Aerobic oxidation of benzyl alcohol in supercritical CO2 catalyzed by perruthenate immobilized on polymer supported ionic liquid

The catalyst for aerobic oxidation of benzyl alcohol to produce benzyl aldehyde was prepared by immobilization of perruthenate on polymer supported 1-vinyl-3-butyl imidazolium chloride, and the catalytic reaction was conducted in supercritical (SC) CO2, toluene and dichloromethane at 80 degrees C. The phase behavior of the reaction system with SC CO2 as solvent was also determined. It was demonstrated that the catalyst was very active and highly selective. The reaction rate in SC CO2 depended strongly on pressure and reached a maximum at about 14 MPa, which can be explained by the effect of pressure on the phase behavior of the reaction system, diffusivity of the components and solvent power of SC CO2. The catalyst could be reused directly after extraction of the products using SC CO2, and it was still active after several runs, although the yield decreased continuously with run times. This work integrated the advantages of green solvent, green supporting material and green oxidant.