Studies on the Synthesis of Aromatic Tetracarboxylic Acid (Part 1)

A method for synthesizing pyromellitic acid by liquid phase air oxidation of durene was studied. The air oxidation of durene was carried out in glacial acetic acid, using Co(OAc)2•4H2O, Mn(OAc)2•4H2O and KBr as catalysts, at the reaction temperature of 205-210°C and the total pressure of 20kg/cm2•G. The solid materials obtained by the oxidation were recrystallized into pyromellitic acid in an aqueous solution of nitric acid. The following results were obtained.(1) Cobalt and manganese used as catalysts were found, after oxidation, as salts in the solid material and had to be removed by treating with mineral acid to obtain pyromellitic acid.(2) The oxidation of durene into pyromellitic acid required a far larger amount of catalysts than the oxidation of p-xylene into terephthalic acid.(3) In the presence of heavy metal component, bromine component in the catalysts accelerated the latter stage of the oxidation, thereby promoting the formation of pyromellitic acid.(4) Bromine component in the catalysts suppressed the deactivation of heavy metal caused by the oxidation product.(5) Pyromellitic acid was produced from durene with the maximum yield of about 90mol%.