The conversion of carbohydrates into 5-hydroxymethylfurfural (5-HMF) has been studied in binary mixtures of ionic liquids (ILs), using strongly acidic resin Amberlyst 15 as the catalyst. In particular, both mono- and disaccharides, such as fructose, glucose and sucrose have been investigated. Considering the favorable effect exerted by chloride-based ionic liquids in the dissolution of carbohydrates, we used binary mixtures of 1-butyl-3-methylimidazolium chloride ([bmim][CI]) with [bmim(+)] based ionic liquids differing in size, shape and coordination ability of the anion ([bmim][BF4], [bmim(+)][N(CF3SO2)(2)], [bmim][N(CN)(2)], [bmim][SbF6] and [bmim][CF3SO3]). Carbohydrate conversion in [bmim][BF4]/[bmim][Cl] binary mixtures, has been studied under both magnetic stirring and ultrasound (US) activation. The catalytic system used led to the formation of 5-hydroxymethylfurfural in good yield under mild conditions. A significant influence of IL binary mixture composition on the outcome of the target processes was evidenced. Improvements in both reaction time and temperature have been observed, under US activation. (C) 2014 Elsevier B.V. All rights reserved.