GB756472A - A process for converting naphthalic acid into naphthalene-2.6-dicarboxylic acid - Google Patents

Abstract

In a process for the conversion of naphthalic acid into naphthalene-2,6-dicarboxylic acid or a derivative thereof the dipotassium salt of naphthalic acid is heated to temperatures above 340 DEG C., thereby obtaining the dipotassium salt of naphthalene-2,6-dicarboxylic acid. Elevated or normal pressures may be employed and carbon dioxide may be present. Metals such as zinc, cadmium and lead and their compounds, e.g. the oxides, are mentioned as catalysts which may be employed and the catalysts may be applied to carrier materials. The potassium salt of naphthalic acid may be mixed with sand, coke, inert salts, e.g. potassium carbonate, sulphate and chloride or pieces of inert metal to facilitate thermal conduction within the heated salt. Reaction mixtures which produce the dipotassium salt of naphthalic acid on heating may be used as starting materials, e.g. mixtures of naphthalic acid, anhydride and potassium carbonate. Free naphthalene-2,6-dicarboxylic acid can be obtained by acidifying an aqueous solution of the salt or the latter may be converted directly, e.g. to the dichloride or esters. In exaples: naphthalene-2,6-dicarboxylic acid is obtained by heating anhydrous potassium carbonate and naphthalic anhydride under carbon dioxide at elevated pressure, dissolving the product in water and acidifying with hydrochloric acid (1) and in similar processes cadmium oxide, zinc oxide, litharge and metallic lead are employed as catalysts (2). The conversion of naphthalene-2,6-dicarboxylic acid to the dichloride, the dimethyl ester and the diamide is mentioned.