Catalytic process for preparing aliphatic straight-chain and -alkyl-branched carboxylic acids

A catalytic process for preparing aliphatic straight-chain and -alkyl-branched carboxylic acids of 5 to 13 carbon atoms by catalytic oxidation of the corresponding aldehydes by means of oxygen or oxygen-containing gas mixtures in the liquid phase in the presence of a catalyst system contains alkali metal carboxylates or alkaline earth metal carboxylates or a mixture thereof in an amount, calculated as alkali metal or alkaline earth metal, of 0.5 mmol to 15 mmol per mol of aldehyde used and also metals of groups 4 to 12 of the Periodic Table of the Elements, cerium or lanthanum in amounts of not more than 5 ppm, based on the aldehyde used, or compounds of such metals, with the catalyst system being the reaction product from an aldehyde oxidation reaction.