Ion Pair Formation of Alkylimidazolium Ionic Liquids in Dichloromethane
The 1:1 ion pair formation constants (K IP 0) of 1-alkyl-3-methylimidazolium ([RMeIm]+; R = butyl, hexyl, and octyl) and 1-butyl-2,3-dimethylimidazolium ([BuMe2Im]+) ions with tetrafluoroborate ([BF4]−), hexafluorophosphate ([PF6]−), bis(trifluoromethanesulfonyl)amide ([NTf2]−), and 2,4,6-trinitroph...
Saved in:
Published in | Journal of chemical and engineering data Vol. 53; no. 7; pp. 1528 - 1532 |
---|---|
Main Authors | , , , , , |
Format | Journal Article |
Language | English |
Published |
Washington, DC
American Chemical Society
10.07.2008
|
Subjects | |
Online Access | Get full text |
Cover
Loading…
Summary: | The 1:1 ion pair formation constants (K IP 0) of 1-alkyl-3-methylimidazolium ([RMeIm]+; R = butyl, hexyl, and octyl) and 1-butyl-2,3-dimethylimidazolium ([BuMe2Im]+) ions with tetrafluoroborate ([BF4]−), hexafluorophosphate ([PF6]−), bis(trifluoromethanesulfonyl)amide ([NTf2]−), and 2,4,6-trinitrophenolate (picrate, [Pic]−) ions have been determined conductometrically in dichloromethane at 25 °C. The K IP 0 determinations have also been made for symmetric tetraalkylammonium ions ([R4N]+; R = methyl, ethyl, propyl, and butyl) for comparison. For a given anion, the K IP 0 value of the [RMeIm]+ salt is almost independent of the length of the alkyl chain (R), whereas that of the [R4N]+ salt decreases with increasing alkyl chain length. Such a difference in the alkyl chain length dependence of the ion pair formation ability can be explained on the basis of the structures of the ion pairs calculated by density functional theory. The K IP 0 values of [BuMeIm]+, [BuMe2Im]+, and [Et4N]+, which are similar in the van der Waals volume, are in the order of [BuMeIm]+ ≫ [BuMe2Im]+ ≈ [Et4N]+, showing that the C2−H atom on the imidazolium ring makes an important contribution to the strong ion pair formation ability of [RMeIm]+. For a given cation, the K IP 0 value is generally smaller for the larger anion, i.e., [BF4]− ≥ [PF6]− ≥ [NTf2]− > [Pic]− for [Et4N]+ and [BuMe2Im]+, and [BF4]− > [PF6]− ≥ [Pic]− ≥ [NTf2]− for [RMeIm]+. |
---|---|
Bibliography: | istex:F50EB54BEF502B9920AE2ED157FED4B415B4A805 ark:/67375/TPS-JTLHJ74P-5 The authors are grateful for a Grant-in-Aid for Scientific Research on Priority Areas (No. 18045007) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan. |
ISSN: | 0021-9568 1520-5134 |
DOI: | 10.1021/je800152d |