Products of Ozonization of Some Olefins RUDOLF CRIEGEE
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Technical University, Institute for Organic Chemistry, Karlsruhe, Germany
The products of the ozonization of 2-butene in acetic acid a n d of 2,3-dimethyl-2-butene in isopropyl alcohol are compared with known substances. The monomeric ozonides of methyl trimethylacrylate a n d of trimethylacrolein are described. Some unsymmetrically disubstituted ethylenes give epoxides instead of ozonides, when ozonized in inert solvents.
Through t h e w o r k of m a n y i n v e s t i g a t o r s i t h a s b e e n s h o w n i n t h e l a s t f e w y e a r s t h a t t h e r e a c t i o n of olefins w i t h ozone t a k e s p l a c e i n t h e f o l l o w i n g w a y :
>c Ν >
o
+
—»
3
z
>c. | > >
>
c
=
0
+
3
c
>C-00"
1. Polymerization 2. Addition of H - X 3. Addition of aldehydes and, under special conditions, also of ketones 4. Rearrangement to esters, lactones, or anhydrides
> c-oo" +
T h e first i n t e r m e d i a t e , w h i c h n e v e r h a s b e e n i s o l a t e d a n d t h e r e f o r e m u s t b e v e r y u n s t a b l e , is c a l l e d t h e Pnmârozonid o r i n i t i a l ozonide (1). N o t h i n g c a n be said w i t h certainty at this moment about its special structure. T h e m o s t i m p o r t a n t i n t e r m e d i a t e seems t o be t h e z w i t t e r i o n w h i c h arises f r o m t h e s p o n t a n e o u s cleavage of t h e i n i t i a l ozonide. F r o m the zwitterion a l l reaction p r o d u c t s w h i c h h a v e been f o u n d f r o m different s t a r t i n g m a t e r i a l s u n d e r different c o n ditions c a n be explained. I n s t e a d of o z o n i z i n g t e t r a m e t h y l e t h y l e n e i n t h e presence of m e t h a n o l , t h e m e t h a n o l as s o l v e n t h a s been r e p l a c e d b y i s o p r o p y l a l c o h o l : CHU >
C H ^
^CH =
(CH î CH.0H 3 2
CH . / > - O - C H 3
n
3
3
Q
H
^
\
Q
(
)
H
^
C H
ChW
3
- A -
3
C
H
^
C H
3
> H - O - C H
/
^
T h e h y d r o p e r o x y e t h e r , f o r m e d as r e a c t i o n p r o d u c t , w a s i d e n t i c a l w i t h t h e first a u t o x i d a t i o n p r o d u c t of d i i s o p r o p y l e t h e r . A f u r t h e r e x a m p l e f o r t h e o z o n i z a t i o n of a n olefin i n t h e presence of a s o l v e n t c o n t a i n i n g a c t i v e h y d r o g e n is t h e o z o n o l y s i s of 2-butene i n acetic a c i d as s o l v e n t . T h e h y d r o p e r o x y ester w a s i s o l a t e d as a p u r e a n d r a t h e r s t a b l e l i q u i d . I t is different f r o m a c r y s t a l l i n e a u t o x i d a t i o n p r o d u c t of a c e t a l d e h y d e ( t h e " p e r o x i d e of L ô s c h " ) w h i c h 133
OZONE CHEMISTRY AND TECHNOLOGY Advances in Chemistry; American Chemical Society: Washington, DC, 1959.
A D V A N C E S IN CHEMISTRY SERIES
134
h a s t h e same e m p i r i c a l f o r m u l a . of a h y d r o p e r o x y ester.
Therefore, this peroxide cannot have the constitution
0 CH —CH=CH-CH 3
CH —CH=0
2
° > 0°
3
+
3
HOAc
CH —CH=0
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^OOH *>
3
CH —CH—OOAc \ OH 3
CH —CH—OAc 3
(peroxide of Losch)
O n e i m p o r t a n t f a c t w h i c h i s c o n s i s t e n t w i t h t h e t h e o r y t h a t olefins a r e b u i l t b y a n a d d i t i o n process i s t h e i m p o s s i b i l i t y o f g e t t i n g m o n o m e r i c ozonides f r o m a l i p h a t i c olefins w i t h f o u r s u b s t i t u e n t s a t t h e d o u b l e b o n d . I n t h i s case t h e o n e cleavage p r o d u c t o f t h e olefin i s a k e t o n e w h i c h , because o f i t s r e l a t i v e l y i n e r t C = 0 d o u b l e b o n d , c a n n o t a d d t o t h e z w i t t e r i o n i n a n i n t e r m o l e c u l a r process. If this inertness of t h e keto group is t h e reason t h a t n o a l i p h a t i c ketozonide could be o b t a i n e d , t h e n i n s u c h cases, w h e r e e s p e c i a l l y h i g h l y r e a c t i v e k e t o n e s w o u l d b e produced, ketozonides should be obtained. V o n B o r n h a u p t (δ) t h e r e f o r e i n v e s t i g a t e d t h e o z o n i z a t i o n o f m e t h y l t r i m e t h y l a c r y l a t e i n p e n t a n e as t h e s o l v e n t a n d f o u n d a m o n g t h e r e a c t i o n p r o d u c t s i n 4 5 % y i e l d t h e m o n o m e r i c ozonide ( b o i l i n g p o i n t 29-30°, melting point —3°) : 0 5
CH
^CH,
CHf
^COOCH
.
CH,^ CH
3
0 0 ^ .CH, ^ c r
3
^COOCH
3
T h e c o n s t i t u t i o n of t h e o z o n i d e w a s p r o v e d b y a n a l y s i s a n d b y r e d u c t i o n t o a c e tone a n d m e t h y l p y r u v a t e . T h e f o r m a t i o n of this n e w ozonide c a n be explained b y CH \ /OCT ^ C . . CH^ 3
the a d d i t i o n of m e t h y l p y r u v a t e t o t h e zwitterion
Indeed, i t is k n o w n
t h a t t h e k e t o g r o u p of p y r u v i c a c i d i s m u c h m o r e r e a c t i v e t h a n t h a t i n s i m p l e k e t o n e s . I n a n o t h e r p a r t o f h i s w o r k v o n B o r n h a u p t (5) s y n t h e s i z e d t h e c o r r e s p o n d i n g a l d e h y d e , t h e t r i m e t h y l a c r o l e i n . A l s o i n t h i s case t h e f o r m a t i o n o f a k e t o z o n i d e seemed possible, because t h e k e t o g r o u p i n m e t h y l g l y o x a l i s v e r y r e a c t i v e : C
H
> \
C
=
C
/
CHf
C
H
C
3
H
3^ /OO^ c
^CH=0
CH,""
c
/
CH
3
^CHO
H o w e v e r , t h e ozonide obtained (boiling p o i n t 3 7 - 9 ° ) was shown b y i t s i n f r a r e d s p e c t r u m t o be identical w i t h t h e ozonide of m e s i t y l oxide. Therefore, t h e m e t h y l g l y o x a l ( w h i c h i n b o t h cases s h o u l d b e t h e one i n t e r m e d i a t e ) a d d s t o t h e z w i t t e r i o n n o t as a k e t o n e b u t as a n a l d e h y d e :
?> H
CH / 3
C
=
C
-CHO
7C=CH-CO-CH,
^
CH^ /CO"
CH
>C°°>
CHO
I
CH ' 3
I f t h e f o r m a t i o n of a n o z o n i d e h a d i n v o l v e d a n i n t r a m o l e c u l a r r e a r r a n g e m e n t i n s t e a d of t h e r e c o m b i n a t i o n o f t w o cleavage p r o d u c t s , t w o different ozonides w o u l d h a v e been p r o d u c e d . T h e s e e x p e r i m e n t s g i v e some f u r t h e r e v i d e n c e a b o u t t h e f o r m a t i o n o f t h e ozonides f r o m t h e i n i t i a l ozonides. C o n c e r n i n g t h e f o r m a t i o n o f t h e i n i t i a l ozonides f r o m t h e olefins a n d ozone, t h e l a t t e r seems t o b e a n e l e c t r o p h i l i c reagent. M e i n w a l d (4) p r o p o s e d t h a t i t reacts i n t h e f o l l o w i n g m a n n e r w i t h t h e p o l a r i z e d o l e f i n :
OZONE CHEMISTRY AND TECHNOLOGY Advances in Chemistry; American Chemical Society: Washington, DC, 1959.
CRIEGEE—OZONATION PRODUCTS O F OLEFINS
135
^0.
.
+
>c=c
•
0
I >c— < c
Usually this first addition product instantaneously gives the initial ozonide b y a nucleophilic attack of the second or third oxygen atom on the carbonium ion. There are some cases i n which the double bond of the unsaturated compound was not cleaved during the ozonation. This is especially true for some unsymmetrical p olefins of the structure
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types
R ^CH—CHO K
and
^X=CH . 2
I n these cases aldehydes or carboxylic acids of the
R ^CH—COOH were found. π
Products which were more closely
related to the original olefins in their structure were the epoxides, found by Bartlett (2) in the case of highly branched aliphatic olefins of this type, and enols, found many years ago b y Fuson (3) with corresponding aromatic olefins. One of the examples of Fuson —namely, the ozonization of 1-phenyl-1-mesitylethylene—was reinvestigated. T h e epoxide (melting point 1 0 1 - 2 ° ) was actually the initial product, just as i n the case of Bartlett :
This compound, under the influence of acids, easily rearranges to the enol of Fuson. T o avoid this rearrangement during the ozonization, some drops of triethylamine were always added. Exactly the same reaction takes place with the unsymmetrical dimesitylethylene (epoxide, melting point 1 0 2 ° ) . Ο — Ο — Ο
In these cases the first intermediate, ^ > ; c
C
H
2 owing to steric hindrance, can
not be transformed to an initial ozonide but instead loses one molecule of oxygen with the formation of an epoxide. Di-p-anisylethylene reacts with ozone to give dianisyl ketone; under very mild conditions dianisylethylene gives an ozonide, which is very unstable at room tem perature, either exploding or decomposing to give the ketone. Therefore the forma tion of epoxides during ozonizations seems to be limited to olefins with strong hindrance at one of the carbon atoms. Diphenylethylene reacts normally under formation of a liquid ozonide. Also mono-p-anisylethylene (p-methoxystyrene) gives only the ozonide (melting point 7 0 - 1 ° ) . It therefore seems that an unsymmetrical olefin with two strong electron-donating groups prefers the formation of an epoxide instead of an ozo nide, though this fact at the moment cannot be explained satisfactorily. In the case of the irans-di-ieri-butylethylene there was formed a crystalline compound which rearranges even at —50° to the ozonide i n a n exothermic reaction. T h e nature of this compound is now being investigated. Literature C i t e d (1) (2) (3) (4) (5)
Bailey, P. S., Chem. Ber. 88, 795 (1955). Bartlett, P. D., Stiles, M., J. Am. Chem. Soc. 77, 2806 (1955). Fuson, R. C., Armstrong, M. D., Wallace, W. E., Kneisley, J. W., Ibid., 66, 1274 (1944). Meinwald, J., Chem. Ber. 88, 1889 (1955). von Bornhaupt, B., unpublished manuscript. RECEIVED for review April 19, 1957. Accepted June 19, 1957.
OZONE CHEMISTRY AND TECHNOLOGY Advances in Chemistry; American Chemical Society: Washington, DC, 1959.
