the Ministry of Science and Innovation of Spain (‘‘Ramon y
´
Cajal’’ program).
Notes and references
Scheme 4 One pot synthesis of symmetrical 1,3-dialkylimidazolium
acetate (1, R1 = R2) and statistical mixture of 1-alkyl-3-methyl-, 1,3-
dialkyl-, 1,3-dimethylimidazolium acetates (1 + 2 + 3, R1 = methyl,
R1 a R2).
1 (a) R. P. Swatloski, S. K. Spear, J. D. Holbrey and R. D. Rogers,
J. Am. Chem. Soc., 2002, 124, 4974–4975; (b) D. A. Fort,
R. C. Remsing, R. P. Swatloski, P. Moyna, G. Moyna and
R. D. Rogers, Green Chem., 2007, 9, 63–69; (c) H. Mizuuchi,
V. Jaitely, S. Murdan and A. T. Florence, Eur. J. Pharm. Sci.,
2008, 33, 326–331; (d) E. Boros, M. J. Earle, M. A. Gılea,
A. Metlen, A.-V. Mudring, F. Rieger, A. J. Robertson,
K. R. Seddon, A. A. Tomaszowska, L. Trusov and J. S. Vyle,
Chem. Commun., 2010, 46, 716–718.
To further explore the utility of this thione synthesis, we
investigated the one-pot reaction of both symmetrical
1,3-dialkylimidazolium acetate and 2 : 1 : 1 statistical mixtures
of 1-alkyl-3-methyl-, 1,3-dialkyl-, and 1,3-dimethylimidazolium
acetates, prepared in situ through cyclization of the corres-
ponding amines with glyoxal, formaldehyde, and acetic acid,19
with sulfur. The mixtures of ILs over the ‘pure’ IL alone have
potential environmental benefits and cost advantages over
current technologies. Unlike the single cation hydrophilic
ILs, the IL mixtures can be prepared in a one-pot, single step
process, using aqueous, readily available, cheap raw materials,
and therefore reducing or even eliminating the use of the
organic solvents (Scheme 4). By adding sulfur to a statistical
imidazolium acetate mixture, partial conversion to the corres-
ponding mixture of thiones was achieved. Interestingly, the
same ratios of the starting cations ratios were obtained in the
resulting thiones mixture product. In the case of symmetric
imidazole-2-thiones, only one product would be obtained,
which can be easily prepared, as seen, via a simple one-pot
strategy from cheap, commodity chemicals.
2 Y. Fukaya, A. Sugimoto and H. Ohno, Biomacromolecules, 2006,
7, 3295–3297.
3 T. Cremer, C. Kolbeck, K. R. J. Lovelock, N. Paape, R. Wolfel,
¨
P. S. Schulz, P. Wasserscheid, H. Weber, J. Thar, B. Kirchner,
F. Maier and H.-P. Steinruck, Chem.–Eur. J., 2010, 16, 9018–9033.
¨
4 For instance: (a) L. Yang, L.-W. Xu, W. Zhou, L. Li and
C.-G. Xia, Tetrahedron Lett., 2006, 47, 7723–7726; (b) L. Huang,
M. Zhai, J. Peng, L. Xu, J. Li and G. Wei, Carbohydr. Polym.,
2008, 71, 690–693.
5 N. Sun, M. Rahman, Y. Qin, M. L. Maxim, H. Rodrı
R. D. Rogers, Green Chem., 2009, 11, 646–655.
6 O. Holloczki, D. Gerhard, K. Massone, L. Szarvas, B. Ne
T. Veszpremi and L. Nyulaszi, New J. Chem., 2010, 34, 3004–3009.
´
guez and
´
´
meth,
´
´
7 (a) W. L. Hough-Troutman, M. Smiglak, S. Griffin,
W. M. Reichert, I. Mirska, J. Jodynis-Liebert, T. Adamska,
J. Nawrot, M. Stasiewicz, R. D. Rogers and J. Pernak, New J.
Chem., 2009, 33, 26–33; (b) M. Smiglak, A. Metlen and
R. D. Rogers, Acc. Chem. Res., 2007, 40, 1182–1192;
(c) W. L. Hough, M. Smiglak, H. Rodrıguez, R. P. Swatloski,
´
S. K. Spear, D. T. Daly, J. Pernak, J. E. Grisel, R. D. Carliss,
M. D. Soutullo, J. H. Davis, Jr. and R. D. Rogers, New J. Chem.,
2007, 31, 1429–1436.
8 V. Nair, S. Bindu and V. Sreekumar, Angew. Chem., Int. Ed., 2004,
43, 5130–5135.
Finally, it can be noted that ILs such as 1-alkyl-3-methyl-
imidazolium acetates are among the most widely used in the
promising field of biomass treatment and processing with ILs.
It is important to understand the chemistry of the IL itself in
order to help explain such reports as side reactions at the C(2)
position with reducing end sugars,20 or other unexplained
decomposition pathways or reactivity.
9 X.-L. Tao, M. Lei and Y.-G. Wang, Synth. Commun., 2007, 37,
399–408; and references therein.
10 For instance: (a) R. C. Haynes, Jr. and F. Murad, in Goodman and
Gilman’s The Pharmaceutical Basis of Therapeutics, ed.
A. G. Gilman, L. S. Goodman, T. W. Rall and F. Murad,
Macmillan, New York, 1985; (b) L. I. Kruse, C. Kaiser,
W. E. DeWolf, J. A. Finkelstein, J. S. Frazee, E. L. Hilbert,
S. T. Ross, K. E. Flaim and J. L. Sawyer, J. Med. Chem., 1990,
33, 781–789.
11 A. J. Arduengo, III and P. H. Corcoran, PCT Pat., 9 118 937,
1991.
12 G. Roy and G. Mugesh, J. Am. Chem. Soc., 2005, 127,
15207–15217.
Overall, our work has shown that pure 1,3-dialkylimidazolium
ILs can be induced to undergo reactive transformations via NHC
carbenes as both reactant and solvent even in the absence of
additional external sources of base. Here, this has been illustrated
by reaction of [C2mim][OAc] (or the corresponding statistical
mixture) with sulfur or selenium to directly form the corres-
ponding imidazole-2-chalcogenones. However, the acidity of the
C(2) proton of the IL imidazolium cation and the basicity of the
IL anion are in themselves not sufficient criteria to understand
13 P. Li, X. Wang, X. Yuan, S. Wang and S. Lu, Cuihua Xuebao,
2007, 28, 495–497.
14 (a) H. Kucukbay, R. Durmaz, E. Orhan and S. Gunal, Farmaco,
2003, 58, 431–437; (b) B. Cetinkaya, E. Cetinkaya and
H. Kucukbay, Arzneim.–Forsch., Beih., 1996, 46, 1154–1158.
15 (a) B. L. Benac, E. M. Burgess and A. J. Arduengo, III,
Org. Synth., 1986, 64, 92–95; (b) A. J. Arduengo, III, US Pat.,
5 104 993, 1992.
this chemistry, as suggested by Hollo
´
czki et al.6 The anion must
also be capable of stabilization of the parent acid through the
formation of complex anions, thus preventing the unchecked
reaction and decomposition of the IL.
16 A. J. Arduengo, US Pat., 0 171 883, 2008.
17 (a) N. Kuhn, G. Henkel and T. Kratz, Chem. Ber., 1993, 126,
2047–2049; (b) A. J. Arduengo, III, F. Davidson, H. V. R. Dias,
J. R. Goerlich, D. Khasnis, W. J. Marshall and T. K. Prakasha,
J. Am. Chem. Soc., 1997, 119, 12742–12749.
18 (a) K. M. Johansson, E. I. Izgorodina, M. Forsyth,
D. R. MacFarlane and K. R. Seddon, Phys. Chem. Chem. Phys.,
2008, 10, 2972–2978; (b) K. Bica and R. D. Rogers, Chem.
Commun., 2010, 46, 1215–1217.
19 (a) A. J. Arduengo, III, US Pat., 5 077 414, 1991; (b) R. X. Ren
and V. R. Koch, US Pat., 7 253 289, 2007.
20 G. Ebner, S. Schiehser, A. Potthast and T. Rosenau, Tetrahedron
Lett., 2008, 49, 7322–7324.
Considered in totality, the chemistry reported here can be
regarded as an example of a ‘carbene-in-a-bottle’, where,
through anion selection, the standing carbene concentration
present in equilibrium in ILs (something we could call the
effective pKa of the C(2) hydrogen in the imidazolium IL) can
be modified to provide both reactive carbene moieties and
solvent for a variety of applications.
We want to thank Petroliam Nasional Berhad (PETRONAS)
for financial support for this project. H.R. is also grateful to
c
3224 Chem. Commun., 2011, 47, 3222–3224
This journal is The Royal Society of Chemistry 2011