One-Pot Conversions of Raffinose into Furfural Derivatives and Sugar Alcohols by Using Heterogeneous Catalysts

Inedible and/or waste biomass reserves are being strongly focused upon as a suitable new energy and chemical source. Raffinose, which is an indigestible trisaccharide composed of glucose, galactose, and fructose, is found abundantly in beet molasses, sugar cane, and seeds of many leguminous plants. Herein, we demonstrate the one-pot synthesis of furan derivatives and sugar alcohols from raffinose by using heterogeneous acid, base, and/or metal-supported catalysts. The combination of Amberlyst-15 and hydrotalcite (HT) showed a high activity (37% yield) for 5-hydroxymethyl-2-furaldehyde (HMF) through continuous hydrolysis, isomerization, and dehydration reactions. In addition, the use of a hydrotalcite-supported ruthenium catalyst (Ru/HT) successfully afforded 2,5-diformylfuran (DFF, 27% yield) from HMF produced by raffinose, directly. Moreover, the hydrogenation of hexoses obtained by raffinose hydrolysis into sugar alcohols (galactitol, mannitol, sorbitol) was also achieved in a high yield (91%) with Amberlyst-15 and Ru/HT catalysts. Thus, we suggest that raffinose has great potential for the synthesis of important industrial intermediates under mild reaction conditions.