Hydrogenation of BHMF with controllable selectivity to tetrahydropyranone and 1-hydroxy-2,5-hexanedione under atmospheric H2 pressure

Abstract

The rearrangement of furan rings for valuable chemicals is an important topic for biomass conversion. In this study, 2,5-di(hydroxymethyl)furan (BHMF) was selectively converted to 6-methyldihydro-2H-pyran-3(4H)-one (MDPO) and 1-hydroxy-2,5-hexanedione (HHD) under atmospheric H₂ pressure in water. The selectivity to MDPO or HHD could be regulated by a catalyst. The parameters (temperature, pH, catalyst loading, and BHMF concentration) for the transformation of BHMF were studied. The selectivity for the transformation of BHMF was very sensitive to the reaction conditions, especially for the conversion of BHMF to MDPO. 68% selectivity to MDPO on Pd/C and 72% selectivity to HHD on Rh/C were achieved under the optimized conditions. Both Pd/C and Rh/C could be reused at least 5 times without the loss of activity. The fresh and used Pd/C and Rh/C were characterized by XRD, XPS, SEM, TEM, EDS mappings and ICP-OES to study the changes during the reaction. The reaction process was studied through controlled experiments, and 6-methylene-2H-pyran-3(6H)-one (MEPO) and 6-hydroxy-6-methyl-2H-pyran-3(6H)-one (HMPO) were identified as intermediates. A reasonable reaction mechanism was proposed and the different selectivity to MDPO and HHD was well explained based on the controlled experiments and DFT calculations. The conditional sensitivity for the selectivity to MDPO and HHD could also be interpreted by the proposed reaction pathway.