GB733322A - Process for the manufacture of polybasic aromatic carboxylic acids - Google Patents

Abstract

Polybasic aromatic carboxylic acids are manufactured, by condensing in known manner benzene or one of its homologues with ethylene chloride in the presence of a Friedel-Craft's catalyst to give a product of high molecular weight, and oxidizing this product to give polybasic carboxylic acids. Aluminium chloride may be used as catalyst, and the chain length of the compounds, in which benzene rings are linked by -CH2-CH2- groups, is dependent on the molecular ratio ethylene chloride: benzene. The chain length increases as the ratio approaches 1, but it is kept below 1 for the production of dicarboxylic acids, and at such a figure that products with an average molecular weight of at least 800 are obtained. The temperature of the reaction is adjusted to give a steady evolution of hydrogen chloride. The reaction product may be oxidized in three ways: (1) with air at 100-150 DEG C. in the presence of a heavy metal catalyst, (2) boiling nitric acid plus vanadic acid as catalyst, (3) bichromate-sulphuric acid mixture at 100-150 DEG C. The acids in the oxidation product can be separated by fractional crystallization, or distillation of esters. Besides minor amounts of benzoic acid, terephthalic and isophthalic acids are obtained. If toluene is used, oxidation of the condensation product yields tricarboxylic acids. A slight excess of ethylene chloride leads to cross-linking between the chains, and to more tricarboxylic acids on oxidation. Further reaction of this condensation product with toluene before oxidation, reduces the formation of benzoic acid and increases the yield of dicarboxylic acids. In examples (1) benzene is condensed with ethylene chloride and a mixture of iso- and terephthalic acids obtained after oxidation with nitric acid, (2) the condensation product from (1) is oxidized with oxygen using cobalt nitrate and copper nitrate as catalysts.