Rsc_cp_c1cp21371g 1..11

Ion association of the ionic liquid [bmim][Cl] in acetonitrile and in water was studied by dielectric spectroscopy for salt concentrations c r 1.3 M at 298.15 K and by measurement of molar electrical conductivities, L, of dilute solutions (c r 0.006 M) in the temperature range 273.15 t T/K r 313.15. Whilst acetonitrile solutions of [bmim][Cl] exhibit moderate ion pairing, with an association constant of KA E 60 M 1 and increasing with temperature, [bmim][Cl] is only weakly associated in water (KA E 6 M ) and ion pairing decreases with rising temperature. Only contact ion pairs were detected in both solvents. Standard-state enthalpy, entropy and heat capacity changes of ion association were derived, as well as the activation enthalpy of charge transport and the limiting conductivity of the cation, l ([bmim]). These data, in conjunction with effective solvation numbers obtained from the dielectric spectra, suggest that the solvation of [bmim] is much weaker in water than in acetonitrile.