Kinetic studies on chromium-catalyzed conversion of glucose into 5-hydroxymethylfurfural in alkylimidazolium chloride ionic liquid

• The reaction is second order in glucose with an activation energy of 134.9 kJ mol−1.
• The order of the reaction in chromium is first.
• The observed rate constant decreases as initial glucose concentration increases.
• A kinetic model was developed to describe glucose conversion and 5-hydroxymethylfurfural formation.

5-Hydroxymethylfurfural (HMF) is a promising green platform chemical derived from biomass. Kinetic studies were performed on chromium chloride-catalyzed conversion of glucose into HMF in alkylimidazolium chloride ionic liquids. The main by-products are disaccharides, fructose, glyceraldehyde, formic acid, and humins. The formation of HMF is strongly affected by reaction temperature and initial glucose concentration. The reaction is second order in glucose, with an activation energy of 134.9 kJ mol−1. The order in chromium is first, indicating that the rate-determining isomerization reaction is catalyzed by a mononuclear chromium species. The observed glucose conversion rate constant decreases as initial glucose concentration increases, suggesting that the catalytic activity of the chloride anion is significantly restrained by the hydrogen bonding with hydroxyl groups. A simplified kinetic model is developed to describe the behaviors of glucose conversion and HMF formation. This model is in good agreement with the experimental results.