GB748276A - Manufacture of iso-and tere-phthalic acids - Google Patents

Abstract

A modification of the processes claimed in the parent Specification and 735,074 is characterized in that the para-xylene is replaced by meta-xylene or by a mixture of metaxylene and para-xylene so that isophthalic acid or a mixture of isophthalic acid and terephthalic acid is obtained and that any catalyst which has been proposed for the catalytic liquid phase oxidation of alkyl benzenes to the corresponding carboxylic acids is used in the process for the oxidation of the meta-xylene or mixture of meta-xylene and para-xylene with oxygen, air or other mixture of gases containing oxygen. Catalysts mentioned include oxides of cobalt, lead, barium, iron, manganese, chromium, copper and nickel or salts of the same metals and in particular suitable metals of which the oxides or salts may be used are to be found in Period 4, Groups 6, 7 and 8 of the Periodic Table of the elements. The catalyst should preferably be soluble in meta-xylene or in the mixture of meta- and para-xylenes. The mixture of acids may be separated into the two acids, e.g. by esterification with methanol and separation of the mixed esters by recrystallization from a suitable solvent, e.g. methanol, or the mixture of acids may be used in the manufacture of alkyd resins or fibre-forming or other polyamides. In examples: isophthalic acid containing some toluic acid is obtained by oxidizing meta-xylene in the presence of cobalt naphthenate with air at elevated temperature, distilling unreacted xylene from the reaction product and heating the residue consisting essentially of meta-toluic acid, isophthalic acid and meta-xylyl-meta-toluate with dilute nitric acid under pressure (1) and in a similar process a mixture of terephthalic, isophthalic, para-toluic and meta-toluic acids is obtained from a mixture of para-xylene and meta-xylene, the products being esterified with and the esters recrystallized from methanol (2). After the removal of dimethyl terephthalate the residue is fractionated to obtain dimethyl isophthalate and a mixture of methyl-para-toluate and methyl-meta-toluate and the latter mixture is oxidized with air to obtain a mixture of methyl hydrogen terephthalate and isophthalate.