The Synthesis of Trifluorovinyl Ethers
Yu.V.Zeifman, S.R.Sterlin
The establishment of Russian Academy of Sciences A.N.Nesmeyanov Institute of
Organoelement Compounds RAS Russian Federation,
119991 Moscow, Vaviliva st. 28
Fax: (499) 135 6549,
E-mail: lsg@ineos.ac.ru
The thermolysis of alkali metals perfluoro-2-alkoxytetrafluoropropionates is
a common method of preparing perfluoroalkylvinyl ethers, including such
important industrial monomers as perfluoromethyl- and propylvinyl ethers, that
are obtained in high yields (<90%)[1]. At the same time in the case of
2-alkoxytetrafluoropropionic acids 1 the thermal degradation of their salts
ROCF(CF3)COOM
(2) (R = Me, Et, CF3CH2; M = alkali metal cation) leads to the formation of
complex mixture of products, containing minute quantities of trifluorovinyl
ethers. Thus the thermolysis of 1 (R = CF3CH2; M = Na) afforded ether 3a in 4%
yield [2].
We have shown that ether 3a can be obtained by thermolysis of salt
2 (R
= CF3CH2; M = K) (2a) in 67% yield. Similarly ether
3b was prepared from 2 (R =
Ph; M = K) (2b) in 63% yield. The starting acids ROCF(CF3)COOH (1) [R =
CF3CH2
(1a); Ph (1b)] were obtained by the reaction of the corresponding alcohols with
hexafluoropropene oxide (HFPO) and alkali in a system H2O-ether in the presence
of phase-transfer catalyst Bu4NBr and subsequent acidification of the reaction
mixture, that simplified the method of synthesis 1 described earlier [3].
The
results obtained confirm the conclusion [2] that chemical behavior of salts 2 under
the conditions of thermolysis depends to a considerable extent on the nature of
both cation and alkoxy substituent.
2-(2,2,2-Trifluoroethoxy)tetrafluoropropionic acid 1a
Hexafluoropropene
oxide (16,6 g, 0,1 mol) was gradually introduced into the mixture of 19,3g (0,19
mol) trifluoroethanol, 19g (0,34 mol) KOH, 40 ml of H2O, 50 ml of ether and 1,5g
of Bu4NBr at <30oC, then the mixture was stirred 1h at room
temperature, acidified with
30% hydrochloric acid, ethereal layer was separated, dried with MgSO4 and
distilled to give a fraction with b.p. 82-92oC/35 Torr. The following
rectification afforded 16g (68% based on HFPO taken into reaction) of 1a, b.p.
61-63oC/10 Torr. (lit. data: b.p. 125-127oC [2]). NMR 19F spectrum ( , p.p.m.): -3.3
(3F1); 4.0 (3F3); 54,5 (1F2).
2-Phenoxytetrafluoropropionic acid 1b
was obtained similarly from HFPO and
phenol in 40% yield, b.p. 93-98oC/3 Torr; NMR 19F spectrum (, p.p.m.): 5,2 (3F);
42,5 (1F). The acid was transformed into its K-salt 2b without further
purification.
2,2,2-Trifluoroethyltrifluorovinyl ether 3a.
A solution of 16g
(0,065 mol) 1a in MeOH was neutralized with solution of KOH in MeOH (phenolphthalein
as indicator), evaporated under reduced pressure, the residue was dried over
P2O5 at 110oC/2-3 Torr., then pulverized, mixed with 20g of dry sand and
subjected to thermolysis at 10-15 Torr by heating in the flame of Bunsen burner
(or in Wood alloy bath at 225-280oC). The volatile products were collected in a
trap (-78oC), the condensate was distilled to give 8.5g (67%) of ether
3a, b.p.
41-44oC (b.p. and NMR 19F spectrum were identical to that described in
[2,4]).
Phenyltrifluorovinyl ether 3b.
A mixture of 10.4g (0.037 mol) salt 2b (dried
over
P2O5 at 110-115oC/3 Torr.) and 13g of dry sand was subjected to thermolysis
under vacuum of oil pump, collecting the volatile products in a trap (-78oC). The
condensate was distilled to give 5.9g (63%) of ether 3b, b.p. 132-134oC (b.p.
and NMR 19F spectrum were identical to that described in [5,6]).
Acknowledgement
Support of the given study by DuPont de Nemours Co. is gratefully
acknowledged.
References
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