Facile catalytic dehydration of fructose to 5-hydroxymethylfurfural by Niobium pentachloride

Different metal chlorides in ionic liquids were examined as catalysts for fructose dehydration to 5-hydroxymethylfurfural (5-HMF). Niobium pentachloride (NbCl₅) exhibited the highest 5-HMF yield. Reaction of 1.0 mmol fructose in 10.0 mmol 1-butyl-3-methylimidozolium chloride ([bmim]Cl) with 0.20 mmol NbCl₅ afforded 79% of 5-HMF at 80 °C after 30 min. No degradation products were formed under these conditions. FTIR analysis indicates the moderate Lewis acidity of NbCl₅, which was found suitable for the selective formation of 5-HMF. Other catalysts with higher Lewis acidities promoted 5-HMF side product formation which ultimately resulted in lower yields.