GB748567A - Improvements relating to the preparation of paratoluic acid - Google Patents

Abstract

A process for the preparation of p-toluic acid from di-p-tolyl-methane hydroperoxide comprises heating the latter in acid medium to decompose it into p-tolualdehyde and p-cresol, separating the p-tolualdehyde and oxidizing it with oxygen or a gas containing free oxygen. The hydroperoxide can be formed by reacting di-p-tolyl-methane with oxygen at 60 DEG to 150 DEG C., e.g. as in Specification 726,362, to produce a solution of hydroperoxide in unconverted hydrocarbon. For the decomposition the solution can be heated with dilute, e.g. 10 to 25 per cent, sulphuric acid. It is preferably effected however, by passing steam into the mixture at normal or elevated pressure. Alternatively steam and the hydroperoxide can be passed continuously to a reaction chamber which contains the dilute acid, the reaction products being entrained by the steam and being recovered from the condensate, e.g. as in Specification 748,566. The oil layer of the condensate, containing tolualdehyde and unconverted hydrocarbon may be treated, after separation of cresol by treatment with aqueous alkali, with air at, e.g. 50 DEG C. to effect the oxidation. The p-toluic acid is then recovered by washing the solution with aqueous alkali metal hydroxide. The liquid in the reaction vessel is also continuously withdrawn and separated into layers, the aqueous layer, containing the acid, being returned and the oil layer being treated with aqueous alkali for the recover of p-cresol before its return to the reaction vessel. An example illustrates the process. The product can be converted to terephthalic acid by treatment with nitric acid.