GB901271A - Ester preparation - Google Patents

Abstract

Methyl esters of aromatic polycarboxylic acids are produced by mixing a polyalkyl aromatic hydrocarbon (wherein the alkyl groups contain 1 to 4 carbon atoms) with a molar excess of methanol, and reacting the mixture with molecular oxygen, e.g. in the form of air, in the presence of a catalyst comprising a salt of a polyvalent metal; the reaction being carried out at a temperature of at least 140 DEG C. and under pressure-conditions (200 to 1000 p.s.i.g.) so that the methanol is maintained to a maximum extent in the liquid phase. Preferably 1.5 to 3 mols of methanol should be used per mol-equivalent of alkyl groups to be oxidised. All the methanol need not be added to the fresh feed, but some of it may be introduced during the course of the reaction. The following polyalkyl hydrocarbons may be used as starting materials:-the xylenes, mesitylene, durene, pentamethylbenzene, hexamethylbenzene, the corresponding ethyl-, propyl- and butyl-benzenes, and polyalkyl-substituted di- and tri-benzyls. Suitable catalysts are the naphthenates, acetates, bromides and chlorides of cobalt and manganese. Promoters such as hydrobromic acid, hydrochloric acid, or sulphuric acid may be added. The Specification includes two flow-sheets, one of which illustrates the production of a mixture of dimethyl terephthalate and monomethyl terephthalate by a continuous two-stage process starting with p-xylene. The mixture is then submitted to a conventional esterification process whereby the monomethyl ester is converted into the diester. Example 1 describes the production of a mixture of dimethyl phthalate and monomethyl phthalate from o-xylene. Appreciable quantities of methyl orthotoluate and phthalide are obtained as by-products. Example 3 and 4 describe the production of trimethyl trimesate and dimethyl terephthalate from mesitylene and p-di-isopropyl benzene respectively.