BACKGROUND: The liquid-phase catalytic oxidation of aromatic hydrocarbons by molecular oxygen is a commercially important process. We consider the MnCO3-promoted oxidation of toluene to produce benzaldehyde and benzoic acid. In this investigation, toluene was oxidized with 25.0% conversion and 80.8% selectivity with respect to benzoic acid in the presence of MnCO3 under 1.0 MPa of oxygen at 190 degrees C for 2 h. RESULTS: Moreover, the oxidation of other aromatic hydrocarbons, such as ethylbenzene, p-xylene, m-xylene, o-xylene, and p-chlorotoluene, were also efficiently promoted by MnCO3. CONCLUSION: It is concluded that an efficient oxidation of aromatic hydrocarbons can be achieved in the presence of MnCO3 under solvent-free conditions. The catalytically active species are high-valence Mn generated via the action of MnCO3 with oxygen. (c) 2007 Society of Chemical Industry