The Reaction Between Ozone and Saturated Compounds - Advances

59 The Reaction Between Ozone and Saturated Compounds M . C . WHITING, A. J. N. BOLT, and J. H. PARISH

Downloaded by CORNELL UNIV on September 6, 2016 | http://pubs.acs.org Publication Date: January 1, 1968 | doi: 10.1021/ba-1968-0077.ch059

University of Bristol, Bristol 8, E n g l a n d

Ozone oxidizes saturated hydrocarbons (Decalin and adamantane) and alcohols even at —78°C. Initial products from hydrocarbons are radical pairs, in which tertiary radicals are formed preferentially from hydrocarbons, and which collapse to alcohols and oxygen with high retention of configuration. Methanol and ethanol are attacked, initially giving radical pairs or ion pairs which yield first α-hydroxyhydrotrioxides, then formic or acetic acid and hydrogen peroxide. Propan-2-ol similarly gives α-hydroxyisopropyl hydrotrioxide, whose breakdown at higher temperatures is affected by trace substituents, and can give either acetone, oxygen, and water, or acetic acid and hydrogen peroxide. Side reactions lead via acetone enol and its ozonide to peracetic acid, formaldehyde, acetone, and hydrogen peroxide, and by a less well understood route to acetic acid and methanol.

" T V u r l a n d a n d A d k i n s ( 5 ) d e s c r i b e d the oxidations of cis- a n d transD e c a l i n w i t h ozone as g i v i n g cis- a n d £rans-9-decalols, respectively. T h e specific a n d stereospecific i n s e r t i o n of a n a t o m into a C - H g r o u p a p p e a r e d to b e a n interesting a n d u n e x p e c t e d r e a c t i o n , a n d w e have r e i n v e s t i g a t e d i t u s i n g gas c h r o m a t o g r a p h y . It proceeds at temperatures as l o w as — 7 8 ° C . , l e a d i n g m a i n l y to t e r t i a r y alcohols, a l t h o u g h significant quantities of ketones are also f o r m e d , a n d it shows a stereospecificity of ca. 9 0 - 9 8 % , v a r y i n g w i t h solvent a n d temperature.

A d a m a n t a n e is also

a t t a c k e d at — 7 8 ° C . , g i v i n g the 1-alcohol a n d the ketone i n ratios of ca. 3 to 1. O z o n a t i o n of a m i x t u r e of trans-cis-/3-deca\o\

a n d trans-T)eca\m

r e s u l t e d i n p r e f e r e n t i a l attack o n the f o r m e r , w i t h the f o r m a t i o n of trans/?-decalone.

T h u s , secondary alcohols are p r o b a b l y intermediates i n the

f o r m a t i o n of ketones f r o m h y d r o c a r b o n s . W e c o n s i d e r e d the p o s s i b i l i t y 4 Mayo; Oxidation of Organic Compounds Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

59.

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ET

AL.

Saturated

Compounds

that singlet o x y g e n rather t h a n ozone m i g h t be the effective

5

oxidant;

h o w e v e r , p r e - p r e p a r e d solutions of ozone i n t r i c h l o r o f l u o r o m e t h a n e

at

—78 ° C , i n w h i c h it is u n l i k e l y that significant concentrations of singlet o x y g e n c o u l d be o b t a i n e d , o x i d i z e d a d a m a n t a n e i n the same w a y as d i d a stream of o z o n i z e d o x y g e n .


Experimental Materials. P r o p a n - 2 - o l ( T y p e A ) was M a y & B a k e r 2 - p r o p a n o l , either u n t r e a t e d or f r a c t i o n a t e d t h r o u g h a 3 0 - i n c h V i g r e u x c o l u m n . P r o p a n - 2 - o l ( T y p e B ) was r e f l u x e d for 1 h o u r w i t h s o d i u m b o r o h y d r i d e before f r a c t i o n a t i o n . B o t h types h a d b . p . , 8 2 ° C . E t h a n o l ( b . p . , 7 8 ° C ) , m e t h a n o l ( b . p . , 6 5 ° C ) , tot-butyl a l c o h o l ( m . p . , 2 5 ° C ) , c y c l o h e x a n o l ( b . p . , 1 6 1 ° C ) , cyclohexane (b.p., 8 1 ° C ) , and adamantane (m.p., 2 6 8 ° - 2 7 0 ° C . ) were p u r i f i e d b y s t a n d a r d methods, cis- a n d f r a n s - D e c a l i n w e r e p r e p a r e d b y p r e p a r a t i v e g a s - l i q u i d c h r o m a t o g r a p h y ( G L C ) , f o l l o w i n g r e m o v a l of T e t r a l i n b y p a s s i n g t h r o u g h s i l i c a gel. Ozone Apparatus and Reaction Procedure. T h e ozone apparatus was a G a l l e n k a m p G E - 1 5 0 y i e l d i n g ca. 6 % ozone i n o x y g e n at a rate of ca. 10 liters/hour. T h e o z o n i z e d o x y g e n stream was passed b y means of a t u b e t e r m i n a t e d i n a h i g h p o r o s i t y sintered glass disc t h r o u g h the s u b strate i n a c y l i n d r i c a l reactor c o o l e d to — 7 8 ° C . w i t h s o l i d C 0 . P r e l i m i n a r y c o o l i n g of the gas stream b y passage t h r o u g h a c o o l e d glass c o i l h a d no a p p r e c i a b l e effect o n the result. Product Analysis. P e r o x i d i c p r o d u c t s w e r e estimated b y the m e t h o d of L e d a l l a n d B e r n a t e k ( 7 ) ; 2 - m l . aliquots w e r e t a k e n w i t h a p i p e t t e p r e v i o u s l y c o o l e d b y w r a p p i n g i n p o l y e t h y l e n e sheet a n d c o v e r i n g w i t h s o l i d C O o (this p r o c e d u r e is p a r t i c u l a r l y i m p o r t a n t w h e n T y p e A p r o p a n - 2 - o l is i n v o l v e d since t e m p e r a t u r e increases result i n c h a n g e d p r o d u c t concentrations). A c i d s other t h a n peracids w e r e estimated b y t i t r a t i o n against c e n t i n o r m a l s o d i u m h y d r o x i d e u s i n g b r o m o t h y m o l b l u e as i n d i c a t o r . ( S p e e d is essential since d e c o m p o s i t i o n of p e r a c i d otherwise results i n a n i n d e f i nite e n d p o i n t ) . C a r b o n y l c o m p o u n d s w e r e estimated b y t h i n - l a y e r c h r o m a t o g r a p h y ( T L C ) u s i n g d i e t h y l ketone as an i n t e r n a l s t a n d a r d . T h e y w e r e c o n v e r t e d to the c o r r e s p o n d i n g 2 , 4 - d i n i t r o p h e n y l h y d r a z o n e s ( D N P ) b y r e a c t i o n for 15 hours w i t h a n excess of aqueous 2 , 4 - d i n i t r o p h e n y l h y d r a z i n e perchlorate. T h e D N P ' s w e r e extracted w i t h benzene, the b e n z e n e extract was concentrated, a n d a p o r t i o n of the concentrate w a s c h r o m a t o g r a p h e d o n s i l i c a . T h e D N P ' s w e r e c o m p l e t e l y separated b y d e v e l o p m e n t w i t h a m i x t u r e of d i e t h y l ether ( 2 0 % ) a n d p e t r o l e u m ( b . p . , 6 0 ° - 8 0 ° C . ; 8 0 % ). T h e r e s u l t i n g b a n d s w e r e r e m o v e d separately a n d e l u t e d w i t h ethanol, the v o l u m e of each eluate b e i n g adjusted to 5 m l . T h e u l t r a v i o l e t spec t r u m of each solution ( d i l u t e d w h e n necessary) was r e c o r d e d , a n d the absolute concentrations of the c a r b o n y l c o m p o u n d s i n the o r i g i n a l reac tion solution were calculated. G L C analysis of v o l a t i l e p r o d u c t s (e.g., acetone, m e t h a n o l ) , i n v o l v e d G P O - 5 0 ( U n i l e v e r L t d . ; 1 5 % ; 3 m e t e r s ) , temperatures b e t w e e n 0 ° a n d 20 ° C . a n d a h e a t e d flame-ionization detector. n - H e x a n e served as an 2

Mayo; Oxidation of Organic Compounds Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

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i n t e r n a l s t a n d a r d for q u a n t i t a t i v e estimation. C a r b o x y l i c acids w e r e a n a l y z e d w i t h a P y e 104 flame i o n i z a t i o n g a s - l i q u i d c h r o m a t o g r a p h y apparatus a n d a m i x e d stationary phase ( 5 % ; 5 0 ° C . ) of g l u t a r i c a c i d ( 2 3 % ) a n d G P O - 5 0 ( 7 7 % ). T h e s u p p o r t ( E m b a c e l ) a n d the 11.5-meter glass c o l u m n s w e r e s i l a n i z e d , a n d c y c l o h e x a n o n e was u s e d as a n i n t e r n a l s t a n d a r d . P e a k areas w e r e o b t a i n e d p l a n i m e t r i c a l l y . S a m p l e c o l l e c t i o n i n v o l v e d the above m i x e d phase ( 2 5 % ; 4 0 ° C . ) a n d a P y e 104 catharometer apparatus. Gas Evolution. T h e c o l d reaction s o l u t i o n was transferred to a c a l i b r a t e d flask at — 78 ° C , c o n n e c t e d to a gas buret, a n d i m m e r s e d i n a n ice b a t h at 0 ° C . T h e s o l u t i o n was s t i r r e d m a g n e t i c a l l y at as near a constant rate as possible, a n d the a p p a r e n t gas e v o l u t i o n was r e c o r d e d at c o n v e n i e n t t i m e intervals. T h e gas was i d e n t i f i e d as oxygen b y its a b s o r p t i o n i n a l k a l i n e p y r o g a l l o l ( n o a b s o r p t i o n was n o t e d i n strong aqueous s o d i u m h y d r o x i d e ) . T h e r e a l gas e v o l u t i o n was o b t a i n e d b y s u b t r a c t i n g f r o m the a p p a r e n t v o l u m e the v a l u e o b t a i n e d i n a b l a n k c o n t r o l experiment i n v o l v i n g u n o z o n i z e d o x y g e n . Low Temperature Infrared Studies. T h e s e studies i n v o l v e d a l o w temperature c e l l ( R e s e a r c h a n d I n d u s t r i a l L t d . , s l i g h t l y m o d i f i e d ) a n d a P e r k i n - E l m e r 225 i n f r a r e d spectrophotometer a u g m e n t e d w i t h a slave r e c o r d e r to r e c o r d o p t i c a l density. T h e c e l l temperature w a s m a i n t a i n e d as close to — 7 8 ° C . as possible w i t h s o l i d C 0 . 2

Oxidation by Solutions of Ozone. Solutions of ozone i n t r i c h l o r o fluoromethane ( b . p . , 2 4 ° C . ) w e r e p r e p a r e d at — 7 8 ° C , u s i n g the above apparatus a n d c o n d i t i o n s . Passage of o z o n i z e d o x y g e n t h r o u g h the solvent (50 m l . ) f o r 45 m i n . y i e l d e d a s o l u t i o n c o n t a i n i n g a p p r o x i m a t e l y 65 /xmole/cc. ozone. C a l c u l a t e d quantities of substrate ( g e n e r a l l y i n s m a l l excess) w e r e a d d e d , a n d the m i x t u r e w a s set aside at — 7 8 ° C . u n t i l , f o r alcohols, loss of color i n d i c a t e d the r e a c t i o n to be c o m p l e t e . T i t r i m e t r i c estimations w e r e m a d e as before, a n d the solvent w a s r e m o v e d t h r o u g h a 30-inch V i g r e u x column before G L C investigation. Solids p r e c i p i t a t e d i n the r e a c t i o n of p r o p a n - 2 - o l i n C C l ^ F w i t h ozone w e r e separated f r o m the supernatant w i t h a filter stick, w a s h e d w i t h c o l d C C 1 F , a n d d i s s o l v e d i n p r o p a n - 2 - o l b e f o r e analysis. P a r t i t i o n of the r e a c t i o n p r o d u c t s of the above r e a c t i o n b e t w e e n C C l . s F a n d 8 0 % m e t h a n o l i n v o l v e d s h a k i n g a p o r t i o n of the supernatant at — 7 8 ° C . w i t h an e q u a l v o l u m e of 8 0 % m e t h a n o l p r e c o o l e d to — 7 8 ° C . T h e aqueous layer, on separation, was r a p i d l y transferred to a n d m i x e d w i t h an e q u a l v o l u m e of C C 1 F at — 78 ° C . O n separation of the t w o layers, 2 - m l . aliquots w e r e r e m o v e d f r o m each a n d a n a l y z e d for p e r a c i d , acetic a c i d , h y d r o g e n p e r o x i d e , acetone, a n d f o r m a l d e h y d e i n the u s u a l w a y . T h e temperature was m a i n t a i n e d as close to — 78 ° C . as possible u n t i l the analysis stage was r e a c h e d . T h e p r o c e d u r e was r e p e a t e d w i t h C C l F solutions of the a u t h e n t i c c o m p o u n d s u n d e r i d e n t i c a l c o n d i t i o n s , a n d p a r t i t i o n coefficients w e r e c o m p a r e d . T h e reactions of h y d r o c a r b o n s w i t h C C l ^ F solutions of ozone at —78 ° C , b e i n g c o n s i d e r a b l y slower t h a n for alcohols, w e r e a l l o w e d to p r o c e e d for u p to 8 days. A n y r e s i d u a l ozone was r e m o v e d b y flushing w i t h n i t r o g e n . E x p e r i m e n t s w e r e c o n d u c t e d on either a G L C or a p r e p a r a t i v e scale. 3

S

; i


59.

WHITING

ET AL.

Saturated

Compounds

7

I n a t y p i c a l G L C scale experiment, a d a m a n t a n e (100 m g . ) w a s a d d e d i n excess to a C C 1 F s o l u t i o n of ozone, a n d the m i x t u r e w a s set aside at — 7 8 ° C . f o r 6 days. A f t e r r e m o v i n g r e s i d u a l ozone, t h e solvent w a s e v a p o r a t e d u s i n g a 3 0 - i n c h V i g r e u x c o l u m n . G L C of a n ethereal s o l u t i o n of the r e s i d u e o n d i g l y c e r o l ( 1 5 % ; 2 meters; 1 0 0 ° C . ) d e m o n s t r a t e d t w o m a i n p r o d u c t s , a d a m a n t a n o n e ( r e l a t i v e r e t e n t i o n t i m e T = 22) a n d 1 - a d a m a n t a n o l ( T = 4 8 ) . I n a s i m i l a r e x p e r i m e n t i n w h i c h the solvent was a m i x t u r e of b r o m o t r i c h l o r o m e t h a n e (13 m l . ) a n d C C 1 F ( 2 1 m l . ) (this m i x t u r e p r e c i p i t a t e d some s o l i d C C l B r at — 7 8 ° C ) , G L C analysis d e m o n s t r a t e d the presence i n the p r o d u c t of 1-chloroadamantane ( T = 2.5), 1 - b r o m o a d a m a n t a n e ( r = 4 ) , a d a m a n t a n o n e ( l o w y i e l d ) , a n d 1-adamantanol. F i v e other c o m p o n e n t s ( T = 6, 12, 17, 23, 6 2 ) w e r e n o t investigated. I n a t y p i c a l p r e p a r a t i v e scale e x p e r i m e n t a d a m a n t a n e ( 1 g r a m ) was o x i d i z e d w i t h a C C 1 . F s o l u t i o n of ozone at — 7 8 ° C . f o r 8 days. A f t e r w o r k i n g u p b y the u s u a l m e t h o d , the residue w a s d i s s o l v e d i n ether a n d w a s h e d w i t h aqueous s o d i u m h y d r o x i d e . T h e ether layer o n evapo r a t i o n y i e l d e d a w h i t e c r y s t a l l i n e s o l i d (870 m g . ) . E l u t i o n w i t h l i g h t p e t r o l e u m ( b . p . , 3 0 - 4 0 ° C . ) f r o m n e u t r a l a l u m i n a (175 g r a m s ) gave u n c h a n g e d a d a m a n t a n e (505 m g . ) , a n d 3 0 % d i e t h y l ether i n p e t r o l e u m e l u t e d a k e t o n i c f r a c t i o n (63 m g . ) . F i n a l l y , p u r e ether e l u t e d 1-ada m a n t a n o l (227 m g . ) . T L C of the k e t o n i c f r a c t i o n separated the major component—adamantanone—from a minor unidentified component. H y d r o c a r b o n s w e r e also o x i d i z e d b y p a s s i n g o z o n i z e d o x y g e n t h r o u g h C C 1 F , C C l B r , a n d C C 1 solutions at temperatures b e t w e e n — 2 0 ° a n d 0°C. cis- A N D £ r a n s - 9 - H Y D R O X Y D E C A L i N S . O z o n i z e d o x y g e n w a s b u b b l e d t h r o u g h a s t i r r e d s o l u t i o n of D e c a l i n ( H a r r i n g t o n , 30 grams; 4 3 . 5 % trans) i n c a r b o n t e t r a c h l o r i d e (250 m l . ) at 0 ° C . f o r 40 hours. A r o m a t i c ozonides ( w h i c h w o u l d b e f o r m e d f r o m T e t r a l i n c o n t a m i n a t i n g the D e c a l i n ) w e r e r e m o v e d as f o l l o w s . C a r b o n t e t r a c h l o r i d e (ca. 120 m l . ) w a s e v a p o r a t e d at 2 1 ° - 2 5 ° C . / 1 0 0 m m . T h e residue w a s stirred w i t h aqueous h y d r o g e n p e r o x i d e ( 2 % w / v , 300 m l . ) f o r 15 m i n . at 2 5 ° C . a n d f o r 30 m i n . at 60 ° C . N o n - a c i d i c p r o d u c t s w e r e o b t a i n e d via ether, a n d d i s t i l l a t i o n a f f o r d e d u n c h a n g e d D e c a l i n a n d a n o i l (9.28 g r a m s ) , b . p . , 7 2 ° - 7 6 ° C . / 0.07 m m . , f r o m w h i c h crystals separated after 20 hours at 1 8 ° C . T h e o i l was d r a i n e d off; r e c r y s t a l l i z a t i o n f r o m l i g h t p e t r o l e u m ( b o i l i n g r a n g e 3 0 ° - 4 0 ° C . ) y i e l d e d d s - 9 - h y d r o x y d e c a l i n (501 m g . ) , m . p . , 6 5 ° - 6 6 ° C . E l u t i o n w i t h l i g h t p e t r o l e u m ( b . p . , 3 0 ° - 4 0 ° C . ) of the residue f r o m a l u m i n u m oxide ( P e t e r Spence G r a d e H , d e a c t i v a t e d w i t h 5 % w / v of an aqueous s o l u t i o n , 1 0 % w / v of acetic a c i d ; 100 g r a m s ) gave ketones. F u r t h e r e l u t i o n gave solids (420 m g . ) w h i c h , after r e c r y s t a l l i z a t i o n f r o m l i g h t p e t r o l e u m ( b e n z e n e free, b . p . , 2 0 ° - 2 7 ° C . ) at - 7 0 ° C . y i e l d e d £rans-9-hydroxydecalin (370 m g . ) , m . p . , 5 2 . 5 ° - 5 3 ° C . , then m o r e of the cis isomer (1.93 g r a m s ) , m . p . , 6 3 ° C . 8

3


3

{

8

: i

4

T h e assignment of these isomers w a s c o n f i r m e d b y n u c l e a r m a g n e t i c resonance spectroscopy o n a P e r k i n - E l m e r 60 M c . / s e c . N M R spectrometer, after r e m o v a l of - O H b y exchange w i t h d e u t e r i u m oxide. T h e s p e c t r u m of the c i s - a l c o h o l s h o w e d a single b r o a d peak, w h i l e that of the transalcohol s h o w e d t w o peaks; t h e y thus r e s e m b l e d the spectra of the corre s p o n d i n g h y d r o c a r b o n s (8).


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O X I D A T I O N O F cis- A N D J r a n s - D E C A L i N . f r a n s - D e c a l i n (1.02 g r a m s ) , c i s - D e c a l i n (1.14 g r a m s ) a n d f r a n s - D e c a l i n (1.38 g r a m s ) + trans-cis-pd e c a l o l (1.54 g r a m s ) w e r e d i s s o l v e d i n 25, 25, a n d 50 m l . of c a r b o n tetra c h l o r i d e , respectively. O z o n e w a s passed t h r o u g h e a c h of t h e solutions for 20 hours, a n d the resultant solutions w e r e treated w i t h aqueous h y d r o g e n p e r o x i d e (6%, 25 m l . ) a n d w i t h c o n c e n t r a t e d p o t a s s i u m h y d r o g e n carbonate (25 m l . ) , d r i e d (MgS0 ) a n d e v a p o r a t e d ( D u f t o n c o l u m n ) . 4

Table I.

Oxidation of Decalin Relative Product


T, °C. frans-Decalin cis-Decalin

0

-78

Solvent CC1 CHoCl

trans9-o/

cis9-ol

100 100

10

4

100

4

0

CC1

2

4

2

Concentrations

trans1-one

cis1-one

trans2-one

cis2-one

27 45

— —

35 50

— —

—

5

—

35

G a s - c h r o m a t o g r a p h i c analysis i n v o l v e d d i g l y c e r o l (15%, 2 meters, 5 0 ° C . ) as stationary phase. F r o m J r a n s - D e c a l i n , peaks w e r e £rans-9-hydroxyd e c a l i n ( T = 41), trans-a-decalone ( T = 53), a n d trans-fi-decsdone (T = 74); f r o m c i s - D e c a l i n they w e r e ds-a-decalone ( T = 30), cis-fi-decalone ( = 55) a n d c i s - 9 - h y d r o x y d e c a l i n (r = 100). R e t e n t i o n times are r e l a t i v e ; p r o d u c t s w e r e i d e n t i f i e d b y c o m p a r i s o n w i t h a u t h e n t i c speci mens, except f o r cis-a-decalone, w h e r e structure w a s assumed f r o m re t e n t i o n t i m e a n d a n a l o g y w i t h t h e trans-series. P e a k areas w e r e o b t a i n e d p l a n i m e t r i c a l l y . R e l a t i v e p r o d u c t concentrations are g i v e n i n T a b l e I. T

Discussion S c h u b e r t a n d Pease ( I I ) p r o p o s e d a m e c h a n i s m f o r isobutane o x i d a t i o n i n the gaseous state, i n w h i c h t h e first stage RH + 0

3

-> R O - + O o H

c a n h a r d l y b e elementary, It c a n b e r e f o r m u l a t e d w i t h a r a d i c a l p a i r ( I ) or a n i o n p a i r ( I I ) as a n a d d i t i o n a l i n t e r m e d i a t e . R H + O , -> R ' O H - » R O ' + 0 . , H (gas phase) H

(I) j \ R H + 0 -> R ~ 0 H - » R O H + O. (liquid phase) 3

+

3

(II) I n s o l u t i o n , r a p i d collapse w i t h consequent h i g h p r e s e r v a t i o n of c o n figuration replaces t h e c o m p l e x sequence of changes o b s e r v e d b y S c h u b e r t a n d Pease, a n d this l e d to a n i n i t i a l preference f o r i n t e r m e d i a t e ( I I ) . U s e of b r o m o t r i c h l o r o m e t h a n e as a c o m p o n e n t of t h e solvent i n t h e o z o n a t i o n of adamantane, h o w e v e r , gave a p r o d u c t m i x t u r e w h i c h c o n t a i n e d several n e w c o m p o n e n t s — t w o h a v i n g retention times c o r r e s p o n d -


59.

WHITING

E TA L .

Saturated

9

Compounds

i n g to 1-chloro- a n d 1-bromo-adamantane;

thus, i t seems p r o b a b l e

that

i n o x i d i z i n g h y d r o c a r b o n s i n n o n p o l a r m e d i a , s h o r t - l i v e d r a d i c a l pairs, c a p a b l e of b e i n g i n t e r c e p t e d b y sufficiently reactive r a d i c a l traps, are i n v o l v e d . C o l l a p s e of t h e r a d i c a l pairs e v i d e n t l y gives m a i n l y the a l c o h o l p l u s oxygen, rather t h a n a h y d r o t r i o x i d e ( R e a c t i o n P ) . I n seeking i n f o r m a t i o n about t h e second stage of the o x i d a t i o n at secondary positions attention w a s t u r n e d to the o z o n a t i o n of s i m p l e alco hols ( T a b l e I I ) . M e t h a n o l gave a b l u e s o l u t i o n w i t h o z o n i z e d o x y g e n ; this f a d e d r a p i d l y , a n d o n w a r m i n g i t w a s f o u n d t o c o n t a i n a n e q u i -


m o l e c u l a r m i x t u r e of f o r m i c a c i d a n d h y d r o g e n p e r o x i d e : HOCH

: i

B + O., -> H O C H . / 0 H - » H O C H 0 — O — O H -> 8

2

H O C H = 0 + OoH + B H

(P)

+

(III) P e r f o r m i c a c i d w a s stable u n d e r the r e a c t i o n c o n d i t i o n s a n d h e n c e w a s not a n i n t e r m e d i a t e ; f o r m a l d e h y d e a n d o x y g e n w e r e f o r m e d i n l o w y i e l d s ( T a b l e I I ) . A hydrotrioxide intermediate

( I I I ) is almost a necessary

postulate; the ^ - e l i m i n a t i o n w h i c h gives f o r m i c a c i d ( R e a c t i o n P ) a n d H0 ~ 2

c a n of course b e i n t r a m o l e c u l a r .

[ F o r m a t i o n of s u c h a n inter

m e d i a t e (see a d d i t i o n a l e v i d e n c e b e l o w ) m i g h t i n d i c a t e a different p r e cursor f r o m the r a d i c a l p a i r (I)—i.e., the i o n p a i r ( I I ) , w h i c h is of course m u c h m o r e p l a u s i b l e i n a p o l a r solvent.]

I n f r a r e d spectra d e t e r m i n e d at

— 7 8 ° C . gave n o e v i d e n c e that s u c h a species as ( I I I ) c o u l d a c c u m u l a t e , however. T h e o x i d a t i o n of e t h a n o l w a s d e c i d e d l y faster t h a n that of m e t h a n o l , a n d t h e m a i n p r o d u c t s w e r e acetic a c i d a n d h y d r o g e n p e r o x i d e

[molar

ratio ca. 1:1.0 ( R e a c t i o n P ) ] . S m a l l y i e l d s of a c e t a l d e h y d e , f o r m a l d e h y d e , and

peracid

a n d the e v o l u t i o n

of s m a l l

quantities

of

oxygen

on

w a r m i n g the o z o n i z e d s o l u t i o n to 0 ° C , suggested t h e i n c u r s i o n of side reactions Q a n d R (see below)

( 2 0 % a n d 1 - 2 % of the w h o l e p r o c e s s ) ,

analogous to t h e o x i d a t i o n reactions

of p r o p a n - 2 - o l ( T y p e

B ) , which

w e r e m u c h m o r e f u l l y investigated. O z o n a t i o n of p r o p a n - 2 - o l gave results w h i c h v a r i e d w i t h the h i s t o r y of the a l c o h o l s p e c i m e n used. A l l p r o p a n - 2 - o l specimens a b s o r b e d ozone r e a d i l y at — 78 ° C , t h e s o l u t i o n never b e c o m i n g b l u e , a n d gave solutions w h i c h s h o w e d a w e a k i n f r a r e d b a n d at 1705 c m . " ( F i g u r e 1 ) , a t t r i b u t a b l e 1

( s h o w n b y c o m p a r i s o n w i t h a u t h e n t i c solutions) to either acetic a c i d or acetone or b o t h . A d d i t i o n of excess t r i e t h y l a m i n e r e d u c e d the i n t e n s i t y of this b a n d b y 6 0 % , so most of i t w a s e v i d e n t l y a t t r i b u t a b l e to acetic a c i d ; authentic specimens b e h a v e d s i m i l a r l y , t h e acetate i o n a b s o r b i n g at 1550-1600 c m . " . T i t r a t i o n at this stage s h o w e d the presence of substan 1

t i a l amounts of p e r a c i d , a c i d , a n d h y d r o g e n p e r o x i d e , w h i l e gas c h r o m a t o g r a p h y (after w a r m i n g to 2 0 ° C . ) i n d i c a t e d the presence of acetic a c i d


10

OXIDATION

OF

ORGANIC

COMPOUNDS

Table II. Number of Runs

Propan-2-ol(B)

III

Oxidation Relative

CH COCH^

before warming after warming Propan-2-ol(A) before warming after warming

CH CHO

c

3

100

b

100

b

3

—

27

Ethanol


Methanol " Average values, taken from several similar experiments. Quoted concentrations were obtained by T L C ; in one experiment the corresponding G L C . estimate was 94 /xmole/cc. c

a n d m e t h a n o l , the f o r m e r i n about the same a m o u n t as i n d i c a t e d b y i n f r a r e d spectroscopy. T h e b e h a v i o r of the s o l u t i o n thus o b t a i n e d at — 78 ° C . o n w a r m i n g to 0 ° C . d e p e n d e d o n its history—i.e.,

o n its T y p e A / B character.

If

the

character w e r e T y p e B , o x y g e n was e v o l v e d i n large q u a n t i t y , a n d a d d i t i o n a l acetone w a s f o r m e d , as estimated

b y c o o l i n g to

—78°C.

and

r e p e a t i n g the i n f r a r e d e x a m i n a t i o n , b y gas c h r o m a t o g r a p h y , or b y p r e p a r i n g a n d separating the 2 , 4 - d i n i t r o p h e n y l h y d r a z o n e s .

N o increase i n

the a c i d titer or h y d r o g e n p e r o x i d e titer was o b s e r v e d , a n d the p e r a c i d titer f e l l s l i g h t l y . T y p e A p r o p a n - 2 - o l e v o l v e d less o x y g e n o n w a r m i n g to 0 ° C .

( v a r y i n g f r o m one s p e c i m e n to a n o t h e r ) ,

but correspondingly

the o r g a n i c p r o d u c t s w e r e o x i d i z e d to acetic a c i d , a n d a p p r o x i m a t e l y 1 m o l e c u l e of h y d r o g e n p e r o x i d e was f o r m e d for each 2 m o l e c u l e s o x y g e n not e v o l v e d .

T y p e A p r o p a n - 2 - o l was s i m p l y the

of

commercial

p r o d u c t b e f o r e or after f r a c t i o n a l d i s t i l l a t i o n ; T y p e B was o b t a i n e d b y d i s t i l l a t i o n f r o m s o d i u m b o r o h y d r i d e ; their r e l a t i o n s h i p , a n d the possible nature

of contaminants

present,

w e r e not ascertained

u n t i l after

the

s y m p o s i u m . C o n t r a r y to our p r e f e r r e d hypothesis then, type A p r o v e d to b e p u r e , a n d T y p e B c o n t a i n e d a c o n t a m i n a n t ; the s i m p l e r T y p e B be h a v i o r c o u l d be s i m u l a t e d b y a d d i n g to T y p e A 2 - p r o p a n o l 2 p . p . m . or m o r e ( e v e n 0.5 p . p . m . h a d a m a r k e d effect) of s o d i u m b o r o h y d r i d e as a s o l u t i o n i n 2 - p r o p a n o l , w h i c h was not i n a c t i v a t e d b y h e a t i n g w i t h excess acetone, hence, it w a s p r o b a b l y present as s o d i u m t e t r a i s o p r o p o x y b o r o n . A s i m i l a r q u a n t i t y of s o d i u m acetate w a s e q u a l l y effective, b u t s o d i u m perchlorate

had

phenomena.

I n the i n i t i a l phase of the o x i d a t i o n , the m a i n process e v i

no

effect.

We

are

currently

investigating

these

d e n t l y i n v o l v e d is the f o r m a t i o n of a c o m p o u n d , itself transparent

at

1705 c m . " b u t c a p a b l e of y i e l d i n g acetone, oxygen, a n d w a t e r o n w a r m i n g 1


59.

WHITING

ET

11

Saturated Compounds

AL.

of A l c o h o l s Product

Concentrations'

1

CH 0

RC0 H

RC0 H

17

11 9

11 16

18 18

71

16

14 13

8 42

18 44

27

2

100

b

100

100*

93

18 10

2

3

2 15

H0 2

2

—

Of

2

Values based on a concentration of 100 /xmole/cc. of major product. Major products are formed at a rate of ca. 50 /miole/cc./hr.


6

( R e a c t i o n Q ) . F o r m a t i o n of w a t e r was a p p a r e n t w h e n filtered h o m o g e n e ous t r i c h l o r o f l u o r o m e t h a n e solutions w e r e w a r m e d .

Solids i n i t i a l l y p r e

c i p i t a t e d f r o m these solutions a p p e a r e d to be either h y d r o g e n p e r o x i d e or a m i x t u r e of a l l other p r o d u c t s aggregated w i t h h y d r o g e n p e r o x i d e . T h e acetone precursor was i n fact s h o w n to b e m o r e p o l a r t h a n acetone, as m e a s u r e d b y d i s t r i b u t i o n coefficient b e t w e e n

trichlorofluoromethane

and 80%

X

methanol.

Its d e c o m p o s i t i o n rate, 2.3

is c o m p a r a b l e w i t h that of di-ter£-butyltrioxide

10"

(1);

sec."

3

1

at

0°C,

slow decomposition

e v e n at — 7 8 ° C . is c a t a l y z e d b y t r i e t h y l a m i n e . T h e r e is every reason f o r a c c e p t i n g the o b v i o u s f o r m u l a ( I V ) : M e , , C H ( O H ) —> M e C ( O H ) 0 H - > M e C ( O H ) 0 H - > M e C O + 0 2

3

2

i

3

2

2

+ H 0

(IV)

Me • C (OH) O : C H s

2

(Q)

+ H 0 2

3

i

\ > (R) )

Me • C 0 H + C H 0 3

2

2

f o r this major intermediate, c o n s t i t u t i n g some 8 0 % of the i n i t i a l r e a c t i o n product.

Its alternative m o d e of d e c o m p o s i t i o n i n T y p e A p r o p a n - 2 - o l

is c o n s i d e r e d b e l o w . P e r a c e t i c a c i d a n d f o r m a l d e h y d e are the expected ozonolysis p r o d ucts f o r acetone e n o l ( 6 ) , a n d they are o b t a i n e d i n r o u g h l y e q u i m o l e c u l a r ratio.

I n f r a r e d spectra cannot be u s e d to i d e n t i f y t h e m since

peracetic

a c i d i n p r o p a n - 2 - o l absorbs at 1755 c m . " , c o i n c i d i n g w i t h a m i n o r solvent 1

peak, w h i l e f o r m a l d e h y d e m o n o m e r w o u l d p r e s u m a b l y exist as h e m i acetal. a

Peracetic a c i d does not s u r v i v e gas c h r o m a t o g r a p h y at 40 ° C . o n

polypropylene

phase.

oxide/glycerol

condensate

(GPO-50)-glutaric

acid

H o w e v e r , the p e r a c i d titer p a r t i t i o n e d b e t w e e n t r i c h l o r o f l u o r o -


12

OXIDATION

methane

O F ORGANIC

a n d 8 0 % m e t h a n o l i n the same ratio

authentic peracetic acid.

COMPOUNDS

III

( 1 : 3 0 ) at — 7 8 ° C . as

T h u s , i t seems that acetone e n o l m o l o z o n i d e

( V ) , i f a n i n t e r m e d i a t e , m u s t break d o w n even at — 7 8 ° C .

A c e t o n e itself

is n o t a t t a c k e d at a significant rate b y ozone at — 7 8 ° C ,

but adding

h y d r o g e n c h l o r i d e results i n r a p i d reaction, p r e s u m a b l y via t h e e n o l , a n d p e r a c i d is i n fact f o u n d b y t i t r a t i o n . It seems p l a u s i b l e that a n i o n p a i r [II; R =

M e C ( O H ) ] m i g h t give acetone e n o l a n d h y d r o g e n t r i o x i d e , 2

a n d t h e c o r r e s p o n d i n g r a d i c a l p a i r ( I ) m i g h t also, or m i g h t u n d e r g o a r e d o x r e a c t i o n to g i v e t h e i o n p a i r . O n c e f o r m e d , acetone e n o l w o u l d b e


m o r e l i k e l y to react w i t h ozone t h a n to k e t o n i z e . W e therefore

—I 1900

i

I 1800

.

FREQUENCY Figure 1.

I 1700 CM."

.

L_ 1600

1

Infrared spectra of propan-2-ol

solutions

Curve 1: Ozonized at —78°C, warmed to °C. and recooled to —7S°C; triethylamine added Curve 2: Ozonized at —78°C. Curve 3: Ozonized at —78°C, triethylamine added Curve 4: At —78°C. before ozonation Peak at 1900 cm.' caused by propan-2-ol; that at 1760 cm.' caused by propan-2-ol and peracetic acid; that at 1710 cm.' caused by acetone and acetic acid. Triethylamine removes the 1710 cm.' peak of acetic acid. Successive curves are displaced by one unit of optical density 1

1

1

1


charac-

59.

WHITING

ET

Saturated

AL.

13

Compounds

terize R e a c t i o n R as one m a i n side r e a c t i o n i n the case of p r o p a n - 2 - o l , ( a n d i n the cases of c y c l o h e x a n o l a n d c y c l o h e x a n e w h i c h b o t h y i e l d per a c i d to a n extent of ca. 1 0 % of the o v e r - a l l r e a c t i o n ) a n d attribute to it the s m a l l y i e l d s of p e r a c i d ( p e r f o r m i c )

and formaldehyde observed i n

the case of e t h a n o l . I n the o x i d a t i o n of p r o p a n - 2 - o l substantial y i e l d s of h y d r o g e n per oxide are o b t a i n e d . I n v i e w of the r e p o r t e d i n s t a b i l i t y of a n i n t e r m e d i a t e b e l i e v e d to be h y d r o g e n t r i o x i d e (2, 3 ) , it seems u n l i k e l y that the t i t r a t i o n for H 0 2

2

at 20 ° C . a c t u a l l y represents H 0 ; f u r t h e r m o r e 2

3

Reaction

R

p r o d u c e s H 0 , w h o s e fate m u s t n o w be c o n s i d e r e d . F i s s i o n to H O " a n d 2

3

0 H seems p r o b a b l e e v e n at l o w temperatures, a n d i n 2 - p r o p a n o l some Downloaded by CORNELL UNIV on September 6, 2016 | http://pubs.acs.org Publication Date: January 1, 1968 | doi: 10.1021/ba-1968-0077.ch059

2

s u c h sequence as H O - 0 H -> H O ' +

0 H

2

2

H O ' + H • C M e O H -> H 0 + 2

CMe OH +

0 H -» H 0

2

CMe OH

2

2

2

2

• CMe

2

• O H -» Me CO + H 0 2

2

2

seems p l a u s i b l e i n v i e w of the d i f f e r e n t i a l r e a c t i v i t y of H O * a n d H 0 " 2

9, J O ) .

(4,

A t a n y rate, R e a c t i o n S does r a t i o n a l i z e the a p p r e c i a b l e y i e l d of

h y d r o g e n p e r o x i d e f o u n d b y t i t r a t i o n . N o p i n a c o l ( < 2 /xmole/cc.) w a s f o u n d i n the r e a c t i o n p r o d u c t s ; hence, d i m e r i z a t i o n of a - h y d r o x y l i s o p r o p y l is i m p r o b a b l e . T h e p r o d u c t s least easily a c c o u n t e d for i n the o z o n a t i o n of T y p e B p r o p a n - 2 - o l are acetic a c i d a n d m e t h a n o l . M e t h y l acetate c o u l d b e f o r m e d easily: M e C — O H -> M e C — O H -> M e C = O H 2

2

O—0 H

0

2

MeO

+

+ 6H 2

but, as expected,

m e t h y l acetate p r o v e d to b e stable to the

reaction

conditions. T h e r e remains the e n i g m a of T y p e A b e h a v i o r , as m e a s u r e d b y the increase i n H 0 2

2

titer a n d a c i d i t y titer o n w a r m i n g a n d the d i m i n u t i o n i n

o x y g e n e v o l u t i o n . E v e r y s p e c i m e n of p r o p a n - 2 - o l gave some o x y g e n o n o z o n a t i o n a n d w a r m i n g , whereas T y p e B m a t e r i a l consistently f a i l e d to f o r m a n y a d d i t i o n a l a c i d a n d H 0 . W e m u s t therefore leave R e a c t i o n T 2

2

i n a n i n c o m p l e t e state. 2 H O M e C • 0 H -> 2 M e • C 0 H + H 0 2

3

2

2

2

+ 2Y

(T)

X I n t r i c h l o r o f l u o r o m e t h a n e , o x i d a t i o n of tert-butyl m u c h s l o w e r ( f a c t o r

p r e f e r r e d estimate

of 61 ±

2 k c a l . (gas p h a s e ) .

E v e n allowing for

solvation, this s i t u a t i o n s t i l l presents a p r o b l e m o n w h i c h w e are t r y i n g to shed m o r e l i g h t . It is possible that a c o n s i d e r a b l e u p w a r d r e v i s i o n of the rather i n d i r e c t l y c a l c u l a t e d b o n d energy estimate m a y b e justified. Cheves W a l l i n g

commented

o n the h i g h

c h l o r i d e / b r o m i d e ratio

o b t a i n e d f r o m a d a m a n t a n e + O3 + C B r C l s , u n u s u a l i n a r a d i c a l - a b s t r a c t i o n process.

A n even h i g h e r ratio has, h o w e v e r , b e e n r e p o r t e d ( J . I. G .

C a d o g a n , D . H . H e y , a n d P . G . H i b b e r t , /. Chem.

1965,

3939) for

attack b y a w e l l - a u t h e n t i c a t e d free r a d i c a l i n the presence

of o x y g e n ;

Soc.

hence, o u r i n t e r p r e t a t i o n of this r e a c t i o n as p r o c e e d i n g via

1-adamantyl

r a d i c a l s stands.


The Reaction Between Ozone and Saturated Compounds - Advances

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