N-methyl-2-pyrrolidonium-based Bronsted-Lewis acidic ionic liquids as catalysts for the hydrolysis of cellulose

We experimentally studied the catalytic performances of a series of Bronsted-Lewis acidic N-methyl-2-pyrrolidonium metal chlorides ([Hnmp]Cl/MClx, where M=Fe, Zn, Al, or Cu) for the hydrolysis of microcrystalline cellulose (MCC) and cotton to produce reducing sugar. A variety of factors, such as temperature, time, ionic liquid (IL) species, IL dosage, and the concentration of the metal chloride were investigated. [Hnmp]Cl/FeCl3 presented the best hydrolysis performance, affording a 98.8% yield of total reducing sugar from MCC (1 h, 100 degrees C, 0.1 g MCC, 0.2 g acidic IL, 2.0 g [Bmim]Cl as solvent), which is better than or comparable to results previously obtained with other -SO3H functionalized acidic ILs. The hydrolysis performances of [Hnmp]Cl/MClx were rationalized using density functional theory calculations, which indicated that interactions between the metal chlorides and the cellulose, including charge-transfer interactions are important in the hydrolysis of cellulose and degradation of glucose. This work shows that Bronsted-Lewis acidic ILs are potential catalysts for the hydrolysis of cellulose to produce sugar.