Toluene Oxidation by Hydrogen Peroxide in Deep Eutectic Solvents

The catalytic effect of several deep eutectic solvents (DESs) on biphasic toluene oxidation by hydrogen peroxide to produce benzaldehyde was studied under various operational conditions. Experiments were performed with sodium tungstate, iron(III) chloride, phosphotungstic acid, and phosphomolybdic acid as catalysts dissolved in three DESs composed of choline chloride and a hydrogen-bond donor molecule such as urea, glycerol, or ethylene glycol. Additionally, a fourth catalytic system composed of iron(III) chloride and choline chloride was tested. The best result was achieved with FeCl₃ dissolved in the DES containing ethylene glycol, which gave 37.9% conversion and 63.6% selectivity. The results are better than those reported for other ionic liquids; this may be due to similar activation of hydrogen peroxide by polarization of the peroxide bond through hydrogen bonding and the low viscosity of the solvent.