An effective approach for chitosan conversion to 5-hydroxymethylfurfural catalyzed by bio-based organic acid with ionic liquids additive

The primary challenges associated with converting chitin biomass into 5-hydroxymethylfurfural (5-HMF) primarily revolve around achieving high 5-HMF yields while overcoming various limitations from traditional acid-based catalysts, including complex post-treatment procedures, by-product generation, and equipment corrosion. In this view, a novel approach was developed to synthesize 5-HMF from chitosan under hydrothermal process using a mixture of DMSO and water as reaction medium. Biomass-derived organic carboxylic acids were used as catalysts due to their weaker corrosiveness compared to mineral acids. The acidity of the bio-based acid was adjusted using inexpensive ionic liquids. By combining 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) with oxalic acid (OA), an excellent 29.1 % yield of 5-HMF conversion was achieved on the optimized condition. The improved dissociation ability of OA by [BMIM]Cl played a crucial role in this outcome. Using FTIR and density functional theory (DFT) techniques allowed for the proposal of a dissociation mechanism for OA induced by [BMIM]Cl, involving hydrogen bond interactions and the weakening of the O–H bond, facilitating the easy dissociation of hydrogen in the O–H group with H+ formation. Furthermore, the untreated chitosan and the solid residues obtained during the conversion process were characterized revealing the gradual conversion and the quaternization in the NH2 group of chitosan.