Conversion of fructose to 5-hydroxymethylfurfural in a ternary deep eutectic solvent-based biphasic system at mild temperature

Abstract

The catalytic conversion of fructose to 5-hydroxymethylfurfural (5-HMF) in a ternary deep eutectic solvent (DES)/methyl isobutyl ketone (MIBK) biphasic system at mild temperatures (50–70 °C) was investigated in this work. The ternary DES consisting of choline chloride (ChCl), benzene sulfonic acid (BSA) and ethylene glycol (EG) was physicochemically characterized by FT-IR and ¹H NMR. The ternary DES(ChCl–BSA–EG)/MIBK biphasic system (ChCl/BSA/EG = 2 : 1 : 1) resulted in an 82.0% 5-HMF yield and 96.2% corresponding selectivity at 60 °C for 2 h. The kinetic analysis further revealed that the rate constant of fructose dehydration (k₁) was much higher than the rate constant of 5-HMF conversion (k₂). The calculated ratio of k₁/k₂ was 16.1. The proposed reaction mechanism suggested that the synergetic effect of the three components of the ternary DES facilitates the elimination of water molecules from fructose and the formation of 5-HMF, while the MIBK extraction phase suppresses the by-products of 5-HMF as well. The present work provides a green and sustainable pathway for 5-HMF production with a high yield and high selectivity at mild temperatures.