Structural Relationships in Addition of Ozone to Double Bonds WILLIAM A. MOSHER
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Department of Chemistry, University of Delaware, Newark, Del.
O z o n e is the best reagent for the location of double bonds in organic molecules, because of its ease a n d velocity of addition a n d general freedom from rear rangements and secondary reactions. Some recently prepared compounds, however, show a very reduced rate of addition of ozone in solution. In general, aromatic double bonds a d d ozone at about 1 0 % the rate of isolated double bonds. Anethole can be converted readily to anisaldehyde without a p preciable attack on the aromatic ring system. βPinene is an unusual case. Its double bond should a d d ozone readily, yet it is almost impossible to get any of the expected product by ordinary ozonolysis. Hydrogens alpha to the double bond peroxidize almost as fast as the double b o n d ozonizes. The large excess of oxygen in the stream soon removes the β-pinene from the reaction mixture. Highly branched olefins such as 3,4,5,5-tetramethyl-2-hex ene a n d 3,5,5-trimethyl-2-heptene ozonize readily with 6% ozone in oxygen to give the expected products on hydrolysis; 3,3,6-trimethyl-4-tert-butyl4-heptene, 3,3,5-trimethyl-4-isobutyl-4-hexene, and 2,2,5-trimethyl-3-tert-butyl-3-hexene a d d ozone from a 6% stream at about one tenth the rate of ordi nary olefinic double bonds. The internal location of the double bonds in these molecules and the small probability of the molecules being so coiled as to be c a p a b l e of attack by ozone account for the observations.
O z o n e has been used to determine the location of double bonds since 1855 (S), although the method did not receive widespread acceptance until after the extensive work of Harries (4) and Briner (1). Present knowledge of the structure of unsaturated hydrocarbon polymers and rearrangements leading to olefin systems is entirely depend ent on the elegant degradation possible through the use of ozone. This method will continue to be of wide application, although some new olefins will be described which show greatly reduced reactivity toward ozone. T h e present work compares the reac tivity of ozone with a variety of types of double bonds. 140
In OZONE CHEMISTRY AND TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1959.
141
MOSHER-STRUCTURAL RELATIONSHIPS
W h e n a s t r e a m of o z o n i z e d o x y g e n o r a i r , u s u a l l y u n d e r 6 % ozone, i s p a s s e d t h r o u g h a s o l u t i o n of a n olefin, s u c h as 2 , 4 , 4 - t r i m e t h y l - 2 - p e n t e n e , a b s o r p t i o n o c c u r s as fast as t h e ozone is i n t r o d u c e d a n d n o ozone escapes t h r o u g h t h e s o l u t i o n u n t i l a l l t h e olefin h a s b e e n c o n v e r t e d t o o z o n i d e . I f a n a r o m a t i c h y d r o c a r b o n s u c h as benzene i s o z o n i z e d r a t h e r t h a n a n a l i p h a t i c olefin, a b s o r p t i o n of ozone is n o t c o m p l e t e a n d s e v e r a l t i m e s t h e t h e o r e t i c a l a m o u n t of ozone m u s t be u s e d t o effect c o m p l e t e o z o n i z a tion. W h e n a molecule has b o t h a n aromatic system a n d a n aliphatic double bond, the a l i p h a t i c b o n d m a y react selectively, w i t h little or n o reaction w i t h t h e aromatic s y s t e m . A n e t h o l e w i l l a b s o r b a m o l e of ozone a n d p r o d u c e , o n h y d r o l y s i s of t h e o z o n i d e , a v e r y g o o d y i e l d of anise a l d e h y d e . C o m p l e t e s a t u r a t i o n of t h e m o l e c u l e r e q u i r e s a l m o s t 10 m o l e s of ozone, h o w e v e r .
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T e t r a p h e n y l e t h y l e n e , w h i c h does n o t a d d b r o m i n e , is r e p o r t e d t o g i v e a g o o d y i e l d of b e n z o p h e n o n e o n o z o n a l y s i s (3). O z o n o l y s i s in t h e T e r p e n e
Field
T h e r e a r e some i n t e r e s t i n g e x a m p l e s of selective o z o n o l y s i s i n t h e t e r p e n e field. L i m o n e n e i s o z o n i z e d a t t h e 8 , 9 - d o u b l e b o n d i n preference t o t h e 1- d o u b l e b o n d . T h i s i s i n d i c a t e d b y t h e f a c t t h a t t h e a m o u n t of f o r m a l d e h y d e f o u n d is a l m o s t e q u a l t o t h e a m o u n t of ozone i n t r o d u c e d , u p t o 1 m o l e . I n l i k e m a n n e r , t e r p i n o l e n e y i e l d s acetone i n a n a m o u n t n e a r l y e q u a l t o t h e ozone passed, u p t o 1 m o l e . β-P'mene s h o u l d a d d ozone r e a d i l y a n d f o r m f o r m a l d e h y d e a n d n o p i n o n e o n o z o n o l y s i s . P r a c t i c a l l y none of these p r o d u c t s c a n b e o b t a i n e d b y o r d i n a r y o z o n o l y s i s t e c h n i q u e s . T h e h y d r o g e n s a l p h a to t h e double bond, w i t h probable additional a c t i v a t i o n f r o m the general strain of t h e s y s t e m , a r e so a c t i v e t o p e r o x i d a t i o n b y o x y g e n t h a t l i t t l e o z o n i d e i s f o r m e d , because o f t h e l a r g e excess o f o x y g e n p r e s e n t . T h e r e a p p e a r s t o b e l i t t l e s e l e c t i v i t y w i t h respect t o o r d i n a r y olefins. I f c o m m e r c i a l d i i s o b u t y l e n e , a m i x t u r e of 2 , 4 , 4 - t r i m e t h y l - l - p e n t e n e a n d 2 , 4 , 4 - t r i m e t h y l - 2 - p e n t e n e , is p a r t i a l l y o z o n i z e d , t h e same r a t i o of p r o d u c t s is o b t a i n e d as o n c o m p l e t e o z o n i z a t i o n . Unusual
Rearrangements
T h e a u t h o r h a s b e e n i n t e r e s t e d i n alcohols a n d olefins i n t h e C and C range w i t h c o n s i d e r a b l e b r a n c h i n g , i n t h e s e a r c h f o r u n u s u a l t y p e s of r e a r r a n g e m e n t s . Some c o m p l e x m o l e c u l e s w h i c h s h o w n o r m a l r e a c t i v i t y t o w a r d ozone a r e : 5 - m e t h y l - 5 - d e c e n e (2), 3 , 5 , 5 - t r i m e t h y l - 2 - h e p t e n e (6), 3 , 4 , 5 , 5 - t e t r a m e t h y l - 2 - h e x e n e (6), a n d 4 - i s o p r o p y l - 5 , 5-dimethyl-3-heptene. Olefins t h a t ozonize a b o u t one t e n t h as fast as n o r m a l a r e 3,3,6-trimethyl-4-£er£-butyl-4-heptene, 3 , 3 , 5 - t r i m e t h y l - 4 - i s o b u t y l - 4 - h e x e n e , a n d 2,2,5trimethyl-3-£er£-butyl-3-hexene. C o m p l e t e d e t a i l s of t h e p r e p a r a t i o n of these c o m p o u n d s w i l l b e p u b l i s h e d elsewhere. F o r e x a m p l e , 3,3,6-trimethyl-4-éeri-butyl-4-heptene w a s p r e p a r e d i n a l m o s t q u a n t i t a t i v e y i e l d b y d e h y d r a t i n g 3,3,6-trimethyl-4-£er£-butyl-4h e p t a n o l w i t h 1 - n a p h t h a l e n e s u l f o n i c a c i d . H i g h e r t e m p e r a t u r e s g a v e cleavage. T h e olefin g a v e n o test f o r d o u b l e b o n d r e a d i l y w i t h b r o m i n e a n d i n f r a r e d s p e c t r a were n e g a t i v e f o r d o u b l e b o n d a b s o r p t i o n a t 6 t o 6.2 m i c r o n s , y e t t h e t h e o r e t i c a l a m o u n t of w a t e r w a s o b t a i n e d o n d e h y d r a t i o n . T h e final p r o d u c t s of o z o n o l y s i s c o n f i r m e d t h e s t r u c t u r e b y y i e l d i n g i e r i - a m y l i e r i - b u t y l k e t o n e a n d i s o b u t y r a l d e h y d e . T h e same p r o d u c t s were o b t a i n e d i n s m a l l e r y i e l d w h e n t h e olefin w a s p a r t i a l l y o z o n i z e d , i n d i c a t i n g n o selective o z o n i z a t i o n of c o m p o n e n t s of a m i x t u r e . 1
0
1
5
S t u d i e s i n t h i s field c o n t i n u e w i t h olefins o b t a i n e d f r o m t h e f o l l o w i n g a l c o h o l s : 3,3-dimethyl-4-£er£-butyl-4-octanol, 2,2-dimethyl-3-£er£-butyl-3-heptanol, 3 , 3 - d i m e t h y l 4-isobutyl-4-ocanol, 3,3,6-trimethyl-4-w-propyl-4-hexanol, a n d 3,3,6-trimethyl-4-isopropyl-4-hexanol. Present limited observations indicate that, i n the C to C range, ozonization w i l l be a b n o r m a l i n r a t e i f t h e r e a r e t h r e e g r o u p s w i t h b r a n c h i n g a t t a c h e d t o t h e d o u b l e bond. 1
0
1
5
In OZONE CHEMISTRY AND TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1959.
A D V A N C E S IN CHEMISTRY SERIES
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Acknowledgment The author thanks the Welsbach Co., American Petroleum Institute, a n d Ε. I . d u P o n t de N e m o u r s & C o . f o r s u p p o r t w h i c h m a d e this w o r k possible. T h e compounds were p r e p a r e d b y H a r r y W . W o l f e , J r . Literature
Cited
(1) Briner, E., Demolis, Α., Poullard, H. Helv. Chim. Acta 14, 794 (1931). (2) Church, J. M., Whitmore, F. C., McGrew, R. V., J. Am. Chem. Soc. 56, 176 (1934). (3) Fischer, Hans, Müller, R., Z. physiol. Chem. 148, 175 (1925). (4)
Harries, C., et al., Ann. 390, 2 3 8 ( 1 9 1 2 ) .
(5) Schönbein, J. prakt. Chem. 66, 282 (1855).
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(6) Whitmore, F. C., Mosher, W. Α., J. Am. Chem. Soc. 63, 1120 (1941). RECEIVED for review M a y 17, 1957. Accepted June 19, 1957.
In OZONE CHEMISTRY AND TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1959.
