Selective oxidation of 5-hydroxymethy furfural into 2,5-formalde furan over Cu-acetonitrile complex

Cu(NO3)2/acetonitrile was proved to be an efficient oxidation system in the oxidation of 5-HMF to DFF in aqueous solution. After optimization of the reaction conditions, a DFF yield of 97.0% was obtained under the condition of 1.5 mmol 5-HMF, 1.5 mmol Cu(NO3)2, 0.48 ml acetonitrile, 10 ml H2O, 80 °C, 18h. The oxidation system could be recycled at least three times by adding HNO3, which avoids the risk of producing Cu-containing waste. The formation of Cu(CH3CN)4+ in aqueous solution plays an important role in enabling the oxidation of 5-HMF by the redox cycle of Cu2+/Cu+. In order to further improve the reaction efficiency, a reactive-extraction process was developed by introducing toluene as the organic phase for its excellent extraction capacity of DFF, through which the reaction time was shorten to 8 h and a highest DFF yield of 98.9% was achieved.