Selective oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran over a Cu-acetonitrile complex

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