Thermal Transformation of Alkali Salts of Aromatic Carboxylic Acids. III

Abstract

Reactions of potassium benzoate in the presence of potassium carbonate and cyanate have been studied under various conditions. The acids formed were analyzed by vapor phase chromatography after esterification with diazomethane. Maximum yield of terephthalic acid (ca. 60%) was obtained at 380-405°C in 3 hrs and longer heating failed to improve the yield. Effects of the pressure of carbon dioxide and of the molar ratio of potassium carbonate to potassium benzoate were evident. The anion moieties of cadmium compounds did not affect the composition of the products, and the yield of terephthalic acid and the conversion of potassium benzoate were rather reduced in the presence of a large amount of potassium cyanate. In an initial stage of this reaction, considerable amounts of phthalic, isophthalic, and benzene tricarboxylic acids were formed together with terephthalic acid. The direct carboxylation of potassium benzoate with potassium carbonate in potassium cyanate was indicated from the fact that the yield of terephthalic acid was higher than that expected from the disproportionation reaction. On the other hand, in the reaction of sodium benzoate in the presence of sodium cyanate and sodium carbonate, the effect of sodium cyanate could not be demonstrated.In an initial stage of this reaction, sodium benzoate gave only sodium phthalate.