A method for converting glucose into 5-hydroxymethylfurfural (5-HMF) without using chromium-containing catalysts was developed. The method uses ionic liquid-water mixtures with a ZrO2 catalyst. Addition of a certain amount of water (10-50 wt.%) into the 1,3-dialkylimidazolium chloride ionic liquid promoted the formation of 5-HMF from glucose compared with that in either pure water or in the pure ionic liquid. A 5-HMF yield of 53% was obtained within 10 min at 200 degrees C in a 50:50 w/w% 1-hexyl-3-methyl imidazolium chloride-water mixture in the presence of ZrO2. The 1,3-dialkylimidazolium ionic liquids having Cl- or HSO4- anions were effective for promoting 5-HMF formation. Addition of protic solvents such as methanol and ethanol to the ionic liquid had a similar synergistic effect as water and promoted fructose and 5-HMF formation. The results reported in this work can be extended to other fields, where the ratio of ionic liquid and protic solvent can be adjusted to promote the desired reactions. (C) 2012 Elsevier Ltd. All rights reserved.