17. 18. 19. 20. 21. 22.

O . A . Reutov, I. P. Beletskaya, and V. I. Sokolov, M e c h a n i s m s for the Reactions of O r g a n o m e t a l l i c Compounds [in Russian], Khimiya, Moscow (1972), Chap. 6. F. Aubke and D. D. Des Marteau, Fluorine Chem. Rev., 8, 73 (1977). F . G . Borgardt, A. K. Seeler, and P. Noble, J. Org. Chem., 31, 2806 (1966). H. Shechter and L. Zeldin, J. Am. Chem. Soc., 73, 1276 (l~q51). N. Kornblum and R. A. Brown, J. Am. Chem. Soc., 86, 2681 (1964). A . I . Ivanov, V. I. Slovetskii, S. A. Shevelev, A. A. F a i n z f l ' b e r g , and S. S. Novikov, Zh. Fiz. Khim., 41, 830 (1967).

ROLE OF

OF

MEDIUM

COMPONENTS

ELECTROCHEMICALLY

IN T H E

GENERATED

REACTIONS RADICAL-ANIONS

3. STEREOCHEMISTRY AND SELECTIVITY OF THE CATHODIC HYDRODIMERIZATION OF ~-THIOPHENALDEHYDE IN NONAQUEOUS MEDIA V.

P.

Gul'tyai

and

L. M.

Korotaeva

UDC 541.138.3:547.733

The study of the feasibility of the s t e r i c a l l y controlled e l e c t r o c h e m i c a l synthesis of o r g a n i c compounds holds i n t e r e s t both for preparative c h e m i s t r y and for c l a r i f y i n g questions r e l a t e d to electrode r e a c t i o n m e c h a n i s m s [1, 2]. In r e c e n t y e a r s , the e l e c t r o c h e m i c a l reduction of c a r b o n y l compounds to pinacols has been studied in detail [3-5]. N e v e r t h e l e s s , there are c o n t r a d i c t o r y opinions on the m e c h a n i s m for the e l e c t r o c h e m ical h y d r o d i m e r i z a t i o n (ECH) and the role of the supporting e l e c t r o l y t e in this p r o c e s s . S t o c k e r e t al. [3, 4] c o n s i d e r that the dimerization of the r a d i c a l - a n i o n s (RA) (or free radicals) generated on the cathode is a c complished in the solution bulk, while Puglisi [1] and Bewick [2, 5] a r g u e in favor of a s u r f a c e methanism for this reaction. In addition, Stocker [4] and Bewick [5] studied ECH r e a c t i o n s in nonaqueous media and concluded that the dimerization o c c u r s with the simultaneous participation of RA and free r a d i c a l s (formed upon p r o t o n ation of the f i r s t t r a c e amounts of w a t e r in the o r g a n i c solvent). This conclusion is not in a c c o r d w i t h the r e sults of e a r l i e r work [6, 7] indicating a low rate of pretonation of the a r o m a t i c HA by w a t e r in nonaqueous m e dia, in p a r t i c u l a r , in DMF. Finally, Stocker et al. [3], without justification, concluded that the e l e c t r o c h e m i c a l reduction of a r o m a t i c aldehydes with the formation of the c o r r e s p o n d i n g pinacols always must p r o c e e d with low s t e r e o s e l e e t i v i t y , which is not in a c c o r d with the e a r l i e r data [8]. In the p r e s e n t work, the effect of the composition of the medium on the yield of 1 , 2 - d i ( a - t h i e n y l ) e t h a n e - l , 2 - d i o l (DTED) and the s t e r i c control of the ECH of a-thiophenaldehyde (TA) w e r e studied in detail EXPERIMENTAL

The e l e c t r o l y s i s method was d e s c r i b e d p r e v i o u s l y [9]. The c h a r a c t e r i s t i c s of all the isolated compounds were given in previous work [10]. The d , / / m e s o ratio was found by g a s - l i q u i d c h r o m a t o g r a p h y on an LKhM8MD-5 c h r o m a t o g r a p h with a flame-ionization d e t e c t o r on a 3 m ~r 3 mm column packed with Chromaton N - A W DMCS with 5% XE-60 at 220~ In o r d e r to d e m o n s t r a t e .that s u r f a c e r e a c t i o n s o c c u r in the ECH of a - t h i o phenaldehyde (TA), a s e r i e s of e x p e r i m e n t s was p e r f o r m e d in the p r e s e n c e of a s u r f a c e - a c t i v e r e s i n f o r m e d upon prolonged storage of TA (Table 1, e x p e r i m e n t s 6 and 10). RESULTS

AND DISCUSSION

Tables 1 and 2 show that the DTED yield and the ratio of its s t e r e o i s o m e r s significantly depends on the composition of the supporting electrolyte o r various additives to the e l e c t r o l y s i s solution. The effect of the composition of the supporting electrolyte on the s t e r i c specificity of ketone reduction was studied by Bewick and Brown [2], who examined the role of hydrogen bonding and the effect of ion p a i r s and adsorption of i n t e r mediates in the ECH of acetophenone in DMF. Unfortunately, Bewick and Brown [2] did not include data on the effect of the medium composition on the total pinacol yield, which, as seen in the w o r k of Stocker [4] and in e a r l i e r work [9], v a r i e s with change in the nature of the supporting electrolyte. N. D. Zelinskii Institute of Organic C h e m i s t r y , A c a d e m y of Sciences of the USSR, Moscow. T r a n s l a t e d from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 165-170, J a n u a r y , 1982. Original a r t i c l e submitted May 20, 1981.

156

0568-5230/82/3101-0156 $07.50 9 1982 Plenum Publishing C o r p o r a t i o n

T A B L E 1. T o t a l Yield and D i a s t e r e o m e r Ratio in the R e d u c t i o n of a - T h i o p h e n a l d e h y d e in DM F Expt. No.

3 4 5 6 7 8 9 i0 tl t2 i3 14

DT~D yield, % d, ratiol/me~ (relative to reacted TAL___"

Base electrolyte o,i M KC104 0,t M BuaNClOa+0,025M KCIO~ 0,1 M Bu~NC10~+0,65M KCIO,, 0,i M Bu~NC10~+0,tM KC1Q 0,1 M KC/0~+0,625M LiC1Ol 0,i M KCIO~* 0,1 M LiC1Ol 0,t M Bu~NCt0~+0,6iM LiC10~ %t M Bu~NCI04+0,05M LiCl01 0,t M LiCl04 * 0,t M NaCIO~ 0,1 M LiNOa+t0% H~O 0,i M LiNOa+Ac0HT 0,i M LiNOa+COz

6,8 6,t 7,0 6,7 8,2 7,6 8,0 t2,2 9,0 8,0 7,0 5,0

65 38 4i 58 79 85 64 4-6 55 92 55 68 50 65

1,9

* In the p r e s e n c e of s u r f a c e - a c t i v e r e s i n . t [AcOH]/[TA] ~ 1.5. T A B L E 2. D i a s t e r e o m e r Ratio in the R e d u c t i o n of ( ~ - T h i o p h e n a l d e h y d e in A c e t o nitrile ExpL No. t 2 ' 3 4 5 6

d,l/mere ratio

Base electrolyte

0,1 M LiC10~ 0,t M Bu~NCIO~ 0,t M Bu~NClO~+0,iM LiC10~ 0,t M Et~NC10a 0,t M Et~NCIO~+I0%H20 0,1 M Et~NCIO~+0,2M thiophenol

2,4 2,0 3,3 2,2 2,9 i,6

In the p r e s e n t w o r k , the d a t a g i v e n in T a b l e s 1 a n d 2 a n d in e a r l i e r w o r k [2-51 a r e e x a m i n e d on the b a s i s of the m e c h a n i s m f o r the E C H of c a r b o n y l c o m p o u n d s d e v e l o p e d by V y k h o d t s e v a [11] a n d in e a r l i e r w o r k [12]. A m a j o r a s p e c t in t h i s a p p r o a c h is c o n s i d e r a t i o n of such f a c t o r s a s the a m b i d e n t n a t u r e shovm by e ! e c t r o c h e m i c a l l y g e n e r a t e d RA [10-12] a n d the p o s s i b i l i t y t h a t the ECH r e a c t i o n p r o c e e d s both in the s o l u t i o n bulk and on the e l e c t r o d e s u r f a c e [13]. A s a c o n s e q u e n c e of the s t e r i c h i n d r a n c e of the d i a n i o n s of a r o m a t i c d i o l s (in o u r c a s e , DTED) f o r m e d upon the d i m e r i z a t i o n of TA r a d i c a l - a n i o n s (TA:), the f o l l o w i n g s t r u c t u r e s a r e the m o s t e n e r g e t i c a l l y f a v o r e d of the six p o s s i b l e c o n f o r m e r s : o~

H/ ~

Th

~'Th

H

6)

9 oj O

Th

mere form

dfl form

where Th = a-thienyl. The f o r m a t i o n of a b r i d g i n g bond with a m e t a l c a t i o n s h o u l d , a c c o r d i n g to Bewick [2], lead to the p r e d o m i n a n t f o r m a t i o n of the d,l f o r m if the two TA- s p e c i e s bind to a s i n g l e c a t i o n of the s u p p o r t i n g e l e c t r o l y t e in the t r a n s i t i o n s t a t e . T a b l e 1 ( e x p e r i m e n t s 1, 7, a n d 11) i n d i c a t e s that, in the c a s e of e l e c t r o l y s i s in 0.1 M LiCIO4, KC104, a n d NaC10 4 a s s u p p o r t i n g e l e c t r o l y t e , t h e r e is r a t h e r high s t e r e o s p e c i f i c i t y e v e n f o r a n o t v e r y high t o t a l p i n a c o l y i e l d . A c c o r d i n g to p r e v i o u s data [9], the e l e c t r o l y s i s of TA in 0.1 M t~atNC10 4 o r Et4NCIO 4 s u p p o r t i n g e l e c t r o l y t e l e a d s to the f o r m a t i o n of D T E D with 7 - 1 5 g y i e l d with d , / / m e s o r a t i o f r o m 2.0 to 3.5 d e p e n d i n g on the a m o u n t of w a t e r in the s o l u t i o n . The d , / / m e s o .ratios for p i n a c o l in the e l e c t r o l y s i s of a c e t o p h e n o n e in D M F c o n t a i n i n g ~ 0.37~ w a t e r o b t a i n e d by Bewick [2] a r e 8.3 : 1 in 0.1 NI RbCIO 4 s u p p o r t i n g e l e c t r o l y t e a n d 5.6 : 1 in 0.1 M Bu4NC10 4 s u p p o r t i n g e l e c t r o l y t e . C o m p a r i s o n of t h e s e v a l u e s p e r m i t s us, t o a f i r s t

157

approximation, to conclude that the stereospecificity of E CH of carbonyl derivatives depends on the nature not only of the substrate but also of the cation of the supporting electrolyte. This is not in a c c o r d with the r e s u l t s of Stocker [3], who found low s t e r e o s p e c i f i c i t y in the ECH of a r o m a t i c aldehydes. F u r t h e r m o r e , the r e s u l t s for the e l e c t r o l y s i s of TA in 0.1 M Bu4NC104 supporting electrolyte in the p r e s e n c e of different amounts of LiC104 and KC10 4 (Table 1, e x p e r i m e n t s 2-4, 8, and 9) indicate that the s t e r e o s p e e i f i c i t y and selectivity of the ECH of TA a r e sharply altered by a change in the lithium salt concentration, while the effect of KC104 is evident only upon the addition of small amounts of salt (experiment 2) relative to the data only for 0.1 M Bu4NC104. A f u r t h e r i n c r e a s e in the KC10 4 concentration has a l m o s t no effect on the s t e r e o s p e c i f i c i t y and a not very s t r o n g effect on the reaction selectivity. The selectivity of the ECH reaction for TA leading to DTED upon e l e c t r o l y s i s in 0.1 M KC104 also depends significantly on. the p r e s e n c e of LiC104 in solution (compare e x p e r i ments 1 and 5 in Table 1) and the p r e s e n c e of a s u r f a c e - a c t i v e r e s i n (experiment 6). In turn, the introduction of the r e s i n to the electrolyzable solution of TA in 0.1 M LiC104 supporting electrolyte (experiment 10) leads to an a l m o s t quantitative yield of DTED. We should note that s m a l l amounts of "anomalous" h e a d - t o - t a i l d i m e r s d e s c r i b e d in previous work [10] a r e found under the e l e c t r o l y s i s conditions in 0.1 M Bu4NC104 and KC104 supporting electrolyte. Thienyl alcohol is also found in the case of KC10 4 supporting electrolyte. On the o t h e r hand, the formation of these products is not found upon the introduction of LiC104. These findings indicate that not only dimerization with the formation of pinacol but also reaction of TA- involving the thiophene ring o c c u r s in Bu4NC104 and, partially, in KC104 supporting e l e c t r o l y t e at a potential c o r r e s p o n d i n g to the formation of TA:. The significant i n c r e a s e in the yield of DTED in the p r e s e n c e of the r e s i n (experiment 6, Table 1) may be taken as proof for the s u r f a c e nature of the second type of reactions. While anomalous d i m e r i c products were not found in the e l e c t r o l y s i s of TA in the p r e s e n c e lithium salts, n e v e r t h e l e s s , if we take account of the high surface activity of [TA~... Li +] tight ion pairs [5, 8], then at sufficiently high concentrations of TA=, not only is an i n c r e a s e in the rate of dimerization leading to pinacol p o s sible, but also an i n c r e a s e in the rate of side r e a c t i o n s involving these species. As a r e s u l t , the quantitative yield of pinacol in lithium salt supporting e l e c t r o l y t e is obtained only in the p r e s e n c e of surfactants (see Table 1, e x p e r i m e n t 10 and previous work [9]). As a l r e a d y mentioned, not only the total DTED yield but also the d , / / m e s o ratio a r e not v e r y high in the ECH reaction of TA in lithium salt supporting electrolyte. Apparently, s u r f a c e - a c t i v e ion p a i r s o r [ L i + . . . TA-" ... Li +] ion triplets f o r m e d in the case of excess lithium salt may p a r ticipate in r e a c t i o n s of the type [ T A - " . . . Li +] -}- T A - ~ Product or

[ T A - " . . . Li*] -l- [Li+ 9 9 9 TA-" . . . Li+] --+ Product even if these r e a c t i o n s lead to pinacol but a r e not s t e r e o s p e c i f i c . The g r e a t e s t s t e r e o s p e e i f i c i t y of the ECH reaction of TA should be expected in the case of a ratio of TA to lithium cations in the l a y e r adjacent to the electrode c o r r e s p o n d i n g t o t w o TA-" species bound through a "bridging" bond to a single lithium cation. This situation is found in the e x p e r i m e n t s in which the e l e c t r o l y s i s was c a r r i e d out in the p r e s e n c e of the s u r f a c e - a c t i v e Bu4N + cation and s m a l l amounts of LiC10 4 (see Table 1, exp e r i m e n t s 8 and 9 and the work of Bewick [2]). The addition of from 10 to 50 m m o l e s LiC104 to TA solutions containing 0.1 M BuI-NC104 sharply i n c r e a s e s the d , l / m e s o ratio. An attempt to obtain optically active pinaeol using an optically active q u a t e r n a r y a m m o n i u m salt (methyla t e d / - e p h e d r i n e ) under conditions in which the predominant formation of its d,l form is found [0.1 M PhCH(OH)CHMeNM3C10 4 + 0.05 M LiC104] was not successful. This r e s u l t , apparently, m a y be considered as evidence for the bulk nature of the d i m e r i z a t i o n of TA: in the p r e s e n c e of a high concentration of s u r f a c e - a c tive cation and for the_ predominant effect of the bridging bond with Li + on the r e a c t i o n stereospeeifieity. If we a s s u m e that the ratio of the m e t a l cation to TA- in the layer adjacent to the electrode should affect the pinaeol d,//meso ratio, then we should expect a change in this value during the c o u r s e of the e l e c t r o l y s i s with a m a x i m u m d,l/meso ratio at the onset. Indeed, the d,l/meso ratio for DTED in the e l e c t r o l y s i s in 0.1 M Bu4NC10 4 supporting e l e c t r o l y t e in the p r e s e n c e of 0.025 M LiC104 is 1 8 : 1 a f t e r 0.5 h, 1 5 . 5 : 1 after 1.0 h, and 10 : 1 a f t e r 2.5 h. Thus, the data given in Tables 1 and 2 are indicated as c o r r e s p o n d i n g to 2.5-3 h e l e c t r o l y s i s time. However, the d , / / m e s o ratio hardly v a r i e s o v e r the e l e c t r o l y s i s in solutions with a high Li + content due to a constant e x c e s s of lithium cation in the l a y e r adjacent to the electrode. Thus in 0.1 M LiC104, this ratio is 10 : 1 a f t e r 0.5 h, 9.0 : 1 a f t e r 1 h, and 8.0 : 1 a f t e r 2.5 h. Analogous behavior was also o b s e r v e d in the ECH reaction of TA in 0.1 iV[ Bu4NC10 4 supporting electrolyte in the p r e s e n c e of 0.1 M LiC104.

158

The m e c h a n i s m for the ECH reaction in DMF in solutions containing different amounts of water (see Table 1, e x p e r i m e n t 12 and the work of Bewick [2]) r e q u i r e s special consideration. In c o n t r a s t to the theor i e s put f o r w a r d by Stocker [4] and Bewick [~5], we proposed in e a r l i e r work [6] that even in the case of r a t h e r high w a t e r c o n c e n t r a t i o n s , the r a d i c a l - a n i o n s of a r o m a t i c carbonyl compounds are not protonated by w a t e r but r a t h e r form various types of aquo complexes. The formation of pinacol in sufficiently dry DMF containing up to 0.1~ water is a c c o m p l i s h e d by " e l e c t r o c h e m i c a l desorption" [5, 14]. If the formation of the d i m e r i c anion is c o n s i d e r e d to r e s u l t from the reaction of a ohemisorbed ion pair with a ketone molecule a r r i v i n g from the solution bulk (with subsequent o r c o n c u r r e n t electron t r a n s f e r ) , it is difficult to expect a high s t e r e o specificity for this reaction since the ketone molecule may have any orientation towards the electrode surface. When electrophilic species such as Lewis acids of compounds with a labile hydrogen a r e present in the solution which a r e capable of f o r m i n g complexes o r a g g r e g a t e s with the r a d i c a l - a n i o n s , the rate of reaction of the c h e m i s o r b e d r a d i c a l - a n i o n s with such a g g r e g a t e s may be g r e a t e r than that with the initial carbony] compound molecules. This would lead to elimination of the e l e c t r o c h e m i c a l desorption m e c h a n i s m . In other' words, the m e c h a n i s m for formation of the diol dianion and, thus, both the s t e r e o s p e c i f i c i t y and selectivity of the r e action m a y be altered by changing e l e c t r o l y s i s p a r a m e t e r s such as c u r r e n t density and the s t o i c h i o m e t r i c a l ratio of all the active species. Thus, an i n c r e a s e in the water content in the reaction mixture up to 6~ in 0.1 M Bu4NCIO 4 m a y lead to the formation of DTED with higher s t e r e o s p e c i f i c i t y relative to "dry" solutions due to d i m e r i z a t i o n of r a d i c a l - a n i o n s bound in an ion pair with Bu4N + and hydrated r a d i c a l - a n i o n s . Thus, the d , ~ / m e s o ratio r e a c h e s 8.5 : 1 [2]. In the p r e s e n c e of sufficiently high water contents ( > 10~), there is a p parent competitive formation of r a d i c a l - a n i o n aquo complexes and ion pairs both on the surface and in the s o lution bulk, w h i c h , in the final a n a l y s i s , leads to the predominant dimerization of the separated ion p a i r s (which contain water molecules); the reaction of this type of species should not be highly stereospecific (see Table 1, e x p e r i m e n t 12). The marked d e c r e a s e in the stereo specificity of the E CH r e a c t i o n of acetophenone due a significant i n c r e a s e in the water content in DMF (> 30~) may be attributed to this effect. In this c a s e , the s t e r e o s p e c i f i c i t y is a l m o s t independent of the nature of the supporting electrolyte cation (the d , / / m e s o r a tio is 3.3 : 1 for 0.1 M BucNC10 4 and 3.6 : 1 for 0.] M RbC10 4 [2]), which, apparently, r e s u l t s from the d i m e r ization of two s i m i l a r r a d i c a l - a n i o n aquo complexes, The effect of strong complexing agents relative to TA= (CO 2 and AcOH, Table 1, experiments 13 and 14) which a r e capable of hindering the formation of the bridging bond involving the lithium cation on the s t e r e o specificity of the ECH reaction of TA is even m o r e significant. In the limiting c a s e , i.e., when running the e l e c t r o c h e m i c a l reduction in solvents which strongly solvate the r a d i c a l - a n i o n s such as water o r ethanol, the s t e r e o s p e c i f i c i t y of the ECH reaction of benzaldehyde o r of unsubstituted acetophenone, without r e g a r d to the nature of the supporting electrolyte cation [3], is sharply r e duced (d, Z/meso ratio = 1-1.5). This drop is related to dimerization of solvated r a d i c a l - a n i o n s o r free r a d i cals (when running the e l e c t r o c h e m i c a l reduction in acidic buffer solutions o r in the p r e s e n c e of strong acids [1, 3]). Table 2 indicates that the s t e r e o s p e c i f i c i t y of the ECH reaction of TA in acetonitrile (which is a better solvating agent for anionic species than DMF [15]) is significantly lower than that in DMY and is only slightly a l t e r e d with change in the nature of the supporting electrolyte. Thus, in examining the nature of the effect of the composition of the medium on the selectivity and s t e r i c control of the ECH reaction, we should take a c count of both the contribution of heterogeneous f a c t o r s and the r e a c t i v i t y of the various ion pairs and a s s o c i ated species. CONCLUSIONS 1. The role of solvation and surface f a c t o r s was shown in the reaction of the r a d i c a l - a n i o n s of a r o m a t i c carbonyl compounds in the case of the e l e c t r o c h e m i c a l h y d r o d i m e r i z a t i o n (E CH) of (~-thiophenaldehyde in DM Y. 2. E l e c t r o l y s i s conditions were found which lead to quantitative formation of 1,2-di((~-thienyl)ethane1,2-diol and also high s t e r e o s p e c i f i c i t y of the ECH reaction of the a r o m a t i c aldehyde. LITERATURE 1.

2. 3. 4.

V. A. J. J.

CITED

I. Puglisi, G. L. Clapper, and D. H. Evans, Anal. Chem., 41, 279 (1.q69). Bewick and D. J Brown, J. Chem. See., Perkin T r a n s . [I, 22 (]977). H. Stocker, R. M. J e n e v e i n , a n d D . H . K e r r , J. Org. Chem., 34, 2810 (196.q). H. Stocker and R. M. Jenevein, Collect. Czech, Chem. Commun., 36, 925 (1971).

159

g. 6. 7. 8. n. 10. 11. 12. 13.

A. Bewick and H. P. Cleghorn, J. Chem. Sot., P e r k i n T r a n s . [I, 1410 (1973). V . P . GuUtyai, S. G. M a i r a n o v s k i i , T. Ya. Rubinskaya, and N. P. Rodionov, E l e k t r o k h i m i y a , 16, 370 (1980). L. E b e r s o n , 7. Blum, B. Helgee, and K. N y b e r g , T e t r a h e d r o n , 34, 731 (1978). V . P . Gul'tyai, Fourth F r u m k i n L e c t u r e s [in Russian], M e t s n i e r e b a , Tbilisi (1980), p. 100. V . P . Gul'tyai, L. M. Korotaeva, A. S. Mendkovich, and I. V. P r o s k u r o v s k a y a , Izv. Akad. Nauk SSSR, Ser. Khim., 834 (1.q81). V . P . Gul'tyai, L. M. K o r o t a e v a , N. P. Rodionov, and A. M. M o i s e e n k o v , [zv. Akad. Nauk SSSR, Ser. Khim., 1150 (1981). L . N . Vykhodtseva and L. N. N e k r a s o v , E l e k t r o k h i m i y a , 13, 1239 (1977). V . P . Gul'tyai and A. M. Moiseenkov, 7h. Org. Khim., 16, 1026 (1980). V . P . Gul'tyat, S. G. M a i r a n o v s k i t , T. Ya. Rubinskaya, and L. M. K o r o t a e v a , E l e k t r o k h i m i y a , 15, 187q

097~). 14. 15.

V . P . Gul'tyai, S. G. M a i r a n o v s k i i , T. Ya. Rubinskaya, I. V. P r o s k u r o v s k a y a , and N. P. Rodionov, E l e k t r o k h i m i y a , 15, 851 (1979). P . H . R i e g e r and G. K. F r a e n k e l , J. Chem. P h y s . , 3_9.9, 609 (1963).

CONDENSATION AND WITH

OF

TRICHLOROTRIFLUOROPROPYLENE

DICH LOROPERFLUOROISOBUTYLEN FLUORINATED

PRESENCE

OF

L. A .

IN T H E

SbF 5

V. A. P e t r o v , L. S. G e r m a n ,

and

ETHYLENES

E

UDC 542.953: 547.413:546.865'161

G. G. Belen'kii, A. P. K u r b a k o v a ,

Leites

It has p r e v i o u s l y been shown [1] that in the p r e s e n c e of SbF 5 p e r f l u o r o p r o p y l e n e condenses with f l u o r i n ated ethylenes to f o r m the c o r r e s p o n d i n g pentenes with a multiple bond a t the 2-position. CF2=CFCF~ sbF; [CF2___CFCF |

SbF,| ~ [CF2~CFu"F 2CF2CF3] SbF,~CF3CF--~CFCF2CF~ " -CF.~=CF:,, -

The last stage of the proposed scheme includes double-bond m i g r a t i o n f r o m the 1-position to the 2-position by the action of SbFa. Such a r e a r r a n g e m e n t has been c o n f i r m e d in n u m e r o u s e x a m p l e s [2, 3], and it has been e s t a b l i s h e d that in the p e r f l u o r i n a t e d chain the multiple bend is c l e a r l y located at the 2-position [2]. When the s t a r t i n g olefin contains H o r C1 in V-position to the double bond, t h e r e is a f u r t h e r shift of the l a t t e r toward those a t o m s , even to the end of the h y d r o c a r b o n chain [3]: CF~.=CFCF~CF2C1

SbF5

~ CFsCF2CF=CFC1

F r o m these data it might be expected that in the alkylation of f l u o r o e t h y l e n e s by fluorinated p r o p e n e s having 1 o r 2 C1 a t o m s in the 1-position at the double bond, the final p r o d u c t s would be the r e s p e c t i v e t e r m i n al pentenes. Indeed, 1 , 1 , 2 - t r i c h l o r o - 3 , 3 , 3 - t r i f l u o r o p r o p y l e n e (1) in the p r e s e n c e of SbFs r e a c t s with t e t r a f l u o r o e t h y l ene (TFE) to f o r m 1 , 1 , 2 - t r i e h l o r o - 3 , 3 , 4 , 4 , 5 , 5 , 5 - h e p t a f l u o r o - l - p e n t e n e (II). The r e a c t i o n a p p a r e n t l y p r o c e e d s by the scheme: CCl2_=CC1CFs sbs. [CCl~=CC1CP=m]SbFs e cs==cF;

(I) C

---+ [CCI~--CClCF2CF~CF2QISbFs | "

b

&

> CC!~=CC1CF=CF2CF3 --SbF~ (II)

A. N. N e s m e y a n o v Institute of H e t e r o o r g a n i c Compounds, A c a d e m y of Sciences of the USSR, Moscow. T r a n s l a t e d f r o m I z v e s t i y a Akademii Nauk SSSR, Seriya K h i m i c h e s k a y a , No. 1, pp. 170-174, J a n u a r y , lq82. O r i g i n a l a r t i c l e submitted May 25, 1981.

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9 1982 P l e n u m Publishing C o r p o r a t i o n