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1. Design and synthesis of new chiral units for potentially ferroelectric liquid crystals : liquid crystals.. 1987

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1. DESIGN AND SYNTHESIS OF NEW CHIRAL UNITS FOR POTENTIALLY FERROELECTRIC LIQUID CRYSTALS: LIQUID CRYSTALS CONTAINING A THI IRAN UNIT. 2. HETEROGENEOUS CATALYSIS OF THE RACEMIZATION OF 1,1'-BINAPHTHYL BY TITANIUM DIOXIDE POWDER. by XIN W A N G A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF CHEMISTRY We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA November, 1987 © XIN WANG, 1987 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 it 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 or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date "Dec DE-6(3/81) Abstract Supervisors: Dr. R.E. Pincock and Dr. G.S. Bates New liquid crystals have been synthesized and their transition phases have been studied. It was found that a family of (-)-2-methyl 2R,3S-epithio-4'-alkoxybiphenyl pentanoates are liquid crystals but a similar system of ( + )-2-methyl 2S,3R-epoxy-4'-alkoxybiphenyl pentanoates are not. Of the liquid crystals, MEAOBP-S-7 exhibits smectic A and B phases; MEAOBP-S-8 and MEAOBP-S-9 show only the smectic B phases; MEAOBP-S-10 shows a monotropic chiral smectic C phase. This distinction is in agreement with the argument that the internal dipolar interaction of the molecule plays an important role in determining liquid crystalline behaviour of this ester system. The reaction rate of the racemization of optically active binaphthyl can be moderately increased in the presence of finely divided titanium dioxide (anatase) powder. This first order catalyzed reaction has a proportional relationship with the concentrations of both the catalyst and the binaphthyl. The catalyzed reaction can be poisoned permanently by the addition of polynuclear aromatic compounds and the poisoning efficiency is dependent of the number of the aromatic rings the poison posesses. By comparison with the catalyzed racemizations of binaphthyl by platinum, nickel and carbon and from the kinetic and mechanistic studies on the titanium dioxide catalyzed racemization, we conclude that (1) this catalytic phenomenon is common among heterogeneous inorganic solids and can be extended to other simple reactions, and that (2) the mechanism of the catalysis probably involves a radical anion intermediate. i i Table of Contents CHAPTER 1 DESIGN AND SYNTHESIS OF NEW CHIRAL UNITS FOR POTENTIALLY FERROELECTRIC LIQUID CRYSTALS: LIQUID CRYSTALS CONTAINING A THIIRAN UNIT 1 1. Introduction „ 2 1.1 Transition phases of liquid crystals 2 1.2 Structure of ferroelectric liquid crystals 7 1.3 Design and synthesis of potentially ferroelectric liquid crystals 10 1.4 The previous work concerning RO-Ph-Ph-OCO-R* 12 1.5 The present work 13 2. Results and Discussion 17 2.1 Synthesis of new compounds 17 2.2 Identification of new liquid crystals 27 2.3 Conclusion 29 3. Experimental 30 3.1 General ".30 3.2 4'-Alkoxy-biphenol: General procedure 31 3.3 (-)2S,3S-Dihydroxy-2-methylpentanoic acid 33 3.4 3-Pentanone acetal of (-)-2S,3S-dihydroxy-2-methylpentanoic acid 34 3.5 3-Pentanone acetal of (-)-2-methyl 2S,3S-dihydroxy- 4'-heptyloxybiphenylpentanoate 34 3.6 (-)2-Methyl 2S,3S-dihydroxy-4'-heptyloxybiphenylpentanoate 35 3.7 ( + )2S-Methyl 2S,3R-epoxy-4'-heptyloxybiphenylpentanoate 37 3.8 2-Methyl 2S,3R-epithio-methylpentanoate 39 3.9 (-)2-Methyl 2R,3S-epithio-4'-heptyloxybiphenylpentanoate (MEAOBP-S-7) ; 40 3.10 S(-)-(c)!v1ethoxy-(0)trifluoromethylphenyl 4'-alkoxybiphenyl acetates .42 CHAPTER 2 HETEROGENEOUS CATALYSIS OF THE RACEMIZATION OF OPTICALLY ACTIVE 1,1'-BINAPHTHYL BY TITANIUM DIOXIDE POWDER 46 i i i 4. Introduction - 4 7 4.1 Heterogeneous catalysis 4 7 4.2 Catalyst titanium oxide 50 4.3 Racemization of binaphthyl 5 7 4.3.1 Uncatalyzed racemization of binaphthyl 57 4.3.2 Photocatalytic racemization of binaphthyl 59 4.3.3 Catalyzed racemization of binaphthyl by C, Ni, and Pt 60 4.3.3.1 The carbon catalyzed racemization 60 4.3.3.2 Platinum catalyzed racemization 61 4.3.3.3 The Interaction of binaphthyl with Raney nickel 61 4.4 The object of the present study 62 5. Results and Discussion 63 5.1 Preliminary kinetic studies and reproducibility 63 5.2 The Effect of concentrations of catalyst, binaphthyl and additives on catalytic activity 72 i. 5.3 Catalytic activity of modified titanium dioxide 75 5.3.1 Preheating titanium dioxide 75 5.3.2 Acid-washing titanium dioxide 77 5.3.3 Illuminating titanium dioxide 77 5.3.4 Reducing titanium dioxide 78 5.3.5 Other sources of titanium dioxide 80 5.3.5.1 Titanium dioxide from titanium tetrachloride .80 5.3.5.2 Rutile materials 82 5.3.6 Colloidal titanium dioxide 82 5.4 Speculation on the catalytic mechanism on the basis of previous and present kinetic results 83 5.5 Conclusion 85 6. Experimental 86 i v 6.1 General .86 6.2 Synthesis of Racemic 1,1'-Binaphthyl .87 6.3 Preparation of Optically Active 1,1'-Binaphthyl .87 6.4 Kinetics of Uncatalyzed and Titanium Dioxide Catalyzed Reactions 88 6.5 Procedure for attempted Titanium dioxide photocatalytic reactions 89 6.6 Product Analysis and Adsorption Experiments using glc 90 6.7 Preparation of Titanium Dioxide from Titanium Tetrachloride 90 6.8 Reduction of Titanium Dioxide 91 BIBLIOGRAPHY 92 v Lists of Tables Table 1: Selected structures of some ferroelectric liquid crystals (page 4) Table 2; Ferroelectric liquid crystals with large spontaneous polarization (page 9) Table 3; Phase transition of liquid crystals C ,H 1 7 -0-Ph-Ph-OCO-R* (page 13) Table 4; 'H nmr chemical shift of the tertiary proton in the thiiran ester and its precursors (page 22) Table 5: 4'-Alkoxybiphenols by alkylation of 4,4'-biphenol (page 32) Table 6: A classification of heterogeneous catalysts according to the their principal functions (page 50) Table 7: Properties of different forms of titanium dioxide (page 51) Table 8: Dependence of Kobs of Aldrich anatase catalyzed racemization of binaphthyl on the concentration of binaphthyl (page 73) Table 9; Catalytic activity of modified titanium dioxide towards the racemization, part 1 (page 76) Table 10: Catalytic activity of modified titanium dioxide towards the racemization, part 2 (page 79) v i Table 11; Catalytic activity of modified titanium dioxide towards racemization, part 3 (page 82) Table 12: Catalytic activity of four inorganic solids towards the racemization of optically active binaphthyl (page 84) Lists of Figures Figure 1: Partial JH nmr spectra of (-)-2-methyl 2R,3S-epithio- 4'-heptyloxy- biphenyl pentanoate (400MHz, CDCI }): (1) normal spectrum; (2) spectrum with irradiation at 3.70 ppm; (3) spectrum with irradiation at 1.15 ppm (page 23) Figure 2: Liquid crystal phases of (-)-2-methyl 2R,3S-epithio4'-heptyloxy- biphenyl pentanoate: (1) smectic A ; (2) smectic B (X100) (page 25) Figure 3; Chiral smectic C phase of (-)-2-methyl 2R,3S-epithio4'-decyloxy- biphenyl pentanoate (X200) (page 26) Figure 4; First order kinetic catalyzed racemization of optically active 1,1'-binaphthyl by highly dispersed titanium dioxide (page 64) Figure 5; Several identical kinetic runs of catalyzed racemization of optically active binaphthyl by highly dispersed titanium dioxide (page 65) Figure 6: Dependence of the concentration of titanium dioxide on the observed kinetic rate constants of catalyzed racemization of optically active 1,1'-binaphthyl by highly dispersed titanium dioxide (page 67) Figure 7: Dependence of the concentration of the additive benzene on the observed kinetic rate constant of catalyzed racemization of optically active 1,1'-binaphthyl by highly dispersed titanium dioxide (page 68) v i i i Figure 8: Dependence of the concentration of the additive naphthalene on the observed kinetic rate constant of catalyzed racemization of optically active 1,1'-binaphthyl by highly dispersed titanium dioxide (page 69) Figure 9: Dependence of the concentration of the additive anthrance on the observed kinetic rate constant of catalyzed racemization of optically active 1,1'-binaphthyl by highly dispersed titanium dioxide (page 70) Figure 10: Dependence of the concentration of the additive pyrene on the observed kinetic rate constant of catalyzed racemization of optically active 1,1'-binaphthyl by highly dispersed titanium dioxide (page 71) i x Acknowledgements I wish to express my grateful thanks to Dr. R.E. Pincock for his encouragement and guidance during the course of this work, and to Dr. G.S. Bates for his generous opportunity and guidance during the last year of this thesis. I would like to thank Barbara Frisken for her time and help in assistance of identifying the liquid crystal materials. My thanks are extended to the staff and the technicians of the Chemistry Department for their excellent sevice. The fiancial assistance from the Chinese government and the University of British Columbia is gratefully acknowledged. Finally, I would like to thank my wife, Chun, for her patience and understanding. x CHAPTER 1 DESIGN AND SYNTHESIS OF NEW CHIRAL UNITS FOR POTENTIALLY FERROELECTRIC LIQUID CRYSTALS: LIQUID CRYSTALS CONTAINING A THIIRAN UNIT 1. I N T R O D U C T I O N The advent of a b is tab le , f a s t - s w i t c h i n g , e lect roopt ic l ight-va lve b a s e d on the propert ies of fer roe lect r i c s m e c t i c l iquid c r y s t a l s 1 has aroused cons iderab le interest in the s y n t h e s i s and engineering of new s m e c t o g e n s suitable for appl icat ions o f this nature. The f irst part of this thesis wi l l deal with the synthes i s of n o v e l organic c o m p o u n d s , which potentia l ly can exhibit the propert ies of l iquid c rysta ls and hopefu l ly a lso be ferroe lectr ic . 1.1 T R A N S I T I O N P H A S E S OF LIQUID C R Y S T A L S The sc ience of l iquid c rys ta l s began in 1888, with the research of Fr iedr ich Reinitzer, an Aust r ian botanist w h o prepared cho lestery l benzoate and found it to have two interest ing propert ies . When heated, its crystal lattice c o l l a p s e s at 145°C to f o r m a turbid l iquid. A t 179°C , the turbid l iquid d isappears and an i sot rop ic l iquid is f o r m e d . S ince then, about one o f every two hundred organic c o m p o u n d s has been found to exhibit l iquid crysta l phase(s). For centur ies , sc ient is ts have c o n s i d e r e d only three states of matter s o l i d s , l iquids, and gases . In s o l i d s , a t o m s or mo lecu les are bound and ordered; in l iquids, they are bound and d i s o r d e r e d ; in gases , they are on ly very w e a k l y bound and a l so are d i sordered . Liquid crysta ls are mater ia ls in which order is p r o g r e s s i v e l y relaxed as one proceeds f r o m a true so l id to a true l iquid. L iquid c rys ta l s o c c u p y a grey area between true s o l i d s and true l iquids. A l though liquid c rysta ls exhibit certain aspects of both the so l id and l iquid s tates , they a lso p o s s e s s propert ies that are not found in either l iquids or s o l i d s . Their order ing propert ies , for example , can be contro l led by ordinary magnet ic and/or e lectr ic f i e l d s . 2 3 The liquid crystals commonly referred in the literature are thermotropic liquid crystals, i.e. their properties are temperature dependent. The other major branch of liquid crystals, called lyotropic liquid crystals, are often two-component systems composed of water and amphiphilic compounds, and will not be described. (See references 2-3 for reviews on this subject) Thermotropic liquid crystals, which form naturally over a specific temperature range, are further classified as either nematic or smectic. "Nematic" comes from the Greek word for thread; nematic crystals have a thread-like pattern when viewed through a microscope equipped with crossed polarizers. "Smectic" from the Greek for soap, decribes these crystals' greasy or soapy properties. \j< Isotropic structure (unordered, nonliquid crystalline) A LlUilKllJl...: Hill llllllllll llllllllll llll nm IIIIIIIIII iin in in 11 ml Smectic A structure /////////// f///////////\ //////////A ////////// Ordinary nematic structure Cholesterfc structure Smectic C structure (Reproduced from reference 2) A general description of many of the various types of liquid crystal phases are given below (page 4). In a typical nematic liquid crystal, the only structural restriction is that the long axes of the molecules maintain a 4 Thermotroplc liquid crystals have either nematic or smectic structures C t o M Qptterf erteertte* Tartan* s w w t a r e N E M A T I C S Crdbtary nematic Unlaxlaity positive Sehlleren; threaded; marbled; pseudo- Isotropic; homogeneous Parallelism of long molecular axes p-Azoxyanisole; jMrwthoxybertzytldene; rtft4utyl)eniline ChoWtttrte- nemetlc Un lax laity negative or Isotropic; optically active Focal conic with Orandjean steps; homogeneous; Isotiopic Nematic packing In planes; superimposed twist m direction perpendicular to long axes of molecules Chotassyy! aunanoate Blue phase * Isotropic; optically active Platelet with ttandjoan steps Cubic Choiestenjl nonanoate S T R U C T U R E D S M E C T I C S Smectic B Uniaxially positive Mosaic; stepped drops; pseudo-isotroplc; homogeneous Layer structure; molecular axes orthogonal to the layers; hexagonal arrangement within the layers Ethylethoxybenzylidene- amlnocinnamate; twephthaUris-butylani- Nne Smectic E Biaxlally positive Mosaic; pseudo-isotroplc Layer structure; molecular axes orthogonal to the layers; ordered arrangement within the layers CH-n-propyBerphenyt- dlcarboxylate Smectic 0 Biaxially positive Mosaic Layer structure with ordered arrangement within the layers 2^4-r>Pentylpheny1)-M4-rt" pentyloxyphenytlpyrlmldlne Snwdlc H Biaxlally positive Fan Tilted analogue of smectic F Smectic 1 Biaxially positive Mosaic; fan-shaped texture with stripes across the fans Hexagonal correlation bv the-plane and the tilt direction Is uniform toward neighboring molecules 4-rKPentytMnzenethlo-4'-/v octyloxybenzoate U N S T R U C T U R E D S M E C T I C S Smectic A Uniaxially positive Focal conic (fan-shaped or polygon); stepped drops; homogeneous; pseudo-isotroplc Layer structure; molecular axes orthogonal to the layers; random arrange- ment within the layers Dietriylazoxybenzoate SfllOCtlC C Biaxlally positive Broken focal conic; echlieren; homogeneous Layer structure; molec- ular axe* mted to the layers; random arrange ment within the layers Oodecytoxyazoxybenzene Smectic D Isotropic Isotropic; mosaic Cubic structure 4'^ctadecytexy-3'-nltrodl- phenyl < carboxyllc acid SmoctJc F Biaxlally positive Sehlleren; broken focal conic Layer structure 2-(4-r> ên1ylphenyt)-5-(4- r>pontyloxyphonyl>- n f l i t • • • .pyrvniora I H M "UqJt Cfy»M» a* ftototfatf Mm" ty A i.« w k a a w w a H f k e M i (Reproduced f r o m r e f e r e n c e 2) 5 parallel or nearly parallel arrangement over macroscopic distances. The nematic phase always changes on heating to an isotropic liquid. Cholesteric liquid crystals, first observed with cholesteryl esters, are formed by some optically active organic compounds, or mixtures of such compounds. They are miscible with ordinary nematic liquid crystals and have local nematic packing of the molecules. There are basically two types of smectic phases, of which orthogonal smectics include the smectic A , B, and E phases; and tilted smectics* include smectics C, F, G, H, I, J , and K. Smectic A liquid crystals are the least ordered of the orthogonal smectic phases. In the smectic A phase, the molecules are arranged with their molecular long axes perpendicular to the phases of the layers. The lateral distribution of the molecules within each layer is random, and the molecules are able to rotate freely about their long axes. In the smectic B phase, the molecules are arranged in layers with the molecular centers positioned in a hexagonal close-packed array. The molecules are also rotating quite rapidly about their long axes. The smectic E phase has in-plane packing which is rectangular, with long-range positional correlations. The smectic C phase is one in which the molecules are randomly close packed in layers; in a given domain the molecules are tilted in particular direction with respect to the layer planes. Like smectics A and B, the molecules in smectic C phase rotate about their long axes with no associated processional rotation. In smectics I and F5-', the molecules are tilted in their layers. In the plane, at right angles to the tilt direction, the molecules are hexagonally close packed. In the I phase the molecules are tilted towards the apex, 6 while in the F phase they are tilted towards one side of the hexagon. In smectics J and G 5* 1, the molecules again are tilted within the layers. In the plane at right angles to the tilt direction they are hexagonally close packed. Smectics J and G are distinguished by their tilt directions, J is tilted towards the apex while G towards the side of the hexagonal net. Smectic H and K phases are similar to J and G except the molecules are packed in a rectangular base centered net which has smaller dimerisons than the hexagonal net of J and G. While liquid crystals have been known for a century or more, ferroelectric liquid crystals were first recognized by Meyer' in 1975. A ferroelectric liquid crystal (FLC) is a compound or a mixture possessing at least one chiral smectic phase which exhibits the ferroelectric property, i.e. shows spontaneous polarization. The material constants 1 0, with which ferroelectric liquid crystals may be characterized, are (1) the transition temperature; (2) the tilt angle; (3) the helical pitch; (4) the refractive index; (5) the spontaneous polarization; (6) the critical field to unwind the helix; (7) the elastic constant and (8) the viscosity coefficient. It is beyond the scope of this thesis to describe all of the elements concerning a ferroelectric liquid crystal. From the applicative point of view, a chemist's greatest interest is the transition temperature, i.e., the temperature range where ferroelectric smectic phases are retained. There are seven smectic modifications which have the symmetry elements required to exhibit ferroelectric behaviour. Of these, three are fluid smectic liquid crystal phases ( Sm* C, Sm* I, and Sm* F, here * denotes a chiral smectic phase ), and another four (Sm* J , G, H, and K) are orientationally disordered crystal phases. Chiral smectogens possessing those 7 smectic phases may exhibit ferroelectic properties. The Sm* C phase is the least ordered phase of the seven known chiral smectic phases and is thus the most important one in so far as the application is concerned. For the purpose of applications, FLC materials are required to exhibit a high spontaneous polarization, to have a wide liquid crystalline temperature range, and to be stable, to exhibit a smectic A phase on cooling from the isotropic liquid required for alignment purposes. It is common practice to broaden the temperature range of desired phases by formulating eutectic mixtures. Indeed, many commercial liquid crystal materials are multi-component mixtures in some cases containing seven or eight individual compounds. In given liquid crystal phases (e.g. the SmA and Sm*C phases) different compounds are in general miscible, and there is no depression observed in, for example, the SmA to Sm*C transition upon mixing. For pure compounds with monotropic phases, it is generally possible to obtain thermodynamically stable liquid crystal phases by such formulation. 1.2 STRUCTURE OF FERROELECTRIC LIQUID CRYSTALS Ferroelectric smectic liquid crystals show potential for becoming increasingly important in electrooptic display device applications. However, the numbers of materials available for these applications are limited, particularly those which exhibit a ferroelectric, chiral smectic C phase. A number of typical ferroelectric liquid crystals are listed in Table 1. They have been classified into two types; type A in which the chiral unit is connected to the core unit by means of etherification f-Ph-O-R*. R*=chiral unit), and type B in which the chiral unit is joined to the core unit by esterification f-Ph-COO-R* or -Ph-OCO-R*i . 8 Table 1. Selected structures of ferroelectric liquid crystals Type A RO-Ph-OCO-Ph-O-CHjC^H^HjJCjH, RO -Ph-COO-Ph-0-CH ,C*H(CH ,pCH, RO -Ph-N rrCH-Ph-O-CHjC'HCCHjJCjH, RO -Ph-CH=CH-COO -Ph-0-CH 1 C«H(CH,)C J H j . RO-Ph-OCO-Ph-OCO-PH-O-CHjC-HCCHj^jH, RO-Ph-Ph-OCO-Ph-CHjCTiCCHjV^Hj Type B RO-Ph-Ph-COO-CH,C»H(CH J )C J H J RO-Ph-Ph-OCO-C»H(CI)C 3 H, RO-Ph-COO-Ph-COO-CHjC'HCCHjJCjH, RO -Ph-COO -Ph-CH = CX-COOCH 3C*H(CH,)C 1H J. X = C N , Cl . H. RO-Ph-CH =N -Ph-CH =CH-COO-C*H(CH }yC,H, RO -Ph-CH=CH-COO -Ph-COO-CH,C»H(CH,)C 1 H J Where R = CnH2n + 1; Ph = 1,4-substituted phenyl group; • = chiral center; (The same notation also is applied in subsequent sections) 9 Examination of the structures of materials which typically exhibit ferroelectric smectic phases shows that the optical center (hereafter simply referred to as the chiral unit) is normally at one end of the molecule. In this position, it is relatively free to rotate independently of the rest of the molecule (hereafter simply referred to as the core unit) which is also rotating, and in particular to the highly sensitive polarizable central core which contains the delocalized T T electrons 1 1. In this situation, the contribution by the core to the dipole associated with the chiral center will be reduced because the lateral dipole of the core will be rotating independently of the asymmetric center and therefore will not contribute greatly to the net resultant dipole 1 1 . Spontaneous polarization is the second most important physical property of a FLC, next to the transition temperature. Tilted chiral smectic phases possess a spontaneous ferroelectric polarization or macroscopic dipole moment, derived from dissymmetry in the orientation of the molecular dipoles in the liquid crystal phase. The strength of the spontaneous polarization can be increased considerably by restricting the freedom of rotation of the chiral center in relation to the molecule as a whole. Movirg the chiral unit closer to the core creats a direct interaction between the the chiral unit and the core unit via dipolar coupling and restricted rotation thus also strengthening the spontaneous polarization. Table 2 Ferroelectric liquid crystals" ' 1 4 with large spontaneous polarizations FLC Ps(nc/cm») C u H„-Ph-OCO-Ph-Ph-0 -C^(CH, )C,H„ 60 C,H,,-0-Ph-OCH,-Ph-COO-C ,H(CH,)C,H T 99 C l H I t-0-Ph-Ph-OCH 1 -Ph-COO-C«H(CH,)C,H, 99 C,^ n-0 -Ph-Ph-OCH,-Ph -COO-C«H(CH J )C < H u 145 C TH I J-0-Ph-Ph-OCO-C«HCIC«H(CH,)C 1H 1 220 10 Type B FLC's generally possess higher spontaneous polarization than type A systems. For instance, C,H1 5OPhPhOCOC*HCIC*H(CH3)CjH5 exhibits the highest spontaneous polarization known to date to the best of our knowledge. It is then concluded that the greater the dipolar interaction between the chiral unit and the adjacent carbonyl group of the core unit and the less internal rotation of the chiral unit with respect to the core unit the greater will be the spontaneous polarization in type B FLC's. Unfortunately, it seems that the dipolar interaction between the chiral and the core unit can have detrimental effects on the stability of the ferroelectric phase. This is especially the type of Sm* C phase which is often lost from the phase diagram as the chiral center is positioned adjacent to the core 1 1 . It may be possible to design the "ideal" FLC's by placing the chiral units, especially those with the strong polar groups attached, into the "right" location in the structure of the type B FLC's, thereby producing a FLC series not only showing a wide range of chiral smectic C phase around room temperature but also exhibiting extremely high spontaneous polarization. 1.3 DESIGN AND SYNTHESIS OF POTENTIALLY FERROELECTRIC LIQUID CRYSTALS The first requirement in the synthesis of materials which possess ferroelectric phases is to produce materials which exhibit tilted smectic phases. Many studies of numerous ferroelectric liquid crystals have already provided guidelines for this initial operation 1 1. Three fundemental criteria 1 1 are in general considered essential: (a) an alkyl-aryl—alkyl system; (b) strong terminal lateral dipoles; and (d) a chiral center which produces the asymmetry of the phase, and produces the ferroelectric properties. In 11 simpler terms, the design of a new potentially FLC is to develop the appropriate chiral and core units and then properly connect them together. The core units found in most known ferroelectric liquid crystals have been well established in the past decade. The greater difficulty in synthesizing new ferroelectric liquid crystals now lies in the preparation of the appropriate chiral units and their fusion with central core uniis in a way that the resulting molecules possess the necessary liquid crystalline properties. Relatively little investigation of new chiral units has occurred. So far, readily available optically active commercial compounds and their derivatives have been successfully incorporated into almost all of the well-established core units. For example one of the main precusors is commercially available S(-)-2-methylbutanol which has been modified to suitable derivatives as shown below." These derivatives have been used in almost all of the known FLC structures. However, a disadvantage of those compounds is the fact that 12 the chiral center is not polar enough to induce very high spontaneous polarizations. There are a number of commerically available optically active amino acids and several have been modified for incorporation into liquid crystals. L-lsoleucine, for instance, was converted to optically active 3-methyl 2-chloropentanoic acid, which could further be reduced to the corresponding optically active alcohol". Optically active 3-methyl 2-chloropentanoic acid and optically active 3-methyl 2-chloropentanol have been reported extremely useful since ferroelectric liquid crystals derived from them possess two chiral centers showing unusual ferroelectric properties 1 6. Similarly, 2-chloro-2-methyl butanoic acid also prepared from the corresponding amino acid has been successfully used in synthesizing many new ferroelectric liquid crystals 1 7 . The advantage for those chlorine containing materials over the alkyl series above is the fact that these chiral units are more polarizable. 1.4 THE PREVIOUS WORK CONCERNING RO-PH -PH-OCO-R* Studying the system of RO-Ph-Ph-OCO-R* (R» = chiral unit) is of great interest to us not only because of the potential for exploring and utilizing new chiral units but also because of its great relationship to general problems involving a wide variety of FLC systems. Table 3 illustrates how in general some chiral units are used in this system. The use of the group -C*HCIC*(CHj)C,H5 was reported by Yoshino et al . 1 6 and the rest of the chiral units in the table was used by Goodby and Lesile 1 7 . The insertion of a new chiral center -C*H(CH 3)- into the chiral unit - C ^ I H C J H J not only changes the phase diagram completely but also lowers the transition temperature considerably. A chiral smectic C phase 13 emerges as three other less important smectic phases are lost and the phase temperature is decreased to near room temperature. Talbe 3. Phase transition of liquid cvrsatlsff 1 C .H„-Q-Ph-Ph-OCO-R» £L! C-HCICn iCCH^jH, CnHCICjH, C H J C ^ C H J ^ J H , CHjCHjCn^CHjyCjH, Phase transition (°C) lso—66—SmA—53—Sm»C—*30—Cryst. Iso—115—SmA—96—Sm"F—93—Sm»G--7l—Sm«H Iso »Sm*G Iso—93—SmA—92JS-*Sm*G As for the non-chlorine containing esters in this table, there are no chiral smectic C phase observed. The smectic A phase is squeezed out of the phase diagram as the chain of the chiral unit is lengthened. It is worth noting that similar esters 1 7 such as C.H , v-0-Ph-Ph-COO-(CH,yiC»H(CHX,H, (n = 1, 2, 3) exhibit Sm"C (n = 1, 2) and S m ' G (n=3) in addition to the SmA phase. It then illustrates that the direction of the carbonyl group in relation to the chiral unit is of less importance in type B FLC's. 1.5 THE PRESENT WORK The original idea of the present study was to incorporate some polar chiral units such as the epoxide unit into the system of RO-Ph-Ph-OR*. The use of an epoxide unit" in a series of type A FLC's was reported shortly after our project started. The proposed chiral units are the acetal unit, the diol unit, the epoxide unit, the thiiran unit and the Mosher unit derived from the so it*1 Since there is a limited information available for a complete series of the listed esters, only the octyloxy homologue of those liquid crystal esters is given in this table. 14 Et, Et J_(.'coc>-0-0-6-CnH2n+1 E t v ] ? H c o o - ^ - 0 " ° " C n H 2 n + 1 HVV C X00-Q - ^ - 0 -CnH2n +1 V V " ' C 0°-O-O"°-C n H 2 n + 1 Pn-r>-coo OCHj 15 called Mosher acid# J . There are a number of reasons for proposing these new chiral units. All of them have a polarizable group be rigidly associated with a tetrahedral stereocenter of a chiral unit. In comparison with the chiral unit -C*HCIC"H(CH 3)C :H }, each of the chiral centers of the proposed chiral units is more polarizable. Especially in the acetal unit, the epoxide unit and the thiiran unit, the cancellation of the two dipole moments due to internal rotation, which occurs in the 2-chloro-3-methylpentyl group and probably also in the diol unit, is eliminated by the bond linkage between the two chiral centers. As a result, the polar contribution by the two chiral centers to the the whole chiral unit is maximized. In addition, the length of those new chiral units is the same as that of the 2-chloro-3-methylpentyl group. This is important because the length of the chiral unit has a detrimental factor on the properties of the FLC's. Furthermore, there are some points with regard to the acetal and the diol units. It is known that the introduction of the hydroxy group into the aromatic rings of some FLC's enlarge the temperature range of ferroelectricity. It is then interesting to see if such effect can be applied in the case of the introduction of the hydroxy group into the chiral units. The existence of a large bulky molecular component of the acetal unit near the molecular dipole like C - 0 may suppress the free rotation and relative intramolecular motion in favour of the increase of the spontaneous polarization. However, it has been known that such a bulky group is not desired in terms of the introducment of liquid crystalline phases. . JThis acid, usually served as a reagent to determine the enantiomeric excess of optically active alcohols, also was used mainly because there was no evidence that it has been used in the synthesis of any FLC's. Finally, those systems are conveniently available synthetically or commercially from two simple starting materials in optically pure form 2S,3S-dihydroxy-2-methylpentanoic acid 1 1 and the Mosher acid ( S(-)-(a)-methyoxy-(o)-trifluoromethyl acetic acid ). By analogy with similar molecules, those target compounds are expected to have chiral smectic phases and also hoped to exhibit even higher spontaneous polarization. 2. RESULTS AND DISCUSSION 2.1 SYNTHESIS OF NEW COMPOUNDS The synthesis of the target compounds started with the resolution of the two enantiomers, (+)2R,3R-dihydroxy-2-methylpentanoic acid and (-)2S,3S-dihydroxy-2-methylpentanoic acid (hereafter simply referred to as the diol acid) and the preparation of 4'-alkoxybiphenol from the starting material 4,4'-biphenol. The reaction of resolving agent D-(-)-threo-2-amino-(4-nitrophenyl)- 1,3-propandiol 1 8 and racemic diol acids (previously prepared in our laboratory) gave a solid [(-)amine-(-)acid] salt which precipitated from the reaction solution and an oily [(-)amine-( + )acid] salt which left in the solution. A simple filtration followed by decomposition of those two salts by ammonia solution yielded the (-) diol acid and the (+) diol acid in good yields. The optical purity was examined by the measurement of optical rotation of the two enantiomers. The (-) diol acid had a value of [a] =-14.0° (ca. 95% ee) and the ( + ) diol acid at [a] = + 11.3° (ca. 77% ee). Because of the optical purity requirement of ferroelectric liquid crystals, only the (-) diol acid was used in the synthesis of the designed materials The conventional Williamson synthesis was employed in preparation of 4'-alkoxybiphenol. In practice, it was found that the key in applying this method to the preparation of the desired phenolic monoether was to choose the appropriate base for the conversion of the biphenol to the corresponding alkoxide, which then reacts with an alkyl bromide or iodide to give 4-alkoxybiphenol. In this case, sodium methoxide in methanol solution was far superior to sodium hydroxide in aqueous solution or sodium hydride in anhydrous tetrafuran solution. The isolated yields are in 1 7 S y n t h e t i c Routo m. *-pontanor>«, HOTt. benzana, raflux Jhr; b. HOH. DCC. DMAP. 18hr; C 6N HCI.dloxane-H,0. reflux Ihr; d. TsCI. pyridine, 2 days; e. (|Et)^. 2 dayo; f. CP,COOH, 3-methylbeniothiarole-2-thione, reflux 18 nr. 19 a range of 50-60% for the preparation of 4'-heptyloxybiphenol to 4'-dodecyloxybiphenol # 3 . The DCC (N,N-dicyclohexyldiimide) esterification reactions of the above 4'-alkoxybiphenols and the Mosher acid yielded a new series of low melting point esters (hereafter simply referred to as the Mosher esters) in good yields. The two hydroxy groups of (—)—diol acid J. were protected by etherification with 3-pentanone in acidic solution to afford the acetal 2 in good yield. This protection reaction did not succeed when acetel formation with acetone was attempted. The esterif ication of 2 and 4'-alkoxybiphenol was successfully carried out by a conventional DCC coupling reaction in the presence of DMAP (4-dimethylaminopyridine) as a catalyst, to produce compound 3 in high yields. The hydrolysis of 3 in a dioxane dilute aqueous HCI solution yielded compound 4 which could also be prepared via direct DCC coupling of the diol acid J. and 4-alkoxybiphenol. A high yield for the direct coupling should not be unreasonable. Because the Ka value of phenol is 105 higher than that for alcohol, the -OH group of 4-alkoxybiphenol is more nucleophilic and thus more reactive to the intermediate acylpyridinium species, the phenol should be able to compete with the alcohols in J.. Unfortunately, the direct coupling could only be achieved in inconsistent yields of 20-50%. 'The lower yields for 4'-propyloxybiphenol to 4-hexyloxybiphenol were due to a less efficient work up procedure. 20 (Reproduced from reference 19) The three step procedure (protection, esterification and deprotection, overall yield 45%) was generally preferred to the direct esterification. The dehydration of the diol ester 4 was accomplished by the reaction of 4 and p-toluenesulphonyl chloride in a methylene chloride, DMAP and pyridine solution, with subsequent treatment with triethylamine to yield the desired compound 5 in 50% yield. The optical purity of 5 should be the same as that of the starting material ±, since there are no steps capable of causing the racemization in the above procedure. The next task was to replace the oxygen atom of the epoxide in 5 with the sulfur atom and to prepare the final target compound 6. The procedure" chosen involved the use of 2-methylbenzothiazole 2-thione and trifluoroacetic acid. The reaction should again retain the optical purity of the target compound 6. It is interesting to note that the configuration of both stereocenters attached to the former epoxide are cleanly inverted. The 21 double inversion can be explained by the following mechanism 1 0 . (Reproduced from reference 20) In a model study, racemic 2R,3R-epoxy 2-methyl methylpentanoate was converted to its thiiran counterpartner at room temperature in 75% yield. The conversion of 5 (50% yield) however required slightly more rigorous condition (refluxing). During the course of the above experiments, it was found that the »H nmr chemical shift of the single hydrogen of compounds 1 to 6 provide a unique fingerprint to identify each compound concerned. The use of l H nmr spectra for the determination of constitution has depended largely on the relationships between chemical shifts and structural environment". The chemical shift of the tertiary proton in these esters is higher for the thiiran ester than for the epoxide ester, as seen in Table 4. The magnitude of chemical shift of the tertiary proton also depends on the type of groups attached to the carbonyl groups. By replacing the methyl group with the 4-alkoxybiphenyl group, the value of the chemical shift of the tertiary proton increases, by up to 0.31 ppm in the epoxide esters. This is apparently attributed to the long-distance deshielding effect by the 22 Table 3 *H nmr chemical shift of the tertiary proton in the thiiran ester and its precursors COMPOUND CHEMICAL SHIFT SIGNAL S H A P E (ppm> CjH, C,H, o X o I H-C»—C*-COOPhPhOC,H„ CJHJ CH) 3.92 double doublet OH OH t i - C * — C*-COOPhPhOC,H u I * I CJH, CH, 3.45 dd t l -C • — C •-COOPhPhOC,H l J 1 1 C,H, CH, 3.36 triplet t l - C * — C*-COOPhPhOC 7 H„ ^ I ^ J CH, 3.70 dd • O H O H I t H T C » — C » - C O O C H , [ a ] C j H . C H , 3.53 triplet C»-COOCH,[a] t l - C * — C ^ C H , 3.05 triplet t l - C *—C » - C O O C H , C,H, CH, 3.56 dd [a]. Excerpted from G.S. Bates' PhD thesis, University of Alberta (1976). 23 Figure 1 Partial *H nmr spectra of (-)-2-methyl 2R.3S-epithio-4'-heptyloxy- biphenyl pentanoate (400MHz, CDCI,): (1) normal spectrum; (2) spectrum with irradiation et 3.70 ppm; (3) spectrum with irradiation at 1.21 ppm 24 4-alkoxybiphenyl group. Another interesting aspect of ! H nmr spectrum of the thiiran ester is that the methylene adjacent to the only tertiary proton gave two multiple signals confirming that those protons are not chemically equivalent, which was verified by the decoupling experiments (see figure 1). If the irradiations are respectively applied at the chemical shifts 3.70 ppm and 1.21 ppm of the two adjacent protons the methylene protons are coupled with, the two multiple peaks of the two protons (at 1.65-1.74 and 1.96-2.07 ppm, respectively) will collapse into less multiple peaks accordingly. It is expected that the shielding effect by the ethylene sulphide ring is different on these two protons. As seen in the following conformation. Ha is shielded by the thiiran ring resulting in the chemical shift for Hb being 0.32 ppm higher than for Ha. Me In the case of the epoxide ester, the corresponding two protons could not be distinguished. 25 22 IDENTIFICATION OF NEW LIQUID CRYSTALS By using a polarizing microscope coupled with a heating stage, the compounds described in the proceeding section were studied in an attempt to identify which are the liquid crystals and whether they possess phases which are capable of being ferroelectric. Unfortunately, it was observed that none of the Mosher esters was the liquid crystal, although the melting points are generally around room temperature. 150-r — . , 0 I i i i i 1 2 4 6 6 10 12 Number of Ca rbons (n) It was disappointing to observe that the n-heptyloxy, the n-decyloxy, the dodecyloxy homologues of the acetal esters, the diol esters and the epoxide esters did not exhibit any liquid crystal phases at all. However, it was pleasing to note that all five compounds of the thiiran esters prepared (MEAOBP-S-7, 8, 9, 10, 12#\ MEAOBP is the abbreviation of 2-methyl 2,3-epithio 4'-alkoxybiphenyl£entanoate) were indeed liquid crystal materials. Identification of the phase types was made by microscopic observations of the textures exhibited by four of the thiiran esters #*The n-dodecyloxy homologue also was prepared and preliminarily measured of the phase temperature, showing similar phase sequence to the decyloxy. 26 I 27 Figure 3 Chiral smectic C phase of (-)-2-methyl 2R,3S-epithio 4 '-decyloxy- biphenyl pentanoate (X200) 28 (MEAOBP-S-7 , 8, 9 10). Typically for the n-heptyloxy homologue the A phase appears from the isotropic liquid on cooling. The n-heptyloxy to n-nonyloxy members inclusive exhibit B phases on cooling from either the A phase or the isotropic liquid. But the decyloxy member shows the desired chiral smectic C phase on cooling directly from the isotropic liquid. L'Quid Crystals Transition Temperatures (°C) M E A O B P - S - 7 | 6 4 — * S m A 6 0 — S m B 5 7 — M E A O B P - S - 8 | 62.6—•SmB 49—*+C M E A O B P - S - 9 I 62.0—•SmB 55—*C M E A O B P - S - 1 0 I 62—*»SmC» 47—e-C Of these liquid crystal materials, MEAOBP-S-8 and M E A O B P - S - 9 only show a crystal like liquid crystal phase and M E A O B P - S - 7 shows smectics A and B. Since they do not possess any chiral smectic phases, they will not be FLC materials. MEAOBP-S-10 is a potentially monotropic ferroelectric liquid crystal ("monotropic" means that this phase is only shown on cooling). A measurement of the spontaneous polarization is required to finally determine the ferroelectric property of this compound. It is rare that a compound shows the chiral smectic C phase directly cooling from the isotropic liquid. Virtually, all of the FLC's exhibit either smectic A or cholesteric phase prior to smectic C phase. However, it was recently reported that the compound" C^Hjj-O-Ph-COO-Ph-COO-CCH^C'HCCHjXCHjJjC^HtCHj^H, also exhibits the same phase sequence (isotropic liquid to smectic C). Like many liquid crystal families, this family of liquid crystals exhibit a variety of different phases dependent of the length of the long 29 chain attached to the core aromatic rings. By comparing the liquid crystal thiiran esters to the other three non-liquid epoxide esters, it has been seen how difficult in practice to discover new liquid crystal materials. It was surprising that the epoxide esters are not the liquid crystal materials. The only essential difference between the epoxide esters and the thiiran esters is the slight difference of polarizability of the two three membered rings. The stabilization of smectic liquid crystal phases in the thiiran esters is ascribed to the presence of the more polarizable thiiran unit. In comparison with the FLC's in Table 3, especially the esters derived from the 2-chloro-3-methylpentyl group, no chiral smectic C phase is observed by rising the temperature, but the temperature range of the n-decyloxy thiiran ester is quite large (15 degree range) and the transition temperature also is not far above room temperature. As mentioned previously, thermodynamically stable smectic A and chiral C phases may be obtained by formulating for instance MEAOBP-S-7 and MEAOBP-S-10 compounds. 2.3 CONCLUSION A new family of potentially ferroelectric liquid crystal materials has been prepared by utilizing a novel chiral unit containing a thiiran unit. Replacing the thiiran unit with an epoxide unit, i.e., substituting an oxygen atom for the sulfur atom of the new liquid crystals above, eliminated any liquid crystalline phases. 3. EXPERIMENTAL 3.1 GENERAL All reactions were carried out under a nitrogen atmosphere. Tetrahydrofuran was freshly distilled from sodium benzophenone ketyl under a nitrogen atmosphere. Dichloromethane and pyridine were distilled from calcium hydride under nitrogen when used as reaction solvents. Sodium hydride was obtained in 50% dispersions in mineral oil from Alfa. All other reagents were obtained from Aldrich and used without further purification. All extraction solvents were distilled before use. Initial melting points were taken on a Gallenkamp melting point apparatus and were uncorrected. Identification of liquid crystals was obtained using a Nikon Optiphot Pol Mircoscope coated with a lab-made heating system accurate to 0.1 °C. The phase photos were taken using Nikon FA camera and using Fuji ISO 1600 or Kodak ISO 1000 color films. The whole measurements were made by Barbara Frisken (Physics, UBC) at Kent State University. Proton magnetic resonance spectra were obtained using WH-400 400MHz spectrometer. Spectra were run in deuterochloroform solution with tetramethylsilane as an internal reference. Chemical shift was reported on the ppm scale. Infrared spectra were recorded either as a liquid film or in chloroform solution using a Perkin-Elmer model 1710 Fourier Transform spectrophotometer. Both Low resolution and high resolution mass measurements were obtained using a Kratos MS-50 mass spectrometer. Specific rotations were determined using a Perkin-Elmer 241 MC polarimeter at the sodium d-line at room temperature. Elemental analyses were performed at the Microanalytic Laboratory, Department of Chemistry, 30 31 Un i v e r s i t y o f B r i t i sh C o l u m b i a . Me r c k P r e - C o a t e d T LC sheets s i l i c a Ge l 60F -254 we r e used f o r ana l y t i ca l th in layer ch romato rg raphy , wh i l e BDH s i l i c a Ge l 6 0 - 120 mesh we r e used f o r c o l umn ch romatog raphy . The f o l l o w i n g abb r i ev i a t i ons are u s ed in the de s c r i p t i on o f the mu l t i p l i c i t y o f each s igna l in the »H nmr s p e c t r u m : s = s i gna l , d = doub le , t = t r i p l e t , m — mu l t i p l e t , dd = doub le t o f doub l e t s . 3.2 4 ' - A L K O X Y - B I P H E N O L : GENERAL PROCEDURE 4 , 4 - B i p h e n o l (9.3g, 5 0 m m o l ) wa s d i s s o l v e d in a s o l u t i o n o f M e O N a / M e O H (0.50M, 100ml) . A f t e r the s o l u t i o n w a s re f l uxed fo r 10min, A l k y l b r o m i d e ( 50mmo l ) and (n-Bu) 4 NI (0.90g) we r e added in to the re f lux ing so l u t i on in one po r t i o n . The reac t i on s o l u t i o n w a s then re f l uxed fo r 3 hr, c o o l e d to r o o m tempera tu re , and next pou red into aqueous HCI s o l u t i on (1N, 100ml) . Ether w a s used to extract the o rgan i c c ompound s (3x100ml) . The c o m b i n e d o rgan i c s o l u t i o n w a s wa shed w i t h sa tura ted N a H C O , s o l u t i o n (3x30ml) , sa tu ra ted NaCI s o l u t i o n (1x50ml) and wa te r (1x50ml) . Th i s s o l u t i on w a s d r i ed o ve r M g S O , and then evapo ra ted to d r ynes s to a f f o r d the crude mix ture con ta i n i ng d i a l k oxy , monoa l k o x y de r i v a t i v e s and unreac ted b i pheno l . The three c o m p o u n d s can be separa ted by us i ng c o l u m n ch roma tog raphy on s i l i c a ge l , e lu t ing w i t h d i ch l o romethane . (See Tab l e 5) 32 Table 5; 4'-Alkoxybiphenols by alkylation of 4.4'-biphenol R YieldfSA mx>/°C^ HHnmr fpprrA C,H, 21 176-177 7.44(t, 4H). 6.96(d. 2H). 6.88(d, 2H), 3.96(t, 2H), 1£3(m=6. 2H), 1.06(t, 3H) C 4 H, 24 171-172 744(d, 2H). 7.38(d, 2H), 6.93(d. 2H), 6.90(d, 2H), 3.99(t, 2H), 1.78(m=5, 2H), 1.5l(m=6, 2H), 1.00(t. 3H) C H , , 38 157-158 7.44(t. 4H), 6.95(d. 2H), 6.88(d, 2H), 3.97(t, 2H), 1.79(m=5, 2H). 1.34-1.53(m. 4H). 0.93(t, 3H) C 4 H„ 43 169-170 7.44(d, 2H), 7.38(d, 2H), 6.93(d, 2H). 6.90(d, 2H), 3.98(t, 2H), 1.80(m=5. 2H), 1.44-1.53(m, 2H). 1.32-1.40(m, 4H), 0.92(t, 3H) C 7 H 1 4 55 148-149 7.43(t. 4H). 6.94(d, 2H), 6.88(d. 2H), 3.98(t, 2H), 1.80(m=5, 2H), 1.41-1.5l(m, 2H). 1.26-140(m, 6H). 0.89(t, 3H) C,H„ 51 160-161 7.45(d, 2H). 7.40(d. 2H), 6.93(t, 4H), 3.99(t, 2H). 1.80(m=5. 2H), 1.43-1.52(m, 2H), 1.25-142(m, 8H), 0.90(t, 3H) C , H l t 49 143-144 745(d, 2H), 7.40(d, 2H). 6.96(d, 2H), 6.93(d, 2H), 3.98(t, 2H). 1.80(m=5, 2H), 1.40-1.50(m, 2H), 1.24-140(m, 10H), 0.89(t. 3H) C I t H „ 56 139-140 7.45(d. 2H), 7.40(d. 2H). 6.95(d. 2H). 6.93(d, 2H). 3.99(t, 2H). 1.80(m=5, 2H). 1.41-1.51(m. 2H), U4-1.40(m, 12), 0.88(t. 3H) C „ H „ 60 160-161 7.44(d. 2H), 7.40(d, 2H), 6.96(d. 2H), 6.93(d,2H), 3.98(t, 2H), 1.80(m=5, 2H), 1.40-1.5l(m, 2H), 1.24-1.40(m, 16H). 0.88(t, 3H) 33 3.3 (•-Y2S.3S-DIHYDROXY-2-METHYLPENTANOIC ACID The procedure used was analogous to that of Bergl 'son". Finely ground racemic acid (3.24g, 21.2mmol) and D-(-)- threo-2-amino 1-(4-nitrophenyl)- 1,3-propanediol (4.5g, 21.2mmol) were mixtured in ethanol (15ml). The sol id dissolved on heating. The solution was then left to stand at room temperature for 18 hr, and the precipitated salt was collected and recrystal l izad from ethanol to give 3.4g of the [(-)base-(-)acid] salt. The salt was then decomposited by using aqueous 10% ammonium hydroxide (40ml). The mixture was fi ltered to recover 1.4g of optical ly active (-)amine. The filtrate was acidif ied to pH 1 with aqueous 2N HCI and continuously extracted with ether for 24 hr to give 1.2 g (70.5%) of crude (— )dioI acid. Recrystall ization from ethyl acetate gave 1.15 g of the pure product. m.p.(°C): 150-151. [c] 2 3=-14.0° (c 3.53, H 2 0, 95% ee). «H nmr (CDCI 3) in ppm : 0.97 (t, 3H); 1.39 (s, 3H); 1.50 (m=5, 2H); 3.25 (dd, 1H). In addition, the (+)-diol acid ([o] = +11.3°, c 4.43, H 2 0, 77% ee) was also obtained from the mother solution via the same procedure in 68% yie ld and 1.5 g of optical ly active (-)amine was recovered. 34 3.4 3-PENTANONE ACETAL OF (-V2S.3S-DIHYDROXY-2-METHYLPENTANOIC ACID (-)-2R,3R-Dihydroxy-2-methylpentanoic acid (1.47g, 10mmol) and p-tolunesulphonic acid (0.l47g) were dissolved into a mixed solvent of pentanone-benzene (1:1, 60ml). The mixture was then heated in a water-extraction apparatus until the solution turned yellow. The reaction solution was cooled to room temperature, and next evaporated to give a yellow oily mixture, which was purified by column chromotography on silica gel, eluting with a solvent of ethyl acetate-petrolum ether (1:4) to afford a yellowish oil 1.61g (yield 75%). The structure was confirmed by 'H nmr spectrum. »H nmr (CDCI3) in ppm: 9.65 (s, IH); 3.88 (dd, 1H); 1.69-1.87 (m, 6H); 1.56 (s, 3H); 1.06 (t, 3H); 0.99 (t, 3H); 0.92 (t, 3H). ir (CHCI3): 1747 cm" 1 . 3.5 3-PENTANONE ACETAL OF (-V-2-METHYL 2S.3S-DIHYDROXY- 4'-HEPTYLOXYBIPHENYLPENTANOATE Eu Et ..C00-Q-O-6-CnH2n + 1 35 3-Pentanone acetal of (-)-2S,3S-dihydroxy-2-methylpentanoic acid (2.l6g, 10mmol), 4-heptyloxybiphenol (3.13g, ll.Ommol), N.N'-dicyclohexylcarbodiimide (225g, 11.0mmol) and 4-dimethylaminopyridine (I.Ommol) were mixed in CHjCI 2 (20ml). The mixture solution was stirred at room temperature for 18 hr. The precipitated N.N'-dicyclohexyl urea was filtered and the filtrate washed with water (1x50ml), 5% acetic acid solution (2x50ml), and again with water (2x50ml), dried over anhydrous MgS0 4 and the solvent evaporated to produce the crude ester. The crude product was further purified by column chromatography on silica gel, eluting with dichloromethane to give a yellowish solid. Recrystallization from petroleum ether gave pure solid 3.60g (yield 80%). m.p.(°C): 71-72. >H nmr (CDC!,) in ppm: 7.53 (d, 2H), 7.47 (d, 2H), 7.14 (d, 2H), 6.96 (d, 2H), 3.99 (t, 2H), 3.92 (dd, 1H), 1.92 (m=5, 2H), 1.80 (m=5, 2H), 1.68-1.80 (m, 4H), 1.67 (s, 3H). 1.28-1.50'(m, 8H), 1.13 (t, 3H), 0.92-1.13 (m, 6H), 0.90 (t, 3H). ir (CHCI,): 1748 cm- 1. exact mass for C J O H ^ O J : cacld 482.3021, found 482.3023 3.6 (-V2-METHYL 2S.3S-DIHYDROXY-4'-HEPTYLOXYBIPHENYLPENTANOATE This ester can be prepared by two methods. Method A; 3-Pentanone acetal of (-)2-methyl 2S,3S-dihydroxy 4'-heptyloxybiphenyl pentanoate (1.2g, 2.5mmol) was dissolved in a mixed solvent of H,0-dioxane (1:5) (60ml) and a solution fo 2N HCI (2ml) was 36 added in one portion. After the mixture solution was refluxed for 1 hr, the solution was cooled to room temperature and diethyl ether used to extract the solution (3x50ml). The combined organic layer was dried over anhydrous MgjS0 4 and evaporated to dryness to produce the crude ester, which was purified by column chromatography on silica gel eluting with dichloromethane, followed by recrystallization from ethyl acetate to give pure ester 0.73g (yield 70%). Method B; (-)2S,3S-dihydroxy-2-methylpentanoic acid (73.5mg, 0.5mmol), n-heptyloxybiphenol (156mg, 0.6mmol), N,N-dicyclohexylidimide (112mg, 0.6mmol), and 4-dimethylaminopyridine (O.lmmol) were mixed in dichloromethane (5ml). The mixture solution was stirred at room temperature for 18 hr. The precipitated N,N-dicyclohexyl urea was removed and the filtrate washed with water (2x5ml), 5% acetic acid solution (1x5ml), and again with water (2x5ml), dried over M g S 0 4 and evaporated to dryness to give the crude product. The purification was the same as Method A. (yield 20-50%). >H nmr (CDCI3) in ppm; 7.56 (d, 2H), 7.47 (d, 2H), 7.14 (d, 2H), 6.96 (d, 2H), 3.99 (t, 2H), 3.68 (dd, 1H), 1.80 (m=5, 2H), 1.84 (s, 3H), 1.50-1.65 (m, 2H), 1.40-1.50 (m, 2H), 1.28-1.40 (m, 6H), 0.89 (t, 3H). mp.(°C): 113-114. ir (CHCI,): 1747 c m 1 . [a] = -0.5° (c 2.10, CHCI,).. exact mass for C 2 5 H 3 4 0s: cacld 414.2397, found 414.2394. microanalysis for C 3 5 H 3 4 0j : calcd C: 72.42, H; 8.27; found C: 72.50, H: 8.33. (-)2-Methyl 2S,3S-dihydroxy-4'-decyloxybiphenyl pentanoate mp.(°C): 121-122. 37 »H nmr: 7.56 (d, 2H), 7.47 (d, 2H), 7.14 (d, 2H), 6.96 (d, 2H), 3.99 (t, 2H), 3.68 (dd, 1H), 1.80 ( m = 5 , 2H), 1.84 (s, 3H), 1.50-1.65 (m, 2H), 1.40-1.50 (m, 2H), 1.28-1.40 (m, 12H), 0.89 (t, 3H). ir (CHCI 3 ): 1747 cm" 1 . [o] = - 0 . 5 ° (c 2.88, CHCI,) . exact mas s fo r C j .H^Oj : c a c l d 456.2865, f o und 456.2866. m i c r o a n a l y s i s f o r C i , H 4 0 O j : c a l cd C: 73.65, H: 8.83; f ound C: 73.68, H: 8.91. ( - ) 2 - M e t h y l 2 S , 3 S - d i h y d r o x y - 4 ' - d o d e c y l o x y b i p h e n y l pentanoate m.p.(°C): 118-119 . »H nmr: 7.56 (d, 2H), 7.47 (d, 2H), 7.14 (d, 2H), 6.96 (d, 2H), 3.99 (t, 2H), 3.68 (dd, IH), 1.80 ( m = 5 , 2H), 1.84 (s, 3H), 1.50-165 (m, 2H), 1.40-1.50 (m, 2H), 128 -1 .40 (m, 14H), 0.89 (t, 3H). ir (CHCI 3 ): 1747 c m - 1 . [a] = - 0 . 5 ° (c, 3.01, CHCI,). exact mas s fo r C , 0 H 4 4 O 5 : cac l d 484.3177, f ound 484.3175. m i c r o ana l y s i s for C J 0 H 4 4 O } : ca l cd C: 74.33, H; 9.16; f ound C: 74.26, H: 9.27 3.7 (+ Y2S -METHYL 2 S . 3 R - E P O X Y - 4 ' - H E P T Y L O X Y B I P H E N Y L P E N T A N O A T E 4 -To l uene su l phony l ch lo r i de ( 3 l 8 m g , 0 .15mmol ) and 4 - d ime t h y l am i nopy r i d i n e (50mg) were added into a so l u t i on o f ( - )d io l ester (414mg, O . lmmo l ) in anhydrous py r i d i ne -d i ch l o r ome thane (1:1 4m l ) at 0 ° C . The reac t i on mixture w a s s t i r red at r oom temperature fo r 48 hr. 38 Distilled triethylamine (2ml) was then added into the reaction solution, which immediately turned a red color. The reaction was stirred at room temperature for an additional 48 hr. The reaction was quenched by adding cold 6N HCI solution extremely slowly until the pH value became seven. The solution was then extracted with dichloromethane and the combined organic solvent was washed with brine (1x20ml), and water (3x10ml), dried over MgS0 4 . The solvent was removed to afford a mixture, which was then purified by column chromatography on silica gel with dichloromethane as eluent, followed by recrystallization from petroleum ether to give I58mg pure product (yield 50%). [o] = +1.3° (c 2.46, CHCI,). m.p.(°C): 89-90. >H nmr (CDCI,) in ppm: 7.46 (d, 2H), 7.48 (d, 2H), 7.14 (d, 2H), 6.96 (d, 2H), 3.99 (t. 2H), 3.36 (t, IH), 1.80 (m=5, 2H), 1.70 (m=5. 2H), 1.67 (s, 3H), 1.40-1.50 (m, 2H), 1.24-1.38 (m, 6H), 1.15 (t, 3H), 0.89 (t, 3H). ir (CHCI,): 1753 cm- 1 . exact mass for C 2 jH 3 j0 4 : cacld 396.2292, found 396.2293. microanalysis for C J } H, ,0 4 : cacld C: cacld C: 75.73, H: 8.13, found C: 75.60, H: 8.28. (+)2-Methyl 2S,3R-epoxy-4'-decyloxybiphenyl-pentanoate [a] = +1.3° (c 3.39, CHCI,). mp.(°C): 85-86. »H nmr in ppm; 7.45 (d, 2H), 7.48 (d, 2H), 7.14. (d, 2H), 6.96 (d, 2H), 3.99 (t, 2H), 3.36 (t, 1H), 1.80 (m=5, 2H), 1.70 (m=5, 2H), 1,67 (s, 3H), 1.40-1.50 (m, 2H), 1.24-1.38 (m, 12H), 1.15 (t, 3H), 0.89 (t, 3H). ir (CHCI,): 1753 cm- 1 . 39 exact mass for C 2 ,H 3 ,0 4 : cacld 438.2760, found 438.2765. microanalysis for C 2 ,H 3 ,0 4 : cacld C: 76.68, H: 8.73; found C: 76.55, H: 8.80. ( + )2-lvlethyl 2S,3R-epoxy-4'-dodecyloxybiphenyl-pentanoate [o] = +1.3° (c 1.98, CHCI,). mp.(°C): 88-89. >H nmr in ppm; 7.45 (d, 2H), 7.48 (d, 2H), 7.14 (d, 2H), 6.96 (d, 2H), 3.99 (t, 2H), 3.36 (t. IH), 1.80 (m=5, 2H), 1.70 (m=5, 2H), 1.67 (s, 3H), 1.40-1.50 (m, 2H), 1.24-1.38 (m, 16H), 1.15 (t, 3H), 0.89 (t, 3H). ir (CHCI3): 1753 c m 1 . exact mass for C 3 C H 4 2 0 4 : cacld 466.3072, found 466.3071. microanalysis for C 3 0 H 4 ,O 4 : calcd C: 77.21, H; 9.07, found C: 77.10, H; 9.11. 3.8 2-METHYL 2S.3R-EPITHIO-METHYLPENTANOATE To a solution of racemic 2-methyl 2R,3S-epoxy methylpentanoate (144mg, 1mmol) and N-methylbenzothiazole-2-thione (220mg, 1.2mmol) in 2 ml dichloromethane was dropwise added a solution of trifluoroacetic acid (140mg, 1.2mol) in dichloromethane (3 ml) at 0 ° C . The mixture was further stirred at room temperature for 18 hr. The solution was then evaporated to dryness. The product was purified twice by column chromatography, on silica gel, eluting with dichloromethane and a mixed solvent of dichloromethane-petroleum ether (3:7), respectively, to afford neat liquid OOCH, 40 171mg (yield 70%). >H nmr (CHCI,) in p p m ; 3.77 (s, 3H); 3.56 (dd, 1H); 1.87-2.02 (m, 1H); 1.76 (s, 3H); 1.58-1.72 (m, IH); 1.18 (t, 3H). ir (CHCI,): 1724 cm->. exact mass for C , H 1 2 0 2 S : cac ld 160.0555, found 160.0554. 3.9 ( -Y2-METHYL 2 R . 3 S - E P I T H l Q-4 ' - H E P T Y L O X Y B I P H E N Y L P E N T A N O A T E fTvlEAOBP-S-7^ CnH2n + 1 T o a so lut ion of ( + )2-methy l 2 S , 3 R - e p o x y - 4 ' - h e p t y l o x y b i p h e n y l - p e n t a n o a t e (100mg, 0 .25mmol) and N - m e t h y l b e n z o t h i a z o l e - 2 - t h i o n e ( 5 5 m g , 0 .3mmol) in 2ml d i ch loromethane w a s dropwise added a so lut ion of t r i f luoroacet ic acid (35mg, 0 .3mmol) in 3ml d ich loromethane at r o o m temperature. The react ion so lut ion w a s next ref luxed for 18 hr. Evaporat ion of the so lvent gave the crude product , which was puri f ied twice by c o l u m n chromatography , on s i l i ca ge l , eluting with d ichloromethane and a mixed so lvent of d i c h l o r o m e t h a n e - p e t r o l e u m ether (3:7), respect ive ly . Recrysta l l i zat ion f r o m petro leum ether-ethy l acetate (20:1) gave 53mg pure product (yield 51%) mjD . (°C) : 67-68 . [o] = - 1 . 2 ° (c 1.80, CHCI,). >H nmr (CHCI,) in p p m : 7.25 (d, 2H), 7.47 (d, 2H), 7.12 (d, 2H), 6.95 (d, 2H), 3.99 (t, 2H), 3.70 (dd, 1H), 1.96-2.07 (m, IH), 1.89 (s, 3H), 1.80 ( m = 5 , 2H), 1.65-1.74 (m, 1H), 1.41-1.51 (m, 2H), 1.28-1.32 (m, 6H), 1.21 (t, 3H), 0.90 (t, 4 1 3H). ir (CHCI,): 1725 cm- 1 . exact mass for C } J H 3 J O J S : calcd 412.2064, found 412.2066. microanalysis for C J J H J J O J S : calcd C: 72.96, H : 7.59, S: 7.79; found C: 72.91, H: 7.43, S: 7.88. (-)2-Methyl 2R,3S-epithio-4'-octyloxybiphenylpentanoate (MEAOBP-S-8). m.p.(°C): 63-64. [a] = -1.2° (c 2.32, CHCI,). ir (CHCI,): 1725 cm- 1 . exact mass for C J 6 H „ 0 , S : calcd 426.2220, found 426.2215. JH nmr in ppm: 7.53 (d, 2H), 7.47 (d, 2H), 7.12 (d, 2H), 6.95 (d, 2H), 3.99 (t, 2H), 3.70 (dd, IH), 1.96-2.07 (m, IH), 1.89 (s, 3H), 1.80 (m=5. 2H), 1.65-1.74 (m, 1H), 1.41-1.51 (m, 2H), 1.28-1.32 (m, 8H), 1.21 (t, 3H), 0.90 (t, 3H). microanalysis for C J 6 H, 4 0,S: calcd C: 73.22, H: 8.04, S: 7.50; found C: 73.11, H: 7.90, S: 7.30. (-)2-Methyl 2R,3S-epithio-4'-nonyloxybiphenylpentanoate (MEAOBP-S-9) m.p.(°C): 62.5-63.5. [a] = -1.2° (c 3.07, CHCI,). ir (CHCI,): 1725 cm- 1 . exact mass for C , 7 H , t O,S : calcd 440.2376, found 440.2377. microanalysis for C J 7 H j 6 0 , S : calcd C: 73.59, H : 8.24, S: 7.28; found C: 73.43, H ; 8.13, S: 7.12. >H nmr in ppm: 7.52 (d, 2H), 7.47 (d, 2H), 7.12 (d, 2H), 6.95 (d, 2H), 3.99 (t, 2H), 3.70 (dd, 1H), 1.96-2.07 (m, 1H), 1.89 (s, 3H), 1.80 (m=5, 2H), 1.65-1.74 (m, IH), 1.41-1.51 (m, 2H), 1.28-1.32 (m, 10H), 1.21 (t, 3H), 0.90 (t, 3H). 42 (-)2-Methyl 2R,3S-epithio-4'-decyloxybiphenyl-pentanoate (MEAOBP-S-10). mp.(°C): 75-76. [a] = -1.2° (c 2.11, CHCI3). »H nmr in ppm: 7.52 (d, 2H), 7.47 (d, 2H), 7.12 (d, 2H), 6.95 (d, 2H), 3.99 (t, 2H), 3.70 (dd, 1H), 1.96-2.07 (m, IH). 1.89 (s, 3H), 1.80 (m=5, 2H), 1.65-1.74 (m, 1H), 1.41-1.51 (m, 2H), 1.28-1.32 (m, 12H), 121 (t, 3H), 0.90 (t, 3H). ir ( C H C I 3 ) : 1725 cm- 1 . exact mass for C „ H „ 0 j S : cacld 454.2532, found 454.2530. microanalysis for C „ H 3 , 0 3 S : calcd C: 73.98, H: 8.43, S: 7.03; found C: 73.87, H : 8.59, S: 7.16. (-)2-Methyl 2R,3S-epithio-4'-dodecyloxybiphenylpentanoate (MEAOBP-S-12). mp.(°C): 64-65. [o] = -1.2° (c 2.38 CHCI3). »H nmr in ppm: 7.52 (d, 2H), 7.47 (d, 2H), 7.12 (d, 2H), 6.95 (d, 2H), 3.99 (t, 2H), 3.70 (dd, 1H), 1.96-2,07 (m, IH), 1.89 (s, 3H), 1.80 (m=5, 2H), 1.65-1.74 (m, 1H), 1.41-1.51 (m, 2H), 1.28-1.32 (m, 16H), 1.21 (t, 3H), 0.90 (t, 3H). ir (CHCIj): 1725 c m 1 . exact mass for C 3 0 H 4 ,OjS: cacld 482.2844, found 482.2843. microanalysis for C 3 0 H 4 jO 3 S: calcd C; 74.66, H: 8.77, S: 6.62; found C: 74.61, H: 8.86, S: 6.79. 3.10 S(-WcW1ETHOXY-foVrRIFLUOROMETHYLPHENYL 4-ALKOXYBI PHENYL ACETATES 43 A solution of S(-)-(o)-methoxy-(o)trifluoromethylphenylacetic acid (0.855mmol, 200mg), N,N-dicyclohexylcarbodiimide (1.03mmol), 4-alkoxybiphenol (1.03mmol), and 4-dimethylaminopyridine (0.09mmol) in dichloromethane (5ml) was stirred at room temperature for 18 hr. The N,N-dicyclohexyl urea was removed by filtration and the filtrate washed with water (3x5ml), 5% acetic acid solution (3x5ml) and again with water (1x5ml), dried over MgSO« and the solvent evaporated to give the crude ester, which was purified by column chromatography on silica gel, eluting with dichloromethane. The ester was further purified either by recrystallization from petroleum ether or by sublimation. The yield was typically 80% or higher, ir (CHCI3): 1766 env 1 (on all samples). The m.p.( 0C), 'H nmr (ppm) data, exact mass, and element analysis data are listed in this order as follows. C 3 H 7 - : 80-81; 7.64-7.71 (m, 2H), 7.57 (d, 2H), 7.45-7.53 (m, 5H), 7.18 (d, 2H), 6.96 (d, 2H), 4.00 (t, 2H), 3.71 (s, 3H), 1.84 (m=6, 2H), 1.06 (t, 3H); cacld 444.1508, found 444.1520; calcd C: 67.71, H: 5.23, found C: 67.67, H: 5.14. C 4 H,- ; 55-56; 7.64-7.71 (m, 2H), 7.57 (d, 2H), 4.00 (t, 2H), 3.71 (s, 3H), 1.80 (m=5, IH), 1.45-1.55 (m, 2H), 1.00 (t, 3H); calcd 458.1664, found 458.1667; calcd C: 68.26. H; 5.51, found C: 68.21, H; 5.42. C s H n - : 20-21; 7.64-7.71 (m, 2H), 7.57 (d, 2H), 7.45-7.53 (m, 5H), 7.18 (d, 2H), 6.96 (d, 2H), 4.00 (t, 2H), 3.71 (s, 3H), 1.80 (m=5, 2H), 1.40-1.52 (m, 2H), 1.25-1.40 (m, 2H), 0.90 (m, 3H); calcd 472.1820, found 472.1817; calcd C: 68.78, H: 5.77; found C: 68.79, H; 5.66. 44 C 4 H 1 3 - : 31-32; 7.64-7.71 (m, 2H), 7.57 (d. 2H), 7.45-7.53 (m, 5H), 7.18 (d, 2H), 6.96 (d, 2H), 4.00 (t, 2H), 3.71 (s, 3H), 1.80 (m=5, 2H), 1.40-1.52 (m, 2H), 1^5-1.40 (m, 4H), 0.89 (m, 3H); calcd 486.1976, found 486.1977; calcd C: 6927, H ; 6.02; found C: 6921, H ; 5.94. C 7 H l 5 - : 16-17; 7.64-7.71 (m, 2H), 7.57 (d. 2H), 7.45-7.53 (m, 5H), 7.18 (d, 2H), 6.96 (d, 2H), 4.00 ( t, 2H), 3.71 (s, 3H), 1.80 (m=5. 2H), 1.40-1.52 (m, 2H), 125-1.40 (m, 6H), 0.88 (m, 3H); calcd 500.2132, found 5002132; calcd C: 69.73, H: 6.26, found; C; 69.66, H; 623. C ,H 1 7 - : 41-42; 7.64-7.71 (m, 2H), 7.57 (d, 2H), 7.45-7.53 (m, 5H), 7.18 (d, 2H), 6.96 (d, 2H), 4.00 (t, 2H), 3.71 (s, 3H), 1.80 (m=5, 2H), 1.40-1.52 (m, 2H), 125-1.40 (m, 8H), 0.89 (m, 3H); calcd 514.2288, found 514.2286; calcd C; 70.16, H; 6.48, found C: 70.10, H; 6.41. C 9 H 1 9 - : 43-44; 7.64-7.71 (m, 2H), 7.57 (d, 2H), 7.45-7.53 (m, 5H), 7.18 (d, 2H), 6.96 (d, 2H), 4.00 (t, 2H), 3.71 (s, 3H), 1.80 (m=5, 2H), 1.40-1.52 (m, 2H), 1.25-1.40 (m, 8H), 0.89 (t, 3H); calcd 528.2444, found 528.2443; calcd C: 70.57. H: 6.69, found C: 70.55, H; 6.63. C J O H J J - : 34-35; 746-7.71 (m, 2H), 7.57 (d, 2H) 7.45-7.53 (m, 5H). 7.18 (d. 2H), 6.96 (d, 2H), 4.00 (t, 2H), 3.71 (s, 3H), 1.80 (m=5, 2H). 1.40-1.52 (m. 2H), 125-1.40 (m. 12H), 0.89 (t, 3H); calcd 5422600, found 542.2603; calcd C: 70.96, H : 6.89, found C: 70.93, H ; 6.77. C 1 3 H J 5 - : 47-48; 7.64-1.71 (m, 2H). 7.57 (d, 2H), 7.45-7.53 (m, 5H), 7.18 (d, 2H), 6.96 (d, 2H), 4.00 (t, 2H), 3.71 (s, 3H), 1.80 (m =5, 2H), 1.40-1.52 (m, 2H), 1.25-1.40 (m, 14H), 0.88 (t, 3H); calcd 570.2912, found 570.2910; calcd 71.68, H: 725, found C: 71.60, H: 7.34. CHAPTER 2 HETEROGENEOUS CATALYSIS OF THE RACEMIZATION OF OPTICALLY ACTIVE 1.1'-BINAPHTHYL BY TITANIUM DIOXIDE POWDER J 46 4. INTRODUCTION Heterogeneous catalysis is crucial in the production of many industrial chemicals and therefore has become a focus of intense efforts in both industry and academia. The second part of this thesis deals with the surface catalysis of the racemization of optically active 1,1'-binaphthyl. 4.1 HETEROGENEOUS CATALYSIS Heterogeneous catalysts are solids which increase the rates of chemical reactions by virtue of the specific properties of their surfaces, and which increase the rates at which chemical systems attain equilibrium without themselves undergoing chemical change. A heterogeneous catalytic system is a process in which catalyst and substrate are to be found in two different phases. The reaction naturally takes place, at least in so far as it is catalytic, only at the phase boundary, at the two dimensional surface bounding the two three dimensional phases. The important distinction of heterogeneous catalysis as compared with homogeneous catalysis lies in the fact that topchemical problems, such as the structure of the surface and the distribution of its active areas, the modification and change of the surface by the reaction occurring, must be considered. Reactions proceeding at the surfaces of solids differ from those proceeding homogeneously in several ways. First, in the former case, the reactants and intermediates are confined to a thin layer over the surface, the volume of which is relatively small. Second, the kinetics of surface reactions are less accessible than those of homogeneous reactions in that the rates of the former are determined by the concentrations of the reactants in the reactive layer. Third, the kinetics of surface reactions are 47 48 less reproducible than those of homogeneous reactions since the nature of the surface and its method of prepartion have profound effects. The progress of a heterogeneous catalytic reaction consists of five steps": (1) the diffusion of the reactants to the catalyst, (2) the formation of the adsorption-compound, catalyst-reactant, (3) the chemical change at the surface, (4) the decomposition of the compound, the catalyst-product, and finally (5) the diffusion of the reaction products away from the catalyst. Unless they all accidentally possess the same velocity, it is the slowest of these five processes which determines the overall velocity since they all follow each other (consecutive reactions). Completely understanding how a catalyst carries out a particular reaction would involve knowing the extent and importance of each of the several steps for all reactants and products during the course of the reaction. Needless to say, this formidable task has yet to be achieved. Nevertheless, a great deal of information has been collected for a variety of heterogeneous catalyzed reactions. Exactly what type of information is obtained is determined to a large extent by the method used to study the reaction. Kinetic methods are useful in determining the number of steps in given reaction and also in determing which step or steps in the catalytical process may be rate-determing. To determine how the reaction rate or product(s) change with the structure and electric character of the catalyst should be one of many mechanistic approaches towards studying heterogeneous catalyzed reactions. In addition, the stereochemistry of the product(s) and the variation of product(s) with reactant stereochemistry could also provide valuable information for analyzing catalyzed reactions. Furthermore, well-developed isotopic tracer method has been applied 49 s u c c e s s f u l l y to studying the nature of a d s o r b e d s p e c i e s , ident i fy ing ra te-determing steps, and studying s tereochemica l changes during the course of a react ion . A great deal of insight into the m e c h a n i s m o f heterogeneous cata lys i s has been gained by studying the nature of the m o l e c u l e or m o l e c u l e s a d s o r b e d on the sur face . There are roughly two t y p e s of adsorpt ion which might occur . The first type invo lves f o r m a t i o n of chemical c o m p o u n d s on the sur face , with a heat of adsorpt ion usual ly in the order of 10 kca l/mole or higher, and is termed c h e m i s o r p t i o n . The s e c o n d type of adsorpt ion invo lves f o r c e s of attraction which are s imi lar to those occurr ing during condensat ion and heats of adsorpt ion are cor respond ing ly less than those in chemisorpt ion , usually less than 10 kca l/mole . This adsorpt ion is ca l led p h y s i s o r p t i o n . However , in a s p e c i f i c heterogeneous cata lyzed react ion , either of t w o adsorpt ions may not be p rec i se ly c l a s s i f i e d . Desp i te the fact that there are a w ide var iety of methods avai lable for s tudy ing heterogeneous cata lys i s , each approach has certain l imitat ions as appl ied to spec i f i c cata lyzed react ions . M e c h a n i s m s of many heterogeneous cata lyzed react ions still remain myster ious and d isputed due to the lack of prec ise mechanist ic m e t h o d s . Kinetic studies have tradit ional ly been hampered by p r o b l e m s of reproduc ib i l ty , which , in many c a s e s , cou ld cause a thorough kinetic study i m p o s s i b l e . Even when a g o o d kinetic ana lys i s is p o s s i b l e , the interpretation of the results may not be s t ra ight forward. T h e r e f o r e , the best understanding of heterogeneous cata lys i s c o m e s on ly w h e n the p r o b l e m are approached f r o m as many points of v iew as p o s s i b l e . 50 Heterogeneous catalysts may be classified according to the functions they perform, and of great significance is the correlation between these and their electrical and thermal conductivity 3 4. Table 6. A Classification of Heterogeneous Catalysts According to their Principal Functions Class Metals Conductivity type conductors Functions hydrogenation dehydrogenation Hydogenolysis Metal oxides and Salts and acids sulphides semi-conductors < or insulators oxidation-reduction polymerization dehydrogenation isomerization isomerization cracking A key aspect of heterogeneous catalysis is the presence of active sites in the solid for which there are no equivalents in the reference reaction run in the absence of a support, thus a finely divided solid is often optimal". The exploration and utilization of new catalysts is fundamantally a matter of trial and error efforts, intuitive assessments, and above all, a great deal of luck. 4.2 C A T A L Y S T TITANIUM OXIDE There are numerous literature references dealing with the chemistry and technology of oxide and sulfide semiconductors, of which T i 0 2 is the most extensively studied over years. Its applications cover a variety of areas such as catalysis, adsorption, supports, and TiOj also is one of the most common pigments. The use of titanium dioxide as a catalyst has 51 received more and more attention since the first report on the sustained oxidation of water on illuminated T i 0 2 in a photoelectric chemical cell in 1972". Titanium dioxide can be formed in the three crystalline modifications, anatase, rutile and brookite, all of which can be prepared synthetically and can occur naturally. Small amounts of impurities Fe, Nb, Ta, Sn, Cr, and V are normally present in the three forms to render T i 0 2 a n-type semiconductor". Brookite is less important because of the nature of its inert chemical activity 2 7. Rutile has 6:3 co-ordination and is isomorphous with cassiterite, S n 0 2 while linear molecules of T i 0 2 are present in anatase. A number of selected properties of the different forms of the titanium dioxide are summarized in Table 2. Table 7. Properties of the Different Forms of Titanium Dioxide Property Anatase Rutile Brookite mp.(°C)[a] change to rutile 1855 change to rutile Density(g/I)[b] 3.90 4.27 4.13 Dielectric 48 (powder) 110-117(powder) 78(natural crystal) Constant[a] Hardnessfa] 5.5-6.0 7.0-7.5 5.5-6.0 (mohs' scale) [a]. JANAF Thermochemical Tables, Air Force Contract AFO 4(611)- 7554, midland, Michigan, Aug. 1965. [b]. P. Pascal, Nouveau Traite de Chemie Minerale, Masson, Paris(1963). Stoichiometric titanium dioxide is an insulator with a resistivity of about 10 3 5 ohm cm at room temperature; this can be lowered to 0.1 ohm cm by controlled introduction of oxygen vancancies". 52 There has been limited reports in studying thermal catalytic activity of titanium dioxide. However, it is known that titanium dioxide could facilitate a number of isomerization of alkenes. Thermal isomerization of o-pinene over T iO, catalyst gave different isomers selectively depending on heat treatment on the activity of T iO, catalyst". It was explained by L i u " that, the difference in catalytical activities of SiO,, AI,Oj and TiO, in converting o camphene are due to their differences in chemical structure and the nature of bonding electrons, and their surface properties are of secondary importance in so far as the activity of isomerizations is concerned. In the case of the isomerization of propylene oxide over T iO, to Me,CO or EtCHO, Fukui 3 1 suggested that an adsorbed substrate was bound to the Ti atom through the O atom in order to covert its isomers. One of the well-established examples is the isomerization of butenes over titanium dioxide. It is concluded by Guisnet", after extensive mechanistic studies, that the isomerization of butenes on TiO, (anatase prepared from TiCI 4) proceeds through three different mechanisms, involving respectively, protonic sites, Lewis acid sites, and basic sites, depending on the pretreatment temperature of the T iO } catalyst. In other words, as has been observed on alumina, those catalytic reactions can take place on Bronsted acid sites of the catalyst. Double bond migration takes place on the basic s i tes" of TiO,, through allylic carbanions as on MgO," while cis-trans isomerization occurs through o-bonded carbocations as in the case of Webb's carbonium ion (A)", where L is a Lewis acid site. A c -< j : - c -c L 53 Such an intermediate (A), which allows only geometrical isomerization, can be formed without any C-H bond-breaking 3 2. Indeed, titanium dioxide has been proven to be able to provide electron (negative charge) and positive charge (hole) to adsorbed molecules on the surface of catalyst due to its semiconductor structure, even under thermal conditions. However, most of organic reactions catalyzed by T i 0 2 can not occur unless the catalyst is being irradiated by photons. It is the photocatalytical activity of TiO, that comprises the special importance of this catalyst. A pioneering approach concerning the production of hydrogen gas by catalytic splitting of water, by Fujishma and Honda 2 6, has stimulated a worldwide effort at discovering new, alternate catalyzed routes for photoredox reactions occurring on illuminated semiconductors. Studying sensitized organic phototransformations by semiconductors is important not only because of its potential for uncovering new techniques for functional group modiification but also because of its relationship to general problems involving heterogeneous photocatalysis and radical ion intermediates. In irradiated heterogeneous systems, either the solid or the contacting liquid may be initially excited. Semiconductor sensitized redox reactions involve the absorption of light and the induction of electron transfer across the semiconductor/liquid interface. Specifically, for reactions occurring at the semicoductor/liquid interface, either the semiconductor itself or the adsorbent may function as the chromophore. In the former case, net chemical change results through direct production of an excited state, whereas in the latter case, sensitization through either electron or energy transfer initiates reactions. The energetics for the critcal interfacial electron transfer can be derived from the working model proposed originally by Gerisher 3 6. As 54 s h o w n b e l o w , a s e m i c o n d u c t o r is characterized by a band structure, i.e., a f i l l ed va lence band (VB) separated by an energy gap f r o m a vacant c o n d u c t i o n band (CB). <«; Ecb E f Evb semiconductor solution semiconductor solution Band structure in a s e m i c o n d u c t o r : (a) before contact with an e l e c t o l y t e ; (b) after contact with an e lectro lyte (Reproduced f r o m reference 37) A f t e r a s e m i c o n d u c t o r is immersed in a l iquid e lect ro ly te so lut ion •containing a redox coup le , charge transfer occurs a c r o s s the interface to equil ibrate the potent ia ls of the two phases , an e lectr ic f ie ld is thus f o r m e d at the sur face o f the semiconductor , and the bands bend f r o m the bulk of the s e m i c o n d u c t o r towards the interface. Photon excit ing the semiconductor p r o m o t e s an e lectron f rom the f i l l ed va lence band to the vacant conduct ion band, leav ing an electron d e f i c i e n c y or p o s i t i v e hole in the valence band. In a n - t y p e semiconductor , fo r example , dop ing with e f f e c t i v e e lectron donors renders the s e m i c o n d u c t o r e lectron rich and band bending prov ides a method for e l e c t r o n - h o l e pair separat ion , i.e., for inhibition of the c o l l a p s e of the photogenerated ho le . Thus when this pair f o r m s in the space charge region of the s e m i c o n d u c t o r by virture of absorpt ion of a p h o t o n , the e lectron wi l l m o v e away f r o m the interface to the bulk of the semiconductor as the pos i t i ve charge hole migrates towards the interface where oxidat ion can 55 occur. A s the oxidation of the adsorbate occurs, sufficient charge can build up in the bulk of semiconductor to render the particle electrophoretically mobile. 3 ' Ultimately, such a charged aggregate can act as a reducing center and effect solution-phase reductions. In the same principle, reduction-oxidation reactions could be also carried out over p-type semiconductors. Numerous photocatalytic organic reactions on semiconductors have been studied, some of which are summarized as follows. Fox 3 ' demonstrated, for instance, that the cyclooctatetraene dianion, a participant in a reversible organic redox couple, could be generated by photocatalytic T iO, in ammonia solution, 4 0 and in addition, closed-shell monoanions could be similarly photogenerated. I I Fox3* also showed that a net endothermic oxidative coupling could be driven by light absorption either by the tetraphenylcyclopentdienide anion adsorbed on a single crystalline TiO, electrode or by the semiconductor itself. One of the first reported oxidative cleavages of an organic molecule induced by long-wavelength ultraviolet irradiation of a semiconductor involves the photodecarboxylation of acetic acid. 4 1 CHjCOOH hv, T i O , — • CH,CH, or CH 4 + CO, Ethane and methane are the different main products formed by using crystalline T iO, and powdered TiO, respectively. It was confirmed by Bard that a methyl radical CH,. is the intermediate of the reaction 4 1 . 56 T h e m o s t s u c c e s s f u l o r g a n i c r e a c t i o n c a t a l y z e d b y i r r a d i a t e d T i0 3 , in s o f a r a s t h e s y n t h e t i c a p p l i c a t i o n is c o n c e r n e d , i s t h e o x i d a t i v e c l e a v a g e o f a r y l a t e d o l e f i n s , w h i c h s o m e t i m e s e x p e r i e n c e s v i r t u a l l y q u a n t i t a t i v e c o n v e r s i o n 4 1 . ( P h ) 3 C = C H 3 h v , T i O , — • (Ph ) 5 C=0 O n e o f t h e m o s t e x c i t i n g e x a m p l e s in t h e i r r a d i a t i o n o f s e m i c o n d u c t o r s u s p e n s i o n s c o n t a i n i n g o r g a n i c m o l e c u l e s i s t h e s y n t h e s i s o f a m i n o a c i d s . T h e p r o d u c t s o f g l y c i n e , a l a n i n e , s e r i n e , a s p a r t i c a c i d , a n d g l u t a m i c a c i d s c a n b e s i m p l y g e n e r a t e d b y i r r a d i a t i o n o f p l a t i n i z e d T i0 3 s u s p e n s i o n s in a q u e o u s a m m o n i a c a l m e t h a n e , a l t h o u g h in p o o r c o n v e r s i o n a n d w i t h n o s e l e c t i v i t y at a l l 4 3 . M o s t o f t h e e x a m p l e s m e n t i o n e d a b o v e , h o w e v e r , m a i n l y d e a l w i t h o x i d a t i o n r e a c t i o n s b y v a l e n c e b a n d h o l e s a n d / o r h y d r o g e n p r o d u c t i o n b y c o n d u c t i o n b a n d e l e c t r o n s . R e c e n t l y , G r a t z a l 4 4 r e p o r t e d that p y r u v a t e c o u l d b e e f f i c i e n t l y r e d u c e d t o l a c t a t e u n d e r i l l u m i n a t i o n o f a q u e o u s s u s p e n s i o n s o f t i t a n i u m d i o x i d e p o w d e r . In a d d i t i o n t o p u r e T i0 3 , m o d i f i e d T i0 2 c a t a l y s t s y s t e m s s u c h a s p l a n t i z e d T i O , a n d t i t a n i u m - s i l i c o n o x i d e s , a r e a l s o e f f e c t i v e c a t a l y s t s in a v a r i e t y o f o r g a n i c r e a c t i o n s . T h e c h o i c e o f a s p e c i f i c c a t a l y s t in o r d e r t o o b t a i n t h e m o s t e f f i c i e n t r e a c t i o n i s n o t p r e d i c t a b l e , b u t t o t a l l y d e p e n d s o n t h e t y p e o f r e a c t i o n c o n c e r n e d . 5 7 4 . 3 RACEMIZATION OF BINAPHTHYL Becau se o f h indered r o t a t i on about the 1 . 1 * b ond , 1 , 1 - b i naph thy l e x i s t s in t w o enan t i omer i c f o r m s . The r a cem i za t i on reac t i on c on s i s t s in the c o n v e r s i o n o f a s o l u t i on w i t h an ex ce s s o f one enan t i omer into an equ imo la r mix ture o f bo th enan t i ome r s . (R)-(-)-l.r-b1naphthyl (SM+M.l'-binaphthyl Th i s is de f i n i t e l y one o f the s imp l e s t r eac t i ons in o rgan i c c hem i s t r y . Fur thermore , th is s imp l e s y s t e m has been p roven to be appropr ia te fo r s tudy ing the ca ta l y t i c a c t i v i t y o f a va r i e t y o f he te rogeneous c a t a l y s t s 4 5 - " and used s u c c e s s f u l l y f o r the s tudy o f p h o t o r a c e m i z a t i o n " - 5 6 . A br ie f r e v i ew o f a l l k inds o f r a cem i za t i ons o f b inaph thy l , spon taneous , h o m o g e n e o u s l y ca ta l y t i c , he te rogeneous l y ca t a l y t i c , and pho t o ca t a l y t i c , w i l l be p r e sen t ed . 4 . 3 . 1 UNCATALYZED RACEMIZATION OF BINAPHTHYL The c on ve r s i o n o f enan t i omer s o f 1 , 1 - b i n a p h t h y l has been s tud i ed b y C o o k e and Ha r r i s " , and later on b y Car ter and L i l j e f o r s 5 ' . A s po i n t ed out b y t ho se resea rchers , h indered ro ta t i on about the 1 , 1 ' - b o n d p reven ts the t w o naphtha lene uni ts f r o m ach iev ing cop l ana r i t y . It has been con s i de r ed that in te r fe rence o f groups in the 1 and 8 p o s i t i o n s in each naphtha lene m o i e t y p reven t s cop lana r i t y f r o m be ing ach i eved in ei ther one o f the t w o r ing s y s t e m s . Each naphthalene unit c onsequen t l y ex i s t s in one o f t w o f o r m s , 58 ca l l ed d or I. (d) (1) d and I f o r m s o f subs t i tu ted naphtha lenes E i ther enan t i omer o f b inaphthy l can then ex i s t in one o f three f o r m s (a) a r a c e m o i d , I - l , (b) a r a c emo i d , d - d , (c) a m e s o i d , l - d , f o r m . Racemoid Mesoid Racemoid and mesoid conformations of S-t-rj-ia'-binaphthyl Ma thema t i c a l l y , there are t o t a l l y s ix d i f fe rent c on f o rma t i o na l con f i gu ra t i ons fo r b i naph thy l : R(d-d) , R(d-I), R( l - I) , S ( d - d ) , S (d - I ) and S ( l - I ) . Because o f rap id d = I c on ve r s i o n at ambient tempera tu res , the c on f o rma t i o n of the ground s ta te mo l e cu l e w o u l d be s imp l y re fe r red to as R or S . Neve r the l e s s , it is b e l i e v ed that in the c r o w d e d t r ans i t i on s ta te lead ing to the c on ve r s i o n o f R t o S or v i c e v e r s a , there is a cons i de rab l e d i f f e r ence be tween a c o n v e r s i o n i n vo l v i n g , s a y , R(d- I ) = S (d - I ) and R( l - I ) = S ( l - I ) . " - ' 4 . In the latter c a se there are t w o s imu l t aneous h yd r ogen - h yd r ogen contac t po in t s b e tween the r i ng s y s t e m s in the t rans i t i on s ta te . In the f o rme r case there is no po in t a l ong the c onve r s i o n path where t w o hyd rogens interact s imu l t anou s l y w i t h two other hyd rogens . Rather, there are t w o su c ce s s i v e h y d r o g e n - h y d r o g e n in te rac t ions as the enan t i omers conve r t . The pa thway 59 involving successive interactions is energetically much more favorable than the simultanous route 5 '. It is thus concluded that it is through the mesoid forms the R and S 1,1'-binaphthyl convert. The activation energy of the reaction was measured 22.5 kcal/mole". 4.3.2 PHOTOCATALYTIC RACEMIZATION OF BINAPHTHYL The work dealing with photoracemization of 1,V-binaphthyl was nicely done by Irie and his c o - w o r k e r s " " . The mechanism for this photoracemization has been studied from the effect of additives (photo sensitizers or quenchers) as well as by a laser photolysis. The effect of additives revealed that photoracemization occurs in the triplet excited state. The conversion to its enantiomer 1,1-binaphthyl has to overcome the barrier at the angle of 0° due to steric hindrance of hydrogens at the 2 and 8 positions in the coplanar conformation. Compared to the higher barrier in the ground state (22 kcal/mol) 5 1, the barrier in the triplet state is only 1.9 kcal/mol. In other words, the photoracemization occurs much faster than the thermal racemization. It is also noted that since the higher bond order in the excited state causes a smaller bond distance and gives rise to a large steric hindrance, the low barrier observed in the triplet state suggests that the electronic stablization energy gained as a result of the interaction of the two naphthyt groups is superior to steric hindrance. The same researchers" further observed that \-ray radiation induced racemization of 1,1'-binaphthyl occurs mainly in a radical anion state of 1,1'-binaphthyl in tetrahydrofuran, while the reaction occurs mainly in the triplet excited state in toluene. The low activation energies of the reaction in both solvents, 1.1 kcal/mol in THF and 1.9 kcal/mol in toluene, as 60 compared to thermal racemization, indicates that the introduction of an electron to the lowest vacant molecular orbital causes an electronic structural change favorable to rotation along the fntraannular C-C bond. 4.3.3 CATALYZED RACEMIZATION OF BINAPHTHYL BY C Nl. AND PT The catalyzed conversion of enantiomers of 1,1'-binaphthyl over carbons, Raney nickel and platinum was extensively investigated by Pincock et a l 4 5 - " . Since they reported the first case of the surface catalysis of this simple reaction", there have been much work about if and how this type of catalysis actually occurs. The conculsions obtained in these studies have contributed a variety of ideas and evidences towards the understanding of the general heterogeneous catalysis, especially in areas of those three different solids. Since our work is closely related to and, in some aspects, similar to the previous work, it is therefore appropriate to review some features of heterogeneous catalysis by carbons 4 '-", nickel 4 5*"and platinum 4 7*" as it applies to this simple reaction. 4.3.3.1 The carbon catalyzed racemization The racemization of binaphthyl on various carbon surfaces probably proceeds by a mechanism in which electron density is donated to the binaphthyl by the carbon surface. The catalytical sites for binaphthyl racemization are located on the basal planes and not on the disorganized areas or the edge atoms, because the catalytic rate is unaffected by oxidations and reductions which occur at the disorganized areas of the surface. Racemization of binaphthyl in the presence of the carbon may involve the "formation of a binaphthyl radical anion on the surface. 61 The idea was supported by the fact that intercalating potassium into graphite enhances the catalytic activity of the graphite. Since intercalating potassium-graphite is well known to catalyze reactions by one electron transfer, it could appear that a radical anion mechanism for this particular catalytic reaction is reasonable. 4.3.32 Platinum catalyzed racemization The platinum catalyzed reaction follows simple first order kinetics. There is no detectable adsorption or interferring reduction during the reaction. The aspect of the reaction that is difficult to explain is that the catalysis shows a peculiar kinetic effect in that the reaction rate is independent of the concentration of platinum. Oxygen present in the reaction solution poisoned the reaction, apparently because of competing adsorption and its reduction to water. Cyclohexane and cyclohexene which is reduced to cyclohexane, however, show a permanent inhibitory effect which increases with the concentration of the compound. It is therefore concluded that the reduction and racemization sites were the same in platinum catalyzed racemization. Variations in activity and the complete loss of the activity probably due to uncontrollable poisoning were pointed out. 4.3.3.3 The Interaction of binaphthyl with Raney nickel Raney nickel catalyzes both the racemization process and the reduction of binaphthyl to 4,5,6,7-octahydro-binaphthyl. There was also a greater adsorption process of binaphthyl than with platinum. 62 The racemization follows first order kinetics after an initial non-first order period, which is probably caused by the concurrent adsorption. The relative effects of added poisons, e.g. sulphur or 1-decylmercaptan, suggested that there were three different catalytic sites, each responsible for a separate type of interaction with binaphthyl. 4.4 THE OBJECT OF THE PRESENT STUDY The aim of the present study is to discover the possible catalytic effect (activity) of highly dispersed titanium oxide on the racemization of optically active binaphthyl and, if so, to experimently examine the kinetics of the catalysis, and thus, hopefully, to formulate a reaction scheme that is consistent with experimental findings. The following sections describe various kinetic results for the titanium dioxide (anatase from Aldrich) catalyzed racemization of binaphthyl. 5. RESULTS AND DISCUSSION 5.1 PRELIMINARY KINETIC STUDIES AND REPRODUCIBILITY It was found that small amounts of highly divided T i 0 2 (anatase, Aldrich) in acetone (ca. 10.0mg/ml) would catalyze the racemization of optically active 1,1'-binaphthyl without concurrent side reaction or detectable adsorption. As in the case the other catalyzed racemizations studied by Pincock and his coworkers 4 5 - 5 2 , the T i 0 2 catalyzed reaction shows good first order kinetics, as seen in Figure 4 for several runs. It was also found that T i 0 2 would show catalytic activity only when commercially available T i 0 2 is further divided into colloidal particles in acetone solvent by the means of stirring. Finely divided T i 0 2 can be simply obtained by intensively stirring powder T i 0 2 over a period of 24 hr in a flask. With a catalytically active batch of finely divided T i 0 2 in acetone it was observed that the colloidal particles of T i 0 2 would not precipitate for a period of 4 hr after the completion of the stirring. A good reproducibility was observed (see Figure 5 for several identical runs), and this reproducibility allowed some quantitative kinetic studies to be done in the subsequent section. The interesting fact is that the titanium dioxide catalyzed racemization was independent of the stirring rate. Although the stirring speeds were varied with a variable speed magnetic stirrer, the rate of a kinetic run was never changed by increasing or decreasing the stirring speed during a run. This is, of course, consistent with a reaction which is not affected by diffusion control factors. .Because increasing the area of liquid-gas (or liquid-solid) interface will increase the rate of reactions 63 [Binaphthyl] =6jB2x10« (mol«/l) Temperature s 10JD*C Solvent sacetone 1.6 | | | I I I 0 100 200 300 400 500 600 _ time (min) Figure 4 First order kinetic catalyzed racemization of optically active 1,1'-binaphthyl by highly dispersed titanium dioxide to 2-1 1.95 H CM + 1.90-, O 1.85-\ 1.80- 1.75-1 1.70 X B B X B x (Binaphthyl) «6A2x10-« (mol/l) (TiOjsioj) (mg/ml) Temperature=10jD*C Sol vent =ecet one " i y i i i I i 1 0 100 200 300 400 500 . 600 time (min) Figure S Several identical kinetic runs of catalyzed racemization of optically ectlva binaphthyl by highly dispersed titanium dioxide * 66 whose rate determining step is diffusion across this interface. There are two characteristic features in these plots in comparison with platinum, nickel and carbon catalyzed racemization of optically active 1,1'-binaphthyl. Like platinum catalyzed racemization of binaphthyl, no initial rapid decrease or increase in optical rotation of binaphthyl was observed when titanium dioxide was used as a catalyst in this simple organic reaction. Another important aspect is that the first order plots were simply straightforward throughout the kinetic runs (up to halftime) in the titanium dioxide catalyzed racemization of binaphthyl, which also was an important discovery in the previous metal or carbon catalyzed reaction. The nonexistence of curvature in the plots might indicate that the catalyst titanium dioxide was not undergoing any progressive deactivation, which many heterogeneous catalysts often experience during the catalysis. The nickel and the carbon, for instance, exhibit the maximum catalytic activity at the very beginning of the catalyzing racemization of binaphthyl 4 9. At this point, it was initially decided to determine how the catalytical activity of T i 0 2 might be influenced by the concentrations of binaphthyl and T i 0 2 in order to draw a further comparison with the other catalyzed racemizations by C, Ni, and Pt. 52 THE EFFECT OF C O N C E N T R A T I O N S OF C A T A L Y S T . B INAPHTHYL A N D ADD IT IVES O N C A T A L Y T I C A C T I V I T Y K ine t i c s we r e s tud i ed by add ing op t i c a l l y a c t i ve b inaphthy l (0.00435g) Into a f i n e l y d i v i ded t i t an ium d iox ide ace tone s o l v en t (25.0ml). A l l r eac t i ons w e r e ca r r i ed out at a l o w temperature ( 10 °C ) in order that the rate o f the unca t a l y z ed , spon taneous r a cem i za t i on w a s m i n i m i z e d . The b inaphthy l c oncen t r a t i on w a s l o w (6.82x10-*mole/ l) and the measu remen t o f the r o t a t i on s o f the s amp l e s w a s car r ied out at the me r cu r y l ine (456nm) rather the mo re usual s o d i u m l ine (589nm) where the abso lu te r o t a t i on is much l e s s . The rate cons tan t s we re de te rm ined f r o m the s l o p e and are p l o t t ed aga ins t the we igh t o f ca ta l y s t in F igure 5. The resu l t s c l ea r l y s howed that the o b s e r v ed rate cons tant (Kobs) is d i r e c t l y p ropo r t i ona l t o the concen t r a t i on o f the t i t an ium d iox ide u sed . Un l i ke the p l an t i um ca ta l y zed r a c em i z a t i o n , but l ike ca rbon ca ta l y zed r a c em i z a t i on , as the concen t ra t i on o f c a t a l y s t T i O j is i nc reased and the concen t r a t i on o f b inaphthy l is kept cons t an t , the r eac t i on rate cons tant (Kobs) i nc reases due to the ava i l ab i l i t y o f mo re ca t a l y t i c a l s i t e s in the s o l u t i on . The dependence o f Kobs on the concen t r a t i on b inaphthy l is the s ame as that f ound f o r ca rbon or p la t inum ca t a l y z ed r eac t i on . A s the concen t r a t i on o f b inaphthy l is i nc reased and the concen t r a t i on o f the c a t a l y s t T i O , r ema in s the s ame , a large number o f bo th R and S b inaphthy l m o l e c u l e s c o m p e t e f o r a l im i t ed number o f r a c em i z a t i on s i t e s and the p r edom inan t m o d e o f r a cem i za t i on is the unca ta l y zed r e a c t i on . Tab le 8 s h o w s the k ine t i c data in wh i c h the k ine t i c rate cons tan t w a s dec reased as the concen t r a t i on o f b inaphthy l w a s gradua l l y i n c r eased . Kobs X 0.0001(1/min) Figure 6 Dependence of the concentretion of titanium dioxide on the observed kinetic rate constants of catalyzed racemization of optically active 1,1'-binaphthyl by highly dispersed titanium dioxide 69 of binaDhthvl on the concentration of binaDhthvl Concentration of binaphthvl (mole/1) Kobe x104(min») 6.82 x 10- 6.8 5.70 x 10-« 6.8 6.11 x 10-* 7.4 7.64 x 10* 6.6 13.3 x 10* 6.0 14.7 x 10-4 5.3 20.5 x 10* 3.1 20.5 x 10- 4.0 fTiOO = 10.0 mg/ml. Following the kinetic work above, it was then decided to pursue an investigation to determine whether the catalysis was sensitive to organic molecules which are planar simple aromatic compounds. Figure 6 to figure 10 illustrate how the course of the catalyzed reaction was effected by the addition of aromatic compounds, benzene, naphthalene, anthracene, end pyrene. As shown in these figures, the presence of very small amounts of additives permanently poisoned the catalyzed racemization. The more aromatic rings the added compound possesses, the more effective does it stop the reaction ( benzene < naphthalene < anthrance < pyrene ). The result was probably due to chemisorption which involves edsorption of the poison on the surface. The decrease of catalyst activity was caused by coverting the active sites into inactive surface compound or pfinsjknthylJsejUxlO-4 (mol/l) (TiOJslOjrj (mg/ml) 0 1000 2000 3000 4000 5000 6000 [Benzene] X 1000(ml) Figure 7 Dependence of the concentration of the additive benzene on the observed kinetic rete constant of catalyzed racemization of optically active 1,!'-binaphthyl by highly dispersed titanium dioxide [Binaphthyl] «SJS2K10-« (mol/I) fTrOJ=10jO (mgAnl) Temperature m 10 J>°C Solvent macetone 300 [Naphthalene] X 10000(mol/l) F i * j r t • De^andence of the concentration of the additive naphthalene on tha observed kinetic rate constant of catalyzed racemization of optically aetive 1,r-oinephthyl by highly dispersed titanium dioxide o o o o X A. I/I fB.o*phthyl] =6*2x10* (mol/l) [TiOJslOjD (mg/ml) Temperature «10JD *C Solvent sacetone " T " 20 30 40 50 [Anthracene X 10000(mol/l) Figure 9 Dependence of the concentration of the additive anthrance on the observed kinetic rete constant of catalyzed racemization of optically active 1,1 '-binaphthyl by highly dispersed titanium dioxide 60 70 IN 7-1 2 - f — — — I 1 1 1 — 1 0 1 2 3 4 5 [Pyrene] X 10000(mol/l) Figure 10 Dependence of the concentration of the additive pyrene on the observed kinetic rata constant of catalyzed racemization of optically active 1,1'-binaphthyl by highly dispersed titanium dioxide 74 by a d v e r s e l y a f fec t ing the number of free e lec t rons , unpaired e lectrons or "ho les" on the surface of the so l id cata lys ts . The m e c h a n i s m f its the other assumpt ion that the act ive surface is substant ia l ly un i fo rm and that act iv ity decl ine is proport ional to the f ract ion c o n v e r t e d to inactive surface c o m p o u n d or that certain f a v o r e d spots r e s p o n s i b l e for the act iv i ty are preferent ia l ly c o v e r e d by the p o i s o n s 5 ' . In our c a s e , the p o i s o n i n g is perhaps best attributed to the c o m p e t i t i o n for adsorpt ion of those addit ives on the cata lyt ica l s i tes . It is worth noting that a s imi lar case has been observed in this lab for the carbon cata lyzed r e a c t i o n 5 2 . 75 5.3 CATALYTIC ACTIVITY OF MODIFIED TITANIUM DIOXIDE In this section are described some experiments involving the kinetic studies on a variety of titanium dioxide modifications. These experiments grew out of attempts to obtain highly efficient, reproducible titanium dioxide towards the racemization of binaphthyl. The kinetic procedure was identical to the previous kinetic studies except for that otherwise mentioned. 5.3.1 PREHEATING TITANIUM DIOXIDE It has been reported that the heat treatment of T i O : can change the catalytical activity 3 2 -". Since preheat-treatment is one of the simplest methods to modify the catalytic effect of titanium dioxide, at the early stage of this project, anatase (Aldrich) was heated in a furnace at the temperature ranging from 500-700°C for one to eighteen hours. The treatment was carried out while a small stream of nitrogen gas passed over the catalyst to maintain a low partial pressure of the evolved vapors. However, preheating of T i 0 2 neither improved nor destroyed the catalytic property. It clearly indicated that the racemization catalytic sites remained the same under heat-treatment. In other words, the catalytical activity of titanium dioxide is independent of the heat treatment, which has modified the catalysis of isomerization of butenes by anatase powders 3 3 3 4 . Apparently, the nature of this catalyzed racemization is different from that for the catalyzed isomerization of alkenes on the same semiconductor catalysts. A lso it meant that this calcination treatment could not activate more catalytic sites in addition to those that existed. 76 Jable 9 Catalytic activity of modified titanium dioxide towards the racemization part 1 Entry rr\OA Kobs (mo/mU xlOVmin-'l Aldrich anatase, 2 hr heat treatment (500°C) 10.0 7.1 Aldrich anatase, 8 hr heat treatment (700°C) 10.0 6.8 Aldrich anatase, 18 hr heat treatment (700°C) 10.0 6.9 Aldrich anatase, acid washed 10.0 no catalytic effect 1. Solvent distilled actone. 2. Concentration of binaphthyl is kept precisely et 6,82 x 10*4 (mole/ml). 77 5.3.2 ACID-WASHING TITANIUM DIOXIDE The object of the washing step is primarily to remove impurities from the catalysts", that is to "polish" the surface of the catalysts. That titanium dioxide is chemically inert to strong acids led us to apply this simple technique. Accordingly, Aldrich anatase powder was immersed in the concentrated HCI or H 2 S0 4 solution for about 20 mintues. The T i 0 2 was used after filtering, rinsing with a lot of water and with acetone, and drying at 120°C overnight. The procedure probably represents the simplest possible washing method. Under the identical kinetic procedure used above, the acid-treated, previously active anatase powder lost their catalytic ability completely. The deactiviation was obviously caused by the destruction of the catalytic sites. This is one of the cases in which a straightforward interpretation is impossible. We only can say that somehow the interaction between the acids and the surface of the catalysts resulted in the deactivation of the catalysts. 5.3.3 ILLUMINATING TITANIUM DIOXIDE As mentioned previously, the exploration of new titanium dioxide photocatalytic reactions is of great interest to chemists. We did some preliminary studies on possible T i 0 2 photocatalytic racemization of binaphthyl (procedure see experimental section) In some irradiated catalytic reactions", catalytic effectiveness can be considerably enhanced by substituting pure titanium dioxide with modified titanum dioxide catalyst systems, such as, platnized titanium dioxides. Accordingly, platnized T i 0 2 prepared by Bard's method" was also tried in 78 this type of experiment. Because the photoracemization occurs via a triplet state intermediate and because oxygen is the best quencher to the photoracemization 5 4 ", some of attempted heterogeneous photocatalytic reactions were carried out in the presence of oxygen gas, which was bubbled through the reaction solution for 30min before the beginning of the kinetic run. This operation was based on the fact that the triplet state of binaphthyl is not likely the intermediate of T i 0 2 photocatalysis. Nevertheless, there was no apparent catalytic activity drawn from the kinetic plots. Namely, the kinetic rate constants of TiO, added solutions were lower than that of the corresponding T i 0 2 free solutions without exception. The T i 0 2 photocatalytic effect (if any) could be outbalanced by much more powerful photoracemization. The kinetic rate constant of the photoracemization was increased as the concentration of binaphthyl was decreased. It was found that the halftime of the photoracemization was as low as 5 seconds in the absence of oxygen at the concentration of binaphthyl (6.82x10-4mole/l, the usual concentration in the kinetic studies), in the experiment, the removal of oxygen was carried out by bubbling a small stream of nitrogen or argon for 30 min before use. 5.3.4 REDUCING TITANIUM DIOXIDE The reduction of an oxide semiconductor is one of the methods to further dope the semiconductor thus increasing the catalytic activity". This process is analogous to the removal of oxygen from the T i 0 2 lattice by evacuation at high temperatures". Loss of oxygen is associated with the generation of surface Ti(lll) sites". We, at this point, simply wanted to test the doping effect on the catalysis. 79 Table 10 Catalytic activity of modified titanium dioxide towards the racemization part 2 Entry mO/l Kobs (mq/mh x l O V m i n n Irradiating Aldrich anatase 10.0 300 Irradiating Aldrich anatase 1.0 730 Irradiating 0.0 833 Irradiating Aldrich anatase, in the presnece O f Oj 0.1 217 Irradiating platinized Aldrich anatase, in the 0.5 53 presence of 0 : Irradiating, in the presence of 0 2 0.0 263 Irradiating Aldrich anatase, in the absence of 0 2 0.1 58,000 Irradiating, in the absence of Oj 0.0 114,000 Reduced Aldrich anatase by H 2 (1hr) 10.0 6.5 ibid (4hr) 10.0 10.3 ibid (4hr) 10.0 7.2 ibid (4hr) 10.0 7.5 ibid (4hr), new batch 10.0 6.9 ibid (4hr), another batch 10.0 7.6 ibid (8hr) 10.0 7.8 ibid (I8hr) 10.0 3.9 1. Solvent distilled ectone. 2. Concentretion of binaphthyl is kept precisely et 6,82 x 10 4 (mole/ml). 80 It has long been known that there exists a correlation between the catalytic activity and electrical conductivity 6 4. Many experimental works 6 5 in which such correlation has been observed were reported. These two properties of the semiconductor vary in the same or in opposite directions from one sample to another depending on the type of the reaction. The procedure of this reduction is described in the experimental section. The results obtained from the reduced anatase catalyzed racemization (Table 10) seemed to be in agreement with the above theory. The kinetic rate constant was slightly higher than that for the unreduced Aldrich anatase. This could be interpreted that the reduction created more Ti(lll) thus increasing the electric conductivity which helped the racemization. In the case of the platinum catalyzed reaction, Pincock and Hutchins 4' reported that in order to obtain highly active platinum by the hydrogen reduction of platinum oxide, at least a period of 120 minutes was required. Since pure Pt0 2 is not catalytically active in the racemization of binaphthyl, it therefore indicated that the above theory also is applied to the Pt catalyzed racemization. That is, in the case of platinum catalyzed racemization, the catalytic sites are generated as the Pt is produced and as the electric conductivity of the surface is increased. This important finding is later used in an arguement to clarify the catalytic mechanism (see subsection 5.4). 5.3.5 OTHER SOURCES OF TITANIUM DIOXIDE 5.3.5.1 Titanium dioxide from titanium tetrachloride In many cases of catalytic studies, the modification of titanium dioxide used was not obtained directly from commercially available materials, but prepared by the hydrolysis 6 6 - 6 7 of titanium tetrachloride. 81 Table 11 Catalytic activity of modified titanium dioxide towards the racemization Dart 3 Entry n m Kobs tfmq/mn xlOVmin-^ TiO, freshly prepared from TiCI4 10.0 7.1 ibid 10.0 6.7 ibid 10.0 6.6 Colloidal Aldrich anatase after one filtration 5.0 5.0 ibid 4.8 5.4 ibid 5.3 4.9 1. Solvent distilled actone. 2. Concentration of binaphthyl is kept precisely at 6.82 x 10* (mole/ml). 82 Titanium dioxide described in experimental section was used to produce freshly precipitated T i 0 2 . This material showed comparable catalytic power to that for Aldrich anatase (see Table 11). 5.3.52 Rutile materials We also examined the catalytical effect of rutile from Alfa Chemical Co., but found out that this material did not catalyze the racemization of binaphthyl under any conditions employed for the anatase case. 5.3.6 COLLOIDAL TITANIUM DIOXIDE As stated previously, titanium dioxide was uneffective in the racemization unless the colloidal solution was used. Therefore, one could ask this question; is there a difference between two individual particles in terms of catalytic activity, provided we could separate finer particles from previously stirred solution by filtration? At one point, it was decided to prepare several batches of colloidal solutions and then filter the larger particles thus obtaining a "true" colloidal catalyst solution, which presumably would be better catalysts. Experimentally, we filtered the stirred suspensions of titanium dioxide, stripped the solvent of the filtrate, weighed the catalyst, added 25.00ml acetone, and then stirred the solution for 1 hr before use. In any event, it has shown that the assumption was correct. The value of Kobs/fTiOJ is higher than that of non-filtered reaction solution at the similar concentration of titanium dioxide (see Table 11, compared to the usual Kobs = 4 .1x10- 4min- 1 at [T iOj = 5.0mg/ml). Indeed, the catalytic activity is enhanced with the smaller titanium dioxide powder. 83 5.4 SPECULATION ON THE CATALYTIC MECHANISM ON THE BASIS OF PREVIOUS AND PRESENT KINETIC RESULTS So far, it has been shown that, our attempt on modifying titanium dioxide in order to increase the kinetic activity and then to understand this catalysis better, seems to be unsatisfactory, but does provide a few interesting points into understanding of this heterogeneous catalysis. Despite the fact that the catalytic activity of titanium dioxide towards this reaction has been compared to that for other catalysts throughtout the proceeding sections, an additional comparison of catalytic activity is compiled in Table 12. Table 12 Catalytic act iv i ty of four heteroqeneous inorqanic so l ids towards the ra i temizat ion of ODtical lv act ive binaohthvl (• K=Kcat/Kuncat ,> Cat. rcat.i [Bina.1 t(°C) K̂  K / rCa t . l Solvent fmq/mh f10«xM^ fmq->) T iO, 10.0 6.82 10.0 3.5 0.35 acetone Ni 37.7 25.0 25.0 5.0 0.13 n-heptane Pt 1.0 5.0 25.0 8.0 8.0 ethanol C 1.0 250 25.0 14.0 14.0 chloroform The most important feature drawn from Table 12 is that the four catalyst are all electron-donating type catalysts and the catalytic activity is obviously related to the electron-donating ability of the catalyst. Hattori et a l " reported that the exposure of T iO, surfaces to nitrobenzene result in the formation of the anion radical of nitrobenzene (confirmed by ESR spectrum) in a course of identifying the intermediate of the TiO, catalyzed isomerization of butenes. This relevant finding definitely favours the arguement that an anion radical of binaphthyl is likely formed in the colloidal T iO, solution and probably plays an intermediate role in the 84 cata lys i s . It is then reasonable to guess that at least one of catalyt ic pathways does invo lve the radical anion intermediate m e c h a n i s m regardless which of the cata lys ts is c o n c e r n e d . M o r e o v e r , one can see that t i tanium dioxide is in s o m e sense as g o o d catalyst as other o n e s . S ince the rate of the racemizat ion a lso depends on the s o l v e n t 5 1 * " , the temperature and the concentrat ion of b inaphthyl , it w o u l d be improper to list those cata lys ts in the order o f the cata lyt ic act iv i ty . But it is certain that the carbon is the m o s t active catalyst and the m o s t s u c c e s s f u l cata lyst as appl ied to the racemizat ion of b inaphthyl . A l s o , it is worth not ing that pre l iminary studies on other s e m i c o n d u c t o r such as M o S 2 s h o w e d s imi lar cata lyt ic results to that for T i 0 2 (the invest igat ion w a s carr ied out by a summer undergraduate in this lab). 85 5.5 CONCLUSION Until the completion of this thesis, four common heterogeneous catalysts have been discovered to be catalytically active towards the racemization of binaphthyl in virtually the same ways. It was therefore believed that this catalytic phenomeon is not unusual at all, and it suggested that many heterogeneous catalysts possessing properties similar to or different from those four catalysts might also be catalytically active in faciliating simple organic reactions like the racemization of binaphthyl. As far as the mechanistic process is concerned, the radical anion intermediate is the favorite one. All present and previous kinetic studies do not exclude this possiblity. In particular, observed first order rate constants increase with the concentration of the catalyst T i0 2 , decrease with binaphthyl concentration, and are sensitive to small amounts of polynuclear aromatic compouds (poison increases in the order of benzene, naphthalene, anthrance, and pyrene). A lso, it appears that the finer anatase particles catalyze the racemization more efficiently. Meanwhile, it is unfortunate that more precise experimental method has not been found to determine the nature of the potential titanium dioxide photocatalytic racemization. 6. EXPERIMENTAL 6.1 GENERAL Melting points were determined with a Thomas Unimelt Capillary Melting Point Apparatus using open tube capillary and are corrected. Gas-liquid Chromotagraph (glc) was performed using a Hewlett Packard 5830A Gas Chromotagraphy equipped with a flame ionization detector and using nitrogen as carrier gas with a 6' by 0.125" stainless steel column packed with 3% OV-17 on Chromosorb W A W - D M S C , 80/100 mesh. Optical rotation was determined using a Perkin Elmer 241 MC polarimeter with a 1dc or 1cm quartz-faced jacketed cell. Specific rotation ([a]) was calculated using the equation; [o]=observed rotation/[(path length in dm) times (concentration in g per ml)]. Solvents for kinetic and adsorption studies were spectrograde with the exception of ethanol and acetone. Ethanol "100%" was used as received. Two methods were adopted for purifying the technical grade acetone. The first one was that, acetone was treated with anhydrous magnesium sulfate, followed by distilling from anhydrous phosphorous pentoxide. Due to a reproducibility problem that occured in the kinetic studies at one time, acetone was then treated as following: acetone was first dried with type 3A Linde molecular sieve, and succesive small portions of KMn0 4 were added to acetone at reflux, until the violet colour persisted, followed by drying with Linda 3A sieve again and distilling. Gases (N 2, 02, H,, Ar) were reagent grade and dried through a column of calcium sulphate. Anthrance, pyrene and naphthalene were recrystallized before being used in the additive experiment. 86 87 6.2 SYNTHES I S OF R A C E M I C 1 . T - B I N A P H T H Y L The procedure used wa s ana logous to that o f Sake l l e r i o s and K r y r i n i s ' 0 . T o a dry 3 -necked f l a sk f i t t ed w i t h ove rheaded st i rrer and condense r w a s added 9.6g magnes ium turn ings , 72ml anhydrous ether, 56 ml c - b romonaph tha l ene and a s ing le c rys ta l o f i od ine . The s t i r red mixture w a s heated to re f lux to start the reac t i on , wh i ch p roceeded w i thout further heat ing fo r 20 m in . The reac t i on mixture wa s then heated to ref lux fo r 6 hours , w i t h the add i t i on o f up to 200 ml dry benzene to thin the s lur ry when nece s sa r y . The reac t i on mixture wa s c o o l e d to r o om temperature and added s l o w l y to a s t i r red su spens i on of 54g anhydrous cup ic ch lo r ide(prepared by dry ing the d ihydrate sal t fo r 4 h at 100 °C ) in 200ml anhydrous ether. A f t e r the insu ing v i go rous reac t i on occur red the mixture w a s then s t i r red overn ight at r o o m tempera ture . The reac t i on mixture wa s quenched by s l o w add i t i on of 100ml 10% hydroch lo r i c ac id and i ce . The e the r -benzene layer wa s ex t rac ted s u c c e s s i v e l y w i t h severa l po r t i ons of 10% hydoch l o r i c a c i d , wa te r , and dr ied over anhydrous magnes i um su l f a te . The so l v en t s were r e m o v e d in vacuo to a f f o r d an o i l , wh i ch c r y s t a l l i z ed on c oo l i ng to 0 ° C . The b rown mater ia l wa s t rans fe r red to a Bunchner funne l , washed w i th a sma l l amount of c o l d pe t ro l eum ether ( 30 -60°C ) , and r e c r y s t a l l i z ed once f r o m pe t ro l eum (65 -110°C ) . The crude 1,1'-binaphthyl (20.9g) wa s then r e c r y s t a l l i z ed f r o m ace tone three t imes to y i e l d lO.Og of wh i t e c r y s t a l s , mp : 143.5-144.5°C. mp in l i terature: 144 -145°C . 6.3 P R E P A R A T I O N OF O P T I C A L L Y ACT IVE 1 . 1 -B INAPHTHYL The procedure used wa s s im i l a r to that o f P i ncock and W i l s o n 7 1 . A so l u t i on of 0 . l 33g of ac t i ve 1 ,V-b inaphthy l in 400ml acetone ( f resh ly d i s t i l l ed f r o m po t a s s i um permagnate) w a s f i l t e red into a 1000ml round 88 bottom flask. The solution was then cooled in a dry ice acetone bath (-78°C) for 10 min with swirling, during which time crystallization began. Without completing the crystallization, the flask was removed and immediately placed on a rotary evaporator (Buchi Rotovapor R). The flask was rotated in air while the full vacuum of a water aspirator was being established (5 min), it was then lowered into the water bath, maintained between 20°C and 25°C. As the flask warmed, some (but not all) of the crystals dissolved, then reprecipiated with the loss of solvent. The evaporation was taken to dryness, and any residual acetone was removed on the high vacuum pump. The material, which was 100% recovered, resolved to [a] =-174° (at 589nm, c 3.7mg/ml acetone) on heating at temperature 135°C. 6.4 KINETICS OF UNCATALYZED AND TITANIUM DIOXIDE CATALYZED REACTIONS Oxide semiconductor (0.25g) was placed in a 100ml R. B. flask fitted with a magnetic stirrer and 25.0ml of dry acetone was added. After 24 hr intensive stirring, a highly divided titanium dioxide acetone solution was formed. Then the flask was fitted with a underwater magnetic stirrer and was immersed into a 10.0°C water bath. A sample of optically active binaphthyl (0.00435g) was next added into the solution, and after about 5 min (for completely dissolving the substrate and equilibrating the temperature of the solution), the kinetic run was started. A sample (app. 2ml each time) was extracted from the solution at various reaction times by using a Pasteur pipette. This was filtered through about 0.7g Celite 530A into a one dc long polarimeter cell. The reading was measured at the Mercury line at 456nm. The cell was next placed into 89 the polarimeter and the reading was taken with integration sec set at 5 sec. The cell was then rinsed with acetone and shaken three times fo l lowed by drying with a stream of dry air. 6.5 PROCEDURE FOR ATTEMPTED TITANIUM DIOXIDE PHOTOCATALYTIC REACTIONS Oxide semiconductor (0.025g) was placed in a 100ml R.B. flask fitted with a magnetic stirrer and 25.0ml of dry acteone was added. After 24 hr intensive stirring, a highly divided titanium dioxide acetone solution was formed. Then the flask f itted with a under-water magnetic stirrer was immersed into a 10.0°C water bath. A sample of optical ly active binaphthyl (0.00435g) was next added into the solution, and after about 5 minutes (for equilibrating the temperature of the solution), the kinetic run was started. A solution (app. 5ml) was extracted from the above solution by using a Pasteur pipette. Two samples (app. 2.5ml each) were obtained from this solution. One was immediately measured of the optical rotation, and the other one was placed into a quartz tube, which was fitted with a magnetic stirrer and immersed in a 10°C bath beside a high-pressure mercury lamp (450 watts). After t_ time, the optical rotation of this sample was measured and then compared to the initial optical rotation of the identical solution. Repeating the above procedure by only changing the reaction time (t) made "P the kinetic data. If a solution was needed to be saturated with one of three gasses (02, N 2 or He), a very small stream of gas, previously passed through a dehumidified apparatus, was bubbled through the solution for 30 minutes before the solution was divided into two parts. 90 6.6 PRODUCT ANALYSIS AND ADSORPTION EXPERIMENTS USING GLC The conditions used were as follows: the gas chromatography runs started at a temperature of 170°C and this increased up to 250°C at a rising rate of 20°C/min and completed within 20 minutes. Binaphthyl appeared at the retention time of 12.29 minutes. In all experiments done, only the binaphthyl signal and solvent signal (retention time = 0.30 min) were present. This indicated that there was no side reaction such as a reduction reaction occured during the catalytic racemization. In order to know exactly what minimal concentration of binaphthyl the glc was able to detect, a solution of binaphthyl (6.82x10-*mole/l, the usual concentration in the kinetic studies) was compared to a series of dilute binaphthyl solutions made up by diluting the initial solution (10.00 ml) with a ml acetone. (6.82x10-4mole/lx[l0.00ml/(10.00ml + a ml)]. It was then found that even a was down to 0.50 ml, the glc still could tell the difference of above two samples tested. In other words, the glc could identify 0.33 x 10'4 mole/1 binaphthyl concentration difference. 6.7 PREPARATION OF TITANIUM DIOXIDE FROM TITANIUM TETRACHLORIDE Hydrochloric acid (1.0M, 50 ml) was charged into a two-necked flask fitted with a condenser, a hotplate-magnetic stirrer combination and a pressure equalizing funnel. After the stirring was started, 50 ml titanium tetrachloride was added dropwise to the flask through the funnel over a period of 25 minutes, and was then heated to reflux for 2 h. 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