GB786747A - Improvements in and relating to the production of aromatic di-carboxylic acids - Google Patents

Abstract

Benzene dicarboxylic acids are prepared by reacting at elevated temperature and pressure and in the presence of an aqueous alkaline medium, free oxygen and a compound of the general formula <FORM:0786747/IV (b)/1> wherein R1 is an alkyl, hydroxyalkyl, acyl, or carboxylic group and R2 is a hydroxyalkyl or acyl group. The preferred temperatures and pressures are 150-250 DEG C. and 10-50 atmospheres. Specified aqueous alkaline media are solutions of the hydroxides or carbonates of alkali metals or ammonia or suspensions of the hydroxides or carbonates of the alkaline earth metals. A combination of two or more of the alkaline substances may be used. Pure oxygen is preferably used, but it may be diluted by gases such as nitrogen or carbon dioxide, or air may be used. Catalysts may be present in the reaction mixture and those specified are one or more of the oxides of iron, aluminium, cerium, barium, zinc, magnesium or zirconium, oxides of other metals of the first, second, third, fourth or eighth groups of the Periodic Table, or the oxides, salts or oxygen acids of chromium, manganese and vanadium. The preferred starting materials are the partial oxidation products of dialkyl benzenes. The reaction products are the salts of the acids, the acids being obtained therefrom by known methods. In examples: (1) the reaction mixture obtained by the oxidation of p-diisopropylbenzene with oxygen at atmospheric pressure and elevated temperature using manganese dioxide as catalyst was further oxidized with oxygen at elevated temperature and pressure in the presence of aqueous sodium hydroxide, the product being terephthalic acid with some p-acetyl-benzoic acid; (2) as in (1) but the starting material is prepared from p-diisopropylbenzene diluted with an equal volume of o-dichlorobenzene and the product of this first stage is isolated before further reaction, the final product being terephthalic acid; (3) p-diacetylbenzene, p-acetyl-benzoic acid or a :a 1 - dihydroxy - p - diisopropylbenzene were oxidized with oxygen at elevated temperature and pressure in aqueous sodium hydroxide and in the presence of manganese acetate to terephthalic acid.