Oxidation of Organic Compounds

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58 Ozone Chemistry of Organic Compounds ROBERT W. MURRAY

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Bell Telephone Laboratories, Inc., Murray Hill, N. J.

To

the best of my knowledge this is only the third time in just over 10 years that a complete session at a symposium has been devoted to the ozone chemistry of organic compounds. The last occasions were at the Southwest Regional ACS meeting in December 1963, the Septem­ ber 1959 ACS meeting in Atlantic City, N. J., and the International Ozone Conference in Chicago in November 1956. We are concerned here with the ozone chemistry of organic materials only. The larger subject of ozone chemistry and technology is far beyond the capacity of a single session, even straining the bounds of a whole symposium, as was seen at the Chicago meeting. In fact, we shall not even be able to cover all areas of current interest in the limited area of organic ozone chemistry, although we have a fairly representative sample of those interests. Interest in ozone chemistry has been stimulated by two sources where the practical consequences of this field are of some importance— namely, the space program and the air pollution problem. It seems safe to predict that both areas will continue to be interested in the results of research on the reactions of ozone with both organic and inorganic materials. More recently it has become apparent that ozone will play an increasingly important role in industrial chemistry, owing to the lower cost a n d greater efficiency of i n d u s t r i a l o z o n e generators. I n 1956, at t h e t i m e of t h e I n t e r n a t i o n a l O z o n e C h e m i s t r y C o n f e r e n c e , less t h a n a m i l l i o n p o u n d s of ozone w e r e u s e d i n i n d u s t r i a l c h e m i s t r y . I n 1967 i t is e x p e c t e d that

24 m i l l i o n

pounds

will

be

used

b y U.S. chemical

and drug

manufacturers. T h e areas of c u r r e n t interest i n o r g a n i c o z o n e c h e m i s t r y f a l l r o u g h l y into five b r o a d categories. T h e first m i g h t b e c a l l e d the c l a s s i c a l use of ozone—i.e., either as a synthetic t o o l to c o n v e r t u n s a t u r a t i o n into c a r b o n y l f u n c t i o n s o r as a v a l u a b l e reagent f o r l o c a t i n g d o u b l e b o n d s i n structure determinations.

B o t h t e c h n i q u e s are s t i l l u s e d w i d e l y b y chemists, a n d

reports of s u c h w o r k p r o b a b l y a c c o u n t f o r m o r e t h a n one-half of a l l the papers i n this

field.

T h i s use of ozone has b y - p r o d u c t s f o r t h e c h e m i s t

w h o is m o r e interested i n m e c h a n i s m — i . e . , p r o d u c t s are o b t a i n e d o c c a 1 In Oxidation of Organic Compounds; Mayo, F.; Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

2

OXIDATION

OF

ORGANIC

COMPOUNDS

III

s i o n a l l y w h i c h are a t t r i b u t e d to anomalous ozonolysis a n d w i t h w h i c h the m e c h a n i s m chemist w i l l h a v e to d e a l . T h e second general area of research

is that c o n c e r n e d w i t h

the

m e c h a n i s m of ozonolysis—i.e., that p a r t i c u l a r ozone r e a c t i o n w h i c h leads to cleavage of a d o u b l e b o n d . T h e s e efforts have h a d the benefit of a u n i f y i n g m e c h a n i s m p r o p o s e d i n the early 1950's b y Prof. C r i e g e e i n Germany.

R e c e n t w o r k i n this area has b e e n d i r e c t e d at d e t e r m i n i n g

the influence of several r e a c t i o n variables o n the ozonolysis

process,

i n c l u d i n g olefin g e o m e t r y steric factors, a n d solvent effects. Some of the

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results suggest that m o d i f i c a t i o n s of the basic m e c h a n i s m scheme m a y b e required.

T h i s area w i l l u n d o u b t e d l y c o n t i n u e to receive

attention.

T h i s category also i n c l u d e s efforts d i r e c t e d at d e f i n i n g the

considerable

stabilities a n d structures of intermediates, rate studies, a n d substituent effects o n the rate a n d m e c h a n i s m .

T w o papers i n this section f a l l into

the category of the m e c h a n i s m of ozonolysis. T h e r e a c t i o n of ozone w i t h saturated h y d r o c a r b o n s has b e e n a sub­ ject of r e n e w e d interest i n recent years.

T w o papers i n this section are

c o n c e r n e d w i t h this subject, w h i l e a t h i r d deals w i t h the analogous reac­ t i o n of o r g a n o s i l i c o n c o m p o u n d s . T h e s e studies are of b o t h synthetic a n d m e c h a n i s t i c i m p o r t a n c e a n d are p e r h a p s most closely associated w i t h the general theme of this s y m p o s i u m since t h e y i n e v i t a b l y i n v o l v e the ques­ t i o n of their r e l a t i o n s h i p to a u t o x i d a t i o n processes.

T h e q u e s t i o n of the

m e c h a n i s m of these saturated h y d r o c a r b o n - o z o n e reactions is presently an active subject w i t h i o n i c , free r a d i c a l , a n d i n s e r t i o n processes a l l b e i n g considered. T h e reactions of ozone w i t h n o n - h y d r o c a r b o n s constitutes a f o u r t h category for discussion. I n c l u d e d are the reactions of ozone w i t h heterocycles, amines, a l d e h y d e s , alcohols, a n d others. T w o papers i n this section d e a l w i t h this subject. S p e c i f i c a l l y , the reactions of amines a n d alcohols are r e p o r t e d . Suggestions for the m e c h a n i s m s of these reactions are also m a d e , a n d a g a i n , these proposals s h o u l d be of s p e c i a l interest to those i n v o l v e d w i t h s i m i l a r reactions of oxygen. T h e last general c a t e g o r y — n a m e l y , the reaction of ozone w i t h aro­ m a t i c h y d r o c a r b o n s , has r e c e i v e d a n enormous a m o u n t of attention b y ozone chemists.

M o s t of this attention has c o n c e r n e d rate a n d r e a c t i v i t y

studies i n a n attempt

to correlate

these e x p e r i m e n t a l quantities

some k n o w n parameters of the h y d r o c a r b o n s .

with

S e v e r a l r e a c t i v i t y corre­

lations h a v e b e e n p r o p o s e d , i n c l u d i n g those w i t h b o n d l o c a l i z a t i o n energy, a t o m l o c a l i z a t i o n energies, a n d o x i d a t i o n - r e d u c t i o n potentials. T h i s cate­ g o r y is also represented b y a p a p e r i n this section, i n w h i c h a possible c o r r e l a t i o n b e t w e e n ozone r e a c t i v i t y a n d c a r c i n o g e n i c i t y of some p o l y c y c l i c a r o m a t i c c o m p o u n d s is e x p l o r e d .

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

58.

MURRAY

Ozone

Chemistry

3

I n s u m m a r y , o r g a n i c ozone c h e m i s t r y is a n active research area a n d w i l l c o n t i n u e to see n e w d e v e l o p m e n t s b o t h f r o m t h e o r e t i c a l a n d i n d u s ­ t r i a l v i e w p o i n t s . I n p a r t i c u l a r , w e shall l i k e l y see the r e l a t i o n s h i p b e t w e e n ozone chemistry, a u t o x i d a t i o n , p h o t o - o x i d a t i o n , a n d singlet o x y g e n c h e m ­ istry m o r e c l e a r l y defined, w i t h a n o t e w o r t h y c o n t r i b u t i o n b e i n g m a d e at this s y m p o s i u m . October

18, 1967.

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RECEIVED

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