into Aldehydes by a Lewis Acid in Aprotic Solvent. H.W. G A R D N E R and R.D. PLATTNER, Northern ... decadienoic acid with H2 SO4 in protic solvent.
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Linoleate Hydroperoxides Are Cleaved Heterolytically into Aldehydes by a Lewis Acid in Aprotic Solvent H.W. G A R D N E R and R . D . P L A T T N E R , Northern Research Service, USDA,^ Peoria, IL 61604
Regional
Research
Center,
Agricultural
ABSTRACT
Treatment o f isomeric methyl linoleate hydroperoxides with a Lewis acid, B F 3 , in anhydrous ether led to a carbon-to-oxygen rearrangement that caused cleavage into shorter-chain aldehydes. Methyl ( 9 Z , l l £ ' ) - 1 3 - h y d r o p e r o x y - 9 , l l - o c t a d e c a d i e n o a t e afforded mainly hexanal and methyl {E)-\2oxo-lO-dodecenoate, whereas methyl (1 OF, 12Z)-9-hydroperoxy-10,12-octadecadienoate cleaved into 2-nonenal and methyl 9-oxononanoate. The 2 aldehydes obtained from each hydroperoxide isomer were uncharacteristic of the complex volatile profile usually obtained by ^-scission o f o x y radicals derived from hemolysis of the hydroperoxide group. Rather, the reaction resembled the one catalyzed by the plant enzyme, hydroperoxide lyase. Lipids, 19:289-293, 1984. INTRODUCTION
The acid-catalyzed, carbon-to-oxygen rearrangement o f o r g a n i c h y d r o p e r o x i d e s has b e e n k n o w n f o r over a h a l f c e n t u r y ( 1 , 2 ) . B e cause t h e m i g r a t o r y a p t i t u d e f o r r e a r r a n g e m e n t is greater f o r g r o u p s able t o s u s t a i n a p o s i t i v e charge, a r y l o r v i n y l g r o u p s r e a r r a n g e i n preference t o H o r a l k y l m o i e t i e s ( 1 ) , as i l l u s t r a t e d b y the w e l l - k n o w n rearrangement of cumene h y d r o p e r o x i d e to p h e n o l and acetone.
9-hydroperoxy-10,12-octadecadienoic acid, b o t h 2-nonenal and h e x a n a l were i d e n t i f i e d . B y c o n t r a s t , G a r d n e r et a l . ( 9 ) f o u n d t h a t t r e a t ment of (9Z,1 l £ ' ) - 1 3 - h y d r o p e r o x y - 9 , l l - o c t a decadienoic acid w i t h H2 SO4 i n protic solvent gave m o s t l y i n t r a m o l e c u l a r c y c l i z a t i o n o f t h e
OOH
A p p l i c a t i o n o f t h i s r e a r r a n g e m e n t to f a t t y h y d r o p e r o x i d e s p r e d i c t s a s i m i l a r cleavage i n t o s h o r t e r - c h a i n a l d e h y d e s ( F i g . 1). T h u s , treatm e n t o f a u t o x i d i z e d t r i g l y c e r i d e s o f f a t t y esters w i t h H C l - t r e a t e d earths, e.g., F u l l e r ' s e a r t h , b l e a c h i n g e a r t h or c e l i t e , c a u s e d i n c r e a s e d p r o d u c t i o n o f volatile aldehydes (3-7). K i m o t o a n d Gaddis (7) r e p o r t e d that H C l - t r e a t e d F u l l e r ' s earth d e c o m p o s e d a u t o x i d i z e d t r i l i n o l e i n i n t o a greater y i e l d a n d m o r e s e l e c t i v e d i s t r i b u t i o n o f volatile aldehydes than those obtained f r o m treatment o f the a u t o x i d i z e d t r i l i n o l e i n w i t h a free-radical catalyst. T h e y further s h o w e d that the v o l a t i l e s w e r e m a i n l y h e x a n a l a n d n o n e n a l i n the c o n s p i c u o u s a b s e n c e o f d i e n a l s . T h e s e results m a y be e x p l a i n e d b y a p p l y i n g t h e m e c h a n i s m o f F i g u r e 1 t o a m i x t u r e o f 9- a n d 13-hydroperoxide isomers in the a u t o x i d i z e d t r i l i n o l e i n . M o r e r e c e n t l y , G r o s c h et a l . ( 8 ) treated pure isomers o f either l i n o l e i c acid h y d r o p e r o x i d e or l i n o l e n i c acid h y d r o p e r o x i d e w i t h trichloroacetic acid in benzene. From (9Z,1 l i T ) - ! 3 - h y d r o p e r o x y - 9 , l 1-octadecadienoic a c i d t h e y o b t a i n e d h e x a n a l , a n d f r o m (1OE, 1 2 Z ) ' Presented in part at the American Oil Chemists' Society Meeting, Chicago, Illinois, May 8-12, 1983. ^ The mention of firm names or trade products does not imply that they are endorsed or recommended by the USDA over other firms or similar products not mentioned. LIPIDS, VOL. 19, NO. 4 (1984)
F I G . 1. Predicted mechanism for acid-catalyzed rearrangement o f ( 9 Z , l l £ ' ) - 1 3 - h y d r o p e r o x y - 9 , l l - o c t a decadienoate.
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