´
important role in successful AER anion loading. When the anion
exchange took place within the resin, alkaline salts (LiOH or
KOH) were formed. In contrast with ammonium hydroxide, the
OH- anion in these strong bases displaced the new anion, which
reversed the process and returned the resin to the OH form (see
Fig. 2).24 This aspect was confirmed when we treated A-26 (OH
form) with a NaCl solution and the Cl- exchange did not take
place, although it was successfully loaded with HCl or NH4Cl
(see Table 1).
3 (a) E. Alcalde, N. Mesquida, M. Vilaseca, C. Alvarez-Ru´a and S.
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Having examined the exchange of the iodide anion, the
same process was explored from the bromide imidazolium salt.
Thus, treatment of [bmim][Br] with the corresponding AER,
conveniently loaded with the selected anion, led to the complete
exchange of Br-, as had occurred with the I- anion.
Regarding other ionic liquids based on imidazolium salts,
[bbim][I] and [bbim][Br] were examined as well as [mmim][I],
and in all cases I- or Br- exchange was obtained. Exception-
ally, treatment of [mmim][I] afforded a quantitative exchange,
although in some instances the recovery of the new ion pair was
only about 90–95%.
In all cases, the purity of the ionic liquids obtained was quali-
tatively determined using 1H-NMR spectra, and/or ESI(-)-MS
experiments, and the original halide was not observed. Ac-
cording to the silver chromate test, most analysis indicated
the low halide contents (< 20 ppm). Further quantification
of possible halide impurity was restricted by instrumental
limitation.
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In summary, we have developed an efficient, simple and
practical procedure for the exchange of iodide or bromide
for a variety of anions in imidazolium ionic liquids, using an
anion exchange resin. The preparation of an AER conveniently
loaded with a new selected anion by treatment with acid or
ammonium salts not only offers an efficient tool to prepare
the appropriate ion pair, including task-specific and chiral
RTILs, but it is also recyclable and minimizes the formation
of toxic by-products, with the corresponding environmental
benefits. Our current efforts are being directed to broadening
the protocol to an increased number of anions and ionic
liquids, using non-aqueous media for the loading and exchange
procedures.
13 (a) Recently, an efficient protocol was described to afford RTILs
bearing non-nucleophilic, non-coordinating anions, based on the
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Acknowledgements
The authors thank the referees for their constructive criticism.
This research was supported by the Direccio´n General de
Investigacio´n (Ministerio de Educacio´n y Ciencia) Project No.
CTQ2006-1182/BQU. Thanks are also due to the AGAUR,
Projects NO. 2005SGR00158 and 2009SGR562 (Generalitat de
Catalunya).
Notes and references
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