Improved Synthesis of Aromatic Aldehydes from Ozonolysis of Olefins

Improved Synthesis of Aromatic Aldehydes from Ozonolysis of Olefins LEE A. SUBLUSKEY and G. C. HARRIS Research Center, Hercules Powder Co., Wilmington,

Del.

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ALLISON M A G G I O L O and A N T H O N Y L. TUMOLO Ozone Processes Division, Welsbach

Corp., Philadelphit, Pa.

Improved yields of aromatic aldehydes have been obtained from the ozonolysis of aromatic substituted olefins by employing a rapid steam distillation of the freshly ozonized olefins. This observation supports a mechanism for ozonolysis which involves a primary ozonide trioxolane structure.

T h e r e a c t i o n of ozone w i t h olefins u s u a l l y r e s u l t s i n cleavage of t h e d o u b l e b o n d a n d t h e f o r m a t i o n of a l d e h y d e s , ketones, a n d / o r c a r b o x y l i c a c i d s , d e p e n d i n g u p o n t h e r e a c ­ t i o n c o n d i t i o n s a n d t h e s t r u c t u r e s i n v o l v e d . F o r a l d e h y d e s , t h e i n t e r m e d i a t e ozonides are o r d i n a r i l y t r e a t e d w i t h a m i l d r e d u c i n g a g e n t — f o r e x a m p l e , h y d r o g e n o r z i n c — o r s u b j e c t e d t o n e u t r a l h y d r o l y s i s . Y i e l d s i n excess of 7 0 % a r e e x c e p t i o n a l f o r t h e r e d u c ­ t i o n m e t h o d s , w h i l e h y d r o l y s i s gives c o n s i d e r a b l y l o w e r y i e l d s . T h i s w o r k describes a s i m p l e m e t h o d w h i c h n o t o n l y e l i m i n a t e s t h e r e d u c t i o n o r h y d r o l y s i s s t e p b u t gives a l d e h y d e y i e l d s t h a t a r e u s u a l l y 86 t o 9 0 % o r b e t t e r . T h e m e t h o d i n i t s p r e s e n t s t a t e of d e v e l o p m e n t seems t o b e l i m i t e d , h o w e v e r , t o t h e p r o d u c ­ t i o n of a r o m a t i c a l d e h y d e s . T h e m e t h o d consists m e r e l y of a r a p i d s t e a m d i s t i l l a t i o n of a f r e s h l y o z o n i z e d olefin. T a b l e I lists a n u m b e r of olefins t o w h i c h t h e m e t h o d h a s b e e n a p p l i e d , w i t h the products a n d the yields t h a t have been obtained. Table I.

Compounds O z o n i z e d and Steam Distilled

Compounds Stilbene 3,5-Dimethoxystilbene „ _., , .„ 3,5-Dihydroxystilbene „ _ .„ «5,5-Diacetoxystilbene 0

btyrene Anethole Isosafrole Estragole 1-Dodecene α b

Aldehyde Products Benzaldehyde Benzaldehyde 3,5-Dimethoxybenzaldehyde Benzaldehyde 3,5-Dihydroxybenzaldehyde Benzaldehyde 3,5-Diacetoxybenzaldehvde Benzaldehyde Anisaldehyde Piperonal p-Methoxyphenylacetaldehyde ...

Yield, % 93» 87 89 86 50 88 94 87 92 87 37 Trace b

Based on 2 moles of benzaldehyde from 1 mole of stilbene. Isolated as thiosemicarbazone from steam distillation pot residue.

I n a l l i n s t a n c e s t h e p r o d u c t s were i s o l a t e d a n d i d e n t i f i e d e x c e p t f o r t h e 1-dodecene e x p e r i m e n t , w h e r e o n l y t r a c e a m o u n t s of w a t e r - i n s o l u b l e a l d e h y d e f u n c t i o n a l i t y w e r e 149

In OZONE CHEMISTRY AND TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1959.

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A D V A N C E S IN CHEMISTRY SERIES

detected. C h a r a c t e r i z a t i o n of t h e s t e a m d i s t i l l a t e a n d p o t residues f r o m t h e o z o n o l y s i s of 1-dodecene i n d i c a t e d t h e presence of w a t e r - i n s o l u b l e c a r b o x y l i c a c i d s ( 1 5 m o l e % ) , w a t e r - i n s o l u b l e a c t i v e o x y g e n c o m p o u n d s (28 m o l e % ) , a n d esters. C h a r a c t e r i z a t i o n of p r o d u c t s f r o m estragole i n d i c a t e d t h e presence of esters a n d w a t e r - i n s o l u b l e a c t i v e oxygen compounds (10 mole % ) . T h e h i g h yields of aromatic aldehydes t h a t are produced b y this m e t h o d c a n be e x p l a i n e d b y , a n d i n d e e d s u p p o r t , C r i e g e e ' s (3) p r o p o s e d m e c h a n i s m f o r o z o n o l y s i s i f t h e e q u i l i b r i a i n v o l v e d a n d r e l a t i v e rates of side r e a c t i o n s a r e c o n s i d e r e d . I n t e r m s of a p r i m a r y ozonide trioxolane structure, I I , w h i c h recently has been argued b y M e i n w a l d ( 7 ) , C r i e g e e (4), a n d M a g g i o l o (6") as t h e m o s t p r o b a b l e i n i t i a l i n t e r m e d i a t e i n t h e o z o n o l y s i s of d o u b l e b o n d s , cleavage r e s u l t s i n t h e f o r m a t i o n of a l d e h y d e a n d t h e z w i t t e r i o n , I I I , w h i c h , i n t h e presence of a p o l a r s o l v e n t ( m e t h a n o l ) , f o r m s t h e h y d r o ­ p e r o x i d e , V . H y d r o l y s i s of V b y s t e a m r e n d e r s t h e a l d e h y d e , V I I . R a p i d r e m o v a l of aldehydes b y steam distillation drives the e q u i l i b r i u m f r o m V to V I I a n d prevents the loss o f cleavage m a t e r i a l t o t h e i r r e v e r s i b l e h e t e r o l y t i c r e a r r a n g e m e n t of V t o V I I I . Ri

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T o s a t i s f y t h e y i e l d s of a r o m a t i c a l d e h y d e s o b t a i n e d ( T a b l e I ) , rates ^ a n d k m u s t b e c o n s i d e r a b l y g r e a t e r t h a n t h e h e t e r o l y s i s r a t e , k . T h i s seems reasonable because e q u i l i b r a t i o n of V a n d V I I w h e n a l d e h y d e is r e m o v e d s h o u l d o c c u r r e a d i l y i n t h e a r o m a t i c series w h e r e R c a n offer s u b s t a n t i a l resonance s t a b i l i z a t i o n t o t h e t r a n s i ­ t i o n s t a t e , V I , b y e n h a n c i n g t h e c a t i o n i c c h a r a c t e r of t h e c a r b o n y l c a r b o n . I n B r i n e r ' s e a r l y w o r k {1, 2) o n t h e h y d r o l y s i s of s t i l b e n e a n d isoeugenol ozonides, a d ­ v a n t a g e w a s n o t t a k e n of these e q u i l i b r i a a n d r a t e differences. A s a consequence a l ­ m o s t h a l f of t h e f i n a l cleavage p r o d u c t s a f t e r extensive h y d r o l y t i c t r e a t m e n t w i t h o u t aldehyde r e m o v a l were carboxylic acids, I X . F a i l u r e of a l i p h a t i c a l d e h y d e s t o be p r o d u c e d i n h i g h y i e l d s b y a p p l i c a t i o n of t h i s s t e a m d i s t i l l a t i o n m e t h o d t o estragole a n d 1-dodecene m a y b e a t t r i b u t e d t o t h e i n c r e a s e d s t a b i l i t y of t h e i n t e r m e d i a t e h y d r o p e r o x i d e s t o w a r d h y d r o l y s i s . I n o t h e r w o r d s , t h e c o n v e r s i o n rates of t h e c o r r e s p o n d i n g i n t e r m e d i a t e s , V t o V I t o V I I , a r e so slow t h a t t h e hydroperoxides are either steam distilled a n d / o r undergo t h e relatively more r a p i d oxidative rearrangement t o V I I I a n d subsequent conversion t o I X . S u p p o r t i n g these a r g u m e n t s b y a n a l o g y is t h e recent w o r k of K r e e v o y a n d T a f t ( 5 ) , i n w h i c h a r o m a t i c acetals were f o u n d t o h y d r o l y z e some 4 0 t o 8 0 0 t i m e s faster t h a n a l i p h a t i c acetals. T h e l o w a l d e h y d e y i e l d f r o m t h e h y d r o x y - s u b s t i t u t e d p o r t i o n of 3 , 5 - d i h y d r o x y s t i l b e n e ( T a b l e I ) c a n b e a t t r i b u t e d t o t h e i n a b i l i t y of t h e h y d r o x y a l d e h y d e t o s t e a m 2

3

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In OZONE CHEMISTRY AND TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1959.

SUBLUSKEY, HARRIS, M A G G I O L O , A N D TUMOLO-SYNTHESIS OF ALDEHYDES

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d i s t i l l a n d c o n s e q u e n t loss t o h e t e r o l y t i c r e a r r a n g e m e n t s , p a r t t o c a r b o x y l i c a c i d s a n d p a r t t o r e s i n i f i c a t i o n . T h e l a t t e r m a y h a v e b e e n c a u s e d t o a c o n s i d e r a b l e degree b y a D a k i n - t y p e rearrangement. C l e a r l y i n t h e case o f t h e s t i l b e n e s , i f t h e a b o v e p r o p o s a l m e c h a n i s m s a r e c o r r e c t , h a l f of t h e a l d e h y d e s p r o d u c e d m u s t h a v e r e s u l t e d f r o m t h e h y d r o l y s i s of h y d r o ­ p e r o x i d e i n t e r m e d i a t e s . W i t h t h e u n s y m m e t r i c a l olefins, s t y r e n e , a n e t h o l e , isosafrole, estragole, a n d 1-dodecene, t h i s m a y n o t be t h e case. I f cleavage of t h e p r i m a r y o z o n i d e i s u n i m o l e c u l a r , t h e n t h e i n d u c t i v e a n d resonance c o n t r i b u t i o n s o f s u b s t i t u e n t s R and R X s h o u l d d e t e r m i n e t h e d i r e c t i o n of c l e a v a g e . T h u s , i f R i is more capa­ x

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ble t h a n R of s t a b i l i z i n g t h e d e v e l o p m e n t of a p o s i t i v e c h a r g e o n t h e a d j a c e n t c a r b o n a t o m , t h e p r e f e r r e d cleavage w i l l b e as w r i t t e n . I n v i e w of these c o n s i d e r a t i o n s , i t is n o t possible t o decide w h e t h e r a l l o r p a r t of t h e a l d e h y d e s o b t a i n e d f r o m t h e u n ­ s y m m e t r i c a l olefins r e s u l t e d f r o m h y d r o l y s i s of a n i n t e r m e d i a t e h y d r o p e r o x i d e o r d i r e c t l y f r o m cleavage. T h e f a c t t h a t l a r g e p o r t i o n s of t h e p r o d u c t s f r o m estragole a n d 1-dodecene w e r e n o t a l d e h y d e s , h o w e v e r , s t i l l i n d i c a t e s t h a t t h e i r r e s p e c t i v e i n t e r ­ m e d i a t e h y d r o p e r o x i d e s d i d n o t p r e f e r h y d r o l y s i s , a n d r e m a i n e d as s u c h , u n d e r ­ w e n t r e a r r a n g e m e n t , o r were l o s t t o o t h e r b y - p r o d u c t f o r m a t i o n s . 2

T h e r e a l i z a t i o n t h a t h i g h y i e l d s c a n be o b t a i n e d u n d e r t h e d r i v i n g c o n d i t i o n s of t h e s t e a m d i s t i l l a t i o n s d e s c r i b e d i n t h i s p a p e r suggests t h a t o t h e r a n d e q u a l l y s i m p l e methods f o r aldehyde r e m o v a l m a y achieve t h e same h i g h yields. R e s e a r c h i n this direction could prove rewarding, p a r t i c u l a r l y where the aldehyde products are not steam distillable or where the ozonolysis intermediates m a y require special conditions for their conversion to aldehydes. E v e n more intriguing for future research, however, is t h e v e r i f i c a t i o n o r d i s p r o o f of t h e m e c h a n i s m s p r o p o s e d h e r e . Experimental T h e f o l l o w i n g o z o n i z a t i o n a n d s t e a m d i s t i l l a t i o n cleavage i s t y p i c a l of t h e p r o ­ cedures e m p l o y e d . S e v e n t y - t w o g r a m s (0.30 m o l e ) of 3 , 5 - d i m e t h o x y s t i l b e n e w e r e d i s s o l v e d i n a s o l u ­ t i o n c o n s i s t i n g of 600 cc. of m e t h y l e n e c h l o r i d e a n d 4 0 0 c c . of m e t h a n o l , t h e n c o o l e d t o d r y ice-acetone temperatures. W h i l e the reaction solution was being stirred, a 5.6% ozone i n o x y g e n s t r e a m w a s b u b b l e d t h r o u g h u n t i l a p p r o x i m a t e l y 14 g r a m s (0.30 m o l e ) of ozone h a d been a b s o r b e d . I m m e d i a t e l y f o l l o w i n g t h e a d d i t i o n of t h e ozone, t h e c o l d r e a c t i o n s o l u t i o n w a s s u b j e c t e d t o a r a p i d s t e a m d i s t i l l a t i o n . F o u r c u t s of s t e a m d i s t i l ­ l a t e w e r e m a d e , e a c h a m o u n t i n g t o a p p r o x i m a t e l y 1.8 l i t e r s . D u r i n g d i s t i l l a t i o n of t h e f o u r t h c u t a crystalline solid, w h i c h later p r o v e d t o be 3,5-dimethoxybenzaldehyde, f o r m e d i n t h e condenser a n d t h e a q u e o u s d i s t i l l a t e . E a c h of these c u t s w a s e x t r a c t e d w i t h e t h e r , a n d t h e e t h e r e x t r a c t s were t h e n d r i e d w i t h a n h y d r o u s s o d i u m s u l f a t e . E v a p o r a t i o n of t h e r e s p e c t i v e e t h e r e x t r a c t s y i e l d e d t h e f o l l o w i n g p r o d u c t s : Analysis by Ultraviolet Absorption, % Cut No. 1 2 3 4

Weight, Grams 30.3 31.8 7.6 8.1

Benzaldehyde 74 14 10 12

3,5-Dimethoxybenzaldehyde 24 84 85 87

T h e s e c u t s w e r e c o m b i n e d a n d t h e n d i s t i l l e d t h r o u g h a s h o r t c o l u m n t o g i v e 27.3 g r a m s o f b e n z a l d e h y d e , b o i l i n g p o i n t , 4 9 - 5 3 ° C . ( 2 m m . ) a n d 44.5 g r a m s of 3 , 5 -

In OZONE CHEMISTRY AND TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1959.

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dimethoxybenzaldehyde, boiling point 121-5° C . (2 m m . ) . Based on the original 72 grams of 3,5-dimethoxystilbene this represents an 8 7 % yield of benzaldehyde and an 8 9 % yield of 3,5-dimethoxybenzaldehyde. O n standing, the 3,5-dimethoxybenzaldehyde cut solidified, melting point, 4 4 - 6 ° C . Recrystallization from hexane raised the melting point to 4 6 - 7 ° C . (literature melting point, 4 5 - 6 ° C ) . A mixture melting point with a highly purified, authentic sample of 3,5-dimethoxybenzaldehyde exhibited no depres­ sion.

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In some instances 100 to 200 cc. of water were added to the freshly ozonized reaction mixture before steam distillation. This in no way affected the yields, provided that steam distillation immediately followed the addition of the water. When experi­ ments with ozonized 3,5-dimethoxystilbene were allowed to stand with or without water overnight before steam distilling, however, the yields of aldehyde were reduced to 51 to 5 9 % . Literature C i t e d (1) (2) (3) (4) (5) (6) (7)

Briner, E., Aguadisch, L., Helv. Chim. Acta 32, 1505 (1949). Briner, E., de Nemitz, S., Ibid., 27, 748 (1938). Criegee, R., Advances in Chem. Ser., N o . 21, 133 (1958). Criegee, R., Ann. 585, 1 (1953). Kreevoy, M. M., Taft, R. W., Jr., J. Am. Chem. Soc. 77, 5590 (1955). Maggiolo, Α., ACS lecture, Oct. 9, 1956, Trenton, N. J., and private communication. Meinwald, J., Chem. Ber. 88, 1889 (1955).

RECEIVED for review M a y 17, 1957. on reactions of ozone.

Accepted June 19, 1957.

Number III in a series

In OZONE CHEMISTRY AND TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1959.