Ordered Fluids and Liquid Crystals

10 Molecular Association i n Mono- and Dihydric Alcohol and Alcohol-Water Systems

Downloaded by STANFORD UNIV GREEN LIBR on May 10, 2012 | http://pubs.acs.org Publication Date: January 1, 1967 | doi: 10.1021/ba-1967-0063.ch010

M. P. MCDONALD

Sheffield College of Technology, Sheffield, England

The results of nuclear magnetic resonance, infrared, dielectric, and viscosity measurements on pure mono- and dihydric alcohols and alcohol-water systems are discussed in terms of the informa tion they provide on the nature and extent of molecular associ ation in these systems. This association leads to the formation of dimeric and multimeric species in the pure liquid alcohols, an unexpectedly high solubility of water in the long-chain alcohols, and the occurrence of a liquid crystalline phase in 1,2-diol-water systems.

Τ η t h e absence of other m o r e specific i n t e r a c t i o n s , h y d r o g e n b o n d i n g leads to a n aggregation of w a t e r i n t o clusters a n d i n l i q u i d alcohols a n d d i o l s to t h e f o r m a t i o n of associated species, w h i c h are t h o u g h t to i n c l u d e d i m e r s , trimers, and higher multimers. T h e i n t e r a c t i o n of w a t e r , t h e simplest h y d r o g e n - b o n d i n g m a t e r i a l , w i t h some alcohols a n d 1,2-diols leads to t h e f o r m a t i o n of s o l i d h y d r a t e s ( p e n t a m e t h y l e t h a n o l , pinacol) w h i l e longer c h a i n 1,2-diols a n d monoglycerides f o r m a l i q u i d c r y s t a l l i n e (I.e.) phase at h i g h e r t e m p e r a t u r e s . T h e factors g o v e r n i n g t h e appearance a n d s t r u c t u r e of t h e I.e. phase i n n o n i o n i c s y s tems are not y e t f u l l y u n d e r s t o o d , a n d w o r k is going o n i n t h i s l a b o r a t o r y o n t h e systems themselves a n d t h e i r s i m p l e l i q u i d a n d s o l i d analogs i n a n a t t e m p t t o d e t e r m i n e these f a c t o r s . T h i s p a p e r discusses some of t h e results of n u c l e a r m a g n e t i c resonance ( N M R ) , i n f r a r e d , dielectric, a n d v i s c o s i t y measurements o n t h e l i q u i d phases of m o n o - a n d d i h y d r i c alcohols alone a n d w i t h w a t e r . F i n a l l y , t h e m o n o l a u r i n - w a t e r phase d i a g r a m is b r i e f l y described. Liquid

Alcohol

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I n f r a r e d measurements h a v e been m a d e o n m o s t s i m p l e alcohols i n d i l u t e s o l u t i o n i n c a r b o n t e t r a c h l o r i d e , a n d i t is agreed t h a t t h e three p r i n 125 In Ordered Fluids and Liquid Crystals; Porter, R., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1967.

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c i p a l b a n d s i n the O H s t r e t c h i n g frequency region denote the existence of s i m p l e monomers, d i m e r s , a n d a n u m b e r of more h i g h l y associated species. C o n t r o v e r s y has arisen o v e r the years as to the exact i n t e r p r e t a t i o n of the i n f r a r e d spectra i n terms of the t y p e of d i m e r f o r m e d . V a n T h i e l , B e c k e r , a n d P i m e n t e l (29) h a v e s h o w n t h a t a c y c l i c d i m e r occurs i n t h e solid state of m e t h a n o l at low temperatures. Q u a n t i t a t i v e i n f r a r e d (18) a n d N M R (2) measurements i n d i l u t e solutions h a v e enabled t h e e n t h a l p y of d i m e r f o r m a t i o n t o be c a l c u l a t e d if c e r t a i n a s s u m p t i o n s are m a d e . The h i g h v a l u e of t h e e n t h a l p y — 9 . 2 k c a l . per mole i n the case of m e t h a n o l — a g a i n suggests t h a t c y c l i c d i m e r s are f o r m e d since t h i s is a r a t h e r h i g h v a l u e for a single h y d r o g e n b o n d . T h e values of the e n t h a l p y o b t a i n e d do not depend o n the m o d e l chosen for t h e d i m e r , as s h o w n b y L u s s a n (19) i n a comprehensive s u m m a r y of t h e possible t h e o r e t i c a l t r e a t m e n t s of t h e N M R d a t a . L u s s a n demonstrates the f o r m of the e q u i l i b r i u m constant c a l c u l a t i o n i n the case of (1) m o n o m e r d i m e r (open or c y c l i c ) , (2) m o n o m e r - c y c l i c t r i m e r , a n d (3) m o n o m e r - h i g h e r a c y c l i c m u l t i m e r s i n t h e t w o cases of (3a) a l l K's e q u a l a n d (3b) ki for m o n o m e r - d i m e r e q u i l i b r i u m u n i q u e , k's for h i g h e r m u l t i m e r s a l l e q u a l . H e t h e n takes the e x p e r i m e n t a l curves for a n u m b e r of alcohols i n c a r b o n t e t rachloride a n d achieves a reasonable fit to the d a t a u p to 0.6 mole f r a c t i o n b y u s i n g one or the other of t h e t h e o r e t i c a l relationships. I n some cases t w o sets of t h e o r e t i c a l p o i n t s are p l o t t e d o n t h e same g r a p h as the e x p e r i m e n t a l d a t a ; b o t h are a good fit i n t h e l o w c o n c e n t r a t i o n region, u p to 0.1 mole f r a c t i o n . A b o v e t h i s c o n c e n t r a t i o n one or t h e other of the t h e o r e t i c a l curves is m u c h closer to the e x p e r i m e n t a l c u r v e . L u s s a n i m p l i e s t h a t hypothesis 3b m a y be a more accurate fit to t h e d a t a i n t h e m o r e c o n c e n t r a t e d solutions. M e t h a n o l , e t h a n o l , 2 - m e t h y l - 2 - p r o p a n o l (tert-butyl a l c o hol) a n d 2 , 2 , 4 - t r i m e t h y l - 3 - p e n t a n o l follow t h e c u r v e for e q u i l i b r i u m 3 a , w h i l e 2 , 2 , 4 , 4 - t e t r a m e t h y l - 3 - p e n t a n o l fits the m o n o m e r - d i m e r d a t a . L u s s a n p o i n t s out t h a t t h e b e h a v i o r of t h e l a t t e r a l c o h o l fits i n w i t h t h a t of t w o s i m i l a r h e a v i l y s u b s t i t u t e d t e r t i a r y alcohols w h i c h h a v e been f o u n d b y i n f r a r e d methods to f o r m o n l y d i m e r s . T h e s e t h e o r e t i c a l t r e a t m e n t s show, as L u s s a n p o i n t s out, t h a t t h e shape of the curves of c h e m i c a l shift vs. c o n c e n t r a t i o n w i l l n o t be affected b y t h e m o d e l chosen for the d i m e r . A n i n t e r e s t i n g a t t e m p t to d i s t i n g u i s h between the occurrence of o p e n or c y c l i c d i m e r s has been m a d e b y J o s i e n et al. (5), w h o h a v e c a r r i e d o u t i n f r a r e d a n d cryoscopic measurements at the same t e m p e r a t u r e o n t h e same d i l u t e solutions of a n u m b e r of alcohols i n F r e o n 112 (1,1,2,2-tetrachloro1,2-difluoroethane). F r o m the cryoscopic d a t a a " m e a n degree of associ a t i o n , " χ, is defined as χ = x/x , where χ is the m o l e f r a c t i o n of the d i s s o l v e d a l c o h o l a n d x is t h e mole f r a c t i o n of particles ( m o n o m e r a n d m u l t i m e r ) i n d i c a t e d b y the freezing p o i n t depression. T h e q u a n t i t y χ is c o m p a r e d w i t h β, where l/β is the f r a c t i o n of free O H groups f r o m t h e i n f r a r e d s p e c t r a , p

p

In Ordered Fluids and Liquid Crystals; Porter, R., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1967.

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a n d J o s i e n shows t h a t w h e n o n l y o p e n d i m e r s are f o r m e d , t h e curves of χ a n d β vs. c o n c e n t r a t i o n s h o u l d be superposable since each species t h e n c o n tains one free O H group.


F o r 2-methyl-2-propanol, 3-ethyl-3-pentanol, 3-ethyl-2,4-dimethyl-3p e n t a n o l , a n d 2 , 2 , 4 , 4 - t e t r a m e t h y l - 3 - p e n t a n o l , t h e curves are superposable w h i l e for 3 - m e t h y l - 3 - p e n t a n o l , 2 , 2 , 4 - t r i m e t h y l - 3 - p e n t a n o l , a n d 1-butanol there is a n appreciable s e p a r a t i o n between the curves. A s J o s i e n p o i n t s out, t h e f o r m a t i o n of o p e n d i m e r s i n 2 - m e t h y l - 2 - p r o p a n o l is i n agreement w i t h the l o w e n t h a l p y of d i m e r f o r m a t i o n , 4.8 k c a l . , o b t a i n e d b y L i d d e l a n d B e c k e r (18). I n 2 , 2 , 4 , 4 - t e t r a m e t h y l - 3 - p e n t a n o l d i m e r s are f o r m e d e x c l u s i v e l y a c c o r d i n g to L u s s a n , a n d t h e y are o p e n d i m e r s a c c o r d i n g t o J o s i e n . O n t h e other h a n d , 2 , 2 , 4 - t r i m e t h y l - 3 - p e n t a n o l , w h i c h L u s s a n finds to f o r m h i g h e r m u l t i m e r s , is p r o b a b l y b e g i n n i n g to f o r m these i n t h e d i l u t e solutions of J o s i e n . W e feel t h a t t h i s higher association c o u l d be another cause of t h e divergence of t h e t w o curves i n her case r a t h e r t h a n the exclusive f o r m a t i o n of closed d i m e r s as J o s i e n i m p l i e s . D u n k e n a n d F r i t z s c h e (6) h a v e s u m m a r i z e d a l l t h e e q u i l i b r i u m c o n s t a n t calculations f r o m i n f r a r e d d a t a used b y earlier w o r k e r s . T h e y h a v e s h o w n t h a t w i t h i n the l i m i t s of a c c u r a c y i n measurement, agreement c a n be reached between the results of t w o m e t h o d s of c a l c u l a t i o n w h i c h c o n t r a d i c t each other i n t h e i r assumptions. B y m a k i n g i n f r a r e d measurements at different temperatures, t h e y also show t h a t these chance agreements c a n come about at one t e m p e r a t u r e a n d not at another. D u n k e n a n d F r i t z s c h e consider t h a t s i m p l i f i e d t r e a t m e n t s of t h e t y p e e n u m e r a t e d b y L u s s a n are o n l y a p p r o x i m a t i o n s to t h e t r u t h , a n d one s h o u l d a l w a y s e m p l o y a general m o d e l of association i n w h i c h a l l t h e associated species (up t o a c e r t a i n m a x i m u m size) are present. T h e a u t h o r s discuss t h e evidence for t h e cyclic d i m e r f o r m b u t do not refer specifically to i t i n t h e i r calculations n o r do t h e y suggest t h a t a n y of the higher m u l t i m e r s are c y c l i c . I n f r a r e d results are presented for 2 - p r o p a n o l , 2 - m e t h y l - 2 - p r o p a n o l , a n d 2 - m e t h y l - 2 - b u t a n o l i n c a r b o n t e t r a c h l o r i d e a n d b y a m e t h o d of successive a p p r o x i m a t i o n s e q u i l i b r i u m constants for the f o r m a t i o n of each m u l t i m e r are w o r k e d o u t f r o m a n e q u a t i o n based o n the general m o d e l of association. R e s u l t a n t graphs of percentage m u l t i m e r vs. c o n c e n t r a t i o n show a greater percentage of pentamers a n d h i g h e r m u l t i m e r s i n IM 2 - m e t h y l - 2 - p r o p a n o l t h a n i n the same c o n c e n t r a t i o n of 2 - m e t h y l - 2 - b u t a n o l . I t is suggested t h a t the f o r m a t i o n of h i g h e r aggregates i n t h e l a t t e r case is p r e j u d i c e d b y steric hindrance. A n u m b e r of w o r k e r s h a v e m a d e dielectric measurements o n alcohols a n d f o u n d t h a t curves of p o l a r i z a t i o n vs. c o n c e n t r a t i o n for several alcohols e x h i b i t m a x i m a or m i n i m a w h i c h h a v e been ascribed t o t h e f o r m a t i o n of associated species of greater or less p o l a r i t y as t h e c o n c e n t r a t i o n is p r o gressively increased.


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I b b i t s o n a n d M o o r e (13) conclude t h a t t h e m a x i m u m i n t h e c u r v e of p o l a r i z a t i o n vs. c o n c e n t r a t i o n for e t h a n o l i n c a r b o n t e t r a c h l o r i d e is caused b y l i n e a r m u l t i m e r s , a n d t h e subsequent f a l l i n p o l a r i z a t i o n is caused b y a n increasing a m o u n t of c y c l i c m u l t i m e r ( F i g u r e 1). T h e c o n c e n t r a t i o n a t w h i c h t h e m a x i m u m occurs coincides w i t h t h a t at w h i c h t h e 3 3 5 0 - c m . b a n d first appears i n t h e i n f r a r e d s p e c t r u m , so t h e y h a v e suggested t h a t this b a n d arises f r o m c y c l i c m u l t i m e r s . T h e y h a v e fitted t h e i r d a t a t o a

- 1


system containing linear dimer and trimer and cyclic tetramer only and h a v e e v a l u a t e d association constants for these species.

θ·6

0-8 lOOw

Figure 1. Variation of dielectric constant ( e , · ) and solute polarization(P2 Ο ) with weight fraction, w, for ethanol in carbon tetrachloride }

T h e m o d e l proposed b y Z a c h a r i a s e n (31) t o e x p l a i n t h e x - r a y d i f f r a c t i o n peaks of l i q u i d alcohols was t h a t of l o n g h y d r o g e n - b o n d e d chains i n w h i c h the h y d r o g e n b o n d s are l i n e a r , the o x y g e n a t o m of each a l c o h o l m o l e cule b e i n g l i n k e d b y h y d r o g e n b o n d s to t h a t of t w o neighbors, t h e a l k y l groups of t h e molecules f a l l i n g c o n s e c u t i v e l y o n opposite sides of t h e c h a i n . O s t e r a n d K i r k w o o d (21) m a d e t h e f u r t h e r s t i p u l a t i o n t h a t there were n o h y d r o g e n bonds between t h e c h a i n s . H a r r i s et al. (8), u s i n g t h e O s t e r a n d K i r k w o o d t h e o r y , deduced f r o m v a l u e s of t h e d i e l e c t r i c c o n s t a n t of 2 m e t h y l - 2 - p r o p a n o l at r o o m t e m p e r a t u r e t h a t these chains h a v e a n average l e n g t h of 3.55 u n i t s , decreasing to 1.77 at 50°C. H u y s k e n s et al. (10, 12) h a v e m e a s u r e d t h e dielectric constants of t h e b u t y l alcohols i n different solvents between 25° a n d 55°C. a n d h a v e c a l c u l a t e d d i p o l e m o m e n t s , μ, u s i n g a s l i g h t l y m o d i f i e d f o r m of the Onsager e q u a t i o n . T h e plots of μ vs. c o n c e n t r a t i o n show m i n i m a w h i c h H u y s k e n s ascribes to c y c l i c m u l t i m e r s of l o w r e s u l t a n t m o m e n t . T h e curves t h e n rise a g a i n w i t h i n c r e a s i n g c o n c e n t r a t i o n a n d i n t h e p r i m a r y alcohols a p p e a r t o r e a c h a m a x i m u m v a l u e a t w h i c h t h e y flatten off a t a b o u t 0.9 m o l e f r a c t i o n . H e notes t h a t t h e m i n i m u m v a l u e of μ occurs at l o w e r c o n c e n t r a t i o n s for t h e m o r e associated alcohols a n d becomes less p r o n o u n c e d as t h e t e m p e r a t u r e rises, v a n i s h i n g altogether at 55°C. for 1-butanol. L a t e r w o r k b y H u y s k e n s et al. (11) o n a range of n o r m a l alcohols u p to o c t a n o l showed results i n each case r a t h e r s i m i l a r t o those o n 1-butanol. 2

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A s s u m i n g t h a t t h e m i n i m u m i n t h e c u r v e of μ vs. c o n c e n t r a t i o n is caused b y the presence of c y c l i c m u l t i m e r s , H u y s k e n s c a l c u l a t e d the r e l a t i v e n u m bers of molecules, r, i n v o l v e d i n t h e c y c l i c structures f r o m the d i p o l e m o m e n t curves. H e t h e n o b t a i n e d values of t h e m o n o m e r concentrations, C\, from infrared d a t a and compared qualitatively the v a r i a t i o n w i t h concen t r a t i o n of r a n d a p p r o p r i a t e functions of ci for t h e case of t w o - , three-, a n d f o u r - m e m b e r e d c y c l i c m u l t i m e r s . B e s t agreement was o b t a i n e d w i t h the c y c l i c t r i m e r c u r v e i n m o s t cases a l t h o u g h the i m p o r t a n c e of bigger rings seemed to increase w i t h t h e c h a i n l e n g t h of t h e alcohol. Downloaded by STANFORD UNIV GREEN LIBR on May 10, 2012 | http://pubs.acs.org Publication Date: January 1, 1967 | doi: 10.1021/ba-1967-0063.ch010

2

A t a mole f r a c t i o n of a b o u t 0.3 i n a l l the p r i m a r y alcohols u p to o c t a n o l , μ is independent of t e m p e r a t u r e . B e l o w t h i s c o n c e n t r a t i o n μ increases w i t h t e m p e r a t u r e , w h i c h is p r e s u m a b l y caused b y the b r e a k i n g u p of c y c l i c m u l t i m e r s of l o w dipole m o m e n t , a n d a b o v e 0.3 mole f r a c t i o n i t decreases w i t h t e m p e r a t u r e , p r e s u m a b l y because of t h e b r e a k i n g u p of l i n e a r m u l t i mers of h i g h dipole m o m e n t . I n 2 - m e t h y l - 2 - p r o p a n o l t h e p o i n t at w h i c h μ is independent of t e m p e r a t u r e occurs at 0.6 mole f r a c t i o n , a n d the m a x i m u m v a l u e of μ is o n l y 6.4 D e b y e c o m p a r e d w i t h 8.75 D e b y e for 1b u t a n o l a n d 8.52 D e b y e for 2 - b u t a n o l . T h e s e facts seem to c o n f i r m H a r r i s ' s d e d u c t i o n t h a t 2 - m e t h y l - 2 - p r o p a n o l forms o n l y short chains a n d also i n d i c a t e a greater s t a b i l i t y for t h e c y c l i c m u l t i m e r i n t h i s a l c o h o l . H u y s k e n s ' results also show t h a t t h e effect of increasing t e m p e r a t u r e o n t h e values of μ for the p u r e alcohols increases m a r k e d l y w i t h the c h a i n l e n g t h of t h e alcohol. I n v i e w of t h i s b e h a v i o r i t w o u l d p r o b a b l y be m o r e realistic to c o m p a r e t h e tendencies to f o r m c y c l i c m u l t i m e r s at c o r r e s p o n d i n g temperatures for the v a r i o u s alcohols r a t h e r t h a n at t h e fixed v a l u e of 25°C. 2

2

2

2

2

2

2

2

T h e field dependence of the dielectric constant is k n o w n as t h e dielec t r i c s a t u r a t i o n effect ( D S E ) , a n d i n a n unassociated m e d i u m Ae/E i n creases l i n e a r l y w i t h c o n c e n t r a t i o n . M a l e c k i (20) has f o u n d t h a t i n a l c o h o l solutions considerable nonlinearities o c c u r — p o s i t i v e s a t u r a t i o n is o b t a i n e d at l o w concentrations a n d negative at h i g h concentrations. T h i s behavior is i n t e r p r e t e d a c c o r d i n g t o t h e t h e o r y of P i e k a r a (22), a n d for 1-hexanol i n hexane M a l e c k i shows t h a t the degree of association increases w i t h i n c r e a s ing concentration. 2

T h e large p o s i t i v e s a t u r a t i o n i n d i l u t e solutions is caused b y t h e h i g h c o n c e n t r a t i o n of dimers, i n w h i c h t h e dielectric s a t u r a t i o n is s h o w n b y P i e k a r a to l e a d t o the largest increase i n dipole m o m e n t . F r o m curves w h i c h show the v a r i a t i o n i n mole f r a c t i o n of each m u l t i m e r w i t h c o n c e n t r a t i o n i t appears t h a t i n 1-hexanol there are 65 mole % p e n t a m e r s , 25 mole % tetramers, a n d 10 mole % t r i m e r s a p p r o x i m a t e l y i n t h e p u r e l i q u i d . M a l e c k i has also c a l c u l a t e d t h a t 6 0 % of d i m e r s a n d 3 7 % of t r i m e r s are cycliC., t h e t e t r a m e r s a n d pentamers r e v e a l i n g no c y c l i c structures. T h e forms of t h e curves s h o w i n g v a r i a t i o n s i n c o n c e n t r a t i o n of m o n o m e r a n d t h e v a r i o u s m u l t i m e r s w i t h t o t a l c o n c e n t r a t i o n of h e x a n o l are s i m i l a r t o


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those o b t a i n e d b y D u n k e n a n d F r i t z s c h e for 2 - p r o p a n o l , 2 - m e t h y l - 2 - p r o p a n o l , a n d 2 - m e t h y l - 2 - b u t a n o l . M a l e c k i has c o m p a r e d the v a l u e s of r f r o m these results w i t h those of H u y s k e n s for 1-hexanol a n d shows t h a t there is a good measure of agreement. T h e influence of s t r u c t u r e o n m o l e c u l a r association i n t h e alcohols w a s s h o w n b y S m y t h (24), w h o d e t e r m i n e d the dielectric constant a n d m o l a r p o l a r i z a t i o n of 22 isomeric octanols i n t h e p u r e state. O n l y general c o n clusions c a n be d r a w n f r o m these results. A s S m y t h says, associations i n w h i c h the dipoles reinforce each other, g i v i n g h i g h Ρ a n d e, seem t o o c c u r w h e n the O H group is at t h e end of a l o n g C c h a i n a n d remote f r o m a b r a n c h i n the c h a i n — i . e . , w h e n l i n e a r m u l t i m e r f o r m a t i o n is most f a v o r e d . W h e n t h e O H group is i n the m i d d l e of t h e c h a i n a n d there is also b r a n c h i n g at t h a t p o i n t as i n 4 - m e t h y l - 4 - h e p t a n o l , Ρ is a p p r o x i m a t e l y h a l f t h e v a l u e for 1-octanol, as w o u l d be expected if c y c l i c m u l t i m e r s p r e d o m i n a t e . T h o m a s (25, 26) s t u d i e d the effects of association i n alcohols o n t h e i r viscosities a n d v a p o r pressures. U s i n g a c o m b i n a t i o n of e m p i r i c a l r e l a t i o n ships, he o b t a i n e d values of h y d r o g e n b o n d enthalpies a n d average degrees of association, y, for a large n u m b e r of alcohols. H e finds y is constant Table I.

Summary of Data

Methods

Ref. Lussan (19)

NMR

Josien (5)

Infrared-colligative

Dunken and Fritzsche (6)

Infrared

Ibbitson and Moore (13)

Infrared-dielectric measurements Infrared-dielectric measurements Dielectric measurements

property

Huyskens (10, 11, 12) Malecki (20)

Thomas (25, 26)

Viscosity measurements

Conclusions Reached Range of acyclic multimers, no distinction possible between cy clic and acyclic dimer structures Acyclic dimers only in some cases, acyclic + cyclic in others Cyclic dimers discussed, higher multimers formed but all as sumed acyclic Linear dimers and trimers, cyclic tetramers Some cyclic multimers, predomi nantly trimers Calculated percentages of cyclic and acyclic dimers and trimers, all tetramers and pentamers acyclic Cyclic dimer in n-alkanols, higher cyclic multimers in branchedchain alkanols

a r o u n d the v a l u e 2 for n o r m a l s t r a i g h t - c h a i n alcohols u p t o o c t a n o l — i . e . , the p r e p o n d e r a n t associated species is the d i m e r — w h i l e values of γ u p to 5 are o b t a i n e d for b r a n c h e d - c h a i n alcohols. O n t h e basis of these results T h o m a s suggests t h a t t h e n o r m a l alcohols associate i n d o u b l e - l e n g t h rod-shaped molecules b y f o r m i n g t w o bonds be tween t h e t w o h y d r o x y l g r o u p s — t h e c y c l i c d i m e r . I t is proposed t h a t the



10.

MCDONALD

I 4000

Molecular

I 3500 , cm." 1

Figure 2.

131

Association

I 3000

I 4000

I 3500

cm".'

1 3000

OH stretching vibrations in solutions of 1-heptanol in CCU

b r a n c h e d c h a i n alcohols w i l l h a v e less reason t o f o r m dimers i n this w a y , p r i n c i p a l l y because of the s m a l l e r L o n d o n forces between t h e i r h y d r o c a r b o n portions. D i r e c t conclusions h a v e been d r a w n f r o m t h e viscosities of alcohols i n different solvents b y H u y s k e n s (9), w h o infers f r o m the greater v i s c o s i t y of 2 - m e t h y l - 2 - p r o p a n o l at 25°C. t h a n the other b u t a n o l s t h a t c y c l i c m u l t i m e r s h a v i n g a greater resistance t o flow t h a n l i n e a r m u l t i m e r s are present i n greater p r o p o r t i o n s i n t h e t e r t i a r y a l c o h o l . O u r o w n w o r k o n 1-heptanol a n d a n u m b e r of its isomers has i n v o l v e d i n f r a r e d a n d N M R measurements o n t h e p u r e l i q u i d s a n d t h e i r solutions i n c a r b o n t e t r a c h l o r i d e . I n f r a r e d measurements h a v e been m a d e o n a U n i c a m S P 1 0 0 spectrophotometer a n d N M R measurements o n a V a r i a n A - 6 0 spectrometer. T h e O H s t r e t c h i n g region of the i n f r a r e d s p e c t r u m has been c o m p a r e d for d i l u t e solutions of five heptanols i n c a r b o n t e t r a c h l o r i d e ; t h e s p e c t r u m at 0.1 m o l a r i t y a n d 25°C. gives a good i n d i c a t i o n of t h e association b e h a v i o r of the a l c o h o l . T h e p i c t u r e for t h e t w o extreme t y p e s of b e h a v i o r , as exemplified b y 1-heptanol a n d p e n t a m e t h y l e t h a n o l , is s h o w n i n F i g u r e s 2 a n d 3. T h e three O H s t r e t c h i n g bands occur i n 1-heptanol a t 3630,


132


3500, a n d 3350 c m . a n d h a v e been assigned b y m o s t w o r k e r s t o m o n o m e r , d i m e r , a n d m u l t i m e r O H groups, respectively. S i n c e t h e m u l t i m e r b a n d is t h e furthest shifted f r o m t h e m o n o m e r b a n d , w e c a n assume t h a t t h e h y d r o g e n b o n d s f o r m e d i n t h i s a s s o c i a t i o n are of h i g h e r energy t h a n i n t h e d i m e r . W e therefore presume t h a t t h i s


- 1

I 4000 Figure 3.

I 3500

cm.-

1

I 3000

I 4000

I 3500

cm.

I 3000

-1

OH stretching vibrations in solutions of penlamethylethanol in CCU

b a n d arises f r o m h y d r o g e n b o n d s i n either t h e l o n g - c h a i n m u l t i m e r s d e scribed b y Z a c h a r i a s e n , o r t h r e e - a n d f o u r - m e m b e r e d c y c l i c m u l t i m e r s , o r p o s s i b l y i n a l l these species. Since t h e l i n e a r chains m a y w e l l c u r l u p i n t o helices of l o w r e s u l t a n t dipole m o m e n t b y i n t e r n a l r o t a t i o n of t h e h y d r o g e n bonds (17, 21), t h e i r f o r m a t i o n is n o t i n c o m p a t i b l e w i t h t h e p o l a r i z a t i o n d a t a of I b b i t s o n . I n p e n t a m e t h y l e t h a n o l t h e m u l t i m e r b a n d never appears, b u t t h e d i m e r b a n d becomes broader as t h e c o n c e n t r a t i o n increases. I n 2 , 4 d i m e t h y l - 3 - p e n t a n o l t h e m u l t i m e r b a n d is o n l y j u s t perceptible a t 0 . 1 M a n d develops m u c h m o r e s l o w l y w i t h i n c r e a s i n g c o n c e n t r a t i o n t h a n i n t h e case of 1-heptanol. 4 - H e p t a n o l shows s l i g h t l y m o r e evidence of m u l t i m e r s at 0 . 1 M , a n d t h e c y c l o h e p t a n o l s p e c t r u m is p r a c t i c a l l y i n d i s t i n g u i s h a b l e f r o m t h a t of 1-heptanol.


10.

MCDONALD

Molecular

Association

133

I t seems t h a t m u l t i m e r f o r m a t i o n occurs w i t h i n c r e a s i n g ease i n t h e series p e n t a m e t h y l e t h a n o l , 2 , 4 - d i m e t h y l - 3 - p e n t a n o l , 4 - h e p t a n o l , c y c l o h e p t a n o l , 1-heptanol. S i n c e we h a v e detected the a b o v e differences b e t w e e n alcohols, three of w h i c h are secondary isomers, t h e process of associ a t i o n does n o t seem t o d e p e n d o n t h e class of a l c o h o l .


Space models of these alcohols shows i m m e d i a t e l y h o w i m p o r t a n t m u s t be the steric influences o n the association processes. O n e c a n see h o w d i f ficult i t is for molecules s u c h as p e n t a m e t h y l e t h a n o l t o f o r m l i n e a r h y d r o gen-bonded chains of the Z a c h a r i a s e n t y p e . T h e a l k y l groups of alternate molecules c a n be seen to be close together if no b e n d i n g occurs i n the h y d r o g e n b o n d c h a i n , a n d w h e n a l k y l s u b s t i t u t i o n occurs i n the a p o s i t i o n , there is c e r t a i n to be some h i n d r a n c e to free r o t a t i o n a r o u n d the — C — Ο — b o n d . A c c o r d i n g l y , f r o m the l a c k of a m u l t i m e r b a n d i n t h e i n f r a r e d spec t r u m a n d the l i n e a r i t y of the c u r v e of N M R c h e m i c a l shift vs. c o n c e n t r a t i o n o u t to 0 . 3 5 M we c a n presume t h a t o n l y d i m e r s are f o r m e d i n i t i a l l y i n pentamethylethanol, w i t h possibly cyclic multimers at higher concentra tions. B e c a u s e of t h i s b e h a v i o r w e h a v e been able to o b t a i n v a l u e s for t h e e n t h a l p y of d i m e r i z a t i o n f r o m i n f r a r e d d a t a b y t h e m e t h o d of L i d d e l a n d B e c k e r (18) a n d f r o m N M R d a t a b y t h e m e t h o d of D a v i s , P i t z e r , a n d R a o (2) w i t h o u t h a v i n g t o resort t o s u c h l o w c o n c e n t r a t i o n s as u s u a l . E x t r a p o l a t e d v a l u e s of t h e i n f r a r e d m o l a r e x t i n c t i o n coefficients, e m , of the m o n o m e r O H b a n d at zero c o n c e n t r a t i o n were o b t a i n e d f r o m curves of e vs. c o n c e n t r a t i o n at 25° a n d 50°C., a n d f r o m these a v a l u e of 5.4 k c a l . per m o l e was o b t a i n e d for t h e e n t h a l p y of d i m e r i z a t i o n . T h e l i m i t i n g slopes of t h e curves of N M R c h e m i c a l shift vs. c o n c e n t r a t i o n at 0° a n d 35°C. gave a v a l u e of 6.1 k c a l . per m o l e . T h e s e v a l u e s are i n reasonable agreement w i t h each o t h e r a n d s i g n i f i c a n t l y l o w e r t h a n the v a l u e s of 8 k c a l . for 1h e p t a n o l a n d 7.9 k c a l . for 2 , 4 - d i m e t h y l - 3 - p e n t a n o l , o b t a i n e d f r o m N M R data only. m

A l t h o u g h t h e association of t h e l a t t e r a l c o h o l is h i n d e r e d b y s u b s t i t u t i o n i n the 2 a n d 4 positions, one c a n see t h a t l i n e a r m u l t i m e r s are possible, a n d t h i s is e v e n m o r e t r u e of 4 - h e p t a n o l because of t h e greater freedom of m o v e m e n t of t h e u n s u b s t i t u t e d m e t h y l e n e groups. I n c y c l o h e p t a n o l w e feel t h a t complete r o t a t i o n of t h e molecule m a y be h i n d e r e d i n t h e l i n e a r m u l t i m e r , b u t there is s t i l l r o o m for appreciable t o r s i o n a l m o v e m e n t . Josien's results i n d i c a t e a difference i n t h e t y p e of d i m e r f o r m e d i n 3m e t h y l - 3 - p e n t a n o l a n d 3 - e t h y l - 3 - p e n t a n o l , a n d we w o u l d prefer t o e x p l a i n t h i s b e h a v i o r b y t h e f o r m a t i o n of l i n e a r m u l t i m e r s at l o w c o n c e n t r a t i o n s i n t h e f o r m e r b u t n o t i n t h e l a t t e r case. A g a i n space models show t h a t a n e t h y l group o n t h e α-carbon a t o m i n 3 - p e n t a n o l w i l l be a c o n s i d e r a b l y greater h i n d r a n c e t o l i n e a r m u l t i m e r f o r m a t i o n t h a n a m e t h y l g r o u p . S t e r i c factors w i l l affect t h e f o r m a t i o n of c y c l i c as w e l l as l i n e a r m u l t i m e r s , a n d i n t h e case of p e n t a m e t h y l e t h a n o l i t is t h o u g h t t h a t o n l y i n


134


c y c l i c t r i m e r w i l l there be sufficient " e l b o w r o o m " for free r o t a t i o n of t h e b u l k y a l k y l radicals. T h e N M R c h e m i c a l shifts of t h e h y d r o x y l p r o t o n l i n e i n the p u r e a l c o hols m e a s u r e d at 30°C. bear o u t t h e general conclusions o b t a i n e d f r o m t h e i n f r a r e d s p e c t r a since t h e greater association shifts o c c u r i n t h e

alcohols

s h o w i n g t h e greater tendencies t o w a r d m u l t i m e r f o r m a t i o n i n e v e r y case. T h e r e is s t i l l no c e r t a i n i n f o r m a t i o n o b t a i n a b l e f r o m i n f r a r e d a n d N M R measurements o n c y c l i c d i m e r s or m u l t i m e r s .

The dimer band m a y

arise f r o m a c y c l i c species i n v o l v i n g n o n l i n e a r h y d r o g e n bonds, a n d one


m i g h t expect t h a t if a c y c l i c t r i m e r exists, t h e O H s t r e t c h i n g frequency w o u l d be s i m i l a r to a n d s l i g h t l y l o w e r t h a n t h a t of a c y c l i c d i m e r .

This

w o u l d account for the b r o a d e n i n g of the d i m e r b a n d i n p e n t a m e t h y l e t h a n o l at h i g h concentrations. T h e higher values of e n t h a l p y for d i m e r f o r m a t i o n i n t h e n o r m a l a l c o hols, p o s s i b l y representing t h e f o r m a t i o n of t w o h y d r o g e n bonds,

could

m e a n t h a t t h e y f o r m a c y c l i c d i m e r at low concentrations m o r e r e a d i l y t h a n the h e a v i l y s u b s t i t u t e d alcohols, a g a i n for steric reasons. T h e i n f r a r e d , N M R , a n d dielectric results are t h u s i n general agreement o n t h e n a t u r e of the association processes i n l i q u i d alcohols a l t h o u g h there are m a n y differences i n d e t a i l .

O b v i o u s l y steric considerations are of p r i m e

i m p o r t a n c e i n these systems.

M o r e specific a n d c e r t a i n conclusions m a y

f o l l o w f r o m a n e x t e n s i o n of t h e dielectric m e t h o d s of I b b i t s o n , H u y s k e n s , a n d M a l e c k i t o some of t h e isomeric alcohols s t u d i e d b y the i n f r a r e d workers. Diols I n f o r m a t i o n o n i n t e r m o l e c u l a r h y d r o g e n b o n d i n g i n a l i p h a t i c 1,2-diols is h a r d to

find.

T h e O H s t r e t c h i n g v i b r a t i o n of i n t e r m o l e c u l a r bonds was

observed b y K u h n (14) i n a n u m b e r of a r o m a t i c a n d a l i p h a t i c diols.

The

b a n d occurs between 3400 a n d 3500 c m , i n a l l cases, b u t K u h n does n o t - 1

discuss t h e i n t e r m o l e c u l a r association processes.

H e d i d , however, i n

vestigate the influence of s t r u c t u r e o n t h e i n t r a m o l e c u l a r h y d r o g e n

bond

a n d f o u n d t h a t w h e n b u l k y a l k y l groups are a t t a c h e d to t h e g l y c o l residue i n meso 1,2-disubstituted glycols, t h e y c a n p r e v e n t t h e f o r m a t i o n of t h e i n t r a m o l e c u l a r h y d r o g e n b o n d b y f o r c i n g t h e t w o O H groups to o c c u p y t r a n s positions.

B y u s i n g different s u b s t i t u e n t a l k y l groups he p r o v e d

f a i r l y c o n c l u s i v e l y t h a t t h i s effect is of steric r a t h e r t h a n p o l a r o r i g i n .

It

w o u l d be i n t e r e s t i n g to k n o w t h e effect of these changes o n t h e n a t u r e a n d degree of i n t e r m o l e c u l a r b o n d i n g . R e c e n t l y T h o m a s (27) m e a s u r e d y v a l u e s for a n u m b e r of a l i p h a t i c a n d a r o m a t i c diols.

H e finds a g a i n , as i n t h e alcohols, t h a t t h e degree of a s

s o c i a t i o n is low for t h e s t r a i g h t - c h a i n diols a n d h i g h for t h e h i g h l y s u b s t i t u t e d ones (7 = 2.1 for ethylene g l y c o l , y = 3.7 for t e t r a m e t h y l e t h y l e n e



10.

MCDONALD

Molecular

Association

135

glycol) a n d therefore concludes t h a t the association is n o t h i n d e r e d b y steric factors. Because γ for these diols is o n l y s l i g h t l y h i g h e r t h a n for the c o r r e s p o n d i n g m o n o h y d r i c alcohols, i t is suggested t h a t m u l t i m e r s are chiefly f o r m e d t h r o u g h o n l y one of t h e O H groups, a c o n c l u s i o n w h i c h is s u p p o r t e d b y the values of a f u n c t i o n q/m d e r i v e d f r o m e n t h a l p y considerations. Thomas concludes t h a t c y c l i c t e t r a m e r s are f o r m e d i n t h e h i g h l y associated diols i n v o l v i n g o n l y one O H group f r o m each molecule. I n less associated diols the values of q/m suggest t h a t b o t h O H groups are i n v o l v e d i n t h e associ a t i o n , a n d p o l y d e n t a t e structures i n v o l v i n g t w o a n d three molecules of d i o l are suggested a n d s h o w n to be g e o m e t r i c a l l y feasible. D e b y e et al. (5, /+) p u b l i s h e d t w o papers c o n t a i n i n g i n f r a r e d measure ments o n monoglycerides. T h e y assigned o v e r l a p p i n g bands (at 3584 a n d 3460 c m , i n t h e first p a p e r a n d 3676 a n d 3572 i n t h e second) t o " f r e e " a n d " b o n d e d " O H groups, respectively, a n d f o u n d the r a t i o of t h e e s t i m a t e d o p t i c a l densities of these b a n d s ; O H f r e e / O H b o u n d decreased l i n e a r l y w i t h c o n c e n t r a t i o n i n c a r b o n t e t r a c h l o r i d e s o l u t i o n because of i n c r e a s i n g m o l e c u l a r association. I n c h l o r o f o r m a n d benzene, h o w e v e r , the r a t i o r e m a i n e d a l m o s t constant, i n d i c a t i n g t h a t association w a s t a k i n g place between - 1


136


glyceride a n d s o l v e n t molecules. U n f o r t u n a t e l y , D e b y e does n o t d i s t i n g u i s h between i n t r a - a n d i n t e r m o l e c u l a r h y d r o g e n b o n d i n g . W e h a v e observed t h e O H s t r e t c h i n g v i b r a t i o n s for a p u r e s a m p l e of m o n o c a p r i n i n c a r b o n t e t r a c h l o r i d e a n d at 0 . 0 0 8 M h a v e f o u n d a m o n o m e r or " f r e e " O H b a n d at 3620 c m . a n d a b a n d w h i c h we t h i n k is caused b y t h e i n t r a m o l e c u l a r h y d r o g e n b o n d a t 3540 c m . A t 0 . 0 4 M the O H b a n d is m u c h broader, w i t h a m a x i m u m at 3460 c m . , p r e s u m a b l y o w i n g t o ex tensive i n t e r m o l e c u l a r association. I t seems therefore t h a t t h i s t y p e of association sets i n a t s i m i l a r O H g r o u p concentrations i n t h e d i o l s a n d t h e m o n o h y d r i c alcohols, as c a n also be seen i n K u h n ' s s p e c t r u m of t e t r a m e t h y l ethylene g l y c o l , i n w h i c h the i n t e r m o l e c u l a r b a n d i n 0 . 0 5 M s o l u t i o n h a s a p p r o x i m a t e l y the same i n t e n s i t y as i n 0 . 1 M solutions of the n o r m a l alkanols. - 1

- 1


- 1

Liquid

Alcohols

Plus

Water

T h e lower a l i p h a t i c alcohols are c o m p l e t e l y m i s c i b l e w i t h w a t e r ; h i g h e r homologs h a v e a p a r t i a l m i s c i b i l i t y as s h o w n b y a t y p i c a l conjugate s o l u t i o n d i a g r a m ( F i g u r e 4), a n d f r o m h e x a n o l u p w a r d t h e y are v i r t u a l l y i n soluble i n w a t e r . T h e s o l u b i l i t y of w a t e r i n t h e a l k a n o l s does n o t f a l l off so d r a s t i c a l l y , a n d F i g u r e 5 shows a p l o t of s o l u b i l i t y vs. c h a i n l e n g t h . F u r t h e r m o r e , t h e w a t e r - i n - a l c o h o l p o r t i o n of F i g u r e 4 shows the s m a l l change i n s o l u b i l i t y over a w i d e range of t e m p e r a t u r e ; i n fact, t h i s c u r v e (for t h e 1 - b u t a n o l w a t e r system) is b i n o d a l . T h i s b e h a v i o r reflects the delicate balance be t w e e n t h e association a n d the i d e a l m i x i n g tendencies i n a l c o h o l - w a t e r mixtures. G i n n i n g s a n d H a u s e r (7) d e t e r m i n e d some m u t u a l solubilities i n a n u m b e r of isomeric h e p t a n o l - w a t e r systems o v e r a l i m i t e d t e m p e r a t u r e range. T h e t e m p e r a t u r e coefficients for t h e s o l u b i l i t y of w a t e r i n a l c o h o l are p o s i t i v e i n some cases a n d n e g a t i v e i n others, a n d there is a p e r c e p t i b l e g r o u p i n g of the a c t u a l s o l u b i l i t y v a l u e s . I n t h e heptanols chosen a l l t h e t e r t i a r y isomers t a k e u p a p p r o x i m a t e l y 6 % w a t e r at 20°C., w h i l e t h e sec o n d a r y isomers dissolve a p p r o x i m a t e l y 3 % w a t e r . T h e solubilities of t h e heptanols i n w a t e r decrease w i t h t e m p e r a t u r e i n a l l cases. N M R s p e c t r a h a v e been observed i n t h i s l a b o r a t o r y of samples of heptanol, octanol, and dodecanol saturated w i t h water. W i t h pure speci mens of o c t a n o l a n d d o d e c a n o l we h a v e o b t a i n e d a p i c t u r e at l o w t e m p e r a tures s i m i l a r t o t h a t of W e i n b e r g a n d Z i m m e r m a n (30), t h e a l c o h o l a n d w a t e r O H groups g i v i n g separate resonances. A s the t e m p e r a t u r e was i n creased i n these samples, the lines coalesced to give a single v e r y b r o a d peak. W h e n the lines are d i s t i n c t , the a l c o h o l O H resonance r e m a i n s at the same v a l u e of c h e m i c a l shift, δ, as i n the a n h y d r o u s m a t e r i a l , whereas for the w a t e r line, δ decreases b y a p p r o x i m a t e l y 0.4 p . p . m . i n each a l c o h o l f r o m t h e v a l u e i n p u r e w a t e r . O n e deduces t h a t t h e h y d r o g e n b o n d i n g


10.

Molecular

MCDONALD

137

Association


l-li

4

8

12

C Figure a. Ο 9

16

20

c

n

n

Solubilities of water in normal alkanols

25°C. 60°C.

w i t h i n the a l c o h o l is n o t affected b y t h e a d d i t i o n of w a t e r , b u t t h e a m o u n t of b o n d i n g between the w a t e r molecules is decreased i n t h e a l c o h o l s o l u t i o n . T h e r a t e of change of δ w i t h t e m p e r a t u r e has also been m e a s u r e d i n the p u r e alcohols a n d a l c o h o l - w a t e r s y s t e m s ; here i t is e v i d e n t t h a t t h e c o m b i n e d O H l i n e varies w i t h t e m p e r a t u r e i n t h e same w a y as t h e m e a n v a l u e of the separate a l c o h o l a n d w a t e r O H lines. A g a i n t h i s indicates t h a t there is no m a j o r change i n the n a t u r e of the h y d r o g e n b o n d i n g w h e n w a t e r is a d d e d to alcohols i n these a m o u n t s . F r o m the i n f r a r e d a n d N M R results s h o w i n g different degrees of as s o c i a t i o n a m o n g the different alcohols, i t is t e m p t i n g t o t r y t o correlate t h i s association w i t h t h e a m o u n t of w a t e r t a k e n u p at c o r r e s p o n d i n g t e m p e r a tures. One m i g h t conclude f r o m t h e figures of G i n n i n g s a n d H a u s e r t h a t the t e r t i a r y alcohols t a k e u p m o r e w a t e r because t h e y p r o b a b l y c o n t a i n more of the s m a l l n o n l i n e a r m u l t i m e r s w h i c h m o r e r e a d i l y associate w i t h i n d i v i d u a l w a t e r molecules. Ο Η

M e a s u r e m e n t s of dielectric constant i n t h e 2 - m e t h y l - 2 - p r o p a n o l - w a t e r s y s t e m b y B r o w n a n d I v e s (1 ) are explicable i n terms of a w a t e r - c e n t e r e d



138

O R D E R E D FLUIDS A N D LIQUID CRYSTALS

association, a n d t h e authors assemble other evidence i n f a v o r of t h i s hypothesis. D i e l e c t r i c measurements o n a n u m b e r of s t r u c t u r a l l y isomeric a l k a n o l s w i t h w a t e r w o u l d p r o b a b l y help t o elucidate t h e n a t u r e of t h i s association. I n t h e s o l i d state, however, t h e n o r m a l l o n g - c h a i n a l i p h a t i c alcohols t a k e u p almost e x a c t l y the same a m o u n t of w a t e r as i n t h e l i q u i d (15), a n d T r a p e z n i k o v (28) has suggested t h a t specific h y d r a t e s are f o r m e d , as i n t h e w e l l k n o w n case of p e n t a m e t h y l e t h a n o l . Since t h e s t r u c t u r e of s o l i d a l c o hols c e r t a i n l y contains l i n e a r chains of h y d r o g e n bonds, i t seems unneces s a r y t o evoke t h e specific association of s m a l l clusters of a l c o h o l molecules w i t h i n d i v i d u a l w a t e r molecules i n t h e l i q u i d state. Diols

Plus

Water

C o m p l e t e m i s c i b i l i t y of a l i p h a t i c diols w i t h w a t e r occurs u p t o higher c h a i n lengths t h a n i n t h e a l c o h o l series, a n d h e x a n e - l , 2 - d i o l is described as m i s c i b l e w i t h w a t e r . A s t h e c h a i n l e n g t h increases f u r t h e r , a d d i n g w a t e r

—ι

I Η,Ο

U

1

i_l

I

I

ΙΟ]

20

|30

40

50

2H 0

Figure 6.

2

6H 0 2

ΙΟΗ Ό 2

•/•Water phase diagram Monolaurin-water

Lower dotted line refers to transition between a metastable solid plmse and an I.e. phase



10.

MCDONALD

Molecular Association

139

leads to the formation of a smectic I.e. phase which has been observed i n a number of monoglycerides and in hexadecane-l,2-diol (15) over limited ranges of temperature. A t higher temperatures i n the presence of large amounts of water, only a brief region of liquid miscibility occurs before the system separates into two liquids. A similar behavior is seen i n some of the longer chain amines in the presence of water (28). The monolaurin-water system, which has been fully described elsewhere (16), is shown in Figure 6. A feature of these systems is the large amount of water taken up by the I.e. phase. I n octylamine a maximum stability of this phase occurs at a ratio of 6 mole cules of water to 1 of octylamine, but in monolaurin the stability is still at a maximum when the system reaches the point at which it can take up no more water. The conjugate solution curve at the top of the diagram is steep, showing that monolaurin can contain up to 10 molecules of water per molecule i n the liquid or I.e. phase without breaking down at any tem perature. One of the conditions for the formation of the I.e. phase is the same as i n the well characterized soap-water systems—the chain must be at least six carbon atoms long, by which time the London forces between chains are sufficient to maintain the structure of the smectic phase. Further work i n this field will involve the study of some of the inter mediate chain length 1,2-diol-water, monoglyceride-water, and aminewater systems. W e would like to establish all the conditions necessary for formation of the I.e. phase in these systems and to determine the factors governing its stability and final instability as the percentage of water in the system increases. Acknowledgmen

t

The author thanks G . Porter for the use of N M R and infrared facilities at the Department of Chemistry, Sheffield University, and A . S. C . Law rence for many helpful discussions. Literature

Cited

(1) Brown, A. C., Ives, D. J. G., J. Chem. Soc. 1962, 1608. (2) Davis, J. C., Pitzer, K. S., Rao, C. N. R., J. Phys. Chem. 64, 1744 (1960). (3) Debye, P., Prins, W., J. Colloid Sci. 13, 86 (1958). (4) Debye, P., Coll, H., J. Colloid Sci. 17, 220 (1962). (5) Dos Santos, J., Pineau, P., Josien, M.-L., J. Chim. Phys. 1965, 628 (6) Dunken, H., Fritzsche, H., Spectrochim. Acta 20, 785 (1964). (7) Ginnings, P. M . , Hauser, M . , J. Am. Chem. Soc. 60, 2581 (1938). (8) Harris, F. E., Haycock, E. W., Alder, B. J., J. Chem. Phys. 21, 1943 (1953). (9) Huyskens, P., J. Chim. Phys. 62, 158 (1965). (10) Huyskens, P., Cracco, F., Bull. Soc. Chim. Belg. 69, 422 (1960). (11) Huyskens, P., Gillerot, G., Zeegers-Huyskens, Th., Bull. Soc. Chim. Belg. 72, 666 (1963). (12) Huyskens, P., Henry, R., Gillerot, G., Bull. Soc. Chim. France. 1962, 720. (13) Ibbitson, D. Α., Moore, L . F., Chem. Commun. 1965, 339. (14) Kuhn, L., J. Am. Chem. Soc. 74, 2492 (1952); 80, 5950 (1958).



140


(15) Lawrence, A. S. C., Capper, B., Hume, K., J. Phys. Chem. 68, 3470 (1964). (16) Lawrence, A. S. C., McDonald, M . P., Molecular Crystals 1, 205 (1966). (17) Le Fèvre, R. J. W., Williams, A. J., J. Chem. Soc. 1960, 108. (18) Liddel, U., Becker, E. D., Spectrochim. Acta 10, 70 (1957). (19) Lussan, C., J. Chim. Phys. 1963, 1100. (20) Malecki, J., J. Chem. Phys. 43, 1351 (1965). (21) Oster, G., Kirkwood, J . G., J. Chem. Phys. 11, 175 (1943). (22) Piekara, Α., J. Chem. Phys. 36, 2145 (1962). (23) Ralston, A. W., Hoerr, C. W., Hoffman, E. J., J. Am. Chem. Soc. 64, 1516 (1942). (24) Smyth, C. P., Chem. Revs. 6, 549 (1929). (25) Thomas, L . H., J. Chem. Soc. 1963, 1995. (26) Thomas, L . H., Meatyard, R., J. Chem. Soc. 1963, 1986. (27) Ibid., 1966, A92. (28) Trapeznikov, Α. Α., "Proceedings of 2nd International Congress of Surface Ac tivity" Vol. 1, p. 109, Butterworth & Co., London, 1957. (29) Van Thiel, M . , Becker, E . D., Pimentel, G. C., J. Chem. Phys. 27, 95 (1957). (30) Weinberg, I., Zimmerman, J. R., J. Chem. Phys. 23, 748 (1955). (31) Zachariasen, W. H., J. Chem. Phys. 3, 158 (1935). RECEIVED January 27, 1966.


Ordered Fluids and Liquid Crystals

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