Efficient conversion of chitin into 5-hydroxymethylfurfural via a simple formylation step under mild conditions

Abstract

Improper disposal of large quantities of crustacean shell waste from the food industry has caused serious environmental problems and waste of resources. Shell biorefinery is an emerging concept that upcycles the major components of crustacean shell waste, such as chitin, into value-added chemicals and materials. Producing biomass-derived 5-hydroxymethylfurfural (HMF) has been a hot topic over the past decades, while efficient conversion of shell-derived chitin into HMF is not available due to its water-insoluble and chemically-stable features. Herein, we develop a sustainable and efficient HMF production route from chitin. Chitin was treated with formic acid under mild conditions to synthesize formylated chitin (FC), which was subsequently converted to HMF in dimethyl sulfoxide (DMSO)–H₂O media. Results showed that FC achieved a 53.2% HMF yield at 160 °C for 10 min catalyzed by AlCl₃ in the co-solvent system (DMSO : H₂O = 4 : 1, v/v), which is 11 times higher than the yield obtained from chitin under the same condition. The grafted formyl groups on FC significantly enhanced its noncovalent interactions with DMSO molecules, enhancing the accessibility and reactivity for HMF production. The reaction mechanisms were proposed and simulated with density functional theory calculations, and the intramolecular hydrogen migration is the rate-determining step in the reaction pathways. This study highlights a green and simple approach for chitin valorization.