Multiple-SO3H functionalized ionic liquid as efficient catalyst for direct conversion of carbohydrate biomass into levulinic acid

A series of new SO3H-functionalized ionic liquids (ILs) were synthesized and characterized, which were successfully applied to catalyze cellulose to produce levulinic acid (LA) via one-pot reaction. The structure, thermal property, and acidity of ILs were characterized by NMR, TGA, and Hammett acidity measurement. The Hammett acidity (H-0) of ILs increase in the following order: [BSim]H2PO4 <[BSim]TsO < [BSim]CF3SO3 < [BSim]HSO4, which is consistent with their yield of LA order using these ILs as catalysts. Under the optimum conditions, the yield reached up to 65% when [BSim]HSO4 was used as catalyst and solvent, which is one of the best results compared to those reported in literature. Moreover, the ILs were easily recycled without structural change even after four cycles, and the yield of LA was up to 44% at the fifth cycle. Furthermore, TGA indicated that these SO3H-functionalized ILs exhibited excellent thermal stability. These efficient ILs will provide new options for converting biomass resources to LA and other chemicals.