The Direct Conversion of Cellulose into 5-Hydroxymethylfurfural with CrCl3 Composite Catalyst in Ionic Liquid under Mild Conditions

Direct transformation of cellulose (PH101: DP similar to 200) into 5-hydroxymethylfurfural (HMF) was investigated using the single CrCl3 or the combination of metal chlorides (CrCl3 with AlCl3, FeCl3, SnCl4, MnCl4, and CuCl2) in ionic liquid [Bmim]Cl under oil-bath heating. As a result, a novel co-catalysis CrCl3-AlCl3 was determined to be the most efficient catalyst for the production of HMF. Compared with single CrCl3, the reaction time with CrCl3-AlCl3 was reduced by nearly 1/3 when a similar HMF yield (58.3%) was obtained at 120 degrees C. Additionally, the catalytic mechanism of CrCl3-AlCl3 was discussed. Furthermore, when celluloses with higher polymerization degree (filter paper: DP similar to 1500 and cotton: DP similar to 1950) were used, exceedingly higher yields of HMF (54.7% for filter paper and 59.5% for cotton) were obtained compared with previous work. This important result strongly indicates the general applicability of CrCl3-AlCl3 for various kinds of natural cellulose with a huge range of DP.