1-Ethyl-3-methylimidazolium Ethylsulfate in Water, Acetonitrile, and Dichloromethane: Molar Conductivities and Association Constants

Molar conductivities, Lambda, of dilute solutions of the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate in water, acetonitrile (AN), and dichloromethane (DCM) were determined as a function of temperature (AN: T = (273.15 to 313.15) K; DCM: T = (273.15 to 308.15) K; water: T = (278.15 to 313.15) K) in the concentration range c = (approximate to 0.25 to approximate to 5).10(-3) mol.dm(-3). The data were analyzed with Barthel's low-concentration chemical (lcCM) model to obtain the limiting molar conductivities, Lambda(infinity)(T), and association constants, K-A(circle)(T), of this electrolyte in the investigated solvents. From Lambda(infinity)(T) the Eyring activation enthalpy of charge transport was determined and found to be slightly larger than the corresponding value for viscous flow of the solvent. Strong ion pairing was found for the electrolyte in DCM (K-A(circle) approximate to 6.10(4) mol(-1).dm(3)), whereas ion association in AN is rather weak (K-A(circle) approximate to 40 mol(-1).dm(3)). From the temperature dependence of K-A(circle)(T) the enthalpy and entropy of the ion-pairing process were calculated, and ion association was found to be entropy-driven for both nonaqueous solvents. In water the salt is fully dissociated.