Terephthalic acid and a salt thereof

In a process for the manufacture of a potassium salt of terephthalic acid, a mixture of benzoic acid anhydride and potassium carbonate is heated to an elevated temperature above 300 DEG C., preferably above 400 DEG C., in an inert atmosphere. Catalysts mentioned include cadmium benzoate, other cadmium salts and salts of other metals, e.g. zinc. Inert atmospheres may consist of carbon dioxide or nitrogen. In an example, potassium terephthalate is obtained by heating benzoic anhydride in the presence of cadmium benzoate at 425 DEG C. under pressure rising to 200 atmospheres in an atmosphere of carbon dioxide. Terephthalic acid is obtained on acidifying the potassium salt. Specifications 744,721 and 777,609 are referred to.