Add time:08/01/2019         Source:sciencedirect.com

2,5-Diformylfuran (2,5-DFF) is an important furan-based chemical with broad application potential. To address the difficulties in isolating/purifying the product and recycling the 2,2,6,6- tetramethylpiperidine-1-oxy (TEMPO)-based catalysts, we employed a solvent with a low boiling point in which TEMPO has a low solubility to investigate the effects of TEMPO and its analogs on catalyzing the oxidation of 5-hydroxymethylfurfural (5-HMF). The results indicated that in ethyl acetate with the substitution of one H of TEMPO at the C4 position with either an acetamido (NH-Ac), methoxy (OCH3), hydroxy (OH) or isothiocyanato (NCS) group, the resulting compound had a product selectivity similar to that of TEMPO (>86%), except for the 4-isothiocyanato-TEMPO-catalyzed reaction. However, after two Hs were substituted with an oxo group (O), the catalytic efficiency significantly decreased (product yield 16%, selectivity 52%). Based on both the catalytic efficiency and catalyst solubility, a highly efficient method for preparing 2,5-DFF was established using ethyl acetate as the solvent, 4-acetamido-TEMPO as the catalyst and Fe(NO3)3 and NaCl as cocatalysts. At 40 °C with a substrate concentration of 0.125 mol/L, 5-HMF was completely converted in 2 h, and the yield of 2,5-DFF was 89%. Moreover, when the substrate concentration increased to 0.25 mol/L, the yield of 2,5-DFF was 87%. When 4-acetamido-TEMPO was recovered by centrifugation, the product yield remained as high as 86% after three cycles, demonstrating good recyclability.

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