Microwave-assisted HMF production from water-soluble sugars using betaine-based natural deep eutectic solvents (NADES)

Abstract

In this work, HMF was produced from fructose-based carbohydrates using a NADES system composed of betaine hydrochloride (BHC) as the hydrogen bond acceptor (HBA), carboxylic acids as hydrogen bond donors (HBDs) and water as the third component of the mixture. Among twelve green solvents evaluated for HMF production, ethyl acetate was the best extraction solvent. Thanks to the use of microwave irradiation, the reaction time could be reduced from 45 min to 11 min and, under optimized conditions, the NADES system composed of BHC/malic acid/H₂O afforded HMF in 94% and 72% yield from fructose and sucrose, respectively. Thermogravimetric analyses provided a better understanding on the behavior of the NADES system upon heating, which in turn explained the results obtained for the sugar dehydration and recycling experiments.