Efficient conversion of chitin to 5-hydroxymethylfurfural in a formic acid/calcium chloride system

Chitin is a class of biomass second only to cellulose in abundance, and the preparation of platform compounds from chitin holds great promise. Herein, a pretreatment biphasic solvent system and a catalytic two-stage process are combined for the direct synthesis of 5-hydroxymethylfurfural (HMF) from chitin. The first step of the process, i.e., the pretreatment of chitin with a CH₃OH/CaCl₂ solution, alters the structure of chitin, allowing it to be depolymerized more easily. In the second step of the process, a green and recyclable biphasic catalytic solvent system comprising a formic acid solution and n-butanol is prepared using pretreated chitin (Ca-PC) as the starting reactant, realizing an HMF yield of 47.65 % in 32 min. This HMF yield surpasses that reported in the literature (19.3 %-30 %). The synergistic interaction of Ca²⁺, introduced via formic acid pretreatment, is the key to the catalytic system of chitin, which disrupts the internal hydrogen bonding of chitin and simultaneously improves HMF selectivity. In summary, we have promoted the depolymerization of chitin using a simple and effective pretreatment process, designed a catalytic system with a green recyclable reaction, and effectively improved the yield of HMF directly prepared from chitin.