Production of 5-hydroxymethylfurfural from chitosan using choline chloride-based deep eutectic solvents as catalyst

This study explores an efficient catalytic system for the conversion of chitosan into 5-hydroxymethylfurfural (5-HMF) under hydrothermal conditions. The catalysts used are deep eutectic solvents (DESs) comprising choline chloride (ChCl) as the hydrogen bond acceptor (HBA) and various organic acids as the hydrogen bond donor (HBD). Among the DESs tested, the ChCl: oxalic acid (OA) combination exhibits the highest catalytic activity, resulting in a yield of 27.5% 5-HMF employed the optimized conditions. To elucidate the interaction between ChCl and OA, various analytical techniques were employed, including quantum chemical calculations, nuclear magnetic resonance (NMR), and Fourier transform infrared spectroscopy (FTIR). These investigations confirmed the formation of strong hydrogen-bonds between ChCl and OA. Furthermore, the solid residues obtained during the conversion process were characterized using FTIR, X-ray diffraction (XRD), and scanning electron microscopy (SEM). These analyses provide insights into the chemical structures and morphologies of the residues, revealing the gradual conversion of chitosan, along with the formation of humin by-products.