Studies Of Aerobic Oxidation Of Secondary Alcohols And Benzylic Methylenes Catalyzed By NHPI

Oxidation is one of the most important fundamental reactions, through which various alcohols and hydrocarbons could be converted to aldehydes, ketones, carboxylic acids and so on. The traditional oxidation process usually involves large quantity of metal oxidants, which may lead to severely environmental problems. It is necessary to develop green oxidant.Oxygen is a kind of clean oxidant since it’s main by-product is water. However, molecular oxygen is stable under common conditions. So catalysts are needed to activate molecular oxygen to take part in the reactions. NHPI (N-Hydroxyphthalimide), which is a kind of organocatalysts has been recognized as one of powerful catalysts for aerobic oxidation of various organic compounds in recent years. Usually, these reactions need co-catalyses such as Co and Mn salts and relatively higher temperature and oxygen pressure. So it’s one of the research hots to develop lower toxicity, cheaper and more efficient co-catalyses as well as research milder reaction conditions.Herein, we develop a novel system NHPI/Fe(NO3)3·9H2O for the oxidation of secondary alcohols and benzylic methylenes. We study the solvent, the kind and amount of catalysts’ effect in the reactions. The result indicates that the yield of acetophenone convert from a-phenylethanol which acts as the model substrate reaches 92% in the presence of 10 mol% NHPI and and 5 mol% Fe(NO3)3-9H2O in acetonitrile under 1 atm O2 at 25℃ for 48h.16 secondary alcohols are surveyed under the above conditions and 13 of them could obtain corresponding ketones with moderate to high yields (57-92%). For benzylic methylenes, we choose diphenylmethane as the model substrate, the yield of acetophenone reaches 84% in the presence of 10 mol% NHPI and 8 mol% Fe(NO3)3-9H20 in acetonitrile under 1 atm O2 at 25℃ for 40h.15 benzylic methylenes are surveyed under the above conditions and 11 of them obtained corresponding ketones with moderate to high yields (50-97%). We also explore the mechanism of the oxidation of secondary alcohols and benzylic methylenes catalyzed by NHPI and Fe(NO3)3·9H2O.