Efficient process for the direct transformation of cellulose and carbohydrates to 5-(hydroxymenthyl)furfural with dual-core sulfonic acid ionic liquids and co-catalysts

The direct transformation of cellulose and carbohydrates into 5-(hydroxymethyl)furfural (HMF) in the solvent [BMIM] Cl using dual-core sulfonic acid ionic liquids (ILs) as catalysts and metal salts as co-catalysts was investigated, aiming at a more environmentally friendly process not involving chromium. From the high throughput screening of various metal salts, a combination of [bi-C3SO3HMIM][CH3SO3] (IL-2) and manganese chloride (MnCl2) was found to be the most effective catalyst. HMF was directly afforded from cellulose in 66.5% yield. Thus, synthesis of HMF was successfully performed from cellulose using ILs and MnCl2. Following the principles of green engineering, we recycled the catalyst in our system for cellulose hydrolysis and this catalyst maintained its good performance even after four runs. Furthermore, various sugars and lignocellulosic raw materials could be directly converted into HMF in reasonable yields under these conditions. The mechanism that explains the high activity of ILs in combination with MnCl2 is also proposed.