Purification of terephthalic acid

Terephthalic acid purified by recrystallisation from an organic solvent by dissolving the acid at 50-250 DEG C., cooling the solution and separating the precipitated acid, the solvent being a lactone containing 5-9 ring atoms, a nitrogen free cyclic ether containing 5-6 ring atoms or a nitrogen free substituted derivative thereof or a mixture of water and at least one of the aforementioned solvents. The purification is applicable to an acid obtained by any method, particularly to acid obtained by nitric acid or air oxidation of disubstituted benzenes. Solvents p mentioned are butyric, valeric, caproic and caprylic lactones and furans, pyrans, dioxans and their alkoxy, hydroxy and methyl substituted derivatives. The preferred solvents are the aqueous mixtures containing approximately equimolar proportions. The crude acid is preferably dissolved in about 15-40 parts by weight of solvent by heating to reflux, the hot solution treated with activated carbon and the purified acid precipitated, if necessary after concentration and addition of numeral acids. Examples are given.