GB835774A - Preparation of aromatic carboxylic acids - Google Patents

Abstract

Aromatic carboxylic acids are prepared by the oxidation of halo-alkyl substituted benzene hydrocarbons, suspended or dissolved in a carboxylic acid medium, by means of oxygen or an oxygen-containing gas, the oxidation being carried out in the conjoint presence of a metal, metal oxide or metal salt (or variable valency) and of bromine or a bromine. The oxidation is advantageously carried out in the presence of manganese bromide and/or cobalt bromide, or it may be carried out in the presence of manganese acetate and/or cobalt acetate together with a substance capable of producing bromide ions under the reaction conditions. The process is particularly suitable for the economical manufacture of terephthalic acid from halogenated derivatives of toluene. Toluene is readily halomethylated to give a mixture of halogenated derivatives of xylene containing only the ortho-and para-isomers, and these can then be oxidized by the process of the invention to give high yields of phthalic acid and terephthalic acid. In Example 1, benzyl chloride was dissolved in propionic acid and refluxed in the presence of cobalt bromide while oxygen was passed through the boiling mixture. After 20 hours the solution was cooled, the excess propionic acid distilled off, and the residual benzoic acid was recrystallized from water. Example 3 relates to the preparation of terephthalic acid by the oxidation of p-xylylchloride. In Example 4, a mixture of p-xylyl chloride and o-xylyl chloride, obtained by chloromethylation of toluene, was dissolved in propionic acid and oxidized in the presence of cobalt bromide. Terephthalic acid was obtained by hot filtration of the oxidation-products, and phthalic acid by distilling off the propionic acid from the mother-liquors and recrystallizing the residue from water. In Example 5, p-xylylene dibromide was dissolved in acetic acid, and oxidized at 120 DEG C. using cobalt acetate as catalyst. There was a 99% yield of terephthalic acid. Example 6 relates to the oxidation of p-xylylene dichloride, dissolved in benzoic acid, in the presence of cobalt bromide. Specification 783,220 is referred to.