The Direct Conversion of Cellulose into 5‐Hydroxymethylfurfural with CrCl 3 Composite Catalyst in Ionic Liquid under Mild Conditions

Direct transformation of cellulose (PH101: DP∼200) into 5‐hydroxymethylfurfural (HMF) was investigated using the single CrCl 3 or the combination of metal chlorides (CrCl 3 with AlCl 3 , FeCl 3 , SnCl 4 , MnCl 4 , and CuCl 2 ) in ionic liquid [Bmim]Cl under oil‐bath heating. As a result, a novel co‐catalysis CrCl 3 ‐AlCl 3 was determined to be the most efficient catalyst for the production of HMF. Compared with single CrCl 3 , the reaction time with CrCl 3 ‐AlCl 3 was reduced by nearly 1/3 when a similar HMF yield (58.3%) was obtained at 120 °C. Additionally, the catalytic mechanism of CrCl 3 ‐AlCl 3 was discussed. Furthermore, when celluloses with higher polymerization degree (filter paper: DP∼1500 and cotton: DP∼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 CrCl 3 ‐AlCl 3 for various kinds of natural cellulose with a huge range of DP.