Synthesis of a novel ionic liquid with both Lewis and Br?nsted acid sites and its catalytic activities

Article abstract of DOI:10.1016/j.catcom.2011.01.018

The novel ionic liquid with both Lewis and Br?nsted acid sites has been synthesized and its catalytic activities for acetalization and Michael addition were investigated carefully. The novel ionic liquid was stable to water and could be used in aqueous solution. Furthermore, the molar ratio of the Lewis and Br?nsted acid sites could be adjusted according to different reactions. The results showed that the novel ionic liquid was very efficient for the traditional acid-catalyzed reactions with good to excellent yields in short time.

Full text of DOI:10.1016/j.catcom.2011.01.018

Catalysis Communications 12 (2011) 808–812
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Synthesis of a novel ionic liquid with both Lewis and Brønsted acid sites and its
catalytic activities
⁎
Xuezheng Liang, Chenze Qi
Institute of Applied Chemistry, Shaoxing University, Shaoxing, 312000, China
a r t i c l e i n f o
a b s t r a c t
Article history:
The novel ionic liquid with both Lewis and Brønsted acid sites has been synthesized and its catalytic activities
for acetalization and Michael addition were investigated carefully. The novel ionic liquid was stable to water
and could be used in aqueous solution. Furthermore, the molar ratio of the Lewis and Brønsted acid sites could
be adjusted according to different reactions. The results showed that the novel ionic liquid was very efficient
for the traditional acid-catalyzed reactions with good to excellent yields in short time.
© 2011 Elsevier B.V. All rights reserved.
Received 21 December 2010
Received in revised form 18 January 2011
Accepted 21 January 2011
Available online 31 January 2011
Keywords:
Lewis and Brønsted acid functionalized ionic
liquid
Acetalization
Michael addition
1. Introduction
(Scheme 1). The catalytic activities of the novel ionic liquid for
acetalization and Michael addition were investigated. The results
Acid-catalyzed reactions were very important in chemical indus-
tries for the production of various chemicals [1]. Chloride and sulfonic
alkyl groups functionalized ionic liquids were both reported as the
environmental-friendly acid catalysts due to the combination of the
advantages of liquid acids and solid acids, e.g. uniform acid sites, easy
separation and reusability [2]. Chloride ionic liquids were found to be
very efficient for alkylation, but they were very sensitive to water and
could be used only under anhydrous condition [3]. Cole et al. reported
the functional ionic liquid (FIL) with strong Brønsted acidity in 2002
[4]. After that, the research and application of various ―SO3H
functionalized ionic liquids have received more and more attention
[5–16]. As we all know, both Lewis and Brønsted acid sites were
important for acid-catalyzed reactions and the ionic liquid functio-
nalized with both Lewis and Brønsted acid sites would become more
efficient, which combined the advantages of Lewis and Brønsted acid
sites. However, the water-sensitivity of chloride ionic liquid limited its
application in aqueous conditions. Here we present a novel ionic
liquid with both Lewis and Brønsted acid sites. In order to avoid
drawbacks of chloride ionic liquid, Cu2+ ion was used as Lewis acid
site. The novel ionic liquid was synthesized through three steps. In the
first step, zwitterion was obtained through the condensation of
isoquinoline and 1,4-butane sulfonate. Then, equimolar sulfuric acid
and zwitterion were mixed together to form the homogeneous liquid
phase. Some H+ ions were substituted by Cu2+ in the third step
showed that the ionic liquid was very efficient for the traditional acid-
catalyzed reactions with the average yields over 90%.
2. Experimental
All organic reagents were commercial products of the highest purity
available (N98%) and were used for the reactions without further
purification. Cyclohexanone, isoquinoline, 1,4-butane sulfonate, buta-
none, 1,2-propylene glycol, neopentyl glycol, n-butyraldehyde, 4-
methoxybenzaldehyde, 2-methylbenzaldehyde, 4-nitrobenzaldehyde,
acetophenone, 4-bromoacetophenone, cyclohexamine, acrylonitrile,
butyl acrylate, methyl acrylate, methylamine, morpholine and benzal-
dehyde were purchased from Shanghai Chemicals Co.
2.1. Synthesis of the novel ionic liquid
The procedure for the novel IL: isoquinoline (12.9 g, 0.1 mol) and
1,4-butane sulfonate (13.6 g, 0.1 mol) were mixed and stirred magnet-
ically for 72 h at room temperature. Then, thewhite solid zwitterion was
formed. The zwitterion was filtrated and washed repeatedly with ether.
After dried in vacuum (110 °C, 1.33 Pa), the zwitterion was obtained in
good yield (94%). A stoichiometric amount of sulfuric acid was added to
the zwitterion and the mixture was stirred for 4 h at 60 °C to form the
homogeneous liquid phase. Then, CuO (3.97 g, 0.05 mol) and 10 ml
water were added to the liquid phase and the mixture was stirred until
the solid was dissolved completely. Then, the water was removed by
distillation and dried in vacuum (110 °C, 1.33 Pa). The product was
formed quantitatively and in high purity. 1H NMR for the zwitterion
⁎
Corresponding author. Tel./fax: +86 575 88345681.
E-mail address: qichenze@usx.edu.cn (C. Qi).
1566-7367/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2011.01.018

X. Liang, C. Qi / Catalysis Communications 12 (2011) 808–812
809
Scheme 1. The synthesis route of the novel ionic liquid.
(400 MHz, D2O, TMS): δ 1.75 (m, 2H), 2.17 (m, 2H), 2.90 (t, JH–H
=
anticipated, all carbonyl compounds were successfully transformed to
the corresponding products. The results in Table 1 clearly demon-
strated that the novel ionic liquid was very efficient, with high yields
for most reactions. Aliphatic aldehydes transformed to the
corresponding acetals smoothly under the reaction conditions
(entries 1–5). The ketalization reactions were also examined under
the same condition. Cyclohexanone worked well with almost
complete conversion and selectivity for less steric hindrance of the
carbonyl group (entries 6–8). The linear ketones such as butanone
owned relatively low activity for the reactions with moderate yields
(entries 9–10). Aromatic aldehyde, such as benzaldehyde could also
be acetalized to afford the corresponding 1,3-acetals with high yields
(entries 11–13). The groups attached to aromatic ring were also very
important for the reactivities. Aromatic aldehydes with electron-
donating groups such as methyl or methoxyl groups showed
relatively low activity, which reduced the reactivity of the carbonyl
groups (entries 14–19). On the other hand, electron-withdrawing
groups enhanced the nucleophilicity and the aromatic aldehydes with
F and nitro groups showed higher activities (entries 20–23). Different
diols such as 1,2-ethanediol, 1,2-propylene glycol and neopentyl
glycol were all transformed to products smoothly. The reactivities
reduced as follows: 1,2-ethanediolN1,2-propylene glycolNneopentyl
glycol for the steric hindrance of the diols.
7.2 Hz, 2H), 4.67 (d, 2H), 7.91 (t, 1H), 8.10 (q, 2H), 8.29 (t, 2H), 8.41 (d,
1H), 9.60 (s, 1H). IR(KBr): 1037 cm−1 and 907 cm−1 (―SO3H),
1166 cm−1 (C―N), and 3409 cm−1 (O–H).
2.2. Acetalization of carbonyl compounds
Acetals were synthesized via the acetalization of carbonyl com-
pounds with diols. In the typical procedure (Scheme 2): carbonyl
compounds (0.1 mol), 10 mL cyclohexane, diols (0.15 mol) and the
catalyst (0.05 g, 0.138 mmol) were mixed together in a three necked
round bottomed flask equipped with a magnetic stirrer and thermom-
eter. Here a Dean–Stark apparatus was used to remove the water
continuously from the reaction mixture. The mixture was refluxed for
the specified time. The progress of the reaction was monitored by GC
analysis of the small aliquots withdrawn. On completion, the catalyst
was recovered by centrifugation, washing with acetone and drying in an
oven at 80 °C for about 1 h.
2.3. Conjugate addition of amines to electron deficient alkenes
Typical procedure for the conjugate addition of amines (Scheme 3)
was shown as follows: A mixture of amine (20 mmol), alkene
(24 mmol) and the catalyst (0.05 g, 0.138 mmol) were stirred at room
temperature for certain time as shown in Table 2. The process of the
reaction was monitored by GC analysis. The reaction mixture was
extracted with ethyl acetate (2×20 ml) and the combined extract was
dried over anhydrous Na2SO4 and evaporated to leave a crude product,
which was separated by column chromatography using neutral alumina
as stationary phase and petroleum ether/ethyl acetate mixture (95: 5)
as eluent to give the corresponding product.
Selected NMR data for the compounds in Table 1
Entry 2 1H NMR (400 MHz, CDCl3, TMS): δ 1.23 (d, 3H), 3.61 (d,
2H), 3.81 (d, 2H), 4.08 (m, 1H), 5.20 (t, JH–H =7.2 Hz, 1H). 13C NMR
(400 MHz, CDCl3, TMS): 18.8, 50.7, 74.6, 75.8, 111.5.
Entry 5 1H NMR (400 MHz, CDCl3, TMS): δ 0.95 (t, JH–H =7.2 Hz,
3H), 1.12 (s, 6H), 1.64 (m, 2H), 3.68 (s, 4H), 4.68 (t, JH–H =7.3 Hz,
1H). 13C NMR (400 MHz, CDCl3, TMS): 4.8, 20.7, 29.6, 31.8, 77.9,
105.5.
Entry 8 1H NMR (400 MHz, CDCl3, TMS): δ 1.11 (s, 6H), 1.44(t, JH–H
=
3. Results and discussions
7.2 Hz, 4H), 3.72 (s, 4H). 13C NMR (400 MHz, CDCl3, TMS): 16.2, 20.1,
29.0, 32.1, 35.6, 75.4.
3.1. Acetalization of carbonyl compounds
Entry 9 1H NMR (400 MHz, CDCl3, TMS): δ 0.97 (t, JH–H=7.2 Hz, 3H),
1.22 (d, 3H), 1.46 (s, 3H), 3.74 (d, 2H), 4.08 (m, 1H). 13C NMR
(400 MHz, CDCl3, TMS): 2.3, 19.2, 23.6, 31.8, 72.3, 74.1, 109.5.
The acetalization of various carbonyl compounds and diols
catalyzed by the novel ionic liquid was performed first (Table 1). As
Scheme 2. Catalytic acetalization of carbonyl compounds.
Scheme 3. Conjugate addition of amines to electron deficient alkenes.

810
X. Liang, C. Qi / Catalysis Communications 12 (2011) 808–812
Table 2
Table 1
The conjugate additions of various amines with alkenes.
Preparation of various acetals from the corresponding carbonyl compounds.
Entry
Amines
Alkenes
Reaction time/min Yield, % a, b
Entry
Substrate
Product
Reaction Yield/% a, b
time/h
1
2
2
2
99
99
1
2
0.5
0.5
99
99
3
4
5
99
95
10
3
4
1.0
1.0
99
99
5
6
5
8
99
98
7
15
94
5
1.5
98
8
9
4
7
99
98
6
7
1.0
1.0
99
99
10
19
92
aThe reaction conditions: amine 20 mmol, alkenes 24 mmol, ionic liquid (0.05 g,
0.138 mmol), R.T. (25 °C).
8
9
2.0
2.0
98
92
bThe yield was estimated by GC analysis.
10
3.5
90
11
12
2.0
2.0
95
93
13
3.5
92
14
15
3.0
4.0
92
88
16
17
18
19
3.5
2.5
3.0
3.5
90
92
91
89
Fig. 1. The reuse of the novel ionic liquid.
Entry 11 1H NMR (400 MHz, CDCl3, TMS): δ 3.85 (s, 4H), 6.18 (s, 1H),
7.21 (m, 5H). 13C NMR (400 MHz, CDCl3, TMS): 66.2, 109.1, 127.6,
128.4, 129.6, 137.3.
Entry 14 1H NMR (400 MHz, CDCl3, TMS): δ 3.71 (s, 3H), 3.84 (s, 4H),
6.18 (s, 1H), 6.68 (d, 2H), 7.08 (d, 2H). 13C NMR (400 MHz, CDCl3,
TMS): 55.9, 66.7, 109.6, 114.8, 128.5, 129.7, 159.8.
20
21
1.0
2.0
98
95
Entry 19 1H NMR (400 MHz, CDCl3, TMS): δ 1.12 (s, 6H), 2.35 (s, 3H),
3.77 (s, 4H), 5.98 (s, 1H), 6.94 (d, 2H), 7.07 (d, 2H). 13C NMR
Notes to Table 1
22
23
1.5
2.0
95
93
a
All reactions were carried out under Dean–Stark conditions: ionic liquid (0.05 g,
0.138 mmol), diols (0.15 mol), carbonyl compound (0.1 mol) and cyclohexane (10 ml),
refluxed.
b
The yield was taken by GC according to carbonyl compounds. In all cases, the
corresponding products were exclusively obtained.

X. Liang, C. Qi / Catalysis Communications 12 (2011) 808–812
811
Scheme 4. The chemoselectivity of the novel ionic liquid.
Table 3
slightly dropped with the increasing carbon atomicity of the amines for
the steric hindrance (entries 1–4, 5–7, 8–10). The primary amines
underwent the single substitution reaction under the reaction condi-
tion. These results indicated the usefulness of the novel catalyst for the
reactions and the reaction conditions were mild and not sufficient
enough to cause double substitution reaction. The multi-substitution
reactions could also be activated when more alkenes and high
temperature applied, then the double substituted products were
obtained with high yields. As to the alkenes, the reactivity was affected
by the electron withdrawing groups (EWG) and the steric hindrance
also had the certain effect on the reactions. Furthermore, the novel ionic
liquid was stable in aqueous condition such as methylamine aqueous
solution and could be reused after the reaction without loss of activity.
Selected NMR data for the compounds in Table 2
The effect of the Cu2+ content on the catalytic activities.
Entry Cu2+ content/%c Catalyst amount/mmol Reaction time/h Yield/%a,b
1
2
3
4
5
0
25
0.14
0.14
0.14
0.14
0.14
2.0
2.0
2.0
2.0
2.0
86
90
95
91
85
50
75
100
a
All reactions were taken at R.T. (25 °C) conditions: benzaldehyde: 10 mmol; 1,2-
ethanediol: 15 mmol.
b
GC yields.
c
Cu2+ content was measured as follows: n(Cu2+)/[n(Cu2+)+n(H+)]⁎100%.
(400 MHz, CDCl3, TMS): 19.8, 24.7, 31.6, 77.8, 104.9, 127.5, 129.0,
134.3, 137.5.
Entry 1 1H NMR (400 MHz, CDCl3, TMS): δ 2.01 (m, 1H), 2.35 (t, JH–H
=
7.2 Hz, 2H), 2.47 (m, 3H), 5.98 (s, 1H), 2.94 (m, 2H), 3.67 (s, 3H). 13C
NMR (400 MHz, CDCl3, TMS): 34.4, 35.7, 51.6, 53.8, 174.1.
Entry 6 1H NMR (400 MHz, CDCl3, TMS): δ 0.96 (t, JH–H =7.2 Hz,
3H), 1.35 (m, 2H), 1.57 (m, 2H), 2.37 (m, 6H), 2.74 (m, 2H), 3.67
(t, JH–H =7.3 Hz, 4H), 4.07 (t, JH–H =7.2 Hz, 2H). 13C NMR
(400 MHz, CDCl3, TMS): 14.1, 19.0, 31.2, 33.8, 50.3, 53.4, 65.0,
66.8, 174.1.
Entry 21 1H NMR (400 MHz, CDCl3, TMS): δ 1.11 (s, 6H), 3.77 (s, 4H),
5.99 (s, 1H), 6.65 (m, 2H), 7.15 (d, 1H). 13C NMR (400 MHz, CDCl3,
TMS): 19.9, 31.7, 77.6, 93.5, 104.6, 111.0, 119.8, 130.3, 161.5, 163.7.
Entry 22 1H NMR (400 MHz, CDCl3, TMS): δ 3.91 (s, 4H), 6.19 (s, 1H),
7.45 (d, 2H), 8.12 (d, 2H). 13C NMR (400 MHz, CDCl3, TMS): 66.3,
109.7, 121.0, 128.5, 143.6, 147.5.
Entry 10 1H NMR (400 MHz, CDCl3, TMS): δ 1.43 (m, 6H), 2.01 (m,
1H), 2.57 (m, 1H), 2.36 (m, 6H), 3.61 (m, 2H). 13C NMR (400 MHz,
CDCl3, TMS): 23.4, 28.7, 33.6, 35.5, 55.3, 114.9.
3.2. Catalytic procedure for the conjugate addition
Besides acetalization, the conjugate additions of various amines with
alkenes under solvent-free condition were also investigated (Table 2).
The results showed that the reactions underwent smoothly at room
temperature just within several minutes. The methylamine showed
extremely high activity for all electron deficient alkenes with almost
complete conversion within 5 min (entries 1, 6, and 11). The yields
3.3. The reuse of the catalyst
One property of ionic liquid is the reusability. The recovery of the
catalyst was very convenient. After reactions, the reaction mixture
Scheme 5. The probable catalytic procedure of the novel ionic liquid.

812
X. Liang, C. Qi / Catalysis Communications 12 (2011) 808–812
Table 4
3.6. The comparative study on the catalytic activities of the
different catalysts
The comparison of different catalyst.
Entry Catalyst
Catalyst amount/mmol Reaction time/h Yield/%a,b
A comparative study on the catalytic activities of the novel ionic
liquid with traditional catalysts was carried out using benzaldehyde
and 1,2-ethanediol (Table 4). From this study, it can be concluded that
the novel ionic liquid owned the comparative activity to the
homogeneous catalysts, furthermore it added the advantage of
reusability. It clearly showed that the novel catalyst should be
considered as one of the best choice for the economically convenient,
user-friendly catalyst and for the scaling up purpose.
1
2
3
4
5
6
Novel ionic liquid 0.14
2.0
2.0
2.0
2.0
2.0
2.0
95
91
88
80
89
75
H2SO4
PTSA
BF3–OEt2
0.14
0.14
0.14
[imibSO3H][HSO4] 0.14
ZnCl2 0.14
a
All reactions were taken at R.T. (25 °C) conditions: benzaldehyde: 10 mmol; 1,2-
ethanediol: 15 mmol.
b
GC yields.
4. Conclusion
was extracted with ethyl acetate–ethyl ether=1:1 and the lower
phase, the ionic liquid, could be reused easily. The recovered activities
were investigated through the reaction of benzaldehyde and 1,2-
ethanediol carefully (Fig. 1). The yields remained unchanged even
after the catalyst had been recycled for five times.
The novel ionic liquid with both Lewis and Brønsted acid sites has
been synthesized and its catalytic activities were investigated through
theacetalization and Michael additioncarefully. The results showed that
the novel ionic liquid was very efficient for the traditional acid-catalyzed
reactions and the Lewis and Brønsted acid sites cooperated during the
catalytic process. Operational simplicity, water-tolerance, low cost of
the catalyst used, high yields, and applicability to large-scale reactions
are the key features of this methodology. The cooperation of the Lewis
and Brønsted acid sites during the catalytic procedure made the catalyst
hold great potential to replace the tradition homogeneous acid catalysts
for the environmental-friendly processes.
3.4. The chemoselectivity of the novel ionic liquid
It was noteworthy that aromatic amines could not be transformed
to the corresponding products under the same conditions (Scheme 4).
This result indicated that the present protocol could be applicable to
the chemoselective addition of aliphatic amines in the presence of
aromatic amines.
3.5. The Cu2+ content on the catalytic activities of the novel ionic liquid
Acknowledgement
In order to investigate the effect of Cu2+ on the catalytic activities,
ionic liquids with different Cu2+ content were utilized as the catalysts
for the reaction of benzaldehyde and 1,2-ethanediol (Table 3). It could
be seen from Table 3 that both Cu2+ and H+ were important for the
reaction. Low catalytic activities were obtained when the ionic liquids
with single acid site used (entries 1 and 5). The peak value achieved
when the Cu2+ content was 50% with the Lewis to Brønsted acid sites
molar ratio of 1:1 (entry 3). These results indicated that the two acid
sites cooperated with each other during the catalytic process and led
to the higher activities than the single acid site. Here the probable
catalytic procedure was demonstrated in Scheme 5. In the first step,
Cu2+ ion with two positive charges owned strong attraction to
negative charges and cooperated with carbonyl group and diols,
which made the oxygen atoms in hydroxyl groups collide with the
carbon atoms in carbonyl groups in the right direction. Then, the H+
attached to the oxygen atom in carbonyl group, which reduced the
negative charge greatly and caused the release of the Cu2+. Both acid
sites functioned during the catalytic procedure and equimolar Lewis
and Brønsted acid sites cooperated during the catalytic cycle, which
made the novel ionic liquid more efficient for the reactions with the
optimal molar ratio of 1:1.
This work was supported by the Zhejiang Provincial Natural
Science Foundation No. Y4100658 and the Zhejiang Science and
Technology projects (2010C31G2180006).
References
[1] D. Kuang, S. Uchida, R. Humphry-Baker, S.M. Zakeeruddin, M. Graetzel, Angew.
Chem. Int. Ed. 47 (2008) 1923.
[2] N.S. Gupta, G.L. Kad, J. Singh, Catal. Commun. 8 (2007) 1323.
[3] T. Singh, A. Kumar, J. Phys. Chem. B 112 (2008) 4079.
[4] A.C. Cole, J.L. Jensen, I. Ntai, K.L.T. Tran, K.J. Weaver, D.C. Forbes, J.H. Davis, J. Am.
Chem. Soc. 124 (2002) 5962.
[5] R. Sugimura, K. Qiao, D. Tomida, C. Yokoyama, Catal. Commun. 8 (2007) 770.
[6] B.A. Da Silveira Neto, G. Ebeling, R.S. Goncalves, F.C. Gozzo, M.N. Eberlin, J. Dupont,
Synthesis (2004) 1155.
[7] Y. Gu, F. Shi, Y. Deng, Catal. Commun. 4 (2003) 597.
[8] A. Kamal, G. Chouhan, Adv. Synth. Catal. 346 (2004) 579.
[9] J. Yang, H. Zhou, X. Lu, Y. Yuan, Catal. Commun. 11 (2010) 1200.
[10] A. Kamal, G. Chouhan, Tetrahedron Lett. 44 (2003) 3337.
[11] H. Firouzabadi, N. Iranpoor, A.A. Jafari, M.R. Jafari, J. Mol. Catal. A Chem. 247 (2006) 14.
[12] A.S. Amarasekara, O.S. Owereh, Catal. Commun. 11 (2010) 1072.
[13] H.H. Wu, F. Yang, P. Cui, J. Tang, M.Y. He, Tetrahedron Lett. 45 (2004) 4963.
[14] X. Liu, M. Liu, X. Guo, J. Zhou, Catal. Commun. 9 (2008) 1.
[15] J.S. Yadav, B.V.S. Reddy, G. Kondaji, Chem. Lett. 32 (2003) 672.
[16] Y. Gu, F. Shi, Y. Deng, Catal. Commun. 4 (2003) 597.