Copper-catalyzed functionalization of cyclohexane and relevant hydrocarbons

Abstract

The oxidation of cyclohexane could proceed at room temperature and atmospheric pressure when Cu(OAc)2.H₂O as a catalyst, hydrogen peroxide (H₂O₂) as an oxidant, and pyridine-acetic acid as solvents were employed. Cyclohexane was selectively converted to cyclohexanone with a small amount of cyclohexanol as a co-product. Percent conversion of cyclohexane was about 10% and the half-life of the reaction was around 5-10 minutes. The reaction time was found to be the fastest one when compared with other catalytic systems reported. Furthermore, this particular oxidation reaction was more reactive towards alkyl C-H bonds than those of allylic and benzylic C-H bonds. Comparative studies on the relative reactivity of cyclic saturated hydrocarbons and chemoselectivity study showed that the oxidation reaction mechanism did not occur via free radical pathway. The copper-catalyzed oxidation of cyclohexane could also take place when H₂O₂ was replaced by tert-butyl hydroperoxide (TBHP) at 60℃. The oxidation reaction mechanism, on the other hand, was believed to occure via a radical pathway. In addition, cyclohexane could be transformed to bromocyclohexane, chlorocyclohexane and cyclohexyl azide by employing the latter reaction.