View Article Online
To demonstrate the usefulness of our new systems in synthetic
applications we decided to study the carbonylation of toluene as a
test reaction (see Scheme 1). The reaction is known to require
highly acidic catalysts systems to obtain any conversion at all. The
carbonylation of toluene has been previously studied by Knifton
and Saleh9 using classical imidazolium and pyridinium chloro-
aluminate ionic liquids. Our catalytic results are displayed in Table
are convinced that the easy recycling of the quite expensive cation
component is an important advantage in comparison to the well-
known chloroaluminates (where an aqueous waste containing the
organic cation is obtained in the hydrolysis step).
In conclusion we have reported for the first time new highly-
3 2 2 3
acidic ionic liquid systems based on [cation][(CF SO ) N]–AlCl
8
mixtures. These systems show interesting cation and temperature
dependent phase behaviour as well as surprisingly high solubilities
2. In this context, it is important to note that all mixtures
[
cation][(CF SO N]–AlCl in our catalytic experiments were
3
2
)
2
3
3
for AlCl . For the carbonylation of toluene we could demonstrate
homogeneous, monophasic systems under the conditions of the
experiment. However, the catalytic transformation was carried out
as a biphasic reaction due to the limited solubility of toluene in the
acidic ionic liquid. The product isolation was carried out by a
hydrolysis step followed by extraction with cyclohexane to
guarantee proper product analysis.
The results show a clear dependency from the ionic liquid’s
cation with a maximum yield in tolualdehyde for the ethyl
substituted pyridinium cation. This is attributed to solubility
effects, taking into account that the reaction requires both sufficient
solubility for toluene and CO in the catalyst layer.
their potential as highly acidic, liquid catalysts.
Finally, we assume that the usefulness of the systems described
here might be not restricted to classical synthetic applications. The
3
high AlCl solubility combined with the known wide electro-
chemical window of the bis(trifluoromethanesulfonyl)imide ionic
liquids10 may open up other interesting applications such as e.g. for
Al electroplating. Furthermore, preliminary studies suggest that the
observed solubility of AlCl
bis(trifluoromethanesulfonyl)imide may be not a unique feature of
this specific Lewis acid. For example SbCl , SbCl and GaCl also
show high solubility in [N-butyl-4-methylpyridinium]
[(CF N].
3
in ionic liquids of the type [cation]
3
5
3
Most interestingly we could demonstrate that the [cation]-
3 2 2
SO )
[
(CF
3
SO
2
)
2
N] can be isolated and recycled after the hydrolysis of
BMBF (N.B.) and Novartis Foundation (A.M.) are gratefully
acknowledged for financial support for this project.
the reaction mixture due to the hydrolytical stability and the
hydrophobicity of the bis(trifluoromethanesulfonyl)imide anion.
3 2 2 3
The recovered [cation][(CF SO ) N could be reloaded with AlCl
and reused in the catalysis without loss in activity or selectivity. We
Notes and references
1
Comprehensive information about this field can be found in many recent
reviews: T. Welton, Chem. Rev., 1999, 99, 2071; P. Wasserscheid and
W. Keim, Angew. Chem., Int. Ed., 2000, 39, 3772; H. Olivier-Bourbigou
and L. Magna, J. Mol. Catal. A: Chem., 2002, 182/3, 419; P.
Wasserscheid and T. Welton, Ionic Liquids in Synthesis, Wiley-VCH,
Weinheim, 2003; S. A. Rorsyth, J. M. Pringle and D. R. MacFarlane,
Aust. J. Chem., 2004, 57, 113.
Scheme 1 Carbonylation of toluene
2
3
F. H. Hurley and T. P. Wier, J. Elektrochem. Soc., 1951, 98, 207.
A. A. Fannin, D. A. Floreani, L. A. King, J. S Landers, B. J. Piersma, D.
J. Stech, R. L. Vaughn, J. S. Wilkes and J. L. Williams, J. Phys. Chem.,
Table 2 Carbonylation of toluene using ionic liquid/AlCl
3
systemsa
% Sel.c
1
984, 88, 2614.
AlCl
3
/IL
Yield
4 M. Earle in P. Wasserscheid and T. Welton (Eds.), Ionic Liquids in
Synthesis, Wiley-VCH: Weinheim, 2003.
b
Ionic liquid (IL)
(mol/mol)
tolualdehyde
5
P. U. Naik, S. J. Nara, J. R. Harjani and M. M. Salunkhe, Can. J. Chem.,
2003, 81, 1057.
[
[
[
[
1][(CF
2][(CF
5][(CF
3
3
3
SO
SO
SO
2
2
2
)
)
)
2
2
2
N]
N]
N]
2.5
2.5
2.5
1.0
21.67
12.85
29.51
7.5
85.8
84.8
85.9
88,0
6 O. Stenzel, R. Brull, U. M. Wahner, R. D. Sanderson and H. G.
Raubenheimer, J. Mol. Catal. A: Chem., 2003, 192, 217.
7 K. Herbst, J. Houzvicka, B. J. Tofte and J. Zavilla, US 2003181780.
8 J. F. Knifton, US 4554383, (Texaco Inc. White Plains. N. Y.), [Chem.
Abstr. 1985, 104, 129634].
d
6][Cl]
a
Conditions: T = 80 °C, p(CO) = 70 bar, 2 h, AlCl
3
to toluene 1 : 1 (50
b
c
mmol). Isolated yield %. Selectivity to para-tolualdehyde in all
tolualdehydes; 1 = N-methylpyridinium; 2 = N-hexylpyridinium; 5 = N-
9
R. Saleh, WO 2000015594, (Exxon Chemicals Inc.); [Chem. Abstr.
d
8
2000, 132, 222341].
ethylpyridinium Comparison with 6 = N-butylpyridinium; conditions: T
00 °C, p(CO) 204 atm, 4 h, [6]/[AlCl ] to toluene 1 : 1.
1
0 P. Bonhote, A. Dias, N. Papageorgiou, K. Kalyanasundaram, M.
1
4
Armand and M. Graetzel, Inorg. Chem., 1996, 35, 1168.
C h e m . C o m m u n . , 2 0 0 4 , 1 5 5 2 – 1 5 5 3
1553