GB655074A - An improved process for the preparation of terephthalic acid - Google Patents

Abstract

<PICT:0655074/IV (b)/1> Terephthalic acid is prepared by reacting a p-dialkyl benzene or a p-dialkyl benzene in which the alkyl groups may be partially oxidized with nitric acid, having an initial strength between 5 and 60 per cent, at superatmospheric pressure at a temperature above 150 DEG C. The said benzene may be p-xylene, p-cymene, p - diisopropylbenzene, p - divinylbenzene or p-tolualdehyde. An alkyl ester of p-toluic acid may be added to the said benzene. The crude reaction product may be separated from the residual acid liquor and any p-toluic acid therein is subjected to the above oxidation process. An oxygen containing gas may be introduced to assist the oxidizing reaction. Mercury or uranium salts may be used as a catalyst. Oxidized groups which may be present in the benzene include aldehyde, alcohol and carboxyl groups. In the examples, terephthalic acid is prepared in admixture with toluic acid. The terephthalic acid may be converted by known methods into its dimethyl or other alkyl ester and any esters of toluic acid recovered from the reaction product may then be oxidized as above. A suitable apparatus for carrying out the process comprises an autoclave 1 provided with stirrer 2 and heating or cooling jacket 4. Reactants are introduced at 9, nitric acid at 10, while condenser 8 returns condensible liquids to the autoclave and outlet 12 is used for gaseous materials. The Specification as open to inspection under Sect. 91 refers to the preparation of terephthalic acid by the reaction of dilute nitric acid in accordance with the above process with p-dialkyl benzenes and such compounds containing substituents in at least one side chain, e.g. g -nitro-p-xylene or g -hydroxy-p-xylene. This subject-matter does not appear in the Specification as accepted.