Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

The ion pair formation constants at infinite dilution (KIP0) of bis(trifluoromethanesulfonyl)amide ([NTf2]-) salts in dichloromethane were determined conductometrically at 298.2 K. The cations used were nine monovalent organic ions having similar molecular size, i.e., 1-butyl-3-methylimidazolium ([BuMeIm]+), 1-butyl-2,3-dimethylimidazolium ([BuMe2Im]+), 1-butylpyridinium ([BuPy]+), 1-propyl-2,3,5-trimethylpyrazolium ([Me3PrPyra]+), 1-butyl-1-methylpyrrolidinium ([BuMePyrr]+), 1-methyl-1-propylpiperidinium ([MePrPip]+), methyltripropylammonium ([MePr3N]+), propyltrimethylammonium ([Me3PrN]+), and tetraethylammonium ([Et4N]+), where the results for [BuMeIm]+, [BuMe2Im]+, and [Et4N]+ were cited from our previous study. It was found from the KIP0 values that the ion pair stability varies with the cation in the order [BuMeIm]+ greater than [Me3PrN]+ greater than [BuPy]+ ? [BuMePyrr]+ ? [MePrPip]+ greater than [MePr3N]+ ? [Et4N]+ ? [BuMe2Im]+ ? [Me3PrPyra]+, which was explained on the basis of the structures of the cations. For the salts used, the fundamental properties as ionic liquids, such as density, viscosity, and electric conductivity, were also measured. The activation energies for viscous flow were determined from the temperature dependence of the viscosity, and their relation with the KIP0 values was discussed.