Method for preparing alkylbenzoic acid

A method for preparing an alkylbenzoic acid is herein disclosed which comprises subjecting an alkylbenzene having at least two alkyl groups of 1 to 3 carbon atoms to a liquid phase oxidative reaction with a molecular oxygen-containing gas in the presence of a soluble heavy metal catalyst to convert one alkyl group into a carboxylic acid, thereby preparing the alkylbenzoic acid, and impurities contained in the alkylbenzene recovered from the reaction solution are removed therefrom by distillation, water washing, alkali washing, a treatment with an anion exchange resin or a treatment with a solid adsorbent, and the impurities-free fraction is reused as a raw material. Furthermore, the conversion of the desired product is regulated to 25% or less in the liquid phase oxidative reaction, whereby the reaction is carried out in a boiling heat removal state and reaction heat is removed as the heat of vaporization. Thus, there can be decreased a dicarboxylic acid secondarily produced during the manufacture of the alkyl-benzoic acid which is a monocarboxylic acid by subjecting the alkylbenzene to the liquid phase oxidation, whereby problems such as the trouble of equipment operation and the deterioration of product quality can be solved.