Selective hydrogenation of trans-cinnamaldehyde and hydrogenolysis-free hydrogenation of benzyl cinnamate in imidazolium ILs

Article abstract of DOI:10.1039/b815566f

trans-Cinnamaldehyde is selectively hydrogenated to hydrocinnamaldehyde using a commercially available palladium catalyst in novel imidazolium ILs. The selective hydrogenation extends to benzyl cinnamate, in which the ester is protected from hydrogenolysis under similar conditions.

Full text of DOI:10.1039/b815566f

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COMMUNICATION
www.rsc.org/greenchem | Green Chemistry
Selective hydrogenation of trans-cinnamaldehyde and hydrogenolysis-free
hydrogenation of benzyl cinnamate in imidazolium ILs
Saibh Morrissey, Ian Beadham and Nicholas Gathergood*
Received 5th September 2008, Accepted 14th October 2008
First published as an Advance Article on the web 3rd November 2008
DOI: 10.1039/b815566f
trans-Cinnamaldehyde is selectively hydrogenated to hydro-
cinnamaldehyde using a commercially available palladium
catalyst in novel imidazolium ILs. The selective hydrogena-
tion extends to benzyl cinnamate, in which the ester is
protected from hydrogenolysis under similar conditions.
for olefin hydrogenation. However its efficient catalytic activity
may lead to poor selectivity. Furthermore, the product ratio
of unsaturated alcohol to saturated aldehyde depends on many
14,15
factors, including the nanostructure of the metal catalyst,
the
degree of polarisation of the carbonyl group and the phase-
12
13,16
distribution of reagent, substrate and catalyst.
The Pd-H
bond is also amphipolar and can transfer hydrogen as either
Introduction
d-
d+
d+
d-
Pd –H or Pd –H , the latter being favoured by catalyst
17
One of the principal present day problems facing the field of
transition metal catalysis is inefficient recycling and reuse of
costly catalysts. Even with cost-effective catalysts, selectivity
can be poor and elaborate poisons or conditions may be
needed to improve the results. ILs have been shown to extend
catalyst lifetime in heterogeneous hydrogenations and facilitate
product isolation by simple extraction with non-polar solvents
or facile distillation. Many common ILs have been investigated
as alternative solvents for catalytic hydrogenations. Of these
studies, the greater part focus on the commercially available
poisons, such as quinoline, and the Lindlar catalyst. With
so many factors influencing selectivity it is not surprising that
some of the solutions to the problem have been elaborate.
14
Tessonier et al., for instance, calcined hydrated palladium(I)
1
◦
nitrate at 350 C (which had previously been added to carbon
2
nanotubes and distilled water) for 2 hours to generate Pd
nanoparticles. 100% conversion was achieved, resulting in 90%
hydrocinnamaldehyde and 10% undesired 3-phenylpropanol.
This compares very favourably with a commercial Pd-C catalyst
that gave a 1:1 ratio of hydrocinnamaldehyde to 3-phenyl-
+
-
3
14
ILs of the form Rmim (R = alkyl chain) X .
1-propanol. Tessonier suggested that the improvement in
While it is easy to achieve selective olefin reduction in a,b-
unsaturated ketones using simple Pd/C reduction, with a,b-
unsaturated aldehydes the situation is more challenging and
selectivity with carbon nanotubes stemmed from the absence of
either an oxygenated surface, or the micropores typically present
on a conventional activated carbon support. Additionally an
‘electronic modification through electron transfer between the
4
,5
product mixtures often arise. trans-Cinnamaldehyde is widely
used as a model substrate because the products of its hydro-
genation are extensively used in the fine chemical industry.
metal and the support, which in turn modifies the absorption
4,6,7
18,19
and selectivity of the products
was hypothesized to explain
The selectivity varies due to the possibility of reduction of either
the olefin moiety, to give hydrocinnamaldehyde, or the aldehydic
moiety, to give cinnamyl alcohol. Owing to the thermodynami-
the simultaneous hydrogenation of C=C and C=O bonds on
activated carbon, compared with the rapid desorption of C=C
reduced product from the nanotubes. Notably, in neither case
is reduction observed if hydrocinnamaldehyde is the substrate,
indicating that it is not an intermediate in the reaction.
4,8
cally favoured reduction of the C=C bond over the C=O bond,
the selectivity towards cinnamyl alcohol is generally poor. This
can be frustrating as cinnamyl alcohol is used widely in the
flavouring and perfume industries. Hydrocinnamaldehyde is also
an important chemical and has uses in the perfumery industry
A more selective process, also involving a palladium catalyst,
15
was developed by Ledoux et al. After first impregnating a
carbon nanofibre support with the palladium salt, palladium(I)
9
◦
and in the synthesis of anti-HIV compounds. In the field of
nitrate was dried overnight at 110 C and reduced under a flow
metal catalysed hydrogenation ruthenium complexes generally
of hydrogen for 2 hours. This support was the major difference
from Tessonier’s procedure, with the nanofibres, prepared by
a gas phase deposition using ethane and hydrogen over a
nickel catalyst (from Al O , Ni(NO ) /glycerol), followed by
sonication of the fibres and cleaning with acid at 650 C. In
this case the hydrogenation was 98% selective for the C=C
double bond of cinnamaldehyde, compared with a commer-
cial Pd–C catalyst that gave mixtures of C=C hydrogenation,
C=O hydrogenation, and complete reduction to 3-phenyl-1-
10
leadtohydrogenation ofthe carbonyl moiety, whereas rhodium
complexes lead to hydrogenation of the olefin moiety but
11–13
typically high pressures of hydrogen are required.
2
3
3 2
◦
Herein we present the results obtained for the hydrogena-
tion of trans-cinnamaldehyde and benzyl cinnamate using the
commercially available Pd/C catalyst at 1 atmosphere hydrogen
pressure with the use of alternative green solvents (1–10).
Palladium on carbon is well known as a universal catalyst
propanol. Ledoux suggested that presence of residual acid on
the charcoal, as well as the property that commercial Pd–
C is covered with micropores to the extent of 60%, could
explain the poor selectivity of palladium on ordinary activated
carbon.
School of Chemical Sciences, National Institute for Cellular
Biotechnology, Dublin City University, Glasnevin, Dublin 9, Ireland.
E-mail: Nick.Gathergood@dcu.ie; Fax: +353 1 700 5503; Tel: +353 1
7
00 7860
4
66 | Green Chem., 2009, 11, 466–474
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Our research effort is directed by the development of
biodegradable, low toxicity solvents which can also offer perfor-
mance advantages over established methods. This work began
20
with Gathergood and Scammells in 2002 where the same prin-
ciples that are used in the synthesis of biodegradable surfactants,
were applied to the design of environmentally friendly ILs.
Subsequent studies showed the presence of an ester linkage in the
21
side chain of the IL cation (1) promoted biodegradation. The
counterion was also a significant factor, with the octyl sulfate
present in examples (3) which were readily biodegradable. We
recently reported that key features which improve biodegrada-
tion and reduce antimicrobial toxicity were also required for
improved catalyst performance in the selective hydrogenation of
22
phenoxyocta-2,7-diene. Herein, we present our work studying
the changes in conversion and selectivity in the hydrogenation
reactions of cinnamaldehydes and benzyl cinnamate using
novel biodegradable and/or low toxicity ILs and comparison
with conventional ILs and common organic solvents. (Fig. 1).
Recycling of the catalyst/IL media is also investigated.
Results
Synthesis of designer ILs for selective catalytic hydrogenation
Novel ILs (2,4–10) have been prepared containing ester and
20,21
ether moieties in the side chain (Fig. 2).
The ILs were readily
synthesised from inexpensive alcohols and glycols, thus leading
to imidazolium ILs with oxygen in the side chain of the cation.
trans-Cinnamaldehyde
The selective formation of hydrocinnamaldehyde is of both
academic interest and of interest to the fine chemical industry
Fig. 1 Ionic liquids used as reaction solvents.
23
(
Fig. 3).
Using the pentyl derivative of imidazolium ILs 1 and 5,
selectivity towards hydrocinnamaldehyde generally ranged from
0 to 100%. The most impressive results obtained were achieved
using the dimethyl derivative of the ILs, where under 1 atm.
pressure 100% conversion and selectivity were reached at
to be still applicable when an oxygen atom is present in the side
chain of the IL (Table 2).
Upon increasing the number of oxygen atoms in the side
chain from one to two, the selectivity is only slightly negatively
affected. There is however a significant drop in conversion by
the 3 recycle (to 64%) (Table 3).
In order to compare the novel ILs with commercially avail-
able solvents, trans-cinnamaldehyde was hydrogenated using
9
H
2
2
st
4 h upon the 1 recycle (Table 1). Although slight variations
rd
in conversion and selectivity occurred during the recycling
procedure, almost the same reaction efficiency can be seen upon
the fourth recycle (conversion 97%, selectivity 100%) (Table 1).
When the side chain length is increased, and also contains an
oxygen atom (2), the result obtained does not vary significantly;
the conversion remains consistent at 100% and the selectivity
still does not decrease below 90%. Thus, the method is shown
[Bmim][NTf
seen in Table 4. The results show that under 1 atm. H
[Bmim][OctOSO ] exhibits essentially the same selectivity as
toluene, while [Bmim][NTf ] gives a higher selectivity of 87%,
2
] as well as [Bmim][OctOSO
3
] and the results can be
2
pressure
3
2
Fig. 2 Synthesis of novel ILs.
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Table 1 Results from reactions using solvent 5 and 1
Table 3 Results from reactions using solvent 6
Experiment
Experiment
Solvent (E)/Recycle (R) Time (h) % conversion % selectivity 8
Solvent (E)/Recycle (R) Time (h) % conversion % selectivity 8
5
E1
R1
R2
R3
R4
24
8
36
100
100
48
97
79
100
89
97
98
100
100
100
100
93
73
98
99
96
100
100
94
6
E1
R1
R2
R3
24
48
24
48
24
48
24
48
32
97
100
100
31
85
34
100a
88
100
88
100
91
90
4
8
24
4
8
24
4
8
24
4
8
64
93
24
a
Isolated yield = 77%.
4
8
1
E1
R1
48
48
93
of a rhodium (I) complex (chlorotris(meta-trisulfonato triph-
enylphosphine). The reactions were carried out in a batch
Table 2 Results from reactions using solvent 2
◦
reactor (10–40 atm. H
2
, 50–90 C) and up to 99.9% selectivity
Experiment
towards the saturated aldehyde was observed using a biphasic
system (water/toluene). Reductions of cinnamaldehyde based
Solvent (E)/Recycle (R) Time (h) % conversion % selectivity 8
25
on ruthenium catalysts were carried out by Hajek et al. and Qiu
a
2
E1
48
100
93
2
6
et al. At 50 atm. H
2
using a 5% Ru/Y catalyst (Y: alumosilicate
a
25
Isolated yield = 87%.
zeolite used in petrochemistry), Hajek et al. achieved selectivity
up to 70% towards the unsaturated alcohol. Qiu et al. achieved
26
similar selectivity (79.1%), also towards the reduction of the
carbonyl moiety, using a carbon nanotubes-supported Pd-Ru
◦
catalyst at 120 C and 50 atm. H
2
pressure. Better results were
obtained using the combined metal system than with each metal
alone, speculated by the group to be due to a synergic effect
or a promoting effect exerted by ruthenium. Our investigations
using recyclable Pd/C catalysts in ILs at 1 atm. H pressure to
2
give selective reduction of the double bond in cinnamaldehdyde
represent a significant result.
Factors influencing selectivity
Selective reductions using imidazolium ILs have been ratio-
nalised on the basis of three parameters of the IL cation:
1
) the presence or absence of a methyl group on the C
2
position of the imidazolium moiety, 2) the terminal alkyl chain
length and, 3) the presence of oxygen atoms in the side chain.
During their investigation into asymmetric hydrogenation in
27
ILs, Jessop et al. demonstrated that side chain length and
substitution at the C position of the imidazolium cation
influenced enantioselectivity. Among their results, a comparison
between ILs [emim][NTf ] and [dmpim][NTf ] ([dmpim]: 1,2-
2
2
2
Fig. 3 Reduction pathway of cinnamaldehyde.
dimethyl-3-propylimidazolium) displayed differences in %ee
obtained for the hydrogenation of tiglic and atropic acids. The
%ee obtained when using ILs as reaction solvents was shown
to be solvent-dependent. Chandrasekhar et al. compared
hydrogenation reactions using Adams¢ catalyst in poly(ethylene
which is still lower than the selectivities of 93% achieved with
28
ILs 1 and 2, or 100% obtained with ILs 5 and 6.
24
Nuithitikul and Winterbottom selectively reduced the
olefin moiety of cinnamaldehyde using an aqueous solution
glycol) (400) and [emim][BF ] and found that the yield dropped
4
Table 4 Hydrogenation of trans-cinnamaldehyde with commercially available solvents
Experiment
(E)/Recycle (R)
Solvent
Time (h)
% conversion
% selectivity 8
[
[
Bmim][NTf
Bmim][OctOSO
2
]
E1
E1
E1
24
24
24
100
100
100
87
69
67
3
]
Toluene
4
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by as much as 78% when [emim][BF
4
] was used in place of
Table 5 Effect of catalyst loading on hydrogenation
PEG 400. An investigation of the quantitative adsorption of
hydrogen on the catalyst in both solvents showed PEG 400 to
allow superior adsorption, compared to the IL. The presence
of repeated oxygen atoms in the PEG solvent was shown to
affect the results obtained. Berger et al. found the anion
also had a significant effect on hydrogen solubility in ILs.
Catalyst
loading (g) (h)
Time
Solvent
% conversion % selectivity 12
1
2
0.01
0.005
0.01
24
24
24
24
24
48
24
24
24
24
48
48
24
48
48
48
24
24
24
24
24
100
100
100
100
100
100
32
100
5
10
0
0
0
29
0
0
.005
.005
100
100
100
100
53
100
100
100
0
[
Bmim][BF
effectively than [bmim][PF
it was only possible to achieve highly selective hydrogenation
of trans-cinnamaldehyde in the presence of the NTf anion.
We tentatively propose that steric effects around the cation
substitution at the C position and the presence of ether oxygens
4
] was found to solubilise hydrogen four times more
]. Our results also demonstrated that
0.005
.0025
0.01
6
0
3
4
2
0
.0025
0.005
0
0
.005
.0025
19
0
(
2
in the cation side-chain) together with a subtle alteration in the
uptake of hydrogen (influenced by the choice of anion) either in
solution or at the catalyst surface, may be contributing to the
superior selectivity exhibited by our novel ILs.
0.005
.01
0.005
.0025
11
100
56
100
0
0
100
100
0
0
[
Bmim][NTf
2
]
0.005
0.005
0.005
0.005
0.005
100
100
100
100
100
0
0
0
0
[
Bmim][OctOSO
3
]
THF
Ethyl acetate
Methanol
Benzyl cinnamate
0
In order to achieve the selective hydrogenation of the olefin
moiety of benzyl cinnamate without hydrogenolysis of the benzyl
30
Table 6 Hydrogenation of benzyl 3-phenylpropanoate (12)
ester (Fig. 4), elaborate conditions are often required.
The effect of catalyst loading, as well as the solvent effect
was investigated during hydrogenations of benzyl cinnamate
Solvent
Catalyst loading (g)
0.01
Time (h)
24
No reaction
(
Table 5).
2
The least amount of catalyst effective in inducing 100%
conversion under 1 atm. H
this value, only 32% conversion was achieved after 24h with IL
. The octylsulfate ILs (3 and 4) gave promising results in terms
of selectivity; however this was only achieved when conversion
was low for IL 3, but with optimal conversion for IL 4. The
most compelling results from this data set are obtained using
ILs 2 and 4. Using 0.005 g catalyst, after 24 h, 100% conversion
2
pressure was 0.005g. Using half
Table 7 Recycling of IL 2 system
2
Experiment
(E)/Recycle (R)
Solvent
% conversion
% selectivity 12
2
E1
R1
R2
R3
R4
R5
R6
R7
R8
100
100
100
100
100
97
91
91
81
100
100
100
100
100
100
100
100
100
and selectivity were obtained under 1 atm. H pressure. More
2
surprising is that the selectivity was retained up to 48h, thus
suggesting that hydrogenolysis of this compound in this IL
system only occurs with the unsaturated ester. More evidence of
this is observed when the non-hydrogenolysed reduced product
12 is further subjected to hydrogenation conditions using an
increased amount of catalyst, under 1 atm. H pressure, no
2
a small drop in conversion observed (81%). This represents an
improvement on previous recycling experiments using Pd(acac)
in IL 3 to selectively reduce phenoxyocta-2,7-diene, where a
hydrogenolysis is observed (Table 6). The significance of this
result is that IL 2 completely prevents hydrogenolysis of the
benzyl ester.
The system used to obtain 100% selectivity using IL 2 was
recycled 4 times with no loss in activity (Table 7). After the fourth
recycle, the selectivity remains constant, but the conversion
decreases slightly to 91% upon recycle 7. Only on recycle 8 was
2
decrease in yield from 85 to 55% was observed on the first
22
recycle.
Varying catalytic amounts were tested for the hydrogenation
of benzyl cinnamate using IL 4. As can be seen from the results
displayed in Table 8, the increasing amount of catalyst favours
Fig. 4 Reduction of benzyl cinnamate.
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Table 8 Varying catalytic amount for the hydrogenation of benzyl
cinnamate in IL 4
Table 10 Hydrogenation of allyl cinnamate
IL
% conversion
% selectivity 15
Catalyst
Solvent loading (g)
Time (h)
24
% conversion
% selectivity 12
2
100
100
100
100
100
84
71
0
0
0
4
4
0.005
100
100
100
100
100
100
68
55
26
25
[Bmim][NTf
[Bmim][OctOSO
Ethyl acetate
2
]
0
0
0
0
.006
.007
.008
.009
3
]
Table 11 Hydrogenation of vinyl cinnamate
Table 9 Effect of ILs of differing cation on the selective reduction of
benzyl cinnamate
IL
% conversion
% selectivity
Catalyst
loading (g) Time (h)
2
100
100
100
0
49
0
Solvent
% conversion
% selectivity 12
4
Ethyl acetate
6
7
8
9
0.005
0.005
0.005
0.005
0.005
24
24
24
24
24
100
100
100
100
100
44
7
0
34
0
Vinyl cinnamate
1
0
Vinyl cinnamate was also used as a test-substrate in order
to evaluate the selectivity obtained using the novel ILs in
comparison with other more frequently used solvents (Fig. 6).
Only 49% selectivity was obtained using the octylsulfate IL,
hydrogenolysis, optimum conditions being observed with 0.005 g
catalyst.
The effect of cation chain length and the number of oxygens
in the side chain was investigated to determine whether only the
cation from ILs 2 and 4 gave the best selectivity (Table 9).
It is evident from the results obtained that any difference in the
length of the side chain or the number of oxygen atoms contained
within, negatively affects the selectivity of the reaction. This
reaction is therefore sensitive to many changes in IL composition
concerning the IL cation.
4, in comparison with no selectivity for IL 2 and ethyl acetate
(
Table 11).
Conclusion
We have demonstrated that novel imidazolium ILs display
superior selectivity in olefin hydrogenation compared with
conventional organic solvents and classic ILs. Hydrogenolysis-
free hydrogenation of benzyl cinnamate was achieved using
novel ILs without the need for a catalyst poison, under 1 atm.
Based on the conditions from the result obtained using ILs
2
and 4 and 0.005 g catalyst, this system was used to test other
compounds comprising hydrogenolysable functionalities.
H pressure. Furthermore trans-cinnamaldehyde was selectively
2
Allyl cinnamate
reduced to hydrocinnamaldehyde with little or no over-reduction
of the aldehydic moiety. The reactions were performed with only
the use of the IL, substrate, a simple heterogeneous catalyst and
The hydrogenation of allyl cinnamate can lead to the reduction
either of the olefinic bonds, or even hydrogenolysis of the allyl
functionality may be observed (Fig. 5).
under H at 1 atm. pressure. Successful recycling of the systems
2
Using both ILs 2 and 4 under 1 atm. H
selectivities were reached in comparison with common organic
solvents and classic ILs displaying no selectivity (Table 10).
2
pressure, impressive
was achieved without significant loss of activity. Overall, the
novel ILs were found to be robust media for hydrogenation
reactions as a replacement for harmful VOCs.
Fig. 5 Reduction of allyl cinnamate.
Fig. 6 Reduction of vinyl cinnamate.
4
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1
3
Experimental
C NMR (100 MHz, CDCl
26.50, 62.33, 34.30, 33.67.
3
) d ppm 141.20, 129.01, 128.93,
1
Hydrogenation
34
Data consistent with literature.
Typical procedure. 10% Pd/C (5.0 mg unless otherwise
stated) was weighed into a dry 2-neck round bottom flask. The
pre-dried IL (2.0 mL) was then added to the flask, followed
1
Propyl cinnamate. H NMR (400 MHz, CDCl
3
) d ppm 7.74
(
(
7
d, J = 16 Hz, 1H), 7.56-7.54 (m, 2H), 7.42-7.38 (m, 3H), 6.50
d, J = 16 Hz, 1H), 4.21 (t, J = 6.7 Hz, 2H), 1.79 (tq, J = 6.7,
by the desired substrate (4 mmol) and 3 N
were performed. The reaction mixture was allowed to stir for
0 minutes or until reaching the desired reaction temperature,
2
/vacuum cycles
.8 Hz, 2H), 1.04 (t, J = 7.8 Hz, 3H).
13
C NMR (100 MHz, CDCl ) d ppm 166.25, 143.20, 131.70,
3
1
1
29.29, 129.26, 129.00, 118.03, 61.52, 22.83, 17.01.
Data consistent with literature.
or until all the substrate had dissolved in the IL. Hydrogen
35
was then introduced to the reaction via a balloon, and the
1
1
progress of the reaction was monitored by H NMR at 24 and
Propyl 3-phenylpropanoate. H NMR (400 MHz, CDCl ) d
3
4
8 hour intervals. Quantitative analysis of the reaction products
ppm 7.34-7.30 (m, 2H), 7.25-7.22 (m, 3H), 4.09 (t, J = 7.0 Hz,
2H), 3.02 (t, J = 7.8 Hz, 2H), 2.69 (t, J = 7.8 Hz, 2H), 1.71 (tq,
J = 7.0, 7.3 Hz, 2H), 0.97 (t, J = 7.3 Hz, 3H).
was carried out by measuring the integration ratio of the peaks
from the crude NMR spectrum. These values were then verified
by purification of the product by column chromatography and
thus the calculation of isolated yields. Upon termination of the
reaction, the products were extracted using hexane (10 ¥ 3 mL).
The mass recovery after extraction from the IL was always >
1
3
C NMR (100 MHz, CDCl ) d ppm 173.06, 140.60, 128.50,
3
128.32, 126.25, 66.29, 37.43, 31.03, 21.98, 10.40.
Data consistent with literature.
36
1
Ethyl cinnamate. H NMR (400 MHz, CDCl
3
) d ppm 7.73
9
8%. In the case of reactions carried out in octylsulfate ILs, the
(
(
3
d, J = 16 Hz, 1H), 7.55-7.52 (m, 2H), 7.42-7.38 (m, 3H), 6.48
product was either distilled from the IL using high vacuum or a
brief column was prepared to separate product from IL. These
procedures generally led to a lower mass recovery (> 80%), due
to product being lost on the column or lost during the distillation
d, J = 16 Hz, 1H), 4.31 (q, J = 7.1 Hz, 2H), 1.38 (t, J = 7.1 Hz,
H).
1
3
C NMR (100 MHz, CDCl
30.55, 128.58, 128.06, 118.64, 60.50, 14.53.
Data consistent with literature.
3
) d ppm 166.99, 144.93, 134.74,
1
procedure. All reactions carried out in the NTf ILs were carried
2
35
◦
◦
out at 55 C and 65 C in the octylsulfate ILs.
1
Ethyl 3-phenylpropanoate. H NMR (400 MHz, CDCl
3
) d
Recycle procedure. Following extraction of the products
ppm 7.34-7.30 (m, 2H), 7.25-7.23 (m, 3H), 4.19 (q, J = 7.2 Hz,
2H), 3.01 (t, J = 7.8 Hz, 2H), 2.67 (t, J = 7.8 Hz, 2H), 1.29 (t,
J = 7.2 Hz, 3H).
from the IL, the IL (containing the catalyst) was dried and
1
analysed by H NMR. Following confirmation that the IL was
substrate/product-free and had not degraded, fresh substrate
was then added to the system and the reactions recommenced
as described.
1
3
C NMR (100 MHz, CDCl ) d ppm 172.92, 140.62, 128.51,
3
1
28.34, 126.26, 60.43, 35.98, 31.01, 14.24.
37
Data consistent with literature.
1
Benzyl 3-phenylpropanoate. H NMR (400 MHz, CDCl
3
) d
ppm 7.29-7.09 (m, 10H), 5.03 (s, 2H), 2.91 (t, J = 7.8 Hz, 2H),
IL preparation
ILs 1 and 3 were synthesised in accordance with the
2
.62 (t, J = 7.8 Hz, 2H).
1
3
C NMR (100 MHz, CDCl
3
) d ppm 172.80, 140.44, 135.94,
21
literature.
128.60, 128.56, 128.46, 128.36, 128.27, 126.33, 66.34, 35.21,
3
0.74.
Representative procedure for the preparation of a-bromoesters
2-propoxyethyl 2-bromoacetate). To a stirred solution of
31
Data consistent with literature.
(
dichloromethane (350 mL), propoxyethanol (47.84 mL,
1
3
-Phenylpropanoic acid. H NMR (400 MHz, CDCl
3
) d ppm
4
60 mmol), and triethylamine (69.3 mL, 500 mmol), under a
1
1.00 (br s, 1H), 7.23-7.19 (m, 2H), 7.14-7.11 (m, 3H), 2.89 (t,
◦
nitrogen atmosphere at -78 C was added dropwise bromoacetyl
bromide (92.92 g, 460 mmol). After stirring at -78 C for
3
J = 7.8 Hz, 2H), 2.69 (t, J = 7.8 Hz, 2H).
C NMR (100 MHz, CDCl ) d ppm 178.97, 140.16, 128.59,
28.29, 126.40, 35.59, 30.58.
◦
1
3
3
◦
h, the reaction mixture was allowed warm up to -20
C
1
and quenched by addition of water (50 mL). The organic
phase was washed with distilled water (3 ¥ 25 mL), saturated
ammonium chloride (3 ¥ 25 mL), saturated sodium bicarbonate
32
Data consistent with literature.
1
Hydrocinnamaldehyde. H NMR (400 MHz, CDCl
3
) d ppm
(
3 ¥ 25 mL) and brine (2 ¥ 25 mL). The organic phase was then
9
2
.85 (t, J = 1.4 Hz, 1H), 7.35-7.31 (m, 2H), 7.26-7.22 (m, 3H),
dried over magnesium sulfate, filtered and solvents removed via
.99 (t, J = 7.4 Hz, 2H), 2.83-2.79 (m, 2H).
1
3
rotary evaporation. The crude product was distilled (bp 100–
C NMR (100 MHz, CDCl ) d ppm 203.49, 141.32, 128.01,
3
◦
1
02 C) to give a pale yellow liquid in 83% yield (85.91 g,
1
27.99, 127.89, 40.33, 29.63.
Data consistent with literature.
33
382 mmol).
1
H NMR (400 MHz, CDCl
3
) d (ppm) 4.34 (t, J = 4.6 Hz, 2H),
1
3
-Phenylpropan-1-ol. H NMR (400 MHz, CDCl
3
) d ppm
3.88 (s, 2H), 3.67 (t, J = 4.6 Hz, 2H), 3.47 (t, J = 6.9 Hz, 2H),
7
2
1
.23-7.18 (m, 2H), 7.14-7.10 (m, 3H), 3.62 (t, J = 6.6 Hz, 2H),
1.66 (tq, J = 6.9, 7.3 Hz, 2H), 0.94 (t, J = 7.3 Hz, 3H).
1
3
.62 (t, J = 7.4 Hz, 2H), 1.82 (tt, J = 6.6, 7.4 Hz, 2H), 1.55 (br s,
C NMR (100 MHz, CDCl ) d (ppm) 167.31, 73.07, 68.10,
3
H).
65.42, 25.90, 22.81, 10.52.
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-
1
Representative method for the preparation of bromide salts (3-
Methyl-1-(propoxyethoxycarbonylmethyl)imidazolium bromide).
To a stirred solution of 1-methylimidazole (65.0 mmol, 5.33 g)
IR (cm ) 3154, 2962, 2930, 2862, 1751, 1595, 1558, 1546,
1539, 1495, 1452, 1354, 1197, 1137.
-
+
-].
MS m/z, 225.2 [M-NTf
2
] ; MS: m/z, 280.0 [NTf
2
◦
in diethyl ether (60 mL) at -15 C under a nitrogen atmosphere
was added dropwise propoxyethyl 2-bromoacetate (78.0 mmol,
3-Methyl-1-(methoxyethoxycarbonylmethyl)imidazolium NTf
(7). The title compound was prepared from 3-methyl-
1-(methoxyethoxyoxycarbonylmethyl)imidazolium bromide
(1.74 g, 6.26 mmol) and LiNTf (2.16 g, 7.51 mmol) according
to the general procedure in 91% yield (2.73 g, 5.70 mmol).
2
◦
1
7.55 g). The reaction mixture was stirred vigorously at -15 C
for 1 h, then at RT for 24 h. The diethyl ether top phase was
decanted and the IL washed with diethyl ether (2 ¥ 20 mL), then
residual solvent removed on the rotary evaporator. The product
was dried under high vacuum for 8 h yielding a pale yellow solid
2
1
H NMR (400 MHz, CDCl
3
) d (ppm) 8.85 (s, 1H), 7.39 (t, J =
in 88% yield (17.59 g, 57.3 mmol).
1.8 Hz, 1H), 7.33 (t, J = 1.8 Hz, 1H), 5.07 (s, 2H), 4.40 (t, J =
1
H NMR (400 MHz, CDCl ) d (ppm) 10.25 (s, 1H), 7.48 (t,
3
4.6 Hz, 2H), 3.98 (s, 3H), 3.66 (t, J = 4.6 Hz, 2H), 3.40 (s, 3H).
1
3
J = 1.8 Hz, 1H), 7.35 (t, J = 1.8 Hz, 1H), 5.46 (s, 2H), 4.30 (t,
J = 4.8 Hz, 2H), 4.02 (s, 3H), 3.61 (t, J = 4.8 Hz, 2H), 3.37 (t,
J = 6.8 Hz, 2H), 1.54 (tq, J = 6.8, 7.5 Hz, 2H), 0.85 (t, J =
C NMR (100 MHz, CDCl ) d (ppm) 165.73, 137.75, 123.78,
3
123.18, 119.70 (q, J = 319 Hz), 69.75, 65.72, 63.24, 58.89, 49.93.
-
1
IR (cm ) 2926, 2855, 1750, 1636, 1558, 1539, 1495, 1452,
1365, 1204, 1129.
7
.5 Hz, 3H).
C NMR (100 MHz, CDCl
1
3
-
+
-].
3
) d (ppm) 166.12, 138.74, 123.68,
MS m/z, 199.1 [M-NTf
2
] ; MS: m/z, 280.0 [NTf
2
1
22.77, 73.08, 67.89, 65.87, 50.28, 36.93, 22.75, 10.50.
◦
◦
M ( C) 25–27 C.
3-Methyl-1-(ethoxyethoxycarbonylmethyl)imidazolium NTf
2
-
1
IR (cm ) 3099, 2967, 2927, 1751, 1578, 1568, 1558, 1539,
495, 1452, 1216, 1176.
(8). The title compound was prepared from 3-methyl-1-
(ethoxyethoxycarbonylmethyl)imidazolium bromide (2.93 g,
1
2
-
+
MS m/z, Found 227.1410 [M-Br ] , Calcd. C11
H
19
N
2
O
3
10.0 mmol) and LiNTf
2
(4.59 g, 16.0 mmol) according to the
27.1396.
general procedure in 90% yield (4.42 g, 8.97 mmol).
1
H NMR (400 MHz, CDCl
3
) d (ppm) 8.82 (s, 1H), 7.39 (t, J =
Representative method for the preparation of NTf
2
salts
1.8 Hz, 1H), 7.34 (t, J = 1.8 Hz, 1H), 5.06 (s, 2H), 4.38 (t, J =
4.6 Hz, 2H), 3.97 (s, 3H), 3.68 (t, J = 4.6 Hz, 2H), 3.56 (q, J =
7.1 Hz, 2H), 1.22 (t, J = 7.1 Hz, 3H).
(
(
3-Methyl-1-(propoxyethoxycarbonylmethyl)imidazolium NTf
2). A flask was charged with 3-Methyl-1-(propoxyethoxy-
2
)
1
3
carbonylmethyl) imidazolium bromide (3.55 g, 7.00 mmol) and
distilled water (20 mL). LiNTf (2.15 g, 7.50 mmol) in distilled
C NMR (100 MHz, CDCl ) d (ppm) 165.76, 137.63, 123.80,
3
2
123.25, 119.70 (q, J = 319 Hz), 67.62, 66.67, 65.97, 49.92, 36.56,
water (3 mL) was added in one portion and the suspension
was stirred vigorously for 6 h at RT. The top aqueous layer was
removed and the IL was washed with distilled water (3 ¥ 10 mL).
The solvent was then removed on the rotary evaporator and the
product was dried under high vacuum for 3 h to give a yellow
15.01.
-
1
IR (cm ) 3169, 3116, 2967, 2927, 2859, 1751, 1581, 1569,
1558, 1495, 1452, 1352, 1196, 1135.
-
+
-].
MS m/z, 213.1 [M-NTf
2
] ; MS: m/z, 280.0 [NTf
2
viscous oil in 68% yield (2.43 g, 4.79 mmol).
3-Methyl-1-(butoxyethoxycarbonylmethyl)imidazolium NTf
(9). The title compound was prepared from 3-methyl-1-
(butoxyethoxycarbonylmethyl)imidazolium bromide (1.85 g,
2
1
H NMR (400 MHz, CDCl
3
) d (ppm) 8.78 (s, 1H), 7.39 (t, J =
1
4
6
3
.8 Hz, 1H), 7.36 (t, J = 1.8 Hz, 1H), 5.04 (s, 2H), 4.37 (t, J =
.8 Hz, 2H), 3.95 (s, 3H), 3.67 (t, J = 4.8 Hz, 2H), 3.43 (t, J =
.7 Hz, 2H), 1.61 (tq, J = 6.7, 7.3 Hz, 2H), 0.92 (t, J = 7.3 Hz,
H).
5.77 mmol) and LiNTf
2
(1.99 g, 6.92 mmol) according to the
general procedure in 84% yield (2.73 g, 4.82 mmol).
1
H NMR (400 MHz, CDCl ) d (ppm) 8.71 (s, 1H), 7.38
3
1
3
C NMR (100 MHz, CDCl
3
) d (ppm) 165.76, 137.50, 123.82,
(t, J = 1.8 Hz, 1H), 7.36 (t, J = 1.8 Hz, 1H), 5.00 (s, 2H), 4.32 (t,
J = 4.8 Hz, 2H), 3.91 (s, 3H), 3.64 (t, J = 4.8 Hz, 2H), 3.44 (t,
J = 6.7 Hz, 2H), 1.54 (tt, J = 6.7, 7.2 Hz, 2H), 1.34 (tq, J = 7.2,
7.5 Hz, 2H), 0.89 (t, J = 7.5 Hz, 3H).
1
23.34, 119.60 (q, J = 319 Hz), 72.99, 67.79, 65.91, 49.87, 56.49,
22.68, 10.37.
-
1
IR (cm ) 3164, 3117, 2968, 2927, 2862, 1751, 1569, 1558,
539, 1495, 1452, 1353, 1198, 1135.
1
3
1
C NMR (100 MHz, CDCl ) d (ppm) 165.78, 137.32, 123.83,
3
-
+
-].
MS m/z, 227.2 [M-NTf
2
] ; MS: m/z, 280.0 [NTf
2
123.40, 122.33 (q, J = 319 Hz), 71.09, 67.78, 65.81, 49.78, 36.37,
3
1.50, 19.11, 13.78.
-
1
2
,3 Dimethyl-1-(pentoxycarbonylmethyl) imidazolium NTf
2
IR (cm ) 3164, 3123, 2959, 2934, 2864, 1756, 1582, 1569,
(
1
5). The title compound was prepared from 2,3-dimethyl-
1558, 1495, 1453, 1354, 1197, 1135.
21
-
+
-].
-(pentoxycarbonylmethyl)imidazolium bromide
(3.36 g,
MS m/z, 241.2 [M-NTf
2
] ; MS: m/z, 280.0 [NTf
2
1
1.0 mmol) and LiNTf (4.59 g, 16.0 mmol) according to the
2
general procedure in 95% yield (5.30 g, 10.5 mmol).
3-Methyl-1-(propoxyethoxyethoxycarbonylmethyl)imidazol-
ium NTf (6). The title compound was prepared from 3-methyl-
1-(methoxyethoxyethoxycarbonylmethyl)imidazolium bromide
(1.91 g, 5.45 mmol) and LiNTf (1.88 g, 6.54 mmol) according
to the general procedure in 82% yield (2.46 g, 4.46 mmol).
1
H NMR (400 MHz, CDCl
3
) d (ppm) 7.28 (d, J = 2.2 Hz,
2
1
2
4
H), 7.26 (d, J = 2.2 Hz, 1H), 4.93 (s, 2H), 4.21 (t, J = 6.8 Hz,
H), 3.82 (s, 3H), 2.56 (s, 3H), 1.68-1.60 (m, 2H), 1.34-1.27 (m,
H), 0.92 (t, J = 7.0 Hz, 3H).
2
1
3
1
C NMR (100 MHz, CDCl
3
) d (ppm) 165.78, 145.45, 122.38,
H NMR (400 MHz, CDCl ) d (ppm) 8.92 (s, 1H), 7.40 (t,
3
1
22.37, 119.70 (q, J = 319 Hz), 67.21, 49.17, 35.48, 27.93, 27.75,
J = 1.7 Hz, 1H), 7.31 (t, J = 1.7 Hz, 1H), 5.08 (s, 2H), 4.41 (t,
22.18, 13.85, 9.75.
J = 4.8 Hz, 2H), 4.00, (s, 3H), 3.77 (t, J = 4.8 Hz, 2H), 3.67
4
72 | Green Chem., 2009, 11, 466–474
This journal is © The Royal Society of Chemistry 2009

View Article Online
(
2
t, J = 4.8, 2H), 3.61 (t, J = 4.8 Hz, 2H), 3.44 (t, J = 6.8 Hz,
3 (a) P. Dyson, D. Ellis, W. Henderson and G. Laurenczy, Adv. Synth.
Catal., 2003, 345; (b) P. Dyson, G. Laurenczy, C. Andre Ohlin, J.
Vallance and T. Welton, Chem. Commun., 2003, 2418; (c) L. Rossi,
G. Machado, P. Fichtner, S. Teixeira and J. Dupont, Catalysis Letters,
2004, 92(3–4), 149–255; (d) M. Steffan, M. Lucas, A. Brandner, M.
Wollny, N. Oldenburg and P. Claus, Chem. Eng. Technol., 2007, 30,
481; (e) K. Anderson, P. Goodrich, C. Hardacre and D. Rooney,
Green Chemistry, 2003, 5, 448.
H), 1.61 (tq, J = 6.8, 7.2 Hz, 2H), 0.93 (t, J = 7.2 Hz, 3H).
1
3
C NMR (100 MHz, CDCl ) d (ppm) 165.71, 137.92, 123.80,
3
1
5
23.07, 122.00 (q, J = 319 Hz), 73.09, 70.58, 69.89, 68.42, 65.86,
0.02, 36.66, 22.76, 10.47.
-
1
IR (cm ) 3164, 3119, 2966, 2927, 2865, 1751, 1568, 1558,
495, 1452, 1353, 1198, 1135.
1
4
P. Gallezot and D. Richard, Catal. Rev.–Sci. Eng., 1998, 40, 81.
-
+
-].
MS m/z, 271.3 [M-NTf
2
] ; MS: m/z, 280.0 [NTf
2
5 H. Miura, Shokubai, 2007, 49, 232.
6
7
8
X. Cheng, L. Hexing, D. Weilin, W. Jie, R. Yong and Q. Minghua,
Applied Catalysis A: General, 2003, 253, 359.
P. Maki-Arvela, J. Haje, T. Salmi and D. Murzin, Applied Catalysis
A: General, 2005, 292, 1.
U. Singh and M. Vannice, Applied Catalysis A: General, 2001, 213,
1.
3
- Methyl - 1 - ( methoxyethoxyethoxyethoxycarbonylmethyl ) -
imidazolium NTf (10). The title compound was prepared from
-methyl-1-(methoxyethoxyethoxyethoxycarbonylmethyl)imi-
dazolium bromide (2.20 g, 6.00 mmol) and LiNTf (2.01 g,
.00 mmol) according to the general procedure in 93% yield
2
3
2
7
9 (a) A. Muller, J. Bowers, J. Eubanks, C. Geiger, J. Santobianco, 1999,
WO/1999/008989; (b) F. Bennett, A. Ganguly, V. Girijavallabhan,
N. Patel, 1993, EP0533342; (c) P. Jadhav and H.-W. Man, Tetrahedron
Lett., 1996, 37, 1153.
(
3.17 g, 5.60 mmol).
1
H NMR (400 MHz, CDCl
3
) d (ppm) 8.78 (s, 1H), 7.37 (t, J =
1
4
6
.6 Hz, 1H), 7.26 (t, J = 1.6 Hz, 1H), 4.99 (s, 2H), 4.31 (t, J =
10 P. Kluson and L. Cerveny, Applied Catalysis A: General, 1995, 128,
1
3.
.6 Hz, 2H), 3.89 (s, 3H), 3.66 (t, J = 4.6 Hz, 2H), 3.57-3.54 (m,
1
1
1 I. Kostas, Journal of Organometallic Chemistry, 2001, 634, 90.
2 K. Nuithitikul and M. Winterbottom, Catalysis Today, 2007, 128,
H), 3.49-3.47 (m, 2H), 3.28 (s, 3H).
1
3
C NMR (100 MHz, CDCl ) d (ppm) 165.78, 137.75, 123.96,
3
7
4.
1
6
23.18, 119.70 (q, J = 319 Hz), 71.79, 70.42, 70.38, 70.32, 68.35,
13 K. Nuithitkul and M. Winterbottom, Chemical Engineering Science,
2
006, 61, 5944.
5.57, 58.82, 49.92, 36.53.
1
4 J. P. Tessonnier, L. Pesant, G. Ehret, M. Ledoux and C. Pham-Huu,
-
1
IR (cm ) 3161, 3116, 2925, 2859, 1751, 1569, 1558, 1539,
495, 1452, 1354, 1198, 1135.
MS m/z, 287.2 [M-NTf
Applied Catalysis A: General, 2005, 288, 203.
1
15 C. Pham-Huu, N. Keller, L. Charbonniere, R. Ziessel and M. Ledoux,
-
+
-].
Chem. Commun., 2000, 1871.
2
] ; MS: m/z, 280.0 [NTf
2
1
6 M. Bhor, A. Panda, S. Jagtap and B. Bhanage, Catal. Lett., 2008,
1
24, 157.
Representative method for the preparation of OctOSO
salts (3-Methyl-1-(propoxyethoxycarbonylmethyl)imidazolium
OctOSO ) (4). To a solution of 3-Methyl-1-(propoxyethoxy-
carbonylmethyl)imidazolium bromide (3.68 g, 12.0 mmol) in
distilled water (20 mL) was added in one portion sodium octyl
sulfate (2.09 g, 9.00 mmol) and stirred at 60 C for 2 h. The
water was then slowly removed under vacuum. The precipitate
was dissolved in DCM (5 mL) and washed with distilled water
3
1
1
7 T. Mallet and A. Baiker, Applied Catalysis A: General, 2000, 200, 3.
8 R. Schlogl, Surface composition and structure of active carbon, in:
F. Schuth, K. S. W. Sing and J. Weitkamp, (Eds.), Handbook of Porous
Solids, Wiley-VCH, 2002, 1863.
3
1
2
2
9 C. Pham-Huu, N. Keller, G. Ehret and M. Ledoux, J. Cataly., 2001,
2
00, 400.
◦
0 N. Gathergood and P. J. Scammells, Aust. J. Chem., 2002, 55,
557.
1 (a) N. Gathergood, M. T. Garcia and P. J. Scammells, Green
Chemistry, 2004, 6, 166; (b) M. T. Garcia, N. Gathergood and
P. J. Scammells, Green Chemistry, 2004, 7, 9; (c) N. Gathergood,
P. J. Scammells and M. T. Garcia, Green Chemistry, 2006, 8,
156.
(
2 ¥ 3 mL). The product remaining was dried on the rotary
evaporator and then under high vacuum for 8 h to give a pale
yellow grease in 85% yield (3.33 g, 7.62 mmol).
1
22 S. Bouquillon, T. Courant, D. Dean, N. Gathergood, S. Morrissey,
H NMR (400 MHz, CDCl
3
) d (ppm) 9.45 (s, 1H), 7.48 (t, J =
B. Pegot, P. J. Scammells and R. Singer, Aust. J. Chem., 2007, 60,
1
4
6
.6 Hz, 1H), 7.41 (t, J = 1.6 Hz, 1H), 5.25 (s, 2H), 4.36 (t, J =
.7 Hz, 2H), 4.01 (m, 5H), 3.67 (t, J = 4.7 Hz, 2H), 3.43 (t, J =
.8 Hz, 2H), 1.63-1.58 (m, 4H), 1.56-1.29 (m, 10H), 0.92-0.86
8
43.
23 (a) F. Benvenuti, C. Carlini, M. Marchionna, A. M. Galletti and
G. Sbrana, Journal of Molecular Catalysis A, 1999, 145, 221;
(
b) Y. Kume, K. Qiao, D. Tomida and C. Yokoyama, Catalysis
(
m, 6H).
Communications, 2008, 9, 369; (c) Y. Kanazawa and H. Nishiyama,
Synlett, 2006, 19, 3343; (d) F. Lopez-Linares, G. Agrifoglio, A.
Labrador and A. Karam, Journal of Molecular Catalysis A, 2004,
1
3
C NMR (100 MHz, CDCl ) d (ppm) 166.45, 138.89, 123.71,
3
1
23.06, 73.04, 67.92, 67.89, 65.67, 49.91, 36.58, 31.83, 29.50,
9.36, 29.26, 25.87, 22.73, 22.66, 14.13, 10.47.
IR (cm ) 3118, 2958, 2927, 2855, 1750, 1569, 1558, 1539,
495, 1455, 1217, 1178, 1108.
MS m/z, 227.1 [M-OctSO
2
07, 115; (e) Y. Zhang, S. Liao, Y. Xu and D. Yu, Applied Catalysis
2
A, 2000, 192, 247.
-
1
2
4 K. Nuithitikul and M. Winterbottom, Chem. Eng. Sci., 2004, 59,
1
5439.
-
+
-].
4
] ; MS: m/z, 209.0 [OctSO
4
25 J. Hajek, N. Kumar, P. Maki-Arvela, T. Salmi and D. Murzin, Journal
of Molecular Catalysis A: Chemical, 2004, 217, 145.
2
2
6 J. Qui, H. Zhang, X. Wang, H. Han, C. Liang and C. Li, React. Kinet.
Catal. Lett., 2006, 88, 269.
7 P. Jessop, R. Stanley, R. Brown, C. Eckert, C. Liotta and T. P. Ngo,
Pollet, Green. Chem., 2003, 5, 123.
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74 | Green Chem., 2009, 11, 466–474
This journal is © The Royal Society of Chemistry 2009