Process for preparing alpha-bromo-acyl-fluorides

Abstract: α-Bromo-acyl fluorides of formula R¹-CFBr-COF wherein: R¹ is a fluorine atom or a perfluoroalkyl radical R F contai­ ning from 1 to 10 carbon atoms, are prepared by reacting, in the presence of activated charcoal, a perfluoroepoxide of for­ mula with a trialkyl-silyl bromide of formula wherein R², R³ and R⁴, the same or different from each other, are alkyl groups containing from 1 to 8 carbon atoms.

Description: The present invention is concerned with the preparation of α-bromo-acyl fluorides of formula R¹-CFBr-COF wherein R¹ is a fluorine atom or a perfluoroalkyl radical R F containing from 1 to 10 carbon atoms. These compounds are generally disclosed in EP-A-194 862 and are prepared according to the process of IT-A-1 134 028. IT-A-1 134 028 describes a process for preparing CF₃COCl by reacting CF₃-CCl₃ with SO₃ using a Hg catalyst. The CF₃ COCl obtained may be reacted with HF to produce CF₃COF. It has been found, according to the present invention, that the above α-bromo-acyl fluorides can be prepared in good yield and with high selectivity by reacting the corresponding perfluoroepoxides with a trialkyl-silyl bromide in the presence of activated charcoal. One object of the present invention thus is the provision of a process for the preparation of the above α-bromo-acyl fluorides, which makes it possible to obtain the desired products in good yield and with high selectivity. This object is achieved by means of the process according to the present invention for preparing α-bromo-acyl fluorides of formula R¹-CFBr-COF wherein: R¹ is a fluorine atom or a perfluoroalkyl radical R F containing from 1 to 10 carbon atoms. This process is characterized in that a perfluoroepoxide of formula is reacted, in the presence of activated charcoal, with a trialkyl-silyl bromide of formula wherein R², R³ and R⁴, the same or different from each other, are alkyl groups containing from 1 to 8 carbon atoms. The above reaction may be represented as follows: The reaction temperature generally is within the range of from -100° to +150°C. The reaction is preferably carried out under a pressure between atmospheric pressure and 5 atm. The molar ratio of trialkyl-silyl bromide to perfluoroepoxide generally ranges from 0.5 to 2. Preferably, said ratio is from 0.9 to 1.1. As far as the amount of activated charcoal is concerned, good results may be obtained, for instance, with a weight ratio of activated charcoal to epoxide (calculated as hexafluoropropene oxide) within the range of from 0.1 to 100. The reaction can be carried out in a solvent medium, in particular in a chlorofluorocarbon solvent such as, e.g., CFCl₃, CF₂Cl₂ or CF₃-CF₂Cl. In the perfluoroepoxide used as the starting compound, the R¹ group preferably is a fluorine atom or a perfluoroalkyl radical R F of from 1 to 5 carbon atoms. The most preferred epoxides are: and In the trialkyl-silyl bromide used as the starting material, R², R³ and R⁴ preferably are -CH₃, -C₂H₅ or -C₃H₇ groups. The three groups R², R³ and R⁴ usually are identical. The α-bromo-acyl fluorides obtainable by means of the process according to the present invention are highly valuable intermediates. By fluorination, they can be converted into the corresponding fluoro-oxy-compounds of formula R¹-CFBr-CF₂OF which can react with CFCl=CFCl to yield ethers of formula R¹-CFBr-CF₂O-CFCl-CF₂Cl which, by de-chlorination, yield fluoro-bromo-alkyl-vinyl ethers of formula R¹-CFBr-CF₂O-CF=CF₂ The latter compounds are suitable for use as comonomers in polymerization reactions with fluorinated monomers. In the copolymer obtained, the bromine atoms may serve as sites for crosslinking. The fluorination of the α-bromo-acyl fluoride can be carried out, e.g., according to the process of EP-A-194,862, and the reaction of the fluorooxy-compound obtained with CFCl=CFCl can be carried out, e.g., according to the process disclosed in EP-A-201,871. When the present invention is practiced at an industrial level, a gaseous stream of both reactants often is advantageously passed over a layer of activated charcoal. The following examples are given for illustrative purposes only. Example 1 A reactor of 250 ml capacity was charged with 3.2 g of activated charcoal. The reactor was cooled down to -196°C and 5 mmol of were introduced. Thereafter, 5.2 mmol of (C₂H₅)₃SiBr were added. The reactor was allowed to reach room temperature within 14 hours wehreafter it was cooled down to -196°C and its content was distilled under vacuum through a line containing traps kept at -60°C and -196°C. (C₂H₅)₃SiF was collected inside the trap at -60°C, and in the trap at -196°C 4.7 mmol of CF₃CFBrCOF were collected. This corresponds to a yield of 94%, based on hexafluoropropene oxide. Example 2 A gas containing tetrafluoroethylene epoxide was bubbled, at a rate of 10 l/h, into 50 ml of trichlorofluoromethane cooled at -78°C and containing 12.5 g of (CH₃)₃SiBr and 15 g of charcoal powder previously dried at 400°C in a N₂ stream. The gas composition was: 16% C₂F₄O; 59% C₂F₄; 14% COF₂; 11% O₂. The main part of C₂F₄O and C₂F₄ condensed in the liquid phase while most of the O₂ and COF₂ escaped with the gases. After 2 hrs the stream was interrupted and the mixture was stirred at -78°C for additional 20 hrs. The slurry was then warmed to 0°C and degassed. A sample of the slurry, diluted in carbon tetrachloride, was analysed by NMR, revealing the presence of CF₂BrCOF beside some CF₂BrCOBr (¹⁹F NMR signals at +64 ppm and +60 ppm referred to CFCl₃). By distillation 6.5 g of CF₂BrCOF (yield 57% referred to C₂F₄O) were recovered.

Claims: Process for preparing α-bromo-acyl fluorides of formula R¹-CFBr-COF wherein: R¹ is a fluorine atom or a perfluoroalkyl radical R F containing from 1 to 10 carbon atoms, characterized in that a perfluoroepoxide of formula is reacted, in the presence of activated charcoal, with a trialkyl-silyl bromide of formula wherein R², R³ and R⁴, the same or different from each other, are alkyl groups containing from 1 to 8 carbon atoms. Process according to claim 1, characterized in that the reaction is carried out at a temperature of from -100° to +150°C. Process according to any one of claims 1 and 2, characterized in that in the perfluoroepoxide used as the starting compound R¹ is a fluorine atom or a perfluoroalkyl radical R F of from 1 to 5 carbon atoms. Process according to claim 3, characterized in that in the perfluoroepoxide used as the starting compound R¹ is a fluorine atom or a -CF₃ radical. Process according to one or more of the preceding claims, characterized in that in the trialkyl-silyl bromide used as the starting compound the radicals R², R³ and R⁴ are -CH₃, -C₂H₅ or -C₃H₇ groups.

Inventors: DESMARTEAU DARRYL D DR C O CLE, GREGORIO GUGLIELMO DR, NAVARRINI WALTER DR, DESMARTEAU, DARRYL D., DR., C/O CLEMSON UNIV., GREGORIO, GUGLIELMO, DR., NAVARRINI, WALTER, DR.
Applicants: AUSIMONT SPA, AUSIMONT S.P.A.
Application year: 1990
Main classification: C07C53
IPC codes: B01J21, C07C53, C07C51, C07B61