Ion association constants of ionic liquids, 1-hexyl-3-methylimidazolium halide, in aqueous d-fructose solutions

Abstract

In this paper, the interactions of 1-hexyl-3-methylimidazolium halides ([HMIm]Cl and [HMIm]Br) with aqueous d-fructose solutions have been studied by using conductance properties. Limiting molar conductivity (Λ0), association constant (KA) and distance parameter (R) were calculated using low concentration Chemical Model (lcCM) at temperatures ranges of (298.15–328.15)K and concentrations (0.05, 0.10 and 0.20)molkg−1 of d-fructose solutions. The Λ0 values increase with increasing temperature and decrease during the addition of d-fructose. The greater values of association constant for [HMIm]Cl relative to [HMIm]Br is due to the high surface charge density of the Cl− anion proposing strong association tendency with [HMIm]+ cation. Moreover, an enhancement was observed in the KA values as temperature is increased suggesting that ion-pair formation is an endothermic process. The mobility of ions was found to be completely controlled by the bulk viscosity (η) and consequently the Walden products (Λ0η) were estimated and discussed. The association constants were used to study the thermodynamic of association process. Consequently, Gibbs free energy (ΔGA0), enthalpy (ΔHA0) and entropy (ΔSA0) of ion-pair formation have been obtained at different temperatures. It was observed that the ion-association process exhibits a negative value of ΔGA0 and becomes more negative with increasing temperature proposing the spontaneity and feasibility of the association at high temperatures.