Verfahren zur Herstellung von Schwefeltetrafluorid

摘要

SF4 is prepared by reacting an alkali metal fluoride with a sulphur chloride or with a mixture of (a) free chlorine and free sulphur, (b) free chlorine and a sulphur chloride, or (c) free chlorine and an anhydrous binary sulphide which under the rection conditions acts as a source of sulphur or sulphur chloride. Preferably the reaction mixture comprises, in addition to the alkali metal fluoride, free sulphur and free chlorine or the compounds S2Cl2 or SCl2 with or without additional chlorine. Certain anhydrous binary sulphides, e.g. sulphides of the alkali metals preferably Na or K, sulphides of Group II metals, e.g. CaS, BaS, and ZnS or Fe, Co, or Ni sulphides, for example FeS, which form sulphur or a sulphur chloride when mixed with chlorine under reaction conditions may also constitute reaction mixtures with the alkali metal fluoride and free chlorine. The alkali metal fluorides preferably NaF and KF may be in 5-50% molar excess of the stoichiometric amount required. The Cl : S atom ratio of the reactants should be at least 1 : 1 preferably at least 2 : 1. The process may be carried out in the absence of any diluent or in any inert organic liquid medium having a dielectric constant of less than 20 at 20 DEG C., e.g. perfluorinated hydrocarbons, for example perfluoro-n-heptane, perfluoro-n-decane and perfluoro-(methyl cyclohexane), but preferably in an inert organic liquid medium, having a dielectric constant greater than 20 at 20 DEG C., which contains only C and H and one of the functional groups -O-SO2-O- of which a number of specified, e.g. acetonitrile or dimethyformamide. The reaction media should preferably be miscible with Cl2 or chlorine-containing reactants and be used in a proportion at least equal to the weight of alkali metal fluoride present. In the absence of a diluent or in the presence of a diluent of low dielectric constant the reaction temperature is 150-250 DEG C. depending on the alkali metal fluoride employed. When using S2Cl2 or Sel2 the reaction may be carried out under atmospheric pressure whereas otherwise the reaction is carried out in an autoclave under autogenous pressure. Reaction temperatures, when using high dielectric constant media range from 20- 150 DEG C. and pressures of rear atmospheric are employed. SF4 is removed from the reaction products, e.g. S2Cl2, Sel2 and thionyl chloride, by evaporation and fractional distillation. Any SF6 present in the products is removed by fractional distillation or by contacting the reaction mixture with a tertiary amine, e.g. pyridine or triethylamine at 100 DEG C. whereby SF4 forms as a solid adduct which may be separated and the purified SF4 recovered by dissociation. Specification 758,477, [Group IV (b)], is referred to.