME, SECONDS)  Avrami-Erofeev p l o t s f o r the s o l i d - s t a t e r e s o l u t i o n of n e a t , p o l y c r y s t a l l i n e 1,  b i n a p h t h y l , S-2 K i n e t i c Batch a t 135°,  125°  ( o r i g i n a l r u n ) , 115°,  and  105°.  + 1.5  +1.0  +0.5  4 u o  0.0  -0.5  -1.0  O  A  O  O r i g i n a l k i n e t i c run  A  Run performed a f t e r s i x weeks' s t o r a g e a t 25  c  O  Run u s i n g ground samples -1.5  A  10  20  _L 30  J_  40  50  60  70  80  90  100  110  120  TIME (MINUTES)  F i g u r e 27.  Prout-Tompkins p l o t s f o r the s o l i d - s t a t e r e s o l u t i o n o f n e a t , p o l y c r y s t a l l i n e 1,1'-  b i n a p h t h y l , S - l K i n e t i c Batch a t 135°.  E f f e c t of g r i n d i n g and o f s t o r a g e a t 25° f o r s i x weeks.  +1.0  S-2 K i n e t i c B a t c h  10  15  20  25 TIME  F i g u r e 28.  Prout-Tompkins  30  35  40  (HOURS)  p l o t s f o r the s o l i d - s t a t e r e s o l u t i o n of n e a t , p l o y c r y s t a l l i n e  b i n a p h t h y l , S-2, S-3 and R - l K i n e t i c Batches at  115°.  50  45  1,1'-  130  r e s u l t s s h o u l d , wherever p o s s i b l e , be supplemented by a d d i t i o n a l i n f o r m a t i o n , such as the d i r e c t o b s e r v a t i o n of the n u c l e a t i o n and growth under the m i c r o s c o p e .  processes  Indeed, t h e r e a r e even cases o f agreement w i t h 58  b o t h the A v r a m i - E r o f e e v  and Prout-Tompkins E q u a t i o n s ,  89 '  and  i n such  cases r e c o u r s e must be made t o n o n - k i n e t i c o b s e r v a t i o n s b e f o r e any mechanism can be proposed.  Even when the f i t i s poor when the e n t i r e r e a c t i o n  i s c o n s i d e r e d t h e r e has been a tendency to l o o k f o r s t r a i g h t p o r t i o n s 21 89 over o n l y p a r t of the r e a c t i o n  '  ( e . g . , y = 0.2  to y = 0.5),  the  j u s t i f i c a t i o n f o r t h i s b e i n g t h a t d i f f e r e n t mechanisms a p p l y to d i f f e r e n t p a r t s o f the r e a c t i o n .  However, any m e a n i n g f u l  a n a l y s i s from such p a r t i a l  f i t s s h o u l d be backed by many k i n e t i c p o i n t s known v e r y p r e c i s e l y , as w e l l as by a d d i t i o n a l o b s e r v a t i o n s . No m i c r o s c o p i c o b s e r v a t i o n s of the s o l i d - s t a t e r e s o l u t i o n of b i n a p h t h y l were made, so t h a t any  1,1'-  i n t e r p r e t a t i o n o f the e m p i r i c a l p l o t s  must be c o n s i d e r e d as s u b j e c t to v e r i f i c a t i o n by independent methods. L e t us c o n s i d e r f i r s t The  s l o p e of Equation  the A v r a m i - E r o f e e v  p l o t s ( F i g u r e s 25 and  22 g i v e s the exponent n ( T a b l e X I V ) .  W i t h the S - l  K i n e t i c B a t c h the r e s u l t s f i t a s t r a i g h t l i n e ( w i t h n n e a r two) well.  L e s s p e r f e c t f i t s a r e found w i t h the S-3  rather  and R - l m a t e r i a l (not  shown), where the p l o t i s b e t t e r d e s c r i b e d a t some t e m p e r a t u r e s by s t r a i g h t l i n e s (both s l o p e s a r e l i s t e d i n T a b l e X I V ) . bend o c c u r s w i t h the S-2 s l o p e s o f c a . 0.65 The  and  K i n e t i c Batch  1.7  at a l l four  26).  The most  ( F i g u r e 2 6 ) , which g i v e s  two  obvious limiting  temperatures.  s t r a i g h t l i n e o b t a i n e d w i t h the S - l m a t e r i a l m e r i t s some  discussion.  The  exact m e c h a n i s t i c  i m p l i c a t i o n o f t h i s f i t i s not  gether c e r t a i n , c o n s i d e r i n g that Equation  alto-  21 has been d e r i v e d i n a number  131  T a b l e XIV A v r a m i - E r o f e e v Exponents f o r the S o l i d - S t a t e R e s o l u t i o n of 1 , 1 ' - B i n a p h t h y l  K i n e t i c Batch  Temperature, °C  S-l  Exponent  135.0  1.8  II  135.0  II  105.1  S-2  135.0  0.7  to  1.6  b  124.9  0,7  to  1.9  b  114.9  0.6  to  1.6  b  105.1  0.6  to  1.6  b  it it it S-3 tt  2.0  a  1.8  135.0  1.6  124.9  1.7  II  114.9  1.2  to  1.7  b  II  105.1  0.8  t o 1.3  b  R-l  135.0  1.0  t o 2.0  tt it it  124.9  1.0  114.9  0.7  105.1  0.8  Run performed a f t e r s i x weeks' s t o r a g e a t 25°. Minimum and maximum v a l u e s .  132  of d i f f e r e n t w a y s . ^ ' ^  One  D  common i n t e r p r e t a t i o n " ^ ' ^ of t h e exponent  n i s t h a t i t i s composed o f two q u a n t i t i e s , namely, n = 3 + X.  The  exponent B r e f e r s t o the number of s t e p s r e q u i r e d t o form a n u c l e u s ,  and  i s r e v e a l e d i n a power law o f t h e type N = k t , where N i s the number o f n u c l e i formed i n time t .  The number B i s u s u a l l y determined  from the  i n i t i a l k i n e t i c s o f a s o l i d r e a c t i o n o r from c o u n t i n g the n u c l e i under a m i c r o s c o p e 3.5.1  as a f u n c t i o n o f t i m e .  However, as shown i n S e c t i o n  (p 103), the S - l and S-3 K i n e t i c Batches  o f new  m a t e r i a l , so t h a t S = 0.  The  visible  do not undergo n u c l e a t i o n  exponent X i s the number o f dimen-  s i o n s i n w h i c h growth of e x i s t i n g p r o d u c t c r y s t a l l i t e s  occurs.  Hence  our o b s e r v a t i o n of n = X = 2 w i t h the S - l m a t e r i a l can be t a k e n as p l y i n g t h a t the growing  S crystallites  spread i n two dimensions  f o r example, p r e f e r r e d l a t t i c e p l a n e s o r b o u n d a r i e s  im-  along,  between racemate  crystallites. Although  lower v a l u e s o f n r e s u l t from p l o t s of t h e o t h e r k i n e t i c  b a t c h e s , t h e s e have l i t t l e s i g n i f i c a n c e i n v i e w of the r a t h e r poor f i t . The  S-2  K i n e t i c Batch  partway through  the r e a c t i o n , but the k i n e t i c p o i n t s a r e too i m p r e c i s e  to j u s t i f y such an The  ( F i g u r e 26) might s u f f e r a change i n mechanism  interpretation.  r a t e c o n s t a n t k^  ( E q u a t i o n s 20-22) has  a t e d from a p l o t o f [ l o g ( ^ •) ] " ^  n  sometimes been e v a l u -  a g a i n s t t i m e , once n has been d e t e r -  58 mined.  T h i s procedure  a l l o w s the d e t e r m i n a t i o n o f an 88  energy, but t h e r e have been o b j e c t i o n s  activation  to the comparison of  a c t i v a t i o n energies to those f o r other molecular processes.  such This  o b j e c t i o n i s based on the f a c t t h a t k^ a r i s e s i n a r a t e e q u a t i o n e x p r e s s i n g dy/dt  i n terms of time as w e l l as y ( E q u a t i o n 2 0 ) , whereas  133  the most commonly encountered  r a t e c o n s t a n t r e s u l t s from an e x p r e s s i o n 88  of dy/dt as a f u n c t i o n o f y o n l y . The Prout-Tompkins y = 0.3  ( l o g ( j ~ ) - 0.37)  p l o t s ( F i g u r e 27-28) show l i n e a r i t y beyond f o r a l l k i n e t i c batches.  Prout-Tompkins  o f t e n show two s t r a i g h t l i n e s , y i e l d i n g r a t e c o n s t a n t s which may 44b 58 may  not have t h e same a c t i v a t i o n e n e r g i e s .  c a s e , t h e r e may  be a second  '  l i n e o f g r e a t e r s l o p e below y = 0.3,  The r a t e c o n s t a n t s d e r i v e d from the Prout-Tompkins  has been done i n F i g u r e 29.  possibility.  p l o t s are  f o r the S - l , S-2,  S-3,  Such a p l o t  The A r r h e n i u s a c t i v a t i o n e n e r g i e s , c a l c u -  l a t e d from 2.303 R ( s l o p e o f l i n e ) , a r e 57.7, 1  62.5,  59.4  and R - l K i n e t i c B a t c h e s ,  The t h e o r e t i c a l b a s i s f o r the Prout-Tompkins  and 67.0  the p o l y c r y s t a l l i n e s o l i d .  kcal  respectively.  Equation l i e s i n  c o n s i d e r i n g t h e r e a c t i o n as p r o c e e d i n g by a b r a n c h i n g p r o c e s s 90 spreads throughout  but  S i n c e the c o n s t a n t k^ i s d e f i n e d i n terms o f y  o n l y ( E q u a t i o n 2 3 ) , an a c t i v a t i o n p l o t i s w o r t h w h i l e .  mole  or  I n the 1 , 1 ' - b i n a p h t h y l  t h e r e a r e f a r too few p o i n t s i n t h i s r e g i o n t o v e r i f y t h i s  l i s t e d i n T a b l e XV.  plots  which  While the exact nature  o f the b r a n c h i n g s p e c i e s i s u n c e r t a i n , one l i k e l y mechanism i n v o l v e s the s p r e a d o f r e a c t i o n p r o d u c t a l o n g g r a i n b o u n d a r i e s ,  dislocations,  and t h e l i k e , c a u s i n g t h e b r e a k i n g a p a r t o f r e a c t a n t c r y s t a l l i t e s 58 t h e c r e a t i o n o f new  avenues f o r the advance of the p r o d u c t .  and  Since i n  the case o f the S - l and S-3 K i n e t i c B a t c h e s , h i g h r e s o l u t i o n s were o b t a i n e d , the c h a i n b r a n c h i n g p r o c e s s i s most l i k e l y a growth o n l y and does not i n v o l v e the n u c l e a t i o n of new That growth from E q u a t i o n 23.  process  material.  i s a b r a n c h i n g p r o c e s s can be seen  qualitatively  The r a t e of t r a n s f o r m a t i o n depends both on the amount  134  2.20  2.30  2.40  1  TEMPERATURE  Figure 29.  3 X  1  0  (DEGREES  2.50  -1 )  Relation of log (k^) (from Prout-Tompkins plots)  temperature for the s o l i d - s t a t e resolution 1,1'-binaphthyl, a l l four k i n e t i c batches. squares f i t s to data for each batch.  to r e c i p r o c a l  of neat, p o l y c r y s t a l l i n e Straight  l i n e s are least  135  T a b l e XV Prout-Tompkins Rate C o n s t a n t s ( k ^ ) f o r t h eS o l i d - S t a t e R e s o l u t i o n o f 1,1'-Binaphthyl  i i n k^ x 10  K i n e t i c Batch  Temperature, °C  S-l  135.0  II  135.0  a  103.6  II  135.0  b  377.1  II  105.1  S-2  135.0  it  124.9  ti  114.9  2.766  II  105.1  0.4638  S-3  135.0  514.3  It  124.9  100.8  II  114.9  If  105.1  R-l  135.0  II  124.9  II  114.9  4.782  II  105.1  0.4216  sec  107.6  Run performed a f t e r s i x weeks' s t o r a g e a t 25°. Run performed w i t h ground samples.  5  0.4036 194.8 22.71  11.45 1.733 340.7 25.11  -  1  136  of m a t e r i a l t r a n s f o r m e d (y) and t h a t which has n o t y e t r e a c t e d  (1-y).  44b 88 The r a t e e q u a t i o n i s t h a t o f an a u t o c a t a l y t i c r e a c t i o n .  '  In order  f o r a dependence on y, t h e p r o d u c t ( c r y s t a l s o f pure enantiomer) must be a v a i l a b l e t o t h e r e a c t a n t ( t h e r a c e m a t e ) , a s i t u a t i o n w h i c h i s approached i f the product i s h i g h l y dispersed.  This i s i n contrast to i n d i v i d u a l ,  compact spheres o f growing p r o d u c t , w h i c h would i s o l a t e t h e r e a c t a n t phase from much o f t h e p r o d u c t . Some a t t e n t i o n s h o u l d now be g i v e n t o t h e r a t h e r l a r g e a c t i v a t i o n energy f o r t h e growth o f c r y s t a l s o f pure enantiomer t h r o u g h o u t t h e p o l y c r y s t a l l i n e racemate.  For the r e s o l u t i o n to occur, 1,1'-binaphthyl  m o l e c u l e s must be r e l e a s e d from t h e racemate c r y s t a l l i t e s ,  interconvert  i n t h e r e a c t a n t - p r o d u c t i n t e r f a c e , then add t o t h e g r o w i n g p r o d u c t crystallites.  The r a t e - d e t e r m i n i n g s t e p f o r t h e p r o c e s s cannot be  s i m p l y t h e r e l e a s e o f m o l e c u l e s from t h e racemate t o an i n t e r f a c e r e s e m b l i n g t h e m e l t , s i n c e o n l y some 7 k c a l mole ^ a r e r e q u i r e d t o m e l t the  racemate  ( S e c t i o n 3.3.2, p 7 5 ) .  More p r o b a b l y , t h e s l o w e s t s t e p  i n v o l v e s n o t o n l y t h e r e l e a s e o f 1 , 1 ' - b i n a p h t h y l from t h e racemate, b u t a l s o the simultaneous i n t e r c o n v e r s i o n of enantiomers.  But t h e r a c e m i z -  a t i o n o f 1 , 1 ' - b i n a p h t h y l i n n-heptane s o l u t i o n r e q u i r e s o n l y 21.7 —1 66 k c a l mole a c t i v a t i o n energy, a f i g u r e w h i c h , when added t o 7 k c a l mole \ i s s t i l l f a r from t h e o b s e r v e d 62 k c a l mole ^. The l a r g e s t p o s s i b l e energy increment a s s o c i a t e d w i t h t h e removal of m o l e c u l e s from a m o l e c u l a r c r y s t a l i s the h e a t o f s u b l i m a t i o n , a l s o c a l l e d t h e b i n d i n g energy, o f t h e c r y s t a l .  Binding energies f o r aromatic  h y d r o c a r b o n s a r e u s u a l l y o f t h e o r d e r o f 20 k c a l mole ^ ( a n t h r a c e n e i s -1 94 " f a i r l y t y p i c a l " a t 22 k c a l mole  ).  However, t h e energy (per m o l e c u l e )  r e q u i r e d t o remove a s i n g l e m o l e c u l e from i n s i d e a c r y s t a l t o t h e vapour  137  i s twice the energy (per molecule) needed to vaporize the entire c r y s t a l , since twice as many Van der Waals bonds are broken in the former case.'' Doubling the binding energy and adding the 21.7 kcal mole  1  required for  enantiomer interconversion i s much closer to the a c t i v a t i o n energy of 62 kcal mole . 1  For 1,1'-binaphthyl, the heat of sublimation of the c r y s t a l can be estimated as follows.  With nonpolar molecules, the heat of vaporization  of the melt i s related empirically to the normal b o i l i n g point through  ,  _  Trouton s r u l e :  95  AH  •  •  vaporization — b.p.  i  =  i  „, , , - 1 , - 1 21 c a l deg mole  96 The b o i l i n g point of 1,1'-binaphthyl has been determined  as 240° at a  pressure of 13 t o r r , which converts to a b o i l i n g point of 410°C (638°K) at atmospheric pressure, using a common vapour pressure-temperature 97 -1 The heat of vaporization i s therefore 14.3 kcal mole  nomograph. If AH  . i s the same at 105-135°C as i t i s at 410°C (probably vaporization  a crude approximation), and i f AH. . i s the same i n this * ' fusion r  temperature r  range as at 145°C, then;  AH  ^  , sublimation  =  AH^ . fusion  +  AH  . _ . vaporization  If the coordination number of the c r y s t a l i s n, then there are n/2 bonds per molecule i n the c r y s t a l , i . e . , vaporizing the entire c r y s t a l breaks n/2 bonds per molecule. However, i f a single molecule i s removed, a l l n bonds to i t must be broken. Therefore, twice the energy per molecule i s required.  138  from 105-135°C and a t a t m o s p h e r i c * f o r the l o w - m e l t i n g The  pressure.  T h e r e f o r e , AH  (racemate) form i s 14.3 + 7.3  energy r e q u i r e d t o remove one  = 21.6  , sublimation  k c a l mole ^.  1,1'-binaphthyl molecule  ( e f f e c t i v e l y , 2 &) i s t h e r e f o r e 43.2  k c a l mole  to i n f i n i t y  and i f the  molecule  must s i m u l t a n e o u s l y i n t e r c o n v e r t , the a c t i v a t i o n energy c o u l d be h i g h as 43.2  + 21.7  = 64.9  as  kcal mole" . 1  Such a h i g h a c t i v a t i o n energy r e p r e s e n t s an upper l i m i t  t o the  s i m p l e b r e a k i n g of Van der Waals f o r c e s i n the racemate c r y s t a l a c companied by t h e c o n f o r m a t i o n a l f l i p w h i c h i n t e r c o n v e r t s e n a n t i o m e r s . The  fact that 1,1'-binaphthyl  seems t o r e q u i r e almost a l l o f t h i s energy  to r e a c h the t r a n s i t i o n s t a t e means t h a t the m o l e c u l e needs c o n s i d e r a b l e freedom t o i n t e r c o n v e r t i n the r e a c t a n t - p r o d u c t i n t e r f a c e . o f a c t i v a t i o n would have t o be q u i t e f a v o u r a b l e i n r e a c t i o n t o be o b s e r v a b l e a t a l l . of 1 , 1 ' - b i n a p h t h y l solid  The  entropy  o r d e r f o r the  T h e r e f o r e , b o t h w i t h the  resolution  and the r a c e m i z a t i o n o f the ( + ) - d i a c i d 29_ i n the  phase, a h i g h a c t i v a t i o n energy i s observed  and i s compensated by  a h i g h a c t i v a t i o n e n t r o p y , f a c i l i t a t i n g the s o l i d - s t a t e r e a c t i o n s . In summary, we  s h o u l d emphasize t h a t a l t h o u g h some h i g h degree o f  c o n t r o l can be e x e r c i s e d over the s o l i d - s t a t e r e s o l u t i o n each p r e p a r e d b a t c h remains an i n d i v i d u a l . such i n t e r f a c e - c o n t r o l l e d  of  1,1'-binaphthyl,  The k i n e t i c c o m p l e x i t i e s o f  s o l i d - s t a t e r e a c t i o n s s h o u l d n o t , however,  overshadow the s i g n i f i c a n t f a c t t h a t r e a c t i o n s i n o r g a n i c s o l i d s  can  o c c u r w i t h f a c i l i t y and w i t h f a s c i n a t i n g s t e r e o c h e m i c a l consequences.  139  3^6  The Spontaneous Generation of Optically Active 1,1'-Binaphthyl ' In this section are described some experiments involving the  crystallization of 1,1'-binaphthyl from the melt in a closed system.  These  experiments grew out of our earlier attempts (Section 3 . 4 . 2 , p 9 1 ) to obtain, reproducibly, 1,1'-binaphthyl of high specific rotation by seeding the supercooled melt in open test tubes.  A few preliminary  crystallizations in sealed ampules in which optically active seeds were purposefully excluded had shown that optical activity could develop even in a closed system consisting i n i t i a l l y of a racemic 1,1'-binaphthyl meltc  Both enantiomers could be obtained.  It  then became of interest,  as a separate problem, to examine the behaviour of a large number of individual sealed samples, keeping a tally of the direction and magnitude of the specific rotations obtained. Accordingly, two hundred individual ampules containing about 20 mg of carefully weighed 1,1'-binaphthyl crystals (from various racemic batch preparations) were sealed and then held, in groups of twelve, at temperatures of 170 to 185° for five minutes to melt and destroy a l l forms of solid 1,1'-binaphthyl,,  The totally melted samples were then  quickly transferred to a bath maintained at 1 5 0 ° . At this temperature the melt w i l l remain supercooled almost indefinitely.  Crystallization  was induced, however, by removing each sample, holding i t against a piece of Dry Ice for a few seconds, then quickly replacing i t in the 150° bath.  In this manner, a small area of the bulk of the melt was  cooled drastically, forming some seed crystals on which the remaining melt could crystallize at 1 5 0 ° . three hours.  Crystallization was complete within  The solid samples were then cooled to room temperature,  140  opened, and a n a l y z e d f o r o p t i c a l a c t i v i t y .  The m a t e r i a l o b t a i n e d was  almost always o p t i c a l l y a c t i v e , a l t h o u g h e x c e s s i v e a p p l i c a t i o n o f the c o o l i n g Dry I c e r e s u l t e d i n no a c t i v i t y .  These few cases of s p e c i f i c  r o t a t i o n s l e s s than -2° were not c o n s i d e r e d i n the f o l l o w i n g  statistical  analysis. The d i s t r i b u t i o n of the 200 s p e c i f i c r o t a t i o n s i s shown i n F i g u r e 30, w h i c h i s a p r e s e n t a t i o n o f p e r c e n t a g e of o b s e r v a t i o n s f a l l i n g various rotations. [a] is  = -218°  within  The l a r g e s t o b s e r v e d r o t a t i o n s o f the 200 were  and +206° ( o p t i c a l l y pure l , l ' - b i n a p h t h y l (Appendix A, p 178)  [a] = ^245°) ; however, as shown, samples o f low r o t a t i o n ("±2° t o ±48°)  were most common.  The o b s e r v e d r o t a t i o n s f i t a G a u s s i a n d i s t r i b u t i o n  w i t h a mean o f [a] = +0.14°and a s t a n d a r d d e v i a t i o n of 86.4°.^  From t h i s  d i s t r i b u t i o n i t i s apparent t h a t o b t a i n i n g 1 , 1 ' - b i n a p h t h y l w i t h an o p t i c a l p u r i t y above 90% by t h i s method would be a v e r y e x c e p t i o n a l event ( o b s e r v a b l e about once i n 150  trys).  The symmetry of the d i s t r i b u t i o n i s r e f l e c t e d i n F i g u r e 31 by the r a t i o o f t h e number o f S-(+)  samples t o t h e t o t a l number of samples  p l o t t e d f o r two runs of 100 samples each. i n c r e a s e s , the r a t i o tends toward 0.5  As the t o t a l number o f samples  and i t f a l l s a t a l l p o i n t s w e l l  w i t h i n the 99% c o n f i d e n c e l i m i t s c a l c u l a t e d f o r a p r o b a b i l i t y of 50% and 50% (-) of  samples.  (+)  A f t e r 200 independent c r y s t a l l i z a t i o n s , the number  d e x t r o r o t a t o r y samples o b t a i n e d (95) i s i n s i g n i f i c a n t l y  different  from the number of l e v o r o t a t o r y samples o b t a i n e d (105) . ^  I f the cases of [a] = 0° o b t a i n e d from o v e r c o o l i n g the samples were i n c l u d e d i n t h i s t r e a t m e n t , the symmetry o f the d i s t r i b u t i o n would, of c o u r s e , be p r e s e r v e d , but the s t a n d a r d d e v i a t i o n would be reduced.  141  F i g u r e 30,  P e r c e n t a g e o f 1 , 1 ' - b i n a p h t h y l samples g i v i n g s p e c i f i c  between ±240°. calculated  The c u r v e shows t h e G a u s s i a n normal  distribution  f o r t h e mean o f +0.14° and s t a n d a r d d e v i a t i o n  o f 86.4°.  rotations  142  j~  5  F i g u r e 31.  r~ IO  1  ~r~' 20  i " 30  1  1  AO  1  50  1  eO  1  1  TO  R a t i o o f samples h a v i n g p o s i t i v e r o t a t i o n s  as two s e t s o f 100 each.  calculated  1  Number of Samples  of samples o f 1 , 1 ' - b i n a p h t h y l c r y s t a l l i z e d treated  1  a t 150°.  1  1  80  1  90  r—  1  lOO  t o t h e t o t a l number  The 200 samples a r e  The c u r v e s a r e c o n f i d e n c e  limits  f o r a 0.99 degree o f c o n f i d e n c e and a p r o b a b i l i t y o f 50%  p o s i t i v e and 50% n e g a t i v e f o r each sample.  1  143  An i m p o r t a n t c o n c l u s i o n can be drawn from the symmetric distribution.  probability  The development o f o p t i c a l a c t i v i t y i n each sample was  d e t e r m i n e d by o n l y t h e chance f o r m a t i o n of R o r S c r y s t a l s from t h e r a c e m i c melt.  The g e n e r a t i o n of o p t i c a l a c t i v i t y i n the 1 , 1 ' - b i n a p h t h y l system  i s t r u l y spontaneous.  H e r e , "spontaneous" i s t a k e n as meaning " p e r t a i n i n g  o n l y t o t h e system i t s e l f . "  A spontaneous r e s o l u t i o n , t h e r e f o r e , o c c u r s  when measurable o p t i c a l a c t i v i t y i s produced from a t o t a l l y r a c e m i c system i n the complete absence o f e x t e r n a l d i s s y m m e t r i c i n f l u e n c e s o f any t y p e - p h y s i c a l , c h e m i c a l , o r human.  The p r o b a b i l i t y d i s t r i b u t i o n o f a  l a r g e number o f i n d i v i d u a l r e s o l u t i o n s i s a s e n s i t i v e check f o r the p r e sence o f any such e x t e r n a l i n f l u e n c e , w h i c h w i l l be r e v e a l e d as a mean s p e c i f i c r o t a t i o n s i g n i f i c a n t l y d i f f e r e n t from z e r o , and as a g r e a t e r number of samples of one handedness t h a n the o t h e r , as shown by an approach to  t h e 99% l i m i t s o f c o n f i d e n c e c a l c u l a t e d f o r t h e t o t a l l y random s i t u a t i o n . A l t h o u g h the spontaneous g e n e r a t i o n o f o p t i c a l i s o m e r s i n a t o t a l l y  symmetric environment seems i n t u i t i v e l y r e a s o n a b l e , i t has n e v e r b e f o r e 98 been c a r e f u l l y d e m o n s t r a t e d . served.  I n f a c t , q u i t e t h e o p p o s i t e has been ob-  The r e p o r t e d examples of a t t e m p t s t o e l i m i n a t e a l l d i s s y m m e t r i c 98 99  i n f l u e n c e s from s e v e r a l systems, w h i c h a r e r e c e n t l y r e v i e w e d shown a tendency f o r p r e f e r e n t i a l c r y s t a l l i z a t i o n of one T h i s may  '  have  enantiomorph.  s i m p l y be a r e f l e c t i o n on the s m a l l number of i n d i v i d u a l  trials  i n some i n v e s t i g a t i o n s ( a f t e r 10 samples, even 1 , 1 ' - b i n a p h t h y l showed e i g h t n e g a t i v e and two p o s i t i v e r o t a t i o n s ) , but n e v e r t h e l e s s , such apparent b i a s has engendered  the f e e l i n g t h a t the t o t a l l y  symmetric  experiment i s e i t h e r e x t r e m e l y d i f f i c u l t because of omnipresent o p t i c a l l y active impurities  o r c o m p l e t e l y i m p o s s i b l e because o f a weak d i s s v m -  144  m e t r i c b i a s i n the u n i v e r s e . of  101  The f a c t t h a t 1 , 1 ' - b i n a p h t h y l i s c a p a b l e  t r u l y spontaneous r e s o l u t i o n not o n l y proves t h a t such a phenomenon  i s p o s s i b l e , but a l s o t h a t d i s s y m m e t r i c m a t e r i a l s w h i c h were almost  certain  p r e s e n t as d u s t p a r t i c l e s or l e s s w e l l d e f i n e d d i s s y m m e t r i c f o r c e s , do n o t always i n f l u e n c e the development o f o p t i c a l a c t i v i t y .  Perhaps  one  c o u l d say t h a t because 1 , 1 ' - b i n a p h t h y l i s a r e l a t i v e l y u n n a t u r a l compound, its  n u c l e a t i o n and c r y s t a l l i z a t i o n i s i n s e n s i t i v e t o d i s s y m m e t r i c  p u r i t i e s d e r i v e d from  life.  The q u e s t i o n t h e r e f o r e a r i s e s as t o w h i c h , i f any, m a t e r i a l s can i n f l u e n c e t h e 1 , 1 ' - b i n a p h t h y l r e s o l u t i o n . performed  im-  dissymmetric We t h e r e f o r e  s e v e r a l i n d i v i d u a l c r y s t a l l i z a t i o n s i n the p r e s e n c e o f b o t h  d- and 1-mandelic  acid  (37) .  The a d d i t i o n of 5% by w e i g h t o f  d-mandelic  OH  37  a c i d i n experiments  at 130°  s i m i l a r to t h o s e d e s c r i b e d above  produced  1 , 1 ' - b i n a p h t h y l w i t h an excess (+) r o t a t i o n ( a f t e r c o r r e c t i n g f o r the s m a l l r o t a t i o n a r i s i n g from m a n d e l i c a c i d ) i n 18 out o f 19 samples. the o t h e r hand, 5% 1-mandelic (-)  On  a c i d i n 1 , 1 ' - b i n a p h t h y l gave samples w i t h  r o t a t i o n s i n 17 t r i e s out o f 17.  These d i s t r i b u t i o n s f a l l  well  o u t s i d e those c a l c u l a t e d f o r a 50-50 p r o b a b i l i t y and they i n d i c a t e t h a t the c o n f i g u r a t i o n o f m a n d e l i c a c i d e s s e n t i a l l y c o m p l e t e l y c o n t r o l s c o n f i g u r a t i o n of 1 , 1 ' - b i n a p h t h y l o b t a i n e d .  the  145  It i s possible  t o d i s t i n g u i s h t h r e e t y p e s o f systems i n w h i c h  spontaneous r e s o l u t i o n i s p o s s i b l e .  The f i r s t , e x e m p l i f i e d  by R- and S-  1 , 1 ' - b i n a p h t h y l , i s a system i n w h i c h c r y s t a l l i z a t i o n can o c c u r from a racemic l i q u i d c o n t a i n i n g  rapidly interconverting  p r e s e n c e o f a mechanism f o r i n t e r c o n v e r s i o n  enantiomers.  means t h a t  t h e system  f i n i s h e s c r y s t a l l i z i n g i n a thermodynamically s t a b l e s t a t e . f i n a l p r o d u c t can t h e r e f o r e activity  The  The  be a n a l y z e d a t l e i s u r e f o r any o p t i c a l  (provided, of course, that interconversion  room t e m p e r a t u r e t o p e r m i t a n a l y s i s ) . c r y s t a l l i z a t i o n from s o l u t i o n r a t h e r  i s s l o w enough a t  Other examples,  involving  than from t h e m e l t , a r e t h e systems  102 and ( - ) - m e t h y l e t h y l a l l y l a n i l i n i u m i o d i d e (38) and ( + ) - and ( - ) 103 t r i - o - t h y m o t i d e (39) . A l t h o u g h t h e s e systems d e v e l o p o p t i c a l a c t i v i t y (+)-  CH  3  38 39 from a r a c e m i c s o l u t i o n , t h e number o f samples t a k e n i n each i s too few to d e c i d e whether d i s s y m m e t r i c i m p u r i t i e s  are i n f l u e n c i n g  i . e . , whether o r n o t t h e r e s o l u t i o n i s t r u l y  the r e s o l u t i o n ,  spontaneous.  The second t y p e o f system i n which i t might be p o s s i b l e s t r a t e spontaneous  t o demon-  r e s o l u t i o n i s one i n w h i c h enantiomers a r e o p t i c a l l y  s t a b l e , but a s o l u t i o n ( o r melt) i s only p a r t i a l l y c r y s t a l l i z e d .  In  146  such a system, t o t a l c r y s t a l l i z a t i o n would, o f c o u r s e , l e a d t o a racemic batch of c r y s t a l s .  In a p a r t i a l c r y s t a l l i z a t i o n , the c r y s t a l s  c o u l d w e l l have an excess o f one enantiomer w h i l e t h e l i q u i d phase cont a i n s an excess o f t h e o t h e r .  However, t h i s r e p r e s e n t s an u n s t a b l e  s t a t e , s i n c e t h e l i q u i d phase w i l l always be s u p e r s a t u r a t e d i n one e n a n t i o m e r , and t h e two phases must be s u c c e s s f u l l y s e p a r a t e d (by f i l t r a t i o n ) without d i s t u r b i n g the metastable l i q u i d .  I n s p i t e of the 85  s e e m i n g l y p r e c a r i o u s p r o c e d u r e , t h i s method i s r a t h e r w i d e l y u s e d , t o r e s o l v e enantiomers under non-spontaneous p u r p o s e f u l a d d i t i o n o f seed  c o n d i t i o n s (e.g. the  crystals).  The t h i r d system w h i c h can i n p r i n c i p l e show spontaneous  resolution  i s one w h i c h c o n t a i n s an a c h i r a l m o l e c u l e i n s o l u t i o n ( o r i n t h e m e l t ) . I f such a compound c r y s t a l l i z e s i n an enantiomorphous an excess o f m o l e c u l e s i n one enantiomorphous  space g r o u p , then  crystal constitutes, i n a  sense, a r e s o l u t i o n of o p t i c a l l y a c t i v e c r y s t a l s .  As w i t h t h e f i r s t  t y p e o f system, t h e f i n a l s t a t e i s t h e r m o d y n a m i c a l l y s t a b l e .  However,  a n a l y s i s p r e s e n t s some p r o b l e m s , s i n c e i n an i n d i v i d u a l crop o f c r y s t a l s each must be weighed  and examined f o r h e m i h e d r a l f a c e s o r o p t i c a l  r o t a t i o n , b e f o r e i t can be c o n c l u d e d t h a t t h e g i v e n crop c o n t a i n e d an excess o f m o l e c u l e s i n one enantiomorphous  crystal.  S u f f i c i e n t crops  must a l s o be examined b e f o r e any c o n c l u s i o n s as t o s p o n t a n e i t y can be 104 drawn.  I n s p i t e o f t h i s time-consuming  requirement, Soret  examined  844 c r y s t a l l i z a t i o n s o f sodium c h l o r a t e from s o l u t i o n i n s e a l e d .ampules, and o b s e r v e d an excess o f r i g h t - h a n d e d c r y s t a l s i n 51.3% o f t h e samples, w h i l e 48.7% o f the samples had l e f t - h a n d e d c r y s t a l s i n e x c e s s .  Other  105 results  r e c o r d a w e i g h t e d average o f 50.08 d e x t r o r o t a t o r y  crystals  147  from 46 independent c r o p s .  As f a r as we know, t h i s i s the o n l y o t h e r  c a r e f u l l y demonstrated case o f the spontaneous g e n e r a t i o n of o p t i c a l l y active material. U n l i k e t h e enantiomorphous  sodium c h l o r a t e c r y s t a l , w h i c h  loses  a l l o p t i c a l a c t i v i t y i m m e d i a t e l y on d i s s o l u t i o n , the 1 , 1 ' - b i n a p h t h y l system i n v o l v e s t h e spontaneous  c r e a t i o n of o p t i c a l l y a c t i v e molecules which  r e t a i n t h e i r c o n f i g u r a t i o n f o r a c o n s i d e r a b l e l e n g t h of t i m e i n s o l u t i o n (at 0°).  The r e s o l u t i o n o f 1 , 1 ' - b i n a p h t h y l i s t h e r e f o r e a s i m p l e  i l l u s t r a t i o n o f C a l v i n ' s h y p o t h e t i c a l scheme"'"^ f o r t h e a u t o c a t a l y t i c s e l e c t i o n o f one enantiomer i n the g e n e s i s o f o p t i c a l l y a c t i v e m o l e c u l e s .  3.7  Conclusion The development  o f o p t i c a l a c t i v i t y s i m p l y by h e a t i n g and  a r a c e m i c m a t e r i a l l i k e 1 , 1 ' - b i n a p h t h y l seems, a t f i r s t impossible process.  cooling  t h o u g h t , t o be an  The thought a r i s e s because t h e i n t e r c o n v e r s i o n o f  enantiomers i n s o l u t i o n always l e a d s t o r a c e m i z a t i o n , n o t because o f an i n c r e a s e i n e n t r o p y due t o g r e a t e r d i s o r d e r .  resolution, But i n g o i n g  from such a homogeneous system t o a heterogeneous system such as the phases formed between two e n a n t i o m e r s , r e s o l u t i o n can become a p o s s i b l e , even p r o b a b l e , p r o c e s s . R e s o l u t i o n i s c o m p a t i b l e w i t h the achievement o f l o w e r f r e e energy because e n t h a l p y and e n t r o p y changes accompanying  phase t r a n s f o r m a t i o n s  can more than compensate f o r any l o s s e s i n f r e e energy due t o f o r m a t i o n of m o l e c u l e s of o n l y one k i n d .  These l o s s e s a r e , i n f a c t , v e r y s m a l l .  F o r example, even the most i n t i m a t e o f m i x t u r e s o f enantiomers - the l i q u i d s o l u t i o n of one i n the o t h e r - would l o s e o n l y 1.37  c a l deg ''"mole  148  o f e n t r o p y and no e n t h a l p y ( i n t h e case o f i d e a l s o l u t i o n s ) i n hypo46 t h e t i c a l l y c h a n g i n g from a r a c e m i c t o a f u l l y r e s o l v e d s t a t e . 150°,  t h i s e n t r o p y change amounts t o 580 c a l mole  1  of free  At  energy.  The e n t r o p y d i f f e r e n c e between t h e f a r l e s s i n t i m a t e m i x t u r e found i n a e u t e c t i c c o n g l o m e r a t i o n o f l a r g e a g g r e g a t e s ( c r y s t a l l i t e s ) o f pure e n a n t i o m e r s and t h e p o l y c r y s t a l l i n e s i n g l e enantiomer i s even  smaller.  I n f a c t , t h e e n t r o p y , e n t h a l p y and f r e e energy o f m i x i n g a r e i m p l i c i t l y t a k e n as z e r o when two pure s o l i d s form a m e c h a n i c a l m i x t u r e and t h e f r e e energy o f t h e m i x t u r e i s l i n e a r l y r e l a t e d t o i t s c o m p o s i t i o n . " ' Therefore, there i s l i t t l e ,  1  i f any, thermodynamic p r e f e r e n c e f o r t h e  formation of a racemic e u t e c t i c m i x t u r e over that of a p o l y c r y s t a l l i n e single  enantiomer. The c h o i c e o f w h i c h i s formed i s governed e n t i r e l y by k i n e t i c s .  I n t h e spontaneous  c r y s t a l l i z a t i o n o f 1 , 1 ' - b i n a p h t h y l from t h e m e l t ,  t h e chance f o r m a t i o n o f one enantiomer l o w e r s t h e f r e e energy o f a c t i v a t i o n towards t h e f u r t h e r c r y s t a l l i z a t i o n o f t h a t enantiomer by p r e s e n t i n g a s u r f a c e on w h i c h m o l e c u l e s o f o n l y one c o n f i g u r a t i o n may be d e p o s i t e d . The element o f chance can be c o m p l e t e l y e l i m i n a t e d by p e r f o r m i n g a c o n t r o l l e d s o l i d - s t a t e r e s o l u t i o n through the p r e p a r a t i o n of a h i g h l y s t e r e o s p e c i f i c s o l i d c o n s i s t i n g o f a racemate and seed c r y s t a l s o f t h e desired  enantiomer.  The R- and S - l , 1 ' - b i n a p h t h y l system i l l u s t r a t e s t h e n o v e l t y o f w o r k i n g w i t h t h e phase t r a n s f o r m a t i o n s o f o p t i c a l l y l a b i l e  enantiomers.  A sample o f neat 1 , 1 - b i n a p h t h y l ( [ a ] = +234°) h e l d a t 160° r a c e m i z e s 1  c o m p l e t e l y i n l e s s than f i v e m i n u t e s . activity  A n o t h e r sample o f low o p t i c a l  ([«] = +11°) can be p r e p a r e d so t h a t i s w i l l r e s o l v e t o  149  [a] = +214° i n l e s s than f i v e minutes a t 150°, o n l y 10° l o w e r i n t e m p e r a t u r e . How g e n e r a l  i s t h i s phenomenon?  The development o f o p t i c a l  by c r y s t a l l i z a t i o n o f t h e melt r e q u i r e s t h a t the enantiomers  activity  interconvert  r e l a t i v e l y q u i c k l y i n t h e m e l t and y e t be o p t i c a l l y s t a b l e ( u n l i k e t h e ( + ) - d i a c i d 2_9, S e c t i o n 2) as a e u t e c t i c m i x t u r e .  The c o n t r o l l e d s o l i d -  s t a t e r e s o l u t i o n r e q u i r e s t h e e x i s t e n c e o f two r a c e m i c m o d i f i c a t i o n s , e i t h e r a racemate o r a s o l i d s o l u t i o n w h i c h decomposes to a e u t e c t i c m i x t u r e a t t e m p e r a t u r e s where i n t e r c o n v e r s i o n i s r e l a t i v e l y  rapid.  The e x i s t e n c e o f more than one c r y s t a l l i n e m o d i f i c a t i o n o f a s i n g l e compound i s more w i d e s p r e a d than commonly supposed. a l l organic  Over o n e - t h i r d o f  compounds s t u d i e d t h e r m o d y n a m i c a l l y up t o 1969 e x h i b i t p o l y -  , . 107a „ . . . , 81a _ morphism. I t i s the opinion of s e v e r a l authors that every T  organic  compound p o s s e s s e s more than one s o l i d s t a t e , w h i c h have o n l y t o be discovered  through s u i t a b l y o r i e n t e d  research.  The unprecedented s o l i d - s t a t e r e s o l u t i o n o f  1,1'-binaphthyl,  a l t h o u g h s u r p r i s i n g when f i r s t e n c o u n t e r e d , i s a c t u a l l y e a s i l y e x p l a i n e d and  should  isomers.  be a n t i c i p a t e d i n f u t u r e s t u d i e s w i t h phase systems o f o p t i c a l  150  4. 4.1  EXPERIMENTAL  General Reagents and s o l v e n t s used were r e a g e n t grade and were employed  without f u r t h e r p u r i f i c a t i o n , unless otherwise noted.  Melting points,  d e t e r m i n e d on a Thomas Hoover C a p i l l a r y M e l t i n g P o i n t a p p a r a t u s i n u n s e a l e d c a p i l l a r i e s , were c o r r e c t e d .  Infrared spectra ( a l l  m u l l s ) were r u n on a P e r k i n - E l m e r 137 sodium c h l o r i d e A n a l y t i c a l p r o c e d u r e s r e q u i r i n g a more d e t a i l e d (polarimet'ry, d i f f e r e n t i a l scanning  nujol  spectrophotometer.  description  c a l o r i m e t r y , and X-ray powder  d i f f r a c t i o n ) a r e d e s c r i b e d i n S e c t i o n 4.6.  4.2  Preparations  4.2.1  P r e p a r a t i o n o f Racemic N a p h t h i d i n e (31) The p r o c e d u r e f o l l o w e d f o r t h e p r e p a r a t i o n o f r a c e m i c n a p h t h i d i n e  was s i m i l a r t o t h a t of Cohen and O e s p e r . ^ of p u l v e r i z e d a-napthylamine  I n a 1 i b e a k e r , 27.9 g  were s t i r r e d i n t o 500 ml w a t e r , 33.8 ml  o f c o n c e n t r a t e d h y d r o c h l o r i c a c i d was added, and the m i x t u r e warmed on a steam b a t h t o g i v e a l i g h t p u r p l e p r e c i p i t a t e of cc-nap thy lamine hydrochloride.  The m i x t u r e was then c o o l e d i n an i c e b a t h t o 0-3°  and c o l d , d i l u t e d s u l f u r i c a c i d (21 ml o f the c o n c e n t r a t e d a c i d p l u s 200 ml w a t e r ) was s t i r r e d i n . The suspended amine s a l t was then d i a z o t i z e d ( w i t h v i g o r o u s s t i r r i n g , k e e p i n g the temperature n e a r 0°) by  151  s l o w l y a d d i n g a c o l d s o l u t i o n o f 14 g sodium n i t r i t e d i s s o l v e d i n 90 ml water.  The r e d d i s h brown s o l u t i o n o f the d i a z o n i u m s a l t was a l l o w e d  to s t a n d f o r 5 min i n t h e i c e b a t h then s u c t i o n f i l t e r e d ,  the f i l t r a t e  b e i n g r e c e i v e d i n a p r e c o o l e d f i l t e r f l a s k s u r r o u n d e d by an i c e b a t h . The  c o l d f i l t r a t e was t r a n s f e r r e d to a 2 £ b e a k e r  c o l d s o l u t i o n o f 79.9 g anhydrous  ( i c e b a t h ) and a  p o t a s s i u m a c e t a t e i n 300 ml w a t e r  was s l o w l y s t i r r e d i n , t h e temperature b e i n g k e p t below 4°.  A cooled  s o l u t i o n o f 31 g sodium s u l f i t e i n 200 ml water was then s l o w l y added, c a u s i n g a v i g o r o u s e v o l u t i o n o f n i t r o g e n and the appearance azonaphthalene was completed min.  crystals.  of 1,1'-  A f t e r the a d d i t i o n o f sodium s u l f i t e  solution  the s o l u t i o n was a l l o w e d t o s t i r f o r an a d d i t i o n a l 5  The s u s p e n s i o n was then t a k e n o u t of the i c e b a t h , warmed on a  steam b a t h t o ~60°, and the orange p r e c i p i t a t e was f i l t e r e d o f f , washed w i t h w a t e r , and d r i e d i n a i r . W i t h o u t f u r t h e r p u r i f i c a t i o n the crude a z o n a p h t h a l e n e was p u l v e r i z e d and suspended weak b o i l .  ( c a . 18 g)  i n 200 ml 95% e t h a n o l , and b r o u g h t t o a  A s o l u t i o n o f 48 g stannous c h l o r i d e d i h y d r a t e i n 100 m l  c o n c e n t r a t e d h y d r o c h l o r i c a c i d was s l o w l y added over c a . 5 min ( w i t h occasional swirling).  A c o l o u r change (from y e l l o w t o reddish-brown)  o c c u r r e d , and t h e m i x t u r e was i m m e d i a t e l y c o o l e d t o room t e m p e r a t u r e . C o n c e n t r a t e d h y d r o c h l o r i c a c i d (100 ml) was then added t o p r e c i p i t a t e any r e m a i n i n g n a p h t h i d i n e h y d r o c h l o r i d e . The p r e c i p i t a t e was washed w i t h w a t e r , then suspended  i n 200 m l w a t e r .  Twenty ml o f 20% sodium  h y d r o x i d e was then added, and the m i x t u r e a l l o w e d to s t i r a t 40° f o r 10 min.  The s l u r r y was c o o l e d i n an i c e b a t h , f i l t e r e d , washed w i t h  w a t e r and d r i e d i n a i r . The crude n a p h t h i d i n e was d i s s o l v e d i n 160 m l  152  o f a hot 3:1  ethanol-pyridine solvent pair.  f i l t e r e d and a l l o w e d to c o o l s l o w l y .  The  The  h o t s o l u t i o n was  p u r i f i e d naphthidine  26% from a-naphthylamine) was  o b t a i n e d as w e l l - f o r m e d ,  plates  198-199°).  (m.p.  4.2.2  201-202°, l i t .  7  0  (7.1  g,  l i g h t brown  P r e p a r a t i o n o f (+)-Naphthidine-a-bromo-D-camphor-~-sulfonate T h i s s a l t was  Hopp.  71  u s i n g the p r o c e d u r e of T h e i l a c k e r  To 400 ml w a t e r and 40 ml 1 N h y d r o c h l o r i c a c i d was  s o l u t i o n of 2.84 T h i s was  prepared  g (10 mmoles) r a c e m i c n a p h t h i d i n e  followed immediately  bromo-D-camphor-ir-sulfonate.  w i t h 6.54  and added a  i n 50 ml hot  acetone.  g (20 mmoles) (+)-ammonium-a-  A l i g h t - b r o w n p r e c i p i t a t e soon formed  the m i x t u r e was  a l l o w e d t o s t a n d a t room temperature o v e r n i g h t .  p r e c i p i t a t e was  f i l t e r e d and r e c r y s t a l l i z e d from 70 ml 60%  ethanol-water.  Two  crops  (4.27  g, 46%)  were o b t a i n e d .  25 71 gave a s p e c i f i c r o t a t i o n of [ c t ] = +80° ( l i t .  20  4.2.3  33  P r e p a r a t i o n of S - ( + ) - l , l ' - B i n a p h t h y l from s a l t 33 was  d i r e c t l y deaminated to  of 150 ml w a t e r , 3.45  The  (by volume)  =  +99°).  S-(+)-1,1'-binaphthyl  u s i n g a p r o c e d u r e s i m i l a r t o t h a t o f C o l t e r and i c e - c o l d suspension  and  This m a t e r i a l  D  The  (33)  Clemens.^  g of s a l t J3J3, 2.3  To  an  ml  concen-  t r a t e d h y d r o c h l o r i c a c i d , and 50 ml 50% hypophorphorous a c i d i n a 3-necked f l a s k f i t t e d w i t h an overhead s t i r r e r was nitrite.  A f t e r 2 h an a d d i t i o n a l 1 g sodium n i t r i t e was  cold mixture was  added 1.2  and  s t i r r i n g was  then s t o p p e r e d  continued  f o r a n o t h e r 3 h.  g sodium  added t o the The  flask  l i g h t l y and p l a c e d i n the r e f r i g e r a t o r o v e r n i g h t  (0°).  153  F o r two days the f l a s k was s t i r r e d and k e p t c o l d d u r i n g the daytime and s t o r e d i n the r e f r i g e r a t o r o v e r n i g h t , d u r i n g w h i c h time a  total  o f 6 g sodium n i t r i t e were added i n 1 g p o r t i o n s . The c o l d m i x t u r e was  f i l t e r e d and the s o l i d m a t e r i a l suspended i n  200 ml c o l d (8°) benzene.  The s u s p e n s i o n was  f i l t e r e d and the  s o l u t i o n e x t r a c t e d s u c c e s s i v e l y w i t h 10% sodium h y d r o x i d e , w a t e r , 10% h y d r o c h l o r i c a c i d , and w a t e r MgSO^.  After f i l t r a t i o n  ( a l l a t ^ 8°), and d r i e d o v e r  ( c o l d a p p a r a t u s ) , the benzene was  anhydrous removed on  the r o t a r y e v a p o r a t o r (25-30°), and the s o l i d p l a c e d on a column ( w i t h a w a t e r j a c k e t ) packed w i t h 25 g a l u m i n a (Woelm, n e u t r a l , grade 1) i n p e t r o l e u m e t h e r (30-60°). through the j a c k e t .  C o l d w a t e r was  The f r a c t i o n s , e l u t e d w i t h 4%  p e t r o l e u m e t h e r (30-60°) a f f o r d e d w h i t e c r y s t a l s D  [a]  =  +145-192°, m.p.  156-159°; l i t .  6  4  [a]  5 7 9 1  circulated  (by volume)  (0.536 g, 55%)  25 o p t i c a l l y a c t i v e 1 , 1 ' - b i n a p h t h y l ( [ a ] = +97°; m.p.  activity  benzeneof  156-157°; l i t .  = +245°, m.p.  65  157-  159°) .  4.2.4  P r e p a r a t i o n o f Racemic 1 , 1 ' - B i n a p h t h y l The p r o c e d u r e used was  analogous t o t h a t of S a k e l l a r i o s and K r y i m i s .  To a d r y 3-necked f l a s k f i t t e d w i t h an overhead s t i r r e r and was added (under d r y n i t r o g e n ) 9.6 e t h e r , 56 ml a-bromonaphthalene  condenser  g magnesium t u r n i n g s , 72 ml  anhydrous  and a s i n g l e c r y s t a l o f i o d i n e .  The  s t i r r e d m i x t u r e was h e a t e d t o r e f l u x t o s t a r t the r e a c t i o n , w h i c h proceeded w i t h o u t f u r t h e r h e a t i n g f o r 20 min. was  The r e a c t i o n m i x t u r e  then h e a t e d to r e f l ux f o r 6 h, w i t h the a d d i t i o n of up to 200 ml d r y  benzene t o t h i n the s l u r r y when n e c e s s a r y .  The r e a c t i o n was  cooled  t o room temperature and added s l o w l y t o a s t i r r e d s u s p e n s i o n of 54 g  154  anhydrous c u p r i c c h l o r i d e ( p r e p a r e d  by d r y i n g  f o r 4 h a t 100°) i n 200 ml anhydrous e t h e r .  the d i h y d r a t e The e n s u i n g  r e a c t i o n was c o n t r o l l e d w i t h an i c e - w a t e r b a t h .  salt  vigorous  The s u s p e n s i o n  was  then s t i r r e d o v e r n i g h t a t room temperature under d r y n i t r o g e n . The  r e a c t i o n m i x t u r e was quenched by slow a d d i t i o n t o 100 ml 10%  h y d r o c h l o r i c a c i d and i c e .  The e t h e r - b e n z e n e l a y e r was e x t r a c t e d  s u c c e s s i v e l y w i t h s e v e r a l p o r t i o n s o f 10% h y d r o c h l o r i c a c i d , w a t e r , s a t u r a t e d sodium b i c a r b o n a t e anhydrous magnesium s u l f a t e .  s o l u t i o n and w a t e r , and d r i e d o v e r The s o l v e n t s were removed in_ vacuo t o  a f f o r d an o i l , w h i c h c r y s t a l l i z e d on c o o l i n g t o 0°.  The brown m a t e r i a l  was t r a n s f e r r e d t o a Buchner f u n n e l , washed w i t h a s m a l l amount o f cold petroleum ether ether  (65-110°).  (30-60°), and r e c r y s t a l l i z e d once from p e t r o l e u m  The crude 1 , 1 ' - b i n a p h t h y l  (^ 12 g) was then mixed  w i t h an e q u a l w e i g h t o f a l u m i n a ( S h a w i n i g a n r e a g e n t ) and p l a c e d on a column o f 300 g a l u m i n a packed i n p e t r o l e u m e t h e r  (30-60°).  After  1 I had been e l u t e d w i t h 10% b e n z e n e - p e t r o l e u m e t h e r (30-60°), the f i r s t appearance o f 1 , 1 ' - b i n a p h t h y l white  was r e v e a l e d by the p r e s e n c e o f  c r y s t a l s a t the t i p o f t h e column.  r e q u i r e d 3 I f o r complete e l u t i o n .  The e n t i r e b i n a p h t h y l  Evaporation  fraction  o f the s o l v e n t  i n vacuo and r e c r y s t a l l i z a t i o n o f the b i n a p h t h y l from acetone a f f o r d e d 10 g (20%) o f w h i t e  c r y s t a l s , m.p.'s 144-145° ( l o w - m e l t i n g  form) and  73 157-158° ( h i g h - m e l t i n g f o r m ) . (low-melting  Badar, e t a l .  form) and 157-159° ( h i g h - m e l t i n g  r e p o r t m.p. form).  144.5-145°  155  4.3  P r o c e d u r e s f o r the R e s o l u t i o n of Racemic 1 , 1 ' - B i n a p h t h y l  4.3.1  R e s o l u t i o n i n C o m p l e t e l y M e l t e d Samples  4.3.1.1  Spontaneous R e s o l u t i o n  To observe r e s o l u t i o n from a m e l t w h i c h i s t o t a l l y  racemic,  c a r e f u l l y weighed samples of 1 , 1 ' - b i n a p h t h y l (from s e v e r a l d i f f e r e n t b a t c h p r e p a r a t i o n s ) r a n g i n g from 10-30 g l a s s ampules.  mg i n w e i g h t were s e a l e d i n 1 ml  I n groups of 12, the s e a l e d ampules were h e l d i n a  s i l i c o n e - o i l a t 170-185° t o d e s t r o y a l l forms o f s o l i d 1 , 1 ' - b i n a p h t h y l . The c o m p l e t e l y m e l t e d samples were t h e n q u i c k l y t r a n s f e r r e d t o a second s i l i c o n e o i l b a t h m a i n t a i n e d a t p r e c i s e l y 149.6°, where they would have remained was  as a s u p e r c o o l e d m e l t i n d e f i n i t e l y .  i n d u c e d by removing  Crystallization  the ampules i n d i v i d u a l l y from the b a t h ,  h o l d i n g each one a g a i n s t a p i e c e o f Dry I c e f o r ca. 5 s e c , then i m m e d i a t e l y r e p l a c i n g i t i n the 149.6° b a t h . was  p e r f o r m e d q u i c k l y , so t h a t no sample was  f o r more than 10 s e c .  The  cooling operation  o u t s i d e o f the b a t h  The samples r e q u i r e d about 2 h to c r y s t a l l i z e  c o m p l e t e l y , a f t e r w h i c h time they were c o o l e d t o room t e m p e r a t u r e , opened, and a n a l y z e d f o r o p t i c a l  activity.  P o l y c r y s t a l l i n e 1 , 1 ' - b i n a p h t h y l c o n t a i n i n g a known amount o f a d i s s y m m e t r i c " i m p u r i t y " ( d - and £-mandelic a c i d ) was follows.  I n 50 ml acetone  p r e p a r e d as  ( d i s t i l l e d from p o t a s s i u m permanganate)  0.49252 g r a c e m i c 1 , 1 ' - b i n a p h t h y l and 0.02639 g d-mandelic dissolved.  The s o l u t i o n was  a c i d were  f i l t e r e d and the s o l v e n t removed i r i  The r e s u l t i n g m i x t u r e , which c o n t a i n e d 5.08%  (by w e i g h t )  d-mandelic  a c i d , was  s e a l e d i n ampules, m e l t e d , and c r y s t a l l i z e d i n a manner  analogous  t o the above p r o c e d u r e w i t h the c o m p l e t e l y r a c e m i c  binaphthyl.  A s i m i l a r p r o c e d u r e was  vacuo.  used f o r the m i x i n g of  1,1'£-mandelic  156  a c i d w i t h racemic  4.3.1.2  1,1'-binaphthyl.  Deliberate Addition of Crystals of Active  1,1'-Binaphthyl  To t e s t t h e e f f e c t o f o p t i c a l l y a c t i v e l , l ' - b i n a p h t h y l  seed  c r y s t a l s on c r y s t a l l i z a t i o n from c o m p l e t e l y m e l t e d samples ( T a b l e XI, p  93), ca_. 200 mg o f s o l i d r a c e m i c 1,1'-binaphthyl  (from v a r i o u s  b a t c h p r e p a r a t i o n s ) were p l a c e d i n t h e bottom o f a t e s t tube 15 cm i n l e n g t h and f i t t e d w i t h a ground g l a s s s t o p p e r .  The s o l i d was  i n t r o d u c e d t h r o u g h a long-stemmed f u n n e l t o a v o i d c o a t i n g the upper p a r t o f t h e t e s t tube w i t h c r y s t a l s .  The e n t i r e tube ( e x c e p t f o r t h e  top 2 cm) was then immersed i n a b a t h a t 170-180°, where a l l 1,1'-binaphthyl  m e l t e d , and i m m e d i a t e l y t r a n s f e r r e d t o a 149.6° b a t h  and immersed t o t h e same l e v e l .  The s t o p p e r was removed f o r ca. 10 s e c  w h i l e t h e a c t i v e 1,1'-binaphthyl  seeds were dropped  of a spatula. complete.  i n from t h e t i p  C r y s t a l l i z a t i o n r e q u i r e d o v e r n i g h t (16 h) t o become  The sample was then c o o l e d t o room t e m p e r a t u r e , t h e cake  o f s o l i d b r o k e n up w i t h a s p a t u l a , and d u p l i c a t e a n a l y s e s f o r o p t i c a l activity  performed.  4.3.2  Resolution i n the S o l i d State  4.3.2.1  The H e a t i n g o f Racemic  1,1'-Binaphthyl  As a s t a n d a r d c h a r a c t e r i z a t i o n o f f e s h l y p r e p a r e d r a c e m i c 1,1'b i n a p h t h y l , a few i n d i v i d u a l samples form a g i v e n b a t c h o f r a c e m i c m a t e r i a l were h e a t e d a t 149.6°.  Samples were c o o l e d t o room  temperature and a n a l y z e d f o r o p t i c a l a c t i v i t y T a b l e VIII, p  85 ).  ( T a b l e III, p  51 and  157  I n some e x p e r i m e n t s  ( T a b l e X, p  92) c a r e f u l l y weighed  optically  a c t i v e b i n a p h t h y l was added t o the weighed r a c e m i c m a t e r i a l b e f o r e the ampules were s e a l e d .  The s e a l e d samples were then  mixed  t h o r o u g h l y by h o l d i n g them i n c o n t a c t w i t h a L a b - L i n e  "Super-Mixer"  f o r 5 m i n , h e a t e d a t 149.6° and a n a l y z e d f o r s p e c i f i c  rotation.  4.3.2.2  C y c l i n g S o l i d 1,1'-Binaphthyl t o High S p e c i f i c R o t a t i o n  A t t h e bottom o f a 15 cm t e s t tube was p l a c e d 2.00 g o f r a c e m i c 1 , 1 ' - b i n a p h t h y l (Racemic B a t c h G).  The t e s t tube was s e a l e d , p l a c e d  i n a 149.6° b a t h f o r 2 h ( t h e sample appeared  t o remain s o l i d  out) , then c o o l e d t o room temperature and opened. a n a l y s i s gave [ a l = +42°.  through-  Polarimetric  The s o l i d was d i s s o l v e d i n 400 ml pentane,  D  and the s o l u t i o n was f i l t e r e d , b o i l e d down t o 150 ml a l l o w e d t o c o o l to room temperature  ( t o t a l time a t the b.p. o f pentane  m i n ) , and p l a c e d i n t h e r e f r i g e r a t o r (0°) f o r 1 h.  (36°) was 15-20  The pentane was  removed on the r o t a r y e v a p o r a t o r t o a f f o r d 94% m a t e r i a l h a v i n g the same s p e c i f i c r o t a t i o n ( [ a l  D  = +43°).  The 1 , 1 ' - b i n a p h t h y l was then  s e a l e d i n a second t e s t tube and h e a t e d , as b e f o r e , a t 149.6° f o r 2 h. The  r e c r y s c a l l i z a t i o n from pentane was r e p e a t e d i n e x a c t l y the same  manner as b e f o r e , p r e p a r i n g t h e m a t e r i a l f o r t h e t h i r d h e a t i n g a t 149.6°.  The c y c l e was r e p e a t e d a f o u r t h time t o o b t a i n 1.10 g ( t h e  w e i g h t l o s s e s due m a i n l y t o samples t a k e n f o r p o l a r i m e t r i c and d i f f e r e n t i a l s c a n n i n g a n a l y s e s ) of S - ( + ) - l , l ' - b i n a p h t h y l , Other c y c l i n g e x p e r i m e n t s above p r o c e d u r e .  (Table I V , p  [-l^  =  +194°.  54 ) were p a t t e r n e d a f t e r t h e  158  4.3.2.3 (a)  The Heating of S l i g h t l y Active 1,1'-Binaphthyl The Preparation of S - l K i n e t i c Batch  A solution of 0.181 3.819  g of active 1,1*-binaphthyl ( M  D  = +208°) and  g of racemic 1,1'-binaphthyl (comprising together 4.000 g of  material with t a ] = +9.4°) i n 280 ml acetone (Fisher reagent) was Q  prepared and f i l t e r e d into a 500 ml Erlenmeyer f l a s k . was  The s o l u t i o n  then placed i n a Dry-Ice-acetone bath, with occasional s w i r l i n g .  P r e c i p i t a t i o n , which began i n ~10 min, appeared to be complete i n 1 h.  The crystals were suction f i l t e r e d immediately on removal from  the cold bath.  The 1,1'-binaphthyl obtained (2.97 g, 74% recovery)  possessed a s p e c i f i c rotation of [a]^ = +1.4°.  Samples taken from  this batch resolved to [ a ] = +211° within 16 h at 149.6°. D  Other  batches prepared by this procedure did not always resolve w e l l on heating.  (b)  The Recrystallization-Evaporation Procedure - The Preparation of S-3 K i n e t i c Batch  A solution of 0.133  g of active 1,1'-binaphthyl and 5.57 g of  racemic 1,1'-binaphthyl (comprising together 5.70 [a]  = +2.2°) i n 400 ml acetone (freshly d i s t i l l e d from potassium  permanganate) was was  g of material with  f i l t e r e d into a 1 £ round-bottom f l a s k .  The solution  then cooled i n a Dry Ice-acetone bath (-78°) for 10 min with  s w i r l i n g , during which time c r y s t a l l i z a t i o n began.  Without  completing  the c r y s t a l l i z a t i o n , the f l a s k was removed and immediately placed on a rotary evaporator (Buchi Rotavapor <R>  ) . The flask was rotated i n a i r  while f u l l vacuum (water aspirator) was being established (5 min), then was  lowered into the rater bath, maintained between 20 and 25°.  As the  159  f l a s k warmed, some (but not a l l ) o f the c r y s t a l s d i s s o l v e d , reprecipitated  w i t h the l o s s o f s o l v e n t .  then  The e v a p o r a t i o n was  taken  to d r y n e s s , and any r e s i d u a l acetone was removed on the h i g h vacuum pump. activity  The m a t e r i a l , w h i c h was 100% r e c o v e r e d , p o s s e s s e d an  of (a) = +2.0°, and r e s o l v e d t o (a) > +200° on h e a t i n g a t any  temperature between 105° and 150°. K i n e t i c b a t c h e s S-2 and R - l were p r e p a r e d by an procedure.  analogous  The s o l i d 1 , 1 ' - b i n a p h t h y l ( [ a ] = -2° t o ±15°) o b t a i n e d n  by t h i s method almost always r e s o l v e d t o a t l e a s t  [ a ] = ±190° on Q  h e a t i n g t o 150° f o r 2 h.  4.3.3  Resolution Involving O p t i c a l l y Inactive Solvents  4.3.3.1  H e a t i n g o f Racemic 1 , 1 ' - B i n a p h t h y l Under a S o l v e n t  A g l a s s tube 20 cm i n l e n g t h and c o n t a i n i n g a c o a r s e  fritted  d i s c 10 cm from e i t h e r end was h e l d i n a v e r t i c a l p o s i t i o n w h i l e 200 mg r a c e m i c 1 , 1 ' - b i n a p h t h y l was p l a c e d on the d i s c . s e a l e d , the tube i n v e r t e d , and 0.5 ml  2-propanol  from stannous c h l o r i d e ) p l a c e d t h r o u g h  The top end was (freshly  then  distilled  the r e m a i n i n g open end.  The s e a l e d end was immersed i n a d r y i c e - a c e t o n e b a t h to p u l l the 2-propanol  through t h e d i s c and i n t o the b i n a p h t h y l chamber.  The  open end was then s e a l e d , and t h e e n t i r e tube submerged i n a b a t h m a i n t a i n e d a t 120°, and o r i e n t e d so t h a t the b i n a p h t h y l / 2 - p r o p a n o l m i x t u r e remained  a t the bottom end.  About h a l f the s o l i d b i n a p h t h y l  dissolved.  A f t e r 43 h the tube was i n v e r t e d i n the b a t h , a l l o w i n g the  2-propanol  t o d r a i n from the  disc.  Residual  1 , 1 ' - b i n a p h t h y l t h r o u g h the f r i t t e d  2 - p r o p a n o l was removed by t a k i n g the tube from the  b a t h and q u i c k l y immersing  the 2 - p r o p a n o l  chamber i n Dry I c e - a c e t o n e .  160  This procedure allows complete removal of the solution from the crystals at 120°.  Then binaphthyl end was then opened and the crystals were  analyzed for optical activity.  In this example, [a]^ = +198°, but  such a high rotation was not consistently obtained (see Table IX, p 90).  4.3.3.2  Seeding of a Racemic, Supersaturated Solution  Using a procedure identical to the above (Section 4.3.3.1), 200 mg racemic 1,1*-binaphthyl and 0.5 ml isopropanol (freshly distilled) were  placed i n the sealed end of the fritted disc tube.  In the open  end was placed a glass capillary containing some seed crystals of active binaphthyl ([a] = -212°) at the tip remote from the fritted disc.  The open end was then sealed and the tube immersed i n a 135°  bath.  A l l of the binaphthyl i n contact with the isopropanol dissolved.  The tube was transferred to a 120° bath and inverted. The isopropanol solution of binaphthyl drained through the fritted disc and came i n contact with the active seed crystals.  After 20 h at 120°, some crystals  had grown from the supersaturated solution, and the tube was again inverted to drain the solution from the crystals.  The crystals  were recovered as before, and analysis gave la]^ = -2.3°.  Seeding  from solution, even with considerable care, did not consistently give highly-resolved  4.4  1,1'-binaphthyl.  Characterization of the R- and S-l,1'-Binaphthyl Phase System  4.4.1  The Crystal Picking Experiment  The batch of large (2-4 mm) crystals obtained by slow recrystallization (2 days) from actone solution was examined under a microscope  w i t h permanently c r o s s e d p o l a r i z e r and a n a l y s e r and r o t a t a b l e s t a g e . C r y s t a l s w h i c h were n o t members of clumps were examined c l o s e l y . Any s m a l l c r y s t a l s a d h e r i n g t o the s u r f a c e were removed, and i f the e n t i r e c r y s t a l , viewed a t any a n g l e e x c e p t normal t o t h e c o r d f a c e s ( F i g u r e 10, p  62 ) e x t i n g u i s h e d s h a r p l y as t h e s t a g e was r o t a t e d , i t  was s e t a s i d e f o r p o l a r i m e t r i c a n a l y s i s .  No attempt was made t o  p o l i s h the c r y s t a l f a c e s , a few o f w h i c h were rough i n appearance.  4.4.2  C r y s t a l l i z a t i o n o f Low and H i g h - M e l t i n g Forms In a t y p i c a l r e c r y s t a l l i z a t i o n from p e n t a n e , 0.50 g o f r a c e m i c  1 , 1 ' - b i n a p h t h y l was d i s s o l v e d i n 100 ml b o i l i n g pentane.  The warm  s o l u t i o n was f i l t e r e d and t h e f i l t r a t e r e d u c e d t o 40 ml by b o i l i n g o f f the pentane.  The s o l u t i o n was e i t h e r a l l o w e d t o c o o l s l o w l y t o 0°  c o o l e d r a p i d l y i n an i c e b a t h , o r seeded w i t h v a r i o u s samples o f racemic b i n a p h t h y l .  Racemic Batches A t o J were p r e p a r e d by v a r i o u s  r e c r y s t a l l i z a t i o n s from pentane  ( e x c e p t D, w h i c h was p r e p a r e d by  r e c r y t a l l i z i n g 0.50 g r a c e m i c 1 , 1 ' - b i n a p h t h y l from 10 ml g l a c i a l acetic acid).  Racemic B a t c h e s K, L, and N were p r e p a r e d by r e c r y s t a l -  l i z a t i o n from p e t r o l e u m e t h e r (65-110°), u s i n g 25 ml s o l v e n t f o r each gram t o be r e c r y s t a l l i z e d .  Racemic B a t c h M was r e c r y s t a l l i z e d  from acetone a t -78° (see S e c t i o n 4.4.3 f o r a s i m i l a r p r o c e d u r e ) , and Racemic B a t c h 0 was a commercial sample o f 1 , 1 ' - b i n a p h t h y l (K and K Laboratories,  Inc.).  To check f o r the c r y s t a l m o d i f i c a t i o n s o f 1 , 1 ' - b i n a p h t h y l produce by s l o w and f a s t removal o f s o l v e n t , 100 mg p o r t i o n s o f r a c e m i c m a t e r i a l were d i s s o l v e d i n 15 ml s o l v e n t ( e t h e r , a c e t o n e , o r benzene).  162  Slow e v a p o r a t i o n :  The s o l u t i o n s were f i l t e r e d i n t o t h r e e 25 ml  E r l e m e y e r f l a s k s and p l a c e d under an u p t u r n e d b e a k e r f o r s e v e r a l days. The e t h e r s o l v e n t d i s a p p e a r e d w i t h i n one day, the acetone i n two days, and t h e benzene i n f o u r days.  Fast evaporation:  The t h r e e  s o l u t i o n s ( p r e p a r e d as above) were n o t f i l t e r e d , b u t were s u b j e c t e d t o a stream of d r y a i r w h i l e  b e i n g h e l d i n a w a t e r b a t h a t room t e m p e r a t u r e .  S o l v e n t s were removed w i t h i n 5 m i n .  The c r y s t a l s from a l l s i x samples  were a n a l y z e d on the d.s.c. Slow and f a s t s o l i d i f i c a t i o n o f t h e r a c e m i c m e l t was s t u d i e d on t h e d.s.c. ( S e c t i o n 4.6.2).  S o l i d r a c e m i c 1 , 1 ' - b i n a p h t h y l was m e l t e d i n  a d.s.c. sample p l a n c h e t t e a t 160°, then c o o l e d a t a r a t e o f 20 deg min  1  t o o b t a i n pure l o w - m e l t i n g form.  A f e s h sample ( o r the same one)  was m e l t e d a t 160° and c o o l e d r a p i d l y by removing and p l a c i n g i t on a m e t a l s u r f a c e .  t h e sample p l a n c h e t t e  R e p l a c i n g t h e sample i n t h e d.s.c.  and warming t o 90-100° gave pure h i g h - m e l t i n g form.  The most sudden  c o o l i n g o f t h e m e l t was o b t a i n e d by p a c k i n g a c a p i l l a r y f o r X-ray powder d i f f r a c t i o n  ( S e c t i o n 4.6.3) w i t h r a c e m i c l , l ' - b i n a t > h t h y l m e l t i n g  the sample a t 175°, and i m m e d i a t e l y immersing t h e ( u n s e a l e d ) c a p i l l a r y i n a l i q u i d nitrogen bath.  The c a p i l l a r y was r e t r i e v e d and mounted  i n a D e b y e - S c h e r r e r camera f o r a n a l y s i s .  4.4.3  Phase L i m i t o f R e s o l u t i o n The f o l l o w i n g p r o c e d u r e used f o r R - ( - ) - 1 , 1 ' - b i n a p h t h y l was  s i m i l a r l y applied to S-(+)-1,1'-binaphthyl.  I n 180 m l acetone  ( d i s t i l l e d from p o t a s s i u m permanganate) was d i s s o l v e d 1.53 g o f R-l,l'-binaphthyl ([ct]  n  = -216°).  The s o l u t i o n was f i l t e r e d and immersed  163  i n a Dry I c e - a c e t o n e b a t h (-78°). t u r e was  15 min.  The l e n g t h o f time a t room  tempera-  C r y s t a l l i z a t i o n was complete a f t e r 30 min a t -78°  (occasional swirling).  The c r y s t a l s were then r a p i d l y  through a s i n t e r e d g l a s s f u n n e l .  Both c r y s t a l s  suction-filtered  (1.26 g, 82%) and  m a t e r i a l from s o l u t i o n were a n a l y z e d f o r o p t i c a l a c t i v i t y , t h e l a t t e r made p o s s i b l e by removal o f acetone s o l v e n t i n vacuo 15 min.  a t 25° w i t h i n  The r e c r y s t a l l i z e d R - l , 1 ' - b i n a p h t h y l p o s s e s s e d  the m a t e r i a l from s o l u t i o n h a v i n g [ a ] ^ = -111°.  Three  [ a ] = +228°, Q  further  r e c r y s t a l l i z a t i o n s were p e r f o r m e d , w i t h the r e s u l t s l i s t e d i n T a b l e X V I , p 179.  4.5  K i n e t i c Methods  4.5.1  Standard  Procedure  The p r o c e d u r e f o r t h e k i n e t i c s t u d y o f t h e r a c e m i z a t i o n o f the d i a c i d 29_ i n t h e s o l i d and t h e m e l t e d s t a t e s , was i d e n t i c a l w i t h t h a t o f the s o l i d - s t a t e r e s o l u t i o n o f 1 , 1 ' - b i n a p h t h y l . 10-30  I n both cases,  mg o f t h e n e a t , p o l y c r y s t a l l i n e m a t e r i a l was c a r e f u l l y weighed  i n 1 ml ampules.  The ampules were s e a l e d i n a i r , and c o m p l e t e l y  immersed i n a c o n s t a n t - t e m p e r a t u r e s i l i c o n e o i l b a t h . times i n d i v i d u a l samples were w i t h d r a w n , opened, and a n a l y z e d f o r o p t i c a l  At appropriate  c o o l e d t o room t e m p e r a t u r e ,  activity.  F o r the s o l u t i o n phase r a c e m i z a t i o n o f (+)-29, s e a l e d ampules c o n t a i n e d ^ 10 mg o f c a r e f u l l y weighed (+)-29 and 0.2 ml p u r i f i e d tetralin.  The d i a c i d 29_ d i s s o l v e d o n l y when the samples were h e a t e d  f o r the r u n ; c o n c e n t r a t e d s o l u t i o n s possible.  ( c a . 0.27 M) were t h e r e f o r e  164  First-order rate constants (^ ^ ) were obtained by plotting log 0  g  ( [ a ] / [ a ] ) +2 against time, where [al i s t^- specific rotation (sodium e  Q  D line) at time zero.  The rate constant was calculated from  k , = 2.303 x (slope of line), obs r  4.5.2  Kinetic Runs with 1,1'-Binaphthyl from 64° to 98° Samples of 1,1'-binaphthyl were sealed in the standard way and  placed in a drying pistol with a jacket for refluxing solvents. Temperatures were maintained by the following solvents:  64.2°, methanol;  76.9°, carbon tetrachloride; 83.3°, 1,2-dichloroethane; 87.6°, 1:3 tetrachloroethylene-water; 93.0°, 1:3 1-butanol-water; and 97.7°, n-heptane.  Activities obtained at these temperatures are listed in  Table XIII, p 111.  4.5.3  Kinetic Runs with Ground Samples Samples of 1,1'-binaphthyl were ground i n a small (1 cm o.d.)  test tube using a glass stirring rod which had been molded the bottom of the test tube.  to f i t  This method was more satisfactory than  pulverization in a mortar and pestle, which caused the buildup of a static charge on the crystals and made the handling of large (100 mg) quantities d i f f i c u l t .  4.5.4  Product Studies In the racemization of (+)-29, samples remained colourless and  crystalline throughout the runs at 130-155°.  In the melt (176-194°)  some yellowing occurred, but did not become significant before  165  r a c e m i z a t i o n was complete.  A t 161 and 166°, y e l l o w i n g was more  apparent than i n t h e m e l t , and t h e samples p a r t i a l l y  melted.  Racemic d i a c i d 29_ was h e a t e d i n t e t r a l i n a t 140° f o r 96 h ( g r e a t e r t h a n 15 h a l f - l i v e s f o r r a c e m i z a t i o n o f (+)-29).  Extraction  of the d i a c i d i n t o 10% sodium h y d r o x i d e and a c i d i f i c a t i o n g i v e r a c e m i c 29_, whose n u c l e a r m a g n e t i c  resonance spectrum was i d e n t i c a l  w i t h that of the o r i g i n a l d i a c i d .  No f u m a r i c a c i d s i g n a l was p r e s e n t  i n t h e spectrum.  I n a n o t h e r r u n , 0.45 g o f t h e r a c e m i c d i a c i d 29_  was h e a t e d w i t h 10 ml o f t e t r a l i n a t 140° f o r 52 h ( c a . 9 h a l f - l i v e s ) . On c o o l i n g , 0.32 g (71%) o f r a c e m i c 29, m.p. 180-184° was r e c o v e r e d . E x t r a c t i o n o f mether l i q u o r s w i t h d i l u t e base gave 0.094 g (21%) o f s t i c k y , probably polymeric, s o l i d .  E s s e n t i a l l y complete  interconversion  o f enantiomers o c c u r s b e f o r e s i d e r e a c t i o n s become i m p o r t a n t a t l o n g reaction times. The k i n e t i c b a t c h e s o f 1 , 1 ' - b i n a p h t h y l remained w h i t e , c r y s t a l l i n e s o l i d s from 105-150° u n t i l w e l l beyond c o m p l e t i o n o f the r e s o l u t i o n . At 98°, some y e l l o w i n g o c c u r r e d a t l o n g r e a c t i o n times (3-6 months). The p r o d u c t o f the r e s o l u t i o n g i v e s the d . s . c , i n f r a r e d , and X-ray a n a l y s e s o f t h e h i g h - m e l t i n g form o f 1 , 1 ' - b i n a p h t h y l ( i n f r a r e d s p e c t r a 73 r e p o r t e d by Badar, e t a l .  ).  C o - i n j e c t i o n of the s t a r t i n g  and r e s o l v e d p r o d u c t i n t o a g a s - l i q u i d chromatograph  material  [ u s i n g an 8%  SE-30 on Chromosorb W (80/100) (6 f e e t x 1/8 i n c h ) column; c a r r i e r gas: h e l i u m ; f l o w r a t e : 110 ml min "*"; t e m p e r a t u r e : 150° f o r 3 m i n , the h e a t i n g a t 32 deg min ^ t o 270°, m a i n t a i n e d f o r 10 m i n ; i n s t r u m e n t : P e r k i n - E l m e r 900 Gas Chromatograph] gave a s i n g l e peak.  166  4.6  A n a l y t i c a l Procedures  4.6.1  Polarimetry A B e n d i x type 143 A a u t o m a t i c  sample c e l l .  p o l a r i m e t e r was used w i t h a m o d i f i e d  The s u p p l i e d c e l l h o l d e r assembly was used t o c o n t a i n  a c e l l composed o f a round m e t a l s p a c e r h a v i n g a t h i c k n e s s o f 1 cm. separated  a c o n c e n t r i c h o l e and  C e l l windows were composed o f round g l a s s  slides  from t h e s p a c e r and t h e r e s t o f t h e assembly by round T e f l o n  wafers w i t h  h o l e s punched i n t h e c e n t e r .  The p i e c e s o f t h e c e l l were  sandwiched t o g e t h e r i n t h e c e l l h o l d e r assembly i n t h e i n t e n d e d  fashion.  Sample s o l u t i o n s were i n t r o d u c e d t h r o u g h a h o l e d r i l l e d i n t h e s i d e of t h e m e t a l s p a c e r w h i c h formed t h e c e l l . Each sample ampule (1 ml) from t h e k i n e t i c runs was opened and t h e s o l i d m a t e r i a l completely  d i s s o l v e d i n acetone ( f o r the ( + ) - d i a c i d  29, w h i c h does n o t r a c e m i z e a p p r e c i a b l y i n acetone a t 25°) o r i n benzene ( f o r o p t i c a l l y a c t i v e 1 , 1 ' - b i n a p h t h y l ,  which possesses a h a l f 74  l i f e o f 11.4 h f o r r a c e m i z a t i o n i n benzene a t 25° was  ).  The s o l u t i o n  t r a n s f e r r e d t o a 3 ml v o l u m e t r i c f l a s k and d i l u t e d t o t h e mark  w i t h washings from t h e opened ampule. filling  Three r e a d i n g s were made by  the p o l a r i m e t e r c e l l s u c c e s s i v e l y w i t h three samplings ( c a .  0.8 ml each) o f t h e s o l u t i o n . solvent.  Zero r e a d i n g s were taken u s i n g t h e pure o  A l l measurements were made a t t h e sodium D l i n e  s p e c i f i c r o t a t i o n s were c a l c u l a t e d from [ct]p = 3 x 10^ x a  (5890 A ) , and x c/  (sample wt. i n mg) where a i s t h e o b s e r v e d r o t a t i o n and c = 0.80 i s a c e l l constant solutions.  o b t a i n e d by c a l i b r a t i o n w i t h known s t a n d a r d  sucrose  167  4.6.2  D i f f e r e n t i a l Scanning The  Calorimetry  d i f f e r e n t i a l s c a n n i n g c a l o r i m e t e r ( d . s . c . ) used was  Elmer DSC-1B.  For q u a l i t a t i v e r u n s , c a . 5 mg  a Perkin-  c r y s t a l s were p l a c e d i n  an aluminum sample p l a n c h e t t e and covered w i t h an aluminum l i d . l i d was  p r e s s e d f i r m l y a g a i n s t the p l a n c h e t t e , p a r t i a l l y c r u s h i n g the  c r y s t a l s , but t h e p l a n c h e t t e and l i d were not crimped s t a n d a r d programming r a t e o f 10 deg min ^ was noted.  The  The  temperature  readout was  together.  used u n l e s s  A  otherwise  c a r e f u l l y c a l i b r a t e d f o r 10 deg  min  heating r a t e w i t h m e l t i n g p o i n t standards, u s i n g slope s e t t i n g s of 545-585, and d i f f e r e n t i a l and average temperature and 522, r e s p e c t i v e l y . beginning  T r a n s i t i o n temperatures  s e t t i n g s of  were measured a t the  ( i . e . , a t f i r s t d e p a r t u r e from b a s e l i n e ) o f r e c o r d e d p e a k s .  F o r q u a n t i t a t i v e e n t h a l p y d e t e r m i n a t i o n s , the sample was on a  Cahn  485  E l e c t r o b a l a n c e (Model M-10)  on the d.s.c.  and run through  a t a programming r a t e of 10 deg min \  a c h a r t speed of 4 i n min ^ (Leeds N o r t h r u p  the  weighed transition  a range o f 16x  Speedomax W c h a r t r e c o r d e r ) .  A c a l i b r a t i o n run u s i n g the weighed h i g h - p u r i t y i n d i u m s t a n d a r d was  and  performed under i d e n t i c a l c o n d i t i o n s , from w h i c h i t was  provided  learned  t h a t a t the s e t t i n g s used, each square i n c h of c h a r t paper r e p r e s e n t e d a heat f l o w of 27.3 m i l l i c a l o r i e s .  Peak areas were i n t e g r a t e d by  t a k i n g the average o f s i x d e t e r m i n a t i o n s w i t h a p l a n i m e t e r Instrument r  Co.).  The  (Gelman  e n t h a l p y of the t r a n s i t i o n i n k c a l mole  was  47 The c a l i b r a t i o n f a c t o r changes somewhat w i t h t e m p e r a t u r e , but v a l u e of 27.3 meal i n ^ w i l l not change s i g n i f i c a n t l y i n the temperature range 140-190°. -  the  168  calculated  from:  2 AH = ( a r e—a of sample — ; t r a n s ir t i o n ,- i n ) (weight of sample, mg)  x (,., m o l e c u l.,a r w e i•g h t  ;  27.3  The heat  x  10~  c a p c i t y (Cp) measurements ( T a b l e X V I I , p  i \ x of sample) c  3  190  ) were  p e r f o r m e d u s i n g the S p e c i f i c Heat K i t , an a c c e s s o r y to the DSC-1B. method i n v o l v e d comparison t o a s t a n d a r d , w h i c h was p u r i t y sapphire.  The  The  a d i s c of h i g h -  s a p p h i r e s t a n d a r d was w e i g h e d , p l a c e d i n a sample  47 p l a n c h e t t e , and c o v e r e d i n the recommended  manner.  i s o t h e r m a l l y t o e s t a b l i s h a b a s e l i n e , then i t was min  The  d.s.c. was  programmed a t 10  ^ (range: 4 x ) , c a u s i n g a pen d e f l e c t i o n p r o p o r t i o n a l t o  c a p a c i t y o f the s a p p h i r e .  The programming was  the  run deg  heat  discontinued after  h e a t i n g f o r t e n d e g r e e s , and the b a s e l i n e r e - e s t a b l i s h e d . I n t h i s manner, the s a p p h i r e was  heated  from 50°  to 150°  i n t e n degree'  i n t e r v a l s w h i c h o v e r l a p p e d so t h a t two measurements of the o f t h e d e f l e c t i o n c o u l d be made a t 60°, was  removed and a b l a n k run was  i d e n t i c a l fashion.  repeated.  ...  140°.  The  then f i l l e d w i t h a weighed  (pure h i g h - m e l t i n g form) and  the  A l l t h r e e ( s a p p h i r e , b l a n k and sample) runs were  w i t h pure l o w - m e l t i n g b i n a p h t h y l , from 50° d i d any w e i g h t the a m p l i t u d e  t o 140°.  l o s s o r phase t r a n s f o r m a t i o n o c c u r . of the b l a n k was  and b i n a p h t h y l samples, and Cp  sapphire  performed w i t h the same p l a n c h e t t e i n an  The p l a n c h e t t e was  amount of 1 , 1 ' - b i n a p h t h y l  70°,  amplitude  procedure repeated  I n n e i t h e r sample At each  s u b t r a c t e d from t h a t of the  temperature sapphire  ( i n c a l deg ''"mole ''") c a l c u l a t e d  from:  169  = r  ( a m p l i t u d e sample) (amplitude sapphire)  (weight s a p p h i r e ) (weight sample)  x  %  Q f  (molecular weight of  The two s a p p h i r e runs agreed  g  h ±  ( i n amplitude) t o w i t h i n 1% a t a l l  a c c u r a c y o f the method was  t e s t e d by measuring  n a p h t h a l e n e a t 51°  as 43.7  (lit."'"  0 8  44.0  and 45.9  was b e t t e r than  4.6.3  x  1,1'-binaphthyl)  t e m p e r a t u r e s , good e v i d e n c e of the p r e c i s i o n of the method.  and 61°  -1,  c a l  and 46.0  c a l mole "*"deg \  The  the h e a t c a p a c i t y o f  c a l mole "'"deg \  respectively).  The  respectively accuracy  1%.  X-Ray Powder D i f f r a c t i o n The  f o l l o w i n g p r o c e d u r e f o r q u a n t i t a t i v e phase a n a l y s i s was  The sample to be a n a l y z e d was  adopted.  t h o r o u g h l y p u l v e r i z e d i n a s m a l l agate  m o r t a r , and packed f i r m l y i n a 0.3 mm  g l a s s c a p i l l a r y by p l a c i n g the  c a p i l l a r y i n a t e s t tube and h o l d i n g the assembly a g a i n s t a L a b - L i n e "Super M i x e r " .  The bottom 1.5  and a l i g n e d i n a Debye-Scherrer  cm of the c a p i l l a r y was b r o k e n o f f , powder camera ( P h i l i p s PW  equipped w i t h the s m a l l e r (0.5 mm) camera  was  1024/10)  c o l l i m a t o r and beam s t o p .  then l o a d e d w i t h Kodak No-Screen NS-392 T 35 mm  The X-ray  film  and mounted on the n o n - d i v e r g e n t q u a r t e r o f the P h i l i p s PW 1008/85 X-ray g e n e r a t o r (CuK^ r a d i a t i o n , N i f i l t e r ) . and 15 mA,  and the f i l m exposed  The f i l m was  The s o u r c e was  a c t i v a t e d (40 kV  f o r e x a c t l y 20 h.  developed w i t h Kodak D-19  d e v e l o p e r (a s t o c k s o l u t i o n  p r e p a r e d as recommended, but u s i n g d i s t i l l e d w a t e r and b u b b l i n g n i t r o g e n through the s o l u t i o n ) d i l u t e d t e n times w i t h w a t e r at 20°C (68°F).  170  Development, performed  i n an Anscomatic  4 min w i t h s w i r l i n g e v e r y 30 s e c . stop bath (stock s o l u t i o n : rinsed, After  and f i x e d  rinsing  d e v e l o p i n g t a n k , took  f i l m was  13 ml g l a c i a l a c e t i c  then immersed i n a acid i n 1 £ water),  (Kodak R a p i d F i x , f r e s h l y p r e p a r e d )  f o r 30 min, the f i l m was  to d r y f o r 3-4 The  The  35 mm  immersed i n P h o t o f l o w and hung  h.  d e n s i t y of the d i f f r a c t i o n l i n e s on the photograph  on a J o y c e double beam r e c o r d i n g m i c r o d e n s i t o m e t e r following control: slit:  f o r four minutes.  s e t t i n g s were used.  Mode: Forward  5; pen damping: 5; i r i s :  o p t i c a l d e n s i t y was  units  background  (mk I I I C ) .  o p t i c a l d e n s i t y (O.D.) u n i t s  (B 335); r a t i o arm:  The  10 t i m e s .  The  O.D.  d e n s i t y wedge.  between 0.40  and 1.20  O.D.  units  zero of  undeveloped  range o f o p t i c a l d e n s i t y (from the  fog l e v e l t o the most dense measured peak) was  w i t h the 0-2  The  Integrate; d i f f e r e n t i a l  taken as the d e n s i t y o f unexposed,  f i l m w h i c h had been f i x e d .  measured  f u l l y open; s l i t h e i g h t : f u l l h e i g h t ;  25; a p e r t u r e : 25; d e n s i t y wedges: 0-2  (D 453) and 0-1 O.D.  was  measured  I n a l l f i l m s t a k e n , t h i s range ( t h e l i n e a r range  (where O.D.  was  is 109  p r o p o r t i o n a l to exposure)  o f Kodak No-Screen f i l m i s 0.2  to 1.5  ).  The d i f f r a c t i o n l i n e s t o be measured were t r a c e d as peaks u s i n g the (more p r e c i s e ) 0-1 O.D. The  d e n s i t y wedge.  d i f f r a c t i o n l i n e s chosen f o r i n t e n s i t y measurement were the  o  10.1 A l i n e  o  o f the racemate and the 6.4  A l i n e of the e u t e c t i c  I n t e g r a t e d i n t e n s i t i e s were measured from the d e n s i t o m e t e r u s i n g the average o f s i x a r e a d e t e r m i n a t i o n s w i t h  form.  tracings  the p l a n i m e t e r .  f r a c ta ir oe na of the et uo tteaclt iacr e a( hof The i g h the - m e l two t i n g )peaks: form (A^) was  e x p r e s s e d as a  171  a r e a f r a c t i o n ( h i g h - m e l t i n g form) =  C a l i b r a t i o n samples c o n s i s t i n g of known w e i g h t s  of low- and  forms were p r e p a r e d by grinding and t h o r o u g h l y m i x i n g the two  high-melting forms  t o g e t h e r , then a n a l y z i n g t h e s e samples u s i n g the d e s c r i b e d X - r a y procedure.  The  r e s u l t i n g weight  fractions:  W  weight f r a c t i o n ( h i g h - m e l t i n g form)  =  W  H  H L + W  were p l o t t e d a g a i n s t t h e i r c o r r e s p o n d i n g a r e a f r a c t i o n s ( F i g u r e 23, p and t h e r e s u l t i n g c a l i b r a t i o n curve used t o determine o f samples of the S-2 ( F i g u r e 24, p The  the phase  K i n e t i c Batch at v a r i o u s stages of  121)  content  resolution  123) .  d s p a c i n g s o f the low- and h i g h - m e l t i n g forms ( T a b l e V, p  58)  were c a l c u l a t e d by measuring the d i f f r a c t i o n l i n e s on the p h o t o g r a p h w i t h an a c c u r a t e m i l l i m e t e r s c a l e , and c o n v e r t i n g t o 28. c o n v e r s i o n was 1 mm  c o n s t r u c t e d so t h a t  r e p r e s e n t e d 2° 2 9 , a l l o w i n g f o r "normal f i l m s h r i n k a g e "  development. and  easy s i n c e the P h i l i p s camera was  This  the  The  d s p a c i n g s were then o b t a i n e d from the 28  on values  relation:  d  =  where X i s the w a v e l e n g t h o f CuK^  2sin8  r a d i a t i o n (1.5418 A ) .  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Soc., 93, 1291 (1971)  c  178  APPENDIX A  THE PHASE LIMIT OF RESOLUTION  S i n c e a l l o f our e x p e r i m e n t s w i t h 1 , 1 ' - b i n a p h t h y l  produced samples  h a v i n g v a r i o u s s p e c i f i c r o t a t i o n s , i t was v e r y d e s i r a b l e t o know t h e h i g h e s t p o s s i b l e r o t a t i o n ( a t t h e sodium D l i n e , where a l l o f our s p e c i f i c r o t a t i o n s were measured) o b s e r v a b l e  i n t h e R- and S - l , 1 ' - b i n a p h t h y l  system.  An i n d i c a t i o n as t o how t h i s might be a c c o m p l i s h e d was o b t a i n e d when s e v e r a l samples o f h i g h l y a c t i v e 1 , 1 ' - b i n a p h t h y l  were r e c r y s t a l l i z e d  from  a c e t o n e a t -78°, as a f i n a l p u r i f i c a t i o n measure b e f o r e t h e f u r t h e r s t u d y o f samples w i t h h i g h a c t i v i t y .  The m a t e r i a l o b t a i n e d  from t h e r e c r y s t a l -  l i z a t i o n p o s s e s s e d a s p e c i f i c r o t a t i o n h i g h e r than t h a t o f t h e o r i g i n a l solid. A s t u d y o f t h e t e r n a r y system formed between R and S - l , 1 ' - b i n a p h t h y l and an o p t i c a l l y i n a c t i v e s o l v e n t r e v e a l e d t h a t s i m p l y from phase e q u i l i brium c o n s i d e r a t i o n s alone, a h i g h l y r e s o l v e d m a t e r i a l should s p e c i f i c r o t a t i o n u n t i l a constant  f i g u r e i s obtained  increase i n  (see below).  We  t h e r e f o r e performed m u l t i p l e r e c r y s t a l l i z a t i o n s on a sample o f w e l l - r e s o l v e R-l,1'-binaphthyl  t o see how h i g h an a c t i v i t y c o u l d be o b t a i n e d .  w i t h 1.53 g o f m a t e r i a l h a v i n g  Starting  [ a ] = -216°, we o b t a i n e d , a f t e r f o u r r e -  c r y s t a l l i z a t i o n s from a c e t o n e a t -78°, 0.56 g o f 1 , 1 ' - b i n a p h t h y l a s p e c i f i c r o t a t i o n o f [ a ] = -245° ± l°(Table X V I ) .  having  We proceeded no  f u r t h e r because t h e r o t a t i o n d i d not i n c r e a s e i n t h e l a s t  recrystallization  179  T a b l e XVI Low  Temperature R e c r y s t a l l i z a t i o n  o f R- and S - l , 1 ' - B i n a p h t h y l  Weight a f t e r  [a] a f t e r  [a] of  Recrystallization,  Recrystallization,  Solution,  g  degrees  degrees  Recrystallization Number  R- ( - ) - 1 , 1 ' - B i n a p h t h y l : 0  1.53  -216  1  1.26  -228  -110  2  0.94  -244  -151  3  0.74  -247  -219  4  0.56  -245  -230  3  a  S-(+)-1,1'-Binaphthyl: 0  1.41  1  1.19  +234  +202  2  0.95  +236  +220  3  0.70  +238  +225  Weight and s p e c i f i c r o t a t i o n  The  +226  a  of i n i t i a l  a  material.  a c t i v i t y o f t h e m a t e r i a l i n s o l u t i o n was a l s o m o n i t o r e d .  s o l i d i s completely r e s o l v e d , the m a t e r i a l i n s o l u t i o n same a c t i v i t y as t h e r e c r y s t a l l i z e d s o l i d .  When t h e  s h o u l d have t h e  However, our method o f  i s o l a t i n g t h e s o l u t e (by removal o f s o l v e n t _in_ vacuo a t 25°) caused some  180  r a c e m i z a t i o n , and t h e h i g h e s t s o l u t e a c t i v i t y was t h e r e f o r e [a] = -230°. Assuming  that a f t e r the f o u r t h r e c r y s t a l l i z a t i o n the s o l u t i o n possessed  [a] = -245° a t -78°, we e s t i m a t e d  the l o s s i n a c t i v i t y i n recovering the  s o l u t e from s o l u t i o n (based on a h a l f - l i f e o f r a c e m i z a t i o n o f 11.4 h i n 74 benzene a t 25°  ) as 14°.  I t would n o t be p o s s i b l e , t h e r e f o r e , t o o b s e r v e  a s o l u t e a c t i v i t y above 231°, c l o s e t o t h e f i n a l o b s e r v e d v a l u e . A sample o f S - l , 1 ' - b i n a p h t h y l was a l s o r e c r y s t a l l i z e d t o see i f the same s p e c i f i c r o t a t i o n o f t h e c r y s t a l s ( [ a ] = |245[°) c o u l d be o b t a i n e d . The i n i t i a l a c t i v i t y o f t h e 1.41 g sample o f S - l , 1 ' - b i n a p h t h y l was [a] = +226°.  A f t e r t h r e e r e c r y s t a l l i z a t i o n s , an a c t i v i t y o f [ a ] = +238 ± 1°  (0.70 g) r e s u l t e d ( T a b l e X V I ) .  The t h i r d r e c r y s t a l l i z a t i o n d i d n o t  r e p r e s e n t much o f an i n c r e a s e over t h e second.  The s p e c i f i c r o t a t i o n  o f t h e r e c o v e r e d s o l u t e was 13° l o w e r than t h a t o f t h e c r y s t a l s , to  the estimated  l o s s e s by r a c e m i z a t i o n d u r i n g s o l v e n t  close  evaporation.  F u r t h e r r e c r y s t a l l i z a t i o n s were t h e r e f o r e n o t performed. The increment i n s p e c i f i c r o t a t i o n on r e c r y s t a l l i z a t i o n o f t h e s o l i d can be seen from t h e t e r n a r y phase diagrams w h i c h d e s c r i b e t h e r e c r y s t a l l i z i n g system a t -78° ( F i g u r e 3 2 ) .  The phase r e l a t i o n s h i p s  between s o l v e n t and R- and S-enantiomers when t h e l a t t e r form a racemate ( F i g u r e 32 ( b ) ) have a l r e a d y been e x p l a i n e d i n S e c t i o n 3.4.3 (p 95) and F i g u r e 17 (p 102). system a t -78 .  T h i s diagram r e p r e s e n t s  t h e most s t a b l e t e r n a r y  The phase system formed between the e u t e c t i c form and  the s o l v e n t i s a l s o shown ( F i g u r e 32 ( a ) ) . Because o f t h e i m p e r c e p t a b l e slowness o f t h e s o l u t i o n phase t r a n s f o r m a t i o n e u t e c t i c -> s o l u t i o n ->• racemate a t -78° ( S e c t i o n 3.4.1, p 8 3 ) , t h e e u t e c t i c form can e x i s t f o r indeterminable  l e n g t h s o f time a t t h i s temperature i n c o n t a c t w i t h s o l v e n t .  181  SOLVENT  F i g u r e 32.  Schematic r e p r e s e n t a t i o n of t h e two p o s s i b l e t e r n a r y  systems formed between s o l v e n t , R- and S - l , 1 ' - b i n a p h t h y l (a)  R- and S-enantiomers  S-enantiomers  form a e u t e c t i c m i x t u r e .  form a racemate.  (b)  at -78°. R-  A l t h o u g h (b) i s more s t a b l e ,  (a) can e x i s t f o r i n d e f i n i t e p e r i o d s of time at  -78°.  and  182  Although the original samples in both of the above recrystallization sequences were the eutectic form (having been produced at 150°), the f i r s t batch of crystals could have been either form, or even both. That i s , the "racemic part" of the less-than-fully-resolved samples could have been either a racemate or a eutectic mixture of R and S crystals, or both, after the f i r s t recrystallization. Consider point y on the eutectic isotherm (Figure 32 (a)), which represents a possible allover composition of the solvent, R- and S-l,I'll inaph thy 1 mixture.  At room temperature, the solubility curve abc w i l l  be found closer to the 1,1'-binaphthyl edge of the diagram, and y w i l l be in the (single phase) solution region. At -78°, y w i l l be in the (threephase) R + S + solution region, so that precipitation can occur. If equilibrium in this eutectic ternary system i s attained, then the solution w i l l have composition b (racemic). The solid, however, w i l l have a higher activity x' than i t originally had (x). When x' i s filtered from the solution and redissolved in acetone, the allover composition w i l l now be y  f  (which, in this example, is in the two-phase R + solution region)  at -78°.  On attainment of equilibrium, the solid w i l l be fully resolved  R and the solution composition w i l l be d, as determined by the tie-line Rd.  Therefore, by such an equilibrium process, the excess of one enantiomer  can be separated from a non-racemic material. If attainment of equilibrium at -78° i s particularly slow, a solid material having a rotation greater than x may separate, leaving a meta1  stable solution having an excess of the other enantiomer (R). When crystals Similar considerations hold for the racemate isotherm (Figure 32 (b)). By a similar process, the very small excess of one enantiomer in a "racemic" preparation can be made observable, as discussed on p 88.  183  and  s o l u t i o n a r e s e p a r a t e d , n e t r e s o l u t i o n has been performed.  n o n e q u i l i b r i u m methods o f r e s o l u t i o n , u s u a l l y  Such  a c c o m p l i s h e d be s e e d i n g  r a c e m i c s o l u t i o n s , have been t r i e d w i t h a number o f p a i r s o f e n a n t i o 85 mers. I n o u r c r y s t a l l i z a t i o n s , the n o n e q u i l i b r i u m p r o c e s s  i s probably  o p e r a t i n g t o some e x t e n t , s i n c e d u p l i c a t e c r y s t a l l i z a t i o n s do n o t g i v e m a t e r i a l w i t h t h e same r o t a t i o n . The l i m i t o f r e s o l u t i o n w h i c h we have d e t e r m i n e d (+238°, -245°) s h o u l d perhaps be r e f e r r e d  t o as a "phase l i m i t " o f r e s o l u t i o n ,  the t e r m i n a l s o l i d s o l u t i o n s ^ ' e x i s t i n g 0  since  a t t h e edges o f t h e b i n a r y  R- and S - l , 1 ' - b i n a p h t h y l phase diagram ( F i g u r e 14 ( a ) , p 80) may have a composition  range o f a few p e r c e n t .  thus be s l i g h t l y o p t i c a l l y impure.  The R and S c r y s t a l s o b t a i n e d may  In t h i s t h e s i s , the value  [ a ] = ±245°  i s however t a k e n as t h e f u l l y r e s o l v e d s p e c i f i c r o t a t i o n , and where i t i s used, " p e r c e n t  r e s o l u t i o n " has been c a l c u l a t e d  from t h i s  figure.  184  APPENDIX B  T )H  CALCULATION OF AG  AS A FUNCTION OF TEMPERATURE  I n S e c t i o n 3.3.2.3 (p 7 3 ) , t h e s t a t e m e n t was made t h a t t h e e n a n t i o t r o p i c o r d e r i n g o f r a c e m i c 1 , 1 ' - b i n a p h t h y l m o d i f i c a t i o n s ( F i g u r e 11 ( b ) , p 67) c o u l d be proven by c a l c u l a t i n g t h e f r e e energy d i f f e r e n c e between the racemate ( l o w - m e l t i n g ) form and t h e r a c e m i c e u t e c t i c ( h i g h - m e l t i n g ) L->H form, AG  , as a f u n c t i o n o f t e m p e r a t u r e .  However, a c a l c u l a t i o n o f  t h i s d i f f e r e n c e a t 150°C (423°K) u s i n g m e l t i n g e n t h a l p i e s and e n t r o p i e s o f t h e two m o d i f i c a t i o n s gave a n u m e r i c a l r e s u l t , 212 + 490 c a l mole  \  w h i c h was v e r y i m p r e c i s e when t h e l i m i t s o f e r r o r were a d d i t i v e l y propagated through the c a l c u l a t i o n .  Any s o l i d - s o l i d t r a n s i t i o n L->H  T r e s u l t i n g from an e x p r e s s i o n o f AG  temperature  as a f u n c t i o n o f t e m p e r a t u r e  would a l s o be i m p r e c i s e . However i f o u r o r i g i n a l g o a l o f d e t e r m i n i n g x e x a c t l y i s abandoned, some u s e f u l i n f o r m a t i o n can s t i l l be o b t a i n e d L~*H from t h e c a l c u l a t i o n o f t h e t e m p e r a t u r e dependence o f AG see i f i t i n c r e a s e s o r d e c r e a s e s w i t h t e m p e r a t u r e .  , i f only to  Referring again to  F i g u r e 11, t h e monotropic system p o s s e s s e s an i m a g i n a r y s o l i d - s o l i d t r a n s i t i o n p o i n t i n t h e r e g i o n where t h e m e l t i s s t a b l e ^ ' 1  8 1 b  whereas  i n an e n a n t i o t r o p i c system, t h e t r a n s i t i o n p o i n t i s a t l o w e r t e m p e r a t u r e s . T h e r e f o r e , some d i s t i n c t i o n between t h e two can be made by n o t i n g whether o r n o t t h e f r e e energy s u r f a c e s f o r racemate o r e u t e c t i c converge o r d i v e r g e i n g o i n g t o l o w e r t e m p e r a t u r e s from 150°C.  185  The f r e e energy d i f f e r e n c e a t any t e m p e r a t u r e can be c a l c u l a t e d i f the e n t h a l p y and e n t r o p y d i f f e r e n c e s a r e known as a f u n c t i o n o f t e m p e r a t u r e . These, i n t u r n , can be c a l c u l a t e d from t h e heat c a p a c i t y d i f f e r e n c e as a f u n c t i o n o f t e m p e r a t u r e , as f o l l o w s . E n t h a l p y and e n t r o p y a r e f u n c t i o n s o f s t a t e . change i n g o i n g from t h e racemate  Therefore, the enthalpy  t o t h e r a c e m i c e u t e c t i c ( i . e . , L->H) a t  any t e m p e r a t u r e T i s e q u a l t o t h e e n t h a l p y change i n t a k i n g t h e racemate from T t o 150°C (423°K), p l u s t h e change on g o i n g t o t h e e u t e c t i c form at 150°C (which i s known), p l u s t h e change on b r i n g i n g t h e e u t e c t i c back t o T.  That i s :  AH  L->H  423 C  dT  L  p  +  AH™ 423  +  C 423  H  dT  P  L H where C and C a r e heat c a p a c i t i e s a t c o n s t a n t p r e s s u r e o f t h e l o w P P (racemate) and h i g h - m e l t i n g ( e u t e c t i c ) forms, r e s p e c t i v e l y . simplifies to:  [25]  AH  L->H  423 (C  - C ) dT P P L  H  E n t r o p y can be t r e a t e d i n a s i m i l a r  [26]  The  AS  L->H  423 (C  - c ) P P L  H  +  L->H AH 423  fashion:  4?T  +  AS  L->H 423  f r e e energy d i f f e r e n c e a t t e m p e r a t u r e T i s t h e r e f o r e :  This expression  186  A £*  [27]  =  G  AH™  -  T A s f  L~*H  We a r e i n t e r e s t e d i n f i n d i n g whether A G w i t h temperature  T  i n c r e a s e s or decreases  from 150°C t o , s a y , room t e m p e r a t u r e .  As a f i r s t (and  r a t h e r crude) a p p r o x i m a t i o n , we can assume t h a t t h e e n t h a l p y and e n t r o p y L^H  L-*H  d i f f e r e n c e s AH^  and AS^  Thus, AH^  of i n t e r e s t .  a r e independent = AH^^-j  a n  u AS^,  o f temperature = AS423 >  a  n  °  l t ;  i n t h e range c  a  °  n  e  s  e  e  n  from E q u a t i o n s 25 and 26 t h a t t h i s a p p r o x i m a t i o n amounts t o assuming t h a t the heat c a p a c i t i e s o f b o t h m o d i f i c a t i o n s a r e i d e n t i c a l i n t h i s L  range, i . e . , C  temperature  H  = C .  The a p p r o x i m a t i o n g r e a t l y s i m p l i f i e s E q u a t i o n 27, Lr*"H  and s u b s t i t u t i o n o f o u r e n t h a l p y and e n t r o p y v a l u e s a t 150 C g i v e s AG^, as a f u n c t i o n o f t e m p e r a t u r e : _L+H AG  [28] r  9  8  1  A  T  _ =  .„Lr>H AH  =  (1620 - 4.33T) c a l m o l e  4 2 3  -  Lr>H T A S ^ - 1  L-*H  The  e q u a t i o n becomes t h a t o f a s t r a i g h t l i n e , h a v i n g a n e g a t i v e AG^  v a l u e a t 150°C, a z e r o v a l u e a t 102°C, and becoming more p o s i t i v e a t Lr^H  lower temperatures  (Figure 33). Taking the u n c e r t a i n t i e s i n A H  a n 4 2 3  ^  Lr*"H  AS  4 2 3  individually  102° i 52°C.  (dotted l i n e s , F i g u r e 3 3 ) , the u n c e r t a i n t y i n x i s  T h i s a p p r o x i m a t i o n t h e r e f o r e i n d i c a t e s t h a t t h e system  i s e n a n t i o t r o p i c w i t h t h e racemate s t a b l e below about 102°C. we have o b s e r v e d  However,  the L,-*H t r a n s i t i o n as low as 76°C ( S e c t i o n 3.5.1, p 1 0 3 ) .  T a k i n g t h e s e two o b s e r v a t i o n s t o g e t h e r , we s h o u l d  more c o r r e c t l y  con-  c l u d e t h a t t h e e u t e c t i c i s s t a b l e a t l e a s t from 150°C t o 76°C, w i t h t h e racemate becoming s t a b l e a t l o w e r  temperatures.  187  F i g u r e 33.  R e l a t i o n o f the f r e e energy d i f f e r e n c e between racemate  racemic e u t e c t i c form of 1 , 1 - b i n a p h t h y l 1  L mation, assuming i n AG  C  T  First  approxi-  H - C  P  to temperature.  and  = 0 (see t e x t ) .  P  caused by e r r o r s i n A H ^ ^  Dotted l i n e s are u n c e r t a i n t i e s  and A S ^ ^ ,  taken i n d i v i d u a l l y .  188  As a second a p p r o x i m a t i o n , the q u a n t i t y C  L  - C  P c o n s t a n t from room t e m p e r a t u r e to 150°C.  H  can be assumed  P  E q u a t i o n s 25 and 26 can be  i n t e g r a t e d to give: [29]  AH™ T  =  (C - C ) p p  [30]  AS™ T  =  2.303 ( C - C ) p p  The q u a n t i t y  L  (423 - T)  H  L  (C^ - C^) was  H  +  1620 c a l mole  l o g (~) T  +  4.33  d e t e r m i n e d on the d.s.c.  i n v o l v e d u s i n g a sapphire standard ( f o r which a f u n c t i o n o f t e m p e r a t u r e ) and measuring  L Although the C  c a l deg "'mole  The  4  f o r b o t h the racemate  v a l u e s a t each  A  -  deg  1  1  temperature  P  i n d i v i d u a l u n c e r t a i n t i e s a r e reduced by a f a c t o r o f /To - C P  and  The r e s u l t s a r e  i n v o l v e s u b t r a c t i o n of two measured q u a n t i t i e s , the r a t h e r  The d i f f e r e n c e  as  H - C  P  mean o f t e n v a l u e s .  1  procedure ^  i s known a c c u r a t e l y  the e u t e c t i c ( [ a ] = -8°, i . e . , almost r a c e m i c ) form. l i s t e d i n Table XVII.  1  H  large  by t a k i n g the  I s t h e r e f o r e -13 ± 4 c a l  P  "I  mole When the r e s u l t i n g f r e e energy d i f f e r e n c e ( E q u a t i o n 27) i s p l o t t e d  a g a i n s t t e m p e r a t u r e , the s o l i d l i n e i n F i g u r e 34 r e s u l t s . The e r r o r i n L~*H L-*-H L-*-H AG i n t r o d u c e d by the i n d i v i d u a l u n c e r t a i n t i e s i n AH,„„, A S , , and T 423 423 L H L H C - C i s a l s o shown ( d o t t e d l i n e s ) . The u n c e r t a i n t y i n C - C does P P P P L~**H L-^H L~**H not cause n e a r l y so l a r g e an e r r o r i n AG^ " as do t h o s e i n A H ^ ^ d ^423' m  0 0  a n  As i n the f i r s t a p p r o x i m a t i o n , the most p r o b a b l e v a l u e o f the f r e e  A  energy  d i f f e r e n c e becomes l e s s n e g a t i v e as the temperature i s lowered from 150°C, becoming z e r o at about 86°C.  T h i s most p r o b a b l e t r a n s i t i o n temper-  a t u r e T i s c l o s e t o the l o w e s t o b s e r v e d t r a n s i t i o n L+H  (76°C).  The  second  189  500 -  Figure 34.  Relation of the free energy difference between racemate and  racemic eutectic form of 1,1'-binaphthyl to temperature. L mation, assuming C certainties in AG T  H - C  P  1_>H  individually.  Second approxi-  = constant (see t e x t ) . Dotted l i n e s are unP caused by errors i n A H ^ , AS ^ and C - C , taken 423 423 p p 1  1  L  190 T a b l e XVII Heat C a p a c i t i e s at  Constant P r e s s u r e f o r  Melting  Temperature  ( E u t e c t i c ) Forms of  Low-Melting  (Racemate) and High  l,l'-Binaphthyl  c  <v.  H  -c , L  P P -1 -1 c a l deg mole  C  K  , -1mole , -1 • c a l deg  50  323.16  85.7  71.7  14.0  60  333.16  87.6  73.8  13.8  70  343.16  90.4  76.3  14.1  80  353.16  94.3  82.1  12.2  90  363.16  96.2  85.4  10.8  100  373.16  98.2  85.5  12.7  110  383.16  99.7  87.1  12.6  120  393.16  101.6  90.1  11.5  130  403.16  105.8  92.8  13.0  140  413.16  112.9  96.9  16.0  150  423.16  117.9  c a l deg  approximation t h e r e f o r e also implies that system  -1  , -1  mole  Mean:  the racemic  13.07  1,1'-binaphthyl  i s e n a n t i o t r o p i c , w i t h t h e • t r a n s i t i o n temperature  probably only  s l i g h t l y below 76 C. L H A t h i r d a p p r o x i m a t i o n i n v o l v e s the d e t e r m i n a t i o n o f C - C as a P P f u n c t i o n o f temperature. The i n d i v i d u a l heat c a p a c i t y d i f f e r e n c e s i n L T a b l e XVII were f i t t e d t o a p o l y n o m i a l o f the type  -2 a + bT + cT  to o b t a i n :  C  H - C  =  191  • 180.5  c  =  T h i s polynomial"'' ' 08  Equations  3  58.6  +  +  0.3511  i  +  8.528 x 10  +  + 6  0.1066 2.589 x 1 0  was s u b s t i t u t e d i n E q u a t i o n s  + 6  25 and 26, and t h e t h r e e  25, 26 and 27 were s o l v e d s i m u l t a n e o u s l y f o r AH  , AS and x. x x was 84°C, not much d i f f e r e n t from the v a l u e x  The t r a n s i t i o n temperature  E~*"H o b t a i n e d from t h e second a p p r o x i m a t i o n . mole  1  and 2.16 c a l deg "'"mole \  AH  x respectively.  L"*"H and AS x  were 772 c a l  These thermodynamic c a l c u l a t i o n s , performed w i t h t h e measurements made w i t h t h e d i f f e r e n t i a l s c a n n i n g c a l o r i m e t e r , y i e l d an i m p r e c i s e v a l u e o f x but s u p p o r t an e n a n t i o t r o p i c o r d e r i n g o f racemic modifications.  1,1'-binaphthyl  A more e x a c t v a l u e o f t h e t r a n s i t i o n temperature  could 59b  be o b t a i n e d w i t h t h e v e r y p r e c i s e methods o f a d i a b a t i c c a l o r i m e t r y .

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UBC Theses and Dissertations

UBC Theses and Dissertations

Racemization and resolution in the organic solid state Wilson, Keith Rainier 1972

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UBC Theses and Dissertations

Racemization and resolution in the organic solid state Wilson, Keith Rainier 1972

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