The Meerwein–Ponndorf–Verley–Oppenauer type reaction in supercritical or high-temperature alcohols or acetone without catalyst: Effect of oxidation enthalpy and solvent concentrations on yield

In the traditional Meerwein–Ponndorf–Verley (MPV) reduction, it is known that the yield of the produced alcohol is dependent on the oxidation enthalpy and the concentration of the alcohol used as the reducing reagent. In this study, we investigated the reduction of acetophenone to 1-phenylethanol with alcohols under their supercritical or high-temperature conditions without catalyst to confirm the mechanistic resemblance of the MPV type reduction with supercritical or high-temperature alcohols to the traditional MPV reduction. It was found that the yields of the 1-phenylethanol were dependent on the oxidation enthalpies and the concentrations of the alcohols used as the reducing reagents in common with the traditional MPV reduction. The Oppenauer type oxidation of secondary alcohols afforded the corresponding ketones in around 90% yield with excess amounts of supercritical acetone without catalyst. On the other hand, the Oppenauer type oxidation of primary alcohols to aldehydes resulted in low yields. The low yields were assumed to result from the aldol condensation of the resulting aldehydes with the acetone.