Mechanism of Glucose Conversion into 5‑Ethoxymethylfurfural in Ethanol with Hydrogen Sulfate Ionic Liquid Additives and a Lewis Acid Catalyst

Hydrogen sulfate ionic liquid additives with aluminum chloride catalyst in ethanol were found to promote efficient (30 min) one-pot, one-step transformation of glucose into 5-ethoxymethylfurfural (5-EMF) in 37% yields. Spectroscopic measurements (FT-IR, ¹H NMR) showed that ionic liquids form multiple hydrogen bonds with glucose and promote its ring opening through ionic liquid–AlCl₃ complexes to enable formation of 5-EMF via 5-hydroxymethylfurfural (5-HMF). Reactions performed in dimethyl sulfoxide using (protic, aprotic) ionic liquid additives with and without AlCl₃ catalyst showed that both the ionic liquid and AlCl₃ were required for efficient transformation of glucose into 5-EMF. The proposed reaction mechanism for 5-EMF synthesis in the ethanol–1-butyl-3-methylimidazolium hydrogen sulfate–AlCl₃ reaction system consists of ring opening of glucose to form the 1,2-enediol and dehydration to form 5-HMF that is followed by etherification to the 5-EMF product. The reaction system is effective for glucose transformation and has application to biomass-related compounds.