The catalytic transformation of biomass carbohydrates into furfural as a biobased platform chemical represents an important route within biorefinery. In this work, deep eutectic solvents (DESs) prepared from choline chloride and ethylene glycol were used as the reaction solvent for xylose dehydration to furfural over an AlCl3 catalyst. An optimized furfural yield of 74% was obtained at 140 °C in 20 min, 20 wt % of water, and 10 mol % of AlCl3 loading under biphasic operation using methyl isobutyl ketone (MIBK) as the extraction solvent. A positive influence of water addition in the DES was observed due to the enhanced furfural stability in the monophasic DES and improved mass transfer in the DES-MIBK biphasic system. Xylose is readily alkoxylated with ethylene glycol to form 2-hydroxyethyl xyloside, which can be further converted to furfural. ESI-MS and 27Al NMR analyses revealed the speciation of Al(III) in the DES-water mixture and the catalytically active Al(III) species to be AlCl4−, responsible for xylose conversion to furfural. Based on these results, a possible reaction mechanism was proposed for xylose conversion to furfural in the ChCl/EG DES over the AlCl4− species.
Ruan et al. (Wed,) studied this question.