Microwave-assisted condensation of bio-based hydroxymethylfurfural and acetone over recyclable hydrotalcite-related materials.

Abstract The microwave-assisted neat aldol condensation of biomass-derived platform chemical 5-hydroxymethyl furfural (HMF) and acetone over hydrotalcite-based catalysts has been studied. High conversions are obtained in very short times with relatively low catalyst loadings. The condensation products, which are biofuel and functional polymer precursors, are selectively obtained. Heterogeneous catalysts with different basic properties derived from the same parent hydrotalcite have been tested. The solids were characterized by PXRD, ICP-AES, ESEM-EDX, TEM, FT-IR and Raman spectroscopy, N2 physisorption, CO2 chemisorption and TGA-MS. The products in the final reaction mixtures were determined by GC-FID and -MS, HPLC-DAD and -TOF, and NMR. NMR was also used to determine the stereoconfiguration of the obtained products and pointed to a complete E-selectivity of our process. Different catalyst recycle strategies have been explored, and the most active catalyst, a meixnerite-type solid, can be recycled with low activity loss.