GB756027A - Process for the manufacture of fluorine-containing unsaturated aliphatic hydrocarbons - Google Patents

Abstract

Fluorine-containing aliphatic hydrocarbons are made by reacting at least the theoretical proportion of finely-divided iron with a saturated aliphatic hydrocarbon - containing fluorine and at least two atoms of another halogen bound to vicinal carbon atoms in the presence of a solvent and at a raised temperature to eliminate at least 2 atoms of halogen (other than fluorine) from the saturated hydrocarbon. Raised pressure may be used, e.g. by the introduction of nitrogen under pressure. Pressures of about 10-200 atmospheres are mentioned. Advantageously a small proportion of finely-divided zinc may be added so that the reaction starts at a lower temperature and the fluorine-containing unsaturated hydrocarbon formed produces the required pressure. The reaction is advantageously effected at the vapour pressure of the reactant at the reaction temperature. Temperatures of about 90-200 DEG , especially about 130 DEG C., are indicated although with iron of high activity the temperature may be about 80 DEG C. Advantageously, an excess of about 40 per cent of the theoretical quantity of iron is added. The quantity of zinc added may be up to about 10 per cent of the theoretical. When a small quantity of zinc is used less than the theoretical quantity of iron may be present but the total quantity of iron and zinc should be sufficient to remove at least 2 atoms of halogen from the saturated hydrocarbons. Specified solvents are methanol, ethanol, propanol, isopropanol, butanol, isobutanol, benzyl alcohol and acetamide. Preferably, the solvent should be capable of dissolving the starting material and FeHal2 and be at least partially miscible with water. Chlorine may be eliminated from 1,2,3,4-tetrachloro-1,1,2,3,4,4-hexafluorobutane or 1,2-dichloro-1,1,2,3,3,3 - hexafluoropropane to form hexafluoro - butadiene and -propylene respectively, and bromine may be eliminated from the corresponding bromo compounds. In examples, 1,1,2 - trichloro - 1,2,2 - trifluoroethane is treated with iron powder in (1) aqueous methanol and (2) methanol under nitrogen to produce trifluoro-chlorethylene, the addition of 5 per cent of zinc based on iron being optional in (2); in (3) 1,1,2,2 - tetrachloro - 1,2 - difluorethane is treated with iron and zinc in methanol under nitrogen to yield 1,2-dichloro-1,2-difluorethylene; (4) 1,1,2 - trichloro - 2,2 - difluorethane is treated with iron and zinc in ethanol under nitrogen to yield 1-chloro-2,2-difluorethylene; and in (5) 1,2-dichloro-1,2,3,3,4,4-hexafluorocyclobutane is treated as in (4) to yield hexafluorocyclobutylene. If the last example is effected in methanol, 1-methoxy-pentafluorocyclobutylene is obtained as a by-product.