two-phase systems are formed in which the IL (dense) phase
absorbs organic solvent without itself dissolving into the less dense
organic phase. Such responses to aromatic solvents by ‘‘conven-
tional’’ imidazolium ILs have been reported and ascribed to the
formation of liquid clathrates.13 It is also behavior that is highly
evocative of the solvent swelling of polymers—analogies between
polymers and ionic liquids having been previously drawn.14
Indeed, this model has been invoked to describe the swelling of
ionic liquids by sc-CO2.14c In the present case, the interactions of
[bmim]Tf2N, 2?Tf2N and 3?Tf2N with benzene are illustrative. The
swelling ratios Qv for these are 2.35, 1.50 and 1.29, respectively.
These numbers indicate that the IL phase is less effectively swollen
by benzene as the nature of the cation side chain is varied in nature
from hydrocarbon to sulfoxide to sulfone, a trend mirroring that
in polymers containing comparable functionalities.
JHD thanks Chevron for support of this research, Rhodia for a
gift of LiTf2N, Prof. Joan Brennecke for helpful discussions, and
acknowledges Merck KGaA as the licensee of SOx TSILs. DWA
thanks the National Institutes of Health for NIH R01 430-21-23.
NKS and AJR thank the US EPA for partial support of this
research.
Notes and references
1 (a) Y. Wang and G. A. Voth, J. Am. Chem. Soc., 2005, 127, 12192; (b)
M. J. Earle, B. S. Engel and K. R. Seddon, Aust. J. Chem., 2004, 57, 149
and extensive references therein; (c) Ionic Liquids in Synthesis, ed.
P. Wasserscheidand and T. Welton, Wiley-VCH, Weinheim, 2003.
2 J. H. Davis, Jr., Chem. Lett., 2004, 33, 1072 (review).
3 See for example: (a) H. Hakkou, J. J. Vanden Eynde, J. Hamelin and
J. P. Bazureau, Tetrahedron, 2004, 60, 3745; (b) A. C. Cole, J. L. Jensen,
I. Ntai, K. L. T. Tran, K. J. Weaver, D. C. Forbes and J. H. Davis, Jr.,
J. Am. Chem. Soc., 2002, 124, 5962; (c) E. D. Bates, R. D. Mayton,
I. Ntai and J. H. Davis, Jr., J. Am. Chem. Soc., 2002, 124, 926.
4 S. V. Dzyuba and R. A. Bartsch, Tetrahedron Lett., 2002, 43, 3745.
5 (a) M. H. Abraham, Chem. Soc. Rev., 1993, 22, 73; (b) J. L. Anderson,
J. Ding, T. Welton and D. W. Armstrong, J. Am. Chem. Soc., 2002,
124, 14247.
6 J. J. Roy and T. E. Abraham, Chem. Rev., 2004, 104, 3705.
7 (a) C. Reichardt, Solvents and Solvent Effects in Organic Chemistry,
VCH, Weinheim, 1988, pp. 69–71; (b) K.-M. Roy, in Ullman’s
Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 6th edn,
2003, vol. 34, pp. 571–587; (c) D. Martin and H. G. Hauthal, Dimethyl
Sulfoxide, John Wiley & Sons, New York, 1975.
8 (a) A. E. Visser, R. P. Swatloski, W. M. Reichert, J. H. Davis, Jr.,
R. D. Rogers, R. Mayton, S. Sheff and A. Wierzbicki, Chem. Commun.,
2001, 135; (b) A. E. Visser, R. P. Swatloski, W. M. Reichert, J. H. Davis,
Jr., R. Mayton, S. Sheff, A. Wierzbicki and R. D. Rogers, Environ. Sci.
Technol., 2002, 36, 2523; (c) J. H. Davis, Jr., US Pat. 60/970,130, 2002;
J. H. Davis, Jr., US Pat. 10/407,473, 2003; J. H. Davis, Jr., US Pat.
PCT/US 03/10318, 2003.
9 By appropriate choices of synthetic approach and purification
procedures, products are isolated which give negative silver ion tests
for chloride as well as giving contacted aqueous solutions with chloride
levels below ISE detection limits. Water contents (Karl Fischer) of 350–
500 ppm may be obtained after azeotropic drying with benzene and
prolonged storage under high vacuum with P2O5 in a vacuum
dessicator. See references in 1b for further information on techniques
for assessing IL purities.
10 (a) M. D. Joesten and R. S. Drago, J. Am. Chem. Soc., 1962, 84, 2037;
(b) M. D. Joesten and R. S. Drago, J. Am. Chem. Soc., 1962, 84, 2696;
(c) M. D. Joesten and R. S. Drago, J. Am. Chem. Soc., 1962, 84, 3817.
11 (a) R. M. Silverstein, G. C. Bassler and T. C. Morrill, Spectrometric
Identification of Organic Compounds, John Wiley & Sons, New York,
1991; (b) S. A. Katsyuba, P. J. Dyson, E. E. Vandyukova,
A. V. Chernova and A. Vidiˇs, Helv. Chim. Acta, 2004, 87, 2556.
12 S. A. Markarian, L. S. Gabrielian, S. Bonora and C. Fagnano,
Spectrochim. Acta, Part A, 2003, 59, 575.
13 J. D. Holbrey, W. M. Reichert, M. Nieuwenhuyzen, O. Sheppard,
C. Hardacre and R. D. Rogers, Chem. Commun., 2003, 476.
14 (a) C. S. Consorti, P. A. Z. Suarez, R. F. de Souza, R. A. Burrow,
D. H. Farrar, A. J. Lough, W. Loh, L. H. M. da Silva and J. Dupont,
J. Phys. Chem. B, 2005, 109, 4341; (b) J. Dupont, J. Braz. Chem. Soc.,
2004, 15, 341; (c) L. A. Blanchard, D. Hancu, E. J. Beckman and
J. F. Brennecke, Nature, 1999, 399, 28.
15 (a) J. L. Kaar, A. M. Jesionowski, J. A. Berberich, R. Moulton and
A. J. Russell, J. Am. Chem. Soc., 2003, 4125; (b) S. Kamat, J. Barrera,
E. J. Beckman and A. J. Russell, Biotechnol. Bioeng., 1992, 40, 158; (c)
J. A. Berberich, J. L. Kaar and A. J. Russell, Biotechnol. Prog., 2003, 19,
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Given the differences in properties between these TSILs and
more conventional ILs, we decided to screen one of the former in a
process in which one widely-used conventional IL—[bmim]PF6—
has proven particularly useful, that being as the solvent for
transesterification reactions catalyzed by the enzyme Candida
rugosa lipase. The latter is one of several enzymes with which we
have extensive experience using in conjunction with ILs.15
Choosing 3?Tf2N as our test bed, we evaluated the aforemen-
tioned lipase in the transesterification of methyl methacrylate with
2-ethylhexanol. Under conditions similar to those used successfully
with [bmim]PF6, we observed no reaction. This was also the case at
higher enzyme concentrations. After a series of unsuccessful
screenings{ involving other enzymes, we were gratified to find that
a cross-linked enzyme, Lipase PC ‘CLEC’, shows significant
transesterification activity in 3Tf2N. In this TSIL, the Lipase PC
(Pseudomonas cepacia) CLEC catalyzed the alcoholysis of
methyl methacrylate by 2-ethylhexanol at an initial rate of
95.4 mM h21 mg21. While the enzyme loses 40% of its initial
activity over a 10 hour period, it is notable that it is wholly inactive
in [bmim]PF6, normally the IL of choice for biocatalysis studies.
To date TSILs have been used largely in applications in which
the desired outcome depended on a reaction between the substrate
and the ion-appended functional group.2,3 However, the use of
functionalized ILs in more clearly ‘‘solvent’’ applications16 is of
growing interest and is likely to be facilitated by a better
understanding of functional group contributions to global IL
solvent properties. Here, the incorporation of functionality into
imidazolium IL cations—specifically the tethering of sulfone and
sulfoxide groups to them—has been plainly shown to induce
meaningful, quantifiable, individually distinctive changes in an
array of IL solvent attributes, with attendant ramifications for
utility. Further, the nature of these changes (increases in polarity,
H-bonding, etc.) is consistent with those which would be logically
expected from the addition of SO or SO2 groups to an existing
molecular structure, and renders them distinctive from otherwise
similar conventional ILs. These results thus constitute a powerful
affirmation that the solvent properties of imidazolium ILs are
rightly regarded as being amenable to tuning by functional group
incorporation as well as ion choice.
16 See for example: D. Zhao, Z. Fei, T. J. Geldbach, R. Scopolleti and
P. J. Dyson, J. Am. Chem. Soc., 2004, 126, 15876.
648 | Chem. Commun., 2006, 646–648
This journal is ß The Royal Society of Chemistry 2006