Immobilized ionic liquid on superparamagnetic nanoparticles as an effective catalyst for the synthesis of tetrasubstituted imidazoles under solvent-free conditions and microwave irradiation

Article abstract of DOI:10.1016/j.crci.2013.01.019

The ionic liquid 1-methyl-3-(3-trimethoxysilylpropyl) imidazolium chloride was immo- bilized on superparamagnetic Fe₃O₄ nanoparticles (IL-MNPs) and used as an efficient heterogeneous catalyst for the one-pot synthesis of 1,2,4,5-tetr

Full text of DOI:10.1016/j.crci.2013.01.019

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Full paper/Memoire
Immobilized ionic liquid on superparamagnetic nanoparticles as an
effective catalyst for the synthesis of tetrasubstituted imidazoles
under solvent-free conditions and microwave irradiation
*
Javad Safari , Zohre Zarnegar
Laboratory of Organic Compound Research, Department of Organic Chemistry, College of Chemistry, University of Kashan, PO Box: 87317-51167, Kashan, Islamic
Republic of Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
The ionic liquid 1-methyl-3-(3-trimethoxysilylpropyl) imidazolium chloride was immo-
bilized on superparamagnetic Fe3O4 nanoparticles (IL-MNPs) and used as an efficient
heterogeneous catalyst for the one-pot synthesis of 1,2,4,5-tetrasubstituted imidazoles
under solvent-free conditions using microwave irradiation. The reactions in conventional
heating conditions were compared with the microwave-assisted reactions. The combined
merits of microwave irradiation and immobilized ionic liquid on superparamagnetic
nanoparticles make the four-component condensation with safe operation, low pollution,
and rapid access to products and simple work-up.
Received 30 October 2012
Accepted after revision 28 January 2013
Available online xxx
Keywords:
Microwave
Ionic liquid
Imidazole
´
ß 2013 Published by Elsevier Masson SAS on behalf of Academie des sciences.
Multicomponent
Solvent-free
1. Introduction
biochemical processes [8,9]. In recent years, the synthesis
of 2,4,5-trisubstituted imidazoles has been performed by
The developing of new multicomponent reactions
(MCRs) and improving the known MCRs are an area of
considerable current interest [1–3]. As opposed to the
classical way to synthesize complex molecules by sequen-
tial synthesis, MCRs allow the assembly of complex
molecules in one-pot and show a facile execution, high
atom-economy and high selectivity [4–7]. As a one-pot
reaction, MCRs generally afford good yields and are
fundamentally different from two-component and step-
wise reactions in several aspects [4] and permit a rapid
access to combinatorial libraries of complex organic
molecules for an efficient lead structure identification
and optimization in drug discovery.
catalysts such as Yb(OPf)3 [10], ZrCl4 [11], NiCl2ꢀ6H2O/
Al2O3 [12], silica sulfuric acid (SSA) [13], polymer-
supported ZnCl2 [14], and phosphomolybdic acid [15].
Also some catalysts used for 1,2,4,5-tetrasubstituted
imidazoles, including silica gel or zeolite InCl3ꢀ3H2O
[16], silica gel/NaHSO4 [17], HClO4–SiO2 [18], heteropo-
lyacids [19], BF3ꢀSiO2 [20], and FeCl3ꢀ6H2O [21], are applied
as some common catalysts for 2,4,5-trisubstituted and
1,2,4,5-tetrasubstituted imidazoles.
Despite the many methods available for the synthesis
of imidazoles, some of these synthetic methods are not
environmentally friendly and suffer from one or more
drawbacks, such as harsh reaction conditions, complex
work-up and purification, strongly acidic conditions, high
temperature, the use of toxic metal catalysts, unsatisfac-
tory yields, occurrence of side reactions, and long
reaction time. Therefore, the development of clean,
Multi-substituted imidazoles are a very interesting
class of heterocyclic compounds because they have many
pharmacological properties and play important roles in
high-yielding, mild, and green approach is still
a
challenge for the synthesis of substituted imidazole
derivatives [9].
* Corresponding author.
E-mail address: Safari@kashanu.ac.ir (J. Safari).
1631-0748/$ – see front matter ß 2013 Published by Elsevier Masson SAS on behalf of Acade´mie des sciences.
http://dx.doi.org/10.1016/j.crci.2013.01.019
Please cite this article in press as: Safari J, Zarnegar Z. Immobilized ionic liquid on superparamagnetic nanoparticles as
an effective catalyst for the synthesis of tetrasubstituted imidazoles under solvent-free conditions and microwave
irradiation. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.01.019

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CHO
O
R
N
MNPs-IL
+
+
R NH2
(3)
+
4 NH4OAc
(4)
R
MW or
O
1
N
R
1
(1)
R=C6H5, n-Pr
(2)
(5 a-n)
Scheme 1. One-pot synthesis of 1,2,4,5-tetrasubstituted imidazoles catalyzed by IL-MNPs conventional heating conditions or using microwave irradiation.
Ionic liquid (IL) technology is a new environmentally
benign approach toward modern synthetic chemistry
[22–25]. ILs have attractive properties, including unde-
tectable vapour pressure, reasonable thermal stability,
reusability, and talent to dissolve many organic and
inorganic substrates [23–25], Additionally, IL as catalyst
has been exploited in controlling organic reactions
[26,27]. ILs have been used as an efficient catalyst for
an improved and rapid synthesis of imidazoles [28–30].
Zang et al. synthesized 2-aryl-4,5-diphenyl imidazoles,
using IL 1-ethyl-3-methylimidazole acetate as an efficient
catalyst at room temperature under ultrasound irradia-
tion [31]. IL, N-methyl-2-pyrrolidonium hydrogen sulfate
has been used as a reusable catalyst for the one-pot
synthesis of highly substituted imidazoles under thermal
solvent-free conditions in excellent yields of products
[32].
Since the introduction of a controlled and precise
microwave reactor, microwave-assisted organic synthesis
(MAOS) has had
a significant impact on synthetic
chemistry, especially those reactions under solvent-free
circumstances, with the remarkable merits of reduced
reaction time, improved yields, suppressed side reactions,
decreased environmental pollutions and safe operations.
Therefore, a large and continuing survey has been made
throughout nearly all classes of thermal reactions for
improvements upon microwave heating. The polar nature
of ILs makes them ideal for use in solvent-free microwave
irradiation [40].
One of the aims we have in mind is to introduce an
efficient catalyst for synthesis of 1,2,4,5-tetrasubstituted
imidazoles with cost effectiveness and mild conditions in
high yields. In this work, our objective is to functionalize
magnetite nanoparticles with 1-methyl-3-(3-trimethox-
ysilylpropyl) imidazolium chloride to obtain a heteroge-
neous catalyst for the synthesis of 1,2,4,5-tetrasubstituted
imidazoles under solvent-free conditions and microwave
irradiation. To the best of our knowledge, there is no report
about the synthesis of highly substituted imidazoles by
such a magnetically recoverable nanocatalyst. The hetero-
geneous catalyst could be recovered easily by an external
magnet and reused many times without significant loss of
its catalytic activity (Scheme 1).
Though ILs possessed such promising advantages, their
widespread practical application was still hampered by
several disadvantages:
ꢁ
high viscosity, which resulted in only a minor part of ILs
taking part in the catalyzed reaction for chemical
production;
ꢁ
ꢁ
homogeneous reaction, which was difficult for separa-
tion and reuse procedures;
consequently high cost for the use of relatively large
amounts of ILs as opposed to economic criteria [33,34].
2. Results and discussion
Thus, in order to solve these problems mentioned
earlier, immobilized IL catalyst as a novel solid catalyst
combining the advantageous characteristics of ILs, inor-
ganic acids and solid acids had been designed for catalysed
reactions [35,36].
2.1. Characterization of the prepared IL-MNPs
Scheme
2 shows the sequence of events in the
functionalization of MNPs with 1-methyl-3-(3-trimethox-
ysilylpropyl)-1H-imidazol-3-ium chloride. In the first step,
the magnetite nanoparticles of 18–20 nm were prepared
by coprecipitation of iron(II) and iron(III) ions in basic
solution at 85 8C, using the method described by Massart
[41,42]. Then, 1-methyl-3-(3-trimethoxysilylpropyl) imi-
dazolium chloride (IL), was prepared from the reaction of
N-methyl imidazole with (3-chloropropyl)trimethoxysi-
lane at 80 8C [43]. In the second step, the external surface of
MNPs was coated with IL to obtain IL-MNPs.
Fig. 1 shows the Fourier transform infrared (FT-IR)
spectra of both the unfunctionalized and functionalized
MNPs. The Fe–O stretching vibration near 580 cmꢂ1, the O–
H stretching vibration near 3432 cmꢂ1 and the O–H
deformed vibration near 1625 cmꢂ1 were observed for
During the past decades, advances in nanoscience and
nanotechnology have pushed forward the synthesis of
functional magnetic nanoparticles (MNPs), which is one of
the most active research areas in advanced materials.
MNPs that have unique magnetic properties and other
functionalities have enabled a wide spectrum of applica-
tions [37]. Iron oxide magnetic nanoparticles (Fe3O4-
MNPs) are approximately 20–30 nm in size containing a
single magnetic domain with a single magnetic moment
and exhibit superparamagnetism [38]. Additionally, recent
studies show that MNPs are excellent supports for
catalysts [39]. The supported catalysts proved to be
effective and easily separated from the reaction media
by applying an external magnetic field.
Please cite this article in press as: Safari J, Zarnegar Z. Immobilized ionic liquid on superparamagnetic nanoparticles as
an effective catalyst for the synthesis of tetrasubstituted imidazoles under solvent-free conditions and microwave
irradiation. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.01.019

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3
Scheme 2. Preparation steps for fabricating 1- methyl -3-(3-trimethoxysilylpropyl)-1H-imidazol-3-ium chloride -functionalized magnetic Fe3O4
nanoparticles.
Fig. 2. X-ray powder diffraction patterns of (a) magnetic nanoparticles,
(b) IL-MNPs.
Fig. 1. The comparative FT-IR spectra for (a) magnetic nanoparticles, (b)
IL-MNPs.
both in Fig. 2 a and b. The significant features observed
for Fig. 2(b) are the appearance of the peaks at 1007 cmꢂ1
(Si–O stretching) and at 2800 cmꢂ1 (–CH2 stretching).
These results provided the evidences that IL-methyl
were successfully attached to the surface of Fe3O4
nanoparticles.
Fig. 2 presents the X-ray powder diffraction (XRD)
patterns of the prepared MNPs and IL-MNPs. The position
and relative intensities of all peaks confirm well with
standard XRD pattern of Fe3O4 (JCPDS card No. 79-0417),
indicating retention of the crystalline cubic spinel struc-
ture during functionalization of MNPs. The XRD patterns of
the particles show six characteristic peaks, revealing a
cubic iron oxide phrase (2u = 30.35, 35.95, 43.45, 53.70,
57.25, 62.88, 71.37, 74.46). These are related to their
corresponding indices (2 2 0), (3 1 1), (4 0 0), (3 3 1), (4 2 2),
(3 3 3), (4 4 0) and (5 3 1), respectively [35]. It is implied
that the resultant nanoparticles are pure Fe3O4 with a
spinel structure and that the grafting process did not
induce any phase change of Fe3O4.
Please cite this article in press as: Safari J, Zarnegar Z. Immobilized ionic liquid on superparamagnetic nanoparticles as
an effective catalyst for the synthesis of tetrasubstituted imidazoles under solvent-free conditions and microwave
irradiation. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.01.019

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Fig. 3. The Scanning electron microscope image of (a) magnetic nanoparticles, (b) IL-MNPs.
The crystal size of MNPs and IL-MNPs nanoparticles can
be determined from the XRD pattern by using Debye–
Scherrer’s equation:
obtained MNPs had an excellent magnetic responsivity,
which prevents composite nanoparticles from aggregation
and enables them to redisperse rapidly when the magnetic
field is removed.
0:94
l
The scanning electron microscope (SEM) image shows
that magnetite (Fe3O4) particles have a mean diameter of
about 18 nm and a nearly spherical shape as shown in
Fig. 3. Fig. 3 a and b shows that IL-MNPs particles still keep
the morphological properties of Fe3O4, except for a slightly
larger particle size and smoother surface (more than 20 nm
in size), where silica are uniformly coated on the Fe3O4
particles to form silica shell.
Dðh k lÞ ¼
b
cosu
where D (h k l) is the average crystalline diameter, 0.94
is the Scherrer’s constant, is the X-ray wavelength, is
the half width of XRD diffraction lines and is the Bragg’s
angle in degree. Here, the (3 1 1) peak of the highest
intensity was picked out to evaluate the particle diameter
of the nanoparticles. MNPs and IL-MNPs were calculated to
be 12 nm and 30 nm, respectively.
The IL-functionalized magnetic Fe3O4 nanoparticles
could be separated to the sidewall of the container after
30 s, using a magnet of 2000 Gs, suggesting that the
l
b
u
The magnetization curve for Fe3O4 nanoparticles and
IL-MNPs is shown in Figure 4. Room temperature specific
magnetization (M) versus applied magnetic field (H) curve
measurements of the sample indicate
a saturation
magnetization value (Ms) of 40.5 emu/g, lower than that
Fig. 4. Magnetization curves for the prepared magnetic nanoparticles and IL-MNPs at room temperature.
Please cite this article in press as: Safari J, Zarnegar Z. Immobilized ionic liquid on superparamagnetic nanoparticles as
an effective catalyst for the synthesis of tetrasubstituted imidazoles under solvent-free conditions and microwave
irradiation. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.01.019

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5
Table 1
Optimization one-pot synthesis of tetrasubstituted imidazoles under classical heating conditionsa.
Experimental number
Catalyst (g)
Time (min)
Temperature (8C.)
Yield (%)
1
0.0
60
35
35
35
45
30
30
30
40
25
25
25
35
20
20
20
90
90
10
40
50
50
15
60
70
70
25
79
90
90
30
63
90
90
2
0.08
0.1
3
90
4
0.12
0.0
90
5
110
110
110
110
120
120
120
120
130
130
130
130
6
0.08
0.1
7
8
0.12
0.0
9
10
11
12
13
14
15
16
0.08
0.1
0.12
0.0
0.08
0.1
0.12
a
Benzil (1 mmol), benzaldehyde (1 mmol), aniline (1 mmol) and ammonium acetate (5 mmol).
of bare MNPs (60.1 emu g) due to the coated shell. In
Figure 4, we can also see that the two magnetization curves
both follow a Langevin behavior over the applied magnetic
field and the coercivity (HC) could be ignored, which can be
considered as superparamagnetism [44].
The successful results of IL-MNPs catalyzed synthesis of
tetrasubstituted imidazoles under solvent-free classical
heating conditions or using microwave irradiation in the
absence of solvent are given in Table 2. In a typical
experiment,
a mixture of aldehyde (1 mmol), benzil
(1 mmol), aniline (1 mmol), ammonium acetate (5 mmol)
and IL-MNPs (0.1 g) was stirred for 35–70 min in a tube
under conventional heating conditions at 120 8C or using
microwave irradiation at 100 W for 5–25 min. After the
reaction was completed, the reaction mixture was
dissolved in acetone and the catalyst was separated by
an external magnet and the reaction mixture was filtrated.
The filtrate was concentrated on a rotary evaporator under
reduced pressure and the solid product obtained was
washed with water and recrystallized from acetone–water.
Results from IL-MNPs-catalyzed condensation reaction
of benzil, ammonium acetate with different aromatic
2.2. Evaluation of the catalytic activity of IL-MNPs through
the synthesis of 1,2,4,5-tetrasubstitutedimidazols
Efficiency of the reaction is mainly affected by the
amount of catalyst and temperature. As indicated in Table
1, the best results have been obtained at 120 8C with an
amount of 0.1 g IL-MNPs (Table 1, entry 11) and the yield of
reaction with increasing the amount of IL-MNPs or
temperature is not considerably increased. It is important
to note that in the absence of catalyst, the yield of the
product was found to be low.
Table 2
One-pot synthesis of tetrasubstituted imidazoles in the presence of IL-MNPs as a heterogeneous catalyst under solvent-free classical heating conditions or
using microwave irradiation.
Entry
R1
(R) amine
Producta
Yield (%)a
Time (min)
MWc
M.p.(8C.) Found/Reported
Db
1
H
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
n-Pr
n-Pr
n-Pr
n-Pr
5a
5b
5c
5d
5e
5f
88(45)
87(60)
82(60)
92(35)
80(35)
80(70)
73(70)
80(60)
85(50)
77(70)
90(40)
93(35)
85(50)
82(55)
95(15)
92(18)
90(18)
98(10)
95(15)
86(20)
80(25)
90(20)
94(20)
90(20)
95(10)
98(5)
216–218d
184–186e
186–188f
160–163f
243–246g
252–254f
282–285g
177–180f
207–211f
178–180
87–89
2
3-Me
4-Me
4-Cl
3
4
5
3-NO2
2-OH
4-OH
4-OMe
2-OMe
3,4-(OMe)2
H
6
7
5g
5h
5i
8
9
10
11
12
13
14
5j
5k
5l
4-Cl
85–87
4-Me
4-OMe
5m
5n
93(15)
91(15)
78–83
76–80
a
Isolated yield based on aldehyde.
b
c
d
e
f
Under classical heating conditions at 120 8C.
Using microwave irradiation.
Reference [42].
Reference [44].
Reference [45].
g
Reference [46].
Please cite this article in press as: Safari J, Zarnegar Z. Immobilized ionic liquid on superparamagnetic nanoparticles as
an effective catalyst for the synthesis of tetrasubstituted imidazoles under solvent-free conditions and microwave
irradiation. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.01.019

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Fig. 5. Recyclability of IL-MNPs in the reaction of benzil (1 mmol), benzaldehyde (1 mmol), aniline (1 mmol) and ammonium acetate (5 mmol) under
microwave irradiation.
aldehydes and primary aliphatic and aromatic amine
under solvent-free classical heating conditions and using
microwave irradiation are given in Table 2. As shown, the
presence of electron-withdrawing groups on the aromatic
aldehydes and primary amines produced high yields of
1,2,4,5-tetrasubstituted imidazoles. Also, microwave irra-
diation has shown better yields and especially reaction
times.
Most of the products are known and were identified by
comparison of their physical and spectral data with those
of authentic samples. All melting points were compared
satisfactorily with those reported in the literature.
The possibility of recycling the catalyst was examined
using the reaction of benzil, benzaldehyde, aniline and
ammonium acetate under optimized conditions. Upon
completion, the catalyst was separated by an external
magnet and was washed with acetone, and the recycled
catalyst was saved for the next reaction. The recycled
catalyst could be reused six times without any further
treatment. No observation of any appreciable loss in the
catalytic activity of nanocatalyst was observed (Fig. 5). As
observed in Fig. 6, the XRD of the recovered nanocatalyst
was indexed according to the magnetite phase (JCPDS card
No. 79-0417), and so there is no considerable change in its
magnetic phase. Thus, the magnetite nanocatalyst is stable
during the synthesis of tetrasubstituted imidazoles.
In summary, we have been able to introduce an
efficient and environmentally friendly approach for the
synthesis of biologically active tetrasubstituted imida-
zoles by one-pot four-component condensation of benzil,
aldehydes, amines and ammonium acetate using IL-MNPs
as a recyclable catalyst under solvent-free conditions and
microwave irradiation. This method offers several advan-
tages, including high yield, short reaction time, simple
work-up procedure, and ease of separation by an external
magnet.
Fig. 6. X-ray powder diffraction patterns of recovered IL-MNPs after four recovery.
Please cite this article in press as: Safari J, Zarnegar Z. Immobilized ionic liquid on superparamagnetic nanoparticles as
an effective catalyst for the synthesis of tetrasubstituted imidazoles under solvent-free conditions and microwave
irradiation. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.01.019

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3. Conclusions
The black precipitate formed was isolated by magnetic
decantation, exhaustively washed with double-distilled
water until neutrality, and further washed twice with
ethanol and dried at 60 8C under vacuum.
An efficient and environmentally friendly method has
been developed for the synthesis of 1,2,4,5-tetrasubsti-
tuted imidazoles catalyzed by IL-MNPs under solvent-free
conditions and microwave irradiation. This method offers
several advantages, including high yield, short reaction
time, simple work-up procedure, easiness of separation,
and recyclability of the magnetic catalyst, as well as the
ability to tolerate a wide variety of substitutions in the
reagents.
4.2. Synthesis of 1-methyl-3-(3-trimethoxysilylpropyl)-1H-
imidazol-3-ium chloride (IL)
1-Methylimidazole (13.6 mL, 0.17 mol) and (3-chlor-
opropyl) trimethoxysilane (31 mL, 0.17 mol) were refluxed
at 80 8C for three days in the absence of any catalyst and
solvent under Ar atmosphere. The unreacted materials
were washed with diethyl ether (3 ꢃ 8 mL). The diethyl
ether was removed under reduced pressure at room
temperature, followed by heating under high vacuum, to
yield a yellowish viscous liquid. Isolated yield was 98%
[43].
FT-IR (KBr, cmꢂ1): 1656, 1612, 1584. 1H NMR (400 MHz,
CDCl3): dH (ppm): 10.22 (broad, 1H, Are-H), 7.59 (1H, dd,
J = 7.89 and 2.86 Hz, Are-H), 7.26 (1H, dd, J = 7.89 and
2.79 Hz, Are-H), 4.06 (2H, t, J = 7.25 Hz, –NCH2), 3.86 (3H, s,
–NCH3), 3.30 (9H, s, OCH3), 1.74 (2H, tt, J = 7.14 Hz, –CH2),
0.37 (2H, t, J = 7.09 Hz, SiCH2). 13C NMR (100 MHz, CDCl3,
4. Experimental method
High-purity chemical reagents were purchased from
the Merck Chemical Company. All materials were of
commercial reagent grade. Melting points were deter-
mined in open capillaries using an Electrothermal Mk3
apparatus and are uncorrected. 1H NMR and 13C NMR
spectra were recorded with a Bruker DRX-400 spectrome-
ter at 400 and 100 MHz, respectively. NMR spectra were
obtained in DMSO-d6 and CDCl3 solutions and are reported
as parts per million (ppm) downfield from tetramethylsi-
lane as an internal standard. The abbreviations used are:
singlet (s), doublet (d), triplet (t) and multiplet (m). FT-IR
spectra were obtained with potassium bromide pellets in
TMS):
dC = 138.13, 123.34, 121.58, 58.53, 51.66, 36.51,
24.32, 18.2, 7.03. Anal. Calcd.: C, 48.45; H, 8.39; N, 8.69.
Found: C, 48.35; H, 8.32; N, 8.79.
the range 400–4000 cmꢂ1 with
a Perkin-Elmer 550
spectrometer. A mass spectrum was recorded by a QP-
1100EX Shimadzu spectrometer. The element analyses (C,
H, N) were obtained from a Carlo ERBA Model EA 1108
analyzer carried out on Perkin-Elmer 240c analyzer. The
UV-vis measurements were obtained with a GBC cintra 6
UV-vis spectrophotometer. Nanostructures were charac-
terized using a Holland Philips Xpert XRD diffractometer
4.3. Modification of magnetic manoparticles with ionic liquid
to obtain IL-MNPs.
IL-MNPs were prepared using the method described in
the literature [47] with little modification. Typically,
freshly prepared magnetite nanoparticles (2 g) were
suspended in ethanol (95%, 250 mL), and sonicated for
60 min. The resulted suspension was mechanically stirred,
followed by addition of a solution of ethanol (95%, 100 mL)
containing IL (6 g, 18.5 mmol) and concentrated ammonia
(28%, 1 mL). The stirring under Ar was continued for 36 h.
The modified magnetite nanoparticles were magnetically
separated and washed three times with ethanol (95%,
50 mL) and then dissolved in methanol (200 mL) and
stirred mechanically for 30 min. Ether (50 mL) was added
and the modified nanoparticles were magnetically sepa-
rated, washed with ether (50 mL) and dried under vacuum
for 24 h. Typically, 3–3.5 g of brownish-black powder could
be obtained.
(CuK, radiation,
28/min from 108 to 1008 (2
l
= 0.154056 nm), at a scanning speed of
). SEM was performed on a FEI
u
Quanta 200 SEM operated at a 20 kV accelerating voltage.
The samples for SEM were prepared by spreading a small
drop containing nanoparticles onto a silicon wafer and
being dried almost completely in air at room temperature
for 2 h, and then were transferred onto SEM conductive
tapes. The transferred sample was coated with a thin layer
of gold before measurement. Microwave synthesis was
carried out on a Sanle SPII-2 singlemode microwave
reactor (made in Nanjing, China) with infrared tempera-
ture probe and successively adjustable 0–700 W output
power.
4.4. General procedure for the synthesis of 1,2,4,5-
tetrasubstituted imidazoles
4.1. Preparation of the magnetic Fe3O4 nanoparticles
Fe3O4-MNPs were prepared using simple chemical
coprecipitation as described in the literature [41] with
little modification. Typically, 20 mmol of FeCl3ꢀ6H2O and
10 mmol of FeCl2ꢀ4H2O were dissolved in 75 ml of distilled
water in a three-necked round-bottom flask (250 mL)
under Ar atmosphere for 1 h. Thereafter, under rapid
mechanical stirring, 10 ml of NaOH (10 M) were added into
the solution within 30 min with vigorous mechanical
stirring and ultrasound treatment under continuous Ar
atmosphere bubbling. After being rapidly stirred for 1 h,
the resultant black dispersion was heated to 85 8C for 1 h.
A mixture of benzil (1 mmol), ammonium acetate
(5 mmol), aldehyde (1 mmol), primary aliphatic and
aromatic amine (1 mmol) and IL-MNPs (0.1 g) was stirred
with a glass bar at 120 8C or irradiated in a microwave oven
at 100 W for the appropriate time. The progress of reaction
was followed by TLC. After the reaction was completed, the
catalyst was separated by an external magnet and reused
as such for the next experiment. The reaction mixture was
dissolved in acetone and filtered. The filtrate was
concentrated on
a rotary evaporator under reduced
pressure and the solid product obtained was washed with
Please cite this article in press as: Safari J, Zarnegar Z. Immobilized ionic liquid on superparamagnetic nanoparticles as
an effective catalyst for the synthesis of tetrasubstituted imidazoles under solvent-free conditions and microwave
irradiation. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.01.019

G Model
CRAS2C-3704; No. of Pages 9
8
J. Safari, Z. Zarnegar / C. R. Chimie xxx (2013) xxx–xxx
water and recrystallized from acetone–water 9:1 (v/v).
Pure products were obtained in excellent yields, as
summarized in Table 2.
3.81 (t, J = 7.2 Hz, 2H), 7.10–7.30 (m, 12H), 7.46 (d, J = 8 Hz,
2H) ppm; 13C NMR (100 MHz, DMSO-d6): dC 11,5, 24.3,
53.4, 55.9, 117.1, 121.2, 122.8, 123.8, 125.3, 126.2, 126.8,
128.7, 130.1, 132, 132.6, 156.7, 160.8 ppm;, MS (70 eV) m/z
(%): 368 (M+, 59), 337 (52), 323 (59), 309 (48), 234 (46), 31
(30); Anal. Calcd. for C25H24N2O: C 81.49, H 6.56, N 7.60%;
found: C 51.46, H 6.58, N 7.61%.
4.5. Spectral data for new derivatives of 1,2,4,5-
tetrasubstituted imidazoles 5j-n
4.5.1. 2-(3,4-dimethoxyphenyl)-1,4,5-triphenyl-1H-
imidazole (C29H24N2O2, 5j)
Acknowledgments
M.p = 178–180 8C, UV-Vis (EtOH)
lmax: 311 nm; IR
(KBr)
y
: 3045, 1617, 1578 cmꢂ1 1H NMR (400 MHz,
;
We gratefully acknowledge the financial support from
the Research Council of the University of Kashan for
supporting this work by Grant No. 159198/IX.
DMSO-d6): dH 3.61 (s, J = 8.4 Hz, 6H), 6.85 (d, J = 8.8 Hz,
2H), 7.15–7.33 (m, 16H) ppm; 13C NMR (100 MHz, DMSO-
d6): dC 55.9, 112.7, 115.6, 121.2, 122, 122.3, 123.8, 126.9,
128.7, 130.1, 130.5, 132.5, 132.8, 150.4, 152.8,
153.3 ppm; M.S. (70 eV) m/z (%): 432 (M+, 55), 417 (50),
402 (44), 77 (32); Anal. Calcd. for C29H24N2O2: C 87.80, H
5.60, N 6.60%; Found: C 87.82, H 5.58, N 6.61%.
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.crci.2013.01.019.
4.5.2. 2,4,5-triphenyl-1-propyl-1H-imidazole (C24H22N2, 5k)
M.p = 87–89 8C, UV-Vis (EtOH) lmax: 284 nm; IR (KBr) y:
3025, 1597, 1479 cmꢂ1;1H NMR (400 MHz, DMSO-d6) dH
0.51 (t, J = 6.8 Hz, 3H), 1.32 (m, J = 6.8 Hz, 2H), 3.81 (t,
J = 7.2 Hz, 2H), 7.10–7.55 (m, 13H), 7.7 (d, J = 6.8 Hz, 2H)
ppm; 13C NMR (100 MHz, DMSO-d6): dC 11.5, 24, 53.6,
121.5, 122.8, 124, 125.2. 126.2, 126.9, 128.4, 128.8, 130.1,
132.8, 156.7 ppm; M.S. (70 eV) m/z (%): 338 (M+, 68), 323
(65), 309 (57), 295 (43), 15 (40); Anal. Calcd. for C24H22N2:
C 85.17, H 6.55, N 8.28%; found: C 85.14, H 6.56, N 8.30%.
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Please cite this article in press as: Safari J, Zarnegar Z. Immobilized ionic liquid on superparamagnetic nanoparticles as
an effective catalyst for the synthesis of tetrasubstituted imidazoles under solvent-free conditions and microwave
irradiation. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.01.019

G Model
CRAS2C-3704; No. of Pages 9
J. Safari, Z. Zarnegar / C. R. Chimie xxx (2013) xxx–xxx
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an effective catalyst for the synthesis of tetrasubstituted imidazoles under solvent-free conditions and microwave
irradiation. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.01.019