Green synthesis of 5-hydroxymethylfurfural and 5-acetoxymethylfurfural using a deep eutectic solvent in a biphasic system assisted by microwaves

Abstract

Fructose was subjected to a dehydration reaction to produce 5-hydroxymethylfurfural (HMF) using a deep eutectic solvent (DES) composed of choline chloride ([Ch]Cl) as a hydrogen bond acceptor (HBA), fructose as a hydrogen bond donor (HBD), water as the third component of the mixture and p-sulfonic acid calix[4]arene (CX4SO₃H) as an organocatalyst. Among various solvents evaluated for the biphasic system for HMF production, ethyl acetate was determined to be the best extraction solvent. Using microwave irradiation, only 1 mol% of CX4SO₃H as the organocatalyst, a reaction temperature of 110 °C, a biphasic system (DES/ethyl acetate) and a short reaction time (10 min), HMF was obtained with a 90% yield. The synthesized HMF was used as a substrate to obtain 5-acetoxymethylfurfural (AMF), which is a promising biofuel. AMF was obtained with 99% yield by reacting HMF with acetic acid used CX4SO₃H (1 mol%) with an organocatalyst, at 80 °C for 5 min, indicating an efficient methodology for carrying out the conversion of fructose to HMF and HMF to AMF. Furthermore, the potential of this reaction in terms of coherence with green chemistry principles is addressed, and several sustainable features of this transformation are achieved. It is demonstrated that the transformation of fructose to HMF has many advantages, such as (i) a biphasic system containing a DES and ethyl acetate as a green solvent, (ii) creation of two π-bonds, (iii) water as the sole waste and (iv) the metal-free process.