GB807091A - Process for the production of aromatic polycarboxylic acids - Google Patents

Abstract

Aromatic polycarboxylic acids are prepared by the oxidation in the liquid phase of an aromatic compound having two or more aliphatic nuclear suhstituents that are oxidizable to carboxy groups or an intermediate oxidation product thereof, with molecular oxygen in the presence of a catalyst comprising in conjoint presence bromine and a heavy metal oxidation catalyst. Specified heavy metal oxidation catalysts are manganese, cobalt, iron and nickel. The heavy metal and bromine may be added as salts and be present in ionic form, for example as heavy metal bromides or as separate salts. Thus manganese bromide and/or cobalt bromide may be used, or a heavy metal carboxylate plus a bromide, e.g. ammonium bromide or a soluble organic bromide. The reaction may be carried out in an inert organic medium such as a saturated aliphatic monocarboxylic acid containing 2 to 8 carbon atoms, e.g. acetic acid, or benzoic acid. The oxygen used may be pure or diluted with inert gases, i.e. air may be used. The process may be carried out batchwise or continuously with recycling of partially oxidized material. The process is carried out under pressure and at a temperature between 120 DEG and 275 DEG C. The intermediate oxidation products which may be used in the process are those wherein the aliphatic substituents have been converted to derivatives containing carboxylic, hydroxy, aldehyde, ketone and peroxide groups. The aliphatic substituted aromatic compounds may be derivatives of benzene, naphthalene, anthracene, phenanthrene, diphenyl and triphenyl. The aliphatic substituents may also be bivalent and attached to two different nuclear carbon atoms, e.g. as in tetrahydronaphthalene. Specified compounds are alkylbenzenes containing 2-4 alkyl groups having 1-4 carbon atoms, dimethylbiphenyl, toluic acids, methylacetophenones, acetobenzoic hexylnaphthalene, which is further reacted acids and 1 : 3-dimethyl-4-chlorobenzene. In an example, p-diisopropylbenzene is heated under pressure in caproic acid and in the presence of manganese bromide, oxygen is passed in and the terephthalic acid obtained is washed with acetic acid to remove small amounts of isophthalic acid. In a similar manner o- or m- or p-xylene, o- or m- or p-cymene and o- or m- or p-n-propyl- or -n-butyl- or -isobutyl-toluene give phthalic, isophthalic or terephthalic acids; mixtures of ethyltoluenes and diethylbenzenes give mixed phthalic acids; mesitylene gives methyl isophthalic acid or trimesic acid; pseudocumene gives trimellitic acid; ditolylethane gives a mixture of iso- and tere-phthalic acids; pentamethylbenzene gives methylbenzene tetracarboxylic acid; ethylxylene gives benzene tricarboxylic acids and durene gives methylbenzene - tricarboxylic acid. Further catalysts specified in examples are manganese acetate and ammonium bromide; cobalt naphthenate and hydrogen bromide; manganese bromide, manganese acetate, cobalt naphthenate and ammonium bromide; cobalt naphthenate, manganese acetate and ammonium bromide. Results obtained using catalysts such as manganese chloride or fluoride or iodide or acetate and ammonium bromide are described for comparison. Ditolylethane is prepared by condensing toluene with ethylene dichloride in the presence of aluminium chloride and distilling the product to separate ditolylethane from higher polytolylethanes.