GB758665A - Process for the oxidation of mono-methyl naphthalenes - Google Patents

Abstract

Monomethyl naphthalene is oxidized in the side chain by subjecting a monomethyl naphthalene in solution in a solvent comprising one or more fatty acids and containing a metallic oxidation catalyst in solution, to the action of oxygen at a temperature of from 150 DEG to 250 DEG C. with continuous removal of water formed from the reaction mixture, and recovering the resultant oxidation products. The process may be carried out at atmospheric or higher pressures. Specified solvents are fatty acids boiling below 250 DEG C.-such as acetic, propionic, butyric, isobutyric, isovaleric and caproic acids, the acids boiling between 150 DEG and 250 DEG C. being used at atmospheric or elevated pressures and those boiling below 150 DEG C. at elevated pressures. The acids form azeotropes with water and are used to remove water from the reaction mixture. The water may also be removed by a water-binding agent and the anhydrides of acetic, butyric, isobutyric and isovaleric acids are mentioned. The catalysts are organic salts such as cobalt and manganese acetates. Either a - or b -methyl naphthalene or a mixture of isomers may be used, and the material must be free of sulphur or sulphur compounds. The products are naphthoic acid, naphthaldehyde, naphthyl-methyl-naphthoate and, since the solvent is a fatty acid, the naphthyl-methyl ester thereof. These products may be separated from the oxidation product. Alternatively the oxidation product is hydrolysed, the naphthoic acid separated and the naphthyl carbinol, naphthaldehyde and unchanged methyl naphthalene recycled. In examples (1) b -methyl naphthalene, butyric acid and a mixture of cobalt and manganese acetates are placed in a cylindrical glass reactor heated to 195-200 DEG C., oxygen is passed in at the bottom, water is separated from the condensed vapours, and the products are separated by known methods; (2) as in (1) but using a mixture of a - and b -isomers; (3) as in (1) but the oxidation product is stripped free of butyric acid and catalyst and hydrolysed by refluxing with aqueous caustic soda, the naphthoic acid is removed and the non-acidic oxidation products recycled.