Production of terephthalic and isophthalic acids

Isophthalic and/or terephthalic acids are prepared by heating ammonium isophthalate and/or ammonium terephthalate to a temperature at which ammonia is evolved and continuously removing the evolved ammonia. The salt may be heated to 140-250 DEG C. in the dry state or suspended in an inert liquid such as kerosene or diisopropylbenzene or dissolved in an inert solvent or partial solvent such as water. The mixture is agitated and the liberated ammonia removed by passing an inert gas such as hydrogen, nitrogen, carbon dioxide or steam through the reaction mixture. The reaction may be carried out at normal, above or below atmospheric pressure and at super-atmospheric pressures the reaction may be carried out in the presence of a volatile liquid such as water which provides its vapour as the inert gas. In examples: (i) diammonium isophthalate is heated dry and with diisopropylbenzene at 180 DEG and 196 DEG C. respectively in the presence of nitrogen; (ii) as (i) using diammonium terephthalate; (iii) diammonium iso-phthalate is heated at 180 DEG C. in the presence of paraffin with nitrogen as the inert gas.