Anal. Chem. 2004, 76, 6819-6822
Chiral Ionic Liquids as Stationary Phases in Gas
Chromatography
†
‡
,†
Jie Ding, Thomas Welton, and Daniel W. Armstrong*
Department of Chemistry, Iowa State University, Ames, Iowa 50011
in terms of their interaction/solvation parameters and abilities.9
There also has been a great deal of interest in the application of
Recently, it has been found that room-temperature ionic
liquids can be used as stable, unusual selectivity station-
ary phases. They show “dual nature” properties, in that
they separate nonpolar compounds as if they are nonpolar
stationary phases and separate polar compounds as if they
are polar stationary phases. Extending ionic liquids to the
realm of chiral separations can be done in two ways: (1)
a chiral selector can be dissolved in an achiral ionic liquid,
or (2) the ionic liquid itself can be chiral. There is a single
precedent for the first approach, but nothing has been
reported for the second approach. In this work, we
present the first enantiomeric separations using chiral
ionic liquid stationary phases in gas chromatography.
Compounds that have been separated using these ionic
liquid chiral selectors include alcohols, diols, sulfoxides,
epoxides, and acetylated amines. Because of the synthetic
nature of these chiral selectors, the configuration of the
stereogenic center can be controlled and altered for
mechanistic studies and reversing enantiomeric retention.
10
11
the ionic liquids as novel biphasic catalysts, extraction solvents,
12
highly selective transport membranes, and stationary phases for
gas chromatography.1
3,14
The first application of molten salts as gas chromatographic
stationary phase was reported by Barber et al.15 Since the early
1980s, Poole and co-workers have published a series of papers
1
6-20
on using organic molten salts as GC stationary phases.
Although the initial alkylammonium- and alkylphosphonium-based
molten salts had been used as GC stationary phases, they had
limitations, such as relatively narrow liquid ranges, thermal
instability, and poor wetability toward the surface of fused silica.
Later-emerging ionic liquids containing alkylimidazolium or alky-
lpyridinium cations possessed improved properties (wider liquid
range and better thermal stability) and were more suitable for
GC stationary phases. Recently, we demonstrated that alkylimi-
dazolium-based ILs can be used as stable, unusual selectivity
stationary phases.1 They show “dual nature” properties. They
separate nonpolar compounds as if they are nonpolar stationary
phases and separate polar compounds as if they are polar
stationary phases. We also introduced the achiral ILs to the realm
of chiral separations by dissolving the chiral selector (methylated
cyclodextrins) in 1-butyl-3-methylimidazolium chloride and 1-butyl-
3-methylimidazolium hexafluorophosphate ILs.21
3,14
Room-temperature ionic liquids (RTILs) are low-melting (<100
°
C) salts which represent a new class of nonmolecular, ionic
solvents. These solvents possess a number of interesting proper-
ties, such as negligible vapor pressure, ease of preparation and
reuse, and high thermal stability. In recent years, considerable
attention has been focused on the use of RTILs as alternatives to
classical organic solvents. There are many reports concerning the
applications of ionic liquids (ILs) as excellent solvents for a
Although there have been many publications on ionic liquids,
only a few examples of chiral ILs have been reported so far.
Howarth and co-workers described the use of chiral imidazolium
1
-4
22
number of organic reactions, such as Diels-Alder reactions,
cation in Diels-Alder reactions; however, the synthesis of these
Friedel-Crafts reaction,5,6 isomerizations, and hydrogenation.
7
8
(9) Anderson, J. L.; Ding, J.; Welton, T.; Armstrong, D. W. J. Am. Chem. Soc.
Ionic liquids are among the most versatile and complex solvents
2
002, 124, 14247.
*
To whom correspondence should be addressed. Email: sec4dwa@
(10) Aqueous-Phase Organometallic Catalysis: Concepts and Applications; Cornils,
B., Herrmann, W. A., Eds.; Wiley-VCH: Weinheim, 1998.
(11) Huddleston, J. G.; Willauer, H. D.; Swatloski, R. P.; Visser, A. E.; Rogers,
R. D. Chem. Commun. 1998, 1765.
iastate.edu.
†
Iowa State University.
‡
Current address; Imperial College of Science Technology and Medicine,
South Kensington, London SW7 2AY, U.K.
(12) Branco, L. C.; Crespo, J. G.; Afonso, C. A. M. Angew. Chem., Int. Ed.
(
1) Fischer, T.; Sethi, A.; Welton, T.; Woolf, J. Tetrahedron Lett. 1999, 40,
93.
Commun. 2002, 41, 2771.
7
(13) Armstrong, D. W.; He, L.; Liu, Y.-S. Anal. Chem. 1999, 71, 3873.
(14) Anderson, J. L.; Armstrong, D. W. Anal. Chem. 2003, 75, 4851.
(15) Barber, D. W.; Phillips, C. S. G.; Tusa, G. F.; Verdin, A. J. Chem. Soc. 1959,
18.
(
(
(
2) Lee, C. W. Tetrahedron Lett. 1999, 40, 2461.
3) Ludley, P.; Karodia, N. Tetrahedron Lett. 2001, 42, 2011.
4) Earle, M. J.; McCormac, P. B.; Seddon, K. R. Green Chemistry 1999, 1,
2
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5) Adams, C. J.; Earle, M. J.; Roberts, G.; Seddon, K. R. Chem. Commun. 1998,
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6) Stark, A.; Maclean, B. L.; Singer, R. D. J. Chem. Soc., Dalton Trans. 1999,
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7) Chauvin, Y. L.; Mussmann, L.; Olivier, H. Angew. Chem., Int. Ed. Commun.
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(16) Pachole, F.; Butler, H. T.; Poole, C. F. Anal. Chem. 1982, 54, 1938.
(17) Poole, C. F.; Butler, H. T.; Coddens, M. E.; Dhanesar, S. C.; Pacholec, F.
J. Chromatogr. 1984, 289, 299.
(18) Furton, K. G.; Poole, C. F. Anal. Chem. 1987, 59, 1170.
(19) Pomaville, R. M.; Poole, C. F. Anal. Chem. 1988, 60, 1103.
(20) Poole, S. K.; Poole, C. F. Analyst 1995, 120, 289-294.
(21) Berthod, A.; He, L.; Armstrong, D. W. Chromatographia 2001, 53, 63.
(22) Howarth, J.; Hanlon, K.; Fayne, D.; McCormac, P. Tetrahedron Lett. 1997,
38, 3097.
(
(
(
(
2
6
1
8) Suarez, P. A. Z.; Dullius, J. E. L.; Einloft, S.; de Souza, R. F.; Dupont, J.
Polyhedron 1996, 15, 1217.
1
0.1021/ac049144c CCC: $27.50 © 2004 American Chemical Society
Analytical Chemistry, Vol. 76, No. 22, November 15, 2004 6819
Published on Web 10/21/2004