GB744721A - Process for the manufacture of salts or other derivatives of aromatic dicarboxylic acids, especially of terephthalic acid - Google Patents

Abstract

Salts or other derivatives of aromatic dicarboxylic acids are prepared by a process which includes the step of heating the potassium salt of an aromatic monocarboxylic acid in the presence of carbon dioxide, to obtain a potassium salt of an aromatic dicarboxylic acid. The temperature used is above 340 DEG C. in order to obtain a reasonable rate of reaction, and to avoid oxidation the heating is carried out in the presence of carbon dioxide, usually under pressure in an autoclave fitted with a stirrer. Specified starting materials are potassium benzoate and naphthoates and these may be mixed with inert substances such as sand or inert salts such as potassium carbonate, sulphate or chloride. The salts obtained may be converted directly by known methods into derivatives such as the dichlorides and esters. The reaction is promoted by metal, e.g. lead, zinc, or mercury, or metal oxide catalysts. The process yields are calculated on the theory that, for example, 2 molecules of benzoic acid are converted into one molecule of terephthalic acid and 1 molecule of benzene. In examples (1-8) potassium terephthalate and terephthalic acid are prepared from potassium benzoate using various catalysts and reaction conditions; (9-11) potassium a - and b -naphthoates are converted into naphthalene-2:6-dicarboxylic acid and the corresponding potassium salt.