Highly efficient catalysts of chitosan-Schiff base Co(II) and Pd(II) complexes for aerobic oxidation of cyclohexane in the absence of reductants and solvents

Three chitosan-Schiff base Co(II) and Pd(II) complexes were prepared in a simple way and characterized by FT-IR, XPS and TG. Their abilities to catalyze oxidation of cyclohexane into cyclohexanone and cyclohexanol with oxygen in the absence of any solvents or reducing agents were studied. It has been revealed that the complexes had high catalytic activities for heterogeneous cyclohexane oxidation with oxygen. Especially, the oxidation of cyclohexane catalyzed by chitosan-salicyaldehyde Schiff base Co(II) complex under 1.6MPa of initial oxygen pressure at 418 K gave excellent results with 9100 turnover numbers (based on the cobalt atom) and 96% selectivity for cyclohexanone and cyclohexanol after reaction of 4.5 h. The influences of oxygen pressure, reaction temperature and reaction time on the oxidation of cyclohexane were also investigated. It has been also revealed that the complexes were efficient for the oxidation of bulky cyclic alkanes and linear alkanes. (c) 2005 Elsevier B.V. All rights reserved.