Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Kinetics of some oxidation-reduction reactions in aqueous solutions. Harkness, Alan Chisholm 1963

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1963_A1 H2 K4.pdf [ 5.83MB ]
Metadata
JSON: 831-1.0062052.json
JSON-LD: 831-1.0062052-ld.json
RDF/XML (Pretty): 831-1.0062052-rdf.xml
RDF/JSON: 831-1.0062052-rdf.json
Turtle: 831-1.0062052-turtle.txt
N-Triples: 831-1.0062052-rdf-ntriples.txt
Original Record: 831-1.0062052-source.json
Full Text
831-1.0062052-fulltext.txt
Citation
831-1.0062052.ris

Full Text

KINETICS OF SOME OXIDATION-REDUCTION REACTIONS IN AQUEOUS SOLUTIONS  by  ALAN CHISHOLM HARKNESS B.A.,  University  o f B r i t i s h Columbia,  1947  M.Sc, University  o f B r i t i s h Columbia,  1957  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 accept t h i s required  THE  t h e s i s as conforming t o t h e  standard  UNIVERSITY OF BRITISH COLUMBIA March,  1963  In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make i t freely available for reference and study.  I further agree that permission  for extensive copying of this thesis for scholarly purposes may  be  granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.  Department of Chemistry The University of British Columbia, Vancouver 3, Canada. Date March 28,  1963.  The U n i v e r s i t y o f B r i t i s h  Columbia  FACULTY OF GRADUATE STUDIES  PROGRAMME OF.THE FINAL ORAL EXAMINATION FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  ' '  of  ALAN CHISHOLM HARKNESS PUBLICATIONS B.A., The U n i v e r s i t y o f B r i t i s h Columbia, 1947 K i n e t i c s o f t h e O x i d a t i o n o f Uranium (IV) by T h a l l i u m ( I I I ) . , J.Am.Chem.Soc., 81, 3526 (1959). A.C. Harkness and J . H a l p e r n . Medium E f f e c t s i n the Homogeneous C a t a l y t i c A c t i v a t i o n o f M o l e c u l a r Hydrogen by M e t a l S a l t s . I I I . S i l v e r and M e r c u r i c S a l t s . J.Am.Chem.Soc. , 8_1_, 5854 (1959),. A . J . Chalk, J . H a l p e r n and A.C. Harkness.  M . S c , The U n i v e r s i t y o f B r i t i s h Columbia, 1957  TUESDAY. APRIL 30th,  1963, AT 9:30 A.M.  IN ROOM 261, CHEMISTRY BUILDING  ;  COMMITTEE IN CHARGE Chairman: F.H. Soward  S p e c t r a o f Some T r a n s i t i o n M e t a l Ions- and Complexes i n D 0., J.Chem.Phys., 31, 1147 (1959) J . H a l p e r n and A.C. Harkness. 2  O x i d a t i o n o f Carbon Monoxide by M e t a l Ions, J.Am.Chem.Soc., 83, 1 2 5 8 ( 1 9 6 1 ) . A.C. Harkness and J . H a l p e r n .  W.A. Bryce B.A. D u n e l l . L.G. H a r r i s o n  C.A. McDowell E; P e t e r s R. Stewart  E x t e r n a l Examiner:. H. Taube Stanford  University  KINETICS OF SOME OXIDATION-REDUCTION REACTIONS IN AQUEOUS SOLUTIONS  =  ABSTRACT The k i n e t i c s of the. e l e c t r o n t r a n s f e r U(IV) + T l ( I I I )  /TMn 7 04  w i t h A H * = 13 kcal/mole and A S# = -17 e.u., both subs t a n t i a l l y c o n s t a n t over the pH range 1 t o 13. The r a t e d e t e r m i n i n g s t e p i s c o n s i d e r e d t o be the f o r m a t i o n o f hypomanganate  reaction  i U(VI) + T 1 ( I )  were examined i n aqueous p e r c h l o r i c a c i d s o l u t i o n . r a t e law was found to be o f the form  k/TOj  The  Mn0 " + CO + H 0 4  > Mn0  2  3 _ 4  + C0  2  + 2H+ .  which then undergoes f u r t h e r f a s t r e a c t i o n s t o y i e l d MnO^ " i n b a s i c s o l u t i o n and Mn0 i n a c i d and n e u t r a l s o l u t i o n s . 2  2  -d/u(iv)7  ^4+7  =  m  j^ZSt?- +k./H+7_2j  3fj  1  2  The two r a t e c o n s t a n t s were i d e n t i f i e d w i t h r e a c t i o n paths i n v o l v i n g a c t i v a t e d , c o m p l e x e s o f the c o m p o s i t i o n s (U'0H*T1) and ( U « 0 " T 1 ) ' , r e s p e c t i v e l y . The c o r r e s ponding heats and e n t r o p i e s o f a c t i v a t i o n , e v a l u a t e d from r a t e measurements over the temperature range 16 t o 25°, a r e ^ H i # = 2 4 . 6 k c a l / m o l e , A H # =21.7 kcal/mole, AS]# = 16 e.u. and A S * = 7 e.u. The e f f e c t o f i o n i c s t r e n g t h and the s p e c i f i c e f f e c t s o f v a r i o u s anions and c a t i o n s on the r a t e were examined. The r e s u l t s s u g g e s t , but do not prove, t h a t the r e a c t i o n o c c u r s through a s i n g l e two-equiv a l e n t s t e p r a t h e r than through s u c c e s s i v e one e l e c t r o n changes. 6+  2  The homogeneous o x i d a t i o n o f carbon monoxide by m e t a l ions i n aqueous s o l u t i o n s was s t u d i e d . At temperatures below 80° o n l y Hg + and were found to o x i d i z e carbon monoxide. The ions Cu +, Ag+, H g o , F e + , T l + and Cr 0y were i n a c t i v e . 2  2 +  3  K i n e t i c measurements o f the r e a c t i o n + CO + H 0  2 +  ——>  2  Hg  + C0  2 + 2  2  +  2H+  i n d i l u t e p e r c h l o r i c a c i d over the temperature to 54° y i e l d e d the r a t e  range  26  law  = kZco7 /Hg 7  zAML  24  The a c t i v a t i o n parameters are AH' = 14.6 k c a l / m o l e and A S ^ = -13 e.u. I t i s b e l i e v e d t h a t the r e a c t i o n proceeds by a mechanism which i n v o l v e s the i n s e r t i o n o f CO between Hg"*" and a c o o r d i n a t e d water m o l e c u l e , f  -Hg ~ 0 H J + CO  ^—>.  2  2  - C - 0H Hg + H g  2 +  3  -d/co7  =  +  -Hg -c - 0H+ + H  >  Hg + C 0  >  Hg + 2  2  2  + H+  +  (fast)  (fast)  The o x i d a t i o n o f carbon monoxide by Mn04~ was found to proceed r e a d i l y over the temperature range 28 to 5 0 ° . The r a t e law was found to be  k  /-  3  /K/  /gno :7  co7  4  where M = A g or Hg +. F o r Ag+, k at 0° i s 1.10 x l O M" s e c " w i t h A H * = 1.3 kcal/mole and As# = -30 e.u. For H g , k a t 0° i s 1.09 x 1 0 M~ s e c " w i t h AH*= 6.5 k c a l / mole and A S * = -21 e.u. I t i s s u g g e s t e d t h a t the remarka b l y h i g h r e a c t i v i t i e s e x h i b i t e d by carbon monoxide i n these c a t a l y t i c r e a c t i o n s are r e l a t e d to f a v o u r a b l e o x i d a t i o n paths i n v o l v i n g i n t e r m e d i a t e s such as 0 -Ag - C ••- 0Mn0 . +  2  5  1  2 +  3  2  1  3  GRADUATE STUDIES  3  2  g  2  M11O4-  2  -Hg  2  5+  2  2H  A remarkable f e a t ure o f the l a t t e r r e a c t i o n i s i t s v e r y marked s e n s i t i v i t y to c a t a l y s i s by Ag+ and Hg + (but not by Cu +, Cd +, F e + , or T l + ) . The r a t e law o f the c a t a l y z e d path i s , i n each case,  F i e l d o f Study:  P h y s i c a l Inorganic Chemistry  Advanced i n o r g a n i c c h e m i s t r y H.C Clark Molecular structure C. R e i d , R.. H o c h s t r a s s e r S t a t i s t i c a l mechanics L.G. H a r r i s o n Surface chemistry J . H a l p e r n , L.G. H a r r i s o n . Chemical k i n e t i c s W . A . B r y c e , G.B. P o r t e r , J.. H a l p e r n P h y s i c a l organic chemistry Related studies: : Theory and a p p l i c a t i o n s o f d i f f e r e n t i a l equations Atomic p h y s i c s Theory o f measurements Metal physics  ; R.  C.A.  Stewart  Swanson M. Bloom J . Prescott J.A.H. Lund  2  (i)  ABSTRACT  The k i n e t i c s o f the e l e c t r o n t r a n s f e r r e a c t i o n  U(IV)  +  T1(III)  >  U(VI)  were examined i n aqueous p e r c h l o r i c a c i d s o l u t i o n .  +  T1(I)  The r a t e law was  found  to be o f the form  -d  -  •  •-  -  1  2 1  The two r a t e c o n s t a n t s were i d e n t i f i e d w i t h r e a c t i o n paths i n v o l v i n g vated complexes o f the compositions (TJ«0H»T1)  and  (U'OTl)  acti-  , respectively.  The c o r r e s p o n d i n g h e a t s and e n t r o p i e s o f a c t i v a t i o n , e v a l u a t e d from r a t e measurements o v e r the temperature /\Krf  ~  2  1  »  kcal/mole,  7  range 16 to 25°,  = 16 e.u. a n d ^ S *  are AH]*  24.. 6 k c a l / m o l e ,  =  = 7 e.u.  The e f f e c t o f  i o n i c s t r e n g t h and the s p e c i f i c e f f e c t s o f v a r i o u s anions and c a t i o n s on the r a t e were examined.  The r e s u l t s suggest, but do not prove, t h a t the r e a c t i o n  o c c u r s through a s i n g l e t w o - e q u i v a l e n t s t e p r a t h e r than through s u c c e s s i v e one e l e c t r o n  changes.  The homogeneous o x i d a t i o n o f carbon monoxide by metal i o n s i n aqueous s o l u t i o n s was  studied.  At temperatures  found t o o x i d i z e carbon monoxide.  below 80° o n l y H g ^  The i o n s Cu  2H"  , Ag  *4"  , Hg  2  C0  2  +  and MnO^~  2*^~ 3"t" 3"^~ , Fe , Tl and  2CrgOr,  were i n a c t i v e .  K i n e t i c measurements o f the r e a c t i o n  2Hg  2 +  +  CO  +  ILjO  >  Hg  2 + 2  +  were  +  2H  +  (ii) i n d i l u t e p e r c h l o r i c a c i d over the temperature range 26 to 54° y i e l d e d the r a t e law -*m  The a c t i v a t i o n parameters are A H  =k[C0][Hg2 J +  = 14..6 kcal/mole and A S  =-13  e.u. I t  i s b e l i e v e d t h a t the r e a c t i o n proceeds by a mechanism which i n v o l v e s t h e i n s e r t i o n o f CO between H g * and a c o o r d i n a t e d water m o l e c u l e , 2  -Hg - 0 H  2+  +  2  k  CO  0 II  . >  -Hg - C - OH  )  Hg  >  Hg  +  +  H  +  0 II -Hg - C - 0 H  Hg  +  Hg  +  2 +  +  dt w i t h A H * = 13 k c a l / m o l e and A S * over the pH range 1 t o 13.  ^  J L  +  2  H  (fast)  +  (fast)  2 + 2  The o x i d a t i o n o f carbon monoxide by MnO^ r e a d i l y over t h e temperature range 28 t o 50°.  C0  was found t o proceed  The r a t e law was found t o be  4  = -17 e.u., both s u b s t a n t i a l l y c o n s t a n t  The r a t e d e t e r m i n i n g s t e p i s c o n s i d e r e d t o be  the f o r m a t i o n o f hypomanganate  MnO^"  +  CO  +  H 0  >  2  MnO^ " 3  +  C0  +  2  2H  +  2which then undergoes f u r t h e r f a s t r e a c t i o n s t o y i e l d MnO^ and Mn0  2  i n a c i d and n e u t r a l  i n basic  solution  solutions,  t A remarkable f e a t u r e o f t h e l a t t e r r e a c t i o n i s i t s v e r y marked s e n s i t i v i t y t o c a t a l y s i s by A g  +  and H g  2 +  (but n o t by C u  2 +  , Cd  2 +  , Fe^ , or +  (iii)  3+ T]/  ).  The r a t e law o f t h e c a t a l y z e d p a t h i s , i n each c a s e ,  -dgQi where M = A g  +  o r Hg " ". 2  1  =  k [ c o ] r M n 0  ^j(; ] M  F o r A g , k a t 0° i s 1.10 x 1 0 +  5  M~  2  s e c " with A B *  1.3 kcal/mole and A S* = -30 e.u.  F o r Hg"*", k a t 0° i s 1.09 x 1 0  with A H *  = -21 e.u.  = 6.5 kcal/mole and A S *  2  3  M"* s e c " 2  1  I t i s suggested t h a t t h e  remarkably h i g h r e a c t i v i t i e s e x h i b i t e d by carbon monoxide i n these r e a c t i o n s are r e l a t e d  =  1  catalytic  t o f a v o u r a b l e o x i d a t i o n paths i n v o l v i n g i n t e r m e d i a t e s  such as 0 m -Ag - C - OMnO,.  (x)  ACKNOWLEDGEMENTS  I wish t o express my a p p r e c i a t i o n f o r t h e a s s i s t a n c e g i v e n me by Dr. J . Halpern  i n a l l aspects d u r i n g t h e course o f t h i s work.  The awards o f a F e l l o w s h i p from t h e C o n s o l i d a t e d M i n i n g and S m e l t i n g Company o f Canada L i m i t e d and o f a S b h o l a r s h i p from t h e B r i t i s h Columbia Sugar R e f i n i n g Company were most h e l p f u l and are g r e a t l y appreciated.  Above a l l a g r e a t debt i s owed t o my f a m i l y .  (iv)  TABLE OF CONTENTS Page No.  KINETICS OF SOME OXIDATION-REDUCTION REACTIONS IN AQUEOUS SOLUTIONS  GENERAL INTRODUCTION  1  1  PART I THE KINETICS OF THE OXIDATION OF URANIUM  ( I V ) BY THALLIUM ( I I I )  12  Introduction  12  Experimental  26  Materials  26  Analytical  28  K i n e t i c a l Measurements  29  R e s u l t s and D i s c u s s i o n s  30  PART I I KINETICS OF THE HOMOGENEOUS OXIDATION OF CARBON MONOXIDE BY METAL IONS  62  Introduction  62  Experimental  67  Materials  67  Analytical  68  Procedure  68  Results  and D i s c u s s i o n  74  Oxidation  o f CO by H g ( l l )  74  Oxidation  o f CO by MnO^"  85  C a t a l y s i s o f t h e CO - MnO^~ Tracer Studies with 0  Reaction  1 8  Mechanism o f t h e CO - H g ( l l ) R e a c t i o n  by A g ( l ) and H g ( l l )  94 109 113  R e s u l t s o f R e l a t e d CO  Reactions  Mechanisms o f the U n c a t a l y z e d  and C a t a l y z e d CO -  MnO^  Reactions Comparison o f CO, Hg and HCOOH as Reductants Comparison o f the I s o e l e c t r o n i c S p e c i e s CO, N_  and CN  (vi) LIST OF TABLES Table No.  Page No.  I  Exchange rate constants for thallium chloro complexes  21  II  Stoichiometry of U(IV) - Tl(lII) reaction  32  III  Effect of i n i t i a l concentrations of U(IV) and Tl(III) on second order rate constant of U(IV) - T l ( l l l ) reaction  34-  IV  Effect of NaCl on rate of U(IV) - Tl(lII) reaction  35  V  38  VI  Effect of Na SO on rate of TJ(lV) - Tl(III) reaction 2 4 Effect of some metal ions on rate of U(IV) - Tl(IIl) reaction  VII  Effect of NaClO^ on rate of U(IV) - Tl(III) reaction  41  VIII  Effect of HCIO^ on rate of U(IV) - T l ( l l l ) reaction  44  IX  Effect of HCIO^ on rate of U(IV) - Tl(lII) reaction  45  X  Effect of HCIO^ on rate of U(IV) - T l ( l l l ) reaction  46  XI  Effect of HCIO^ on rate of U(IV) - Tl(lII) reaction  47  XII  Effect of HCIO^ on rate of U(IV) - T l ( l l l ) reaction  48  XIII  Hydrolysis constants of  54  XIV  Kinetic data for the oxidation of U(IV) by Tl(lII)  54  XV  Variation of rate of U(IV) - T l ( l l l ) reaction with temperature  56  XVI  Solubility of CO i n water  75  XVII  Effect of reactant concentrations on rate of the CO - Hg(Il)  and T l  3 +  40  reaction  78  XVIII  Effect of HCIO^ on the rate of the CO - Hg(ll) reaction  79  XIX  Effect of NaClO^ on the rate of the CO - Hg(II) reaction  80  XX  Activation parameters of the CO - Hg(ll) reaction at 40.0°  82  XXI  Effect of temperature on the CO - Hg(ll) reaction  83  XXII  Kinetic data for the oxidation of CO by MnO^" i n acid and neutral solutions at 50,0°  86  (vii) Table No.  XXIII  Page No.  E f f e c t o f temperature on t h e r a t e o f t h e o x i d a t i o n  o f CO by  MnO^" i n a c i d and n e u t r a l s o l u t i o n s  87  XXIV  K i n e t i c d a t a f o r t h e CO - MnO^~ r e a c t i o n i n a l k a l i n e s o l u t i o n  93  XXV  K i n e t i c parameters f o r t h e CO - MhO^" r e a c t i o n a t  XXVI  K i n e t i c data f o r the H g ( l l ) catalyzed  50.0°  94  o x i d a t i o n o f CO by MnO."  102  4 XXVII  Kinetic data f o r the Ag(I) catalyzed  oxidation  XXVIII  E f f e c t o f temperature on t h e r a t e o f t h e H g ( l l )  o f CO by MnO^" catalyzed  104  CO - MhO^" r e a c t i o n XXIX  XXX XXXI XXXII  103  E f f e c t o f temperature on t h e r a t e o f t h e A g ( l ) c a t a l y z e d CO - MnO^" r e a c t i o n  105  A c t i v a t i o n parameters f o r t h e c a t a l y z e d CO - Mn0^~ r e a c t i o n s 18 Summary o f 0 t r a n s f e r experiments Summary o f k i n e t i c d a t a f o r some o x i d a t i o n s o f H , HCOOH,  108 114.  2  HCOO" and CCT  125  (viii) LIST OF FIGURES' Fig. No. 1.  Page No. Profile of potential energy surfaces showing intersection of surfaces corresponding to reactants and products  9  2.  Rate of U(IV) - T l ( l l l ) reaction in 3M HCIO^ at 25.0°  33  3.  Effect of C l " on rate of TJ(IV) - Tl(III) reaction  36  4.  Effect of SO^ "  39  5.  Effect of NaClO^ on rate of TT(IV) - T l ( l l l ) reaction  6.  Rate plots of U(IV) - Tl(lII) reaction for various HCIO^  2  on rate of U(IV) - T l ( l l l ) reaction  concentrations 7.  49  Effect of HCIO^ on second order rate constant of U(IV) - T l ( l l l ) reaction  8.  50  Effect of acidity on rate of U(IV) - Tl(IIl) reaction at 53  various temperatures 9.  42  Arrhenius plots for rate constants  and kg of U(IV) - Tl(lII)  reaction  55  10.  Gas contacting apparatus  69  11.  Gas absorption apparatus  73  12.  Rate plots for CO - Hg(ll) reaction at 4-0.0°  77  13.  Effect of CO pressure on rate of CO - Hg(ll) reaction  81  14.  Arrhenius plots for CO - Hg(II) reaction  84  15.  Rate plots for CO - MnO^"  reaction in acid and neutral solutions  at 50.,0°  88  16.  Effect of CO pressure on rate of CO - MnO^~  reaction  17.  Rate of CO absorption by alkaline MnO^~  91  18.  Rate plot for data of Figure 17  92  19.  Arrhenius plot for CO - MnO,"  95  reaction in acid solution  89  (ix) Fig. No.  Page No.  20.  A r r h e n i u s p l o t f o r CO - MnO^~  reaction i n neutral  21.  A r r h e n i u s p l o t f o r CO - MnO^  reaction i n alkaline solution  22.  Rate p l o t s f o r u n c a t a l y z e d and c a t a l y z e d  CO - MhO^~  solution  97  reaction  at 13,0° 23.  96  100  Arrhenius p l o t f o r H g ( l l ) catalyzed  CO - MnO  ~ reaction  106  4 24.,  Arrhenius plot f o r A g ( l ) catalyzed  25,  Apparatus f o r decomposing  CO - MnO 4" r e a c t i o n  BaCO, and c o l l e c t i n g CO-  107 110  1.  KINETICS OF SOME OXIDATION-REDUCTION REACTIONS IN AQUEOUS SOLUTIONS  General  Introduction  T h i s t h e s i s i s concerned w i t h  t h e k i n e t i c s o f some o x i d a t i o n -  r e d u c t i o n r e a c t i o n s i n aqueous s o l u t i o n s and comprises two p a r t s . describes (III) and  Part I  an i n v e s t i g a t i o n o f t h e k i n e t i c s o f t h e r e d u c t i o n o f t h a l l i u m  by uranium ( I V ) ,  T h i s i s a r e a c t i o n between a two e q u i v a l e n t  a two e q u i v a l e n t r e d u c t a n t .  oxidant  One o f t h e o b j e c t s o f t h e i n v e s t i g a t i o n  was t o determine whether i t proceeds i n a s i n g l e s t e p o r i n s u c c e s s i v e one e l e c t r o n steps.  Part II describes  o f some m e t a l i o n s by t h e m o l e c u l a r  a k i n e t i c i n v e s t i g a t i o n o f the r e d u c t i o n reducing  agent, carbon monoxide.  This  was p r i m a r i l y an e x p l o r a t o r y i n v e s t i g a t i o n o f ' a new c l a s s o f r e a c t i o n s r e l a t e d i n some r e s p e c t s  t o t h e homogeneous r e a c t i o n s o f m o l e c u l a r  hydrogen  which have been e x t e n s i v e l y i n v e s t i g a t e d i n t h i s l a b o r a t o r y ( l ) .  In recent years  g r e a t i n t e r e s t has d e v e l o p e d i n o x i d a t i o n - r e d u c t i o n  or electron t r a n s f e r reactions.  The s u b j e c t has been reviewed by Z w o l i n s k i ,  R. J . Marcus and E y r i n g (2), Basolo and Pearson (3), Taube (4)* George and Griffith  (5), S t r a n k s (6)" and H a l p e r n (7).  Oh t h e b a s i s o f e x p e r i m e n t a l  e v i d e n c e i t has been p o s s i b l e t o d i s -  t i n g u i s h two f a i r l y d e f i n i t e forms o f t h e a c t i v a t e d complex f o r e l e c t r o n t r a n s f e r r e a c t i o n s between m e t a l i o n s .  These a r e d e f i n e d by t h e r e l a t i v e  c o n f i g u r a t i o n o f t h e l i g a n d s i n t h e complex. i n b e h a v i o u r and i n o n l y a c o m p a r a t i v e l y  The two types r e p r e s e n t  extremes  few c a s e s has i t been p o s s i b l e t o  assign reactions to either class. The outer sphere complex i s characterized by the constancy of the f i r s t coordination spheres of the reactants.  That i s , both the number and  identity of the ligands around each metal ion remain unchanged i n the comr plex.  This i s the mode by which substitution inert pairs react,,  are MnO^" - MnC^ ", Fe(CN)^" - Fe(CN) " and Fe(phen) 2  3  6  2+ 3  Examples  - Fe(phen) , 3+  3  (Note). The outer sphere complex has also been established for pairs of reactants i n which one member i s substitution labile.  In such a case i t  i s necessary to establish that the rate law corresponds to an activated complex containing the same number of ligands as are held by the metal ions separately.  Examples are Co(en)^  - Co(en)<j  3  and C r  2 +  - CoCNH^)^ .. 3  The question of how close the reacting pairs approach in this type of complex remains unanswered. point.  Sheppard and Wahl (8) found that substituting CsOH for NaOH as the  medium i n the MnO^ rate.  There i s no direct evidence on this  - MnO^  exchange resulted i n a threefold increase i n  The reason for this i s not clear, but i t does suggest that consider2-  ation be given to a cation bridged structure, e.g. oyfnO — The inner-sphere  Cs — OMnO^ .,  activated complex i s characterized by the  sharing of ligands by the reacting ions.  Its formation i s quite analogous  to that of ordinary ligand substitution reactions.  In this case one of the  reactants with i t s own inner coordination sphere acts as a ligand being (Note)s Abbreviations used for ligands are* phen = 1,10-phenanthroline; en = ethylenediamine; bip = 2,2 -bipyridine  3.  substituted into the coordination sphere of the other reactant.  In order  to demonstrate the existence of this type of complex the coordination spheres of one metal ion reactant and the other metal ion product must be substitution inert. The most extensive investigations of this type of mechanism have been done by Taube and his school on the reduction of Co(ill) complexes by 2+ Cr  .  Co (III)) and Cr(IIl) complexes are relatively inert to substitution 2+  whereas Cr  i s very labile.  One of the f i r s t demonstrations of an inner-  sphere complex was i n the reduction of (NH^CoCl " " by Cr " " (9). The oxidized 2+ 3+ product was found to be CrCl rather than CrCKjO)^ .. This was taken to mean that a Cr - Cl bond was formed in the active complex leading to the 2  1  2  1  structure (NH ) Co - Cl - CrCEjOj^ " 4  3  5  Further evidence for this structure was adduced by repeating the experiment in the presence of radioactive chloride ions {10%. Substantially no radio2+ activity was found in the product CrCl „, Recently Haim and Wilmarth (11) have reported the isolation of a complex ion resulting from the oxidation of the pentacyano complex of Co(II) 3-  by Fe(CN)^  .  They considered the product to have the bridged structure (CN) Fe - CN - Co(CN) 5  5  It must not be assumed that the bridged activated complex always leads to atom transfer as the redox mechanism. For example, in the case of pi p 3+ the reaction between Cr and I r C l ^ (10): the products are C r ^ O ) ^ and IrCl^ . The mechanism i s considered to involve an inner-sphere complex and spectral evidence suggests this.  The point here i s that the bridging ligand  w i l l f o l l o w ; t h a t p a r t n e r which has t h e g r e a t e s t a f f i n i t y f o r i t .  It before  i s apparent t h a t f a i r l y r e s t r i c t i v e c o n d i t i o n s must be met-  a r e a c t i o n can be a s s i g n e d  any degree o f c e r t a i n t y .  t o e i t h e r o f the f o r e g o i n g c l a s s e s  Unfortunately  with  r e a c t i o n s o f aquo i o n s i n g e n e r a l  do n o t meet t h e s e c o n d i t i o n s .  The  o v e r r i d i n g d i f f i c u l t y i n t h e case o f aquo i o n s i s i n attempting  to d e f i n e the r e a c t i n g species.  Inferences  e f f e c t s o f such v a r i a b l e s as a c i d i t y , i o n i c r a r e l y p o s s i b l e t o do more than  may be drawn by o b s e r v i n g t h e s t r e n g t h and a n i o n s ,  this.  Some o f these p o i n t s may be i l l u s t r a t e d 2+ such as t h e Fe it  i sfirst  but i t i s  by c o n s i d e r i n g  reactions  3+ - Fe  exchange.  o r d e r i n each r e a c t a n t  L i k e most e l e c t r o n t r a n s f e r r e a c t i o n s (12).  There i s an i n v e r s e f i r s t  dependence on hydrogen i o n c o n c e n t r a t i o n .  T h i s i s q u i t e common and i s  u s u a l l y taken t o i n d i c a t e a r e a c t i o n path i n v o l v i n g an h y d r o l y z e d in  t h i s case F e O H . 24  other formulations.  2 +  - Fe  2 +  , Fe  3 +  - FeOH , F e +  3 +  - Fe  2 +  - GH°  The f a c t t h a t t h e f e r r i c i o n i s more s t r o n g l y hydro-  l y z e d than t h e f e r r o u s i o n i s t h e excuse f o r c o n s i d e r i n g FeOH^ A' s i m i l a r s i t u a t i o n p r e v a i l s w i t h r e g a r d other  species?  However, t h i s cannot be c o n f i r m e d as t h e r e i s no  k i n e t i c d i f f e r e n c e between F e O H and  order  +  as a reactant..  t o t h e e f f e c t o f c h l o r i d e i o n and  anions. The  the s u g g e s t i o n  c a t a l y s i s o f t h e r e a c t i o n ( a f a c t o r o f 1000) by 0H~ l e d t o (13) t h a t a hydrogen b r i d g e d i n t e r m e d i a t e (H 0) Fe0 H 2  5  S i m i l a r l y the intermediate  H  - - - OTe(E 0j) * 2  may be i n v o l v e d ,  +  5  H  f o r the uncatalyzed  reaction i s  5. H  (HjOj-Pe 0 - - - H - - - 0 H H  The  Fe(lLO)/ ^ 5  r e a c t i o n s are completed by t r a n s f e r r i n g the hydrogen atom.  Dodson  Hudis  found t h a t the r a t e s f o r both paths were lowered by  o f 2 when the r e a c t i o n was t o the p r o p o s a l s .  conducted i n heavy water.  and  a factor  T h i s g i v e s some support  However, hydrogen i s o t o p e e f f e c t s i n aqueous s o l u t i o n s 2+  are not  at present  o f much d i a g n o s t i c v a l u e .  by C r  which proceeds by a c h l o r i d e b r i d g e to D^O  i n changing the s o l v e n t from HgO The u n c e r t a i n t y attempt (4) Fe^  +  o f arguing  by  I n the r e d u c t i o n t h e r e i s a 30%  Both C r * and F e 2  analogy i s i l l u s t r a t e d i n Taube's  reduce s e v e r a l f e r r i c  2 +  Fe-  i s formed q u a n t i t a t i v e l y i n the one  2  CrCl  the c o r r e s p o n d i n g F e C l  2 +  c a t a l y z e d by c h l o r i d e and  CrCl  The  i s not  Cr  2 +  reduction  formed (16).  +  and  t h e r e f o r e , the Fe I t has  the  Fe  —  2 +  case (10),  but  o f C r ^ O ) ^ " " i s not 4  T h i s evidence was  t o mean t h a t c h l o r i d e must a c t as a b r i d g i n g agent to e f f e c t  2+ and,  is labile.  Fe  complexes a t  c h l o r i d e c a t a l y z e s both the C r * - F e ^  reactions.  i n rate  (15).  to a s s i g n a b r i d g e d mechanism t o the c h l o r i d e c a t a l y z e d  exchange.  preted  (NH^)^CoCl  reduction  same r e l a t i v e r a t e s and 7  of  inter-  catalysis  3+ - Fe^  r e a c t i o n has  s i n c e been shown (16A)  p l a c e w i t h o u t the p r i o r f o r m a t i o n  a bridged  a c t i v a t e d complex.  t h a t the Cr " " - F e ^  of F e C l  2  2 +  .  1  +  r e a c t i o n takes  A l s o the o x i d a t i o n o f  V  2 +  by s u b s t i t u t i o n i n e r t C o ( l l l ) complexes i s c a t a l y z e d by c h l o r i d e as i s the r e a c t i o n between C r " and 2 4  Co(NH^)^  (17).  These r e s u l t s show t h a t c h l o r i d e  does n o t have to a c t as a b r i d g i n g l i g a n d to e x e r t a c a t a l y t i c e f f e c t the p r e v i o u s are  conclusions  concerning  the Cr " " - Fe-* and 2  4  +  Fe  2 +  - Fe^  +  and  reactions  vitiated.  I n c i d e n t a l l y the experiments w i t h  showed t h a t i t s r e a c t i o n s  6. were c l o s e r t o those o f C r C b i p ^ " " than those o f C r 2  1  2 +  ,  The  implication  i s t h a t V"*" r e a c t s through o u t e r - s p h e r e complexes j a t l e a s t w i t h s u b s t i t 2  ution inert oxidizing  agents.  I t i s o f course n o t n e c e s s a r y t h a t a b r i d g i n g l i g a n d be an anion. The 0  18  t r a c e r work o f Murmann, Taube and Posey (16) shows t h a t a s u b s t a n t i a l 3+  2"^"  p o r t i o n o f the water i s t r a n s f e r r e d i n the r e d u c t i o n o f (NH^J^CoHgO  by C r  .  3+ If  (NH^jyJoHgO  can be c o n s i d e r e d an aquo i o n t h i s i s the o n l y case where  the mechanism o f a r e a c t i o n between aquo i o n s i s known. I n many cases the c a t a l y t i c e f f e c t s o f anions are a t t r i b u t e d t o a p o s s i b l e b r i d g i n g mechanism.  While t h i s may  be so f o r a p a r t i c u l a r  reaction  o r s e r i e s o f r e a c t i o n s i t i s by no means u n i v e r s a l . F o r example, the reduet i o n o f (NH^J^CoOHg.3+ w by CnJ2+ r i s a c c e l e r a t e d by pyrophosphate which appears 2+ i n the C r ( l l l ) p r o d u c t (18).  When the c o r r e s p o n d i n g (NH^J^CoCl  both c h l o r i d e and pyrophosphate  i s reduced  are found i n the C r ( l I I ) p r o d u c t . 2+  The r e d u c t i o n s o f v a r i o u s pentamino C o ( I I I ) complexes by C r ( b i p ) 3 proceed by o u t e r - s p h e r e complexes (19).  Here t h e r e i s marked v a r i a t i o n i n  r a t e brought about jqy d i f f e r e n t  T h i s may  medium o r s a l t  anions.  be due t o what are  termed  effects.  Medium e f f e c t s are r e l a t e d to such f a c t o r s as i o n i c s t r e n g t h and the n a t u r e o f the s u p p o r t i n g e l e c t r o l y t e .  The i n f l u e n c e may  be e x e r t e d  through changes i n a c t i v i t y c o e f f i c i e n t s o r ease o f adjustment pheres i n f o r m i n g the a c t i v a t e d complex. i s not w e l l u n d e r s t o o d  of ionic  This aspect o f k i n e t i c s i n general  and can l e a d to d i f f i c u l t i e s o f i n t e r p r e t a t i o n .  d a t a o f Bonner and Hunt (20) on the C o  2 +  atmos-  - Co  3 +  The  exchange show t h a t the r a t e  d e c r e a s e s as HCIO^ i s i n c r e a s e d a t c o n s t a n t i o n i c  strength.  The r e s u l t  can  be i n t e r p r e t e d e q u a l l y w e l l as e i t h e r a medium e f f e c t o r an h y d r o x y l path.  7. It i s useful to consider the theoretical aspects of electron transfer insofar as light i s shed on the importance of various factors. One of the earliest advances was made by Libby (21) who suggested that the Franck-Condon principle i s applicable to electron transfer processes in solution.  This principle states simply that as electronic motion i s much  faster than atomic motion an electronic transition leaves the atomic configuration unchanged.  This has led to the recognition that atomic reorgani-  sation provides a barrier to electron transfer.  Some controversy has arisen  as to whether or not electron transfer precedes or follows atomic reorganization.  It would appear that the f i r s t law of thermodynamics requires that  substantial reorganization take place prior to electron transfer.  Otherwise  the electron transfer would result i n the production of two energy rich species (an oxidized ion i n the environment of a reduced ion and vice versa) which would give off energy in attaining their equilibrium configurations. Energy i s conserved i f both reactants assume an intermediate configuration prior to electron transfer.  The energy released to the medium as the products  assume their equilibrium configuration i s balanced by the energy taken up by the reactants.  The Franck-Condon restriction i s most pronounced for reactions  in which there i s no free energy change. R. J. Marcus, Zwolinski and Eyring (22, 2) developed a treatment of electron transfer based on a tunnelling model.  In this treatment the free  energy of activation i s broken down into three components % an electrostatic term representing the free energy of repulsion between the reacting ions, the free energy of reorganization of the ionic environments and the probabi l i t y of the electron penetrating the coulombic barrier.  The distance of  approach of the reactants i s chosen to effect a compromise between the repulsion term and the probability term.  No attempt was made to calculate  8.  2+ the r e o r g a n i z a t i o n s ! term.  I t was taken as c o n s t a n t by c h o o s i n g t h e Fe  3+ - Fe  exchange as a s t a n d a r d and making the c a l c u l a t e d  v a l u e s o f t h e f r e e energy  o f a c t i v a t i o n agree.  o b t a i n e d on t h i s model are o f l i m i t e d  and e x p e r i m e n t a l  The q u a n t i t a t i v e  significance.  results  Being made t o agree  with  one v a l u e may be the r e a s o n f o r n e a r agreement w i t h o t h e r s , b u t t h i s may be fortuitous.  Thus the c a l c u l a t e d v a l u e f o r the f r e e energy  + the NpOg  2+ exchange was I 4 . 6 kcal/mole which i s i n e x c e l l e n t  - NpCv,  ment w i t h the e x p e r i m e n t a l v a l u e o f 14.3 al  of activation of  kcal/mole  (23).  However, Cohen e t  (24) r e p e a t e d the exchange r e a c t i o n w h i l e v a r y i n g t h e d i e l e c t r i c  from 68 t o 88.  agree-  constant  C o n t r a r y t o t h e p r e d i c t i o n s o f t h e t h e o r y , they found t h a t  the r a t e o f exchange remained c o n s t a n t . R. A. Marcus i n a s e r i e s o f papers  (25, 26, 27, 2 8 ) has attempted  to f o r m u l a t e a q u a n t i t a t i v e t h e o r y t a k i n g i n t o account  a l l the i n t e r a c t i o n s  o f t h e r e a c t a n t s and the medium. I n g e n e r a l , a system can be r e p r e s e n t e d by a p o t e n t i a l s u r f a c e i n many atomic  coordinates.  energy  A r e a c t i o n can be r e p r e s e n t e d by t h e  i n t e r s e c t i o n o f two s u r f a c e s c o r r e s p o n d i n g t o the system o f r e a c t a n t s and A p r o f i l e o f the two s u r f a c e s and t h e i r i n t e r s e c t i o n i s  that o f products. shown i n F i g u r e 1.  There are f o u r c a s e s i 1.  No e l e c t r o n i c i n t e r a c t i o n .  A system  will  s t a y on i t s own s u r f a c e on p a s s i n g through t h e i n t e r s e c t i o n and no r e a c t i o n takes p l a c e .  2.  Strong e l e c t r o n i c i n t e r a c t i o n .  This leads to substantial  s p l i t t i n g o f the s u r f a c e s and a p p r e c i a b l e l o w e r i n g o f t h e a c t i v a t i o n which i s a t p r e s e n t n o t c a l c u l a b l e .  3. Weak i n t e r a c t i o n , a d i a b a t i c  energy transfer.  S p l i t t i n g o f t h e s u r f a c e s o c c u r s so t h a t a system p a s s i n g through t h e i n t e r s e c t i o n w i l l remain on t h e lower s u r f a c e .  The i n t e r a c t i o n energy  i s small  9.  Products  Atomic c o n f i g u r a t i o n Figure  1.  P r o f i l e of p o t e n t i a l energy s u r f a c e s showing i n t e r s e c t i o n o f s u r f a c e s c o r r e s p o n d i n g to r e a c t a n t s and p r o d u c t s .  10. enough to be ignored i n the calculations. 4. adiabatic transfer.  Very weak interaction, non-  This i s like the previous case except that there i s now  a probability that the system will jump from the lower to the upper surface on passing through the intersection. The free energy of activation i s , as by Zwolinski et a l , s p l i t into components. AT*  = A F j + AF^  - RTlnk  Here /SF-^ ^ the free energy of repulsion of the reactants and^AFg i s i s  the reorganizational free energy, remain on the lower surface.  k i s the probability that the system will  In the adiabatic case k = 1.  The complete evaluation of these quantities i s not easy, but f a i r l y simple expressions are obtained by making these approximations.  Each reac-  tant including i t s coordination shell i s treated as a rigid sphere of radius r.  The separation of the reactants i n the activated complex i s the sum of  their radii (a = r^ + r ) .  The results are  2  Da  1  and  AFg*  =  2 m  E  where  t e^, e  2  2  r  l  2y  2  ff  j(n  2  "'j  are the charges of the reactants and e-^', e ' are those of the products, 2  Ae represents the number of electrons transferred, D i s the dielectric constant and n i s the refractive index of the solvent.  11. F o r an exchange r e a c t i o n the f r e e energy  of a c t i v a t i o n i s given  by  1~ 2r F a i r agreement i s o b t a i n e d between e x p e r i m e n t a l  •»  v a l u e s f o r r e a c t i o n s such as the MnO^° - MnO. c o n f i g u r a t i o n s o f the i n i t i a l  2—  and  calculated  exchange i n which the  and f i n a l s t a t e s are n e a r l y i d e n t i c a l .  atomic In  the case o f aquo i o n s the ebove e x p r e s s i o n s are not a p p l i c a b l e because l i g a n d motion has not been c o n s i d e r e d .  The more complete t h e o r y i s supposed t o  account f o r t h i s .  The  t h e o r y c o r r e s p o n d s more c l o s e l y t o the o u t e r - s p h e r e model  r a t h e r than t o the i n n e r - s p h e r e model o f the a c t i v a t e d complex, because o f the r e s t r i c t i o n on a low i n t e r a c t i o n energy.  I n as much as f r e e e n e r g i e s  o f r e p u l s i o n and r e o r g a n i z a t i o n are i n v o l v e d i n b o t h models, however, the q u a l i t a t i v e c o n c l u s i o n s are common.  Perhaps the most s e r i o u s o m i s s i o n o f  the t h e o r y i s i t s f a i l u r e t o take i n t o account the i n d i v i d u a l i t y o f the r e a c t a n t s and l i g a n d s .  These are p r o b a b l y r e f l e c t e d i n the ^ F °  v a l u e s , but  t h i s term v a n i s h e s i n exchange r e a c t i o n s .  R e c e n t l y Hush (29) to t h a t o f Marcus.  has p r e s e n t e d a t h e o r y which i s q u i t e s i m i l a r  I n t h i s t h e o r y the parameter, m,  which Marcus i n t r o d u c e d  as a L a g r a n g i a n m u l t i p l i e r , t a k e s on the p h y s i c a l s i g n i f i c a n c e o f an e l e c t r o n probability density.  12,  PART I  THE KINETICS OF THE OXIDATION OF URANIUM ( I V ) BY THALLIUM  (III)  Introduction  I n many redox r e a c t i o n s oxidation  a t l e a s t one o f the r e a c t a n t s  s t a t e by more than one u n i t .  changes i t s  The r e s o l u t i o n o f the o v e r a l l  mechanism i n t o elementary s t e p s makes i t p o s s i b l e t o determine how many electrons  are t r a n s f e r r e d i n a s i n g l e  The  question  o f one v e r s u s two e l e c t r o n t r a n s f e r s has been d i s -  cussed f o r some time. inorganic  K i r k and Browne (30) f i r s t c l a s s i f i e d  o x i d i z i n g agents a c c o r d i n g  t i o n s with hydrazine, and  step.  t o the s t o i c h i o m e t r i e s  a number o f o f t h e i r reac-  H i g g i n s o n , S u t t o n and Wright (31, 32, 33) c l a r i f i e d  expanded t h i s c l a s s i f i c a t i o n ,  the p r o d u c t s o f the o x i d a t i o n  H i g g i n s o n and M a r s h a l l  of sulfurous  (34) showed t h a t  a c i d a l s o depended on t h e n a t u r e  o f the o x i d i z i n g agent.  T h i s d i s c r i m i n a t i n g a c t i o n can be r e p r e s e n t e d s c h e m a t i c a l l y  i n the  f o l l o w i n g manner,  The  1.  S(n)  >  S(n+1)  2.  2S(n+l)  >  |[S(n+l)J  3.  2S(n+l)  )  S(n+2)  4.  S(n+1)  >  S(n+2)  5.  S(n)  >  S(n+2)  substrate,  S, e x i s t s i n o x i d a t i o n  2  +  S(n)  s t a t e n,  o x i d i z i n g agent produces t h e r a d i c a l , S ( n + l ) ( S t e p l ) .  A one-equivalent T h i s r a d i c a l may then  13. d i m e r i z e (Step 2 ) , d i s p r o p o r t i o n a t e (Step 3 ) o r undergo a f u r t h e r onee q u i v a l e n t o x i d a t i o n (Step 4 ) . on S(n) w i l l produce  Thus a o n e - e q u i v a l e n t o x i d i z i n g agent  two p r o d u c t s S(n+l)2 and S(n+2).  o x i d i z i n g agent w i l l produce  acting  A two-equivalent  o n l y one product, S(n+2) (Step 5 ) .  With h y d r a z i n e t h e i n i t i a l p r o d u c t s are n o t s t a b l e and f u r t h e r reactions follow. agents produce  The t w o - e q u i v a l e n t agents produce Ng and t h e o n e - e q u i v a l e n t  both N2 and NH^.  Two-equivalent  N  2H  .  N  N  —>  N H 2  -— >  N H  —>  N H  —>  N  H  2  3  N H 2  2N H  (b)  2  N  4 6  "—  H  + 2H  +  +  H  +  3  +  H  +  2  2  2  +  2  — >  3  + 2H  2  —>  2 4  N H  (a)  2  -  ¥*2 One-equivalent  N H  -— >  4  H  +  H  N  + 2NH  2  The o x i d a t i o n o f s u l f u r o u s a c i d produces  Two- e q u i v a l e n t  so ~  One-equivalent  S0  2  3  3  2  "  -  so  — >  On t h e b a s i s o f t h e observed  suli  (so/ ) -  3  3  —>  3  3  so "  -— >  2S0 ~  +  4 6  N  •  +  2  H  +  S  2°6 " 2  s t o i c h i o m e t r i e s three c l a s s e s o f  o x i d i z i n g agents were d i s t i n g u i s h e d .  One-equivalent%  C e ( l V ) , C o ( l I I ) , F e ( l l l ) , OH  Two-equivalent»  I  2  , B r , C l , BrO", B r 0 " , 2  2Mixed-equivalentt  ^ 2°7 T  3  2  I 0 " , HgO.,, 3  ?«.  » 4. Ma0  »  P^Ol^  , V0  -42  T  1  (  1  1  1  )  H . From these and o t h e r o b s e r v a t i o n s  H i g g i n s o n and M a r s h a l l  put f o r t h  these g e n e r a l i z a t i o n s * 1)  Redox r e a c t i o n s between two t r a n s i t i o n metal i o n s u s u a l l y occur i n one-equivalent  2)  steps.  Redox r e a c t i o n s between d e r i v a t i v e s o f two n o n - t r a n s i t i o n elements u s u a l l y o c c u r i n t w o - e q u i v a l e n t  3)  steps.  Redox r e a c t i o n s between t r a n s i t i o n metal i o n s and d e r i v a t i v e s o f n o n - t r a n s i t i o n elements may o c c u r i n e i t h e r one- o r twoequivalent  s t e p s w i t h the o n e - e q u i v a l e n t mechanism predomi-  nating. U)  I f one o f the r e a c t a n t s  i s a free radical  a one-equivalent  r e a c t i o n i s more l i k e l y .  From a c o n s i d e r a t i o n o f the c h a r a c t e r i s t i c s o f t h e o x i d a t i o n reduct i o n r e a c t i o n s of organic  compounds,  p a r t i c u l a r l y quinones, M i c h a e l i s  proposed t h a t any o x i d a t i o n has t o proceed i n s u c c e s s i v e u n i v a l e n t w i t h the f o r m a t i o n  of free r a d i c a l s .  n o t n e c e s s a r i l y so w i t h e i t h e r o r g a n i c  (35)  steps, i . e .  Westheimer (36) has shown t h a t t h i s i s or i n o r g a n i c r e a c t i o n s .  He a l s o  p o i n t s o u t t h a t t h e r e i s p r o b a b l y no t h e o r e t i c a l grounds f o r o b j e c t i n g t o a two e l e c t r o n t r a n s f e r between i o n s i n p o l a r s o l v e n t s .  The major o b j e c t i o n  to a two e l e c t r o n t r a n s f e r appears t o have a r i s e n through the assumption such a t r a n s f e r i s v e r y improbable quantum m e c h a n i c a l l y  (e.g. 3 7 ) .  that  I f atom  t r a n s f e r i s i n v o l v e d , even i n d i r e c t l y as w i t h s o l v e n t m o l e c u l e s , t h e r e would appear t o be no r e s t r i c t i o n on the number o f e l e c t r o n s t r a n s f e r r e d . connection,  both theory  In t h i s  and experiment put the c r o s s s e c t i o n f o r two e l e c t r o n  t r a n s f e r between r a r e gas atoms and t h e i r i o n s lower by o n l y  a factor of 2 to  4 than f o r the c o r r e s p o n d i n g s i n g l e e l e c t r o n t r a n s f e r ( 3 8 ) .  S h a f f e r compared the r e l a t i v e r a t e s o f s e v e r a l redox r e a c t i o n s and  15. was moved to enunciate a p r i n c i p l e of equi-valence change (39,  4-0).  This  states that only those reactions w i l l be f a s t i n which the oxidation states of the reactants change by an equal number, i . e . complementary reactions. Non-complementary reactions were considered to be slow i n the absence of catalysts.  For example, Ce(lV) i s reduced to C e ( l l l ) very r a p i d l y by the  one-equivalent reducing agents T i ( l I I ) , F e ( l l ) , Br".  On the other hand the 2+  actions of the two-equivalent  agents T l ( l ) , A s ( I I l ) , Hgg  S i m i l a r l y the reductions of T l ( l l l ) by S n ( l l ) , H g those by F e ( I l ) and T i ( l l l ) are slow.  2 + 2  , H^POg  B T Q  slow.  , ^ 8 0 3 are f a s t while  One implication of t h i s p r i n c i p l e i s  that reactions between two-equivalent reactants involve the transfer of two electrons i n one step. In e f f e c t , the p r i n c i p l e of equi-valence change states that noncomplementary reactions are slow because they must proceed through a termolecular mechanism or through the formation of unstable valence states. + simple mechanisms are i l l u s t r a t e d below f o r the oxidation of A the reduction of B * to B 2  1)  Termolecular  2)  2A + B > 2A + B Bimolecular, i n i t i a l one-equivalent step +  A  +  A  3)  g2+  +  +  +  B  +  > >  A  2+ A  +  + B  +  2 +  B  Bimolecular, i n i t i a l two-equivalent step  A A 4)  2 +  2 +  +  +  +  B*  >  A  +  A  >  2A  2  3 +  +  3 +  B  2 +  Bimolecular, i n i t i a l disproportionation 2A A  +  B  +  2 +  >  A  >  A  + 2 +  A +  2 +  B  Four 2+  to A  and  16. The main f a i l i n g o f the p r i n c i p l e i s t h a t i t i g n o r e s o t h e r f a c t o r s and i t i s not s u r p r i s i n g t h a t t h e r e are many e x c e p t i o n s .  Remick  (41)  3+ suggested  t h a t the f a s t o x i d a t i o n s o f S n ( I I ) by C e ( l V ) , F e ( p h e n )  and  3  3_ Mo(CN)g Halpern  are due (42)  to the l a r g e d i f f e r e n c e s i n p o t e n t i a l s o f the  has g i v e n examples and has suggested  couples.  other f a c t o r s o f  importance.  F o r example, the r a t e o f o x i d a t i o n o f F e ( I l ) by T l ( l l l ) i s i n t e r m e d i a t e between the c o r r e s p o n d i n g  i s o t o p i c e l e c t r o n exchange r e a c t i o n s .  This  was  a t t r i b u t e d t o the more p o s i t i v e e n t r o p y o f a c t i v a t i o n f o r the mixed r e a c t i o n . Another f a c t o r i s t h a t the mixed r e a c t i o n has  a n e g a t i v e f r e e energy change.  Another type o f v i o l a t i o n o f the p r i n c i p l e i s t h e r e d u c t i o n o f Cu  (43).  by Hg  determining  R e a c t i o n by e i t h e r mechanism 2 o r 3 would g i v e as the r a t e  step  or  Cu  2 +  +  Hg  »  Cu  Cu  2 +  +  Hg  >  Cu  +  +  +  H  +  2H  +  +  H  (^H°  = 54  Kcal)  (AH°  = 66  Kcal)  but the a c t i v a t i o n energy i s o n l y 26 K c a l , The  p o s t u l a t e d mechanism i s Cu  2 +  CuH  +  +  Hg  +  Cu  2 +  CuH  +  +  H  +  > 2Cu  +  +  H  +  The d e t e r m i n i n g f a c t o r here i s the s t a b i l i z a t i o n o f the i n t e r m e d i a t e by  co-  v a l e n t bonding. R e a c t i o n s i n which both p a r t n e r s undergo a t w o - e q u i v a l e n t are w e l l known. two  However, i n o n l y a few  r e d u c t i o n o f C l O ^ " by SO^  a  cases have the k i n e t i c s supported  e l e c t r o n t r a n s f e r and t h i s i s accomplished  The  change  -  through  is first  group t r a n s f e r .  o r d e r i n each r e a c t a n t  and  18 by u s i n g G  H a l p e r i n and Taube {UU)  t r a n s f e r i n the r a t e d e t e r m i n i n g  step  showed t h a t t h e r e was  complete oxygen  17.  CIO3  +  SO3  4  >  C1CT  +  2  SD^  (4.5)' has shown t h a t the r a t e d e t e r m i n i n g s t e p i n the permanganate  Stewart  o x i d a t i o n o f b e n z h y d r o l i s the t r a n s f e r o f a h y d r i d e  (C H ) 6  5  Both U(IV) i t was  felt  o f two  electrons.  pertinent.  2  CHO"  and  +  MnC^"  Tl(lll)  >  ion.  ( 6 5% C  H  0 0  In t h i s context,  considered  a simultaneous two  t h a t t h e r e c o u l d be no  before  ^"  vent cage; a time o f the o r d e r o f I O  are  p r a c t i c a l d i s t i n c t i o n between  successive  the " i n t e r m e d i a t e "  one  electron transfers  c o u l d break out o f i t s s o l -  second.  - 1 1  S e v e r a l r e a c t i o n s i n v o l v i n g the o x i d a t i o n o f TI(lV) to U(VT) been s t u d i e d . with other dations  These i n c l u d e the i s o t o p i c exchange (4-6,  a c t i n i d e s , P u ( I V ) (48),  w i t h F e ( l l l ) (51)  Pu(VT) (49)  and C e ( l V ) (52)  0 (53), H 0 (54) 2  2  There i s one from the v a l e n t as  2  2  (56),  4  The  have a l s o been  p l u s a s s o c i a t e d water m o l e c u l e s .  oxiThe  reported.  , first  4 +  and  I t i s to be  hexa-  expected  w i l l show an i n v e r s e dependence  so.  - u ( V l ) exchange has  i n v e s t i g a t e d t h i s i n d i l u t e HC1 second o r d e r i n U  reactions  multi-equivalent  T e t r a v a l e n t uranium e x i s t s as U  t h i s i s found to be  The U(IV)  the  have a l s o been s t u d i e d .  CIO3" (55)  t h a t the k i n e t i c s o f the o x i d a t i o n o f on a c i d i t y and  and  have  f e a t u r e common t o a l l the r e a c t i o n s and which f o l l o w s  c h e m i s t r y o f uranium. TO  and  47)  and Np(VI) (50).  k i n e t i c s o f the r e a c t i o n s w i t h the non m e t a l l i c and o x i d i z i n g agents  and  simultaneous t r a n s f e r  the remarks o f Westheimer (36)  e l e c t r o n t r a n s f e r and  i f t h e second f o l l o w e d  m n 0  are n o r m a l l y t w o - e q u i v a l e n t r e a c t a n t s  t h a t t h e i r r e a c t i o n might w e l l i n v o l v e the  He  +  some i n t e r e s t i n g f e a t u r e s .  s o l u t i o n s and  o r d e r i n UO-j  and  Rona  found t h a t the r e a c t i o n  was  inverse f o u r t h order  H.  in  +  (47)  18. She suggested the mechanism  UOH  3+  + U0  2 + 2  +  0=0"(OH) - 0 U ( 0 H ) which explains the kinetics. dinuclear intermediate. result.  0=U(0H> - 0" - U(0H)  j—*  2^0  3 + 2  +  U0H  >  3+  3+ 2  +  2H  +  products  The interesting thing here i s the postulated  A" dinuclear U(IV) species would lead to the same  Newton (A-9) postulated a similar intermediate i n the U(IV) - Pu(Vl)  reaction although i t is f i r s t order in both reactants.  Very recently Newton  and Baker (57) have shown that the reduction of U(VI) by C r ( l l ) proceeds by way of an intermediate which w i l l reduce other oxidants. Masters and Schwartz (46) investigated the uranium exchange in perchloric acid.  They found that in addition to the path described by Rona  another path predominated at low TI(lV) levels and higher temperatures.  This  path i s described by the rate law Rate  =  k [U^ ][U0 +  2+ 2  ]  CH ] +  It leads to exchange through the formation of U(V) and involves the same activated complex as does the disproportionation reaction of U(V). The reactions of U(IV) with the other cations follow similar mechanisms which can be illustrated with respect to Fe(III) (neglecting the acid dependence). U(IV) U(V)  + +  Fe(lII) Fe(lII)  U(V) u(VI)  +  Fe(ll) +  F e  (n)  There i s no direct evidence for this sequence but the arguments are theses A two electron transfer as the rate determining step is unlikely since Fe(l)  19. and Ce(ll) are unknown. For the reactions involving Pu(Vl) and Np(Vl) the second step would be slow and the kinetics would be altered.  Granted the one  electron f i r s t step, the disproportionation of U(V) i n the second step i s unlikely as not being consistent with the known rate and steady state concentration. Except for the exchange reaction in dilute hydrochloric acid the foregoing reactions a l l show a rate increase with an increase of ionic strength.  They are subject to catalysis by sulfate, but not by chloride ions.  (The Fe(lII) reaction was not tested)'. The oxidation of U(lV )' by 0 r  2  and H 0 both appear to proceed by 2  2  chain mechanisms although the overall reactions are nearly second order ( f i r s t order in each reactant). The mechanism proposed by Halpern and Smith (53) for the oxidation with 0  2  is  u(iv)  +  U(T)  +  °2  "—>  °2  "  U(IV) + H0  u(v)  +  H0  U(V) •  +  +  -— >  u(v)  2  -— >  U(VI) + >  2  U(VI) + H0  2  TJ(IV) + *2°2 ~  H0  H  2  2°2  TJ(VI)  which accounts for the kinetics and the inhibition by Cl  and Ag . However,  Gordon and Taube (58) found that there i s complete transfer of oxygen from 0  2  according to the equation 2U  4+  +  0  2  +  H^O  > 2U0  2+ 2  The chain mechanism predicts at most 50$ transfer.  +  AH  +  20. The most interesting reaction of thallium i s the T l ( l ) - Tl(IIl) exchange reaction. I t has been studied by many workers who have emphasized different aspects. In common with many reactions there i s an acid dependent path so that the rate expression may be written Rate = k  [Tl jrTl +  Q  3 +  ]  + ^ [ T l ] [ T10H""] +  2  4  However, there has been lack of agreement as to which path i s the more important.  The very careful work of Roig and Dodson ( 5 9 ) i n 3M HCIO^ -  NaClO^ solutions result i n values of k 0.089  and k-^ equal to 0 . 2 5 3 M" h r " 1  c  1  and  M" h r " respectively. That i s , the rate increases as the acidity 1  1  i s increased.  This fact had been obscured before because of medium effects.  Gilks and Waind ( 6 0 ) have shown that the exchange rate decreases linearly with increase i n ionic strength.  Furthermore, substitution of HCIO^ for  NaClO^ increases the rate at a CIO^ concentration of 1.22M, has no effect at 3 . 0 M and decreases the rate at 6 . 0 M. available for this behaviour.  No convincing interpretation i s  I t may be related to changes in activity coef-  ficients or degree of hydration. The effects of chloride, bromide and cyanide ions on the exchange rate are similar.  As the concentration of halide ion i s increased the rate  decreases, passes through a minimum and then increases sharply.  This i s at-  tributed to complexing, the lower thallic complexes being less reactive and the higher thallic complexes and the thallous complexes being more reactive than the aquo ions.  Baysal ( 6 1 ) has determined the rate constants i n terms  of reactions between various complexes.  These are shown i n Table I.  In the case of bromide ion, exchange also occurs through the reversible oxidation of Br" by Tl(lII) ( 6 2 ) .  Table I  Exchange r a t e c o n s t a n t s f o r t h a l l i u m c h l o r o  Ionic strength  Exchanging S p e c i e s  Tl  +  Tl  +  Tl  +  Tl  +  --  Tl  •-  T1C1  • *  "  T 1 C 1  3  2  +  2 +  +  TICI3  +  Temperature 30.0°  Rate C o n s t a n t M"  8.22  X  IO"  3.5  X  10-5  1.06  X  10"  0  5.8  Tl T1C1 T1C1  3.0 M,  2  ••  TlCl^  •'  T1C1 " A  complexes  0.32 151  X  3  4  1  min'  22 S u l f a t e has k i n e t i c s are not i n v o l v i n g one  a pronounced c a t a l y t i c e f f e c t on the exchange and  simple,  and  three  64)  Brubaker e t a l (63, (but not two)  T i - cr  i n t e r p r e t the r e s u l t s as  s u l f a t e groups,  1  the  e.g.  2+  - s - 0 Tl 1 0  and (SD )T1 -  0  A  « 0 - S" - 0 - T1(S0,) 1  2-  4  0 The  reduction  o f T l ( l I I ) by F e ( I I ) has  several investigations. and  The  i n i t i a l rate i s f i r s t  T I ( I I I ) , but the r a t e f a l l s  Higginson (66) A two  a l s o been the  o f f above 60%  showed t h a t t h i s was  due  subject  of  o r d e r i n each o f F e ( I l ) (65).  reaction  Ashurst  and  to i n h i b i t i o n by the product F e ( I I I ) ,  s t e p mechanism w i t h the f o r m a t i o n of T l ( l l )  explains  the k i n e t i c  behaviour. TI(III)  +  Fe(II)  ^  "-1 T1(II)  +  T1(II)  Tl(l).  The  +  Fe(III)  e l e c t r o n s t e p i s r e j e c t e d as the r a t e i s not a f f e c t e d by  a c i d dependence shows two  paths i n v e r s e f i r s t  + in H ,  Fe(III)  Fe(II) T1(I)  An i n i t i a l two  +  and  adding  second o r d e r  2The  reaction i s accelerated  t i o n , but Duke and  Bornong (67)  the r a t e a g a i n i n c r e a s e d  by SO^  .  C h l o r i d e i o n i n h i b i t s the  found t h a t a t h i g h e r c h l o r i d e  reac-  concentrations  r i s i n g above the c h l o r i d e f r e e r a t e and  then l e v e l i n g  off.  They I n t e r p r e t t h i s as b e i n g caused by complexing o f the T l ( I l ) and  con-  clude  t h a t s i n c e the T l ( l ) - T l ( l I I ) exchange behaves i n a s i m i l a r manner i t  23. must a l s o I n v o l v e T l ( l l ) . explained  s i m p l y by  T h i s does not f o l l o w as the l e v e l i n g o f f i s  assuming complete c o n v e r s i o n  so t h a t f u r t h e r C l " has  no  o f T l ( l l l ) t o , say,  TlCl^  effect, 2+  Irvine apparently  (68)  examined the  proceeds i n two  by c h l o r i d e i o n . with increased  Unlike  by C o ( I I l ) ,  s t e p s and  by T l ( l l l ) .  3  t h i s may  be  H i g g i n s o n (69)  slightly  a medium e f f e c t ,  also studied  the o x i d a t i o n o f T l ( l )  T h i s r e a c t i o n a l s o appears to proceed through the  of T l ( I l ) according  It  l i k e the F e ( l l ) r e a c t i o n , i s i n h i b i t e d  the F e ( I I ) r e a c t i o n the r a t e i n c r e a s e s  a c i d i t y , but  A s h u r s t and  oxidation of Os(bip)  formation  t o the mechanism k  Co ( I I I )  +  T1(I)  Co(lll)  +  T1(II)  l  Co(II)  +  T1(II)  — C o ( l l )  +  TI(III)  ko  The  oxidation  pern (70) i s b e s t law  can  of H g ( l )  explained  be d e s c r i b e d  by  by the  by T l ( l I I ) s t u d i e d  2  a two  by Armstrong and  e l e c t r o n t r a n s f e r mechanism.  Hal-  The  expression  - dfrl(IIll) d  k'[Hg(l) ][Tl(Hl)]  =  2  [Hg(ll)][H ]  t  +  T h i s i s c o n s i s t e n t w i t h a r a t e d e t e r m i n i n g r e a c t i o n between T l ( I I l ) and formed by the H g ( I )  2  dismutation 2+ Hg  Hg  +  rate  equilibrium, 2+  s.  Hg  2  T10H " " 2  1  Hg(0)  +  Hg " " 2  1  Hg " -  +  T l  +  +  OH**  I n c o n t r a s t to o t h e r T l ( l I I ) r e a c t i o n s c h l o r i d e i o n i n c r e a s e s the r a t e , ' 2+ presumably by complexing w i t h Hg and s h i f t i n g the e q u i l i b r i u m to the r i g h t .  24. There i s a l s o a r e t a r d i n g e f f e c t o f p e r c h l o r a t e  i o n which may  be due  to  of a  two  2+ complexing w i t h H g  •  2  Another r e a c t i o n o f T l ( I I I ) which may  proceed by way  e l e c t r o n t r a n s f e r s t e p i s the o x i d a t i o n of C r ( I l ) .  Ardon and P l a n e  found t h a t the chromium p r o d u c t i s a d i n u c l e a r C r ( l I I ) s p e c i e s lowing steps  are  and  (71) the  fol-  suggested  Cr(Il)  +  TI(III)  >  Cr(IV)  Cr(II)  +  Cr(lV)  >  Cr(IIl)  Alternatively, dlmerization  +  2  Tl(l)  2  c o u l d precede the o x i d a t i o n ,  2 Cr(ll)  Cr(ll)  +  Cr(II)  Tl(III)  >  2  Cr(III)  A k i n e t i c study c o u l d d i s t i n g u i s h between these  e.g.  2  +  Tl(l)  possibilities.  H i g g i n s o n e t a l (72) have examined the o x i d a t i o n o f V ( l I I ) and V(IV)  by T l ( I I I ) .  I t was  of a two-equivalent step. n o t determined.  i s preferred  thought t h a t the V ( l l l ) r e a c t i o n might make use T h i s i s a v e r y f a s t r e a c t i o n and  However, the mechanism  TI(III)  +  V(III)  >  T1(II)  +  V(I?)  T1(II)  +  V(III)  >  T1(I)  +  V(IV)  +  V(III)  >  T1(I)  >  2V(IV)  over  TI(III)  V(V)  c h i e f l y because no  +  V(V)  V(III)  is  detected.  +  V(V)  the k i n e t i c s were  25. The apparently  V(IV)  r e a c t i o n i s slow and must be c a r r i e d out above 60'. I t  proceeds i n a manner analogous t o the F e ( I I ) r e a c t i o n and the f o l -  l o w i n g mechanism i s proposed  TI(III)  +  V(IV)  T1(II) k  T1(II)  +  V(I7)  k  +  V(V)  - l  2>  T1(I)  +  V(V)  C o m p l i c a t i o n s a r i s e from t h e slow decomposition o f T l ( l l l ) ,  TI(III)  +  H 0  >  2  i o  T1(I) +  The u n e q u i v o c a l r e s o l u t i o n o f the f o r e g o i n g importance i n view o f S y k e s  1  contention  basis of t h i s contention  +  2H  +  r e a c t i o n i s o f some  (73) t h a t i t proves the e x i s t e n c e  o f a two e l e c t r o n t r a n s f e r i n the T l ( l ) - T l ( l l l )  The  2  exchange.  i s t h a t the T l ( l l l ) - V ( I V ) r e a c t i o n  at 8 0 ° has about t h e same r a t e as the T l ( l ) - T l ( I I l ) exchange ( l x 1 0 " % " min'--'- compared t o 5 x 1 0 " M""*" min"^). 4  a d d i t i o n o f T l ( l ) would c a t a l y s e  I t would be expected then t h a t t h e  the i n i t i a l d i s a p p e a r a n c e o f TI'(III) i f t h e  exchange r e a c t i o n u t i l i z e s T l ( I l ) as an i n t e r m e d i a t e . in  the r a t e o f t h e V(IV)  r e a c t i o n when t h e i n i t i a l  from zero to 0.13 M and, t h e r e f o r e , place  Sykes found no change  T l ( l ) c o n t e n t was v a r i e d  c o n c l u d e d t h a t the T l ( l ) - T l ( I I l )  takes  by a one s t e p two e l e c t r o n t r a n s f e r .  S i m i l a r arguments have been p u t f o r t h by Gryder and Dorfman They r e p o r t e d  on the o x i d a t i o n  o f T l ( l ) by C e ( I V ) i n 6 M HNO^ a t 54°.  e m p i r i c a l r a t e law i s  - d M l J The  1  =  k o  [  C e  (lV)]  +  k^CedV^TKl)]  r e a c t i o n i s i n h i b i t e d by C e ( l l l ) , but n o t by T l ( I I I ) .  (74-). The  26. While Gryder and Dorfman may be c o r r e c t i n assuming e i t h e r a two e l e c t r o n T l ( l ) - T l ( l l l ) exchange o r a two e l e c t r o n C e ( I V ) - T l ( l ) r e a c t i o n it  i s difficult  data.  t o a s s e s s t h e i r c l a i m because o f t h e p a u c i t y  There are q u i t e  reaction  l i k e l y r a d i c a l s involved  o f experimental  i n the Ce(IV) - T l ( l )  (75) which can l e a d t o q u i t e c o m p l i c a t e d mechanisms.  Traces o f  c h l o r i d e would i m m e d i a t e l y d e s t r o y t h e argument as c h l o r i d e i n h i b i t s the exchange r e a c t i o n , b u t c a t a l y s e s  Sykes  1  case i s on b e t t e r  mechanism f o r t h e V(IV)  The by  reaction.  grounds, b u t r e s t s h e a v i l y on t h e proposed  - T l ( l I I ) reaction.  non-metallic  a two e q u i v a l e n t  preted  (40) t h e o x i d a t i o n  r e d u c t a n t , f o r m i c a c i d , appears t o reduce  electron transfer.  Tl(IIl)  H a l v o r s o n and H a l p e r n (76) i n t e r -  t h e k i n e t i c s as p r o c e e d i n g v i a a T l ( l l l ) - HCOOH complex and p r e s e n t e d  s p e c t r a l evidence t o support t h i s .  S u b s e q u e n t l y H a l p e r n and T a y l o r (77)  showed t h a t t h e r e i s no a c i d independent p a t h so c o n s i d e r mediate i s a formate complex.  Tl  3  +  The mechanism i s r e p r e s e n t e d as  +  HCOOT1  Finally,  2+  HCOO"  HC00T1  >  H  +  +  Brubaker (78) has r e p o r t e d  a c i d s on t h e r a t e o f t h e U(IV)  C0  2  2 +  + T l  preliminary  subsequent t o t h e p u b l i c a t i o n o f t h i s work (79)} dicarboxylic  that the i n t e r -  +  results  (obtained  on t h e e f f e c t s o f some  - Tl(lll)  reaction.  Experimental  Materials  Uranium s o l u t i o n s were prepared i n a manner s i m i l a r t o t h a t o f Halpern and Smith (53).  Uranyl perchlorate  s o l u t i o n s were made by d i s s o l v i n g  an u r a n y l and  s a l t , u s u a l l y the n i t r a t e o r a c e t a t e , i n d i l u t e p e r c h l o r i c  p r e c i p i t a t i n g uranium p e r o x i d e by adding hydrogen p e r o x i d e .  p r e c i p i t a t e was then d i s s o l v e d  i n perchloric  acid.  2  2  T h i s gave a f i n e y e l l o w p r e c i p i t a t e which was washed s e v e r a l  while  stirring.  times by decan-  Water was added t o t h e p r e c i p i t a t e and t h e r e s u l t i n g s l u r r y was  heated t o b o i l i n g and allowed t o c o o l w h i l e s t i r r i n g . t a t e which c o u l d The  The peroxide  The most c o n v e n i e n t way  o f a c c o m p l i s h i n g t h e p r e c i p i t a t i o n was s l o w l y t o add 3% H 0  tation.  acid  T h i s gave a p r e c i p i -  be f i l t e r e d r e a d i l y u s i n g a medium s i n t e r e d  p r e c i p i t a t e was d i s s o l v e d  by b o i l i n g i n 3M HCIO^.  r e p e a t e d t w i c e t o ensure the removal o f f o r e i g n was  p r e c i p i t a t e d by u s i n g 30$ H 0  and  could  2  anions.  glass  filter.  The p r e c i p i t a t i o n was I f uranium peroxide  the r e s u l t i n g p r e c i p i t a t e was v e r y  2  slimy  n o t be f i l t e r e d .  Uranium (IV) the u r a n y l  solutions.  s o l u t i o n s were prepared by e l e c t r o l y t i c r e d u c t i o n o f The r e d u c t i o n  was c a r r i e d out u s i n g a g o l d  p l a t i n u m gauze cathode and a p l a t i n u m w i r e anode.  plated  The s o l u t i o n was kept c o l d  by immersion i n an i c e b a t h and was s t i r r e d m a g n e t i c a l l y d u r i n g the r e d u c t i o n . About 9056 r e d u c t i o n  was o b t a i n e d l e a d i n g  U ( I V ) , 0.02 M U(VI)  and 1.7 M HCIO^.  a period  o f s e v e r a l weeks.  o f the i n e v i t a b l e o x i d a t i o n  t o stock solutions  which were 0.22 M  These s o l u t i o n s were q u i t e  When t h e U(IV)  stable  over  c o n t e n t dropped t o o low because  by atmospheric oxygen, t h e s o l u t i o n was again r e -  duced.  Thallium (III) perchlorate Armstrong and H a l p e r n (70). a c i d and was o x i d i z e d  T h a l l i u m ( I ) s u l f a t e was d i s s o l v e d  t o T l ( I I l ) by sodium bromate.  by b o i l i n g and then brown t h a l l i c hydroxide. solved  s o l u t i o n s were prepared by t h e method o f  Excess bromine was removed  h y d r o x i d e was p r e c i p i t a t e d by a d d i n g sodium  The p r e c i p i t a t e was washed s e v e r a l  by b o i l i n g w i t h 6056 HC10,.  i n perchloric  times by d e c a n t a t i o n then d i s -  The p r e c i p i t a t i o n and d i s s o l u t i o n were  28. repeated twice.  The resulting solution was 0.50 M Tl(IIl) > 0.02 s  M T l ( l ) and  8.3 M HCIO^. Silver perchlorate was recrystallized several times from concentrated perchloric acid. Sodium perchlorate solutions were made by neutralizing reagent grade sodium carbonate with perchloric acid.  Sodium perchlorate from G. F.  Smith Chemical Company gave erratic results. A l l other chemicals were reagent grade and were used without further purification. Water redistilled from alkaline permanganate was used in preparing a l l reaction solutions. Analytical Uranium (IV) was determined by titration with a standard solution of Ce(IV) in sulfuric acid. ferroin as the indicator.  Osmium tetroxide was used as a catalyst and The Ce(lV) solution was standardized against pri-  mary standard ferrous ammonium sulfate. Total uranium was determined by passing the solution through a Jones reductor putting a l l the uranium i n the U(IV) state. of U(III) formed was quickly oxidized to U(IV) by air.  The small amount  The solution was then  titrated with Ce(lV). Thallium (I) was titrated with a standard KBrO^ solution using methyl orange as indicator.  The KBrO-j was standardized against primary  standard AsgO^.. Total thallium was determined by reduction of the T l ( l l l ) with sodium sulfite and titration with K B r 0 3 ^"' a  boiling.  ter  removal of excess SGFg by  29. Perchloric  a c i d c o n c e n t r a t i o n s were determined by t i t r a t i o n w i t h  sodium hydroxide s t a n d a r d i z e d a g a i n s t potassium a c i d p h t h a l a t e .  Allowance  was made f o r the m e t a l c o n t e n t i n c a l c u l a t i n g the a c i d i t y o f the m e t a l s t o c k solutions.  K i n e t i c Measurements  The m a j o r i t y o f the r e a c t i o n s were conducted i n the t h e r m o s t a t t e d c e l l compartment o f a Beckman DtT spectrophotometer. lowed the  The k i n e t i c s were f o l -  by d e t e r m i n i n g the l i g h t a b s o r p t i o n a t 6500 X which i s the maximum o f  U(IV) i o n .  I t was  e s t a b l i s h e d t h a t Beers' law i s obeyed and t h a t o t h e r  i o n s d i d not i n t e r f e r e a t t h i s wave l e n g t h .  A s o l u t i o n o f the same i o n i c  medium was used as the r e f e r e n c e s o l u t i o n .  In  c o n d u c t i n g an experiment the u s u a l procedure was  t o prepare  a s o l u t i o n o f T l ( l I I ) c o n t a i n i n g a p p r o p r i a t e amounts o f HCIO^ and NaClO^ and to  b r i n g t h i s s o l u t i o n to the d e s i r e d temperature i n a t h e r m o s t a t t e d water  bath.  A known volume o f t h e U ( l V ) s o l u t i o n , u s u a l l y one ml., was  then  added t o a known volume o f the T l ( I I I ) s o l u t i o n u s u a l l y about 50 ml. r e s u l t i n g r e a c t i o n s o l u t i o n was one cm.  absorption c e l l .  mined i n t e r v a l s .  q u i c k l y mixed and a p o r t i o n t r a n s f e r r e d t o a  The o p t i c a l d e n s i t y was  Zero time was  then r e c o r d e d a t p r e d e t e r -  taken as the time o f m i x i n g .  of m i x i n g , r i n s i n g and f i l l i n g the c e l l meter took about 15 seconds.  The o p e r a t i o n s  and p l a c i n g i t i n the s p e c t r o p h o t o -  The absorbency  a t z e r o time was  determined  r u n n i n g a b l a n k w i t h a l l components except the t h a l l i u m s o l u t i o n . temperature  The  i n the c e l l compartment was  c o n t r o l l e d to ± 0 . 1 °  by  The  C.  Some experiments were conducted by a l l o w i n g the r e a c t i o n to t a k e p l a c e i n f l a s k s c o n t a i n e d i n a t h e r m o s t a t t e d water bath.  Samples were w i t h -  drawn from time t o time and the o p t i c a l d e n s i t y measured a t 6500 X.  Identical  30. r e s u l t s were o b t a i n e d  w i t h both  procedures.  R e s u l t s and D i s c u s s i o n  Assuming t h a t the r e a c t i o n has the s t o i c h i o m e t r y r e p r e s e n t e d  U(IV)  and  +  TI(III)  >  assuming a l s o t h a t the r e a c t i o n i s f i r s t  U(V1)  +  by  T1(I)  o r d e r i n both U ( I V ) and  Tl(lll)  then the r a t e law takes the u s u a l form ( 8 0 ) ,  H  =  k(er - x ) (b - x )  This integrates to  sfLzuc)  l o g  b - a?  =  k  t  b(a — x )  a  :  Here x i s the d e c r e a s e i n r e a c t a n t c o n c e n t r a t i o n concentrations.  I n the p r e s e n t  and a and b are i n i t i a l  case where the r e a c t i o n i s f o l l o w e d by  measuring t h e o p t i c a l d e n s i t y o f the s o l u t i o n and U ( I V ) i s the o n l y  absorbing  s p e c i e s the i n t e g r a t e d e x p r e s s i o n may be w r i t t e n as  b - a  b/a D  or  Jt=~b I n these  expressions  l D g  a/b (D - Doo)  a and b are the i n i t i a l  11(111)'; r e s p e c t i v e l y .  concentrations  o f U(IV)) and  D i s the o p t i c a l d e n s i t y a t time t , D  time and 1 ^ i s t h a t f o r the completed r e a c t i o n .  The f i r s t  0  i s t h a t a t zero  expression  ponds t o T l ( I I l ) i n excess and the second t o an excess o f TI(IV). expression  i s the most c o n v e n i e n t  t o use and, consequently,  The  corresfirst  most experiments  31. were done w i t h the i n i t i a l i n i t i a l TJ(IV)  T l ( l I I ) c o n c e n t r a t i o n 2 to 3 times t h a t o f  concentration.  The  s t o i c h i o m e t r y was  checked by two  procedures.  ments the r e a c t i o n was  allowed  T l ( l l l ) was  the f i n a l T l ( l ) c o n c e n t r a t i o n was  i n excess,  t i t r a t i o n w i t h KBrO^.  was  tf(lV).  to go to c o m p l e t i o n .  In s e v e r a l e x p e r i -  In those  found to be e s s e n t i a l l y equal  When U ( l V ) was  by  initially, its  to the i n i t i a l  i n i t i a l l y i n excess,  found to be the same as the i n i t i a l  cases i n which  determined  A f t e r a l l o w i n g f o r the T l ( l ) p r e s e n t  f i n a l c o n c e n t r a t i o n was t r a t i o n of  the  concen-  the amount consumed  concentration of T l ( l I I ) ,  These  r e s u l t s are shown i n Table II.,  The 2.  second o r d e r n a t u r e  Both the o p t i c a l d e n s i t y and  been p l o t t e d . no  o f the r e a c t i o n i s demonstrated i n F i g u r e  The  the second o r d e r i n t e g r a t e d f u n c t i o n have  f a c t t h a t the r e a c t i o n went e s s e n t i a l l y to c o m p l e t i o n  a p p r e c i a b l e d e v i a t i o n from the l i n e a r second o r d e r p l o t suggests t h a t  products  U(VT)  and  T l ( l ) have no  to  16.7  x-:10" M and 3  of the r e a c t i o n i s g i v e n by  Here i t i s shown t h a t v a r i a t i o n o f U(IV) o f T l ( I I I ) from 5.0  e f f e c t on the second o r d e r r a t e  the  e f f e c t on the r e a c t i o n .  F u r t h e r c o n f i r m a t i o n o f the n a t u r e data of Table I I I .  with  x 10"  3  to 19.7  x IO  from 2.4 - 3  M had  the  x 10~  M  3  no  constant.  I n view o f the e f f e c t o f C l " on the r e a c t i o n s o f T l ( I I I ) i t s i n f l u e n c e was  i n v e s t i g a t e d here.  shown i n Table IV and F i g u r e  The  reagent was  are  i n c r e a s e d the r a t e decreased  reached a minimum a t a C l " / T l ( l l l ) r a t i o o f 2. i n c r e a s e d the r a t e very s l i g h t l y . r a t e i s due  The r e s u l t s  3.  As the c h l o r i d e c o n c e n t r a t i o n was  in  NaCl.  to the f o r m a t i o n  and  F u r t h e r a d d i t i o n s o f NaCl  I t seems v e r y l i k e l y t h a t the  o f T l ( I I l ) complexes, e.g.  T1C1  reduction and  T1C1„  .  32.  Table II Stoichiometry of U(IV) - Tl(IIl) reaction  HlV)  ±  M x 10 5.54 4.40 4.77 4.77 3.55 5.07 4.10 4.10 4.10 4.10 4.10 4.08 3.77 3.77  9.44 16.70 9.61 9.96 10.83 9.87  3  TKIII^  U(IV)  M x 10  M x IO  3  15.0 15.0 16.7 16.7 20.6 15.5 10.1 10.1 10.1 10.1 10.1 9.0 9.4 9.4  6.92 6.92 5.01 6.02 5.02 5.48  Tl(I)  f  f  M x IO  3  -  5.73 4.57 5.00 5.04 3.55 5.22 4.17 4.12 4.07 4.14 4.15 4.09 3.79 3.75  2.91 10.07 4.71 4.05 5.80 4.41  -  (a) R (b)  3  1.04 1.04 1.05 1.06 1.00 1.03 - 1.02 1.00 0.97 1.01 1.01 1.00 1.01 0.99 Ave. 1.02  Ave.  (a)  corrected for i n i t i a l T l ( l )  (b)  for excess T l ( l l l )  R = T1(I) /JJ(lV)  for excess U(IV)  R = T l l I I I ^ / f l K l V ^ - TJ(IV) )  f  1  f  1.06 1.04 1.02 1.02 1.00 1.00 1.02  Table I I I  E f f e c t of i n i t i a l  c o n c e n t r a t i o n s o f U(IV)  and  Tl(IIl)  on second o r d e r r a t e c o n s t a n t o f U(IV) - T l ( I I I ) r e a c t i o n Temperature 2 5 . 0 °  U(IV) M  MxlO  TI(III) 3  M x  10  3  k M'^in"  1  7.6 3.9 9.4 16.7 3.9 3.6 10.0 9.6 10.0  17.0 17.0 6.9 6.9 10.0 10.0 5.0 5.0 6.0'  0.58 0.53 0.72 0.67 0.59 0.59 0.58 0.59 0.61  2.88  5.5 4.4 10.8 9.9  15.0 15.0 5.0 5.5  0.56 0.54 0.55 0.60  2.82  4.3 4.1 3.8 2.4  7.7 9.0 9.4 9.0  0.60 0.63 0.59 0.56  (b) (b) (b)  4.0  19.7  0.52  (b)  3  2.94  Contained 3 . 3  x 10'%  U(VI)  R e a c t i o n s i n spectrophotometer, a l l o t h e r s i n f l a s k s and samples withdrawn f o r a n a l y s e s  (a) (a)  35.  Table IV  Effect of NaCl on rate of II(IV) - Tl(III) reaction Temperature 25.0°  HCIO^ 2.83 M  &(IV)  TI(III)  NaCl  M x 10"  M xlO"  M x 10"  4.1  9.0  0.0  0.629  4.1  9.0  1.5  0.553  4.1  9.0  2.9  0.414  4.1  9.0  5.9  0.297  4.1  9.0  8.8  0.124  4.1  9.0  11.8  0.054-  3.2  9.0  H.1  0.039  4.0  9.5  14.7  0.034  4.0  9.5  17.6  0.021  4.0  9.5  20.6  0.04.7  4.0  9.5  23.5  0.061  4.0  9.5  29.4  0.066  4.0  9.5  32.3  0.065  M'^-min"  1  36.  37. The  f a c t t h a t t h e r e i s no pronounced i n c r e a s e o f r a t e beyond the minimum  i n d i c a t e s t h a t the h i g h e r c h l o r o complexes are a l s o u n r e a c t i v e . t r a s t s w i t h the F e ( l l ) and  The  T h i s con-  T l ( l ) reactions.  b e h a v i o u r o f s u l f a t e , added as NagSO^, was  also studied.  n o t e d i n Table V and F i g u r e 4 s u l f a t e e x e r t s a c a t a l y t i c e f f e c t . higher sulfate concentrations  At  t h e r e i s c o n s i d e r a b l e s c a t t e r i n the  As  the  results.  However, the g e n e r a l t r e n d i s i n a c c o r d w i t h an a d d i t i o n a l p a t h which i s first  order i n s u l f a t e i o n .  T a b l e VI l i s t s  v a l u e s o f the second o r d e r r a t e c o n s t a n t  2+ when m e t a l p e r c h l o r a t e s were added. Small  amounts o f A g  i n r a t e was reason  +  N e i t h e r Cu  2+ n o r Hg  reduced the r a t e by about 30$,  had  2 +  2 +  The r e a c t i o n was  c a t a l y s e t h i s r e a c t i o n , whereas A g  examined.  d a t a f o r these  T h i s was  a t 1.76  M and  explanation.  i s an  2  (53).  o r T l ( l l l ) w i t h C10^" The  Both  inhibitor. the  adding v a r y i n g amounts o f sodium p e r c h l o r a t e . i n Table V I I .  The  second  i n c r e a s e s as the c o n c e n t r a t i o n o f sodium p e r c h l o r a t e i s  i n c r e a s e d as i s shown i n F i g u r e 5. e i t h e r U(IV)  +  by 0  done by h o l d i n g the p e r c h l o r i c a c i d con-  experiments are c o n t a i n e d  order r a t e constant  The  These c a t i o n s were chosen  e f f e c t o f v a r i a t i o n o f t h e i o n i c s t r e n g t h on the r a t e of  c e n t r a t i o n constant The  effect.  accomplished by i n c r e a s i n g the amount o f s i l v e r p e r c h l o r a t e .  f o r t h i s c u r i o u s b e h a v i o u r i s not known.  and H g  any  but no f u r t h e r r e d u c t i o n  because o f t h e i r e f f e c t on the r a t e o f o x i d a t i o n o f U(IV) Cu  obtained  There i s no evidence and  f o r complexing  of  a medium e f f e c t i s t h e most l i k e l y  e f f e c t i s i n the d i r e c t i o n p r e d i c t e d by the Debye-Huckel  t h e o r y f o r a r e a c t i o n between two  i o n s o f l i k e charge.  However, medium  e f f e c t s i n s o l u t i o n s o f h i g h i o n i c s t r e n g t h are not q u a n t i t a t i v e l y p r e d i c table.  As shown i n F i g u r e 5, l o g k v a r i e s l i n e a r l y w i t h the  o f NaClO^,  I t i s n o t c l e a r whether o r n o t t h i s has  any  concentration  significance.  Table V  Effect of NagSO^ on rate of U(IV) - Tl(III) reaction Temperature 25.0° HCIO^ 2.83M  TJ(IV) 3.19 x 1 0 * % H.(III) 9.04 x 1 0 " % k  N a ^  M x 10  3  M" min" 1  0.0  0.59  1.7  1.10  3.5  1.59  5.2  2.O4  7.0  2^30  7.8  3.06  8.7  2.95  9.6  3.16  10.5  2.80  11.3  3.37  14.0  3.61  1  39.  40.  Table VI Effect of some metal ions on rate of U(IV) - T l ( l l l ) reaction Temperature 2 5 . 0 °  U(IV) 3.5 x 10 M  HCIO^ 2.82 M  Tl(III) 9.0 x 10" M  Added Salt  A&CIO^  3  Concentration M x 10  ^ M" m i n  0.0  0.59  4  1  2  20  0.57  2  12  0.61  Cu(C10^) Hg(C10^)  -3  4.2  0.54  8.4  0.50  16  0.42  16.8  0.44  21.0  0. 48  21.0  0.42  33. 7  0.42i  34.0  0.38  52.6  0.42  68..1  0.38  84.1  0.41  -1  Table VII  Effect of NaC10 on rate of U(IV) - Tl(IIl) reaction 4  Temperature 25.0° HCIO^ 1.76 M  NaCIO  U(IV) 3.0 x 10 M -3  TI(III) 9.0 x 10" M 3  M" min1  0  O.64  O.84  0.92  1.29  1.20  1.71  1.34  2; 58  1.85  2.58  1.94  2.96  2.30  :  42.  43. The  r a t e o f the r e a c t i o n was  c o n c e n t r a t i o n o f HCIO^. o f HC10.  T a b l e s V I I I to X I I  on the second o r d e r r a t e c o n s t a n t  4  acid concentrations There was in  found to depend s t r o n g l y on show the e f f e c t of the at 16°, 20°  the r a t e becomes q u i t e f a s t and  considerable  s c a t t e r o f the low  and 2 5 ° .  the variation  A t the  low  s e n s i t i v e to i m p u r i t i e s .  a c i d r e s u l t s and t h i s was  p a r t , to the NaClO^ used i n a d j u s t i n g the i o n i c s t r e n g t h t o a  traced,  constant  value. The  v a r i a t i o n o f r a t e i s i l l u s t r a t e d i n F i g u r e 6 which shows  rate p l o t s obtained strength.  a t d i f f e r e n t HCIO^ c o n c e n t r a t i o n s  These p l o t s are t y p i c a l i n t h a t they  ordinate i n t e r c e p t .  No  t h i s o r o t h e r i m p u r i t i e s may  attempt was  constant  show a s m a l l ,  T h i s i n d i c a t e s t h a t t h e r e may  e r r o r i n the procedure.  and  ionic  positive,  have been a  systematic  made to remove d i s s o l v e d oxygen  have c o n t r i b u t e d .  Local high  and  concentrations  d u r i n g the i n i t i a l m i x i n g o f r e a c t a n t s would l e a d t o such z e r o time e r r o r s .  The f a c t t h a t the r a t e i n c r e a s e s as the a c i d i t y i s  decreased  s u g g e s t s a r a t e law o f the form  - d M l V } l  =  k[U(lV)][TKHl)]fH j" +  A c c o r d i n g l y the second o r d e r r a t e c o n s t a n t , a logarithmic plot. with  p l o t t e d against [ H J +  T h i s i s shown i n F i g u r e 7 and y i e l d e d a s t r a i g h t  a s l o p e o f -1.39.  law was  k, was  n  Since t h i s value  on line  o f n l i e s between 1 and 2 the r a t e  written  At the h i g h e r the simple  aquo i o n s U  4 +  a c i d i t i e s both U(IV) and T l  3 +  .  and  Tl(III) exist largely  as  As the a c i d i t y i s lowered some h y d r o l y s i s  Table VIII  Effect of HCIO^ on rate of U(IV) - Tl(lII) reaction Temperature 25.0° Ionic strength maintained at 2.88M with NaClO^ prepared from NaOH and HCIO^  TI(III)  U(IV)  HCIO^  k  MxlO  MxlO  M  M" min"  10.1  4.1  0.478  5.93  10.1  4.1  0.752  3.16  10.1  4.1  1.026  2.14.  10.1  4.1  1.300  1.54  10.1  4.1  1.57  1.21  10.1  4.1  1.85  1.01  20.1  4.1  0.698  2.83  20.1  4.I  0.754  2.98  20.1  4.1  0.808  2.70  20.1  4.1  2.29  0.70  20.1  4.1  2.56  0.62  20; 1  4.1  2.94  0..52  3  3  1  1  Table IX Effect of HCIO^ on rate of TJ(lV) - Tl(III) reaction Temperature 25.0° Ionic strength maintained at 2.82M with NaCIO 4  prepared from NapCXD- and HC10.  TI(III) MxlO  3  U(IV) M x 10  3  HCIO^  k  M  M'-'-min"  1  9.0  2.7  0.477  6.70  9.0  2.7  0.565  4.66  9.0  2.7  0.740  3.00  9.0  2.7  0.913  2; 15  9.0  2.7  1.44  1.23  NaClO^ from NaHC0 and HCIO^ 3  9.0  2.4  0.567  4.86  9.0  2.4  0.744  3.20  9.0  2.4  0.917  2; 53  Table X Effect of HCIO^ on rate of U(IV) - T l ( l l l ) reaction Temperature 25.0° Ionic strength maintained at 2.82M with NaClO^ prepared from recrystallized NagCO^ and HCIO^  TI(III) MxlO  3  U(;IV) M xlO  3  HCIO^ M  k M'^mln"  1  9.04.  2;  0.4-67  7.02  9.04.  a  2.41  0.556  5.45  9.04  2.41  0.731  3.74  9.04  2.41  0.906  2.78  9.04  2.41  1.43  1.40  9.04  2;41  2.82  0.563  Table XI Effect of HCIO^ on rate of TJ(IV) - Tl(III) reaction Temperature 20.0° Ionic strength maintained at 2,82 M with NaClO^ prepared from recrystallized NagCO^ and HCIO^  TI(III) M x 10  3  U(iy) M x 10  3  HC10. 4 M  k M^min"  9.04.  2,20  1.43  0.703  9.04  2.20  0.906  1.54  9.04  2.20  0.556  2.97  9.04  4.12  1.08  1.12  9.04  4.12  0.731  1.98  9.04  4*12  0.467  3.87  9.04.  3.42  2.83  0.294  1  Table XII  Effect of HCIO^  o n  r a t e  o  f  TT  ^ ^ " IV  T 1  (  I I : [  )  reaction  Temperature 16.0° Ionic strength maintained at 2.82 M with NaClO^ prepared from recrystallized NagCO^ and HC10,  TI(III) M  x 10  3  U(IV)) M X I O L ?  HCIO^  k  M  M~ min" 1  9-04  3.88  0.487  2.63  9.04  3.88  0.556  1.73  9*04  3.88  0.731  1.15  9.04  3.88  02906  0.878  9.O4  3.88  1.08  0.634  9.04  3.88  1.43  0.425  9.04  3.88  2.82  0.158  F i g u r e 6. Second o r d e r r a t e p l o t s a t 25.0 f o r v a r i o u s HC10, c o n c e n t r a t i o n s . a d j u s t e d to 2.8M w i t h NaClO^ a = [U(IV)]  = 2 . 4 x 10" M; 3  Q  b = [Tl(III)J  o  Time min.  = 9.0 x  10" M 3  Ionic  strength  50.  51.  w i l l occur' r e s u l t i n g i n the production of U 0 H  3+  and TIOH * ions. 2  I f , as i s  l i k e l y , these are the only species o f importance one can w r i t e f o r the t o t a l concentrations  fr(iv)] == and  [TI(III)]  [u ]  [UOH ]  4+  == [ T I  3 +  3 +  +  ]  +  [TIOH ] 2 +  -1  LV ] •  Then  +  -1  and  == [TI(III)] / f l + K  [Tl J 3 +  [H j +  T 1  4+  where  and K  are the h y d r o l y s i s constants o f u  3+  and T l .  The r a t e law then becomes -dfo(IV)]  [U(IV)][T1(III)] ( k j H + J + k,)  =  dt  '  -±-r  ([H J +  ~  +K )X[H ] +  tJ  +  K  n  )  In terms o f the experimental second order r a t e constant k  =  kjH*]  +  +  ^ m * ]  +  v  In order t o determine the constants k^ and kg the l a s t equation was w r i t t e n k ([H ] + y d X " ] + K +  1  T 1  )  =  k^H"*] + kg  and the l e f t hand side was p l o t t e d against ^ H J as shown i n Figure 8. The +  slope and i n t e r c e p t of t h i s p l o t y i e l d k^ and kg r e s p e c t i v e l y . The values o f and which were used are given i n Table X I I I , The values at 25° were taken from the l i t e r a t u r e (81, 82). The values at the other temperatures were c a l c u l a t e d u s i n g an enthalpy o f hydrol y s i s o f 11.0 kcal/mole.  This corresponds to the measured value f o r  52. (83, 84) and i s p r o b a b l y a r e a s o n a b l e e s t i m a t e f o r T l o f h y d r o l y s i s o f metal i o n s l i e i n the range 9 - 1 2  as most known heats  kcal/mole  (85).  Fortun-  a t e l y the e x t e n t o f h y d r o l y s i s o f both i o n s i s s m a l l so t h a t the k i n e t i c r e s u l t s are n o t s e n s i t i v e t o e r r o r s i n the h y d r o l y s i s c o n s t a n t s .  The r a t e c o n s t a n t s k-^ and kg are l i s t e d i n T a b l e XIV t o g e t h e r w i t h the a c t i v a t i o n parameters.  These parameters were c a l c u l a t e d from the  A r r h e n i u s p l o t s shown i n F i g u r e 9.  The c o m p a r a t i v e l y narrow temperature mental c o n d i t i o n s . i e n t l y maintained  The l o w e s t temperature  range was imposed by e x p e r i -  was t h a t w h i c h c o u l d be conven-  i n the spectrophotometer.  A t temperatures  h i g h e r than 2 5 °  a l a r g e v a r i a t i o n i n a c i d i t y c o u l d n o t be o b t a i n e d because the r a t e s i n low a c i d s o l u t i o n s were t o o f a s t t o f o l l o w . at a HCIO^ c o n c e n t r a t i o n o f 2,83 M.  The r e a c t i o n was f o l l o w e d up t o 40°  The observed  second  order r a t e constants,  k, are c o n t a i n e d i n T a b l e XV t o g e t h e r w i t h v a l u e s c a l c u l a t e d from k^ and kg. I t i s seen t h a t t h e agreement i s v e r y good.  The k i n e t i c evidence i s c o n s i s t e n t w i t h a simple one s t a g e , two electron t r a n s f e r step,  TJ(IV)  The  +  TI(III)  U(VI)  +  T1(I)  case where U(V) and T l ( I I ) are formed i n the r a t e d e t e r m i n i n g s t e p and  then r e a c t w i t h each o t h e r b e f o r e d i f f u s i n g from the " s o l v e n t cage" must be c o n s i d e r e d as k i n e t i c a l l y e q u i v a l e n t t o the one s t e p mechanism.  The  a l t e r n a t i v e i s a s i n g l e e l e c t r o n t r a n s f e r s t e p which must then  be f o l l o w e d by v a r i o u s f a s t r e a c t i o n s , e.g.  U(IV)  +  TI(III)  —  ^  U(V)  +  T1(II)  53.  1.0  2.0 H  F i g u r e 8. E f f e c t o f a c i d i t y on r a t e a t v a r i o u s I o n i c s t r e n g t h 2.9 M  temperatures,  54 Table XIII Z+ 3+ Hydrolysis constants of U and T l Temp °n  % M"  25  0.021  0.073  20  0.016  0.056  16  0.012  0.041  M  T1  Table XIV Kinetic data for the oxidation of U(IV) by Tl(III) Ionic strength 2.82 M o 20.0  25.0°  kcal/mole  ^H* kcal/mole  0.57  1.02  2. XI  19.7  24.6  0.67  1.17  2.13  16.0 k-LxlO^sec' 2 -1 kgxlO ,Msec 1  o  ^  F  ±  19.7  21.7  ^ e.u. S  ±  16.4 6.7  55.  o  10 /T Figure  r.  J.J  A  9. A r r h e n i u s p l o t s f o r r a t e c o n s t a n t s k i and k2 of U(IV) - T l ( I I I ) r e a c t i o n  the  Table XV Variation of rate of U(IV) - T l ( l l l ) reaction with temperature HC10  4  tJ(iv) ! x 10  3  2.83 M  TI(III)  Temp  k  M x 10  °C  M" min""  3  1  k calculi 1  M" min" 1  3.42 3.42  9.04 9.04  15.0 15.0  O.I4O  3.42 3.42  9.04 9.04  20.0 20.0  0.294 0.294  3.77 3.77  9.40 9.40  25.0 25.0  0.588 0.588  3.27 3.27  9.05 9.05  30.0 30.0  1.16 1.16  1.12  3.28 3.28  9.05 9.05  35.0 35.0  2.16 2.15  2.11  3.28 3.28  9.05  40.0 40.0  3.62  3.84  3.89  9.05  (a) Calculated using k from Table XIII.  x  O.I4O  and kg from Table XIV and  -  and K,  57. U(V)  +  U(IV)  TI(III)  >  TJ(VI)  T1(II)  >  U(V)  2U(V)  >  U(IV)  +  +  +  T1(II)  TI(III)  +  U(VI)  Such a scheme seems l e s s p l a u s i b l e f o r these 1)  reasons?  The k i n e t i c s were found to be q u i t e s t r a i g h t f o r w a r d w i t h  no  2+ s u g g e s t i o n o f competing s t e p s .  The i n s e n s i t i v e n e s s o f the r a t e t o Cu  and  2+ Hg  suggests t h a t no  behaviour of A g  +  a c t i v e i n t e r m e d i a t e s are p r e s e n t .  The  anomalous  i s n e i t h e r pronounced enough nor o f the t y p e t o be  expected  from a c h a i n mechanism. 2)  The f o r m a t i o n o f two u n s t a b l e s p e c i e s as the r a t e d e t e r m i n i n g  s t e p would p r o b a b l y r e q u i r e a h i g h a c t i v a t i o n energy.  The  enthalpy of f o r -  mation o f T l ( I l ) i s n o t known, but an upper l i m i t can be s e t from the d a t a of F e ( l l ) - T I ( I I I ) r e a c t i o n (65). Fe  +  2 +  Tl  The r a t e d e t e r m i n i n g s t e p i s 3  »  +  Fe  3 +  +  Tl  2  +  The e n t h a l p y of r e a c t i o n i s not known, but can be no h i g h e r than A H *  which  i s 17 k c a l / m o l e .  this  U s i n g the known v a l u e s (86) f o r the o t h e r e n t i t i e s  l e a d s to an upt>er l i m i t o f A H ^  for T l  2  +  o f 55 kcal/mole.  n o t much l e s s than t h i s , the c o r r e s p o n d i n g v a l u e f o r T l  I t i s probably i s 4?  kcal/mole.  Tl  +  The e n t h a l p y o f r e a c t i o n f o r  U  +  4 +  Tl  3  +  +  H0 2  can now  be determined  ponding  v a l u e f o r the complete r e a c t i o n  U  i s -12.5  kcal/mole.  4 +  as 44 kcal/mole,  +  Tl  3  +  +  21^0  >  TJ0  + 2  +  2  +  a g a i n an upper l i m i t .  >  U0  2 + 2  Thus, on e n e r g e t i c grounds the one  +  T l  4H  +  The c o r r e s -  +  +  4H  +  step r e a c t i o n i s  58. favoured.  T h i s i s a l s o i n l i n e w i t h the o b s e r v a t i o n s o f Newton and  Rabideau  (87) t h a t f o r a c t i n i d e elements,  lower e n t h a l p i e s o f r e a c t i o n c o r r e s p o n d  lower e n t h a l p i e s o f a c t i v a t i o n .  T h i s argument m i l i t a t e s a g a i n s t t h e  mation o f U(V)  to  for-  and T l ( l l ) as s e p a r a t e e n t i t i e s and thus supports a t r u e s i n g l e  s t e p mechanism.  S i n g l e s t e p r e f e r s o n l y to the e l e c t r o n t r a n s f e r o r v a l e n c e  change p r o c e s s .  There may  o f course be o t h e r r e a c t i o n s n e c e s s a r y f o r the  products t o assume t h e i r c o r r e c t c o n f i g u r a t i o n s .  3)  I n both the F e ( l l ) - T l ( l I I ) and the C o ( I I l ) - T l ( l ) r e a c t i o n s  which produce T l ( l l ) as an i n t e r m e d i a t e , the subsequent r e a c t i o n of i s slow enough t o a f f e c t the k i n e t i c s because the r e v e r s e o f the r e a c t i o n then becomes important.  I t i s c l e a r t h a t the one observed b e h a v i o u r .  such behaviour i s observed  s t e p p r o c e s s does correspond  I t cannot be s a i d t o be proven  such p r o o f i s p o s s i b l e . observance  No  Tl(ll)  initial i n this  with  case.  the  and i t i s d o u b t f u l t h a t  On the o t h e r hand i t c o u l d be d i s p r o v e n by  the  o f T l ( l l ) i n the r e a c t i o n .  As mentioned b e f o r e , t h e r e i s no way  o f d i s t i n g u i s h i n g between a  s i n g l e s t a g e , two e l e c t r o n t r a n s f e r and s u c c e s s i v e one which take p l a c e i n the " s o l v e n t cage".  electron  There i s , however, a fundamental  d i f f e r e n c e i n t h a t the l a t t e r s i t u a t i o n corresponds  t o two  I t i s i n t h i s c o n t e x t t h a t c l a i m s f o r the p r o o f of a two must be judged.  transfers  Thus the c o n t e n t i o n s o f Gryder  separate  electron  and Dorfman (7U)  events.  transfer and  of  Sykes (73) t h a t the T l ( l ) - T l ( l l l ) exchange r e a c t i o n does n o t i n v o l v e T l ( l l ) r e a l l y mean t h a t a f r e e T l ( I I ) i s not formed.  The e v i d e n c e c o n c e r n i n g the composition o f the a c t i v a t e d  complexes  and whether o r n o t i n n e r or o u t e r sphere mechanisms are i n v o l v e d can now examined.  be  59. There are two major (and perhaps o n l y ) a c t i v a t e d complexes i n perchlorate solutions.  These are  k U  and  4 +  TJ  4 +  +  T l  3  +  +  H,0  +  Tl  3  +  +  B^O  — ( U . T l ' O H )  (U'T1'0)  T h i s manner o f d e p i c t i n g a c t i v a t e d complexes was Rabideau (87) and  It  5 +  +  w i t h the l o s s o f a p r o t o n and  o t h e r water m o l e c u l e s  complex i s formed from Tr*  water m o l e c u l e .  present.  The  p o s i t i o n o f the a c t i v a t e d  The  There must  of course,  have been l o s t as the comk i n e t i c s t e l l s o n l y the com-  than path 2.  not be r e a l .  o f +5.  w i t h a charge  Complex 1 w i t h a charge  mole w h i l e complex 2 has  the most i m p o r t a n t  That i s , a complex w i t h a charge  20 e.u. more n e g a t i v e t h a n one the p r e s e n t case.  The u n c e r t a i n t i e s  a charge  o f +5 and  of  has  factor i n  o f -+6 i s about  T h i s i s the o p p o s i t e o f an e n t r o p y of -87  an e n t r o p y o f -96  n  3+  +  2  H  2  O  >  (U.T1.0H.0H)  5 +  +  e.u./  e.u./mole.  p a t h 2 i s w r i t t e n as  +  are  Newton and Rabideau p o s t u l a t e d  o f the a c t i v a t e d complex was  determining i t s entropy.  parameters.  are v e r y s i m i l a r w i t h path 1 h a v i n g a somewhat  such t h a t t h e s e d i f f e r e n c e s may  4+  be  varied.  , but a more p o s i t i v e A S  n  and  complexes w i t h r e s p e c t t o components whose concen-  parameters o f both paths  If  +  and T l  Not much can be s a i d w i t h r e s p e c t t o the a c t i v a t i o n  t h a t the charge  2H  protons.  There may,  p r o t o n s may  p l e x e s were formed or by p r i o r h y d r o l y s i s .  higher  +  i n t r o d u c e d by Newton  the o t h e r by l o s s o f two  be the r e s i d u e o f a t l e a s t one  The  H  has much t o commend i t .  s t a t e s s i m p l y t h a t one  t r a t i o n s can be  +  2H  +  60. the entropy of the complex becomes -80 e.u./mole. i s taken i n Z i S values. ±  The complexes (TJ.T1.0)  different (when they imply, say, an 0  This shows why interest 5+  and (TJ.T1»0H«0H) are 5+  group in one and two OH  the other) but are not experimentally distinguishable.  groups in  The entropy of acti-  vation i s experimentally accessible and thus might allow a choice between two activated complexes, but not between alternative formulations of the same complex.  The d i f f i c u l t y here i s that there i s no standard to which  values can be compared. There can be no real choice between inner and outer sphere mechanisms.  Z.+ 2+ Since the IT*" ion acquires two oxygen atoms i n becoming UOg  i t might be argued that a bridged complex would more easily allow this. This, 'however, i s not necessary as the loss of two electrons from the uranium atom would cause a strengthening of the ligand bonds and a loss of protons, e.g., HgO  - U  -T ^  - OHg  4+  2  o = U = 0**" + 4H 2  +  The catalytic effect of sulfate may be due to a bridged structure  U  /  0 0 \ / \ 5+ ST1 X  \ /\ / 0 and subsequent group transfer.  0  On the other hand, i t s effect may be to  make orbitals available which f a c i l i t a t e electron transfer.  This may or may  not require bridging. The catalysis of the reaction by 0H~ i s most easily interpreted as being due to the H released on going from U +  4+  to flOg "*", This must neces2  sarily occur whether or not a bridged mechanism i s involved.  The T l ( l ) -  61. T l ( I I l ) exchange which does n o t i n v o l v e  a change o f s t r u c t u r e i s o n l y  s l i g h t l y a f f e c t e d by OH".  The i n h i b i t i o n o f t h e r e a c t i o n by c h l o r i d e i s a t t r i b u t e d t o complexing with T l ( l l l ) , again unrelated  There appear t o be two f a c t o r s o f importance which a r e  d i r e c t l y t o i n n e r o r o u t e r sphere mechanisms.  s t a b i l i t y of T l ( l l l ) chloro reduction  complexes makes T l ( I I l ) much more r e s i s t a n t t o  i n a thermodynamic  z a t i o n o r Franck-Condon  sense.  The o t h e r f a c t o r i s the l a r g e r  These f a c t o r s a l s o a f f e c t the T l ( l ) -  and are markedly reduced when t h e c h l o r i d e c o n c e n t r a t i o n i s  s u f f i c i e n t t o cause a p p r e c i a b l e  complexing o f T l ( l ) .  r e a c t i o n , i n c r e a s i n g the c h l o r i d e concentration the  reorgani-  b a r r i e r which a r i s e s from t h e r e l a t i v e s t a b i l i t i e s  o f the T I ( I I I ) and T l ( I ) complexes. T l ( l I I ) exchange  The g r e a t  T l ( I I I ) does not i n c r e a s e  In the U(IV) - T l ( l I I )  beyond f u l l complexing o f  the r a t e because o f the s t r u c t u r a l d i f f e r e n c e  between U ( l V ) and U ( V I ) .  An attempt was made t o reduce H g ( l l ) w i t h U ( I V ) , b u t t h i s r e a c t i o n is  too slow t o f o l l o w .  U  4 +  +  At f i r s t  2Hg  +  2 +  sight this i s puzzling  2^0  >  U0  2 + 2  has a f a v o u r a b l e f r e e energy change o f -27 k c a l .  U  4 +  +  Hg  +  2 +  2^0  >  U0  2 + 2  +  since the r e a c t i o n  Hg  +  2 + 2  4H  +  However, t h e r e a c t i o n  +  Hg  a q  +  4H  +  has a ^ F ° o f -16 k c a l which w h i l e f a v o u r a b l e i s much l e s s than t h e -42 k c a l f o r t h e analogous T J  4 +  - Tl  3  +  reaction.  62.  PART I I  KINETICS OF THE HOMOGENEOUS OXIDATION OF CARBON MONOXIDE BY METAL IONS  Introduction  While carbon monoxide takes p a r t i n many c h e m i c a l r e a c t i o n s i t i s g e n e r a l l y c o n s i d e r e d t o be i n e r t toward common o x i d i z i n g agents.  The r e c e n t  s u c c e s s e s i n d e m o n s t r a t i n g the a b i l i t y o f c e r t a i n m e t a l i o n s and complexes t o r e a c t homogeneously w i t h hydrogen  i n solution  (88, 89) suggested t h a t  s t u d i e s w i t h carbon monoxide might prove f r u i t f u l .  The o x i d a t i o n o f carbon  monoxide d i f f e r s i n an important a s p e c t from t h a t o f hydrogen. o x i d e i s o x i d i z e d i n the c l a s s i c a l  parallel  Carbon mon-  sense by a c q u i r i n g an a d d i t i o n a l oxygen  atom w h i l e t h e o x i d a t i o n o f hydrogen  i n v o l v e s t h e s p l i t t i n g o f the molecule  with l o s s of e l e c t r o n s .  Carbon monoxide i s the s i m p l e s t , s t a b l e , h e t e r o n u c l e a r , d i a t o m i c molecule.  I t i s one o f the few compounds o f carbon e x h i b i t i n g an  v a l e n c e o f two.  apparent  F o r these reasons the s t r u c t u r e and p r o p e r t i e s o f carbon  monoxide have r e c e i v e d much a t t e n t i o n .  The p h y s i c a l p r o p e r t i e s of carbon  monoxide are r e m a r k a b l y s i m i l a r t o those o f n i t r o g e n ( 9 0 ) .  Langmuir (91) has  a t t r i b u t e d t h i s t o the f a c t t h a t these m o l e c u l e s are i s o s t e r i c , h a v i n g the same number o f atoms and e l e c t r o n s .  M u l l i k a n (92) has a s s i g n e d both m o l e c u l e s  the same c o n f i g u r a t i o n KK(zcr) (yo-) (xo-) (w7r) . 2  2  2  4  Moffitt  (93) and Sahni  have g i v e n t h e o r e t i c a l t r e a t m e n t s o f carbon monoxide which  are i n accord w i t h  a t r i p l y bonded s t r u c t u r e w i t h a s m a l l d i p o l e moment d i r e c t e d toward carbon atom.  (94)  the  R e c e n t l y , J a f f e and O r c h i n (95) have g i v e n a more q u a l i t a t i v e  63. discussion emphasizing hybridization effects.  This latter treatment i s more  satisfying i n that i t provides an explanation of the chemical differences between carbon monoxide and nitrogen. Much attention has been directed toward the structure and properties of the transition metal carbonyls.  Mond (96) discovered these compounds i n  1890, but only in the last few years has appreciable progress been made i n establishing their structure.  Richardson (97) and Chatt, Pauson and Venanzi  (98) have summarized the current status.  In the pure carbonyls the metal  atom attains the effective atomic number of the next inert gas.  This i s  borne out by the absence of monomeric carbonyls of metals with odd atomic number.  The implication of the rule i s that outer d orbitals are not used  in bonding.  This finds confirmation i n the tetrahedral structure of Ni(CO) 4  3  which must use sp  hybrid orbitals.  The lone pair on the carbon atom i s used  in forming sigma bonds, but these are relatively weak. Stabilization occurs, in part, because the empty pi orbitals of carbon monoxide can accept electrons from the metal thereby preventing the accumulation df negative charge on the metal. Dicobalt octacarbonyl has achieved considerable importance in the hydroformylation of "Oxo" process. 1  et al (99, 100).  The process has been reviewed by Wender  The mechanism may be described by the sequence Co (C0) 2  HCo(CO)^  +  RCH CH Co(C0)^ 2  2  RCH CH COCo(CO)  +  +  8  +  Hg  «  RCH=CH  2  CO  HC'o(CO),  >  2HCo(C0)^  > RCHgCHgMCO)^ > RCH CH C0Co(C0)'^ 2  2  > RCHgCHgCHO +  Co (C0) 2  8  64. The  s t e p l e a d i n g t o the p r o d u c t i o n o f the aldehyde might a l s o  RCHgCHgCOCoCCO)^  +  ^  >  RCh^CHgCHO  Carbon monoxide e x e r t s an i n h i b i t i n g e f f e c t and t h i s may  Cb (C0)g  +  2  CO  >  Co (C0) 2  +  be  HCo(CO)^  be due t o the r e a c t i o n  9  which r e d u c e s the c o n c e n t r a t i o n o f HCo(CO)^.  The f e a t u r e which i s o f i n t e r e s t here i s the i n s e r t i o n o f CO a metal-carbon bond.  between  There i s some doubt as t o whether t h i s i n s e r t i o n pro-  ceeds d i r e c t l y o r through one o f the CO groups a l r e a d y a t t a c h e d to the c o b a l t .  In the r e v e r s i b l e c a r b o n y l a t i o n o f m e t h y l manganese p e n t a c a r b o n y l ,  CH,Mn(CO) J p  c  +  CO  *  CR"oCOMn(CO )„  5  J  *  the a c e t y l c a r b o n y l group i s n o t t h a t which e n t e r s from the gas phase. was  shown by C o f f i e l d e t a l (101) by u s i n g C ^  tracer.  This  C a l d e r a z z o and C o t t o n  (102) b e l i e v e t h a t the r e a c t i o n proceeds by d i r e c t combination o f CO  and  CH Mn(C0)^, but have n o t p r e s e n t e d a d e t a i l e d mechanism. 3  The heterogeneous o f many i n v e s t i g a t i o n s . and L o n g f i e l d  (IO4).  o x i d a t i o n of carbon monoxide has been the s u b j e c t  The t o p i c has been reviewed by Katz (103) and Dixon  Only i n the h i g h temperature r e d u c t i o n o f metal o x i d e s  i s carbon monoxide o x i d i z e d w i t h o u t the use o f oxygen.  I n the m a j o r i t y o f the  low temperature c a t a l y t i c p r o c e s s e s s t u d i e d , metal o x i d e s have been u s e d catalysts.  as  The c o u r s e o f the o x i d a t i o n can proceed e i t h e r through r e a c t i o n o f  oxygen and carbon monoxide w h i l e one o r both r e a c t a n t s are chemisorbed  or  through r e d u c t i o n o f the m e t a l o x i d e by carbon monoxide f o l l o w e d by r e o x i d a t i o n o f the c a t a l y s t by oxygen.  Both t y p e s o f o x i d a t i o n have been observed w i t h the  second type b e i n g f a v o u r e d a t h i g h e r temperatures.  The low temperature  eata-  65. lysts are generally p-type or electron deficient semi-conductors. The homogeneous, solution oxidations of carbon monoxide have received very l i t t l e attention.  There was a flurry of activity around the turn of  the century perhaps prompted by the discovery of the metal carbonyls or by attempts to u t i l i z e the favourable energy change involved.  In any event l i t t l e  work of a quantitative nature was done. Among the metals which are reportedly produced by homogeneous reduction of aqueous solutions of their salts by carbon monoxide are gold, rhodium, ruthenium, iridium, platinum and palladium (105, 106, 107, 108, 109). The rate of the reaction with palladium i s fast enough so that i t was adopted as an analytical method for carbon monoxide (110, 111). The production of silver from ammoniacal solutions of silver nitrate has also been noted (107, 112).  In most of these cases the reactions may have been complicated by  heterogeneous reduction,  Phillips (108) reported what appears to be a homo-  geneous reduction of platinum (IV) chloride to a lower platinum chlorides metallic platinum was deposited only after a considerable period of time. Several investigators have reported on the oxidation of carbon monoxide by potassium permanganate (105, 109, 113 )i  Of these, Just and Kauko  (113) have presented the only reasonably detailed kinetic study of any of the homogeneous oxidations of carbon monoxide, Hofmann ( I I 4 ) patented the oxidation of carbon monoxide by chromic acid to which mercuric oxide had been added. Mermet (115) reported that a solution of potassium permanganate acidified with n i t r i c acid and containing silver nitrate was decolourized by carbon monoxide. Just and Kauko (113) determined the rate of reduction of permanganate by carbon monoxide in neutral solution at 15° and 25°.  They found that  66. the r e a c t i o n was f i r s t o r d e r i n both permanganate and carbon monoxide. T h e i r r e s u l t s g i v e r a t e c o n s t a n t s o f 0.070 M sec  1  - 1  sec"  1  a t 15° and 0.172 M  1  when t h e r a t e law i s e x p r e s s e d as  The a c t i v a t i o n energy i s 14.7 k c a l / m o l e .  Bauch, Pawlek and P l i e t h (116) have r e p o r t e d k i n e t i c study o f t h e r e d u c t i o n sulfate solutions.  the r e s u l t s o f a  o f A g ( l ) and C u ( l l ) by carbon monoxide i n  The A g ( l ) r e a c t i o n was c a r r i e d o u t a t temperatures o f  70 - 110° and CO p r e s s u r e s o f 5 t o 50 atmospheres. second o r d e r i n A g ( I ) and f i r s t  o r d e r i n CO.  The r a t e was found to be  The r e s u l t s were f i t t e d  to the  r a t e law  -  D  ^ (  T  ) J  = 1.3 x 1 0  When ammonium a c e t a t e  "  d  f f i ^  The r a t e i n c r e a s e for  1  ^  [Ag(I)3 P  6  2  C 0  exp(-l4,000/RT>  was added the r a t e i n c r e a s e d  = 6.0 x 1 0 [ A g ( l ) J P 4  2  C 0  both c o n d i t i o n s  1  and the r a t e law was  exp(-9300/RT)i  was a t t r i b u t e d t o the i n c r e a s e  M min"  M min"  1  i n pH, but the mechanism  was supposed t o be the same,  Ag  AgC0  2  +  +  Ag C0  +  +  2 +  CO  Ag  +  AgC0"  +  Ag C0  +  2 +  2  H 0 2  —k->  2A"g  +  C0  +  2  2H  +  2+ The r a t e d e t e r m i n i n g s t e p b e i n g the h y d r o l y s i s o f the Ag C0 2  not  c l e a r i f t h i s i s meant t o be r e a l o r schematic.  complex.  Itis  67. The r e d u c t i o n o f Cu(.II) was much s l o w e r and was done a t 160 and 10 - 4.0 atm.  o f CO i n s u l f a t e s o l u t i o n s .  - d [Cu(ll)]  2.6  =  190°  The r a t e e x p r e s s i o n was  x 10 [Cu(ll)] P 1 3  c 0  exp(-33,500/RT)  M  min"  1  The work d e s c r i b e d i n t h i s t h e s i s i s concerned w i t h the k i n e t i c s o f the o x i d a t i o n o f carbon monoxide by H g ( I l ) and permanganate.  Preliminary  t e s t s were conducted by b u b b l i n g carbon monoxide through aqueous p e r c h l o r i c acid solutions of Cu(II), A g ( l ) , H g ( l l ) , F e ( I I l ) , T l ( I I l ) , C r 0 2  Only H g ( l l ) and MnO^  were reduced and, c o n s e q u e n t l y , d e t a i l e d  confined to these ions.  and  MnO/.  s t u d i e s were  Research undertaken i n t h i s  laboratory  completed has shown t h a t carbon monoxide r e d u c e s A g ( l )  rapidly i n basic solutions. acid  "  I n no c a s e s were temperatures over 80° o r p r e s s u r e s  g r e a t e r than one atmosphere used. s i n c e t h i s work was  2 y  A d d i t i o n a l work has been done on t h i s system i n  solution.  Experimental  Materials  The CO  and C0-N  2  m i x t u r e s were r e a g e n t grade gases s u p p l i e d by the  Matheson Company, I n c . , E a s t R u t h e r f o r d , New  Jersey.  The CO  c o n t a i n e d 35  ppm  Hg and was used as r e c e i v e d .  N i t r o g e n used f o r e q u i l i b r a t i o n s was  s u p p l i e d by Canadian L i q u i d A i r  Company.  Mercury  ( I I ) p e r c h l o r a t e s o l u t i o n s were prepared by d i s s o l v i n g  a c c u r a t e l y weighed p o r t i o n s o f reagent grade mercury amount o f p e r c h l o r i c  acid.  ( I I ) o x i d e i n a known  The s t o c k s o l u t i o n s c o n t a i n e d a s l i g h t excess o f  68. acid.  Mercury ( I I ) oxide from both F i s h e r C h e m i c a l Company and from Baker  and Adamson Chemical Company was  used and gave i d e n t i c a l  results.  P o t a s s i u m permanganate s t o c k s o l u t i o n s were prepared grade m a t e r i a l .  The  s o l u t i o n s were b o i l e d and,  from  reagent  after standing f o r several  hours, were f i l t e r e d through washed g l a s s wool.  Deuterium oxide was I t was  s u p p l i e d by Atomic Energy o f Canada L i m i t e d .  d i s t i l l e d from a l k a l i n e permanganate b e f o r e use.  pared by Dr.  The DCIO^ was  J . F. Harrod by s u c c e s s i v e e q u i l i b r a t i o n s o f DgO  Other s o l u t i o n s and  chemicals  were prepared  pre-  w i t h HCIO^.  as d e s c r i b e d i n P a r t I ,  Analytical  The  concentrations  o f mercury ( I I ) s o l u t i o n s were checked  c a l l y by t i t r a t i n g w i t h ammonium t h i o c y a n a t e u s i n g an i r o n The  ammonium t h i o c y a n a t e was  S i l v e r was  periodi-  (III) indicator.  s t a n d a r d i z e d w i t h mercury ( I I ) o x i d e .  determined g r a v i m e t r i c a l l y by p r e c i p i t a t i o n as  silver  chloride.  Procedure  The and  g e n e r a l arrangement of the apparatus u s e d i n both the mercury ( I I )  permanganate r e d u c t i o n s i s shown i n F i g u r e 10.  used and d e s c r i b e d by Webster (117). was  The  CO  T h i s i s s i m i l a r to t h a t  a f t e r p a s s i n g through a flowmeter  l e d through the p r e s a t u r a t o r A c o n t a i n i n g a s o l u t i o n of the same concen-  t r a t i o n s o f HCIO^ and NaClO^ as the r e a c t a n t s o l u t i o n . the CO  entered  the r e a c t a n t s o l u t i o n c o n t a i n e d  c o n t a c t between the gas  and  s o l u t i o n was  From the  i n the v e s s e l B.  presaturator Effective  e s t a b l i s h e d by d i s p e r s i n g the  gas  70. through the sintered disc C near the bottom of the reaction vessel.  The gas  stream then continued out through the tube D and was fed into the air inlet of a Mekker burner to dispose of the unreacted CO. Sampling of the reaction solution was done by closing tap E and allowing the gas pressure to force the solution out through tap F.  Both the presaturator and the reaction vessel  were immersed i n a thermostatted water bath controlled to 0.1°. In the experiments with Hg(II), the concentration of Hg(l) formed was determined by pipetting a portion of the sample into a known volume of an Ig solution.  (Usually about 5 ml of sample was collected and 2 ml was taken  for determination of the Hg(l)).  The unreacted Ig was titrated with a thio-  sulfate solution standardized with KBrO^.. Soluble starch or Fisher "Thiodyne"' was used to determine the end points. were stable N  2  To ensure that the Hg(ll) solutions  was passed through for a time comparable to the length of the  run, usually 20 minutes, and samples were taken during this period. not necessary to know the exact concentration of the 1^ solution.  I t was The con-  centration of Hg(ll) remaining i n the solution at the time of sampling was calculated by means of the formula [Hg(Il)]  =  0 - (A - V) N/S  where 0 = original concentration of Hg(ll), M A = volume of SgO^  required to titrate a l l of the I , ml 2  V = volume of S^O^  -2  required at time t, ml  N = normality of SgO^ " 2  S' = volume of sample, ml Time zero was taken as the time when bubbles of CO appeared i n the reaction vessel.  Samples were withdrawn at predetermined intervals and the  sample time was that time at which tap E was closed.  Thus time zero was quite  71. a r b i t r a r y , b u t t h e time i n t e r v a l between samples was known t o w i t h i n  5 seconds.  In t h e f a s t e r runs t h e time i n t e r v a l between samples was 100 seconds.  I n i t i a l l y there  was some s c a t t e r o f t i t r a t i o n v a l u e s which w a s a t t r i 3  buted t o r e s i d u a l CO c o n t i n u i n g  t o r e a c t with H g ( l l ) .  T h i 3 was overcome by  adding i c e to t h e I g s o l u t i o n s and keeping t h e I g - H g ( I l ) s o l u t i o n s i n a r e f r i g e r a t o r u n t i l t h e end o f t h e r u n (about 30 m i n u t e s ) when t h e y c o u l d be titrated.  The  permanganate r e d u c t i o n s  formed i n t h e same apparatus u s i n g uncatalyzed  i n a c i d and n e u t r a l  s o l u t i o n s were per-  t h e same sampling t e c h n i q u e .  reaction i n acid solutions or neutral  F o r the  s o l u t i o n s w i t h added e l e c t r o -  l y t e , t h e suspended MnOg was e a s i l y removed by c e n t r i f u g i n g .  A known volume  o f t h e c l e a r s o l u t i o n was p i p e t t e d i n t o a potassium i o d i d e s o l u t i o n and t h e l i b e r a t e d i o d i n e was t i t r a t e d w i t h sodium t h i o s u l f a t e .  The permanganate con-  c e n t r a t i o n was c a l c u l a t e d from t h e f o r m u l a  [MnO,"]  =  4  VN 5S  where V = volume o f S g O ^ s o l u t i o n , ml -  N = normality  of S g O ^ solution  3" = volume o f sample, ml  With n e u t r a l  solutions containing  remained as a c o l l o i d u n i f o r m l y  no added e l e c t r o l y t e t h e MnOg  d i s t r i b u t e d i n the solution.  I n t h i s case  a c i d i f i e d p o t a s s i u m i o d i d e was.used and t h e t i t r a t i o n i n c l u d e d  both t h e un-  mm r e a c t e d MnO^  and t h e c o l l o i d a l MnOg.  made by means o f t h e e x p r e s s i o n  C a l c u l a t i o n o f MnO^  concentration  was  72. where  V  0  = volume of SgO^ solution before passing i n CO, ml.  In the Ag(l) and Hg(ll) catalyzed reductions of MnO^ by CO i t was found that MnOg formed remained in the solution as a uniformly dispersed colloidal suspension for a considerable period of time even with a perchloric acid concentration of one molar. the combined MnO^  Consequently, i t was possible to titrate  and MnOg.  In alkaline solutions the primary product i n the CO reduction of MnO^ was found to be MnO^ . Titrations of the combined MnO^~ and MnO^~ -  were erratic with unsatisfactory end points.  A better method of following  these reactions proved to be the measurement of the CO uptake at constant pressure.  The apparatus used for this purpose i s shown i n Figure 11. The  reaction flask A which can be immersed into a thermostatted bath i s connected by means of a flexible capillary tubing to the gas burette B i n a constant temperature bath.  The gas burette i s connected to a simple gas handling  system containing a manometer and connections leading to a vacuum pump and a gas cylinder.  In operation a known amount of alkaline permanganate solution  was pipetted into the reaction flask and degassed by repeated freezing and thawing under vacuum. solution.  The condenser C minimized loss of water from the  The degassed solution was then allowed to come to temperature  equilibrium under a low pressure of CO, usually about 100 mm.  CO was then  admitted to the system and the pressure adjusted to the desired value. The reaction flask was attached to a mechanical shaker and this shaker was then started.  Taps D and E were closed after a delay of about 10 seconds.  I t was  established that there was no uptake of CO by the quiescent solution. The rate of solution of CO was very much faster than the rate of reaction and i n i t i a l saturation of the solution was complete i n less than 10 seconds. CO was admitted to the burette through a needle valve to keep the pressure con-  F i g u r e 11.  Gas  absorption  apparatus  74. stant.  The c a p i l l a r y manometer F served as a pressure indicator.  As the  reaction proceeded the mercury rose i n the tube G and i t s l e v e l was measured from time to time by means of a v e r t i c a l l y mounted t r a v e l l i n g  microscope.  The diameter of the tube G was known so a d i r e c t measure of the volume of CO used was obtained. Ah attempt was made to measure the s o l u b i l i t y of carbon monoxide using the gas absorption apparatus. the accuracy was no better than 20%. range so they were used throughout.  Because of the small volumes involved The published values f e l l i n this The s o l u b i l i t y data used are given i n  Table XVI and have been adapted from Seidel (123).  Results and Discussion Oxidation of CO by H g ( l l ) Carbon monoxide i s oxidized by H g ( l l ) according to the equation CO  +  2Hg  2 +  +  H0 2  >  C0  2  +  Hg  2 + 2  There was no i n d i c a t i o n of further reduction of the Hg(I).  +  2H  +  The reaction  was found to be f i r s t order i n both CO and H g ( l l ) and to obey the rate law  --Jg9-  =k[co][H (ii)] g  Experimentally, the reactions were conducted under a constant CO pressure and the rate was followed by determining the concentration of Hg(Il). Log [*Hg(lI)J was plotted against time and the slope of the straight l i n e gave the pseudo f i r s t order rate constant, k'» order rate constant, k, by k = 2.303k' 2 [COl  This i s related to the second  75.  Table XVI  Solubility of CO i n water  Temperature °C  M/mm  CO' CO pressure x 10  (  0  2..08  2  1.98  4  1.89  6  1.81  8  1.73  10  1.66  13  1.55  16  I.46  20  1.36  25  1.26  30  1.17  35  1.11  40  I.O4  45  0.99  50  0.95  60  0.87  76. The f i r s t order rate p l o t s i n Figure 12 are f o r d i f f e r e n t concent r a t i o n s of Hg(II).  In a l l cases good s t r a i g h t l i n e s were obtained even when  the r e a c t i o n was allowed to proceed to over 90$ completion.  This i n d i c a t e s  that there was no f u r t h e r reduction of Hg(l) and that the Hg(l) produced had no i n f l u e n c e on the k i n e t i c s .  The p l o t s show an i n d u c t i o n period of about  one minute which i s probably the time necessary to saturate the s o l u t i o n s with CO. Tables XVII to XIX contain the r e s u l t s of experiments i n which the concentrations  of reactants, HCIO^ and NaClO^ were V a r i e d .  The r e s u l t s  of two experiments conducted i n DgO are also included. The f i r s t order character of the r e a c t i o n with respect to CO i s shown i n Figure 13. Here the f i r s t order rate constant, k', i s p l o t t e d against the p a r t i a l pressure o f CO. There was some v a r i a t i o n of the second order r a t e constant when the HCIO^ concentration was v a r i e d from 0.01 to 2.0 M.  The i o n i c strength was  maintained constant at 2.0 M by the a d d i t i o n o f NaClO^.  The v a r i a t i o n was not  l a r g e , but there was a d e f i n i t e minimum a t a HCIO^ concentration of about 0.2 M.  The i o n i c strength of the medium also had a small, but d e f i n i t e e f f e c t  on the rate as i n d i c a t e d i n Table XIX.  I t i s l i k e l y that the r a t e increase  with added NaClO^ which i s p a r a l l e l f o r HCIO^ concentrations of 0.01 and 0.2 M i s due to an increased s o l u b i l i t y of CO. by HCIO^ above 0.2 M  The increase as NaClO^ i s replaced  HCIO^ i s also probably due to a s o l u b i l i t y e f f e c t . A  s i m i l a r phenomenon has been encountered i n reactions of hydrogen (.119). The increase i n rate as the p e r c h l o r i c acid concentration i s r e duced below 0.2 M can be explained i n terms of a c o n t r i b u t i o n by an hydrol y z e d mercuric species,  S i l l e n (120) has shown that i n a pH range from about  78.  Table XVII  Effect of reactant concentrations on the rate of the CO - Hg(ll) reaction Temperature 40.. 0°  HCIO^  Hg(ll)  M  M x 10  P 2  k'  c o  atm  sec" xlQ  6.5  1  k 4  M^sec*  0.19 0.19 0.19 0.19  1.00 0.99 0.80 0.40  0.92 0.92 0.92 0.92  1.00 1.00 1.00 1.00  1.00 1.00 1.00 1.00  0.92 0.92 0.62 0.31  9.0  1.46 1.43  3.0  1.40  2.04  1.00 1.00 1.00 1.00 1.00 1.00  0.92 0.92 0.92 0.92 0.62 0.31  11.1 12.4 12.3 12.8 8.8 4.0  1.11 1.11  0.92 0.92  8.0 8.3  2.04 2.04  2.04  2.04 2.04  6.7  6.5  7.0  9.5  6.5  1.02 1.05 (a) 1.02 1.10  1.52  1.72 (b) 1.92 (c) 1.92 (d) 2.02 2.09 1.87  DC10 i n D 0 4  2.01 2.01  2  (a)  Reaction 95$ complete  (b)  Flow rate 0.24 l/min  (c)  Flow rate 0.60 l/min  (d)  Flow rate 0.90 l/min  1  1.22 1.29  T a b l e XVIII  E f f e c t o f HCIO^ on the r a t e o f the CO - H g ( l l ) r e a c t i o n I o n i c s t r e n g t h m a i n t a i n e d a t 2.0M Temperature 4O.O , 0  Hg(II) M x  10  HCIO^ 2  M  CO 0.92  w i t h NaClO^ atm  NaClO^ M  k M"  1  sec"  1.00  2.04  1.00  1.11  0.92  1.74  1.00  0.56  1.47  1.59  1.00  0.37  1.67  1.55  1.00  0.19  I.84  1.47  1.00  0.085  1.95  1.61  1.00  O.O48  1.99  1.65  1.00  0.011  2.03  1.80  -  1.77  1  Table XIX Effect of NaClO^ on the rate of the CO - Hg(ll) reaction Temperature 40.0°,  CO 0.92iatm  HCIO^  NaClO^  k  M  M  M^sec"  1.00 1.00 1.00 1.00  0.19 0.19 0.19 0.19  0..28 0.56 1.11  1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00  0.011 0.011 0.011 0.011 0,011 0.011 0.011 0.011 0.011 0.011 0. Oil 0.011 0. Oil  *g(II) 4 x 10  2  «.  0.014  0.014.  0.028 0.056 0.083 0.111 0.128 0.278 0.456 0.479 1.67  2.03  1.05 1.13 1.22 1.26 1.36 1.26 1.39 1.37 1.35 1.31 1.38 1.35 1.43 1.49 1.44 1.73 1.81  81.  12.0  8.0  4.0  CO  p r e s s u r e atm  F i g u r e 13. E f f e c t of CO p r e s s u r e on r a t e of CO - Hg(II) r e a c t i o n at Hg(II) 1.00  40.0°.  x 10" M; HC10. 2  2.04  M  82. 2  to 4 the c o n c e n t r a t i o n  present..  o f HgOH  cannot exceed 14$ o f t h e t o t a l  +  Hg(ll)  Thus, i t would be d i f f i c u l t t o e s t a b l i s h q u a n t i t a t i v e l y the e x i s -  tence o f a r e a c t i o n path i n v o l v i n g HgOH . +  The  temperature a t which t h e r e a c t i o n was c a r r i e d o u t was v a r i e d  over the range 2 5 ° t o 54° a t HCIO^ c o n c e n t r a t i o n s o f 1 and 2 M w i t h no added NaClO^.  The v a l u e s o f t h e v a r i o u s  be n e a r l y t h e same f o r both s o l u t i o n s  a c t i v a t i o n parameters were found t o  and a r e l i s t e d i n T a b l e XX,.  These  were c a l c u l a t e d from the d a t a g i v e n i n Table XXI and t h e A r r h e n i u s  plots  shown i n F i g u r e 14.  T a b l e XX  A c t i v a t i o n parameters o f t h e CO - H g ( I I ) r e a c t i o n  HC10  k  4  E  &  a t 40,0°  AP*  AH*  AS" e.u.  M  M^sec"^  kcal/mole  kcal/mole  kcal/mole  1.0  1.44  15.4  18.1  14.8  -10.6  2.0  2.00  14.2  17.5  13.6  -12.5  The  k i n e t i c s o f the r e a c t i o n r e v e a l t h a t one m o l e c u l e o f CO and  2+ one  Hg  i o n are p r e s e n t i n t h e a c t i v a t e d complex.  dependence of t h e r a t e on i o n i c s t r e n g t h tween an i o n and a n e u t r a l m o l e c u l e . concentration  i s consistent  w i t h a r e a c t i o n be-  The b e h a v i o u r o f t h e r a t e as t h e HC10  4  i s v a r i e d i n d i c a t e s t h a t t h e u n h y d r o l y z e d Hg " " i s t h e main  reactive species. but  The l a c k o f a pronounced  2  As p r e v i o u s l y  1  noted, a t low a c i d i t i e s HgOH may be i n v o l v e d , +  t h i s would appear t o p r o v i d e an a d d i t i o n a l path r a t h e r t h a n b e i n g t h e main  reactive species. involved.  Also  i t i s u n l i k e l y t h a t HgC10  4  o r s i m i l a r s p e c i e s are  Table XXI  E f f e c t of temperature on the CO - H g ( l l ) reaction  HC10  4  p  Hg(ll)  r  M  MxlO  1..00 1.00 1.00 1.00 1..00  1.00 1.00 1.00 1.00 1.00  2.04 2.04 2.04 2.04 2.04 2.04 2.04 2.04 2.04 2.04  1. 00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00  2  co  Temp  atm  °C  0.97 0.95  25.0  0.92  k M"  1  sec  0.92  40.0  40.0  0.42 0. 69 1.43 1.46  0.90  46.0  2.30  0.97 0.97  26.0 26.0 33.0 33.0 40.0 40.0 47.0 47.0 54.0  0.65 0.65 1.19 1.18 2.02 1.98 2.88 2.90 5.00 5.32  0.95 0.95 0.91 Cv91 0.89 0.88 0.84 .0.84  31.0  54.0  3.1  3.2 10 /T 3  °A  F i g u r e 14. A r r h e n i u s p l o t s f o r CO - Hg(II) A. LOOM  HC10  4  3  B. 2.04M  Hg(II) 1.00 x 1 0 " M 2  reaction. HCIO^  85. O x i d a t i o n o f CO by MnO^"  In dioxide.  or  acid  and n e u t r a l s o l u t i o n s permanganate was reduced  t o manganese  T h i s r e a c t i o n c a n be r e p r e s e n t e d by the f o l l o w i n g e q u a t i o n s  3C0  +  2Mn0^"  +  3C0  +  2Mn0^"  +  2H  +  fi^O  >  3C0  2  +  2Mn0  2  +  H^O  >  3C0  2  +  2Mn0  2  +  20H~  E x p e r i m e n t a l l y t h e r a t e o f permanganate r e d u c t i o n was measured.  This rate  can be e x p r e s s e d i n terms o f carbon monoxide o x i d a t i o n by  — The f i r s t  = "/2  = k[C0irMn0^ J  3  o r d e r e x p e r i m e n t a l r a t e c o n s t a n t , k', i s r e l a t e d to k by  k = 3/2 2.303k' [CO]  T a b l e s XXII and XXIII c o n t a i n the k i n e t i c d a t a o b t a i n e d i n a c i d and n e u t r a l s o l u t i o n .  I n g e n e r a l , these c o n f i r m t h a t the r e a c t i o n i s f i r s t  o r d e r i n both carbon monoxide and permanganate. t i o n s w i t h changes i n a c i d i t y o r i o n i c s t r e n g t h .  There were o n l y minor v a r i a Adding  a d d i t i o n a l manganese  d i o x i d e and v a r y i n g the gas f l o w r a t e had no e f f e c t thus d e m o n s t r a t i n g the homogeneous c h a r a c t e r o f the r e a c t i o n .  Some t y p i c a l r a t e p l o t s are shown i n F i g u r e 15.  The e f f e c t o f t h e  p a r t i a l p r e s s u r e o f CO i s shown i n F i g u r e 16.  The r e s u l t s o b t a i n e d w i t h a p a r t i a l p r e s s u r e o f carbon monoxide o f 0.56 atm i s worthy o f comment. v a r i e d through  the use o f N  These compositions  2  The p a r t i a l p r e s s u r e o f carbon monoxide was  - CO m i x t u r e s o f v a r i o u s nominal  were checked  by gas chromatographic  compositions.  a n a l y s i s and were  86,  Table XXII Kinetic data for the oxidation of CO by Mn0  4  in acid and neutral solutions at 50.0° Mn0 ~  CO  4  M x 10  3  atm.  HC10  4  M  NaClO^ M mm  3.0 3.2 3.0 3.1  2.18 2.18 2.18  0.88 0.88 0.88 0.86  0.11 0.11 0.11 0.11  -  2.18 2.02 2.02 2.02 2.18 2.02 2.022.18  0.88 O.64 0.56  0.56 0.59 0.41 0.28 0.30  0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11  -  2.02 2.02 2.02 2.02  0.87 0.86 0.86 0.87  0.11 0.11 0.11 0.11  mm 0.28 0.58 0.89  2.02 2.02 2.02 2.02  0.85 0.85 0.85 0.87  0.26 0.52 0.78 1.00  0.75 0.49 0.23  2; 02 2.02 2.02 2.02  0.87  5  0.88  0.87 0.86  _  -  x 10  _  0.87  0.37 0.37 0.37  2Z.1B  1  2} 9  0.87 0.88  sec"  -  1.94 3.36 6.72  -  k  k'  sec  M  4  1.61 1.61 1.61  2.9 2.9  (a) 1.76 (b) 1.62 (c) 1.70 (d)  I.64  1.66  3.1  1.86 2.49 (e) 2.21 (e) 2.65 (e) 2.06  2.5 2.9  2.7 3.3 1.8  1.0 1.0  1.64  1.58  3.0  1.64  2.8  1.56  2.6  1.45  2.7  1.48  -  2.7 2.9 3.0 3.2  1.50 1.64 1.67 1.75  -  2.1 2.1  1.13 1.16 0.97 1.00  1.00 1.00  1.8 1.8  (a) Flow rate 0.24 l/min  (b) Flow rate 0..50 l/min  (c) Flow rate 1.14 l/min  (d) Contained Mn0  (e)' See text  2  20 mg/100 ml  Table XXIII E f f e c t o f temperature on t h e r a t e o f the o x i d a t i o n o f CO by MnO^  MnO/  4 x 10  P  3  C0  atm  i n a c i d and n e u t r a l  HC10  Temp  k  M  °C  M"-'- sec""-  25.0 33.0 39.1 43.8 50.0  0.542 0.763 1.10 1.66  28.0  0.212 0.316 0.514 0.740 1.10  4  1.68 1.68 1.68 1.68 1.68 1.68  0.96 0.96 0.94 0.92 0.88  0.092 0.092 0.092 0..092 0.092 0. 092  1.68 1.68 1.68 1.68 1.68  0.96 0.94 0.92 0.90 0.88  --  0.90  solutions  _  28.0  33.0 39.1  43.8 50.0  0.298 0.342  88.  89.  90. g e n e r a l l y w i t h i n 5% o f the nominal v a l u e s . r e s u l t s which were o b v i o u s l y out of l i n e ,  The  but which were r e p r o d u c i b l e .  i s even more p u z z l i n g as the same mixture was t i o n and contained  gave normal r e s u l t s .  The  gas mixture i n q u e s t i o n gave This  u s e d i n the CO - H g ( l l ) r e a c -  s i m p l e s t e x p l a n a t i o n i s t h a t the m i x t u r e  a s m a l l amount o f an i m p u r i t y which was  r e a c t i v e toward permangan-  ate, but n o t toward H g ( l l ) .  I n b a s i c s o l u t i o n s carbon monoxide reduces permanganate t o  man-  ganate, i . e .  CO  +  2MnO^"  +  4OH  >  C0  2 3  "  +  2Mn0^ " 2  +  2R" 0 2  Manganese d i o x i d e i s produced e i t h e r by f u r t h e r slow r e d u c t i o n o f the  man-  ganate  CO  +  MnO^ " 2  >  C0  2 3  "  +  Mn0  2  or by a slow d i s p r o p o r t i o n a t i o n  3Mn0 " 4  The  2  production  +  2^0  2 M h 0  4~  F i g u r e 17  s o l u t i o n was  ^2  +  °"  4  H  reduc-  shows the r a t e o f a b s o r p t i o n  an a l k a l i n e s o l u t i o n of permanganate at 30.0°.  o r d e r r a t e p l o t f o r t h i s d a t a i s shown i n F i g u r e  No  +  o f manganese d i o x i d e i s slow compared to the  t i o n o f permanganate to manganate. carbon monoxide by  >  The  of  first  18.  e x t e n s i v e e x a m i n a t i o n of the k i n e t i c s of the r e a c t i o n i n a l k a l i n e made.  Table XXIV l i s t s  the complete d a t a i n c l u d i n g the  o f temperature.  The  second o r d e r r a t e c o n s t a n t ,  mental c o n s t a n t ,  k',  by  v k  "  2.303 k' 2 [CO]  effect  k, i s r e l a t e d t o the e x p e r i -  800  1600 T ime  F i g u r e 18.  2400  s ec  Rate p l o t f o r data of F i g u r e  17.  Table XXIV Kinetic data for the CO - MnO/  reaction i n alkaline solution  k  -, ^4 sec~1xlO  M "^sec  MnO^"  °C  MxlO  30.0  1.69  0.95  0.54  1.66  0.22  40. 0  1.69  0.92  0.54  2.62  0.41  40.0  1.35  0.92  0.43  2.44  0.39  40.0  1.69  0.61  0.54  1.75  0.42  44.2  1.69  0.91  0.54  4.3  0.71  50.0  1.69  0.88  0.54  4.9  0.89  57.0  1.69  0.83  0.54  6.9  1.41  p  2  (a) Contained 0.02 M  co  atm  NaOH  k  Temp  M  Ba(C10.)  -1  94. I n one experiment BatClO^Jg was added t o p r e c i p i t a t e the manganate as i t was  formed.  S i n c e t h i s had no e f f e c t i t may be concluded t h a t o t h e r  reac-  t i o n s i n v o l v i n g manganate a r e unimportant i n t h i s system.  A r r h e n i u s p l o t s f o r t h e CO - MnO^ b a s i c s o l u t i o n s a r e shown i n F i g u r e s  r e a c t i o n s i n a c i d , n e u t r a l and  19, 20 and 21.  The c a l c u l a t e d  v a t i o n parameters based on the o x i d a t i o n o f carbon monoxide a t p r e s e n t e d i n T a b l e XXV, J u s t and Kauko,  50.0°  actiare  I n c l u d e d i n t h e t a b l e a r e t h e r e s u l t s o b t a i n e d by  These v a l u e s were c a l c u l a t e d from t h e i r d a t a f o r n e u t r a l  permanganate a t 15° and 25°,  I t i s seen t h a t t h e agreement i s e x c e l l e n t .  T a b l e XXV  50.0°  K i n e t i c parameters f o r t h e CO - MnO," r e a c t i o n a t  pH  k.M* s e c " 7  1  E a. kcal/mole  AF* kcal/mole  AH" kcal/mole  AS* e.u.  1.0  1.66  13.5  18.7  12.8  7.0  1.10  14.7  18.9  14.0  -15.2  0.89  13.6  19.1  12.9  -19.0  1.16 (a)  H.7  18.5  U.1  -14.7  13.7 7.0  (a) C a l c u l a t e d  •  -18.1  from t h e r e s u l t s o f G. J u s t and Y. Kauko (79)  There i s a s l i g h t i n c r e a s e a l k a l i n e t o weakly a c i d . change i n mechanism,  i n r a t e as t h e s o l u t i o n passes from  I t i s u n l i k e l y t h a t t h i s r e f l e c t s any s i g n i f i c a n t  A s i m i l a r t r e n d has been encountered i n t h e r e d u c t i o n  o f permanganate by m o l e c u l a r hydrogen (117).  C a t a l y s i s o f t h e CO - Mn0 " r e a c t i o n by A g ( I ) 4  and H g ( l l )  When t h e e f f e c t o f added c a t i o n s on t h e CO - MnO;  -  r e a c t i o n was  96.  97.  98. examined i t was found t h a t both A g ( I ) lytic had  effects.  The r e d u c t i o n  t o be f o l l o w e d  ions.  and H g ( l l ) i o n s had pronounced c a t a -  o f permanganate was so f a s t t h a t t h e r e a c t i o n  a t lower temperatures w i t h v e r y low l e v e l s o f the c a t a l y s t  The i o n s o f C d ( I I ) , C u ( l l ) , F e ( l I I ) and T l ( l l l ) d i d n o t f u n c t i o n as  catalysts.  Initially,  t h e c a t a l y z e d r e a c t i o n appeared t o be v e r y e r r a t i c and  poor r a t e p l o t s were o b t a i n e d .  I t was then d i s c o v e r e d  t h a t the t r o u b l e was  l a r g e l y caused by the f a i l u r e o f t h e manganese d i o x i d e t o s e p a r a t e .  This  was unexpected as the r e a c t i o n s o l u t i o n s were one molar i n p e r c h l o r i c a c i d and  no t r o u b l e had been e x p e r i e n c e d w i t h t h e u n c a t a l y z e d  ganate i n a c i d s o l u t i o n s . in  r e d u c t i o n o f perman-  A p p a r e n t l y t h e r a t e o f r e d u c t i o n o f permanganate  t h e c a t a l y z e d r e a c t i o n i s much f a s t e r t h a n the r a t e o f c o a g u l a t i o n  manganese d i o x i d e , r e s u l t i n g i n a c o l l o i d a l  The  o f the  dispersion.  samples were withdrawn and p i p e t t e d i n t o a potassium i o d i d e  s o l u t i o n and t h e l i b e r a t e d i o d i n e was t i t r a t e d w i t h sodium t h i o s u l f a t e .  That  is  first  t o say, t h e product M n ( l V ) was i n c l u d e d i n t h e t i t r a t i o n .  order  r a t e p l o t s were o b t a i n e d  manganese d i o x i d e  appeared.  temperature was i n c r e a s e d  Quite  good  up t o about 50$ r e a c t i o n when a p r e c i p i t a t e o f  Most measurements were made a t 13° and as the  the p r e c i p i t a t e appeared a t lower c o n v e r s i o n .  It  was n e c e s s a r y t o take t h e complete s e t o f samples i n any one experiment and then t i t r a t e .  Somewhat b e t t e r r e s u l t s were o b t a i n e d  i f the samples were  added t o t h e potassium i o d i d e s o l u t i o n as t h e y were taken r a t h e r than  waiting  u n t i l t h e end o f the experiment.  To c o n f i r m  t h e s t o i c h i o m e t r i e s o f the c a t a l y z e d  r e a c t i o n s the f o l l o w i n g experiment was conducted.  and u n c a t a l y z e d  The carbon monoxide was  passed through a s o l u t i o n o f sodium h y d r o x i d e t o remove any carbon and  dioxide  then passed t h r o u g h 24-6 ml o f a s o l u t i o n 6,72 x 1 0 " M i n KMhO, and 0,4 M 3  99. i n HGIO^.  The e x i t gas was then passed i n t o a carbonate f r e e s o l u t i o n o f  sodium h y d r o x i d e .  The permanganate s o l u t i o n was m a i n t a i n e d a t 50.0° and the  gas bubbled t h r o u g h f o r 60 minutes.  A t the end o f t h e time barium  chloride  was added to the t e r m i n a l h y d r o x i d e s o l u t i o n t o p r e c i p i t a t e barium carbonate. T h i s p r e c i p i t a t e was c o l l e c t e d and weighed. of  the r e a c t i o n s o l u t i o n was determined.  The permanganate  I t was found t h a t 1.23 x 10"  moles o f permanganate had been consumed and 1.74 x 10 carbonate had been c o l l e c t e d .  concentration 3  moles o f barium  /According t o the assumed s t o i c h i o m e t r y  I.84  x 10 ^ moles s h o u l d have been produced.  The experiment was r e p e a t e d w i t h the permanganate s o l u t i o n b e i n g 7.93 x 10  M i n AgClO^.  4.0 minutes.  The temperature was 13.0° and gas was passed f o r  The permanganate consumed was 1.29 x 10"* moles. 3  c a r b o n a t e produced was 1.96  x 10  The barium  moles which compares w i t h a c a l c u l a t e d  amount o f 1,93 x 10 ^ moles.  In  another experiment carbon monoxide was passed through a s o l u t i o n  0.11 M HC10 , 2.02 x 1 0 " 4  3  M KMnO^ and 0,021 3M AgClO^.  A t 50.0° t h i s  became c o l o u r l e s s w i t h a brown p r e c i p i t a t e o f manganese d i o x i d e w i t h i n seconds.  300  The c o l o u r l e s s s o l u t i o n was found to c o n t a i n 0.0213 M AgClO^. .  The f o r e g o i n g experiments demonstrate the  solution  t h a t the s t o i c h i o m e t r i e s o f  u n c a t a l y z e d and t h e s i l v e r c a t a l y z e d r e d u c t i o n o f permanganate by carbon  monoxide are the same. catalyzed reaction.  A l s o t h e r e i s no d e t e c t a b l e l o s s o f s i l v e r i n the  The mercury ( I I ) c a t a l y z e d r e a c t i o n has been assumed to  proceed i n the same manner as the s i l v e r c a t a l y z e d  In  reaction.  F i g u r e 22 r a t e p l o t s f o r the permanganate r e d u c t i o n w i t h and  w i t h o u t c a t a l y s t are compared. a pseudo f i r s t  The s l o p e s o f the f i r s t  order plots  yielded  o r d e r r a t e c o n s t a n t which i n c l u d e d b o t h the c a t a l y z e d and  800  1600  2400  T ime s ec F i g u r e 22. Rate p l o t s f o r u n c a t a l y z e d r e a c t i o n at  13.0°.  A.  no  catalyst  B.  H g ( I l ) . 4.00  C.  Ag(I)  7.93  x 10 x  -4  10" M 6  M  and c a t a l y z e d CO  -  MnO^  101. uncatalyzed  reactions.  The  c o n t r i b u t i o n o f the u n c a t a l y z e d  t r a c t e d b e f o r e v a l u e s of the e f f e c t of the r e d u c t i o n n e g l i g i b l e at the low  The T a b l e XXVI. in  sub-  t h i r d o r d e r r a t e c o n s t a n t s were c a l c u l a t e d .  The  o f H g ( I I ) and  temperatures and  The  first  o r d e r r a t e c o n s t a n t , k',  the c o n t r i b u t i o n o f the u n c a t a l y z e d  =  k  i s the  reaction i s f i r s t  metal i o n .  There i s a s m a l l  Ag(l) catalyzed explanation  3/2  The  third  While the  order  by  variation in  i t seems s a f e t o conclude t h a t  apparent d e c r e a s e i n the r a t e c o n s t a n t o f  the  the r a t e c o n s t a n t s i n c r e a s e d 50$  increases.  by  XXIX.  catalyzed  The  I n the  reactions  temperature  a f a c t o r o f 3 f o r the  Hg(ll)  f o r the A g ( l ) c a t a l y z e d r e a c t i o n .  from the S e r i e s B d a t a o f the T a b l e s and  The  the  clear.  e f f e c t of temperature on the r a t e s o f the  and 24*  by  o r d e r i n each o f permanganate, carbon monoxide  r h e n i u s p l o t s were c o n s t r u c t e d  XXX.  reaction.  o f H g ( l l ) or A g ( l ) .  c a t a l y z e d r e a c t i o n , but o n l y by  Table  been c o r r e c t e d  r e a c t i o n as the permanganate c o n c e n t r a t i o n  shown i n F i g u r e s 23  given  mm~  shown by the d a t a g i v e n i n T a b l e s XXVIII and  range 0 - 25°  has  in  2.303 k'  o f t h i s e f f e c t , i f r e a l , i s not  The is  concentration  3/2  c a l c u l a t e d r a t e c o n s t a n t s i s about 20$  catalyzed  employed.  r e a c t i o n are g i v e n  c a t a l y z e d r e a c t i o n , k , i s o b t a i n e d from k'  k  the  low H g ( l l ) c o n c e n t r a t i o n s  C o r r e s p o n d i n g d a t a f o r the A g ( l ) c a t a l y z e d r e a c t i o n are  r a t e c o n s t a n t o f the  where [M]  the r e o x i d a t i o n by permanganate i s  k i n e t i c d a t a f o r the H g ( l l ) c a t a l y z e d  Table XXVII.  subtracting  r e a c t i o n was  a c t i v a t i o n parameters f o r 0° are g i v e n  Arare in  and  Table XXXVI Kinetic data for the Hg(ll) catalyzed oxidation of CO by MnO Temperature 13.0°  MnO/ A  x 10  M x IO  i k-  CO  Hg(H) 3  HC10, 1.00 M  4  M x IO  3  sec" x IO 1  k i 4  M^sec" : 1  3.4 6.7 10.1 13.4 16.8 20.2  4.00 4.00 4.00 4.00 4.00 4.00  1.15 1.15 1.15 1.15 1.15 1.15  2.8 2.6 2.3 2.4 2.3 2.3  2.1 2.0 1.7 1.8 1.7 1.8  10.1 10.1  2.00 8.00  1.16 1.16  1.1 4. 4  1.7 1.6  6.7 6.7 6.7  4.00 4.00 4.00  0.40 0.53 0.'82  0.7 1.3 2.1  1.8 2.2 2.2  103.  Table XXVII  Kinetic data for the Ag(l) catalyzed oxidation of CO by MnO^" Temperature 13.0°  Mn0 "  Ag(I)  4  M x 10  3  M x 10  6  HCIO^ 1.00 M  CO M x IO  2.0 3.4 6.7 10.1 13.4  7.93 7.93 7.93 7.93 7.93  1.15 1.15 1.16  6.7 6.7 6.7  3.96 15.9 31.7  1.15  6,7 6.7 6.7  7.93 7.93 7.93  k' 3  l.H  1.14  sec" x IO 1  5.2 4, 4 3.7 3.6 3.4  k 4  c  M^sec" x IO" 1  2.0 1.7 1.4 1.4 1.3  l.U  1.16  2.1 6.1 11.6  1.5 1.2 1.1  0.40 0..53 0,.82i  1.2 1.9 2>,8  1.3 1.5 1.5  5  104.  Table XXVIII Effect of temperature on the rate of the Hg(ll) catalyzed CO - MhO^  -  MnO " 4 M x IO Series A  Series B  CO 3  M x IO  Hg(ll) 4  M x IO  6.72 6.72> 6.72 6.72 6.72  9.2 10.0 10.8 12.4 15.5  4.00 4.00 4.00 4.00 4.00  7.-88 7.88 7.88 7.88 7.88 7.88 ,  9.43 10.2 10.9 11.8 12.6 15.6  4.00 4.00 4.00 4.00 4.00 4.00  4  reaction  Temp °C 25..0  20.0 16.0 10.2 0.1 25.0  20.4 16.7 13.0 9.1 0.1  k  c  M~ sec"* x 2  1  3.58 3.12 2.44 1.87 1.27 3.26 2.66 2.23 1.85 1.61 1.09  ,-3  Table XXIX  Effect of temperature on the rate of the A'g(l) catalyzed CO - MnO"^" reaction  MnO^" M x 10  CO 3  M x 10  Afc(I) 4  M x IO  Series A  6.72 6.72 6.72 6.72 6.72  9.2 10.0 10..8 12.4 15.5  7.93 7.93 7.93 7.93 7.93  Series B  7.88 7.88 7.88 7.88 7.88  9.4 10.1 10..9 11.8 15.6  7.93 7.93 7.-93 7.93 7.93  Temp °C  6  '  c -1 sec x k  ur2  M  25.0 20.0 16.0 10.0 0.1  1.83 1.55 1.57 1.43 1.29  25.0 21.0 16.7 13.0 0.1  1.47 1.47 1.30 1.28 1.10  3.4  3.5  3.6  •10 /T °A 3  F i g u r e 23. A r r h e n i u s p l o t o f H g ( I I ) c a t a l y z e d CO - MnO^ H g ( I I ) 4.00 x 1 0 M ; CO _4  reaction.  0.98 atm; MnO " 7.88 x 10" M; HC10, LOOM 3  5.2  3.4  3.5 10 /T 3  F i g u r e 24. A r r h e n i u s p l o t o f Ag(I) Ag(I)  3.6  °A c a t a l y z e d CO - MnO^  reaction  7.93 x 10" M; CO 0.98 atm; MnO." 7.88 x 10 M; HC10, 1.00 M 6  _3  108.  Table X X X  A c t i v a t i o n parameters f o r the c a t a l y z e d CO - MnO,"  E  yo°)  act  kcal/mole  AF*  reactions  AH*  AS*  kcal/mole  e.u.  M^sec"  1  Hg(H)  1.09  x  10  3  7.0  12.2  6.5  -20.7  Ag(D  1.10  x  10  5  1.9  9.6  1.3  -30.4  kcal/mole  109. Tracer Studies with  0  X O  The g e n e r a l procedure was  s i m i l a r t o t h a t used by Wiberg  Stewart (121) f o r the formate-permanganate cedure was  reaction.  and  I n o u t l i n e , the pro-  t o pass carbon monoxide t h r o u g h an a l k a l i n e s o l u t i o n o f the  l a b e l l e d permanganate, d e s t r o y the permanganate and manganate w i t h h y d r a z i n e , remove the manganese d i o x i d e and p r e c i p i t a t e the p r o d u c t carbonate as barium carbonate.  The barium carbonate was decomposed and the e v o l v e d carbon  d i o x i d e was  c o l l e c t e d i n the apparatus- shown i n F i g u r e 25.  of barium carbonate was  The  p l a c e d onto f r o z e n c o n c e n t r a t e d s u l f u r i c a c i d con-  t a i n e d i n the s m a l l lower b u l b and the apparatus evacuated. a c i d was melted by immersing was  precipitate  The  sulfuric  the b u l b i n warm water whereupon carbon d i o x i d e  r e l e a s e d and c o l l e c t e d i n the l a r g e upper b u l b .  The l a b e l l e d permanganate c o n t a i n e d 1.14$ by Dr. J . B. Farmer.  and was  supplied  The mass s p e c t r o m e t r i c a n a l y s e s were performed by Dr.  D. C. F r o s t .  I n these experiments i t was ( 12 l6 18p C  0  0  t  o  m  a  s  g  4  5  ( 13 l6^, C  a  g  g  t  h  e  g  c o n v e n i e n t t o compare mass 46 e  a  r  e  o  f  t  h  Q  g  m  e  o  r  d  e  r  o  f  and the v a l u e of mass 45 remains e s s e n t i a l l y c o n s t a n t f o r COg n a t u r a l s o u r c e s and 0  18  magnitude o b t a i n e d from  enriched sources.  The n a t u r a l abundances f o r the i s o t o p e s o f carbon and oxygen are (122) i n per c e n t C  1 2  98..892, C  1 3  1.103 , 0  1 6  99.758 , 0  1 7  0.0373 , 0  T h i s l e a d s t o a r a t i o o f mass 46 to mass 45 e q u a l t o 0.343. t a l l y determined r a t i o u s i n g C 0 Mn0 " was 4  0,332 i  2  formed  The  1 8  0.2039.  experimen-  by o x i d i z i n g CO w i t h u n l a b e l l e d  0.027.  The r e s u l t s o b t a i n e d w i t h l a b e l l e d permanganate f o l l o w .  F i g u r e 2 5 . Apparatus f o r decomposing BaCOo and c o l l e c t i n g CO  111. T e s t 1.  0.999 g KMhO^ i n 25 ml o f 0.2M NaOH a t 25°.  47$ CO was bubbled  2through f o r 60 minutes. NgH^  The MnO^  and MnO^  and MnOg removed by c e n t r i f u g i n g ,  were d e s t r o y e d w i t h  BaClg was added and t h e  r e s u l t i n g p r e c i p i t a t e o f BaCO^ was washed and d r i e d .  The p r e c i -  p i t a t e was decomposed on s u l f u r i c a c i d and t h e e v o l v e d COg c o l lected..  The mass 46/4-5 r a t i o was 0.409 which corresponds t o 0.10  atom o f oxygen t r a n s f e r r e d T e s t 2.  from permanganate p e r CO,  0.099g KMnO^ i n 25 ml water 40 minutes.  a t 25°.  47$ CO bubbled through f o r  The same procedure was f o l l o w e d .  r a t i o was 0,352.  The mass 46/45  E s s e n t i a l l y no oxygen was t r a n s f e r r e d  from t h e  permanganate.  T e s t 3.  0.448g KMnO^ i n 50 ml 0.7M NaOH a t 25°. the  solution  minutes. above.  and took 10 ml samples  The BaCO^ p r e c i p i t a t e s The COg samples  a f t e r 5> 20, 45 and 80  were c o l l e c t e d  were i n a d v e r t e n t l y  o n l y the 45 and 80 minute  samples  18 r a t i o s o f 0,32 i n d i c a t i n g no 0 T e s t 4.  Bubbled 100$ CO through  d i l u t e d w i t h a i r and  c o u l d be a n a l y z e d .  Both gave  transfer.  0.032g KMnO, i n 25 ml o f 0.2 M Ba(0H)_ a t 2 5 ° . A2 through f o r 80 minutes.  and t r e a t e d as  100$ CO was passed  The combined p r e c i p i t a t e s  o f BaMnO^ and  BaCO^ were c o l l e c t e d and the BaMnO^ decomposed w i t h h y d r a z i n e . The BaCO^ was not s e p a r a t e d from t h e MnOg b e f o r e d e c o m p o s i t i o n . The mass 46/45 r a t i o was 0.542 which i s e q u i v a l e n t t o an 0 transfer T e s t 5.  1 8  o f 0.30 atom p e r CO.  0.114g KMnO^ i n 50 ml o f 0.2M B a ( 0 H ) 10$ f o r m i c a c i d s o l u t i o n .  2  was reduced w i t h 1 ml o f a  The p r e c i p i t a t e s  were t r e a t e d  as i n t h e  18 previous t e s t . f e r r e d p e r CO.  The mass r a t i o was 0,42 o r 0,12 0  atom was t r a n s -  112. T e s t 6.  0.078g KMnO  i n 30 ml l.OM NaOH was reduced w i t h 1 ml o f 10$  4 formic a c i d .  The manganate was reduced w i t h h y d r a z i n e and the  MnOg removed, treated  BaCO^ was p r e c i p i t a t e d by adding BaCL, and was  i n the u s u a l manner.  The mass r a t i o was 0,507 c o r r e s p o n -  18 d i n g t o 0.25 0 atom t r a n s f e r r e d T e s t 7.  p e r CO.  0.098g KMnO. i n 50 ml o f a s o l u t i o n 0.6M i n NaOH and 0.08M i n  4 BaClg.  1 ml o f a 10$ f o r m i c a c i d s o l u t i o n was added.  The r e -  s u l t i n g BaMnO^ was c o n v e r t e d t o MnOg ^ - ^ h y d r a z i n e and t h e comn  bined BaCO^ and MhOg P r e c i p i t a t e s were c o l l e c t e d . C0  2  had a 46/45 mass r a t i o o f 0.479.  0.21 0  1 8  The e v o l v e d  atom was t r a n s f e r r e d  per CO, T e s t 8.  O.lOOg KMnO^ i n 25 ml o f 1.8M NaOH a t 4 O . 0  f o r 60 minutes  CO was passed  and t h e carbonate c o l l e c t e d as u s u a l .  through  The mass  r a t i o was-0,410 i n d i c a t i n g a t r a n s f e r o f 0.10 atom o f O ^ p e r CO. 1  T e s t 9.  T h i s t e s t was done p r i m a r i l y t o check t h e s t o i c h i o m e t r y o f t h e s i l v e r catalyzed reaction, in was  0,140g o f l a b e l l e d KMnO^ was d i s s o l v e d  50 ml o f a s o l u t i o n 0,9M i n HCIO^ and 1.6 x 10"4 M i n A g . +  passed through f o r 40 minutes  through a s o l u t i o n o f NaOH.  at 40°.  10.  0.l60g o f KMn0 BaClg.  The p r e c i p i t a t e was  i n t o two p o r t i o n s f o r g e n e r a t i o n o f CO,,.  46/45 r a t i o s o f 0.30 i n d i c a t i n g no 0 Test  The e x i t gas was l e d  BaClg was added to p r e c i p i t a t e BaCO^  which was c o l l e c t e d , d r i e d and weighed. divided  4  Both gave mass  transfer.  i n 70 ml o f a s o l u t i o n l.OM i n NaOH and  CO was bubbled through f o r 40 minutes  bined p r e c i p i t a t e s treated  CO  as u s u a l .  0.06M i n  a t 40° and t h e com-  The mass r a t i o was found t o 18  be  0.763 which i s e q u i v a l e n t t o an 0  atom t r a n s f e r o f  0,64 p e r CO.  113. The tests are summarized in Table XXXI. The results show no clear pattern.  The results obtained for the  formate reduction of permanganate are in f a i r agreement with those of Wiberg and Stewart (121),  These authors showed that the method did not involve any  exchange of carbonate in basic solution.  Mechanism of the CO - Hg(ll) Reaction A" satisfactory mechanism must account for the kinetic behaviour including the lack of a pH dependence. chiometry,  It must also provide for the stoi-  A mechanism which does this i s the followingJ  2+  1.  - Hg - 0H  2.  0 it - Hg - C - OH  3.  Hg  k +  2  +  0 " + - Hg - C - OH  CO  »  + +  H  rate determining > Hg  2+  >  Hg Hg2  +  C0  2  +  H  fast  +  fast  2+  The rate determining step must involve the aquo ion rather than +  HgOH because the reaction i s essentially acid independent.  The lack of acid  inhibition also indicates that the reversal of the rate determining step cannot be important.  This also shows that the formation of the  intermediate  i s not a rapid equilibrium with the rate determining step being i t s decomposition.  The subsequent fast reaction between Hg(ll) and Hg(0) i s postulated  for other reactions of mercury (123). The unique feature of this mechanism i s the insertion of a molecule of CO between an Hg * ion and a coordinated water molecule. 2  The subsequent  114.  Table XXXI  Summary of 0  Test  Reductant  transfer experiments  Atoms 0 from MnO^  Ba M  T°C  5  HCOO"  0.12  20  13.3  0.2  7  n  0.2  20  13.8  0.08  6  n<  0.25  20  14.0  9  CO  0.0  40  0.0  2  0.0  25  7.0  3  0.0  25  13.8  1  0.10  25  13.3  4  0.30  25  13.3  8  0.10  40  14.3  10  0.64  40  14.0  0.2  0.06  115. decomposition of the intermediate takes place by loss of a proton leading to the products. This insertion of a CO between a metal-oxygen bond i s somewhat analogous to the mechanism proposed by Sternberg and Wender (100) to explain the Co (C0)g catalyzed formation of methyl formate according to 2  CH 0H 3  +  2  CH-OCo(CO). + i 4 CH 0C0Co(C0) 3  ->  Co (C0)g  +  4  CH 0Co(C0) 3  4  + HCo(CO)^  CH.OCOCo(CO).  CO  3  Hg  4  ->  HC00CH  +  HCo(C0)  ->  HC00CH  +  Co (C0)g  3  4  The last step may be replaced by CH-OCOCo(CO). + HCo(CO). .7  4  4  3  2  Particularly strong support for the proposed insertion mechanism of the CO - Hg(ll) reaction i s given by the following consideration.  Replace-  ment of the proton of the intermediate by an alkyl group should lead to stabilization and allow the isolation of the intermediate.  This has been  shown to be the case. Schoeller et al (124) observed that methanolic solutions of Hg(ll) acetate readily absorb CO to form a compound with the formula HgC^H^O^.  The  reaction i s reversible, CO being liberated by heating or by treatment with acid.  Schoeller proposed the structure 0 II  CH  3  0 it  - C - 0 - Hg - C - 0CH  3  corresponding to the insertion of a molecule of CO between a monoacetate Hg(ll) and a methoxy group.  On the other hand, Manchot (125) proposed a  116. carbonyl  structure 0 ti CH„  - C C - 0 - Hg - OCH  3  3  C 0  H a l p e r n and K e t t l e (126)  r e c e n t l y r e s o l v e d t h e s t r u c t u r e o f the compound and  showed t h a t i t was t h a t proposed by S c h o e l l e r . CO  i n s e r t i o n r e a c t i o n s a r e known.  s t r u c t u r e i s f i r s t formed which then  r e a r r a n g e s t o g i v e t h e i n s e r t i o n compound.  The  The l a t t e r s i t u a t i o n seems t o  o f acetylmanganese p e n t a c a r b o n y l .  f a c t that the reduction  o f H g ( l l ) by CO i s slower i n D 0 than 2  i n HgO can be i n t e r p r e t e d as s u p p o r t i n g i s displaced.  a mechanism i n which a water molecule  The r a t i o o f the r a t e c o n s t a n t s  Such a change i n r a t e c o n s t a n t s  energies  i s 1,6 a t 40°,  T h i s o f the same o r d e r  as t h e d i f f e r -  o f some i o n s i n D 0 and H^O, a l t h o u g h an unambig2  uous i n t e r p r e t a t i o n i s n o t y e t p o s s i b l e  Kemp (130)  k /lc HgO ^2  c a n be accounted f o r by an i n c r e a s e i n a c t i -  v a t i o n energy o f about 0.3 k c a l / m o l e . ence i n h y d r a t i o n  other  I t i s n o t y e t known whether these a r e  formed d i r e c t l y o r whether a c a r b o n y l  p r e v a i l i n the formation  As noted p r e v i o u s l y ,  (127,  128, 1 2 9 ) .  has examined t h e k i n e t i c s o f t h e r e a c t i o n  0  rti  Cl  i n methanol. tration.  - Hg - C - OCH^ + H  + Cl~  >  The r a t e was found t o be f i r s t o r d e r  This suggests t h a t the reverse  HgClg + CO + CH^OH  i n hydrogen i o n concen-  r e a c t i o n l e a d i n g to the formation  o f t h e carbon monoxide i n s e r t i o n compound i n v o l v e s CH^OH r a t h e r than CH^O . By  analogy, t h e i n t e r m e d i a t e  i n aqueous s o l u t i o n i n v o l v e s H 0 r a t h e r than OH 2  117. Results of Related GO Reactions Following completion and publication of the present work (131) other CO reactions have been examined and the results support the concept of an insertion mechanism. McAndrews (132) has examined the kinetics of the Ag(I) - CO reaction i n perchlorate and acetate media. cult system.  Experimentally this i s a d i f f i -  The reactions are slow and i t was necessary to perform the  experiments i n an autoclave employing pressures up to 30 atm. and of 60 - 110 .  temperatures  The rate of reaction was followed by means of the pressure  changes. The experimental rate law was  =  k a  [C0][AgIc]  VcLcoJUg+jW]"  1  +  -1 + k Kc [CO] [ Ag ] [ AgAc] [ H J +  +  c  where Ac represents the acetate ion.  The f i r s t term i s acid independent and  presumably reflects direct participation of AgAc i n the reaction. The second term i s independent of acetate concentration and i s the same as Bauch's expression (116).  The third term i s complex.  The mechanism proposed to  account for the rate law i s Ag  +  Ac  AgAc  N  rapid equilibrium 0  K  a  AgAc  +  CO  >  Ag - C - Ac  Ag  +  H0  >  2Ag  0 it Ag - C - Ac  +  +  2  +  COg  +  HAc  +  H  +  fast  118. 0 K Ag  +  CO  + HO 2  Ag - C - OH  +  H  rapid equilibrium  H  0 Jr  II  Ag - C - OH  +  0 " Ag - C - OH  4g  —  +  2  A  g  +  C0  2  +  2  A  g  +  C0  2  +  +  k +  AgAc  —  I n a complex system such as t h i s i t i s d i f f i c u l t , to a r r i v e a t d e f i n i t e c o n c l u s i o n s about mechanism.  HAc  i f not impossible,  I t i s o f i n t e r e s t , how-  e v e r , t h a t two carbon monoxide i n s e r t i o n complexes are p o s t u l a t e d .  Nakamura and H a l p e r n (133, 134.) have found t h a t A g ( l ) amine comp l e x e s r e a c t r a p i d l y w i t h carbon monoxide t o p r e c i p i t a t e m e t a l l i c The k i n e t i c s are i n accord w i t h t h e f o l l o w i n g  J L ,  +  AgL  +  2  HO  mechanisms  L-Ag-OH  +  +  LH  0 II  L-Ag-OH  +  CO  L-Ag-C-OH k  - l  0 in L-Ag-C-OH  +  Ag(l)  — p r o d u c t s  L r e p r e s e n t s t h e amine and K = K ^ I ^ which are d e f i n e d  [ W ]  d  K, T>  =  [ H L ] [0H-] [LJ  K  =  CAg-L-OH1  h  +  [ A g L ] [OH" ] +  silver.  by  rapid  equilibrium  119. The experimental rate constant, k, i s defined by the rate law -1 - d C M . == dt  kTclcol [ C 0 ]T[AAPgLL„ 7j r/ H* HLL j' +  +  2  +  +  which i s equivalent to  -<lM2 dt  That i s ,  k  =  k l  =  [  C 0  J [L-Ag-OH]  k K K K 1 d b h  the important feature i s that the v a r i a t i o n i n k i s very n e a r l y accounted f o r by v a r i a t i o n i n K^K^ amine.  so that k^K^ i s i n s e n s i t i v e to the nature of the  This means that the increase i n pH accounts f o r the increase i n rate  on going from a c i d i c to amine-buffered media. For primary amines, the i n s e r t i o n of CO i n the L-Ag-OH complex was found to be the rate determining step and the above rate law describes the behaviour.  With t r i e t h y l a m i n e , the reverse r e a c t i o n , k_-^, becomes f a s t  enough to compete with kg and the Ag(l) species i s i d e n t i f i e d as AgL , When ammonia i s used with high concentrations of NH^ " i t appears t h a t the 4  A g ( l ) species i s L-Ag-OH and the r e a c t i o n becomes second order i n Ag(l) and + i n v e r s e second order i n NH^ . Byerley and Peters (135) have reported on the CO reduction of C u ( I l ) to C u ( l ) i n aqueous s o l u t i o n s at quite high CO pressures.  The rate law can  be expressed as the sum of two terms, _ "  -1 = ^ [ C u d l ) ] [ Cu(l)] [ H ] +  2 - 1 + kgKg [ C u ( l l ) ] [CO] [ H J  The mechanisms which are postulated to give t h i s rate law are  +  120 0 Path 1.  Cu(CO)  +  ==±  HgO  Cu - C - OH  + H  0 it  l -^4 k  Cu - C - OH  +  +  +  +  Cu(ll) ^ 4  CuH  Cu(l) + CuH 2Cu(l)  +  H  +  CQ2  +  Cu(ll) 0  Path 2.  Cu(Il)  + 0 0 + ^ 0  =^  - Cu - C - OH  + H  0 it  - Cu - C - OH  +  Cu(ll)  2Cu(l)  + 2C0  +  >  2Cu(l)  fast at -> high pressures  + C0  2  + H  + 2Cu(C0)  A l l of the foregoing reactions are postulated to proceed via CO insertion mechanisms.  One way in which they differ from the corresponding  Hg(II) reaction i s that the decomposition of the insertion complex must occur by reaction with another metal ion. This i s apparently slow enough i n many cases so that the reversal of the intermediate forming step becomes important.  Mechanisms of the Uncatalyzed and Catalyzed CO - MnO^  -  The reactions between CO and MnO^  Reactions  i n basic, neutral and acidic  solutions exhibit the same kinetics and have very similar activation parameters.  Consequently, i t i s reasonable to assume that the rate controlling  step i s the same i n each case.  The different stoichiometries reflect the  differences i n stability of various manganese species with respect to pH, The proposed mechanism i s the reduction of Mn(VIl) to Mn(V) by CO taking place in two steps:  121. 1.  MnO/  2.  0 MnO - CO" 3  +  CO  — 0  + . HgO  f  a  S  t  3  M n O  )  - CO"  Mno/"  +  COg  +  2H  +  3The hypomanganate, MnO^ manganese s p e c i e s .  , then r e a c t s r a p i d l y t o give t h e f i n a l  In basic s o l u t i o n the r e a c t i o n i s probably  MnO, 4  +  4  which i s known t o be f a s t  3-  MnO,  (136).  22MnO,  >  4  I n a c i d s o l u t i o n b o t h manganate and hypo-  manganate undergo r a p i d d i s p r o p o r t i o n a t i o n to permanganate and manganese dioxide.  An a l t e r n a t i v e f o r m u l a t i o n  CO  +  MnO/  of the r a t e determining step i s  —^->  C0  2  +  Mn0 " 3  However, s i n c e Lux (137) has shown t h a t Mn(V) s a l t s are isomorphous w i t h phosphates t h e f o r m u l a t i o n  MnO^  3-  i s preferred.  The s i m p l e s t method o f d e p i c t i n g t h e r a t e d e t e r m i n i n g s t e p i s by a n u c l e o p h i l i c a t t a c k by a permanganate oxygen on t h e carbon atomoof carbon monoxide.  This intermediate  i s then decomposed by water which can a t t a c k  e i t h e r t h e carbon atom o r t h e manganese  OC  i i  atom, i . e .  0 - - MnO, J  0 H  or  2  OC  0 - - MnO.,"  i i i  '  0 H  2  122. I n the f i r s t  case oxygen i s not t r a n s f e r r e d from MnO^~  whereas i n the second case i t i s .  Water has been shown as the  agent, but the h y d r o x y l i o n would produce  to  CO,  attacking  the same r e s u l t ,  A mechanism s i m i l a r t o t h a t e n v i s i o n e d f o r the H g ( l l ) - CO r e a c t i o n i n v o l v i n g a carbon monoxide i n s e r t i o n complex seems u n l i k e l y i n t h i s case.  Carbon monoxide i s a poor n u c l e o p h i l i c r e a g e n t and r e q u i r e s c o n s i d e r -  a b l e s t a b i l i z a t i o n by back d o n a t i o n o f e l e c t r o n s t o i t s empty p i o r b i t a l s . The f o r m a t i o n o f metal c a r b o n y l s i s a t t r i b u t e d t o t h i s s t a b i l i z i n g because  effect  those m e t a l s which form c a r b o n y l s have d e l e c t r o n s a v a i l a b l e ,  Metals  w i t h h i g h o x i d a t i o n s t a t e s such as Mn(VTI) have no e l e c t r o n s a v a i l a b l e f o r back d o n a t i o n so s t a b i l i z a t i o n o f a CO complex i s n o t p o s s i b l e .  The o x i d a t i o n o f CO  by a l k a l i n e permanganate i s analogous  o x i d a t i o n o f the i s o e l e c t r o n i c cyanide i o n . s t u d i e d by Freund  (138) and by Stewart  are c o m p l i c a t e d a p p a r e n t l y because  T h i s l a t t e r r e a c t i o n has been  and Van d e r L i n d e n (139).  a t low pH HCN  pH a mechanism i n v o l v i n g h y d r o x y l r a d i c a l may  dt  =  k  The  kinetics  takes p a r t and a t v e r y h i g h  be important.  13 and 14 the dominant r e a c t i o n path i s d e s c r i b e d by the r a t e  - dj£Cl  t o the  A t a pH between law  [ -][MnOr] C N  which has the same form as t h a t f o r the CO  ^*  reaction.  Stewart and Van d e r L i n d e n (139) found t h a t oxygen t r a n s f e r  from  MnO^  t o CN"  o c c u r e d and the p r o p o r t i o n t r a n s f e r r e d i n c r e a s e d w i t h i n c r e a s i n g  pH.  T h i s may  i n d i c a t e t h a t i n the decomposition o f the proposed i n t e r m e d i a t e  NC  both HgO  and OH  0 - - Mn0 "  are e f f e c t i v e w i t h the OH"  2  3  attack occurring  preferentially  123. on manganese.  Since attack on the manganese lends to oxygen transfer this  accounts for the increased transfer with increased pH.  & similar situation  may well prevail i n the corresponding CO reaction. In the catalyzed CO - MnO^ reaction there i s no reason to consider that the catalytic actions of Ag(l) and Hg(ll) are any different.  Accordingly  they have both been assumed to act i n the same way. In view of the likelihood of a CO insertion complex providing the mechanism for the CO - Hg(ll) reaction i t i s attractive to postulate a similar complex for the present reaction. When this i s coupled with the proposal for the uncatalyzed reaction, the postulated complex becomes 0 it  - Ag - C - OMnO^ The mechanism i s then written as  Ag  + CO + Mn0 " 4  0 ti Ag - C - OMnO, + H-0  0 " Ag - C - 0Mn0  k ^  3  >  Ag  +  determining rate  + CO, + MnO," + 2H 2 3  4  +  f a s t  A"s with the uncatalyzed reaction the hypomanganate reacts rapidly to give Mn0 . 2  The catalytic action of Ag(l) and Hg(ll) must be to stabilize the equivalent of an insertion complex.  This may be accomplished by donation of  metal d electrons to form a pi bond with the CO molecule. along these lines will be made later.  Further comments  124. Comparison of CO,  Hg  and HCOOH as Reductants  A comparison o f some o f the r e a c t i o n s of hydrogen and f o r m i c a c i d w i t h those  o f carbon monoxide i s o f i n t e r e s t .  v a r i o u s r e a c t i o n s i s g i v e n i n T a b l e XXXII. the r e a c t i o n s o f hydrogen and of formic  A summary of k i n e t i c d a t a f o r  Halpern  T a y l o r and Halpern  (1, 145)  has  discussed  (77) have d i s c u s s e d  those  acid.  When hydrogen i s o x i d i z e d the m o l e c u l e i s s p l i t .  This  splitting  can take p l a c e e i t h e r h o m o l y t i c a l l y to g i v e hydrogen atoms o r h e t e r o l y t i c a l l y to  g i v e an h y d r i d e i o n and  a proton.  but the same form o f i n t e r m e d i a t e  Both types o f behaviour seem l i k e l y ,  can be p o s t u l a t e d i n each case.  For  ex-  ample, C u ( l l ) s p l i t s hydrogen h e t e r o l y t i c a l l y a c c o r d i n g to the mechanism  Cu  2 +  +  Hg  >  CuH  +  +  H  +  It  i s l i k e l y t h a t A g ( l ) i n the b i m o l e c u l a r r e a c t i o n , H g ( I l ) and MnO^  in  the same manner.  -  On  the o t h e r hand H g ( l ) , & g ( l ) i n the  r e a c t i o n and i n the c a t a l y z e d MnO^  Hgg  2 +  +  act  termolecular  r e a c t i o n s p l i t hydrogen h o m o l y t i c a l l y  Hg  >  2HgH  +  An examination of the e l e c t r o n c o n f i g u r a t i o n o f the a c t i v e c a t i o n s shows t h a t they have n e a r l y f i l l e d e l e c t r o n s can t h e n be be made vacant one  or just f i l l e d d - o r b i t a l s .  hydrogen  accommodated i n the d - o r b i t a l s which are vacant  by promotion t o the next s - o r b i t a l .  and  s- l e v e l s .  2+  a c t i v a t e s hydrogen while  the i s o e l e c t r o n i c i o n Tlr  the quantum number i n c r e a s e s the d-s  can  i s the  F o r a f i x e d quantum number, the  energy s e p a r a t i o n depends on the n u c l e a r charge o f the i o n . Hg  or  Thus, i t can be seen t h a t  of the f a c t o r s i n the s t a b i l i z a t i o n o f t h e h y d r i d e i n t e r m e d i a t e s  energy s e p a r a t i o n of the d-  why  The  o+  This  explains  i s inactive.  energy s e p a r a t i o n d e c r e a s e s .  Thus the  As  125.  Table XXXII  Summary of kineti c data for some oxidations ofH , HGOOH , HGOO and CO 2  AH*  AS*  Kcal  e,t,Pt  Temp °C  Ref  krH ][cu j  26  -10  80- HO  HO  k[H ][Hg J  18  -12  65-100  123  k[H2][Hg J  20  -10  65-100  123  Reactants  Rate Law  H -Cu  2+  -Hg  2+  2+  2  2  n -Hg  2+  2  2  +  2+  2  2  -Ag  +  k^Ag "]  H  -25  30-120  141  -Ag  +  k[H ]tAg ]  18  -12  30-120  141  H  -17  30-70  142  4  +  2  -MnO^"  k[H ][MnO ] _  2  -MnO^" + Ag  A  k[H2][Ag J[MnO^J  9  -26  30-60  142  k[HC00H][co(IIl)J  26  19  0-30  143  k[HCOOH]fMnO^" ]  16  -19  15-35  144  k[HGOO"] [Co(lll)]  21  21  0-30  143  k[HC00-][Hg " ]  20  3  36-61  77  u 2+ -Hg  k [HCOO-J [ k g / ]  21  0  60-80  77  -Tl3  k[HC00-][Tl ]  26  ~ 21  65-85  77  k[HCOO-][MnO^"]  12  - H  15-35  144  30  144  +  +  HCOOH-Cb(Hl) -MnO^" HCOCf-Co(lIl) -Hg  2+  2  4  2  +  3+  -MnO^" -MnO^"+ F e  3 +  2+ CO-Hg^ -Ag  f  +  k [HCOO"] [FeMn0^ J  -  k H ^ ]  15  2+  17  k[CO][Ag J [ H ] ~ +  -  +  -13  -  26-54 80-110  132  15-35  134-  120  135  -AgL2 (a)  k[C0][LAg0H]  9  -Cu(ll)  kJcudiO^cud)]^]  -  -  13  -17  28-50  k[C0j[Mn0^']fHg J  6  -21  0-25  k[co][MnO -][Ag J  1  -31  0-25  +  -15  +k [C0][cu(H))[H J +  2  -MnO^ -MnO^"+ H g  k[C0][MhO "] 4  2+  -MnO^~+ Ag (a)  +  L = methylamine  2+  +  A  126. 5d Zh  1 0  ion H g  2 +  i s a c t i v e while  the corresponding  4d and 3d i o n s C d  2 +  and  are i n a c t i v e .  2  The  permanganate r e a c t i o n i s somewhat d i f f e r e n t , b u t may a l s o  i n v o l v e hydride is inactive.  2I n t h i s r e s p e c t t h e i s o e l e c t r o n i c CrO^ i o n  T h i s may be a t t r i b u t e d t o t h e l a r g e r energy gap between t h e  h i g h e s t occupied MhO "  ion transfer.  2and l o w e s t u n o c c u p i e d o r b i t a l s o f CrO as compared t o 4  (146).  It  appears t h a t A g c a t a l y z e s the r e a c t i o n between IL and MnO +  2  4  by a l l o w i n g a one e l e c t r o n t r a n s f e r (H atom) t o MnO^ , i . e .  Ag  +  +  MnO."  +  4 The  The  ions Hg  2+ 2  >  A'gH  +  +  HMnO "  2  oxidation of formic  the m o l e c u l e HCOOH and the o t h e r  H  4  a c i d t a k e s p l a c e by two paths one i n v o l v i n g a t t r i b u t e d t o t h e formate i o n HCOO~.  2+ 3+ , Hg and T l apparently  r e a c t w i t h HCOO  by t h e  same mechanism which i n v o l v e s c o o r d i n a t i o n w i t h t h e oxygen o f formate i o n . T h i s p e r m i t s t h e t r a n s f e r o f two e l e c t r o n s t o the m e t a l i o n s . Tl  +  i s formed d i r e c t l y .  The product  W i t h the mercury c a t i o n s mercury atoms are t h e  d i r e c t p r o d u c t s o f the r e a c t i o n .  The  mechanism o f t h e C o ( l I I ) r e a c t i o n may be d i f f e r e n t .  i s a p o w e r f u l one e l e c t r o n o x i d a n t  Co(lll)  and both t h e formate i o n and f o r m i c  acid  r e a c t i o n s may take p l a c e by an hydrogen atom t r a n s f e r .  The The  permanganate o x i d a t i o n s a r e q u i t e d i f f e r e n t f o r t h e two paths.  formate i o n r e a c t i o n q u i t e l i k e l y t a k e s p l a c e by a h y d r i d e  to MnO/.  ion transfer  T h i s i s i n l i n e w i t h Wiberg and Stewart's (121)' o b s e r v a t i o n  there i s a l a r g e deuterium isotope e f f e c t . t h a t simple,  that  The r e a c t i o n i s n o t a l t o g e t h e r  however, as t h e r e i s a l s o c o n s i d e r a b l e  oxygen t r a n s f e r from  12'  MnO^~ to the product COg. There i s no deuterium isotope effect i n the formic acid reaction and i t has been postulated that the mechanism involves nucleophilic attack on the carbon atom by a permanganate oxygen, OH i ~0 - C - 0 - MnOo i H 3+  The catalysis by Fe  of the oxidation of formate by permanganate  i s attributed to a mediating effect permitting the formation of Mn(Vl) rather than Mn(V) as the i n i t i a l reduction product according to HGOO" + MnO " + F e  3 +  >  H  + GO  +  4  + MnO. ' +  <s  2  Fe  2 +  4  The catalysis has been assumed to apply to the formate reaction rather than the formic acid reaction although this has not been definitely established.. The carbon monoxide reduction of permanganate i s seen to be analogous i n some respects to the formic acid reduction.  In both cases the postu-  lated mechanisms involve attack on the carbon atom by a permanganate oxygen. The reactions of carbon monoxide with Ag(l) and Hg(ll) seem closer to those of hydrogen than to those of formate.  This i s probably related to  the nature of the intermediates? those of hydrogen and carbon monoxide being more covalent than those of formate ion. The catalytic reduction of permanganate by carbon monoxide i s not like the catalytic reduction by hydrogen. Rather i t i s very close to the carbon monoxide reductions of Hg(ll) and Ag(l).  The key to these reductions  seems to be the formation of carbon monoxide insertion complexes.  128. Both A g ( l ) and H g ( I l ) are d s t a b l e CO has  1 0  complexes and A u ( l ) which r e p o r t e d l y o x i d i z e s CO  extensive d - s mixing.  He  Orgel  (147)  enough t o  a t t r i b u t e s the f a c t t h a t these  to form l i n e a r complexes to t h i s m i x i n g .  ions  F o r the i s o e l e c t r o n i c i o n s  tend  Zn(ll)  C d ( I l ) the energy d i f f e r e n c e s are too l a r g e f o r t h i s t o take p l a c e .  T l ( l l l ) ion i s intermediate o f H g ( l l ) , but  having  and  N e i t h e r C d ( l l ) nor  i t i s u n l i k e l y that Zn(Il) i s active.  which are a c t i v e towards CO  The  a d - s s e p a r a t i o n much g r e a t e r than t h a t  somewhat l e s s than t h a t o f Z n ( l l ) .  have any e f f e c t on CO  and  (105).  p o i n t e d out t h a t the d - s s e p a r a t i o n o f these i o n s i s low  permit  and  Ions as are C u ( l ) which forms q u i t e  The  Tl(IIl) ions  presumably donate d - e l e c t r o n s to form p i bonds  can then form r e a s o n a b l y  s t r o n g m e t a l - c a r b o n sigma bonds through  the  d - s hybridization.  Comparison o f the I s o e l e c t r o n i c S p e c i e s CO,  N  2  and  CN''  Carbon monoxide resembles n i t r o g e n i n i t s p h y s i c a l p r o p e r t i e s , but i s c l o s e r to c y a n i d e  i n chemical  behaviour.  The  r e l a t i v e chemical  activity  o f the t h r e e s p e c i e s can be i l l u s t r a t e d by r e f e r e n c e to the ease of the  ad-  d i t i o n o f an oxygen atom.  N  +  &)  CO  +  ^P  CN"  +  io  2  2  2  2  J a f f e and  >  N0  AF°  = 24.8  >  C0  AF°  =  -61.4  kcal/mole  >  OCN"  AF°  =  -63.2  kcal/mole  Orchin  2  2  (95) have g i v e n an e x p l a n a t i o n of the d i f f e r e n c e s  i n the r e a c t i v i t i e s o f n i t r o g e n and  The 2s  and 2 p  x  one  carbon monoxide.  (x i s the i n t e r a t o m i c a x i s ) atomic o r b i t a l s o f  n i t r o g e n atom can h y b r i d i z e o r mix s m a l l amount and  kcal/mole  t o form two  sigma o r b i t a l s one  w i t h a l a r g e amount o f p- c h a r a c t e r .  with  These new  the a  orbitals  129. will have energies somewhat above the original s- level and below the original p- level respectively.  The energies of the remaining pi orbitals  are unchanged from the original p- levels.  The hybridized atomic orbitals  of nitrogen w i l l contain two electrons i n the lowest sigma orbital, one i n the next sigma orbital and two i n the doubly degenerate pi orbitals.  When  two nitrogen atoms combine the f i r s t sigma orbitals remain unchanged and may be identified with the lone pairs of electrons on the two nitrogen atoms. The second sigmse orbitals combine to form a strong sigma bonding molecular orbital and a high energy, vacant, sigma antibonding molecular orbital.. Similarly the pi orbitals combine to form a degenerate pair of pi bonding orbitals and a degenerate pair of pi antibonding orbitals.  The relative  levels of these i n increasing order are bonding sigma, non-bonding sigma, bonding pi a l l f u l l y occupied.  The lowest unoccuDied orbital i s an anti-  bonding pi orbital. The points of interest are that the lone pairs being largely of s- character have no directional tendencies. The highest occupied orbital i s a bonding orbital so that electron promotion or ionization w i l l weaken the interatomic bond.  The lone pairs being in low lying levels will have  l i t t l e or no tendency to take part in sigma bonding. In the formation of the carbon monoxide molecule the atomic orbitals of carbon and oxygen are also hybridized.  Because of the differ*-  ences i n atomic charges the situation will not be the same as with nitrogen. The lowest oxygen sigma orbital w i l l be considerably below the lowest carbon sigma orbital so these w i l l not combine.  The lowest carbon sigma orbital  w i l l contain one electron and w i l l combine with the second oxygen sigma orbital also containing one electron to form the sigma bonding and antibonding orbitals.  The pi orbitals will combine as before to form bonding  130. and  a n t i b o n d i n g o r b i t a l s , but the bonding p i o r b i t a l w i l l l i e below the  second sigma o r b i t a l o f carbon.  T h i s l a t t e r o r b i t a l w i l l c o n t a i n the  carbon  l o n e p a i r and b e i n g l a r g e l y p i n c h a r a c t e r w i l l be s t r o n g l y d i r e c t i o n a l . A l s o w i t h carbon monoxide the h i g h e s t o c c u p i e d o r b i t a l b e i n g non-bonding, i o n i z a t i o n w i l l not weaken the carbon - oxygen bond.  The  c y a n i d e i o n w i l l be q u a l i t a t i v e l y s i m i l a r t o carbon monoxide.  The main d i f f e r e n c e s are t h a t as carbon  and n i t r o g e n are c l o s e r than  and oxygen the s e p a r a t i o n of the l e v e l s w i l l not be as pronounced.  carbon Further-  more, the cyanide i o n w i t h a lower n u c l e a r charge w i l l have one e l e c t r o n h e l d much l e s s s t r o n g l y than i n carbon monoxide.  The i o n i z a t i o n p o t e n t i a l s of the s p e c i e s are* Ng k c a l ; CN*  103  kcal.  359 k c a l ; CO  These f i g u r e s are i n accord w i t h the r e l a t i v e  324.  reac-  tivities.  Another f a c t o r i n c o n s i d e r i n g the r e a c t i v i t i e s i s the energy d i f f e r e n c e s between the non-bonding sigma o r b i t a l s and orbitals.  Both carbon monoxide and  cyanide complexes are s t a b i l i z e d  v a r y i n g degrees by back bonding to t h e i r vacant d o n a t i o n from a l i g a n d  the a n t i b o n d i n g p i  pi orbitals.  sigma o r b i t a l and back d o n a t i o n  2  o r d e r of t h e i r  168  k c a l ; CO 138  reactivities.  k c a l ; CN"  115  kcal.  Electron  to a p i o r b i t a l i s  e q u i v a l e n t to an e l e c t r o n t r a n s i t i o n between these l e v e l s . v a l u e s are* N  to  The p e r t i n e n t  These again are i n the  131.  BIBLIOGRAPHY  1.  J . H a l p e r n , J . Phys. Chem. 63, 398 (1959).  2.  B. J . Z w o l i n s k i , R. J . Marcus and H. E y r i n g , Chem. Rev.,  3.  F. B a s o l o and R. G. Pearson, "Mechanisms o f I n o r g a n i c R e a c t i o n s , John W i l e y and Sons, I n c . , New York, 1958, Chapt. 7.  4.  H. Taube, i n "Advances i n I n o r g a n i c Chemistry and R a d i o c h e m i s t r y " , V o l . 1, Ed. H. J . E m e l i u s and A. G. Sharpe, Academic P r e s s , I n c . , New York, 1959, p. 1.  5.  P. George and J . S. G r i f f i t h , i n "The Enzymes", V o l . 1, 2nd ed., Ed. Boyer, L a r d y and R. Myrback, Academic P r e s s I n c . , New York, 1959, Chapt. 8.  6.  D. R. S t r a n k s , i n "Modern C o o r d i n a t i o n Chemistry", Ed. J . Lewis and  157 (1955).  R. G. W i l k i n s , I n t e r s c i e n c e P u b l i s h e r s I n c . , New York, I960, Chapt. 2. 7.  J . H a l p e r n , Quart. Rev., 15_, 207 (1961).  8.  J . C. Sheppard  9.  H. Taube, H. Myers and R. L . R i c h , i b i d . ,  and A. C. Wahl, J . Am. Chem. Soc. 7 2 , 1020 (1957). 75_, 4118 (1953).  10.  H. Taube, H. Myers, i b i d . ,  11.  A. Haim and W. K. Wilmarth, i b i d . ,  12.  J , S i l v e r m a n and R. W. Dodson, J . Phys. Chem., j>6, 846 (1952).  13.  R. W. Dodson and N. Davidson, i b i d . , j>6, 866 (1952).  14.  J . H u d i s and R. W. Dodson, J . Am. Chem. Soc. 78, 911 (1956).  15.  A. E . Ogard  16.  R. K. Murmann, H. Taube and F. A. P o s e y , i b i d . , 7 2 , 262 (1957).  16A.,  76, 2103 (1954).  and H. Taube, i b i d . ,  8 2 , 509 (1961).  80, 1084 (1958).  M. Ardon, J . L e v i t a n and H. Taube, i b i d . , 84., 872 (1962).  17.  A. Z w i c k e l and H. Taube, i b i d . ,  83, 793 (1961).  18.  H. Taube, i b i d . ,  19.  A. M. Z w i c k e l and H. Taube, D i s c . Faraday Soc., 2 2 ,  20.  N. A. Bonner and J . P. Hunt, J . Am. Chem. S o c , 82, 3826 ( i 9 6 0 ) .  21.  W. F. L i b b y , J . Phys. Chem. ^6, 863 (1952).  22.  R. J . Marcus, B. J . Z w o l i n s k i and H. E y r i n g , i b i d . , j>8, 432 (1954).  77, 4481 (1955). 42  (i960).  132. 23,  D. Cohen, J. C. Sullivan and J. C. Hindman, J . Am. Chem. S o c , 76, 352 (1954).  24,  D . Cohen, J. C. Sullivan, E. S. Amis and J. C. Hindman, ibid., 78, 1543 (1956).  25.  R. A. Marcus, J . Chem. Phys., 2£, 966 (1956).  26.  R. A. Marcus, ibid., 26, 867 (1957).  27.  R. A. Marcus, ibid., 26, 872 (1957).  28.  R. A. Marcus, Disc. Faraday Soc., 29_, 21 (i960).  29.  N. s . Hush, Trans. Faraday Soc, £7, 557 (1961).  30,  R. E. Kirk and A. W. .Browne, J. Am. Chem. Soc. j>0, 337 (1928).  31.  V. C. E. Higginson, D. Sutton and P. Wright, J . Chem. Soc. 1380 (1953).  32.  w. C. E. Higginson and D. Sutton, ibid., 1402, (1953).  33.  w. C. E. Higginson and P. Wright, ibid., 1551 (1955).  34.  w. C. E. Higginson and J. Marshall, ibid., 447 (1957).  35.  L. Michaelis, Cold Spring Harbor Symposia Quant. Biol., 7, 33 (1939).  36.  F. H. Westheimer, i n "The Mechanism of Enzyme Action" Ed. W. D. McElroy and B. Glass, Johns Hopkins Press, Baltimore, 1954, p. 321,  37.  F. Basolo and R. G. Pearson, Reference 3, p. 305.  38.  H. Taube, Reference 4, p. 3.  39.  P. A. Shaffer, J. Am. Chem. Soc. 5J>, 2169 (1933).  40.  P. A. Shaffer, Cold Spring Harbor Symposia Quant. Biol., 7, 50 (1939).  41.  A. E. Remick, J. Am. Chem. S o c , 62, 94 (1947).  42.  J. Halpern, Can. J. Chem., 37, 148 (1959).  43.  J. Halpern, E. R. MacGregor and E. Peters, J. Phys, Chem., 60, 1455 (1956).  44.  J. Halperin and H. Taube, J. Am, Chem. S o c , 74_, 375 (1952).  45.  R. Stewart, ibid., 72, 3057 (1957).  46.  B. J. Masters and L. L. Schwartz, ibid., 83, 2620 (1961).  47.  E. Rona, ibid., 72, 4339 (1950).  48.  T. W. Newton, J. Phys. Chem., 62, 1493 (1959).  49.  T. w. Newton, ibid., 6j2, 943 (1958).  133. 50.  J . C. S u l l i v a n , A. J . Z i e l e n and J . C. Hindman, J . Am, Chem, S o c , 82, 5288 (1960).  51.  R. H. B e t t s , Can. J . Chem., 33_, 1780 (1955).  52.  F. B. Baker, T.  53.  J . H a l p e r n and J . G. Smith, Can. J . Chem.,  54.  F. B. Baker and T. W. Newton, J . Phys. Chem., 6j>, 1897 (1961).  55.  E.  56.  J , J . Katz and G. T. Seaborg, "The Chemistry o f the A c t i n i d e Methuen and Co., L t d . , London, 1957.  57.  T. W. Newton and F . B. Baker, I n o r g . Chem., 1, 368 (1962).  58.  G, Gordon and H. Taube, i b i d . ,  59.  E . R o i g and R. W. Dodson, J . Phys. Chem. 65_, 2175 (1961).  60.  S. W. G i l k s and G. M. Waind, D i s c  61.  B. B a y s a l , A c t e s I n t e r n . Congr. C a t a l y s e , 2 , P a r i s I960, 1, 559 (Pub. 1961).  62.  L . G. C a r p e n t e r , M. H. Ford-Smith, R. P. B e l l and R. W. Dodson, D i s c Faraday Soc., 2<?, 92 (i960)..  63.  C. H. Brubaker, J r . , and J . P. M i c k e l , J . I n o r g . N u c l e a r Chem., ^ , 55 (1957).  64.  C. H. Brubaker, J r . , K. 0. Groves, J . P. M i c k e l and C. P. Knop, J . Am. Chem. S o c , 22, 4641 (1957).  65.  C  66.  K. G. A s h u r s t and W. C. E . H i g g i n s o n , J . Chem. Soc., 3044 (1953).  67.  F. R. Duke and B. Bornong, J . Phys. Chem., 60, 1015  68.  D. H. I r v i n e , J . Chem. S o c , 1841 (1957).  69.  K. G. A s h u r s t and W. C. E. H i g g i n s o n , J . Chem. S o c ,  70.  A. M. Armstrong  71.  M. Ardon and R. JL P l a n e , J . Am. Chem. Soc., 81, 3197 (1959).  72.  W. C. E. H i g g i n s o n , D. R. R o s s e i n s k y , J . B. Stead and A. G. Sykes, Faraday Soc., 2_2, 49 (i960).  73.  A. G. Sykes, J . Chem. Soc.,  74.  J . W. G r y d e r and M. C, Dorfman, J . Am. Chem. S o c , 83, 1254 (1961)..  A. K a n e v s k i i ,  W. Newton and M. Kahn, J . Phys. Chem., 6£, 109 (i960).  34., 1419 (1956).  2216 (i960).  L. A. Fedorova, Zh. Neorg. Khim.,  Elements",  1, 69 (1962).  Faraday S o c , 22, 102  (i960).  e  E . Johnson, J r . , i b i d . ,  74., 959 (1952).  (1956).  343 (1956).  and J . H a l p e r n , Can. J . Chem., 3J5, 1020 (1957).  5549  (1961).  Disc.  134. 75.  A. M. Armstrong  and J . H a l p e r n , u n p u b l i s h e d o b s e r v a t i o n s .  76.  H. N. H a l v o r s o n and J . H a l p e r n , J . Am. Chem. S o c , 78 , 5562 (1956).  77.  J . H a l p e r n and S. M. T a y l o r , D i s c . F a r a d a y Soc., 29_, 174 ( i 9 6 0 ) .  78.  C. H. Brubaker, J r . , i n "Advances i n t h e Chemistry o f C o o r d i n a t i o n Compounds". Ed., S. K i r s c h e n e r , M a c M i l l a n , New York, 1961, p. 117.  79.  A. C. Harkness and J . H a l p e r n , J . Am. Chem. Soc., 81, 3526 (1959).  80.  A. A. F r o s t and R. G. Pearson, " K i n e t i c s and Mechanism" John W i l e y & Sons, I n c . , New York, 1953, p. 17.  81.  G. Biederman, A r k i v Kemi £ , 441 (1953).  82.  K. A. Kraus and F. Nelson, J . Am. Chem. S o c , 72 , 390 (1950).  83.  K. A. Kraus and F. Nelson, i b i d . ,  84.  R. H. B e t t s , Can. J . Chem., 22, 1775 (1955).  85.  "Stability 1958).  86.  W. M. L a t i m e r , "The O x i d a t i o n S t a t e s o f t h e Elements and T h e i r P o t e n t i a l s i n Aqueous S o l u t i o n s " , 2nd ed., P r e n t i c e - H a l l , I n c . , New York, 1952.  87.  T. W. Newton and S. W. Rabideau,  88.  J . H a l p e r n , Quart. Rev., 10, 463 (1956).  89.  J . H a l p e r n , Advances i n C a t a l y s i s 11, 301 (1959).  90.  Y. K. S y r k i n and M. E . D y a t k i n a , " S t r u c t u r e o f M o l e c u l e s and the Chemical Bond", B u t t e r w o r t h s , London 1950, p. 137.  91.  I . Langmuir, J . Am. Chem, S o c , 4JL, 1543 (1919).  92.  R, S. M u l l i k e n , Rev. Mod. Phys.,  93.  W. M o f f i t t , Proc. Roy. Soc., A196, 524 (1949).  94.  R. C. S a h n i , Trans. F a r a d a y S o c , 42, 1246 (1953).  95.  H. H. J a f f e and M. O r c h i n , Tetrahedron, 10, 212 (I960).  96.  C. Mond, C. Langer  97.  J . W. R i c h a r d s o n , i n " O r g a n o m e t a l l i c Chemistry", New York, I960. Chapt. 1.  98.  J . C h a t t , P. L. Pauson, L. M. V e n a n z i , i b i d . , Chapt. 10.  99.  I . Wender, H. W. S t e r n b e r g and M. O r c h i n , i n " C a t a l y s i s " V o l . 5, Ed. P. H. Emmett, R e i n h o l d , New York, 1957, p. 73.  77, 3721 (1955).  C o n s t a n t s , P a r t I I " , Chem. Soc. S p e c i a l P u b l . , No. 7 (London,  J . Phys. Chem., 62, 365 (1959).  and F. Quincke,  1 (1932).  J . Chem. S o c , j>7, 749 (1890). Ed. H. Z e i s s , R e i n h o l d ,  135. 100.  H. W. Sternberg and I . Wender, International Conference on Coordination Chemistry, Chem. Soc. Special Publ. No. 13, London, 1959, p. 35.  101.  T. H. C o f f i e l d , (1957) .  102.  F. Calderazzo and F. A. Cotton, Inorg. Chem., 1, 30 (1962).  103.  M. Katz, Advances i n Catalysis j>, 177 (1953).  104.  J . R. Dixon and J . E. Longfield i n "Catalysis" Vol. 7, Ed. P. H. Emmett, Reinhold, New York, I960.  105.  J . W. Mellor, "A Comprehensive Treatise on Inorganic and Theoretical Chemistry", Longmans Green & Co., London, 1923, pp 909-43.  106.  J . Donan, Monatsh 26, 525 (1905).  107.  J . Donan, i b i d . , 27, 71 (1906).  108.  F. C. P h i l l i p s , Am. Chem. J . 16, 163 (1894).  109.  F. C. P h i l l i p s , i b i d . , 16, 255 (1894).  110.  C. Winkler, Z. Anal. Chem., 28, 269 (1889).  111.  L. M. Dennis and C. G. Edgar, J . Am. Chem. Soc. 12, 859 (1897).  112.  F. Jean, Compt. rend, 135, 746 (1902).  113.  G. Just and Y. Kauko, Z. physik Chem., 82, 71 (1913).  114.  K. A. Hofmann, German Patent 307, 614 (1919).  115.  A. Mermet, Compt. rend. 124, 621 (1897).  116.  G. Bauch, F. Pawlek and K. P l i e t h , (1958) .  117.  A. H. Webster, "A Kinetic Study of Some Homogeneous Reactions of Molecular Hydrogen with Metal Ions i n Aqueous Solution", PhD Thesis, Department of Metallurgy, University of B r i t i s h Columbia, 1957.  118.  S e i d e l , " S o l u b i l i t i e s of Inorganic and Metal Organic Compounds", 3rd ed., Vol. 1, 1940, p. 217.  119.  J . Halpern, J . F. Harrod and P. E. Potter, Can. J . Chem., 37, 1446 (1959).  120.  L. G. S i l l e n , Quart. Rev., 13, 146 (1959).  121.  K. B. Wiberg and R. Stewart, J . Am. Chem. S o c , 78, 1214 (1956).  122.  G. Friedlander and J . W. Kennedy, "Nuclear and Radiochemistry", John Wiley ft Sons, Inc., New York, 1955.  123.  G. J . Korineck and J . Halpern, J . Phys. Chem., 60, 285 (1956).  R. D. Closson, J . Kozikowski, J . Org. Chem., 22, 598  Z. Erz. und Metall., 11, No. 11, 1  136. 124.  W. Schoeller, W. Schrauth and W. Essens, Ber., 46, 2864 (1913).  125.  W. Manchot, ibid., £3, 984 (1920).  126.  J. Halpern and S. F. A. Kettle, Chem. and Ind., 668 (1961).  127.  E. Lange and H. Sattler, Z. physik. Chem., A179, 427 (1937).  128.  J. Halpern and A. C. Harkness, J..Chem. Phys. 31, 1147 (1959).  129.  J. Bigeleisen, ibid., 32.> 1583 (I960).  130.  A. L. W. Kemp, "Kinetics of the Decomposition of Methoxycarbonylmercuric Chloride by Hydrochloric Acid", B.Sc. Thesis, Department of Chemistry, University of British Columbia, 1961.  131.  A. C. Harkness and J. Halpern, J. Am. Chem. S o c , 83_, 1258 (1961).  132.  R. T. McAndrew, "Carbon Monoxide Reduction of Aqueous Silver Acetate", PhD Thesis, Department of Metallurgy, University of British Columbia, 1962.  133.  S. Nakamura and J. Halpern, J . Am. Chem. S o c , 83, 4102 (1961).  134.  S. Nakamura, "Reduction of Silver Amine Complexes", MSc Thesis, Department of Chemistry, University of British Columbia, 1962.  135.  J. J . Byerley and E. Peters, Paper presented at the Annual Meeting of the A.I.M.M.E., Dallas, Feb., 1963.  136.  A. Carrington and M. C. R. Symons, J . Chem. Soc., 3373 (1956).  137.  H. Lux, ZT, Naturforsch, 1, 281 (1946).  138.  T. Freund, J. Inorg. Nuclear Chem., 15_, 371 (i960).  139.  R. Stewart and R. Van der Linden, Can. J. Chem., 38, 2237 (I960).  140.  E. Peters and J. Halpern, J. Phys. Chem., j g , 793 (1955).  141.  A. H. Webster and J. Halpern, ibid., 61, 1239 (1957).  142.  A. H. Webster and J. Halpern, Trans. Faraday Soc, j>3, 51 (1957).  143.  C. E. H. Bawn and A. 0. White, J. Chem. S o c , 339 (1951).  144.  s. M. Taylor and J. Halpern, J. Am. Chem. S o c , 81, 2933 (1959).  145.  J. Halpern, Advances in Catalysis 11, 301 (1959),  146.  A. Carrington, D. Schonland and M. C. R. Symons, J. Chem. Soc 659 (1957).  147.  L. E, Orgel, J . Chem. Soc., 4186 (1958).  

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0062052/manifest

Comment

Related Items