[ACS Symposium Series] Phosphorus Chemistry Volume 171 (Proceedings of the 1981 International...
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105 New Data on the Mechanism of the Perkow- Arbuzov Reaction L Á SZL ÓΤ Ő ΚΕ, IMRE PETNEHÁZY, and GYŐNGYI SZAK Á L — Department of Organic Chemical Technology, Technical University Budapest, 1521 Budapest, M ű egyetem, Hungary HARRY R. HUDSON and LUBA POWROZNYK — Department of Chemistry, The Polytechnic of North London, Holloway Road, London, N7 8DB, England CHRISTOPHER J. COOKSEY — Department of Chemistry, University College London, 20 Gordon Street, London WC1H ΟAJ, England In spite of many previous studies on the mecha- nisms by which trialkyl phosphites interact with α- halogenocarbonyl compounds, the reactive intermediates which lead to ketophosphonate (Arbuzov reaction) and to vinyl phosphate (Perkow reaction) have in no cases been clearly identified. It is generally believed (1), however, that the Arbuzov product 4 results from initial attack by phosphorus at the α-carbon atom, whereas the Perkow product 7 is formed by initial attack at the carbonyl carbon atom, followed by migra- tion of phosphorus from carbon to oxygen (Scheme 1). Scheme 1 Recent kinetic studies, however, provide strong evidence for the involvement of a common first inter- mediate (2). We have now carried out crossover experiments in which the reaction of trimethyl phosphite with a mix- ture of differently substituted chloro- and bromoace- tophenones (e.g. C6H5COCH2Cl and p-MeC6H4COCH2Br) af- fords a mixture of products whose composition shows that halogen exchange has occurred. In other words, the ratio of Perkow to Arbuzov products is that which would be expected if C 6 H 5 COCH 2 Br and p-MeC^H^OCH^l were also present in tne reaction mixture ^5 mol% in benzene, 8 mol% in chlorobenzene, 23 mol% in aceto- nitrile). 0097-615 6/8 1 /0 1 7 1-0513 $05 .00/0 © 1981 American Chemical Society Downloaded by UCSF LIB CKM RSCS MGMT on November 23, 2014 | http://pubs.acs.org Publication Date: November 11, 1981 | doi: 10.1021/bk-1981-0171.ch105 In Phosphorus Chemistry; Quin, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
Transcript of [ACS Symposium Series] Phosphorus Chemistry Volume 171 (Proceedings of the 1981 International...
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105 New Data on the Mechanism of the Perkow-Arbuzov Reaction L Á S Z L Ó ΤŐΚΕ, IMRE PETNEHÁZY, and GYŐNGYI SZAKÁL — Department of Organic Chemical Technology, Technical University Budapest, 1521 Budapest, Műegyetem, Hungary HARRY R. HUDSON and LUBA POWROZNYK — Department of Chemistry, The Polytechnic of North London, Holloway Road, London, N7 8DB, England CHRISTOPHER J. COOKSEY — Department of Chemistry, University College London, 20 Gordon Street, London WC1H ΟAJ, England
In spite of many previous studies on the mechanisms by which trialkyl phosphites interact with α -halogenocarbonyl compounds, the reactive intermediates which lead to ketophosphonate (Arbuzov reaction) and to vinyl phosphate (Perkow reaction) have in no cases been clearly identif ied. It is generally believed (1), however, that the Arbuzov product 4 results from initial attack by phosphorus at the α-carbon atom, whereas the Perkow product 7 is formed by initial attack at the carbonyl carbon atom, followed by migration of phosphorus from carbon to oxygen (Scheme 1).
Scheme 1
Recent kinetic studies, however, provide strong evidence for the involvement of a common f irs t intermediate (2).
We have now carried out crossover experiments in which the reaction of trimethyl phosphite with a mixture of differently substituted chloro- and bromoace-tophenones (e.g. C6H5COCH2Cl and p-MeC6H4COCH2Br) affords a mixture of products whose composition shows that halogen exchange has occurred. In other words, the ratio of Perkow to Arbuzov products is that which would be expected if C6H5COCH2Br and p-MeC^H^OCH^l were also present in tne reaction mixture 5̂ mol% in benzene, 8 mol% in chlorobenzene, 23 mol% in aceto-n i t r i l e ) .
0097-615 6/81/0171-0513$05.00/0 © 1981 American Chemical Society
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514 P H O S P H O R U S C H E M I S T R Y
As d i r e c t h a l o g e n e x c h a n g e between t h e k e t o n e s was e x c l u d e d by s e p a r a t e e x p e r i m e n t s t h e r e s u l t s a r e b e s t e x p l a i n e d by a s s u m i n g t h a t an i o n i c e x c h a n g e r e a c t i o n o c c u r s , i n v o l v i n g h a l i d e i o n f r o m a q u a s i p h o s -p h o n i u m i n t e r m e d i a t e (Scheme 2 ) .
Scheme 2
C . H c C 0 C H o B r + C l ~ C r H c C 0 C H o C l + B r " Ό Ο Ζ χ D b Ζ
C o n f i r m a t i o n o f t h i s e f f e c t was o b t a i n e d by c a r r y i n g o u t e x p e r i m e n t s i n t h e p r e s e n c e o f a d d e d n u c l e o p h i l e s ( i n t h e f o r m o f t r i e t h y l b e n z y l a m m o n i u m c h l o r i d e , o r t e t r ab u t y 1 ammonium b r o m i d e ) w h i c h m o d i f i e d b o t h t h e p r o d u c t r a t i o a n d t h e o v e r a l l r e a c t i o n r a t e .
T o o b t a i n more i n f o r m a t i o n on t h e n a t u r e o f t h e q u a s i p h o s p h o n i u m i n t e r m e d i a t e s i n v o l v e d i n t h e s e s y s tems we have s t u d i e d t h e r e a c t i o n s o f s t e r i c a l l y h i n d e r e d n e o p e n t y l e s t e r s by means o f Ρ nmr s p e c t r o s c o p y . T r i n e o p e n t y l p h o s p h i t e and α - b r o m o a c e t o p h e n o n e gave r i s e t o a peak a t +41 ppm due t o t h e k e t o p h o s p h o n i u m i n t e r m e d i a t e 3 (R = M e ~ C C H 2 ; R' = P h ; X = B r ) w i t h i n h a l f a n . h o u r o f m i x i n g t h e r e a c t a n t s i n a c e t o n e - d f i a t 27 C ( Ρ nmr s h i f t s a r e r e l a t i v e t o 85% H - P O , d ô w n -f i e l d p o s i t i v e ) . Peaks due t o t h e k e t o p h o s p n o n a t e 4
+19 ppm a n d t h e v i n y l p h o s p h a t e 7 ( - 7 ppm) were a l s o o b s e r v e d (compound 4 and 7 have s a t i s f a c t o r y e l e m e n t a l a n a l y s i s a n d s p e c t r o s c o p i c d a t a ). The c o n c e n t r a t i o n o f t h e i n t e r m e d i a t e r e a c h e d a maximum a f t e r a b o u t two h o u r s when i t was p r e c i p i t a t e d f r o m a c e t o n e s o l u t i o n by t h e a d d i t i o n o f a n h y d r o u s e t h e r t o g i v e w h i t e c r y s t a l s o f t r i n e o p e n t y l o x y ( p h e n a c y 1 ) p h o s p h o n i u m b r o m i d e , i d e n t i f i e d by e l e m e n t a l a n a l y s i s a n d nmr s p e c t r o s c o p y ( Ρ 6+41, i n C D C 1 ~ ) . When r e d i s s o l v e d i n a c e t o n e - d ^ , d e u t e r o c h l o r o f o r m , a c e t i c a c i d , o r a c e t i c a c i d - a c e t o n e m i x t u r e s , t h e i n t e r m e d i a t e decomposed t o y i e l d k e t o -p h o s p h o n a t e 4 b u t none o f t h e v i n y l p h o s p h a t e 6 (Perkow p r o d u c t ) . N o r was t h e c o u r s e o f r e a c t i o n a f f e c t e d by t h e a d d i t i o n o f c h l o r i d e i o n o r o f α - c h l o r o -a c e t o p h e n o n e i n a c e t o n i t r i l e .
A p r o p o s a l ( _3 ) t h a t v i n y l p h o s p h a t e m i g h t be f o r med f r o m t h e k e t o p h o s p h o n i u m i n t e r m e d i a t e , a f t e r r e a r r a n g e m e n t v i a a f o u r - m e m b e r e d c y c l i c p h o s p h o r a n e 8 i s t h e r e f o r e e x c l u d e d by o u r r e s u l t s u n d e r t h e s e r e a c t i o n c o n d i t i o n s .
(RO ) Ρ — Ç H ?
ι I, ο — c ( i ) — R ' 8
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105. T Ô K E E T A L . Mechanism of the Perkow-Arbuzov Reaction 515
We a l s o f o u n d t h a t t h e v i n y l p h o s p h a t e was t h e m a j o r r e a c t i o n p r o d u c t i n t h e i n i t i a l s t a g e s o f t h e r e a c t i o n o f t r i n e o p e n t y l p h o s p h i t e w i t h α-bromoaceto-p h e n o n e i n a c e t o n e - d f i , b u t t h a t t h e p r o d u c t r a t i o c h a n g e d i n f a v o u r o f t h e k e t o p h o s p h o n a t e a s t h e r e a c t i o n p r o c e e d e d . T he r e s u l t s a r e c o n s i s t e n t w i t h a r e a c t i o n s c h e me i n w h i c h t h e k e t o p h o s p h o n i u m a n d v i n y l -o x y p h o s p h o n i u m i n t e r m e d i a t e s a r e f o r m e d b y p a r a l l e l p a t h w a y s , e i t h e r d i r e c t l y f r o m t h e r e a c t a n t s , o f f r o m a common f i r s t i n t e r m e d i a t e X a n d i n t h e l i g h t o f o u r p r e v i o u s k i n e t i c s t u d i e s (2) t h e l a t t e r i s i n d i c a t e d ( S c h e m e 3 ) .
Scheme 3 3 r 4
1 + 2 > X 6 * 7
I t i s c l e a r a l s o t h a t t h e v i n y l o x y p h o s p h o n i u m i n t e r m e d i a t e 6 i s much l e s s s t a b l e t h a n t h e k e t o p h o s p h o n i u m i n t e r m e d i a t e 3, a l t h o u g h t h i s d i f f e r e n c e may o n l y b e a p p a r e n t w h en t h e a l k o x y g r o u p (R ) i s s t e r i c a l l y h i n d e r e d a s i n t h e c a s e o f n e o p e n t y l .
I n t e r m e d i a t e s d e r i v e d f r o m d i n e o p e n t y l p h e n y l -p h o s p h o n i t e a n d f r o m n e o p e n t y l d i p h e n y l p h o s p h i n i t e w e r e f o u n d t o b e c o n s i d e r a b l y m o r e s t a b l e . R e a c t i o n w i t h α-bromoacetophenone g a v e t h e c o r r e s p o n d i n g A r b u z o v i n t e r m e d i a t e s 9, 10 a s c r y s t a l l i n e s o l i d s , t h e d i p h e n y l p h o s p h i n i t e d e r i v a t i v e 1 0 b e i n g s u f f i c i e n t l y
Phè ( O R ) 2 C H 2 C O P h B r " P h ^ ( 0 R ) C H 2 C 0 P h B r " 9 1 0
P h 2 P ( 0 R ) 0 C (:CH 2 ) P h C l " ( R = M e 3 C C H 2 ) 1 1
s t a b l e f o r X - r a y c r y s t a l s t r u c t u r e d e t e r m i n a t i o n t o b e c a r r i e d o u t . I n d e u t e r o c h l o r o f o r m a t 1 0 0 C ( s e a l e d t u b e ), t h e i n t e r m e d i a t e s w e r e a g a i n s h o w n t o d e c o m p o s e t o y i e l d . . t h e c o r r e s p o n d i n g A r b u z o v p r o d u c t s e x c l u s i v e l y , t h e Ρ nmr s i g n a l s f o r 9 (ô +6 7.1) a n d f o r 1 0 ( 6 + 6 8 . 3 ) b e i n g r e p l a c e d b y s i n g l e p e a k s a t +32.1 a n d +28.2 ppm, r e s p e c t i v e l y . T he p r e s e n c e o f p h o s p h o r u s -
j b o n d e d C H 2 g r o u p s i n t h e p r o d u c t s w a s c o n f i r m e d b y H nmr s p e c t r o s c o p y ( J f o r P-CLL 1 5 - 2 0 H z ) ; s i g n a l s d u e
t o v i n y l p r o t o n s w e r e n o t d e t e c t a b l e . F r o m n e o p e n t y l d i p h e n y l p h o s p h i n i t e we w e r e a l s o a b l e t o o b t a i n t h e f i r s t e x a m p l e o f a c r y s t a l l i n e P e r k o w i n t e r m e d i a t e 1 1 ( £ +55.9) b y r e a c t i o n w i t h α-chloroacetophenone i n c h l o r o f o r m . A l t h o u g h r a t h e r u n s t a b l e , i t c o u l d b e s t o r e d a t 0°C a n d w a s s h o w n t o d e c o m p o s e t o t h e c o r r e s p o n d i n g v i n y l e s t e r ( 6 + 2 9 . 7 ) w hen d i s s o l v e d i n d e u t e -
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516 PHOSPHORUS CHEMISTRY
t e r o c h l o f o r m ( t , c a . 40 m i n u t e s , a t room temperature ) The p r e s e n c e o f v i n y l p r o t o n s i n t h e i n t e r m e d i a t e a n d i n i t s d e c o m p o s i t i o n p r o d u c t was i n d i c a t e d by c o m p l e x m u l t i p l e t s i n t h e H nmr s p e c t r u m c e n t r e d a t 5.45 a n d 5.1 ppm, r e s p e c t i v e l y .
By c a r r y i n g o u t t h e r e a c t i o n o f t r i n e o p e n t y l p h o s p h i t e w i t h α - b r o m o a c e t o p h e n o n e i n t h e p r e s e n c e o f a c e t i c a c i d (10% i n a c e t o n e - d g ) we have a l s o o b t a i n e d e v i d e n c e f o r t h e t r a n s i e n t e x i s t e n c e o f t h e v i n y l o x y -p h o s p h o n i u m s p e c i e s . U n d e r t h e s e c o n d i t i o n s , we o b s e r v e d the., r a p i d a p p e a r a n c e o f t h r e e t r a n s i e n t i n t e r m e d i a t e s ( Ρ α+92, +40, and -7.3 p p m ) , a l t h o u g h v i n y l p h o s p h a t e was t h e a l m o s t e x c l u s i v e f i n a l p r o d u c t . The peak a t -7.3 ppm d i s a p p e a r e d most r a p i d l y , w i t h t h e s i m u l t a n e o u s d e v e l o p m e n t o f a c o r r e s p o n d i n g peak a t -7.2 ppm due t o v i n y l p h o s p h a t e , and i s t e n t a t i v e l y a s s i g n e d t o t h e v i n y l o x y p h o s p h o n i u m b r o m i d e . - J . t i s known t h a t t e t r a a l k o x y p h o s p h o n i u m i o n s have Ρ c h e m i c a l s h i f t s w h i c h a r e n o t f a r removed f r o m t h o s e o f t h e c o r r e s p o n d i n g p h o s p h a t e e s t e r s ( £ ).
The i d e n t i t i e s o f t h e p e a k s a t +40 a n d +92 ppm a r e u n c e r t a i n . One l i k e l y s p e c i e s t o be p r e s e n t i n a c i d c o n d i t i o n s i s t h e p r o t o n a t e d f o r m o f t h e b e t a i n e 5. Such i n t e r m e d i a t e s a r e assumed t o be f o r m e d i n a c i d c o n d i t i o n s and t o g i v e r i s e t o t h e f o r m a t i o n o f a - h y d r -o x y p h o s p h o n a t e s , ( RO) P (O) C H 2 X (R') OH (1 ). I t i s a l s o l i k e l y t h a t t h e b e t a i n e 5 i s t h e f i r s t common i n t e r m e d i a t e (scheme 3 ) i n t h e f o r m a t i o n o f A r b u z o v and Perkow p r o d u c t s , t h e s e b e i n g formed by a 1 , 2 - m i g r a t i o n o f t h e p h o s p h i t e m o i e t y t o t h e α - c a r b o n atom o r t o o x y g e n , r e s p e c t i v e l y . We d e t e c t e d no s i g n a l a t +13 ppm w h i c h w o u l d be e x p e c t e d i f t h e b r o m o ( t r i n e o p e n t y l o x y ) p h o s p h o n i u m i n t e r m e d i a t e h a d been f o r m e d , a l t h o u g h s u c h i n t e r m e d i a t e s a r e known t o be v e r y s h o r t - l i v e d N o r was t h e c o r r e s p o n d i n g p h o s p h o r o b r o m i d a t e d e t e c t e d a t -8.5ppm ( D ·
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Tetrahedron 1965, 21, 1961. 2. Toke ,L. ; Petneházy,I. and Szaká l ,Gy. J.Chem.Soc.Res.
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RECEIVED July 7, 1981.
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