GB762794A - Process for the preparation of isophthalic acid - Google Patents

Abstract

A process for preparing isophthalic acid comprises reacting in the liquid phase at elevated temperatures metadi-isopropylbenzene with molecular oxygen in the presence of 0.1 to 10 per cent by weight of the reaction mixture of a compound of heavy metal as catalyst and benzoic acid, the ratio of the benzoic acid being in the range of 1 to 8 mols. per mol. of meta-di-isopropylbenzene. The reaction mixture may contain in addition another monocarboxylic acid liquid at room temperature, e.g. an aliphatic, especially a saturated aliphatic, monocarboxylic acid having 1 to 6 carbon atoms. The reaction mixture may also contain water alternatively or in addition to the aliphatic monocarboxylic acid. The meta-di-isopropyl benzene employed as starting material may be pure or may contain some para-di-isopropylbenzene, lower or higher alkylated benzenes and saturated aliphatic hydrocarbon material. Oxidation catalysts mentioned include manganese carboxylates, e.g. derived from carboxylic acids of 2 to 10 carbon atoms, e.g. manganese cumate, cobalt cumate and octanoate, zinc acetate, mercuric oxide and vanadium oxide. Elevated pressure may be employed, e.g. to maintain a liquid phase of the lower carboxylic acid or water. The process may be carried out continuously. In examples: isophthalic acid is obtained by passing oxygen into a mixture of di-isopropylbenzene containing 84 per cent of the meta-isomer, benzoic acid and manganese cumate whilst heating. The crude product may be washed with benzene or a lower carboxylic acid, e.g. glacial acetic acid, which removes terephthalic acid, or methanol, ethanol or propanol. The isophthalic acid may be esterified with methanol using hydrochloric, sulphuric or phosphoric acid as catalyst or it may be converted with thionyl chloride to the acid chloride and esterified (1); in a similar process water is present and elevated pressure is used (2); in a similar process to (1) caproic acid and benzoic acid are present in the reaction mixture and in an additional run cobalt cumate is employed as catalyst with benzoic acid only present (3). The metal carboxylate catalysts are prepared by dissolving the appropriate organic acid in caustic alkali and adding to the solution a solution of the appropriate metal acetate. Manganese cumate is so prepared and when dried, first in air and then over calcium chloride at low pressure, is more soluble in meta-di-isopropylbenzene than when oven dried. Specification 762,793 is referred to.