Highly Efficient and Selective Preparation of 5-Hydroxymethylfurfural from Concentrated Carbohydrates Using Deep Eutectic Solvents

Abstract

Converting carbohydrates to 5-hydroxymethylfurfural (HMF) is an important goal for biorefinery. Although various deep eutectic solvents (DESs) have been reported for HMF production, the field lacks systematic research on the effect of cations and anions and an effective catalytic system for converting concentrated carbohydrates. Here, 12 kinds of DESs containing four cations and six anions were systematically evaluated and tetraethylammonium bromide (TEAB) was confirmed as the most effective DES, which provided HMF yields of 90 and 76% from fructose and glucose, respectively. The stable bromide-substituted intermediate may explain the positive effect of bromide based on the results of density functional theory calculation. A high concentration substrate has an adverse impact on the selectivity of HMF due to the HMF concentration caused by glucose, CrCl3·6H2O, and concentrated HMF. To inhibit the condensation, a biphasic system of TEAB/THF is developed to convert a highly concentrated glucose of 62.5 wt % (83.3 wt % with respect to TEAB), providing an excellent HMF yield of 72%. This study has revealed the impact of cations and anions of DESs on HMF production, which will serve as a base for designing task-specific DESs. Moreover, an efficient catalytic system to produce HMF from concentrated glucose was also provided.

Highly Efficient One-Pot Conversion of Glucose to 5-Hydroxymethylfurfural over Acid–Base Bifunctional MCM-41 Mesoporous Silica under Mild Aqueous Conditions

“…At present, HMF is primarily produced by the simple acid-catalyzed dehydration of fructose. Unfortunately, fructose is not an ideal substrate for HMF production owing to its low availability and high price. , Instead, glucose is regarded as a preferred starting material for the synthesis of HMF as it is the most abundant and cheapest hexose . However, the transformation of glucose to HMF is more difficult than the fructose route and requires two steps.…”