Solvent-free synthesis of unsaturated ketones by the Saucy-Marbet reaction using simple ammonium ionic liquid as a catalyst

Article abstract of DOI:10.1039/b900042a

Simple ammonium ionic liquids are efficient catalysts in promoting Saucy-Marbet reactions of unsaturated alcohols with unsaturated ethers to afford the corresponding unsaturated ketones, eliminating the need for volatile organic solvents. The effect of th

Full text of DOI:10.1039/b900042a

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www.rsc.org/greenchem | Green Chemistry
Solvent-free synthesis of unsaturated ketones by the Saucy–Marbet reaction
using simple ammonium ionic liquid as a catalyst
Congmin Wang, Wenjia Zhao, Haoran Li* and Liping Guo
Received 5th January 2009, Accepted 23rd February 2009
First published as an Advance Article on the web 13th March 2009
DOI: 10.1039/b900042a
Simple ammonium ionic liquids are efficient catalysts in promoting Saucy–Marbet reactions of
unsaturated alcohols with unsaturated ethers to afford the corresponding unsaturated ketones,
eliminating the need for volatile organic solvents. The effect of the anions and the cations of ionic
liquids, quantity of ionic liquid, temperature, and chain-length of unsaturated alcohols on the
reaction was investigated. The results showed that the Saucy–Marbet reaction was heavily
influenced by the acidity of ionic liquid and [Et
3
NH][HSO ] had the best catalytic activity. The
4
conversion and selectivity obtained with this method are significantly increased in comparison to
those catalyzed by traditional acid. Furthermore, the ionic liquid could be easily separated and
reused with a slight loss of its activity. It provided a good alternative way for the industrial
synthesis of unsaturated ketones.
Introduction
volatile organic solvents have so far appeared for the synthesis
of unsaturated ketones.
There is a growing need for greener and more sustainable pro-
cesses in the chemical industry. Replacement or elimination of
some toxic reagents or volatile organic solvents in chemical pro-
cesses is one of the main goals of green chemistry. It is well known
that unsaturated ketones such as 2-methyl-2-hepten-6-one, pseu-
doionone, and farnesylactone, are important substances and
intermediates of flavors, fragrances, pharmaceuticals, and other
In recent years, ionic liquids have attracted more and more
attention due to their special properties, such as an almost un-
detectable vapor pressure, high thermal stability, non-explosive
properties, and strong solvent power for a wide range of organic,
6
inorganic, and polymeric molecules. Some ionic liquids have
been successfully used as environmentally benign solvents or
7
catalysts in a number of reactions, such as the Diels–Alder
1
fine chemicals. The conventional method for the production of
8
9
10
reaction, the Friedel–Crafts reaction, esterification, cracking
these unsaturated ketones is the Carroll reaction of unsaturated
alcohols with alkyl acetoacetates in the presence of organic
11
reactions, and so on. Among these ionic liquids reported
in the past several years, a great deal of attention has been
given to imidazolium ionic liquids. However, the industrial
application of these imidazolium ionic liquids is limiting be-
cause of the difficult preparation, expensive cost and high
2
aluminium compounds. The drawback of this method is a
large amount of carbon dioxide—an atmospheric greenhouse
gas that contributes to global warming—would be produced as a
byproduct. An alternative method is the Saucy–Marbet reaction
12
toxicity. Recently, some non-imidazolium ionic liquids such as
3
of unsaturated alcohols with unsaturated ethers. For example,
phosphonium and ammonium ionic liquids have drawn much
attention. For example, Bradaric et al. reported the industrial
preparation of some representative phosphonium ionic liquids
and discussed the comparisons with relevant imidazolium ionic
6
,10-dimethyl-4,5,9-undecatrien-2-one, a key intermediate of
Vitamin E and Vitamin A, could be produced from 3,7-dimethyl-
oct-6-en-1-yn-3-ol (dehydrolinalool) and 2-ethoxypropene by
4
using the Saucy–Marbet reaction. This reaction can be carried
10
liquids. Han et al. presented the synthesis of guanidinium
out in the presence of various acids used as catalysts, such
as sulfuric acid, phosphoric acid, p-toluene sulfonic acid,
trichloroacetic acid, and so on. The separation and recycling
of catalysts are difficult. Furthermore, this reaction usually
calls for volatile organic solvents such as halohydrocarbon,
ionic liquids and an application for the desulfurization of flue
14
gas. Dai et al. reported a new family of cost-effective, highly
proton conductive room temperature ionic liquids based on
N,N-dimethylformamide and its potential application in the fuel
15
cell industry. Furthermore, we have succeeded in the industrial
5
toluene, and petroleum ether, otherwise the selectivity would
preparations of series of simple ammonium ionic liquids and
the industrial application in the production of cinnamic acid
obviously reduce. Despite numerous attempts to overcome these
drawbacks, no benign methods with the advantages of easy
separation, convenient recycling, and eliminating the need for
16
using these ionic liquids as solvents and catalysts. In special
cases, these simple ammonium ionic liquids have attracted
considerable interest in industry because of their advantages
which include easy preparation, cheap cost, and low toxicity.
Being a part of our systematic research into ammonium
ionic liquids and continuing our investigations into indus-
trial applications, herein we reported a benign approach to
Department of Chemistry, Zhejiang University, Hangzhou, 310027,
P. R. China. E-mail: lihr@zju.edu.cn; Fax: +86 571-8795-1895;
Tel: +86 571-8795-2424
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a
Table 1 The effect of ionic liquids on the Saucy–Marbet reaction
To obtain the higher conversion and selectivity, five different
bisulfate ionic liquids were used in the reaction, also listed in
Table 1. It was found that the conversion of dehydrolinalool
would decrease when the chain-length of the ionic liquids
increased due to its higher lipophilic character. Compared
with the effect of the anions, the effect of chain-length of the
◦
Entry
Catalyst
T/ C
Conv.(%)
Select.(%)
1
2
3
4
5
6
7
8
9
0
1
2
3
[Et
[Et
[Pr
2
3
3
NH
NH]HSO
NH]HSO
2
]HSO
4
95
95
95
95
95
95
95
Reflux
Reflux
Reflux
Reflux
95
81
88
85
83
70
85
68
Trace
2
91
97
95
92
96
94
95
—
85
—
97
72
96
17
4
4
[Bu
[Et
[Hmim]HSO
[Bmim]H PO
[Bmim]PF
3
NH]HSO
4
cations was weak. [Et
3
NH]HSO might be the best catalyst for
4
3
NH]H PO
2
4
the Saucy–Marbet reaction in all the ionic liquids, due to its
cheap cost, low toxicity and convenient preparation.
4
2
4
6
An important feature of the reaction catalyzed by bisulfate
ionic liquids is that there is no evidence for significant formation
of a side reaction, which may be related to the mild acidity
[Bmim]BF
[Bmim]Cl
[Bmim]Tfa
PTSA
4
1
1
1
1
Trace
8
89
b
c
18
of the ionic liquid. During the reaction, the intermediate
PTSA + Toluene
95
86
3
-(1-ethoxy-1-methylethoxy)-3,7-dimethyl-6-octen-1-yne could
a
Dehydrolinalool (0.05 mol), 2-ethoxypropene (0.15 mol), catalyst
0.25 mmol). p-Toluene sulfonic acid was used. p-Toluene sulfonic
transform gradually to the desired product 6,10-dimethyl-4,5,9-
undecatrien-2-one, and diethoxypropane would be formed by
reaction of 2-ethoxypropene and ethanol, which were identified
by GC-MS. However, the volatile organic solvent such as
toluene was necessary when this reaction was carried out using
p-toluenesulfonic acid (PTSA) as a catalyst. Otherwise, the
selectivity would decrease significantly to 72%. The side products
such as 2,6,6-trimethyl-2-ethynyltetrahydro-2H-pyran and a
2-ethoxypropene dimer would form because of the strong acidity
of p-toluentesulfonic acid (Table 1, entry 12). On the other
hand, some other side products such as acetone and diacetone
alcohol would also be produced due to the presence of water,
which was formed by the reaction of p-toluene sulfonic acid
and ethanol. Furthermore, the separation and recycling of
p-toluene sulfonic acid are difficult because of the formation of
b
c
(
acid was used catalyst, and 20 ml toluene was used as solvent.
unsaturated ketones via Saucy–Marbet reactions catalyzed by
simple ammonium ionic liquids under solvent-free conditions.
High conversion and good selectivity could be obtained with
these ammonium ionic liquids, eliminating the need for a volatile
organic solvent and additional catalyst. In particular, these ionic
liquids are very easy to be separate and reuse.
Results and discussion
The reaction of dehydrolinalool with 2-ethoxypropene was
firstly used as an example to investigate the effect of ionic liquid
on the Saucy–Marbet reaction (Scheme 1). Table 1 lists the
effects of different ionic liquids on the reaction without any
volatile solvent. It was clear that both conversion and selectivity
of the reaction were heavily influenced by the anions of ionic
3–5
p-toluenesulfonic acid ethyl ester. Based on previous reports
and the observed reaction products, the reaction pathways under
solvent-free conditions could be postulated, which is shown in
Scheme 2.
liquids. The high conversion and good selectivity could be ob-
It should be noted that the influence of the concentration
of the ionic liquid on the reaction was strong. As can be seen
in Table 2, the conversion of the reaction was low when the
concentration of the ionic liquid was lower than 0.2%. And
the selectivity would decrease when the quantity of the ionic
liquid was higher than 5.0% because of the formation of side
products such as 2-ethoxypropene dimers, acetone, diacetone
alcohol, 2,6,6-trimethyl-2-ethynyltetrahydro-2H-pyran, and so
on. Therefore, the optimal concentration of the ionic liquid to
use as a catalyst is about 0.5%. In addition, the reaction seemed
to be heavily influenced by the temperature (Table 2, entries
2, 5, 6). The conversion would reduce from 88% to 52% when
-
tained when the strongly acidic HSO
4
anion was used (Table 1,
entries 1–5). For example, the conversion of 88% and selectivity
of 97% were achieved when [Et NH]HSO was used. However,
3
4
the reaction was very slow, and therefore the conversion was
lower than 10%, when neutral ionic liquids (Table 1, entries 9, 11)
such as [Bmim]BF were used. Furthermore, the reaction did not
4
proceed at all in the presence of the [Bmim]PF
6
and [Bmim]Cl
-
ionic liquids. When the H
2
PO
4
anion was used (Table 1, entry 5),
although the selectivity of the reaction was higher than 95%,
the conversion of dehydrolinalool was clearly lower than those
obtained with [Et
3
NH]HSO due to the weaker acidity of the
4
◦
◦
dihydrogen phosphate ionic liquid. Above all, the results showed
that the Saucy–Marbet reaction was heavily influenced by the
acidity of ionic liquid.
the temperature of the reaction decreased from 95 C to 75 C.
At the same time, the selectivity would decrease remarkably
from 98% to 45% due to the fact that the thermal cracking
Scheme 1 Saucy–Marbet reaction catalyzed by ionic liquids.
44 | Green Chem., 2009, 11, 843–847
8
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Scheme 2 Postulated reaction pathways under solvent-free conditions.
a
Table 2 The effect of temperature and concentration of ionic liquid on
3 4
Table 4 The recycling of ionic liquid [Et NH][HSO ]
a
the Saucy–Marbet reaction
Entry
Cycle no.
Conv. (%)
Select. (%)
◦
Entry
Concentration T ( C)
Conv. (%)
Select. (%)
1
2
3
4
5
0
1
2
3
4
88
85
87
84
86
97
93
95
94
95
1
2
3
4
5
6
0.2%
0.5%
1.0%
5.0%
0.5%
0.5%
95
95
95
95
85
75
73
88
89
92
75
52
95
97
95
84
86
45
a
◦
All reactions were carried out at 95 C.
a
Dehydrolinalool (0.05 mol), 2-ethoxypropene (0.15 mol),
Et NH]HSO (0.25 mmol).
[
3
4
while the ionic liquid is hydrophilic. When the reaction was
completed, after distilling off the low boiling mixtures, such as
2
-ethoxypropene and formed diethoxypropane, in high vacuum,
Table 3 The effect of unsaturated alcohol and 2-alkoxypropene on the
a
Saucy–Marbet reaction
water was added. Then the aqueous phase was separated from
the organic phase by phase separation, and the ionic liquid could
be recycled by separating out water under reduced pressure from
the aqueous phase. It was necessary to remove traces of water
because even a small amount of water in the ionic liquid would
affect the Saucy–Marbet reaction. The product with a purity of
Conv. Select.
Entry Unsaturated alcohol
2-alkoxypropene
(%)
(%)
1
2
3
4
2-methyl-3-butyn-2-ol 2-ethoxypropene
91
80
98
93
98
95
Dehydronerolidol
Dehydrolinalool
Dehydronerolidol
2-ethoxypropene
2-methoxypropene 90
2-methoxypropene 84
9
8.5% was isolated using vacuum distillation, which showed that
ionic liquids did not contaminate it, although some of these ionic
liquids were volatile. It is shown in Table 4 that the ionic liquid
could be recycled with a slight loss of its activity. It seemed that
a
19
Unsaturated alcohol (0.05 mol), 2-alkoxypropene (0.15 mol), [Et
3
NH]
◦
HSO
4
(0.25 mmol), 95 C.
[
Et
3
NH]HSO could have the potential to be used more than
4
five times.
of the intermediate to the desired product is difficult at lower
temperatures.
To test the influence of chain-length of unsaturated al-
cohols on the Saucy–Marbet reaction, 2-methyl-3-butyn-2-ol
and dehydronerolidol were also investigated. It is shown in
Table 3 that the conversion and selectivity of 2-methyl-3-butyn-
Experimental
Materials
2
-ol would increase in comparison to dehydrolinalool. On the
2-Methyl-3-butyn-2-ol (>99%), 3,7-dimethyl-oct-6-en-1-yn-3-
ol (dehydrolinalool, >99%), and 3,7,11-trimethyl-dodec-10-
en-1-yn-3-ol (dehydronerolidol, >98.5%) were provided by
Zhejiang NHU Co., Ltd. 2-Methoxypropene (>99%) and
2-ethoxypropene (>99%) were provided by Zhejiang Jubang
Hi-Tech Corporation. Sulfuric acid, phosphoric acid, triflu-
oroacetic acid, p-toluenesulfonic acid, diethylamine, triethy-
lamine, n-tripropylamine, n-tributylamine, 1-methylimidazole,
toluente, n-butyl bromide, n-butyl chloride, sodium bisulfate,
sodium hexafluorophosphate, and sodium tetrafluoroborate
were all used as received unless otherwise stated.
contrary, when the long chain unsaturated alcohol such as
dehydronerolidol was used, the conversion in chain length of
unsaturated alcohols. Furthermore, the effect of different
2
-alkoxypropene on the reaction was investigated, which is also
listed in Table 3. The results indicated that the conversion
of 90% and selectivity of 98% were obtained owing to the
higher activity of 2-methoxypropene (Table 3, entry 3), when
2
-methoxypropene was used instead of 2-ethoxypropene.
The separation of products and ionic liquid is very easy be-
cause the raw materials and products are immiscible with water,
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Instruments
and good selectivity of this method, as well as the cheap cost,
convenient preparation, and low toxicity of simple ammonium
ionic liquid, it can provide a good alternative way for the industry
synthesis of unsaturated ketones, which was also important to
reduce carbon dioxide emissions from chemical industry.
The NMR spectra of the ionic liquids and unsaturated ketones
were recorded with a 500 MHz Bruker spectrometer in DMSO
or CDCl and calibrated with tetramethylsilane (TMS) as the
3
internal reference. Samples of the reaction mixture were ana-
lyzed regularly to monitor the reaction by gas chromatography.
The products and intermediates were identified by HP5973
GC-MS with a DP17 column (30 m ¥ 0.25 mm ¥ 0.25 mm)
by comparing retention times and fragmentation patterns with
authentic samples. The reaction conversion and selectivity were
determined using GC112A equipped with an ATSE-30 column
Acknowledgements
This work was supported by National Natural Science Founda-
tion of China (No. 20704035 and No. 20774319).
(
30 m ¥ 0.25 mm ¥ 0.25 mm) and a flame ionization detector.
References
Ethyl benzoate (99.9%) was applied as an internal standard for
quantitative analysis.
1
R. Marbet and G. Saucy, Helv. Chim. Acta, 1967, 50, 2091; H. T.
Joaquim, R. Norbert, B. Klaus, D. Dirk, H. Hartmut, K. Stefan, E.
Heinz, and K. Wulf, US Pat., 6 184 420, 2001.
M. F. Carroll, J. Chem. Soc., 1940, 704; C. Oost, M. Stroezel, H.
Etzrodt, D. Weller, B. Bochstiege, K. Reimer, G. Kaiber, and H.
Jaedicke, US Pat. 6 329 554, 2001.
Typical Saucy–Marbet reaction procedure
2
The simple ammonium ionic liquids of general type [amine][acid]
16
were synthesized according to our former paper. The NMR
data and other physical properties of these simple ammonium
ionic liquids in this paper are in good agreement with our early
reports. Other ionic liquids used in this paper were synthesized
according to standard literature methods. A batch reactor,
which composed of a four-neck flask connected with a reflux
condenser, mechanical stirrer and an oil bath equipped with
a thermostat, was used for this reaction. In a typical Saucy–
Marbet procedure, the 2-ethoxypropene (12.9 g, 0.15 mol) was
added slowly to the mixtures of dehydrolinalool (7.6 g, 0.05 mol)
and triethylamine bisulfate ionic liquid (0.05 g, 0.25 mmol)
at 90 C and stirred for 2 h. Then the reaction mixture was
stirred for an additional period of 24 h at 95 C. After the
reaction was completed, the low boiling mixtures were distilled
off under reduced pressure, and water was added. The organic
phase was separated and analysed by gas chromatography
3 S. Frauchiger and A. Baiker, Appl. Catal., A, 2003, 253, 33.
4
R. Marbet, US Pat., 3 632 860, 1972N. Shi; D. Bernd, K. Steffen, J.
Markus, and H. Klaus, US Pat., 6 586 635, 2003.
G. Saucy and R. Marbet, Helv. Chim. Acta, 1967, 50, 1158; R.
Marbet, and G. Saucy, US Pat., 3 029 287, 1962.
5
20
6 P. Wasserscheid and W. Keim, Angew. Chem., Int. Ed., 2000, 39, 3773;
R. D. Rogers and K. R. Seddon, Science, 2003, 302, 792; R. Sheldon,
Green Chem., 2005, 7, 267.
7
T. Welton, Chem. Rev., 1999, 99, 2071; J. Dupont, R. F. de Souza
and P. A. Z. Suarez, Chem. Rev., 2002, 102, 3667; R. Sheldon,
Chem. Commun., 2001, 2399; Y. L. Chauvin, L. Mussmann and H.
Olivier, Angew. Chem., Int. Ed. Engl., 1996, 34, 2698; N. Brausch,
A. Metlen and P. Wasserscheid, Chem. Commun., 2004, 1552; P.
Wasserscheid, B. Driessen-Holscher, R. Van Hal, H. C. Steffens and
J. Zimmermann, Chem. Commun., 2003, 2038; T. J. Geldbach, D. B.
Zhao, N. C. Castillo, G. Laurenczy, B. Weyershausen and P. J. Dyson,
J. Am. Chem. Soc., 2006, 128, 9773; T. Jiang, X. Ma, Y. Zhou, S.
Liang, J. Zhang and B. Han, Green Chem., 2008, 10, 465.
◦
◦
8 M. J. Earle, P. R. McCormac and K. R. Seddon, Green Chem., 1999, 1,
3; S. Doherty, P. Goodrich, C. Hardacre, H. K. Luo, D. W. Rooney,
2
K. R. Seddon and P. Styring, Green Chem., 2004, 6, 63.
(
typical data are listed in Table 1 and Table 2). The ionic
9
P. Wasserscheid, M. Sesing and W. Korth, Green Chem., 2002, 4,
liquids in the aqueous phase could be collected and reused by
evaporating off water in high vacuum. The product of 8.0 g was
obtained by using vacuum distillation with a purity of 98.5%.
The main impurity was 2,6,6-trimethyl-2-ethynyltetrahydro-2H-
pyran and dehydrolinalool. H NMR (CDCl
1
34; C. J. Adams, M. J. Earle, G. Roberts and K. R. Seddon, Chem.
Commun., 1998, 2097; C. E. Song, C. R. Oh, E. J. Roh and D. J.
Choo, Chem. Commun., 2000, 1743; C. E. Song, W. H. Shim, E. J.
Roh and J. H. Choo, Chem. Commun., 2000, 1695.
0 J. Fraga-Dubreuil, K. Bourahla, M. Rahmouni, J. P. Bazureau and
J. Hamelin, Catal. Commun., 2002, 3, 185; R. Alleti, W. S. Oh, M.
Perambuduru, Z. Afrasiabi, E. Simm and V. P. Reddy, Green Chem.,
2005, 7, 203; C. J. Bradaric, A. Downard, C. Kennedy, A. J. Rovertson
and Y. H. Zhou, Green Chem., 2003, 5, 143.
1
1
3
, 500 MHz) d
(
ppm): 1.91 (s, 9H), 2.01–2.26 (m, 7H), 5.07 (m, 1H), 5.99 (d,
-
1
1
2
9
1
H), 6.10 (d, 1H), 7.40 (m, 1H); IR (v cm ): 2966.6, 2925.4,
856.5, 1684.5, 1667.3, 1628.5, 1445.3, 1360.7, 1316.0, 1252.9,
73.8, 825.5; GC-MS, m/z: 41, 43, 69, 81, 109, 124, 149,
77, 192.
1
1 Y. Wang, H. Li, C. Wang and H. Jiang, Chem. Commun., 2004, 1938;
C. Wang, P. Guo, H. Li, Y. Wang, J. Weng and L. Wu, Green Chem.,
2
006, 8, 603.
2 M. J. Earle, P. B. McCormac and K. R. Seddon, Green Chem., 2000,
, 261; F. C. Liu, M. B. Abrams, R. T. Baker and W. Tumas, Chem.
1
2
Commun., 2001, 433; E. D. Bates, R. D. Mayton, I. Ntai and J. H.
Davis, J. Am. Chem. Soc., 2002, 124, 926; G. A. Olah, T. Mathew,
A. Goeppert, B. Torok, I. Bucsi, X. Y. Li, Q. Wang, E. R. Marinez,
P. Batamack, R. Aniszfeld and G. K. S. Prakash, J. Am. Chem. Soc.,
Conclusion
In summary, simple ammonium ionic liquids are highly efficient
catalysts for Saucy–Marbet reactions of unsaturated alcohols
with unsaturated ethers, eliminating the need for volatile organic
solvents. The effect of ionic liquid on the Saucy–Marbet reaction
was investigated and the results showed that the Saucy–Marbet
reaction was heavily influenced by the acidity of ionic liquid.
The high selectivity of 97% and good conversion of 88% could
2
005, 127, 5964.
1
1
1
3 B. Weyershausen and K. Lehmann, Green Chem., 2005, 7, 15; B.
Weyershausen, K. Hell and U. Hesse, Green Chem., 2005, 7, 283.
4 W. Wu, B. Han, H. Gao, Z. Liu, T. Jiang and J. Huang, Angew.
Chem., Int. Ed., 2004, 43, 2415.
5 J. F. Huang, G. A. Baker, H. M. Luo, K. L. Hong, Q. F. Li, N. J.
Bjerrum and S. Dai, Green Chem., 2006, 8, 599; J. F. Huang, H. M.
Luo, C. D. Liang, I. W. Sun, G. A. Baker and S. Dai, J. Am. Chem.
Soc., 2005, 127, 12784.
be obtained using [Et
3
NH]HSO as the catalyst, which may be
4
related to the mild acidity of ionic liquids. Furthermore, the
separation and recycling of the ionic liquids were easy with only
a slight loss of their activity. Considering the high conversion
1
6 J. Weng, C. Wang, H. Li and Y. Wang, Green Chem., 2006, 8, 92; T. L.
Greaves and C. J. Drummond, Chem. Rev., 2008, 108, 207.
17 H. Zhu, F. Yang, J. Tang and M. He, Green Chem., 2003, 5, 38.
8
46 | Green Chem., 2009, 11, 843–847
This journal is © The Royal Society of Chemistry 2009

View Article Online
1
1
8 Z. Zheng, T. Wu, R. Zheng, Y. Wu and X. Zhou, Catal. Commun.,
007, 8, 39.
20 G. Zhao, T. Jiang, H. Gao, B. Han, J. Huang and D. Sun, Green
2
Chem., 2004, 6, 75; J. S. Wilkes, J. A. Levisky, R. A. Wilson and
C. L. Hussey, Inorg. Chem., 1982, 21, 1263; J. S. Wilkes and M. J.
Zaworotko, J. Chem. Soc., Chem. Commun., 1992, 965; Lauric Ropel,
S. B. Lionel, N. V. K. A. Sudhir, A. S. Mark and J. F. Brennecke,
Green Chem., 2005, 7, 83; T. Nishida, Y. Tashiro and M. Yamamoto,
J. Fluorine Chem., 2003, 120, 135.
9 M. J. Earle, J. M. S. S. Esperanca, M. A. Gilea, J. N. C. Lopes,
L. P. N. Rebelo, J. W. Magee, K. R. Seddon and J. A. Widgren,
Nature, 2006, 439, 831; D. R. MacFarlane, J. M. Pringle, K. M.
Johansson, S. A. Forsyth and M. Forsyth, Chem. Commun., 2006,
1
905.
This journal is © The Royal Society of Chemistry 2009
Green Chem., 2009, 11, 843–847 | 847