GB2119800A

GB2119800A - Process for preparing hexafluoroisobutene and/or hexafluorobutene

Info

Publication number: GB2119800A
Application number: GB08312572A
Authority: GB
Inventors: Yohnosuke Ohsaka; Yoshio Aminoto; Shoji Takagi
Original assignee: Daikin Industries Ltd; Daikin Kogyo Co Ltd
Current assignee: Daikin Industries Ltd
Priority date: 1982-05-10
Filing date: 1983-05-06
Publication date: 1983-11-23
Also published as: JPS6052133B2; GB2119800B; JPS58194826A; DE3316227A1; DE3316227C2; GB8312572D0

Abstract

Hexafluoroisobutene and/or hexafluorobutene are prepared in a simple process comprising reacting hexafluoropropene and methyl halide.

Description

SPECIFICATION Process for preparing hexafluoroisobutene and/or hexafluorobutene The present invention relates to a process for preparing hexafluoroisobutene and/or hexafluorobutene. More particularly, it relates to a process for preparing 2-trifluoromethyl-3,3,3 trifluoro-1 -propene and/or 2,3,3,4,4,4hexafluoro-1 -butene from hexafluoropropene.

Hexafluoroisobutene is known to be copolymerizable with vinylidene fluoride to afford a vinylidene fluoride/hexafluoroisobutene alternating copolymer having excellent heat resistance (Japanese Patent Publication (unexamined) No. 1 50790/1975). It is also known to be useful as a modifier of an ethylene/tetrafluoroethylene or chlorofluoroethylene copolymer, to improve the physical properties of the copolymer (Japanese Patent Publication (unexamined) No.

14791/1975). Hexafluorobutene may be used as a monomer copolymerizable with other fluoromonomers.

There are known several processes for the preparation of hexafluoroisobutene, including a process comprising pyrolysing hexafluoroacetone together with acetic anhydride or ketene (cf.

Japanese Patent Publication (unexamined) No.

142504/1975) and a process comprising dehydrogenfluorinating octafluoroisobutyl lower alkyl ether to obtain heptafluoroisobutenyl lower alkyl ether, reducing and sulfuric esterifying heptafluoroisobutenyl lower alkyl ether, and then treating the obtained sulfate with a base to obtain hexafluoroisobutene (Japanese Patent Publication (unexamined) No. 138127/1981).

However, the former process has several drawbacks such that hexafluoroacetone, to be used as one of the starting materials, is very expensive, and violent reaction conditions are required to pyrolyse it. The latter process has also drawbacks, such that it comprises many reaction steps and therefore needs many kinds of reagents, many facilitates and longer reaction time.

As a result of the extensive study on the commercially advantageous preparation of hexafluoroisobutene and/or hexafluorobutene, it has now been found that these compounds can be easily prepared by reacting hexafluoropropene and methyl halide.

According to the present invention, there is provided a process for preparing hexafluoroisobutene and/or hexafluorobutene comprising reacting hexafluoropropene and methyl halide.

Hexafluoropropene to be used as a starting material in the process of the invention is commercially produced so that it is readily supplied and very economical.

The specific examples of methyl halide are methyl fluoride, methyl chloride, methyl bromide and methyl iodide.

The molar ratio of hexafluoropropene and methyl halide is from 1:0.2 to 1 :5, preferably 1:1 to 1:3. When the amount of methyl halide is less than the given range, the yields of the desired products is lowered. When methyl halide is used in an amount more than the range, the losses of the raw material and of the heating energy is larger while the yield of the desired products are not improved.

The reaction temperature is generally from 400 to 8000C, preferably from 550 to 7000C. At a temperature lower than 4000C, the desired products are not obtained in good yields. At a temperature higher than 8000 C, yields of highly toxic by-products such as (CF3)2=CF2 are larger.

The reaction of the invention may be carried out under reduced or elevated pressure. Usually, the reaction pressure may be from 0.5 to 5 atm.

The reaction time depends on the reaction mode to be employed and/or the reaction temperature and may be usually from 1 second to 1 hour.

The reaction of the invention may be carried out batchwise or continuously.

The produced hexafluoroisobutene and hexafluorobutene may be isolated from the reaction mixture by a per se conventional method such as distillation. However, since these two compounds have close boiling points, the compounds are recovered as a mixture thereof. In order to separate two compounds, the mixture is, therefore, reacted with bromine or chlorine to convert hexafluorobutene into its halide, having a high boiling point, which can be easily separated, for example, by distillation from hexafluoroisobutene which does not react with bromine or chlorine. The halide of hexafluorobutene may be reconverted to hexafluorobutene by dehalogenating the halide, for example, with zinc.

The present invention will be hereinafter explained further in detail by the following Examples wherein % is by weight unless otherwise indicated.

Example 1 In a Hastelloy C (trade mark) made reactor of 19 mm inner diameter and 70 cm in length, about 1 5 cm of which was kept at a temperature of 600"C or more in a vertical type electric furnace having heating length of 50 cm, hexafluoropropene and methyl chloride were charged each at a rate of 20 ml/min for 5 hours.

The exhausted gas was washed with water dried with calcium chloride and trapped by a condenser cooled in a dry ice-acetone bath to obtain a product mixture (46 g). The trapped mixture was subjected to NMR, mass spectroscopy, IR and GLC analyses. Composition of the mixture: CF3CF=CF2, 21.5%; CH3Cl, 6.2%; (CH3)2C=CH2, 37.5%; CF3CF2CF=CH2, 1 5.8%. Conversion of hexafluoropropene, 75.4%. Selectivity of hexafluoroisobutene, 50.6%.

Selectivity of hexafluorobutene, 21.3%.

Example 2 In the same manner as in Example 1 but using methyl bromide in place of methyl chloride, the reaction was carried out to obtain the mixture containing hexafluoroisobutene and hexafluorobutene which were identified by the same analyses as in Example 1.

Example 3 In the same manner as in Example 1 but using methyl fluoride in place of methyl chloride, the reaction was carried out to obtain the mixture containing hexafluoroisobutene and hexafluorobutene which were identified by the same analyses as in Example 1.

Claims

1. A process for preparing hexafluoroisobutene and/or hexafluorobutene, which comprises reacting hexafluoropropene and a methyl halide.

2. A process according to claim 1, wherein the reaction temperature is from 400 to 800at.

3. A process according to claim 1 or claim 2, wherein the molar ratio of hexafluoropropene and methyl halide is from 1:0.2 to 1:5.

4. A process according to any preceding claim, in which a mixture of hexafluoroisobutene and hexafluorobutene is obtained, which further comprises reacting the mixture with bromine or chlorine to convert the hexafluorobutene into a relatively high-boiling halide, separating the halide from the hexafiuoroisobutene by distillation, and then dehalogenating the halide to reconvert it into hexafluorobutene.

5. A process according to claim 1, substantially as described in any of the Examples.