Selective aerobic oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran catalyzed by Cu-based metal organic frameworks with 2,2,6,6-tetramethylpiperidin-oxyl

Abstract

Abstract While Cu combined with 2,2,6,6-tetramethylpiperidin-oxyl (TEMPO) constitutes a novel oxidative catalytic system using O2 for oxidation of 5-hydroxymethylfurfural (HMF), few studies have been conducted to investigate Cu/TEMPO/O2 for oxidation of HMF to 2,5-diformylfuran (DFF). More importantly, existing studies employ homogeneous Cu species, which is difficult for recovery; thus it is crucial to develop heterogeneous Cu catalyst incorporated with TEMPO for oxidation of HMF. Herein, a Cu-based metal organic frameworks (MOFs), HKUST-1, is proposed and employed for the first time as a heterogeneous catalyst with TEMPO for oxidative conversion of HMF to DFF in the presence of O2. Although TEMPO and HKUST-1 are ineffective separately for oxidation of HMF to DFF, the combination of HKUST-1 and TEMPO successfully converts HMF to DFF without by-products. The reaction duration could be as short as 3 h at 120 °C to achieve > 96% of HMF conversion with a selectivity > 99% and a yield of 96%, demonstrating that this HKUST-1+TEMPO+O2 is certainly promising and highly selective for HMF conversion to DFF. HKUST-1 is also reusable for incorporating with TEMPO to oxidize HMF to DFF. These results indicate that HKUST-1 is an advantageous heterogeneous catalyst for HMF conversion using TEMPO as an oxidant catalyst.