GB976316A - Process for preparing fluorinated perhalo compounds - Google Patents

Abstract

An activated anhydrous chromium (III) oxide is produced by dehydrating, at 400 DEG to 600 DEG C. in an inert atmosphere, the gel obtained by reducing chromium trioxide in aqueous solution with, for example, ethanol; the commercial pigment Guignet's Green (C2O3.2H2O); or the material obtained by precipitating water-soluble chromium salts from aqueous solution with alkaline hydroxides. The oxide is employed as a catalyst in the fluorination of perhalo compounds (see Division C2). Specifications 686,678, 720,091, 720,118, 794,075 and U.S.A. Specifications 2,271,356, and 2,807,646 are referred to.ALSO:Perhalo compounds, wherein at least one of the halogen atoms is fluorine, are produced by passing a vapour mixture of a perhaloacetone, a perhaloacetonitrile or a perhaloacetylhalide, in which perhalo reactant the halogens are chlorine or fluorine, at least one of the hydrogen atoms being chlorine, and at least one mole for each mole of the perhalo reactant of anhydrous hydrogen fluoride over a catalyst which consists essentially of an activated anhydrous chromium (III) oxide (see Division C1) at 200 DEG to 500 DEG C. such that the principal reaction is the substitution of fluorine for at least one of the chlorine atoms in the perhalo reactant. The hydrogen fluoride is usually employed in excess of the stoichiometric amount required since the degree of fluorination is primarily dependent upon the reaction temperature and flow rates. The perhalo products are separated from excess hydrogen fluoride and the hydrogen chloride produced by distillation but the perhaloacetone products must then be recovered from hydrogen fluoride complexes by passage over activated sodium fluoride. Perhalofluoacetic acid may be obtained from the perhalo products, e.g. by hydrolysis of the perhaloacetylfluoride. Specifications 686,678, 720,091, 720,118, 794,075 and U.S.A. Specifications 2,271,356, 2,807,646 are referred to.