Diffusion Coefficients of 1-Alkyl-3-methylimidazolium Ionic Liquids in Water, Methanol, and Acetonitrile at Infinite Dilution

The diffusion coefficients of several ionic liquids based on the 1-alkyl-3-methylimidazolium cation, [C(n)C(1)lm], with chloride, tetrafluoroborate, and bis(trifluoromethanesulfonyl)imide, [Ntf(2)], anions were measured, using a Taylor dispersion technique, in three solvents (water, methanol, and acetonitrile) as a function of temperature between (293 and 333) K. The diffusion coefficients vary from 0.57.10(-9) m(2).s(-1) for 1-methyl-3-octylimidazolium bis(trifluoromethanesulfonyl)imide, [C(8)C(1)im][Ntf(2))], in water to 3.48.10(-9) m(2).s(-1) for 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, [C(2)C(1)im][Ntf(2)], in acetonitrile. In general, the diffusivities are lower for water, followed by methanol and acetonitrile, and decrease with an increase in the alkyl side chain of the imidazolium-based ionic liquids. These trends do not follow the Stokes-Einstein relation but can be explained by the solute-solvent interactions. The data were correlated using a modified Wilke-Chang equation in which a correction parameter was introduced. The correction parameter is independent of the temperature and is different for each solvent studied.