One-pot conversion of cellulose to HMF under mild conditions through decrystallization and dehydration in dimethyl sulfoxide/tetraethylammonium chloride

As a crucial bio-based platform chemical, the production of 5-hydroxymethylfurfural (HMF) from the abundant substrate cellulose has garnered significant attention. However, tedious reaction steps are inevitable because of the complex tandem conversions of dissolution, hydrolysis, and dehydration. Furthermore, due to the ultralow solubility of cellulose, harsh reaction conditions are inevitable, which can exacerbate HMF degradation. To this end, we investigated the structural changes in microcrystalline cellulose (MCC) after its dissolution and regeneration in various dimethyl sulfoxide (DMSO)/deep eutectic solvents (DESs) to clarify the mechanisms underlying its dissolution. The results revealed that the highly crystalline cellulose I in MCC was converted into amorphous cellulose II after treatment with DMSO/tetraethylammonium chloride (TEAC), which led to the complete dissolution of MCC. Accordingly, a dissolution-catalysis coupling reaction strategy was proposed for converting MCC to HMF via a one-pot method in DMSO/TEAC, simultaneously reducing the number of steps necessary for the reaction and achieving mild reaction conditions. In addition, the pathway for the one-pot reaction was clarified by analyzing the intermediate yields. The combination of AlCl3 as a catalyst and DMSO/TEAC resulted in a notable MCC conversion of 93.3 wt% and a high HMF yield of 53.1%. Remarkably, the reaction conditions employed in this study (130 °C, 1 h) were milder in terms of shorter reaction times and lower temperatures than those reported in most current literature. This was attributed to the complete dissolution of MCC resulting from decrystallization. Therefore, the proposed reaction strategy enabled the efficient production of HMF from cellulose.