GB977475A - A process for producing a lower alkyl ester of terephthalic acid - Google Patents

Abstract

Lower alkyl esters of terephthalic acid are prepared by treating an alkali metal salt of terephthalic acid with an inorganic acid in the presence of a substantially anhydrous aliphatic alcohol having from 1 to 8 carbon atoms, to effect conversion of the alkali metal salt into free terephthalic acid and the subsequent esterification in a single operation. After completion of the reaction, the reaction mixture is filtered and the filtrate re-used, optionally after purification by distillation. The filtration residue, which includes the lower alkyl ester and the alkali metal salt of terephthalic acid, may be extracted with a suitable solvent, e.g. chloroform, nitromethane, acetone or methanol or mixtures thereof, to separate the lower alkyl ester as the extracted mass and the alkali metal salt as the extraction residue. Alternatively the filtration residue may be treated with a small amount of hot water at a temperature up to 40 DEG C., whereby the lower alkyl ester of terephthalic acid is recovered as undissolved material and the alkali metal salt of the used acid as the concentrated aqueous solution. The alkali metal salt of terephthalic acid is advantageously disodium or dipotassium terephthalate or a mixture of both. Such starting material may contain impurities including cadmium oxide, lead oxide, zinc oxide, inorganic salts and carbonaceous compounds. Preferably the inorganic acid used in the process is HCl or H2SO4 or a mixture of both, and may be used in an amount of 1 to 4 parts by weight per part by weight of the acid salt. The alcohol is preferably used in an amount of 2 to 9 parts by weight per part by weight of the acid salt. The reaction temperature is approximately the boiling point of the lower aliphatic alcohols and pressures may range from normal atmospheric to 3 atmospheres.