ChemComm
Cite this: Chem. Commun., 2012, 48, 3185–3187
COMMUNICATION
Synthesis of chiral ionic liquids by ion cross-metathesis: en route to
enantioselective water–ionic liquid extraction (EWILE), an eco-friendly
variant of the ELLE processwz
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Viacheslav Zgonnik, Chantal Zedde, Yves Genisson, Marie-Rose Mazieres and
Jean-Christophe Plaquevent*
Received 13th December 2011, Accepted 1st February 2012
DOI: 10.1039/c2cc17799d
From two initial ILs two other ILs are obtained by simultaneous
ion exchange. The hydrophobic ions unite in the hydrophobic layer,
whereas the hydrophilic ions gather in water. This protocol is
explored as a variant of the ELLE process, in which an enantiomer
of a racemic mixture is preferentially extracted with water.
force of this process is hydrophobic/hydrophilic interaction.
This means that when two ILs are exposed to each other as a
biphasic aqueous system, their constituent ions redistribute
depending on their hydrophobicity/hydrophilicity. Otherwise
saying, the hydrophobic ions unite together in the hydro-
phobic layer, whereas the hydrophilic ions gather in the
hydrophilic layer. We call this new process ‘‘ionic liquids ion
cross-metathesis’’ (ILICM).
Ionic liquids (ILs) are salts that are liquid under normal
physical conditions. They possess several unique properties,
such as a near-zero vapour pressure, which make them non-toxic
by inhalation and not flammable, and a good ability to dissolve
various substances. These characteristics, along with many
others, render their use favourable for green chemistry.1 The
field of ILs is growing rapidly: during the last decade the
amount of published articles was multiplied by ten.
In regards with our continuous interest in chiral ionic liquids
(CILs),3 we illustrated the principle of ILICM using tartaric acid-
based ILs and imidazolium-based ILs. Tetrabutylphosphonium
tartrates are highly hydrophilic substances despite the presence
of the hydrophobic tetrabutylphosphonium. However, when
dissolved in a hydrophobic IL such as [bmim][NTf2], then
extracted by water, the following phenomenon was observed:
the highly hydrophilic ions (tartaric carboxylate and imidazolium)
unite together in water, while the hydrophobic ions (tetrabutyl-
phosphonium and NTf2ꢀ) gather in the IL (Scheme 1).
Generally, the synthesis of ionic liquids consists of two main
steps: the formation of the cation and the anion exchange
through ion metathesis.1 The basic concept of ion metathesis is
the formation of a new pair of salts, which can be easily
separated based on their distinct physical properties. Commonly,
ion metathesis involves the anion exchange of halide salts with
metal salts. This method has limitations in the preparation of pure
ILs due to the contamination by metal halide salts and is not easily
applied at the industrial scale because of its high cost. Also, ILs are
positioned as ‘‘green solvents’’, but their production often uses
large quantities of organic solvents, mainly for the purification of
ionic liquids from halogen impurities. Thus there is a continuous
need for new methods of preparation of ILs that should overcome
present-day obstacles of their widespread usage.
To respect electro-neutrality of both phases, the tartate
dicarboxylate anion must move to water layer along with
two cations. Worthy of note is that those countercations
are not the former tetrabutylphosphoniums, but the more
hydrophilic cations present in the mixture, i.e. the imidazoliums,
which are much less hydrophobic than tetrabutylphosphonium
cations. The exchange is complete, i.e. equivalent quantity of
cations is extracted to ensure the electro-neutrality of the solution.
To ensure quantitative exchange the presence of two immiscible
phases is required. In our example it was water–hydrophobic IL
([bmim]–, [omim]– or [PBu4]–[NTf2]), and ILs were used in excess
with respect to tartaric carboxylate. Fig. 1 depicts the behaviour of
[PBu4][NTf2], which exhibits a paraffin-like structure and stands as
a ‘‘ball’’ in the aqueous layer during stirring.
Herein we report a simple and fully atom economic way to
obtain new families of ionic liquids. Starting from two initial
ILs, two new ILs are obtained in quantitative yield by mutual ion
exchange based on their physico-chemical properties.2 The driving
Two CILs were prepared using this method: [bmim]2-[(R,R)-
Trtr] and [omim]2-[(R,R)-Trtr] (Scheme 1). In the literature,
[bmim]2-[(R,R)-Trtr] was previously prepared using [bmim][OH]
(obtained via an ion-exchange resin), which was neutralised with
tartaric acid.4 Its [omim]2 congener is new. Both compounds were
obtained from water solution in 100% yield and excellent purity.5
The following issue was: what would happen if the chiral ion
of the CIL (tartrate moiety in our examples) was exposed to a
racemic counter-ion? In other words, is this kind of process
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Laboratoire de Synthese et Physicochimie de Molecules d’Intere
Biologique UMR-CNRS 5068, Universite Paul Sabatier,
118 route de Narbonne, 31062, Toulouse, France.
E-mail: plaquevent@chimie.ups-tlse.fr; Fax: 00 33(0)561556011;
Tel: 00 33(0)561556511
w Electronic supplementary information (ESI) available: Experimental
procedures, compound characterisation data. See DOI: 10.1039/
c2cc17799d
z This article is part of the ChemComm ’Chirality’ web themed issue.
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This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 3185–3187 3185