Dehydration of d-fructose to hydroxymethylfurfural in sub- and supercritical fluids

Hydroxymethylfurfural (HMF) is a key intermediate in the biomass-based chemical product line. Unfortunately, only unsatisfying yields of HMF are achieved by the dehydration of d-fructose in supercritical water (SCW). Previously, we reported on the dehydration of d-fructose to HMF in sub- and supercritical acetone/water mixtures. The use of this reaction media resulted in higher yields of HMF (77% selectivity, 99% conversion). In this work, we conducted the reaction in sub- and supercritical methanol (scMeOH) and subcritical acetic acid (scAcOH) and obtained the resulting furfural-ether (5-methoxymethylfurfural, MMF, 79% selectivity, 99% conversion) and -ester (5-acetoxymethylfurfural, AMF, 38% selectivity, 98% conversion). r investigations on the reaction mechanism via NMR spectroscopy gave a possible explanation for the higher yields of the furfurals when using the above-mentioned solvents compared to water. Finally, a continuous production process for HMF and MMF is proposed.