Precise vapor pressure osmometry (VPO) measurements at 308.15 K were conducted for solutions of three ILs, 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]), 1-butyl-3-methylimidazolium bromide ([Bmim][Br]), and 1-butyl-3-methylimidazolium hydrogen sulfate ([Bmim][HSO4]), in aqueous solutions of three carbohydrates, sucrose, maltose, and maltitol, as well as for solutions of the carbohydrates in aqueous solutions of these ILs. Because of the unfavorable IL–carbohydrate interactions, all the investigated IL + carbohydrates aqueous systems show the soluting-out effect and vapor–liquid equilibria behavior of these systems in the monophasic region show the negative deviation from the semi-ideal behavior (aw + 1 < awIL° + awC° and Δp < ΔpIL° + ΔpC°). For a certain carbohydrate and at the same molality of IL, the magnitude of the departures for the investigated ILs follows the order: [Bmim][BF4] > [Bmim][HSO4] ≫ [Bmim][Br]. In the case of [Bmim][BF4]/carbohydrate aqueous systems, which have a phase separation capability, the soluting-out power of the carbohydrates on [Bmim][BF4] in aqueous solutions (or negative deviation from the semi-ideal behavior) reduced by decreasing the hydrophilicity of the carbohydrates. Aqueous [Bmim][Br]/carbohydrate and [Bmim][HSO4]/carbohydrate systems are unable to form the ABS, and the soluting-out effect of the ILs on the aqueous carbohydrate solutions appears in the form of precipitation of sugars from the aqueous solutions.
