Tandem catalytic conversion of glucose and cellobiose to 5-ethoxymethylfurfural with record yields

Abstract

The conversion of biomass-derived carbohydrates to 5-ethoxymethylfurfural (EMF) is a fascinating reaction with 100% carbon atom utilization. Although effective conversion of 5-hydroxymethylfurfural (HMF) and fructose to EMF have been achieved, the direct conversion of glucose only gave low EMF yields. Herein, we reveal that the combinations of common Lewis acid with Brønsted acid in ethanol universally catalyze rapid etherification of glucose to intractable ethyl glucoside (EGL), as impedes the further conversion toward the desired products. The synergy of large-pore tin phosphate (SnPO) bearing strong Lewis acidic sites with acidic ionic liquid 1-(4-sulfobutyl)-3-methylimidazolium chloride (BSO3HMIMCl) enable tandem catalytic conversion of glucose, cellobiose and starch to EMF with record yields (61.7%, 61.8% and 55.7%, respectively), far exceeding previous reports. This transformation probably occurs via multiple parallel pathways, where water molecules generated by dehydration cooperate with acid and Cl- to hydrolyze EGL back to glucose, thus forming a positive feedback on EMF production.