GB745818A - Improvements in or relating to a process for producing fluorohalo-derivatives of saturated aliphatic hydrocarbons - Google Patents

Abstract

Fluoro-chloro or bromo-substituted derivatives of methane, ethane and propane are prepared by a process wherein methane, ethane, ethylene, propane, or one of these hydrocarbons in which part of the hydrogen has been replaced by chlorine or bromine are treated, for the purpose of substituting both fluorine and chlorine or bromine for hydrogen, in the vapour phase and in the presence of a metallic halide oxidation catalyst with chlorine, bromine, hydrogen chloride, hydrogen bromide or a mixture of two or more of these and hydrogen fluoride and sufficient oxygen to form water by combination with all the hydrogen present in the hydrogen fluoride and other hydrogen halide initially present and also with that portion of the hydrogen originally combined with carbon and which becomes replaced by halogen during the rection. In a modification of the process, there is used the starting material already containing chlorine or bromine and the chlorine, bromine, hydrogen chloride or hydrogen bromide is introduced only in sufficient quantity to start and maintain the reaction, whereby fluorine only is substituted in the starting material. In both processes, the fluorine of the hydrogen fluoride replaces, not hydrogen, but chlorine or bromine in an intermediately formed chlorinated or brominated starting material. The processes are generally effected under atmospheric pressure at temperatures between 400 DEG and 500 DEG C. Fluorination may be allowed to proceed to various intermediate stages by adjustment in the amounts of reactants. The preferred catalyst is aluminium fluoride impregnated with cupric chloride and which may also contain chromic fluoride; chromic fluoride itself may be used as catalyst. In an example, methane and chlorine in equimolar amounts and air and hydrogen fluoride in 100 per cent excess are passed through a heated steel reactor containing aluminium fluoride-cupric chloride catalyst (see Group III) at 400-500 DEG C. with a contact time of 23 seconds resulting in a 30 per cent yield of difluoro dichloromethane; halving the amount of chlorine is stated to result in production of monochloro-difluoro-methane. Other reactions are described by means of equations whereby methane is converted into trichlorofluoro - methane, chloro - trifluoro - methane, monochloro - monofluoro - methane, dibromodifluoro - methane or bromo - chloro - difluoromethane; ethane or ethylene is converted into pentachloro - fluoro - ethane; monochloromethane is converted into trichloro-fluoromethane; and dichloro-methane is converted into dichloro-difluoro-methane. According to the Provisional Specification the processes may be applied to the treatment of aliphatic hydrocarbons or chlorinated, brominated or fluorinated aliphatic hydrocarbons and the proportion of hydrogen fluoride used may be so adjusted that complete fluorination may be effected and fluorocarbons produced as in the production of tetrafluoro-methane from dichloro-methane.ALSO:An aluminium fluoride catalyst impregnated with cupric chloride, useful in certain hydrofluorinations of organic compounds (see Group IV(b)), is prepared by pelleting aluminium silicofluoride containing 9 per cent sodium chloride and heating the pellets to 950 DEG C., whereby silicon tetrafluoride is set free, and then impregnating the pellets with a saturated solution of cupric chloride and drying. The catalyst may also contain chromic fluoride as a promotor.