Ion Pair Formation of 1-Alkyl-3-methylimidazolium Salts in Water

Abstract

Ion pair formation in water of a series of 1-alkyl-3-methylimidazolium cations (1-butyl-, C 4 mim + ; 1-hexyl-, C 6mim + ; 1-octyl-, C 8 mim + ) with BF 4 -, PF 6 -, bis(trifluoromethylsulfonyl)imide (Tf 2 N -), and picrate (Pic -) anions has been investigated by capillary electrophoresis at 25 °C. The formation constants at infinite dilution (K IP °) of the 1:1 ion pairs have been determined. For all the anions, the K IP °value increases with increasing alkyl chain length of the cation (i.e., C 4 mim + < C 6 mim + < C 8 mim + ). Except for Pic -, the anion dependence of the K IP °value is always BF 4 -< PF 6 -< Tf 2 N -. The Picanion has a larger K IP °value with C 8 mim + than the other anions, whereas the K IP °value of Picis smaller than or nearly equal to that of Tf 2 Nwhen the cation is C 4 mim + or C 6 mim + ; the K IP °value for Picvaries most sensitively with the alkyl chain length of the cation. The K IP °values of the picrate salts are compared with those of tetraalkylammonium picrates previously reported.

Weak Binding of N-Alkylpyridinium Ions to Nonionic Surfactant Micelles as Studied by Capillary Zone Electrophoresis

“…Ion pair formation of 1-alkyl-3-methyl-imidazolium ions in water has been investigated by CZE. 19 The binding of some N-alkylpyridinium salts possessing long alkyl chain to dodecyl oxyethylene ether micelles has been investigated by potentiometry; 20 the reaction is mixed-micelle formation rather than binding. In this study, we investigated the binding reaction of N-alkylpyridinium ions to nonionic surfactant micelles through the electrophoretic mobility in CZE.…”

Distribution of 1-Alkyl-3-methylimidazolium Ions and Their Ion Pairs between Dichloromethane and Water

“…[5][6][7] Recently, we have determined the ion-pair formation constants of several 1-alkyl-3-methylimidazolium salts in water under conditions where the micelle formation is negligible. 4 The results show that the ionpair formation constants in water are considerably different in magnitude and tendency from those in dichloromethane. 8 The aqueous ion-pair formation is expected to be strongly affected by the hydration of ions and ion pairs.…”

“…Therefore, the study of the aqueous solution chemistry of ionic liquids is important from the viewpoint of such analytical applications. Ionic liquid salts exist as dissociated ions and ion pairs in aqueous solution, 4 and some of them further aggregate to form micelles. [5][6][7] Recently, we have determined the ion-pair formation constants of several 1-alkyl-3-methylimidazolium salts in water under conditions where the micelle formation is negligible.…”

A Priori Prediction of Dissociation Phenomena and Phase Behaviors of Ionic Liquids

“…The dissociation of ILs also have a profound impact on toxicity, 11 their use in chemical reactions, 12 and applications as an active pharmaceutical ingredient (API). 13−15 Many experimental efforts (e.g., using NMR, 16,17 dielectric relaxation spectroscopy (DRS), 18,19 and conductivity measurements 20 ) have been devoted to investigating the extent of dissociation (α) of ILs. In the dilute solution limit, ILs tend to fully dissociate.…”