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

Abstract

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 °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.