Manufacture of terephthalic acid

A modification of the process for the manufacture of terephthalic acid claimed in the parent Specification, characterized in that in the initial oxidation of p-xylene an oxidation catalyst other than an oil-soluble compound of cobalt is used. Any catalyst that has been proposed for the catalytic liquid phase oxidation of alkyl benzenes to the corresponding carboxylic acids may be used those mentioned being metal oxides and salts, e.g. cobalt oxide, lead oxide, barium oxide, iron oxide, manganese oxide, chromium oxide, copper oxide, nickel oxide or salts of the same metals. Mixtures of these oxides or salts may be used as well as mixtures of these catalysts with an oil soluble compound of cobalt. Especially 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. In examples, air is passed through heated p-xylene containing as catalyst chromium naphthenate (1); nickel naphthenate (2); or both cobalt and nickel naphthenate (3). The reaction mixture is distilled to obtain a residual solid containing terephthalic acid and p-toluic acid which is heated with dilute nitric acid under pressure to obtain terephthalic acid.