Organic solvent- and phase transfer catalyst-free oxidation of cyclohexanol to cyclohexanone with dilute H2O2

The oxidation of cyclohexanol to cyclohexanone with 30% aqueous hydrogen peroxide by using peroxotung-state complexes formed in situ from sodium tungstate dihydrate and various bidentate organic ligands as the catalysts, without organic solvents, halide and phase transfer catalyst has been carried out. The influence of 13 ligands on the oxidation is investigated. The maximum yield of cyclohexanone is obtained when using 1,10-phenanthroline (96%) and oxalic acid (95%) as the ligand. Very high yields (around 90%) have also been obtained for the instances of using salicylic acid, 3,5-dibromosalicylic acid, and 8-hydroxylquinoline as ligands. A research to improve the reaction condition using cheap oxalic acid as the ligand indicates that the optimum condition is that the reaction mixture with a molar ratio of cycohexanol∶tungstate dihydrate∶oxalic acid∶ 30% H₂O₂=100∶2∶2∶120 was stirred at 85–90°C for 12 h.