non-ionic mechanisms, however, should also be considered as
alternatives in environments where the formation of the ion
pairs is limited.
round-bottomed flask under N for 5 minutes resulting in a
black liquid (33.7 g, 100% isolated yield).
2
Preparation of samples for Mössbauer measurements
Conclusions
The Mössbauer spectra were recorded at liquid nitrogen temper-
ature. A few droplets of the sample were sealed in a small poly-
We have established that the ionic liquids prepared from
2
ethylene bag of 1 cm so that the liquid formed a thin film
[bmim]Cl and either AlCl or FeCl contain structurally simi-
3 3
inside. This small sample was then dropped into liquid nitrogen
to provide fast cooling in order to preserve the chemical equi-
librium at room temperature. The frozen sample was placed
into the pre-cooled cryostat to record the Mössbauer spectrum.
All isomer shifts are given relative to α-Fe at room temperature.
lar species such as MCl , [bmim][M Cl ], and M Cl and/or
3
2
7
2
6
[bmim][MCl4]. The relative ratio between these species
depends on the molar ratio of [bmim]Cl and MCl . We have
also confirmed that the acetylium cation [CH CO] [MCl ]
3
ϩ
Ϫ
3
4
(
M = Al or Fe) is the key intermediate in the Friedel–Crafts
acetylation reactions of benzene in these ionic liquids. We
ϩ
Ϫ
Reaction of acetyl chloride with MCl (M ؍
Al, Fe) containing
ionic liquids
have shown that the formation of [(CH CO) CHCO] [MCl ]
3
3
2
4
involves the reaction of the acetylium cation with free acetyl
ϩ
chloride. In general, the formation of [(CH CO) CHCO] -
3
2
A 100 ml three necked round-bottomed flask fitted with gas
inlet tube, Suba-seal, and the IR probe of the ReactIR 1000
instrument was charged with the appropriate amount of MCl3
Ϫ
[
MCl4] could lower the atom economy of the acetylation of
aromatics and can be avoided by keeping the concentration
of the acetyl chloride below one equivalent with respect to the
Lewis acid.
(
M = Al, Fe) containing ionic liquid under N . After collecting
2
the first IR spectrum the calculated amount of acetyl chloride
was injected using a syringe and the reaction was continuously
monitored by IR at room temperature.
Experimental
General
Friedel–Crafts acetylation of benzene with acetyl chloride in
MCl (M ؍
Al, Fe) containing ionic liquids
Acetyl chloride, AlCl (99.99%), 1-chlorobutane, and 1-methyl-
3
3
imidazole were obtained from Aldrich Chemical Co. and were
used as received. Acetic anhydride and benzene were obtained
from Reanal, iron() chloride (98%) from Merck. The halo-
genated solvents were distilled from CaH under a N atmos-
A 100 ml three necked round-bottomed flask fitted with gas
inlet tube, Suba-seal, and the IR probe of the ReactIR 1000
instrument was charged with the appropriate amount of MCl3
2
2
(M = Al, Fe) containing ionic liquid under N . After collecting
2
phere before use. All operations were performed under a N2
the first IR spectrum the calculated amount of acetyl chloride
was injected using a syringe and the reaction was continuously
monitored by IR at room temperature. After a few hours
benzene was added to the reaction mixture and the reaction
monitoring was continued.
atmosphere using a glove box or a dry bag (Aldrich Chemical
Co.). All in situ infrared spectroscopic experiments were per-
formed using the ReactIR 1000 spectrometer (Applied Systems
Inc., a Mettler-Toledo Company: www.asirxn.com). A con-
ventional constant acceleration type Mössbauer spectrometer
57
was used (Ranger) with a Co(Rh) source of 400 MBq activity.
The theoretical computations were carried out in the frame-
Acknowledgements
21
work of the Gaussian 98 quantum chemical program package
This work was partially supported by the Hungarian National
Scientific Research Fund (OTKA T-032850 and D-29446) and
ExxonMobil Research and Engineering Company, Annandale,
New Jersey, USA. The donation of the ReactIR 1000 instru-
ment by Applied Systems Inc, a Mettler-Toledo Company is
greatly appreciated. We thank Prof. András Perczel and the
Eötvös Univeristy’s Compaq High Performance Computing
Center for providing CPU time. Ö. F. thanks the Hungarian
Academy of Sciences for a János Bolyai Research Scholarship.
We also thank Prof. K. Seddon and Dr J. Holbrey, The Queen’s
University of Belfast, Northern Ireland, for providing the
synthetic procedure for 1-butyl-3-methylimidazolium chloride.
at the B3LYP/6-31G(dЈ,pЈ) level of theory and the GDIIS
(
geometry optimization using direct inversion in the iterative
22
subspace) based optimization algorithm. The presented tran-
sition structures were validated by analytical force constant
calculations. The optimized structures are available as Gaussian
input at http://organ.elte.hu/farkas/suppl.mat
Preparation of 1-butyl-3-methylimidazolium chloride,
؉
؊
[
bmim] Cl
The ionic liquid 1-butyl-3-methylimidazolium chloride was
prepared by the method of K. Seddon (The Queen’s University
of Belfast, Northern Ireland): a 100 ml three necked round-
bottomed flask was charged with 1-methylimidazole (22 ml,
2
76 mmol, freshly distilled from CaH ) and 1-chlorobutane
References
2
(
33 ml, 287 mmol) and heated to 75 ЊC for 48 hours under N2.
1
P. T. Anastas and J. C. Warner, Green Chemistry: Theory and
Practice, Oxford University Press, Oxford, UK, 1998.
The excess of 1-chlorobutane was removed in vacuo at 80 ЊC.
The pale yellow ionic liquid solidifies at room temperature
forming a pale yellow solid (99% isolated yield).
2 B. Cornils and W. A. Herrmann, Aqueous-phase Organometallic
catalysis, Wiley–VCH, Weinheim, Germany, 1998.
3
4
W. Keim, Chem. Ing. Tech., 1984, 56, 850.
T. Welton, Chem. Rev., 1999, 99, 2071; P. Wasserscheid and W. Keim,
Angew. Chem., Int. Ed., 2000, 39, 3772.
I. T. Horváth, Acc. Chem. Res., 1998, 31, 641.
P. G. Jessop and W. Leitner, Chemical Synthesis Using Supercritical
Fluids, Wiley–VCH, Weinheim, Germany, 1999.
Preparation of 1-butyl-3-methylimidazolium heptachloro-
؉
؊
dialuminate, [bmim] [Al Cl ]
2
7
5
6
1
-Butyl-3-methylimidazolium chloride (17.5 g, 100 mmol) was
mixed with AlCl (13.3 g, 100 mmol) in a 50 ml three necked
3
7
8
(a) C. Friedel and J. M. Crafts, Bull. Soc. Chim. Fr., 1877, 27, 482;
round-bottomed flask under N for 5 minutes resulting in a pale
2
(
b) C. Friedel and J. M. Crafts, Bull. Soc. Chim. Fr., 1877, 27, 530.
yellow liquid (30.8 g, 100% isolated yield).
(a) G. A. Olah, Friedel–Crafts and Related Reactions, Wiley-
Interscience, New York, USA, 1964, vol. III–IV; (b) G. A. Olah,
Friedel–Crafts Chemistry, Wiley-Interscience, New York, USA,
Preparation of FeCl containing ionic liquid
3
1
973.
1
-Butyl-3-methylimidazolium chloride (17.5 g, 100 mmol) was
9
(a) B. P. Susz and J. J. Wuhrmann, Helv. Chim. Acta, 1957, 40, 971;
(b) D. Cook, Can. J. Chem., 1959, 37, 48; (c) D. Cassimatis, J. P.
mixed with FeCl (16.2 g, 100 mmol) in a 50 ml three necked
3
6
84
J. Chem. Soc., Dalton Trans., 2002, 680–685