Cerium(IV) methanesulfonate in aqueous methanesulfonic acid oxides o-nitrotoluene successively into o-nitrobenzyl alcohol, o-nitrobenzaldehyde, and o-nitrobenzoic acid. The influence of the methanesulfonic acid concentration and of temperature was studied. A maximum aldehyde yield of 40% was reached at 75 degrees C with a methanesulfonic acid concentration of 9.2 mol dm(-3).