GB727989A - Improvements in or relating to the production of benzene polycarboxylic acids or derivatives thereof - Google Patents

Abstract

Benzene polycarboxylic acids and derivatives thereof are obtained by oxidizing alkyl benzenes and converting the relatively difficulty oxidizable intermediately-formed acids into esters, salts or anhydrides, which are further oxidized with oxygen or gases containing oxygen, by themselves, or in the mixtures containing them. In examples, the catalytic oxidation of methyl p-toluate with or without the catalyst and residue from a previous oxidation, methyl m-toluate, and methyl o-toluate to the corresponding mono-methyl terephthalate, isophthalate, or phthalate, the latter product also containing the acid, anhydride and diester, is described; xylene mixtures are catalytically oxidized, the mixture of acids separated is esterified with methanol, and further oxidized to give among the products mono- and di-methyl terephthalate; lead and other salts of p-toluic acid are oxidized to give isophthalic salts; m-toluic anhydride and p-toluic anhydride oxidized similarly give iso- and terephthalic acids, isolated by converting into their methyl esters; pseudo-cumene is oxidized, the acid product esterified and further oxidized, the process being repeated with the residues, mixed with fresh hydrocarbon, the products being repeatedly esterified, and oxidized to give as a final product trimellitic acid trimethyl ester. The acid oxidation products may be esterified with alcohols of up to 4 carbons, and with aromatic alcohols, especially those which on further oxidation give the same carboxylic acid group as the initial acid; all residues may be re-cycled.