GB793160A - A process for the esterification of isophthalic acid - Google Patents

Abstract

Diesters of isophthalic acid are prepared by heating isophthalic acid with an excess of an alcohol, in the absence of a catalyst, at elevated pressure and at a temperature of more than 150 DEG C. The product crystallizes out on cooling and the alcoholic mother liquor obtained is used for further esterification of a fresh quantity of isophthalic acid without the removal or after only partial removal of the water formed in the reaction. The alcoholic mother liquors may be used several times provided the water content remains below 30 per cent. A portion of the mother liquors may be distilled to remove some of the water and reduce the total water content to below 30 per cent. As the water content rises the amount of monoester increases and this is further esterified in the next cycle. The alcohols specified are those containing up to 4 carbon atoms, preferably methanol, and the alcohol is normally present in a 20-40 fold molar excess. An example is given where methanol mother liquors are cycled 6 times to give a yield of diester of 88 per cent and the composition of the product and the amount of water present are given after each step. A further example shows the effect on the composition of the product of increasing the water content of the reaction mixture. Specification 695,566 is referred to.