Method for preparing polyunsaturated perfluorinated compounds

Abstract

The present invention relates to a method for preparing a polyinsaturated perfluorinated compound B from a polyinsaturated perhalogenated compound D having the formula C.sub.nX.sub.2(nm+1), in which X is independently selected from one of the halogens, F, Cl, Br or I, provided at least one X is not fluorine; n is the number of carbon atoms and is at least higher than or equal to 4, m is the number of double carbon-carbon bonds and is higher than or equal to 2, wherein the method comprises a step in which compound D is fluorinated in the presence of a fluorinating agent of general formula AF.sub.p, in which A is hydrogen, an alkali metal or an alkaline earth metal, and p is 1 or 2, and in the presence of an aprotic organic polar solvent; the method being carried out with a molar ratio of AF.sub.p to compound D of less than 1.45*2(nm+1).

Claims

1. A process for preparing a polyunsaturated perfluorinated compound B from a polyunsaturated perhalogenated compound D of formula C.sub.nX.sub.2(nm+1) wherein X is chosen independently from a halogen F, CI, Br or I, provided that at least one X is not a fluorine; n is the number of carbon atoms and is at least greater than or equal to 4; m is the number of carbon-carbon double bonds and is greater than or equal to 2; said process comprising the step of fluorinating the compound D in the presence of a fluorinating agent of general formula AF.sub.p wherein A is hydrogen, an alkali metal or an alkaline-earth metal, and p is 1 or 2; and in the presence of an aprotic polar organic solvent; said process being carried out with an AF.sub.p/compound D molar ratio of less than 1.30*2(nm+1).

2. The process as claimed in claim 1, wherein the compound D is a polyunsaturated perchlorinated compound of formula C.sub.nCl.sub.2(nm+1).

3. The process as claimed in claim 1, wherein the compound D is hexachlorobutadiene.

4. The process as claimed in claim 1, wherein the compound B is hexafluorobutadiene.

5. The process as claimed in claim 1, wherein the AF.sub.p/compound D molar ratio is less than 1.15*2(nm+1).

6. The process as claimed in claim 1, wherein the fluorinating agent is LiF, KF, NaF, MgF.sub.2 or CaF.sub.2.

7. The process as claimed in claim 1, wherein the aprotic polar organic solvent is chosen from the group consisting of an ether, an amide, an amine, a sulfoxide, a ketone, a nitrile and an ester.

8. The process as claimed in claim 1, wherein the aprotic polar organic solvent is chosen from the group consisting of 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, tetrahydrofuran, 1,2-dimethoxyethane, dimethyl sulfoxide, diethyl sulfoxide, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, ethyl acetate, acetone, propanone, 2-pentanone, butanone, n-butyl acetate, triethylamine, pyridine and acetonitrile.

9. The process as claimed in claim 1, wherein a first stream comprising the compound B, coproducts of the fluorination reaction and optionally of the unreacted compound D is recovered and separated by distillation so as to form a second stream comprising the coproducts of the reaction and the unreacted compound D and a third stream comprising the compound B.

10. The process as claimed in claim 1, wherein a first stream comprising the compound B, coproducts of the fluorination reaction and unreacted compound D is recovered, and wherein a compound of formula AX.sub.p is formed and the unreacted compound D is separated from the compound of formula AX.sub.p.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) According to a first aspect, the present invention provides a process for preparing a polyunsaturated perfluorinated compound B. Advantageously, said polyunsaturated perfluorinated compound B can be obtained from a polyunsaturated perhalogenated compound D of formula C.sub.nX.sub.2(nm+1) wherein: X is chosen independently from a halogen F, Cl, Br or I, provided that at least one X is not a fluorine; n is the number of carbon atoms and is at least greater than or equal to 4; m is the number of carbon-carbon double bonds and is greater than or equal to 2.

(2) According to one preferred embodiment, said process comprises a step of fluorinating the compound D in the presence of a fluorinating agent.

(3) Preferably, the fluorinating agent has the general formula AF.sub.p wherein A is hydrogen, an alkali metal or an alkaline-earth metal, and p is 1 or 2.

(4) According to one preferred embodiment, the step of fluorinating the compound D is carried out in the presence of an aprotic polar organic solvent.

(5) Thus, according to one preferred embodiment, the process according to the invention comprises a step of fluorinating the compound D in the presence of a fluorinating agent of general formula AF.sub.p wherein A is hydrogen, an alkali metal or an alkaline-earth metal, and p is 1 or 2; in the presence of an aprotic polar organic solvent.

(6) Preferably, the step of fluorinating the compound D is carried out with an AF.sub.p/compound D molar ratio of less than 1.45*2(nm+1).

(7) Thus, said process according to the present invention comprises a step of fluorinating the compound D in the presence of a fluorinating agent of general formula AF.sub.p wherein A is hydrogen, an alkali metal or an alkaline-earth metal, and p is 1 or 2; in the presence of an aprotic polar organic solvent; the AF.sub.p/compound D molar ratio being less than 1.45*2(nm+1).

(8) According to one preferred embodiment, the compound D is a compound of polyunsaturated perchlorinated type of formula C.sub.nCl.sub.2(nm+1). Preferably, the compound D is hexachlorobutadiene.

(9) According to one embodiment, the compound B may be perfluorohexatriene or hexafluorobutadiene. Preferably, the compound B is hexafluorobutadiene.

(10) According to one preferred embodiment, the AF.sub.p/compound D molar ratio is less than 1.40*2(nm+1); advantageously less than 1.30*2(nm+1), preferably less than 1.25*2(nm+1), more preferentially less than 1.15*2(nm+1), in particular 1.10*2(nm+1). This molar ratio close to the stoichiometry allows complete fluorination of the compound D contrary to what is known from the prior art.

(11) Preferably, the fluorinating agent is LiF, KF, NaF, MgF.sub.2 or CaF.sub.2 or a mixture thereof. Preferably, the fluorinating agent is potassium fluoride KF.

(12) According to one particular embodiment, the aprotic polar organic solvent is chosen from the group consisting of an ether, an amide, an amine, a sulfoxide, a ketone, a nitrile and an ester.

(13) Advantageously, the aprotic polar organic solvent is chosen from the group consisting of 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, tetrahydrofuran, 1,2-dimethoxyethane, dimethyl sulfoxide, diethyl sulfoxide, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, ethyl acetate, acetone, propanone, 2-pentanone, butanone, n-butyl acetate, triethylamine, pyridine and acetonitrile.

(14) Preferably, the aprotic polar organic solvent has a boiling point of greater than 100 C. at atmospheric pressure.

(15) Thus, preferably, the aprotic polar organic solvent is 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, propanone, 2-pentanone, butanone, dimethyl sulfoxide or diethyl sulfoxide.

(16) In particular, the aprotic polar organic solvent is chosen from the group consisting of 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, dimethylformamide and dimethyl sulfoxide.

(17) According to a preferred embodiment, the fluorinating step is carried out at the reflux of the solvent.

(18) According to one preferred embodiment, the fluorinating step is carried out for a period of between 1 hour and 10 hours.

(19) According to one preferred embodiment, a stream comprising the compound B is recovered and separated by distillation from the coproducts of the reaction and the unreacted compound D.

(20) Preferably, the coproducts have the formula C.sub.nX.sub.2(nm+1) as defined by the present application, wherein at least one X is not a fluorine. The coproducts of the reaction can comprise monochloropentafluorinated compounds of formula C.sub.4F.sub.5Cl, and dichlorotetrafluorinated compounds of formula C.sub.4F.sub.4Cl.sub.2.

(21) According to one preferred embodiment, a compound of formula AX.sub.p is formed during the fluorinating step, A, X and p being as defined above. Advantageously, the unreacted compound D is separated from this compound AX.sub.p and then recycled so as to be used again in the fluorinating step of the present process. Said compound AX.sub.p may be KCl, LiCl, NaCl, MgCl.sub.2 or CaCl.sub.2.

EXAMPLE

(22) The fluorinating step is carried out in a glass reactor fitted with a jacket, wherein a thermofluid regulated at the temperature T1 circulates, with a stirrer and with a thermometer and surmounted by a vertical condenser. The vertical condenser is cooled to a temperature T2 of 4 C. The condenser is connected to a stainless steel gas bottle cooled by dry ice. The following are introduced into the reactor: 500 ml of dimethylformamide; 87 g of hexachlorobutadiene (0.33 mol); 120 g of anhydrous potassium fluoride (6.2 mol) pre-milled and dried.

(23) The reaction mixture is stirred and is brought to reflux over the course of 30 min, thus regulating the temperature T1 of the thermofluid circulating in the jacket of the reactor at 165 C. The starting product, the coproducts of the reaction and the solvent are at reflux, while only the C.sub.4F.sub.6 hexafluorobutadiene passes through the condenser. The latter is recovered by condensation in the dry ice trap. The reaction is stopped after 6 hours. 29 g of hexafluorobutadiene, measured by GC to be 99% pure, are recovered.