Manufacture of salts of terephthalic acid

Alkali metal terephthalates are prepared by heating an alkali metal salt of pyromellitic acid to an elevated temperature in the presence of water. The preferred salt is the tetrapotassium salt although the sodium, lithium or rubidium salts may be used. The water may be formed in situ by, for example, treating the acid anhydride with the alkali metal bicarbonate. The reaction takes place in the presence of a heavy metal catalyst and the mixture is heated in the region of 425 DEG C. in an inert atmosphere such as carbon dioxide or nitrogen. The terephthalic acid may be obtained from the alkali metal salt by acidification with a mineral acid. An example describes the process using pyromellitic acid anhydride, and potassium bicarbonate with cadmium benzoate as catalyst.