Efficient synthesis of 5-hydroxylmethxylfufrual from fructose in a phenolic acid-derived ternary deep eutectic solvent

The green synthesis of 5-hydroxymethylfurfural (HMF) from carbohydrates is a significant step for the production of sustainable fuels and fine chemicals, where the solvent plays an important role in terms of conversion efficiency and process sustainability. This work reports the bifunctional use of ternary deep eutectic solvents (TDESs), as both the solvent and catalyst, in the dehydration of fructose to HMF. A series of phenolic acids are used as hydrogen bond donors (HBDs) in TDESs. The combination of choline chloride–1,4-butylene glycol– p -hydroxybenzene propanoic acid (ChCl–BDO–PH) catalysed the quantitative conversion of fructose to obtain the highest HMF yield of 90.2%. Nuclear magnetic resonance and 3D-fluorescence spectroscopy analysis indicated that there were no humins polymers accumulation and it possibly formed the soluble micro-molecules humins byproducts. Moreover, HMF could be readily separated from TDESs, which allowed the stable recycling of TDESs for five recycles. Density functional theory calculations implied that a lower energy of hydrogen bond between TDESs and fructose promoted the fructose conversion and HMF formation, which is due to the methoxy group and side chain structure of phenolic acid that may reduce the ionization activity of hydrogen ions in the carboxyl group, thus reducing the hydrogen bond between TDESs and fructose. This work provides a novel alternative to traditional Brønsted acid towards the greener production of HMF.