Process for the oxidation of substrates containing methyl, methylene or methine groups

In a process for the oxidation of a substrate containing methylene (CH2) groups by means of oxygen oxidation in the presence of a catalyst system consisting of

• a) an imide compound of the formula
• in which R1 and R2 denote H, OH, halogen, a C1-C20-alkyl, alkenyl or alkoxy group, an aryl group, a C1-C6-acyl group, a carboxyl or a C1-C10-alkoxycarbonyl group, or R1 and R2 together form a double bond in formula I or form an aromatic or nonaromatic ring system in formula I or II, X denotes O or OH and n is an integer from 1 to 3, and
• b) a cocatalyst containing one or more elements selected from the group consisting of the transition metals and of the 2A and 3A elements of the Periodic Table,
• in an organic solvent to give the corresponding oxo compounds,
• the improvement wherein the substrate is oxidized together with an aromatic or aliphatic aldehyde having 2-20 C atoms.