Direct conversion of chitin biomass to 5-hydroxymethylfurfural in concentrated ZnCl2 aqueous solution

The direct conversion of chitin biomass to 5-hydroxymethylfurfural (5-HMF) in ZnCl2 aqueous solution was studied systemically. d-Glucosamine (GlcNH2) was chosen as the model compound to investigate the reaction, and 5-HMF could be obtained in 21.9% yield with 99% conversion of GlcNH2. Optimization of the reaction parameters including the screening of 8 co-catalysts was carried out. Among them, AlCl3 and B(OH)3 improved 5-HMF yield, whereas CdCl2, CuCl2 and NH4Cl had no effect. CrCl3, SnCl4 and SnCl2 showed negative effects, i.e. lower yields. Consequently, the optimal reaction conditions were found to be 67 wt.% ZnCl2 aqueous solution, at 120 °C without co-catalyst. The reactions were further studied by in situ NMR, and no intermediate or other byproducts, except humins, were observed. Finally, the substrate scope was expanded from GlcNH2 to N-acetyl-d-glucosamine and various chitosan polymers with different molecular weights, 5-HMF yield from polymers were generally lower than that from GlcNH2.