GB816593A - Process for the introduction of carboxyl groups into aromatic hydrocarbons - Google Patents

Abstract

Aromatic carboxylic acids and their salts and other derivatives are prepared by heating an aromatic hydrocarbon above 350 DEG C. in the presence of carbon dioxide, which may be present in a free or combined form, and an acid binding agent to obtain a salt of the acid which may then be converted to the free acid or other derivative, e.g. ester or amide. Suitable hydrocarbons include benzene, toluene, xylene, cumene, di-isopropyl benzene and other benzene, naphthalene, diphenyl, diphenylmethane and other aromatic compounds substituted by saturated or unsaturated alkyl or cycloalkyl groups. The acid binding agent may be an alkali metal carbonate, bicarbonate, formate or oxalate, preferably potassium carbonate. The reaction may also be carried out in the presence of substances able to bind or react with any water formed in the reaction, for example aluminium carbide, carbides or nitrides of alkali or alkaline earth metals, metals such as aluminium which will react with water under the reaction conditions or an alkali metal carbonate, present in approximately at least a molar excess over the amount required to neutralize the acids formed. The reaction is influenced by catalysts and heavy metals, e.g. zinc, cadmium, mercury, iron, lead or their compounds may be used in the reaction. The reactants, when solid, are heated in a dry, finely divided state and caking and local overheating are minimized by the use of stirring or moving reaction vessels or the addition of inert substances with large surface areas. The reaction is preferably carried out in the presence of gaseous carbon dioxide under pressure. In the examples 1-6 and 8-20 terephthalic acid and/or trimesic acid is obtained by heating benzene in the presence of carbon dioxide under pressure with potassium carbonate or caesium carbonate as acid binding agent; aluminium carbide, calcium carbide, aluminium phosphide, silicon, boron or silicon tetraphenyl as water binding agent; cadmium fluoride K2CdF2Cl2, zinc chloride, mercuric chloride or metallic cadmium as catalyst; and asbestos as the inert diluent. In Example (14) dipotassium terephthalate is added to the reaction mixture. In Example (7) naphthalene 2 : 6-dicarboxylic acid is obtained by heating naphthalene in the presence of carbon dioxide, potassium carbonate, aluminium carbide, cadmium fluoride and asbestos. In Example (20) benzoic and other aromatic acids are identified but not isolated.