Basic polymerized imidazolide-based ionic liquid: An efficient catalyst for aqueous Knoevenagel condensation

Article abstract of DOI:10.1039/c5ra01700a

A novel basic polymerized ionic liquid (BPIL): polymeric 1-[(4-ethenylphenyl)methyl]-3-propylimidazolium imidazolide was synthesized and characterized by Fourier transform infrared (FT-IR), nuclear magnetic resonance (NMR) and electron spray ionization ma

Full text of DOI:10.1039/c5ra01700a

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: L. Ding, H. Li, Y.
Zhang, K. Zhang, H. Yuan, Q. Wu, Y. Zhao, Q. Jiao and D. Shi, RSC Adv., 2015, DOI:
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

RSC Advances
Page 1 of 7RSC Advances
View Article Online
DOI: 10.1039/C5RA01700A
Cite this: DOI: 10.1039/c0xx00000x
www.rsc.org/catalysis
Paper
Basic polymerized imidazolide-based ionic liquid: An efficient catalyst for
aqueous Knoevenagel condensation
Libing Ding,a Hansheng Li,a Yaping Zhang,a Kun Zhang,a Hong Yuan, Qin Wu, ∗a Yun Zhao,a
Qingze Jiaoa,b and Daxin Shi∗a
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
A
novel basic polymerized ionic liquid (BPIL): polymeric 1ꢀ[(4ꢀethenylphenyl)methyl]ꢀ3ꢀ
propylimidazolium imidazolide was synthesized and characterized by fourier transform infrared (FTꢀIR),
nuclear magnetic resonance (NMR) and electron spray ionization mass spectrometry (ESIꢀMS). The BPIL
10 was used as an efficient catalyst for aqueous Knoevenagel condensations with extended substrates. In
comparison with common base catalyst, the BPIL showed high catalytic activity, which was ascribed to
the cooperation between the strong basicity and high surface activity. Moreover, the BPIL with high
molecular weight have high surface activity and low catalytic activity. In addition, the BPIL was easily
recovered and maintain high catalytic activity after five cycles of use in the system using benzaldehyde
15 and malononitrile as substrates.
made to perform the Knoevenagel condensation in aqueous media,
which is usually catalyzed by Lewis acids[ 16 ] or bases, and
requires drastic conditions[17]. Some reactions are performed on
50 solid supports, promoted by infrared, ultrasound or
Introduction
The Knoevenagel condensation is one of the most powerful
strategies for carbonꢀcarbon bond formation in organic
chemistry[1], and its products have numerous applications in the
20 synthesis of fine chemical, as well as carbocyclic and
heterocyclic compounds of biological significance[ 2 , 3 ].This
reaction is generally carried out between a carbonyl group and
active methylene compounds in organic solvents in the presence
of bases, mainly including piperidine[4], pyridine[5], ammonia,
microwave[18,19]
.
A possible way to improve the solubility of substrates is the
use of surfaceꢀactive agents that can form micelles in aqueous
media[ 20 ]. Micelles can improve the solubility of substrates
55 through solubilization[ 21 ]. The solubilization of reactants and
products inside the micelles not only results in high concentration
within the small volume, but the different orientations of the
solubilization may also significantly influence the reaction
mechanism, resulting in much different reaction rates[15,20]. The
60 use of micelle is widespread and has been investigated in detail
for different reactions in aqueous solution[20]. However, it has not
been reported in Knoevenagel condensations.
6
]
25 amines[
or sodium ethoxide. Recently, some novel
heterogeneous catalysts, such as NiꢀSiO2ꢀsupported catalysts[7]
,
nitrogenꢀdoped carbon materials[ 8 ], have been exploited as
catalysts for the Knoevenagel condensation. However, many of
these procedures have some or one of the disadvantages, such as
30 a large amount of catalysts and organic solvent, a long reaction
time, harsh reaction conditions, cumbersome purification process,
no catalyst recovery[ 9 ].In addition, the utilization of volatile,
hazardous, carcinogenic or costly solvents, especially, ethanol
and toluene, has limited the wide application of the reaction in
Longꢀchained ionic liquids have been extensively studied in
the field of colloid and interface science because of the close
65 resemblance of the alkyls in these ionic liquids’ molecules to the
long hydrocarbon chains of conventional surfactant molecules[22]
.
Polymerized ionic liquids (PILs) are synthesized by introducing
polymerizable group into ionic liquids[23 ], which prossess the
unique properties of ionic liquids and macromolecular
70 architecture, such as negligible vapour pressure, good stability,
easily shaping and variety of available structures[ 24 ].PILs are
special ionic liquids. The micelles form in aqueous solutions and
are good surfactant and novel catalysts. Aqueous solution of PILs
with basicity and surface activity is a potential efficient, green,
75 recoverable and lowꢀcost catalytic system. However, it has not
been reported in Knoevenagel condensations.
35 industrial processes [10]
.
With the increasing public concern over environmental
degration, the use of aqueous Knoevenagel condensations
represents very powerful greenchemical technology procedures
from both the economical and synthetic point of view[ 11 ]. In
40 comparison with organic solvent, water is a desirable solvent for
the reasons of cost, nontoxic, nonflammable, cheap and
available[12]. In addition, reactions in aqueous media illustrate
unique reactivity and selectivity that are not usually observed in
organic media[13,14]. However, the major drawback of aqueous
45 media is the limited solubility of various organic compounds in
water to reducing reaction interface area[15]. Efforts have been
In this work, we carried out Knoevenagel condensation
catalyzed by a novel basic polymerized ionic liquid (BPIL):
This journal is © The Royal Society of Chemistry [year]
[journal], [year], [vol], 00–00 | 1

RSC Advances
Page 2 of 7
View Article Online
DOI: 10.1039/C5RA01700A
Methods
polymeric
1ꢀ[(4ꢀethenylphenyl)methyl]ꢀ3ꢀpropylimidazolium
imidazolide. The procedure was environmentally friendly and
efficient, and the BPIL possessed high catalytic activity and could
be easily separated.
The structures of the ionic liquid polymer and its intermediates
were analyzed by IR spectroscopy, NMR and electron spray
ionization mass spectrometry (ESIꢀMS). IR spectra was recorded
55 on a PerkinꢀElmer Spectrum One FTꢀIR spectrometer using KBr
windows suitable for Fourier transform infrared (FTꢀIR)
5
Experimental Section
1
transmittance technology to form a liquid film. H NMR spectra
Materials
was obtained on a Varian Mercuryꢀplus 400 nuclear magnetic
resonance spectrometer. Molecular weight was recorded on a
60 Varian 600MS ESIꢀMS with a flow rate of the flow phase (water:
methanol =2:3) for 200 ꢁL/min, capillary voltage of 80.0 volts,
pinpoint voltage of 5000volts and ꢀ5000volts respectively under
the positive and negative mode and the quality scanning range
from 50 to 500 M/Z. The component contents of mixture after
65 Knoevenagel condensation was analysized by Liquid
Chromatogram (LC) with a flow rate of the mobile phase
(methanol: water = 9:1) for 0.3 mL/s at a wavelength of 256 nm.
1ꢀpropylimidazole was purchased from EnergyꢀChemical. 4ꢀ
chloromethylstyrene was obtained from Tokyo Kasei Kogyo Co.,
Ltd. Imidazole was purchased from Linhai Kaile Chemical
10 Factory. 2,2ꢀazobisisobutyronitrile (AIBN) was obtained from
Sinopharm Chemical Reagent Beijing Co., Ltd. Sodium
hydroxide, methanol, ethanol, ethyl ether (Et2O), ethyl acetate
(EtOAc) and dimethylformamide (DMF) were received from
Beijing Chemical Co., Ltd. All reagents and starting materials
15 were commercially available and used without any further
purification unless, otherwise, noted.
Knoevenagel condensations catalyzed by BPIL
Synthesis of basic polymeric 1-[(4-ethenylphenyl)methyl]-3-
propylimidazolium imidazolide (BPIL)
BPILꢀcatalyzed Knoevenagel condensation of a wide range of
70 aldehydes and ketones with active methylene compounds leading
to the formation of substituted electrophilic alkenes. The typical
process was carried out as follows. 50 mmol benzaldehyde and
50 mmol ethyl cyanocaetate or malonoitrile were charged into a
25 mL roundꢀbottomed flask equipped with a magnetic stirrer,
75 followed by adding aqueous solution containing a certain amount
of BPIL catalyst. The mixture was stirred at room temperature for
150 min. The progress was monitored by LC. After the
completion of the reaction, the reaction mixture was poured into
ice water. The solid product was precipitated and placed for
80 several hours. The product was isolated by direct decantation and
the catalyst was reused after the excessive water was removed.
The reaction process of 4ꢀmethoxybenzaldehyde and ethyl
cyanocaetate or malonoitrile was the same to that of
benzaldehyde and ethyl cyanocaetate.
The synthetic procedure of BPIL was illustrated in Scheme 1.
20 The 1ꢀpropylimidazole was dissolved in methanol and
a
stoichiometric amout of 4ꢀchloromethylstyrene was added and
o
stirred at 60 C for 24 h, resulting in the formation of the 1ꢀ[(4ꢀ
ethenylphenyl)methyl]ꢀ3ꢀpropylimidazolium chlorine [VBPIm]Cl,
which was purified through removing methanol by rotary
25 evaporation and washing with Et2O. [VBPIm]Cl exhibited
excellent solubiliby in high polar solvents such as water,
methanol and ethanol. [VBPIm]Cl monomer, AIBN and DMF
were charged into a 100 ml threeꢀneck flask. The flask, dried at
high temperature, tightly sealed and purged with nitrogen gas,
30 was immersed in an oil bath at 70 oC for 24 h for complete
polymerization. The polymer (PIL) prepared was precipitated
with ethyl acetate (EtOAc) and washed three times with EtOAc
and Et2O to remove solvent. The final product was dried in a
vacuum oven at 55 oC for 24 h to produce a powder.
1.2 equivalents of imidazole, NaOH and deionized water were
added into a threeꢀneck flask, equipped with a condenser tube.
The mixture was stirred at 95 oC for 4 h, resulting in the
formation of sodium imidazole, then PIL methanol solution was
added at room temperature and stirred for 24 h. Methanol was
40 reduced by rotary evaporation and the mixture was washed with
Et2O for three times to remove remaining imidazole. The mixture
was dissolved in DMF and white NaCl was precipitated. The
filtrate was poured into EtOAc, the BPIL was precipitated and
placed in a freezer. The imidazolide anions content of BPIL was
45 determined through hydrochloric acid titration and the exchange
rate was deduced to be only 50%.
85
In the reaction of 4ꢀnitrobenzaldehyde and ethyl cyanocaetate
or malonoitrile, yellow solid containing product and 4ꢀ
nitrobenzaldehyde was precipitated and dissolved in EtOAc after
filtrate. The product was purified though recrystallized from
ethanol.
35
90
When the reaction of 3ꢀmethylbutanone and ethyl cyanocaetate
or malonoitrile was complete, the oily phase was extracted into
EtOAc. After removing EtOAc, the product was obtained.
R
1
CN
R
1
CN
r.t;
BPIL
O
+
+
H O
2
R
2
H O
Z
2
2
R
Z
2
3
1
3a: R = C H ,
R
= H,
Z = COOCH CH
2 3
1
6
5
2
3b: R = (p-OMe)C H ,
R
R
= H,
= H,
= H,
= H,
= H,
Z = COOCH CH
Z = COOCH CH
2 3
Z = CN
Z = CN
Z = CN
1
6
4
2
2
2 3
3c: R = (p-N O)C H ,
1
2
6
4
HC CH2
HC CH2
n
n
3d: R = C H ,
R
1
6
5
2
3e: R = (p-OMe)C H ,
R
R
1
6
4
2
N
NNa
N
N
AIBN
3f: R = (p-N O)C H ,
1
2
6
4
2
Cl
H2
C
CH2
CH2
N
Cl
N
N
Methanol,r.t.,24h
DMF, 70. ,24h
O
Methanol, 60. , 24h
N
N
3g: R ,R
=
Z = COOCH CH
2 3
CH2Cl
1
2
N
N
N
O
[VBPIm]Cl
PIL
BPIL
3h: R ,R
=
Z = CN
1
2
Scheme 1. Synthetic procedure for BPIL
Scheme 2. Knoevenagel condensation of aldehydes and
50
95 ketones with active methylene compounds catalyzed by BPIL
2
| Journal Name, [year], [vol], 00–00
This journal is © The Royal Society of Chemistry [year]

Page 3 of 7
RSC Advances
View Article Online
DOI: 10.1039/C5RA01700A
The products were analyzed by FTꢀIR and 1H NMR
spectroscopy. The IR and 1H NMR spectral data were as follow:
3a: FTꢀIR (KBr, cmꢀ1): 3030, 2223, 1726, 1606, 1573, 1497,
a
b
1
1466, 1445, 1256, 1201, 768. H NMR (400 MHz, DMSOꢀd6): δ
5
= 8.43 (1H, s), 8.06 (2H, d), 7.64 (2H, t), 7.58 (1H, d), 4.34 (2H,
q), 1.31 (3H, t).
3b: FTꢀIR (KBr, cmꢀ1): 3027, 2216, 1716, 1586, 1561, 1514,
1432, 1262, 1090, 838. 1H NMR (400 MHz, DMSOꢀd6): δ = 8.33
(1H, s), 8.10 (2H, d), 7.16 (2H, d), 4.30 (2H, q), 3.88 (3H, s),
c
10 1.29 (3H, t).
3c: FTꢀIR (KBr, cmꢀ1): 3037, 2216, 1721, 1617, 1594, 1514,
1
1471, 1446, 1266, 1091, 860. H NMR (400 MHz, DMSOꢀd6): δ
= 8.73 (1H, s), 8.44 (2H, d), 8.14 (2H, d).
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1)
3d: FTꢀIR (KBr, cmꢀ1): 3032, 2223, 1591, 1568, 1491, 1450,
15 755. 1H NMR (400 MHz, DMSOꢀd6): δ = 8.57 (1H, s), 7.96 (2H,
d), 7.69 (2H, t), 7.63 (1H, d).
Fig. 1 IR spectra of [VBPIm]Cl (a), PIL (b) and BPIL (c)
3e: FTꢀIR (KBr, cmꢀ1):3028, 2225, 1606, 1572, 1513, 1471,
833. 1H NMR (400 MHz, DMSOꢀd6): δ = 8.21 (1H, s), 8.08 (2H,
d), 7.20 (2H, d), 3.89 (3H, s).
1
The BPIL and its intermediates were analyzed by H NMR
50 spectroscopy and ESIꢀMS. The NMR spectral data were as
follows. [VBPIm]Cl: H NMR (400 MHz, DMSOꢀd6): δ = 9.69
1
20
3f: FTꢀIR (KBr, cmꢀ1): 3039, 2230, 1605, 1580, 1521, 1414,
850. 1H NMR (400 MHz, DMSOꢀd6): δ = 8.73 (1H, s), 8.44 (2H,
d), 8.14 (2H, d).
(1H, s), 7.92 (1H, s), 7.89 (1H, s), 7.51 (2H, d), 7.45 (2H, d), 6.73
(1H, m), 5.86 (1H, d), 5.49 (2H, s), 5.28 (1H, d), 4.16 (2H, t),
1.80 (2H, m), 0.83ppm (3H, t). BPIL: 1H NMR (400 MHz,
55 DMSOꢀd6): δ = 10.10ꢀ10.50 (1H, s), 7.85ꢀ8.20 (2H, br), 7.32ꢀ7.44
(4H, br), 5.30ꢀ5.78 (2H, br), 4.13ꢀ4.18 (3H, br), 1.72ꢀ1.76 (4H,
br), 0.75ꢀ0.85ppm (3H, br). The peak of 67 was observed under
the negative ion mode, which also showed the existence of
imidazolide anion.
3g: FTꢀIR (KBr, cmꢀ1): 2987, 2937, 2876, 2265, 1747, 1632,
1
1391, 1378, 1261, 1097. H NMR (400 MHz, DMSOꢀd6): δ =
25 4.45 (2H, q), 3.06 (1H, m), 2.20 (3H, s), 1.12 (3H, t), 1.11 (6H, d).
3h: FTꢀIR (KBr, cmꢀ1): 2977, 2938, 2879, 2231, 1593, 1391,
1
1377. H NMR (400 MHz, DMSOꢀd6): δ = 3.24 (1H, m), 2.19
(3H, s), 1.16 (6H, d).
60
The NMR and ESIꢀMS spectral data of BPIL and its ionic
liquid intermediates agreed with their designed structures
(Scheme 1).
Results and Discussion
30 Characterization of the BPIL and its intermediates
A series of PILs with different molecular weight were prepared
with different amount of AIBN as initiator and molecular weight
The BPIL was characterized and confirmed by IR, NMR and
ESIꢀMS. Fig. 1 showed the IR spectra of BPIL, together with
those of [VBPIm]Cl and PIL. As shown in Fig. 1(a), for the
[VBPIm]Cl, the =CꢀH stretching vibrations was observed at the
35 3130 cmꢀ1 and 3088 cmꢀ1. The bands at 2968 cmꢀ1 and 2877 cmꢀ1
were assigned to the CꢀH vibration. The 1629 cmꢀ1 was assigned
to C=C absorption peak, respectively. The vibration peaks of
imidazole ring were observed at 1560 and 1452 cmꢀ1. As can be
seen from Fig. 1(b), for the PIL, the peak of C=C was
40 disappeared. The formation of PIL was evident from the results
conducted by IR spectra. In addition, a new band at 1663 cmꢀ1
was assigned to C=O stretching vibration in solvent. In
comparison with PIL, BPIL showed obvious enhanced vibration
peaks of imidazole ring, which showed the existence of
45 imidazolide anion.
65 of PIL was measured using Ubbelodhe viscometer. As can be
seen from Fig. 2, its molecular weight desreased sharply firstly,
then reducd slowly and reached equilibrium finally as the amount
of initiator increased.
180
150
120
90
60
30
1
2
3
4
5
6
AIBN addition (%)
70
Fig. 2 Dependence of amount of initiator in the free
radical polymerization
The catalytic application of BPIL in aqueous Knoevenagel
condensations
A preliminary study of the catalytic property of BPIL in the
75 Knoevenagel condensation of benzaldehyde (BE) and ethyl
This journal is © The Royal Society of Chemistry [year]
Journal Name, [year], [vol], 00–00 |
3

RSC Advances
Page 4 of 7
View Article Online
DOI: 10.1039/C5RA01700A
cyanocaetate (EC) was carried out. As can be seen from Fig. 3(a),
35
Table 1. Screening of catalysts for the Knoevenagel
condensation
the product was formed within a few seconds in the presence of
BPILꢀ3% (Amount of AIBN = 3 mol%), and the yield of the
product increased when the reaction time was extended generally.
The reaction had approached equilibrium when the reaction time
was extended to about 150 minutes.
Entry
Catalyst
BPILꢀ3%
NaOH
BIL
Yielda / %
99.2
5
1
2
3
4
5
6
7
44.7
100
a
88.9
80
60
NaOH+CTAB (10 CMC)
NaOH+CTAB (75 CMC)
BPILꢀ2%
73.3
40
20
0
b
89.7
n(BE):n(EC):n(alkaline moieties)=1:1:0.005
V(water):V(row material)=3:1
room temperature
68.8
BPILꢀ1%
60.1
0
30
60
90
120
150
Time(min)
a Yields referred to pure isolated product.
Fig. 3 The relationship between the yield of product
and reaction time
Surface activity was considered as an important factor that
40 affected their catalytic activities. BPIL with a long alkyl chain
processed high surface activity, but NaOH not. Aqueous
Knoevenagel condensation occurred on the tiny liquidꢀliquid
interface between reactants and water due to the insolubility of
reactants in water. When NaOH was used as the catalyst,
45 reactants could not interact with catalytic centers adequately on
the reaction time scale, resulting in low catalytic activity and
yield.
10
Parallel experiments for amount of the catalyst under 150min
were carried out (Fig. 4). The results showed that 0.5 mol%
alkaline moieties had excellent catalytic activity. The target
compound was obtained with 99.2% isolated yield. Catalytic
15 activity cites increased with the increase of catalyst amount, and
reactants could interact with catalytic centers adequately, which
caused higher catalytic activity [25]
.
BPIL with a hydrophobic group showed high surface activity,
so it was also a good newꢀtype surfactant, which reduced the
50 surface tension of aqueous solution and micelles formed in
aqueous medium spontaneously[ 26 ]. To further understand the
superiority of superior surface activity of BPIL, critical micelle
concentration (CMC) value of BPIL was investigated. CMC is of
crucial importance for judging the micelle formation of
55 surfactants. The measurement of electric conductivity was usually
100
80
60
40
20
0
used for determining CMC of aqueous solution of surfactant[25]
.
In this work, electroconductibility of different BPIL
concentration of the aqueous solution were tested at room
temperature (25oC) and results for a typical measurement was
60 shown in Fig. 5. CMC was determined by computing the second
derivative of the local polynomial fit, and the minimum were
0.0
0.1
0.2
0.3
0.4
0.5
Amount of alkaline moieties (mol%)
Fig. 4 Effect of the amount of catalyst on yield
recorded [27]. As can be seen from Fig. 5(a), the CMC of BPILꢀ3%
was deduced to be 178 mg/L. For practical use and application, a
surfactant with low CMC is often considered to play an efficient
65 role in solubilization[ 28 ]. Moreover, the CMC of BPILꢀ1%，
BPILꢀ2% and BIL were deduced to be 33, 90 and 2533 mg/L (Fig.
5(bꢀd)).
20
In order to demonstrate the superiority of BPIL as the catalyst,
the contrast tests were conducted. As shown in the Fig. 3(b),
when NaOH, which was the wellꢀknown strong base, was used as
the catalyst, it presented a low yield of 44.7% in Table 1. In
25 contrast, BPILꢀ3% as the catalyst increased the yield up to 99.2%
easily in a shorter reaction time (Fig. 3(b) and Table 1, entry 1).
Under the same reaction condition, the catalytic activity of NaOH
was obviously lower than that of BPILꢀ3%. Meanwhile, the
catalytic ativity of 1ꢀbenzylꢀ3ꢀpropylꢀimidazolium imidazolide
30 (BIL) with a similar structure to that of the monomer [VBPIm]Cl
was also investigated. The result showed that the catalytic activity
of BIL was lower than that of BPILꢀ3% and the yield of the target
compound was 88.9% yield.
4
| Journal Name, [year], [vol], 00–00
This journal is © The Royal Society of Chemistry [year]

Page 5 of 7
RSC Advances
View Article Online
DOI: 10.1039/C5RA01700A
45 withdrawing groups (such as nitro group) were more reactive
than those with electronꢀdonating groups (such as methoxyl). In
addition, Knoevenagel condensation of aliphatic ketones with
active methylene ingredients also underwent smoothly at room
temperature (Table 2, entries 7ꢀ10).
250
200
150
100
50
0.020
0.015
0.010
0.005
0.000
-0.005
-0.010
-0.015
280
240
200
160
120
80
0.003
0.002
0.001
0.000
-0.001
-0.002
-0.003
Local polynomial
Second derivative
Local polynomial fit
Second derivative
50
Table 2. Results of Knoevenagel condensation between various
aromatic aldehydes/aliphatic ketones and
100
150
200
250
300
350
50
100
150
200
250
300
350
C (mg/L)
C (mg/L)
a
b
30
25
20
15
10
5
0.04
0.03
0.02
0.01
0.00
-0.01
-0.02
0.0000003
0.0000002
0.0000001
0.0000000
-0.0000001
active methylene compounds
80
60
40
20
0
Local polynomial fit
Second derivative
Local polynomial fit
Second derivative
R1
CN
R1
CN
r.t;
BPIL
O
+
+
H2O
R2
Z
H2O
R2
Z
55
Yielda / %
0
Entry R1
R2
H
H
H
H
H
H
Z
0
50
100
150
200
250
0
5000
10000
15000
20000
25000
C (mg/L)
C (mg/L)
c
d
1
2
3
4
5
6
Ph
CO2Et 99.2
CO2Et 44.7
CO2Et 99.5
Fig. 5 Conductivity curves of BPIL
a: BPILꢀ3%; b: BPILꢀ2%; c: BPILꢀ1%; d: BIL
(pꢀOMe)C6H4
(pꢀNO2)C6H4
Ph
5
When BPIL was used for the aqueous Knoeveagel
condensation, organic substances molecules diffused to the
aqueousꢀorganic interface and their aqueous solubility increased
via their incorporation into micelles in surfactants solution[29]
,
CN
CN
CN
99.3
93.3
99.6
which contributed to the interaction of reactants with catalytic
10 centers. Consequently, BPIL showed higher catalytic activity
than NaOH.
(pꢀOMe)C6H4
(pꢀNO2)C6H4
To confirm the above analysis, two parallel experiments with
NaOH and cetyltrimethyl ammonium bromide (CTAB), as
surfactant, were conducted, and the results were shown in Table 1.
15 As can be seen from Table 1, when c(CTAB) was ten times more
than its value of CMC[30,31] , the yield was increased up to 73.3%
(entry 4 in Table 1), and when c(CTAB) was up at 75 times,
which was equal to that of BPILꢀ3% added, a high yield 89.7%
was obtained (Table 1, entry 5).
O
7
CO2Et 74.8
O
8
CN 86.9
a Yield referred to those of pure isolated products.
Finally, from the green chemistry point of view, recycling was
a major concern. The Knoevenagel condensation of benzaldehyde
20
In compared with BIL, BPIL exhibited higher catalytic activity
because it had higher surface activity and its
60 and ethyl cyanocaetate was carried out (Fig. 6). An excellent
yield of 99.2% for the condensational product was achieved. On
the same scale, the recyclability of the catalytic system (S1) was
investigated using the same reaction as model reaction. Upon the
completion of the reaction, the reaction mixture was poured into
65 ice water, the solid product was precipitated. The product was
isolated by direct decantation and the catalyst was reused after the
excessive water was removed by rotary evaporation at 50℃. As
shown in Fig. 6, the catalyst could be recycled three times and the
yield of target product was about 90%. Another catalytic system
70 (S2) using benzaldehyde and malononitrile as substrates was also
investigated. After the reaction, the product was isolated via
filtration and the filtrate containing catalyst was used in
subsequent reactions directly. The catalyst could maintain high
activity after five cycles of use. The analysis result showed that
75 the trades of the catalyst adsorbed on the surface of the solid
product in the filtration led to the loss of the catalyst, but
deactivated due to high temperature treatment in the cycle would
be the major fact.
catalytic active centers were distributed around the main chain
densely, improving the utilization rate of the ionic liquid.
Effect of molecular weight on catalytic activity was
25 investigated. The results were summarized in Table 1. As can be
seen from Table 1, when BPILꢀ2% was used as the catalyst, it
presented a low yield of 68.8% (Table 1, entry 6) and BPILꢀ1%
as the catalyst decreased the yield up to 60.1% (Table 1, entry 7).
The solubility in the water has great effect on the catalytic
30 activity of BPIL beside surface activity. The high the degree of
polymerization of BPIL resulted in low solubility and poor
extensibility in water, which led to BPIL aggregate. And catalytic
centers were enwrapped in alkyl chain to some extent, which
restricted the interaction of reactants with catalytic centers. As the
35 degree of polymerization of BPIL increased, the yield of target
product and catalytic activity of BPIL decreased.
With the optimal reaction system in hand, we then investigated
the Knoevenagel condensation of various aromatic
aldehydes/aliphatic ketones with malononitrile/ethyl cyanoacetate.
40 It can be observed from Table 2 that two active methylene
compounds could react smoothly with various aromatic
aldehydes and aliphatic ketones. The effect of substituent at the
aromatic ring on the Knoevenagel reaction was also studied
(Table 2, entries 1ꢀ6). Generally, substrates with electronꢀ
This journal is © The Royal Society of Chemistry [year]
Journal Name, [year], [vol], 00–00 | 5

RSC Advances
Page 6 of 7
View Article Online
DOI: 10.1039/C5RA01700A
various aromatic aldehyde/aliphatic ketone with active methylene
compounds under room temperature. In comparison with NaOH
catalyst, BPIL showed high catalytic activity due to intensive
35 base sites and high surface activity. Howerer, the BPIL with high
molecular weight have high surface activity and low catalytic
performance. The catalyst could be recovered and maintain high
catalytic activity after five cycles of use in the system using
benzaldehyde and malononitrile as substrates.
S2
S1
100
90
40 Acknowledgments
80
0
This work is financially supported by the International Science &
Technology
Cooperation
Program
of
China
(No:
1
2
3
4
5
2012DFR40240), the National Nature Science Foundation of
China (No: 20976013) and the Foundation of Beijing Key
45 Laboratory for Chemical Power Source and Green Catalysis (No:
2014CX02026).
Cycle Times
Fig. 6 Reuse of catalyst for Knoevenagel condensation
Catalytic reaction process and mechanism of the aqueous
Knoevenagel condensation of aromatic and aliphatic carbonyl
compounds using BPIL were presented in Fig. 7. BPIL formed
micelles because of intermolecular force in aqueous solution.
Then, the micelles solution was added to reaction substrate, the
reaction system formed two phases, then change into a system of
5
Notes and references
a School of Chemical Engineering and the Environment, Beijing Institute
of Technology, Beijing 100081, China.. Fax: +86-10-68918979; Tel:
50 +86-10-68918979; E-mail: dinglibing13@sina.com;
hanshengli@bit.edu.cn; luckynanbin@gmail.com;
zhangkun19910912@163.com; yuanhong@bit.edu.cn;
wuqin_bit@126.com; zhaoyun@bit.edu.cn; jiaoqz@bit.edu.cn;
shidaxin@bit.edu.cn
10 oil in water (O/W) after rapid stirring. Benzaldehyde and ethyl
cyanoacetate molecules diffused to the aqueousꢀorganic interface
easily due to low surface tension of aqueous solution and their
concentrations in the surface of micelle phase were increased due
to the solubilization of reactants, which favored the interaction of
15 reactants with catalytic centers. Water produced in reaction was
into the aqueous phase and organic products into the oil phase.
After the completion of the reaction, the reaction mixture was
poured into ice water, the solid product was precipitated and
placed for several hours. The product was isolated by direct
20 decantation, and the catalyst could be reused after the excessive
water was removed.
55 b School of Chemical Engineering and Materials Science, Beijing Institute
of Technology, Zhuhai, 519085, China.
1
X. Z. Dong, Y. H. Hui, S. L. Xie, P. Zhang, G. P. Zhou and Z. F. Xie,
RSC Adv., 2013, 3, 3222.
2
3
4
5
6
Y. M. Ren and C. Cai, Catal. Lett., 2007, 118, 134.
M. L. Deb and P. J. Bhuyan, Tetrahedron Lett., 2005, 46, 6453.
C. Mukhopadhyay and A. Datta, Synth. Commun., 2008, 38, 2103.
F. Santamarta, P. Verdia and E. Tojo, Catal. Commun., 2008, 9,1779.
Z. J. Zheng, L. X. Liu, G. Gao, H. Dong, J. X. Jiang, G. Q. Lai and L.
W. Xu, RSC Adv., 2012, 2, 2895.
7
8
9
V.S.R.R. Pullabhotla, A. Rahman and S. B. Jonnalagadda, Catal.
Commun., 2009, 10, 365.
N. Kannari, S. Okamura, S. Fujita, J. Ozaki and M. Arai, Adv. Synth.
Catal., 2010, 352, 1476.
A. G. Ying, H. D. Liang, R. H. Zheng, C. H. Ge, H. J. Jiang and C. L.
Wu, Res. Chem. Intermed., 2011, 37, 579.
10 Z. Chen, X. Dong, J. W. Wu and H. Xie, ISRN Org. Chem., 2011, 1.
11 X. L. Zhao, K. F. Yang, X. G. Liu, C. L. Ye, L. W. Xu and G. Q. lai,
Aust. J. Chem., 2013, 66, 500.
12 U. M. Lindstrom. Blackwell Publishing.
13 D. C. Rideout and R. Breslow, J. Am. Chem. Soc., 1980, 102, 7816.
14 J. B. F. N. Engberts and M. Blandamer, Chem. Commun. 2001, 1701.
15 J. J. Shrikhande, M. B. Gawande and R. V. Jayaram, Catal. Commun.,
2008, 9, 1010.
16 A. J. Thakur, D. Prajapati, B. J. Gogoi and J. S. Sandhu, Chem. Lett.,
2003, 32, 258.
17 F. Bigi, M. L. Conforti, R. Maggi, A. Piccinno and G. Sartori, Green
Chem., 2000, 2, 101.
Fig. 7 The process and mechanism of Knoevenagel
condensation catalyzed by BPIL as catalyst and surfactant
18 M. L. Deb and P. J. Bhuyan, Tetrah. Lett., 2005, 46, 6453.
19 B. Tamami and A. Fadavi, Iran. Polym. J., 2006, 15, 331.
20 S. Sobhani and Z. P. Parizi, Tetrahedron, 2011, 67, 3540.
21 T. Dwars, E. Paetzold and G. Oehme, Angew. Chem. Int. Ed., 2005,
44, 7174.
25
Conclusion
In conclusion, we developed a novel polymerized ionic liquid
(BPIL): polymeric 1ꢀ[(4ꢀethenylphenyl) methyl]ꢀ3ꢀ
22 A.L. Ping, P.P. Geng, J.H. Zhang, J. Liu, D.Z. Sun, X.D. Zhang, Q.X.
Li, J.F. Liu and X.L. Wei, T&F, 2014. 12, 326
23 H. Zhang, Z. B. Zhou and J. Nie, Prog. Chem., 2013, 25, 761.
propylimidazolium imidazolide and it was characterized by IR,
30 1H NMR and ESIꢀMS. BPIL was used as efficient homogeneous
catalysts for the aqueous Knoevenagel condensation reaction of
6
| Journal Name, [year], [vol], 00–00
This journal is © The Royal Society of Chemistry [year]

Page 7 of 7
RSC Advances
View Article Online
DOI: 10.1039/C5RA01700A
24 J. K. Wang, Y. X. Zong, R. G. Fu, Y. Y. Niu, G. R. Yue, Z. J. Quan,
X. C. Wang and Y. Pan, Ultrason. Sonochem., 2014, 21, 29.
25 X. W. Chen, X. H. Li and H. B. Song, Chin. J. Cata., 2008, 29, 957.
26 Z. G. Zhao, Chem. Ind. Press, 2006, 7.
27 C. Jungnickel, L. Justyna, R. Johannes, F. F. Jose, M. Anja and T.
Jorg, Colloid. Surface. A., 2008, 316, 278.
28 S. A. Zhou, L. Liu, B. Wang, M. G. Ma, F. Xu and R. C. Sun, T & F.
Group, 2010, 6, 1384.
29 H. Nakahara, Y. Kojima, Y. Moroi and O. Shibata, Langmuir, 2014,
30, 5771.
30 T, Yang, W. J. Li and C. H. Zhou, Petro. Technol. Appl., 2007, 25,
48.
31 H. J. Lu, C. Chen, H. T. Guo, X. H. Zhou, J. F. Dong, X. L. Hong, X.
F. Xi and G. Y. Zhang, Acta Chim. Sinica, 2006, 64, 2437.
This journal is © The Royal Society of Chemistry [year]
Journal Name, [year], [vol], 00–00 | 7