GB801567A - High-purity dimethyl terephthalate and process for its preparation - Google Patents

Abstract

Dimethyl terephthalate is made by reacting terephthalic acid with methanol in the liquid phase in the presence of an esterification catalyst at a temperature of 60 DEG to 200 DEG C., at a pressure of 0 to 750 p.s.i.g., and for a time of 0.5 to 40 hours to give substantially complete esterification, filtering the reaction medium at a temperature above that at which dimethyl terephthalate crystallizes, to remove solid impurities, cooling the filtrate to crystallize crude dimethyl terephthalate and fractionally distilling the latter at a temperature of 145 DEG to 300 DEG C. and at a pressure of 12 to 760 mm. Hg. Any or all of the steps may be conducted in a continuous, intermittent or batch manner. Small amounts of mono-methyl terephthalate obtained from the fractionation are recycled to the esterification. Esterification catalysts are sulphuric acid, toluene sulphonic acid, hydrogen chloride, lead oxide, alkane sulphonic acids, sodium methoxide and zinc oxide and zinc powder. When an acid catalyst is used, a neutralization of the reaction mixture with soda ash precedes cooling. The terephthalic acid used may be that obtained by the oxidation of a para-dialkylbenzene having 1 to 4 carbon atoms in each alkyl group. An example is given.