Solvent-free oxidation of toluene in an ionic liquid with H2O2 as oxidant

• Ionic liquid as an effective catalyst.
• Catalyst for oxidation of toluene.
• Selective oxidation under solvent-free conditions.
• The catalytic activity is ascribed to synergic effect of imidazolium cation with metal chloride.
• Selectivity to biphase catalysis.

A series of 1-alkyl (or acetic acid)-3-methylimidazolium–metal chloride ionic liquids such as AmimBr Cl-,BF4-–MClx (A = ethyl, butyl, acetic acid and benzyl radicals; M = Fe, Cu, Sn, Mn, Ni, Co and Zn; x = 2, 3 and 4) and Et3NHCl–FeCl3 were prepared by conventional method. These prepared ionic liquids were used as catalysts in selective oxidation of toluene with H2O2 as an oxidant. Their catalytic activities were compared in the absence of organic solvents. The ionic liquid bmimBr–FeCl3 showed higher catalytic activity with 10.2% conversion and 99% selectivity to benzaldehyde and benzyl alcohol. However, the catalyst was easily recovered and reused for three times without evident activity loss.