GB802117A - Improvements relating to the production of benzoic acid - Google Patents

Abstract

Pure benzoic acid is prepared by oxidizing toluene, subjecting the oxidation product to a fractional distillation to remove unreacted toluene, extracting this residue with water at a temperature between 95 DEG and 100 DEG C., filtering the solution free from residue and mildly oxidizing the solution of benzoic acid prior to crystallization. The fractional distillation removes most of the volatile compounds in the mixture, e.g. unreacted toluene, and the extraction may then be carried out without foaming. The benzoic acid is extracted preferably at atmospheric pressure and after separation from the organic residue the solution is oxidized with a reagent such as permanganate or hypochlorite. The solution may then be treated with decolorizing charcoal and benzoic acid crystallizes out on cooling. In examples, toluene is oxidized with air and a cobalt catalyst under pressure and portions of the reaction product are purified: (a) by heating until a fusion point of 90 DEG C. is reached, extracting with water at 98 DEG C., oxidizing with potassium permanganate solution and decolorizing with charcoal; (b) by heating until the residue solidifies at 95 DEG C. and extracting counter-currently with water at 98 DEG C., then as in (a); (c) as in (b) but with further extraction and oxidizing with hypochlorite.