69 1,2-Bis(dichlorophosphino)alkanes Ε. H. UHING and A. D. F. TOY
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Eastern Research Center, Stauffer Chemical Company, Dobbs Ferry,NY10522
This paper presents a new method for preparing 1,2-bis(dichlorophosphino)alkanes based on the reaction of unsaturated hydrocarbons with PCl3 and elemental phosphorus at 180-250°C under autogenous pressure1. The basic reaction with ethylene is shown in eq 1.
A prior method for making 1 involved the reaction of 1,2-bis(diphenylphosphino)ethane with PCl3 at 280°C using AlCl3 as a catalyst2. To show that eq 1 could be feasible we hypothesized the reaction occurring via eq 2 and 3. The addition of PCl3 across
a double bond using uv or other free radical initiators to form 2-chloroalkylphosphonous dichlorides is well known3. The thermal initiation of the reaction shown in eq 2 has not been reported. When excess PCl3 and ethylene (eq 2) are reacted at 200-250°C under pressure, our study showed only trace amounts of 2 being formed. At 250°C, with an excess of ethylene, a black solid formed. We believe the low yield of 2 might be due to an un favorable equilibrium or decomposition reaction. Trapping of 2 by some further reaction as shown in eq 3 could allow eq 2 to proceed. The reaction of alkyl chlorides with PCl3 and elemental phosphorus at 200-300°C to yield alkylphosphonous dichlorides has been reported4. Therefore, i f 2 reacts like an alkyl chloride then eq 3 could form 1. One of the proposed mechanisms for the uv initiated addition of PCl3 to isobutene involves a cyclic or bridged free radical 0097-6156/81/0171-0333$05.00/0 © 1981 American Chemical Society Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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i n t e r m e d i a t e to account f o r the absence of c r o s s - t r a n s f e r prod u c t s ^ . A n a l o g o u s l y , the f o r m a t i o n of a t r a n s i t o r y c y c l i c a d d i t i o n c o m p l e x b e t w e e n P C l ^ and e t h y l e n e a s shown i n Scheme I c o u l d a l s o be an a l t e r n a t e r e a c t i o n pathway f o r t h e f o r m a t i o n o f 1. Scheme I CH =CH 2
+
2
PC1
C H — CKL \ Ζ0
3
'
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PCI
3 +
CH -ÇH
Ρ,
0
ζ
2
0
+
PCI,
Cl 4 4_ + P C 1
•
3
1
A c y c l i c p h o s p h i r a n e r e l a t e d t o 4 has b e e n r e p o r t e d - . The p r a c t i c a l s c o p e o f o u r new method f o r p r e p a r i n g 1 , 2 - b i s ( d i c h l o r o p h o s p h i n o ) a l k a n e s u s i n g the r a t i o of alkene to elemental p h o s p h o r u s shown i n eq 1 and a 50-150% e x c e s s o f PC1~ a t 200-250 -C f o r 4-6 h o u r s u n d e r a u t o g e n o u s p r e s s u r e i s shown i n T a b l e I . Table I
Y i e l d s of C1 PCH CH(R)PC1 2
1-Alkene Used ethylene propylene 1-butene 1-pentene 1-octene
2
R H CH„ CH^CH (cL)^CH (CH )^CH 2
3
2
(1) (5) (6) (7_) (8)
% Yield 70 66 47 41 20
T a b l e I shows a s h a r p r e d u c t i o n i n y i e l d s a s t h e m o l e c u l a r w e i g h t of t h e 1 - a l k e n e i n c r e a s e s . F o r a l k e n e s a b o v e 1 - p r o p e n e , I was added a s a c a t a l y s t e v e n t h o u g h i t s b e n e f i c i a l e f f e c t was n o t c l e a r l y e s t a b l i s h e d . A l l t h e above r e a c t i o n s w e r e r u n i n a 316 S t a i n l e s s S t e e l a u t o c l a v e r a t e d a t 5000 p s i g . A t y p i c a l c h a r g e f o r m a k i n g 1 i n a 300 mL a u t o c l a v e i s 1.0m P C 1 0.45m e t h y l e n e and 0.3 gram-atom o f w h i t e p h o s p h o r u s . The maximum p r e s s u r e g e n e r a t e d a t 200°C i s 2000 p s i g . A l l p r o d u c t s w e r e i s o l a t e d by vacuum d i s t i l l a t i o n . I n T a b l e I I we show t h e 31p-NMR o f t h e s e b i s compounds. The o b v i o u s p o i n t o f i n t e r e s t f o r t h e 3Ip-NMR s p e c t r a shown i n T a b l e I I i s t h a t t h e 1^ and .5 b o t h a r e s i n g l e t s a t a b o u t t h e same frequency. S i n c e ,5 i s n o t a s y m m e t r i c a l m o l e c u l e , we r a n t h e 2
3 >
Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
69.
UHiNG A N D T O Y
1,2-Bis(dichlorophosphino)alkanes
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T a b l e I I P-NMR S p e c t r a o f Compounds i n T a b l e I Compound
6 (+ppm f r o m HJP0, )
1
190.6 190.7 194.8(d);191.4(d) 194.5(d);191.6(d) 194.5(d);191.3(d)
5
6 I 8
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Jp-p(Hz)
10 10 10
13C-NMR s p e c t r a t o be s u r e t h a t a 1 , 3 - b i s p r o d u c t d i d n o t f o r m . The 13C-NMR s p e c t r a o f 1_ a n d 5_ a r e shown i n T a b l e I I I . Compound 1_ h a s t h e s p e c t r u m o f a s y m m e t r i c a l 1 , 2 - b i s m o l e c u l e .
Table I I I
I3
Compound
C-NMR S p e c t r a o f 1 a n d 5 6(4- ppm f r o m
(CH^^Si) ^Jc-p
1 .5
3 6 . 1 ( d o f d) 4 5 . 5 ( d o f d) 4 0 . 5 ( d o f d) 16.0(t)
50 53 50
2
Jc-p
^ J c - p (Hz)
10 13 11 13.5
The l^c-NMR s p e c t r u m o f 5^ shows t h e p r e s e n c e o f a m e t h y l g r o u p t h a t i s c o u p l e d t o two m a g n e t i c a l l y e q u i v a l e n t p h o s p h o r u s atoms. To c o n f i r m t h a t 5^ h a s t h e e x p e c t e d 1 , 2 - b i s s t r u c t u r e , we h y d r o l y z e d and o x i d i z e d i t t o t h e b i s - p h o s p h o n i c a c i d . The P - N M R s p e c t r a o f t h i s a c i d shows two d o u b l e t s c o n s i s t e n t f o r a 1 , 2 - b i s structure. The P-NMR s p e c t r a r e p o r t e d f o r t h e 1 , 3 - b i s (phosphonic a c i d ) propane i s a s i n g l e t ? . S e v e r a l i n t e r n a l o l e f i n s were a l s o t r i e d i n t h e r e a c t i o n shown i n eq 1. When t h e r e a c t i o n o f b o t h c i s - o r t r a n s - 2 - b u t e n e w e r e r u n a t 230°C, t h e y gave a l o w ( 1 0 % ) y i e l d o f t h e 2 , 3 - b i s ( d i c h l o r o p h o s p h i n o ) b u t a n e a s e v i d e n c e d b y a s i n g l e 31P_NMR p e a k a t 193.6 ppm a n d a s y m m e t r i c a l l^c-NMR s p e c t r a . When t h e r e a c t i o n t e m p e r a t u r e i s r a i s e d t o 250°C, b o t h c i s - a n d t r a n s - 2 - b u t e n e y i e l d a compound w h i c h h a s t h e same 31p a n d 13c-NMR s p e c t r a a s 6^ i n d i c a t i n g a 1,2-bis(dichlorophosphino)butane product. Along with t h i s r a t h e r complex isomer p r o d u c t change, t h e r e i s an i n c r e a s e i n t h e amount o f b u t y l p h o s p h o n o u s d i c h l o r i d e f o r m e d . A b r a n c h e d a l k e n e , i s o b u t y l e n e , gave a 2 3 % y i e l d o f 1 , 2 - b i s ( d i c h l o r o p h o s p h i n o ) i s o b u t a n e a t a r e a c t i o n t e m p e r a t u r e o f 210°C a l o n g w i t h a t r a c e o f t e r t - b u t y l p h o s p h o n o u s d i c h l o r i d e a n d two isobutenylphosphonous d i c h l o r i d e s . Cyclohexene f a i l e d t o produce 31
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Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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even a t r a c e o f b i s p r o d u c t u n d e r a v a r i e t y o f r e a c t i o n c o n d i tions. The o n l y p r o d u c t i s o l a t e d was c y c l o h e x y l p h o s p h o n o u s d i c h l o r i d e which i s one o f the p r o d u c t s p r e v i o u s l y r e p o r t e d f o r t h e t h e r m a l a d d i t i o n o f PC1« t o c y c l o h e x e n e Z . S i n c e t h e 1 , 2 - b i s ( d i c h l o r o p h o s p h i n o ) a l k a n e s made b y t h i s new process a r e r e a c t i v e i n t e r m e d i a t e s they have a v a r i e t y o f poten t i a l uses. Compound 1 h a s b e e n c o n v e r t e d t o t h e 1 , 2 - b i s ( d i me t h o x y p h o s p h i n o ) e t h a n e a n d u s e d f o r m a k i n g m e t a l c a r b o n y l complexes.?. T h e r e a l s o i s a r e p o r t o n t h e c o n v e r s i o n t o 1 , 2 - b i s (dimethylphosphino)ethane and 1,2-bis(diethylphosphino)ethane^.. The t e t r a - s o d i u m s a l t o f e t h y l e n e d i p h o s p h i n e t e t r a a c e t i c a c i d h a s b e e n made u s i n g i n t e r m e d i a t e The r e a c t i o n s w i t h p h e n o l s and c y c l i c a l i p h a t i c a l c o h o l s a l s o h a v e b e e n r e p o r t e d — .
LITERATURE CITED 1.
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July 7, 1981.
Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
