Synthesis of novel poly(ethyleneglycol)-400 ionic liquid and its application in morita-baylis-hillman reaction

Article abstract of DOI:10.1080/00397911.2010.517889

Novel Poly(ethyleneglycol)-400 ionic liquid containing imidazolium cations have been synthesized by the atom-efficient reaction of 1,2-dimethylimidazole with p-toluenesulfonate; the p-toluenesulfonate provides the anionic component of the resultant ionic

Full text of DOI:10.1080/00397911.2010.517889

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Synthesis of Novel
Poly(ethyleneglycol)-400 Ionic
Liquid and Its Application in
Morita–Baylis–Hillman Reaction
San-Hu Zhao a , Qian-Jun Zhang a , Xin-E Duan b & Li-Heng Feng b
a Department of Chemistry , Xinzhou Teachers University , Xinzhou ,
China
b School of Chemistry and Chemical Engineering , Shanxi University ,
Taiyuan , China
Published online: 26 Jul 2011.
To cite this article: San-Hu Zhao , Qian-Jun Zhang , Xin-E Duan & Li-Heng Feng (2011) Synthesis of
Novel Poly(ethyleneglycol)-400 Ionic Liquid and Its Application in Morita–Baylis–Hillman Reaction,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 41:22, 3289-3297, DOI: 10.1080/00397911.2010.517889
To link to this article: http://dx.doi.org/10.1080/00397911.2010.517889
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Synthetic Communications1, 41: 3289–3297, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.517889
SYNTHESIS OF NOVEL POLY(ETHYLENEGLYCOL)-400
IONIC LIQUID AND ITS APPLICATION IN MORITA–
BAYLIS–HILLMAN REACTION
San-Hu Zhao,1 Qian-Jun Zhang,1 Xin-E Duan,2 and
Li-Heng Feng2
1Department of Chemistry, Xinzhou Teachers University, Xinzhou, China
2School of Chemistry and Chemical Engineering, Shanxi University,
Taiyuan, China
GRAPHICAL ABSTRACT
Abstract Novel Poly(ethyleneglycol)-400 ionic liquid containing imidazolium cations have
been synthesized by the atom-efficient reaction of 1,2-dimethylimidazole with p-toluenesul-
fonate; the p-toluenesulfonate provides the anionic component of the resultant ionic liquid.
It have been used for the first time as a new solvent for the Morita–Baylis–Hillman reaction
under ambient conditions. A wide variety of aldehydes and active olefins participate very
efficiently, resulting in good to excellent yields of products.
Keywords 1,2-Dimethylimidazole; ionic liquid; Morita–Baylis–Hillman reaction;
p-toluenesulfonate; synthesis
INTRODUCTION
Ionic liquids (ILs) are emerging as effective promoters and solvents for green
chemical reactions, and during the past few years, a variety of organic reactions have
been successfully conducted using ILs as solvents.[1] Many interesting results have
been obtained that demonstrate advantages of using ILs as alternative for traditional
organic solvents. One of the most important advantages of ILs is the good solvating
property for both inorganic and organic compounds, which provides a homogeneous
Received August 4, 2009.
Address correspondence to San-Hu Zhao, Department of Chemistry, Xinzhou Teachers
University, Xinzhou, China. E-mail: sanhuzhao@yahoo.cn
3289

3290
S.-H. ZHAO ET AL.
Scheme 1. Synthesis of IL-400 ionic liquid.
system and accelerates multicomponent reactions (MCRs) in comparison with
conventional solvents.
The Morita–Baylis–Hillman (MBH) reaction is an atom-economical and
extremely useful CꢀC bond-forming reaction in organic synthesis.[2] This reaction
involves three components: an activated alkene, an electrophile, and a tertiary amine.
Lewis bases, such as 1,4-diazabicyclo[2.2.2]octane (DABCO),[3] dimethylaminopyri-
dine (DMAP),[4] 1,8-diazabicyclo[5.4.]undec-7-ene (DBU)[5] and trimethylamine[6]
are frequently used in these reactions as catalysts. In addition, Lewis acid-accelerated
[7]
reactions using TiCl4 and BF3.[8] were also reported. However, they suffer from
poor reaction rate and long reaction time. In view of this situation, numerous stu-
dies, including chemical as well as physical attempts, have been made to accelerate
the reaction with some good results.[9] An earlier report described acceleration of
the DABCO-catalyzed MBH reaction in an ionic liquid, 1-n-butyl-3-methyimidazo-
lium hexafluoro-phosphate ([bmim][PF6]).[10] However, it was later shown that the
imidazolium salts, incorporating a hydrogen substituent at the C-2 position, are
deprotonated under mild basic conditions and the corresponding carbenes are
formed, which can cause undesired side reactions.[11] Because we were not satisfied
with the results, we synthesized new imidazolium ionic liquid for the MBH reaction,
in which its C-2 carbon is methylated (Scheme 1). In this article, we present an
efficient and practical synthesis of a new room-temperature ionic liquid based on
bis(1,2-dimethylimidazolium) cations involving ethylene glycol spacers and their
application in the MBH reaction under mild conditions.
RESULTS AND DISCUSSION
Poly(ethyleneglycol)-400 and 1,2-dimethylimidazole are commercially available.
The synthesis of poly(ethyleneglycol)-400 ionic liquid (IL-400) is straightforward
Scheme 2. Morita–Baylis–Hillman reaction in IL-400.

NOVEL PEG-400 IONIC LIQUID
3291
Table 1. Morita–Baylis–Hillman reactions in IL-400a
Entry
1c
Aldehyde
Alkene
Products
Time (h)
4
Yield (%)b
67
2d
4
78
89
3
3.5
4
5
6
7
4
8
3
4
90
68
93
84
8
9
4
5
82
79
10
11
8
88
63
10
12
13
4
5
89
87
(Continued )

3292
S.-H. ZHAO ET AL.
Table 1. Continued
Entry
14
Aldehyde
Alkene
Products
Time (h)
12
Yield (%)b
65
CH3-CHO
aAll reactions were performed with aldehydes (5 mmol) and activated alkenes (10 mmol) in a mixture of
IL-400 and water (v=v, 1:1, 10 ml) in the presence of appropriate catalyst DABCO (5 mmol) at ambient
temperature.
bRefers to isolated, pure products after silica-gel chromatography.
cThe reaction was performed with benzaldehyde (5 mmol) and acrylonitrile (10 mmol) in 5 ml of IL-400
in the presence of appropriate catalyst DABCO (2.5 mmol) at ambient temperature.
dThe reaction was performed with benzaldehyde (5 mmol) and acrylonitrile (10 mmol) in 5 ml of IL-400
in the presence of appropriate catalyst DABCO (5 mmol) at ambient temperature.
(Scheme 1). In the first step, poly(ethyleneglycol)-400 was employed as a starting
material to react with p-toluenesulfonyl chloride according to a literature pro-
cedure,[12] and the desired p-toluenesulfonate I could be obtained in 53% yield,
which is low for practical use. Several improvement measures were used in this
reaction, and when microwave irradiation was applied with triethylamine as cata-
lyst instead of pyridine, we found that an excellent yield (83%) of p-toluenesulfo-
nate I could be achieved and that it is pure enough to use in successive reactions.
In the second step, 1,2-dimethylimidazole was used to react with p-toluenesulfonate
I, and we found that the reaction could be carried out readily to give new IL-400
with 87% yield.
As a continuation of our work in MBH reactions,[13] IL-400 was tested as a
solvent in the MBH reaction of acrylonitrile and benzaldehyde (Scheme 2), and
the results are shown in Table 1. When 0.5 equiv of 1,4-diazabicyclo[2.2.2]octane
(DABCO) was used as a catalyst at room temperature, benzaldehyde and acryloni-
trile formed the desired product with 67% yield after 4 h. When increasing the
amount of catalyst was increased to 1 equiv, better yield (78%) was obtained
(Table 1, entry 2) in pure IL-400, and in the presence of 1 equiv catalyst, the optimal
yield (89%) was achieved in the same volume of IL-400 and water mixture after 3.5 h
(Table 1, entry 3). Under these optimum conditions, the MBH reactions of acryloni-
trile or methyl acrylate with a variety of aldehydes were examined at room tempera-
ture (Table 1, entries 4–14). As demonstrated in Table 1, both aliphatic and aromatic
aldehydes can undergo very efficient MBH reactions in the same volume of IL-400
and water mixture, and the corresponding M-B-H adducts in good to excellent
yieldes (63–93%) were obtained. The electron-rich 4-methoxybenzaldehyde, which
is usually quite an inert substrate, could provide a fairly good yield (68%, entry 5)
under the present conditions, and the reaction of acrylonitrile with the electron-
deficient 4-chlorbenzaldehyde provided an excellent yield of 90% after 3 h. To
evaluate the possibility of recycling the ionic liquid used for the MBH reaction,
the recycling performance of IL-400 was investigated in the reaction of benzladehyde
with acrylonitrile. The results listed in Table 2 showed that the IL-400 could be
reused five times with consistent activity.

NOVEL PEG-400 IONIC LIQUID
3293
Table 2. Reuse of IL-400a
Cycle
Yield (%)
1
2
3
4
5
89
90
91
89
87
aAll reactions were performed with benzal-
dehyde (5 mmol) and acrylonitrile (10 mmol) in
a mixture of IL-400 and water (v=v, 1:1, 10 ml)
in the presence of appropriate catalyst DABCO
(5 mmol) at ambient temperature.
CONCLUSIONS
In summary, we have present
a
novel ionic liquid based on
poly(ethyleneglycol)-400 and 1,2-dimethylimidazole. New imidazolium IL-400 was
prepared conveniently and in an environmentally friendly way in only two steps from
poly(ethyleneglycol)-400 and 1,2-dimethylimidazole with good overall yields.
Further study on its application as a green solvent in the MBH reaction showed that
it is useful for the MBH reactions of a variety of aldehydes, including electron-
deficient and electron-rich aromatic aldehydes and aliphatic aldehydes. In addition,
IL-400 can be reused several times in the MBH reaction without much loss of its
activity.
EXPERIMENTAL
All melting points were measured on a WRS-1B digital melting-point meter
and are uncorrected. The infrared (IR) spectra were determined on a Fourier trans-
1
form (FT)–IR-8400 spectrometer by dispersing samples in neat or KBr disks. H
NMR spectra were measured on a DRX300 NMR spectrometer using tetramethyl-
silane (TMS) as an internal standard with CDCl3 as solvent. All products (except
IL-400) are known compounds, which were characterized by IR and 1H NMR spec-
tral data, and their melting points were compared with literature reports.[14]
Typical Procedure for the Microwave-Assisted Synthesis of IL-400
PEG 400 (23.4 mL, 60 mmol) was dissolved in toluene (180 mL), and then
triethylamine (16.7 mL, 120 mmol) was added, followed by p-toluenesulfonyl chlor-
ide (24.78 g, 130 mmol) in small portions with constant stirring. Then the reaction
mixture was irradiated with microwaves at 150 W at 20 ꢁC for 600 s. when the reac-
tion was completed (monitored by thin layer chromatography, TLC), the mixture
was filtered. The filtrate was added to 1,2-dimethylimidazol (10.6 mL, 120 mmol),
and the mixture was stirred at 85 ꢁC for 22 h under nitrogen atmosphere. After the
reaction, the ionic liquid layer was separated and washed with petroleum ether
(3 ꢂ 10 mL). Evaporation of solvent under reduced pressure gave the desired pure

3294
S.-H. ZHAO ET AL.
product IL-400 in 86% yield. Pale yellow oil; IR (neat, cmꢀ1): 3408.0, 2873.7, 2702.1,
2497.6, 2360.7, 2248.8, 1608.5, 1535.2, 1454.2, 1396.3, 1352.0, 1190.0, 1120.2, 1010.6,
1
943.1, 817.8, 735.8, 582.8. H NMR (300 MHz, CDCl3): d 7.60 d, J ¼ 2.0 Hz, 2CH),
7.48 (d, J ¼ 2.2 Hz, 2H, 2CH), 7.20(d, J ¼ 5.4 Hz, 4H), 7.13 (d, J ¼ 5.2 Hz, 4H),
3.75–3.73 (m, 40H), 3.71 (s, 6H, 2NCH3), 2.56 (s, 6H, CH3), 2.36 (s, 6H), 13C
NMR (300 MHz, CDCl3): d 136.7, 123.3, 122.6, 69.4, 69.3, 68.5, 48.7, 37.5, 36.2.
General Procedure for the Morita–Baylis–Hillman Reaction
A solution of aldehyde (5 mmol) and activated alkene (10 mmol) in a mixture
of IL-400 and water (v=v, 1:1, 10 ml) was stirred at room temperature (20–26 ꢁC)
in the presence of DABCO (5 mmol). The progress of the reaction was monitored
by TLC. Upon completion, the reaction mixture was extracted with ethyl ether
(3 ꢂ 20 ml). Then the combined ethyl ether fractions were evaporated. The crude pro-
ducts thus obtained were purified by flash column chromatography (silica gel,
200–300 mesh; ethyl acetate=petroleum ether, 1:5–1:3). All desired products were
characterized by IR and 1H NMR. The ionic liquid was directly used in the next run.
Spectral Data of the Morita–Baylis–Hillman Adducts
3-Hydroxy-2-methylene-3-phenylpropanenitrile (Table 1, Entry 3).
1
Yellow oil. IR (neat): 3442.8, 2224.7, 1604.9, 1340.8 cmꢀ1. H NMR (300 MHz,
CDCl3): d ¼ 7.41–7.18 (m, 5H), 6.10 (s, 1H), 6.08 (s, 1H), 5.91 (d, J ¼ 5.56 Hz,
1H), 2.85 (br., s, 1H).
3-Hydroxy-2-methylene-3-(4-chlorophenyl)propanenitrile (Table 1,
1
Entry 4). Yellow oil. IR (neat): 3435.1, 2227.1, 1495.9 cmꢀ1. H NMR (300 MHz,
CDCl3): d ¼ 7.36–7.24 (m, 4H), 6.07 (s, 1H), 6.01 (s, 1H), 5.24 (s, 1H), 3.25
(br., s, 1H).
3-Hydroxy-2-methylene-3-(4-methoxy-phenyl)propanenitrile (Table 1,
1
Entry 5). Yellow oil. IR (neat): 3413.5, 2224.7, 1489.6 cmꢀ1. H NMR (300 MHz,
CDCl3): d ¼ 7.32 (d, J ¼ 6.8 Hz, 2H), 6.84 (d, J ¼ 7.3 Hz, 2H), 6.24 (d, J ¼ 1.8 Hz,
1H), 6.12 (d, J ¼ 1.3 Hz, 1H), 5.24 (s, 1H), 3.82 (s, 3H), 2.25 (br., s, 1H).
3-Hydroxy-2-methylene-3-(4-nitrophenyl)propanenitrile (Table 1,
Entry 6). Pale yellow solid, mp 73.8–74.2 ꢁC. IR (KBr): 3424.2, 2865.5,
1
2229.4 cmꢀ1. H NMR (300 MHz, CDCl3): d ¼ 8.26 (d, J ¼ 5.8 Hz, 2H), 7.60 (d,
J ¼ 5.3 Hz, 2H), 6.18 (1s, 1H), 6.10 (s, 1H), 5.44 (s, 1H), 2.85 (br., s, 1H).
3-Hydroxy-2-methylene-3-(4-formyl-phenyl)propanenitrile (Table 1,
Entry 7). Pale white solid, mp 56.2–56.8 ꢁC. IR (KBr): 3465.2, 2882.1, 2227.6,
1
1710.2 cmꢀ1. H NMR (300 MHz, CDCl3): d ¼ 9.94 (s, 1H), 7.87 (d, J ¼ 5.97 Hz,
2H), 7.55 (d, J ¼ 5.86 Hz, 2H), 6.13 (d, J ¼ 1.72 Hz, 1H), 6.02 (d, J ¼ 1.67 Hz,1H),
5.36 (s, 1H), 3.85 (br., s, 1H).
3-Hydroxy-2-methylene-3-(2-furanyl)propanenitrile (Table 1, Entry
1
8). Pale yellow oil. IR (neat): 3431.2, 2874.8, 2227.6 cmꢀ1. H NMR (300 MHz,

NOVEL PEG-400 IONIC LIQUID
3295
CDCl3): d ¼ 7.34 (s, 1H), 6.35 (s, 1H), 6.30 (m, 1H), 6.24 (d, J ¼ 2.8 Hz, 1H), 5.92 (s,
1H), 5.50 (s, 1H), 2.84 (br., s, 1H).
3-Hydroxy-2-methylene-3-phenylpropanoic acid, methyl ester (Table 1,
Entry 9). Colorless oil. IR (neat): 3480.1, 2979.8, 1714.5 cmꢀ1. 1H NMR (300 MHz,
CDCl3): d ¼ 7.42–7.21 (m, 5H), 6.29 (s, 1H), 5.87 (s, 1H), 5.47 (s, 1H), 3.68 (s, 3H),
2.63 (br., s, 1H).
3-Hydroxy-2-methylene-3-(4-chlorophenyl)propanoic
acid,
methyl
ester (Table 1, Entry 10). White solid, mp 43.2–44.0 ꢁC. IR (KBr): 3485.7,
1
2984.8, 1726.4 cmꢀ1. H NMR (300 MHz, CDCl3): d ¼ 7.29 (s, 4H), 6.32 (s, 1H),
5.80 (s, 1H), 5.51 (s, 1H), 3.71 (s, 3H), 2.59 (br., s, 1H).
3-Hydroxy-2-methylene-(4-methoxy-phenyl)propanoic acid, methyl
ester (Table 1, Entry 11). Pale yellow oil. IR (neat): 3480.6, 2979.7, 1720.6 cmꢀ1
.
1H NMR (300 MHz, CDCl3): d ¼ 7.26–7.22 (m, 2H), 6.72–6.69 (m, 2H), 6.38 (s, 1H),
6.24 (s, 1H), 5.18 (s, 1H), 3.78 (s, 3H), 3.71 (s, 3H), 2.71 (br., s, 1H).
3-Hydroxy-2-methylene-3-(4-nitrophenyl)propanoic acid, methyl ester
(Table 1, Entry 12). Yellow solid, mp 71.2–71.6 ꢁC. IR (KBr): 3480.4, 2992.3,
1
1726.5, 1632.3, 1358.5 cmꢀ1. H NMR (300 MHz, CDCl3): d ¼ 8.14 (d, J ¼ 6.4 Hz,
2H), 7.53 (d, J ¼ 6.5 Hz, 2H), 6.36 (1s, 1H), 5.71 (s, 1H), 5.62 (s, 1H), 3.74 (s, 3H),
2.95 (br., s, 1H).
3-Hydroxy-2-methylene-3-(2-furanyl)propanoic acid, methyl ester
1
(Table 1, Entry 13). Pale yellow oil, IR (neat): 3447.3, 1721.4, 1635.1 cmꢀ1. H
NMR (300 MHz, CDCl3): d ¼ 7.35 (s, 1H), 6.36 (s, 1H), 6.24–6.32 (m, 2H), 5.92
(s, 1H) 5.57 (s,1H), 3.74 (s, 3H), 2.87 (br., s, 1H).
3-Hydroxy-2-methylene-propanoic acid, methyl ester (Table 1, Entry
14). Yellow oil, IR (neat): 3470.3, 2937.1, 1723.6, 1637.8 cmꢀ1. 1H NMR(300 MHz,
CDCl3): d ¼ 6.13 (s, 1H), 5.82 (d, J ¼ 0.9 Hz, 1H), 4.74 (m, 1H), 3.72 (s, 3H), 2.88
(br., s, 1H), 1.27 (s, 3H).
ACKNOWLEDGMENTS
We gratefully acknowledge financial support from the Xinzhou Teachers
University Foundation ([2008] 79), the Higher School Science & Technology
Development Project of Shanxi Province Education Department (No. 2010124),
and the National Natural Science Foundation of China (No. 208020421B0211).
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