GB211167A - Manufacture of acetic anhydride - Google Patents

Abstract

Acetic anhydride is prepared by reacting on glacial acetic acid with chlorine together with sulphur or sulphur chloride, the proportions of the reactants being such that for each atom of sulphur, four atoms of chlorine and at least four molecules of acetic acid are present. The chlorine may be employed under pressure. Chlorine is led into a mixture of the calculated proportions of sulphur chloride and acetic acid whilst cooling and stirring until the sulphurchlorine ratio of 1 : 4 is attained; the mixture is then heated and the acetic anhydride finally separated by distillation at ordinary or reduced pressure. Escaping sulphur chloride, as well as any acetyl chloride formed, are recovered by passing the vapours into acetic acid, which is then used as the parent material; the loss of sulphur chloride during the reaction must be made good. If elementary sulphur be employed instead of sulphur chloride, it is suspended in the finely-divided state in the acetic acid. The process may be operated in a continuous manner by treating the mixture of acetic acid and sulphur chloride or sulphur in an irrigation apparatus with a countercurrent of chlorine while cooling, and leading the reaction product continuously to a distilling apparatus. By using excess of acetic acid, a mixture of acetic anhydride and acetic acid results.