Stability of Ion Pairs of Bis(trifluoromethanesulfonyl)amide-Based Ionic Liquids in Dichloromethane

• Published in: Journal of chemical and engineering data 2010-04, Vol.55 (4), p.1588-1593
• Main Authors: Katsuta, Shoichi, Shiozawa, Yuta, Imai, Kazuo, Kudo, Yoshihiro, Takeda, Yasuyuki
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Solution properties; Solutions
• ISSN: 0021-9568; 1520-5134
• DOI: 10.1021/je900694m

The ion pair formation constants at infinite dilution (K IP 0) 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 K IP 0 values that the ion pair stability varies with the cation in the order [BuMeIm]+ > [Me3PrN]+ > [BuPy]+ ≥ [BuMePyrr]+ ≥ [MePrPip]+ > [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 K IP 0 values was discussed.