Switchable Product Selectivity in Dehydration of N-Acetyl-D-Glucosamine Promoted by Choline Chloride-Based Deep Eutectic Solvents

Abstract

The design of green and efficient catalysts to convert biomass into value-added chemicals is a central point of biorefinery and sustainable chemistry. Herein, we report choline chloride-based deep eutectic solvents (DESs) promoted conversion of N-acetyl-d-glucosamine (GlcNAc) into nitrogen-containing compounds, i.e. 3-acetamido-5-(1′,2′-dihydroxyethyl) furan (Chromogen III) and 3-acetamido-5-acetylfuran (3A5AF). The binary deep eutectic solvent choline chloride-glycerin (ChCl-Gly), was found to promote the dehydration of GlcNAc to form Chromogen III, which reaches a maximum yield of 31.1%. On the other hand, the ternary deep eutectic solvent, choline chloride-glycerol-B(OH)₃ (ChCl-Gly-B(OH)₃), promoted the further dehydration of GlcNAc into 3A5AF with a maximum yield of 39.2%. Additionally, the reaction intermediate, 2-acetamido-2,3-dideoxy-d-erythro-hex-2-enofuranose (Chromogen I), was detected by in situ nuclear magnetic resonance (NMR) techniques when promoted by ChCl-Gly-B(OH)₃. The experimental results of the ¹H NMR chemical shift titration showed ChCl-Gly interactions with α-OH-3 and α-OH-4 of GlcNAc, which is responsible for promoting the dehydration reaction. Meanwhile, the strong interaction between Cl- and GlcNAc was demonstrated by ³⁵Cl NMR.