Cycloalkane Oxidation Catalyzed by Copper-based Catalysts with H2O2 under Mild Conditions

Copper-catalyzed cycloalkane oxidation using H2O2 as an oxidant was investigated under mild conditions. The copper catalysts studied in this work ranged from commercially-available copper(II) salts to copper(II) complexes containing polypyridyl ligands. Various factors that affected catalytic activity of copper catalysts were elucidated. It was found that geometry of the copper complex in solution and coordinated anions played important roles in catalytic activity. The copper(II) complex generated in-situ by mixing Cu(OAc)(2) and TMPA ligand (TMPA=tris(2-pyridylmethyl)amine) adopted trigonal bipyramidal geometry and was competent to catalyze cyclohexane oxidation with higher yields, compared to those of other Cu2+ species used in this work. The optimal catalytic condition was achieved using 1.0 % mol of Cu(OAc)(2)/TMPA and 10 equivalents of H2O2 with respect to cyclohexane in CH3CN at 33-35 degrees C for 3 hours, resulting in the total product yield of 44 %. Moreover, since cyclohexyl hydroperoxide was detected as a major product, the Fenton-like mechanism via one electron process was proposed as a plausible mechanism in this cycloalkane oxidation. In addition, our catalytic system was further demonstrated to be applicable for oxidation of various cycloalkane substrates with moderate yields and relatively short time.