Preparation of Heterogeneous Vanadium (VO2+) Catalyst for Selective Hydroxylation of Cyclohexane by Molecular Oxygen

A vanadium(II) Schiff base ligand, [1,4-bis (salicylidene amino)-phenylene] vanadium oxo complex bonded on carbamate-modified silica gel, has been synthesized. The liquid-phase oxidation reaction of cyclohexane with this catalyst was found to give cyclohexanol at moderate condition (reaction temperature 200 °C, pressure 23.8 atm, catalyst concentration 1.0% and 16 h of reaction time) with considerably higher specificity (18:1 ratio with cyclohexanone and negligible acid formation). The catalyst has been tested for 200 h of reaction and the leaching of the metal occurs negligibly.