Homogeneous oxidation of alcohol and alkene with copper (II) complex in water

Abstract

A new water-soluble copper(II) complex bearing 4-bromobenzoate/ 2,2'-dipyridylamine ligands was successfully synthesized and characterized by using single crystal X-ray diffraction and spectroscopic techniques. The catalytic activity of the compound was investigated as a homogeneous catalyst in the oxidation of several alcohols (benzyl alcohol, cinnamyl alcohol, 1-phenylethanol, cyclohexanol, 1-heptanol) and alkenes (styrene, ethylbenzene, cyclohexene) in aqueous medium. The copper(II) catalyst was found to be active for the studied alcohols and alkenes. H2O2 was used as an active oxidant for alcohol oxidation, while t-BuOOH (TBHP) was used for alkenes. The compound exhibited high selectivity toward benzaldehyde (88%) in cinnamyl alcohol oxidation under mild conditions (70 degrees C) after 4 h. Particularly, remarkable results were obtained for the oxidation of styrene and cyclohexene; transformation via allylic oxidation to 2-cyclohexene-1-one as one product in 2 h (TOF = 50 h(-1)) and benzaldehyde in 1 h (100% conversion, TOF = 86 h(-1), 100% selectivity). The Cu(II)/TBHP (or H2O2)/H2O system proved to be an alternative for catalytic oxidations in the green chemistry concept.