Synthesis of 1,2,4,5-tetrasubstituted imidazoles using 2,6-dimethylpyridinium trinitromethanide {[2,6-DMPyH]C(NO2)3} as a novel nanostructured molten salt and green catalyst

Article abstract of DOI:10.1039/c5ra03241e

2,6-Dimethylpyridinium trinitromethanide {[2,6-DMPyH]C(NO₂)₃}, as a novel nanostructured molten salt, efficiently catalyzed the synthesis of 1,2,4,5-tetrasubstituted imidazole derivatives by a one-pot four-component condensation reac

Full text of DOI:10.1039/c5ra03241e

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PAPER
Synthesis of 1,2,4,5-tetrasubstituted imidazoles
using 2,6-dimethylpyridinium trinitromethanide
{[2,6-DMPyH]C(NO2)3} as a novel nanostructured
molten salt and green catalyst†
Cite this: RSC Adv., 2015, 5, 32933
a
a
b
*
*
Mohammad Ali Zolfigol, Saeed Baghery, Ahmad Reza Moosavi-Zare
and Seyed Mohammad Vahdatc
2,6-Dimethylpyridinium trinitromethanide {[2,6-DMPyH]C(NO2)3}, as a novel nanostructured molten salt,
efficiently catalyzed the synthesis of 1,2,4,5-tetrasubstituted imidazole derivatives by a one-pot four-
component condensation reaction of benzil/benzoin, aldehydes, amine derivatives and ammonium
acetate at room temperature under solvent-free conditions. Some advantages of the presented method
are effective catalysis, excellent cost effectiveness and reusability of the catalyst. {[2,6-DMPyH]C(NO2)3}
Received 20th February 2015
Accepted 24th March 2015
1
was fully characterized by IR, H NMR, 13C NMR and mass spectroscopy, X-ray diffraction patterns (XRD),
DOI: 10.1039/c5ra03241e
scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetry (TG)
and derivative thermogravimetry (DTG) analyses.
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only partially miscible with water (W); moreover, they have been
explored to be favorable alternatives to conventional organic
Introduction
solvents and several new features have been observed in RTMS–
W two-phase systems.12–18 Molten salts have a signicant
potential as electrolyte materials. The molten salts, lately
termed as “ionic liquids”, have attracted considerable attention
in numerous scientic elds.12 Molten salts are convenient
materials for transforming solid salts into liquids; moreover,
signicant efforts have also been made to polymerize molten
salts into solid lms. Various experiments have been carried out
to develop an excellent ion-conductive matrix, and in this regard
the polymerization of molten salts is a promising method to
make highly ion-conductive polymer lms.19,20 In addition,
methane reforming and methanol steam reforming are some
applications of molten salts.21,22
It is well-understood that there is an increasing importance
for more environmentally friendly methods in chemical
synthesis, pharmaceutical industries and heterocyclic
synthesis. This advanced development, termed as ‘Green
Chemistry’ or ‘Sustainable Technology’, requires a paradigm
change from traditional notions of process efficiency, which
concentrate mainly on the yield of product, to one that allocates
economic value, which concentrates on eliminating waste and
the use of toxic and dangerous substances.23a
Multi-component reactions have been developed as an effective
and inuential tool in modern synthetic organic chemistry,
facilitating the facile creation of several new bonds in one-pot
reactions. Imidazole was rst synthesized by Debus in 1858.1
Compounds with the imidazole ring system have many phar-
macological properties and play important roles in many
biochemical procedures.2 There are numerous methods avail-
able for the preparation of highly substituted imidazole deriv-
atives, such as synthesis via a hetero-Cope rearrangement,3
cyclization of sulfonamides with mesoionic 1,3-oxazolium-5-
olates,4 four-component condensation of arylglyoxals, primary
amines, carboxylic acids and isocyanides on Wang resin,5
condensation of 1,2-diones, aldehydes, primary amines and
ammonia6 and reaction of N-(2-oxo)-amides with ammonium
triuoroacetate.7 Furthermore, they have attracted considerable
attention because of their fungicidal,8 antiinammatory,2
analgesic,9 herbicidal10 and anti-thrombotic activities.11
Room-temperature molten salts (RTMSs), correspondingly
termed as room-temperature ionic liquids, are immiscible or
aFaculty of Chemistry, Bu-Ali Sina University, Hamedan 6517838683, Iran. E-mail:
zol@basu.ac.ir; mzolgol@yahoo.com; moosavizare@yahoo.com; Fax: +98
8138257407
Solvent-free reactions, as one of the key green chemistry
protocols, have been demonstrated to be an efficient technique
for various organic transformations without using harmful
organic solvents. Easier work up, decrease in reaction times and
increase in yields are some other potential advantages of using
solvent-free conditions.23b,c
bDepartment of Chemistry, University of Sayyed Jamaleddin Asadabadi, Asadabad
6541835583, Iran
cDepartment of Chemistry, Ayatollah Amoli Branch, Islamic Azad University, P.O. Box
678, Amol, Iran
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c5ra03241e
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Scheme 1 The synthesis of 2,6-dimethylpyridinium trinitromethanide
{[2,6-DMPyH]C(NO2)3} as a nanostructured molten salt catalyst.
Fig. 1 The IR spectrum of trinitromethane (a); 2,6-dimethylpyridine (b);
2,6-dimethylpyridinium trinitromethanide {[2,6-DMPyH]C(NO2)3} (c).
in DMSO-d6 are depicted in Fig. 2 and 3. The peak of the acidic
hydrogen (N–H) in the nanostructured molten salt catalyst
1
conrmed that the peak detected at 9.55 ppm in the H NMR
spectra for {[2,6-DMPyH]C(NO2)3} can be correlated to the
hydrogen of the N–H functionalized 2,6-dimethylpyridinium
salt (Fig. 2).
The 13C NMR spectra of {[2,6-DMPyH]C(NO2)3} provided
another evidence to conrm its structure. The peak presented at
70.25 can be related to the carbon of –C(NO2)3 group in trini-
tromethanide (Fig. 3).
Scheme 2 The synthesis of 1,2,4,5-tetrasubstituted imidazole deriv-
atives in the presence of {[2,6-DMPyH]C(NO2)3} as a novel nano-
structured molten salt.
The thermal gravimetric analysis (TGA) of [2,6-DMPyH]-
C(NO2)3 was also carried out. The related diagrams are dis-
played in Fig. S3 and S4.† The thermal gravimetry (TG) and
differential thermal gravimetric (DTG) analyses showed that the
nanostructured molten salt catalyst was very stable and there
was no evident mass loss before 190 ꢁC. The signicant weight
Life, which utilizes the most complex form of organic
compounds on earth, needs the building of chemical bonds in
an aqueous environment. Subsequently, nature's main use of
water as a multipurpose solvent for organic and green chemistry
should be considered as an example.24
In this work, we have designed a novel molten salt and
catalyst, namely, 2,6-dimethylpyridinium trinitromethanide
{[2,6-DMPyH]C(NO2)3} (Scheme 1), and employed it in a green,
environmentally benign and effective method for the one-pot
four-component synthesis of 1,2,4,5-tetrasubstituted imid-
azole derivatives from the reactions of benzil/benzoin, alde-
hydes, amine derivatives and ammonium acetate under solvent-
free conditions at room temperature (Scheme 2).
ꢁ
loss occurred in the range of 190–500 C, which can be attrib-
uted to the loss of [2,6-DMPyH]C(NO2)3.
Nanostructure of {[2,6-DMPyH]C(NO2)3} as a molten salt
catalyst was studied by X-ray diffractometry (XRD) pattern
(Fig. 4), scanning electron microscopy (SEM) and transmission
electron microscopy (TEM) (Fig. 5). In an attempt to conrm
Results and discussion
Characterization of 2,6-dimethylpyridinium
trinitromethanide {[2,6-DMPyH]C(NO2)3} as a nanostructured
molten salt catalyst
The structure of 2,6-dimethylpyridinium trinitromethanide
{[2,6-DMPyH]C(NO2)3} as a novel nanostructured molten salt
catalyst was studied and identied by FT-IR, 1H NMR, 13C NMR,
mass, TG, DTG, XRD, SEM and TEM analyses.
The IR spectrum of the nanostructured molten salt showed a
broad peak at 3437 cmꢀ1, which corresponds to the N–H
stretching group on the pyridinium ring. Moreover, two peaks
detected at 1634 cmꢀ1 and 1384 cmꢀ1 were related to the
vibrational modes of NO2 bonds (Fig. 1).
Furthermore, the 1H NMR and 13C NMR spectra of 2,6-
Fig. 2 The 1H NMR spectrum of the {[2,6-DMPyH]C(NO2)3} as a novel
dimethylpyridinium trinitromethanide {[2,6-DMPyH]C(NO2)3} nanostructured molten salt catalyst.
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Fig. 5 Scanning electron microscopy (SEM) (a and b) and transmission
electron microscopy (TEM) (c and d) of {[2,6-DMPyH]C(NO2)3} as a
nanostructured molten salt catalyst.
Fig. 3 The 13C NMR spectrum of the {[2,6-DMPyH]C(NO2)3} as a novel
nanostructured molten salt catalyst.
Table 1 The X-ray diffraction (XRD) data for the nanostructured
molten salt catalyst
that {[2,6-DMPyH]C(NO2)3} was suitably synthesized, its XRD
pattern was recorded. As presented in Fig. 4, the XRD patterns
of the nanostructured molten salt catalyst reveal peaks at 2q z
12.10ꢁ, 13.30ꢁ, 16.00ꢁ, 20.40ꢁ, 20.80ꢁ, 22.90ꢁ, 24.30ꢁ, 25.60ꢁ,
26.30ꢁ, 26.70ꢁ, 28.00ꢁ and 34.00ꢁ, which were correspondingly
conrmed by scanning electron microscopy (SEM) and trans-
mission electron microscopy (TEM) (Fig. 5). The peak width
(FWHM), size and inter-planar distance linked to the XRD
pattern of {[2,6-DMPyH]C(NO2)3} were considered in the 2q
range from 12.10ꢁ to 34.00ꢁ, and the results obtained are
summarized in Table 1. Average crystallite size D was consid-
ered using the Debye–Scherrer formula: D ¼ Kl/(b cos q), where
K is the Scherrer constant, l is the X-ray wavelength, b is the
half-maximum peak width, and q is the Bragg diffraction angle.
Consequently, the average size of the nanostructured molten
salt catalyst attained from the abovementioned equation, was
found to be in the range of 16.86–36.72 nm, which is funda-
mentally in accordance with the results obtained by scanning
electron microscopy and transmission electron microscopy
(Fig. 5).
Peak width [FWHM]
(degree)
Inter-planar
distance [nm]
Entry
2q
Size [nm]
1
2
3
4
5
6
7
8
12.10
13.30
16.00
20.40
20.80
22.90
24.30
25.60
26.30
26.70
28.00
34.00
0.22
0.22
0.29
0.41
0.26
0.23
0.35
0.25
0.35
0.40
0.25
0.40
36.68
36.72
16.86
19.83
31.31
35.35
23.24
32.30
23.23
20.35
35.71
20.71
0.730578
0.664917
0.553268
0.434819
0.426548
0.387884
0.365844
0.347554
0.338460
0.333479
0.318284
0.263363
9
10
11
12
Application of 2,6-dimethylpyridinium trinitromethanide
{[2,6-DMPyH]C(NO2)3} as a nanostructured molten salt
catalyst
Aer the synthesis of 2,6-dimethylpyridinium trini-
tromethanide {[2,6-DMPyH]C(NO2)3} as a novel nanostructured
molten salt catalyst, to optimize the reaction conditions, we
conrmed the efficacy of the catalyst in the synthesis of 1,2,4,5-
tetrasubstituted imidazole derivatives (Scheme 2). For this
purpose, as a model, the condensation reaction of benzil/
benzoin, 4-biphenylcarbaldehyde, 4-bromoaniline and ammo-
nium acetate was considered using different amounts of the
catalyst in a temperature range of 25–100 ꢁC under solvent-free
conditions (Table 2). As Table 2 shows, the best results were
achieved when the reaction was attained in the presence of 0.5
mol% of nanostructured molten salt catalyst at room temper-
ature (Table 2, entry 3). In the absence of the catalyst, a low yield
of the product was obtained aer 1 h (Table 2, entries 1 and 2).
Increasing the reaction temperature and catalyst loading did
not improve the rate of the reaction (Table 2, entries 4–11).
Fig. 4 The X-ray diffraction (XRD) pattern for the nanostructured
molten salt catalyst.
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Table 2 Effect of the amount of the catalyst and temperature on the condensation of benzil/benzoin, 4-biphenylcarbaldehyde, 4-bromoaniline
and ammonium acetate under solvent-free conditionsa
Reaction time (min)
Yieldb (%)
Method A
Catalyst loading
(mol%)
Entry
Reaction temperature (ꢁC)
Method A
Method B
Method B
1
2
3
4
5
6
7
8
—
—
0.5
0.5
0.5
0.5
1
1
2
2
5
r.t.
100
r.t.
50
60
60
6
6
6
6
6
6
6
60
60
8
8
8
8
8
8
8
12
15
96
96
96
96
96
96
96
96
95
95
10
12
95
95
95
95
95
95
95
95
93
93
75
100
r.t.
100
r.t.
100
r.t.
100
9
10
11
12
6
7
7
8
10
10
5
a
Reaction conditions. Method A: benzil (1 mmol), aldehydes (1 mmol), amine derivatives (1 mmol), ammonium acetate (1 mmol); method B:
b
benzoin (1 mmol), aldehydes (1 mmol), amine derivatives (1 mmol), ammonium acetate (1 mmol). Isolated yield.
To compare the competence of the solution versus solvent- {[2,6-DMPyH]C(NO2)3}, as a novel nanostructured molten salt
free conditions, a mixture of benzil/benzoin, 4-biphenyl- catalyst. The results are presented in Table 4. The substituents
carbaldehyde, 4-bromoaniline and ammonium acetate, as the on the aromatic ring have strong effects on the yields under
model reaction, in the presence of 0.5 mol% of [2,6-DMPyH]- these reaction conditions. All the aromatic aldehydes and
C(NO2)3 as a novel nanostructured molten salt in various amines containing electron-releasing substituents and electron-
solvents, such as H2O, C2H5OH, CH3CN, CH3CO2Et, CH2Cl2, withdrawing substituents on their aromatic ring afforded the
toluene and benzene, was considered at room temperature. The related products in high to excellent yields and in short reaction
results are summarized in Table 3. As can be seen in Table 3, times. The reaction times of aromatic aldehydes with electron
solvent-free was the best condition in this reaction.
withdrawing groups were rather faster than those with the
Stimulated by the good results and to conrm the scope of electron donating groups, but the reaction times of the aromatic
this procedure, various 1,2,4,5-tetrasubstituted imidazole amines with electron releasing groups were faster than those
derivatives were synthesized from the four-component with electron withdrawing groups. Moreover, the reaction in the
condensation reaction of benzil/benzoin, aromatic aldehydes, presence of benzil is faster than that in the presence of benzoin.
amine derivatives and ammonium acetate under solvent-free
conditions at room temperature in the presence of
The suggested catalytic methods are shown in Fig. S5,†
which are in accordance with the literature reports.25–29 The
a
catalytic amount of 2,6-dimethylpyridinium trinitromethanide nanostructured {[2,6-DMPyH]C(NO2)3} has one acidic hydrogen
that can participate in hydrogen bonding. Subsequently,
both benzil/benzoin and aromatic aldehydes were activated by
{[2,6-DMPyH]C(NO2)3} to react with nucleophiles. As can be
realized in Scheme 3, the nucleophilic attack of amine (2) on the
Table 3 The effect of different solvents on the reaction of benzil/
benzoin, 4-biphenylcarbaldehyde, 4-bromoaniline and ammonium
acetate catalyzed by {[2,6-DMPyH]C(NO2)3} as a novel nanostructured
activated carbonyl of aldehydes (7) results in the formation of
imine (10), which can be monitored by the nucleophilic attack
of the in situ-produced ammonia from ammonium acetate to
the imine (10), giving the intermediate (11). From the conden-
sation of the intermediate (11) with the activated carbonyl of
benzil/benzoin (12) and its dehydration, analogous 1,2,4,5-tet-
rasubstituted imidazole derivatives (6) are produced. Moreover,
the formation of various hydrogen bonds between the
substrates and catalyst could simplify a more efficient catalysis
in the reaction. High reaction rates could similarly be inu-
enced by the nanostructured catalyst, as discussed in this study.
Because of the appropriate symmetry of these compounds
via 1,3-aryl sigmatropic symmetry,30,31 almost half of the signals
were observed in 1H NMR and 13C NMR spectra (Scheme 3).
Furthermore, the reusability of the nanostructured molten
salt catalyst was conrmed upon the condensation of benzil/
molten salt (0.5 mol%) at room temperaturea
Reaction time (min)
Yieldb (%)
Entry Solvent
Method A Method B Method A Method B
1
2
3
4
5
6
7
8
Solvent-free
H2O
6
10
10
15
25
45
60
120
8
15
15
20
30
45
60
120
96
95
95
93
93
25
20
20
95
93
93
90
90
20
15
15
C2H5OH
CH3CN
CH3CO2Et
CH2Cl2
Toluene
Benzene
a
Reaction conditions. Method A: benzil (1 mmol), aldehydes (1 mmol),
amine derivatives (1 mmol), ammonium acetate (1 mmol); method B:
benzoin (1 mmol), aldehydes (1 mmol), amine derivatives (1 mmol),
ammonium acetate (1 mmol). b Isolated yield.
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Table 4 Synthesis of 1,2,4,5-tetrasubstituted imidazole derivatives in the presence of 0.5 mol% {[2,6-DMPyH]C(NO2)3} as a nanostructured
molten salt catalysta
Method A
Method B
M.p (ꢁC)
[Ref.]
Entry
Aldehyde
R0
Time (min)
Yieldb (%)
Time (min)
Yieldb (%)
1
2
3
4
5
6
7
8
4-Nitrobenzaldehyde
4-Nitrobenzaldehyde
4-Nitrobenzaldehyde
4-CH3
4-Cl
4-Br
4-CH3
4-Cl
4-Br
4-Cl
4-Br
4-Cl
4-Br
4-Br
4-Br
4-Br
4-Br
1
3
2
5
8
7
10
8
12
10
10
6
98
97
98
96
95
95
92
93
92
93
93
94
96
95
5
10
8
96
95
96
95
93
94
91
92
91
92
92
93
95
94
218–220 [25
235–237
]
262–264
4-Chlorobenzaldehyde
4-Chlorobenzaldehyde
4-Chlorobenzaldehyde
2,4-Dichlorobenzaldehyde
2,4-Dichlorobenzaldehyde
4-Methylbenzaldehyde
4-Methylbenzaldehyde
4-Methoxybenzaldehyde
4-Chloro-3-nitrobenzaldehyde
4-Biphenylcarbaldehyde
Naphthalene-2-carbaldehyde
7
224–226 [26
209–211 [25
217–219
]
]
12
10
15
12
18
15
15
10
8
246–248
251–253
9
221–223 [26
228–230
]
10
11
12
13
14
220–222
223–225
281–283
253–255
6
7
10
a
Reaction conditions. Method A: benzil (1 mmol), aldehydes (1 mmol), amine derivatives (1 mmol), ammonium acetate (1 mmol); method B:
b
benzoin (1 mmol), aldehydes (1 mmol), amine derivatives (1 mmol), ammonium acetate (1 mmol). Isolated yield.
Conclusions
In summary, a novel, green and eco-friendly nanostructured
molten salt catalyst, namely, 2,6-dimethylpyridinium trini-
tromethanide {[2,6-DMPyH]C(NO2)3}, was designed, assessed
1
and completely characterized by IR, H NMR, 13C NMR, mass
spectroscopy, thermal gravimetric analysis (TGA), differential
thermal gravimetric (DTG), X-ray diffraction patterns (XRD),
scanning electron microscopy (SEM) and transmission electron
microscopy (TEM) analyses. The catalytic application of [2,6-
DMPyH]C(NO2)3 was considered in the synthesis of 1,2,4,5-
tetrasubstituted imidazole derivatives by a four-component
Scheme
3 The 1,3-aryl sigmatropic symmetry of 1,2,4,5-tetra-
condensation reaction of benzil/benzoin, aldehydes, amine
derivatives and ammonium acetate under solvent-free condi-
tions at room temperature. Additional studies showed that the
nanostructured molten salt acidity plays a key role in the cata-
lyzed reactions. Some different signicant advantages of this
work are its reasonably cleaner reaction prole, low cost, high
yield, short reaction time, reusability of the nanostructured
catalyst, simplicity of product isolation and agreement with the
green chemistry processes.
substituted imidazole derivatives.
benzoin, 4-biphenylcarbaldehyde, 4-bromoaniline and ammo-
nium acetate. At the end of the reaction, ethyl acetate was added
to the reaction mixture and heated to extract the product and
the remaining starting materials. This solution was then
washed with water to separate the catalyst from other materials
(the product is soluble in hot ethyl acetate, while the nano-
structured molten salt catalyst is soluble in water). The aqueous
layer was decanted, separated and used for alternative reactions
aer removing the water. It was found that the catalytic activity
of the catalyst was restored within the limits of the experimental
errors for ve continuous runs (Fig. S6†). The recycled catalyst
Experimental
General procedure for the preparation of the nanostructured
molten salt catalyst 2,6-dimethylpyridinium
trinitromethanide {[2,6-DMPyH]C(NO2)3}
was also characterized by FTIR, H NMR and 13C NMR spectra
1
aer its application in the reaction. These spectra were identical
to those of the fresh catalyst (Fig. S7–S9†). Moreover, the size of
the catalyst was assessed aer the recovery procedure by scan-
ning electron microscopy (SEM) and transmission electron
microscopy (TEM) analyses. This study showed that the catalyst
was recovered in a nano-size. The related images are shown in
Fig. S10.†
To a round-bottomed ask (50 mL) containing 2,6-dime-
thylpyridine (3 mmol; 0.321 g) in CH3CN (5 mL), trinitro-
methane (3.1 mmol; 0.468 g) was added dropwise and heated
over a period of 60 min at room temperature. Subsequently, the
solvent was removed by distillation under reduced pressure,
and the product was dried under vacuum at 80 ꢁC for 120 min. A
red solid was prepared (Scheme 1) quantitatively.
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2,6-Dimethylpyridinium trinitromethanide {[2,6-DMPyH]-
2-(4-Chlorophenyl)-4,5-diphenyl-1-p-tolyl-1H-imidazole (Table 4,
C(NO2)3}. M.p: 137–139 ꢁC; yield: 98% (0.759 g); spectral data: IR entry 4). White solid; M.p: 224–226 ꢁC; yield: (method A: 96%,
(KBr): n 3437, 3054, 1634, 1384, cmꢀ1 1H NMR (400 MHz, method B: 95%); IR (KBr): n 1624, 1580, 1565, 1504 cmꢀ1; 1H NMR
;
DMSO-d6): d 2.69 (s, 6H, –CH3), 7.74 (d, 2H, J ¼ 8.0 Hz, –CH); (400 MHz, CDCl3): d 2.40 (s, 3H, –CH3), 7.17 (t, 3H, J ¼ 8.4 Hz, ArH),
8.37 (t, 1H, J ¼ 7.8 Hz, –CH), 9.55 (brs, 1H, –NH); 13C NMR (100 7.24 (t, 3H, J ¼ 8.0 Hz, ArH), 7.48 (d, 6H, J ¼ 8.8 Hz, ArH), 7.87 (d,
MHz, DMSO-d6): d 19.7, 70.2, 125.0, 146.0, 153.5; MS: m/z ¼ 258 6H, J ¼ 8.4 Hz, ArH); 13C NMR (100 MHz, CDCl3): d 21.0, 119.7,
[M]+, 259 [M + H]+.
123.3, 125.5, 125.9, 126.3, 127.7, 128.1, 128.6, 128.9, 129.5, 138.5,
142.5, 144.9, 149.9.
1,2-Bis(4-chlorophenyl)-4,5-diphenyl-1H-imidazole (Table 4,
entry 5). Yellow solid; M.p: 209–211 ꢁC; yield: (method A: 95%,
General procedure for the synthesis of 1,2,4,5-tetrasubstituted
imidazole derivatives
1
method B: 93%); IR (KBr): n 1625, 1565, 1489, 1084 cmꢀ1; H
To a mixture of benzil/benzoin (1 mmol), aromatic aldehydes (1
mmol), amine derivatives (1 mmol) and ammonium acetate (1
mmol) in a test tube, 2,6-dimethylpyridinium trinitromethanide
was added as a novel nanostructured molten salt catalyst (0.5
mol%), and the subsequent mixture was stirred magnetically
under solvent-free conditions at room temperature. Aer the
completion of the reaction, as monitored by TLC with n-hexane–
ethyl acetate (5 : 2), ethyl acetate (10 mL) was added to the
reaction mixture, stirred and reuxed for 3 min, washed with
water (10 mL) and decanted to separate the catalyst from the
other materials (the reaction mixture was soluble in hot ethyl
acetate, while the nanostructured molten salt catalyst was
soluble in water). The aqueous layer was decanted and the
catalyst was separated aer removing the water. The remaining
catalyst was used for alternative reactions. The organic layer was
evaporated and the crude product was puried by recrystalli-
zation from ethanol–water (10 : 1). In this study, the nano-
structured molten salt catalyst was recycled and reused ve
times without signicant loss of its catalytic activity.
NMR (400 MHz, CDCl3): d 7.18 (d, 6H, J ¼ 8.8 Hz, ArH), 7.39 (t,
3H, J ¼ 8.8 Hz, ArH), 7.49 (t, 3H, J ¼ 8.4 Hz, ArH), 7.87 (d, 6H, J ¼
8.4 Hz, ArH); 13C NMR (100 MHz, CDCl3): d 111.5, 124.7, 124.8,
126.2, 126.3, 128.5, 128.6, 129.1, 129.2, 138.4, 138.5, 142.3,
142.7, 145.8.
1-(4-Bromophenyl)-2-(4-chlorophenyl)-4,5-diphenyl-1H-imid-
azole (Table 4, entry 6). White solid; M.p: 217–219 ꢁC; yield:
(method A: 95%, method B: 94%); IR (KBr): n 1622, 1567, 1488,
1089 cmꢀ1; 1H NMR (400 MHz, CDCl3): d 7.12 (d, 6H, J ¼ 5.8 Hz,
ArH), 7.49 (t, 3H, J ¼ 5.4 Hz, ArH), 7.54 (t, 3H, J ¼ 5.8 Hz, ArH),
7.86 (d, 6H, J ¼ 5.4 Hz, ArH); 13C NMR (100 MHz, CDCl3): d 104.0,
111.7, 112.2, 115.5, 119.6, 122.6, 129.2, 130.0, 132.3, 134.4, 137.7,
150.6, 159.2, 177.2; MS: m/z ¼ 484 [M]+.
1-(4-Chlorophenyl)-2-(2,4-dichlorophenyl)-4,5-diphenyl-1H-
imidazole (Table 4, entry 7). White solid; M.p: 246–248 ꢁC;
yield: (method A: 92%, method B: 91%); IR (KBr): n 1614, 1576,
1
1486, 1384, 1091 cmꢀ1; H NMR (400 MHz, CDCl3): d 7.37 (t,
3H, J ¼ 5.8 Hz, ArH), 7.50 (t, 3H, J ¼ 5.8 Hz, ArH), 7.59 (d, 6H, J
¼ 5.6 Hz, ArH), 7.80 (s, 1H, ArH), 8.16 (d, 4H, J ¼ 8.4 Hz, ArH);
13C NMR (100 MHz, CDCl3): d 110.0, 112.9, 117.1, 117.4, 122.5,
123.1, 124.6, 125.5, 129.4, 133.5, 134.1, 142.7, 152.5, 155.5,
158.7, 158.9; MS: m/z ¼ 474 [M]+.
Spectral data analysis for compounds
2-(4-Nitrophenyl)-4,5-diphenyl-1-p-tolyl-1H-imidazole (Table 4,
1-(4-Bromophenyl)-2-(2,4-dichlorophenyl)-4,5-diphenyl-1H-
imidazole (Table 4, entry 8). White solid; M.p: 251–253 ꢁC;
yield: (method A: 93%, method B: 92%); IR (KBr): n 1612, 1585,
ꢁ
entry 1). Yellow solid; M.p: 218–220 C; yield: (method A: 98%,
method B: 96%); IR (KBr): n 1598, 1505, 1338 cmꢀ1; 1H NMR (400
MHz, CDCl3): d 2.42 (s, 3H, –CH3), 7.23 (t, 3H, J ¼ 8.4 Hz, ArH),
7.28 (t, 3H, J ¼ 6.4 Hz, ArH), 8.10 (d, 6H, J ¼ 8.8 Hz, ArH), 8.36 (d,
6H, J ¼ 8.8 Hz, ArH); 13C NMR (100 MHz, CDCl3): d 21.1, 112.1,
112.7, 112.8, 112.9, 113.4, 128.2, 128.4, 136.3, 136.5, 145.0, 149.1,
149.2, 151.2, 151.3.
1
1482, 1365, 1096 cmꢀ1; H NMR (400 MHz, CDCl3): d 7.30 (t,
3H, J ¼ 5.8 Hz, ArH), 7.60 (d, 6H, J ¼ 5.4 Hz, ArH), 7.64 (t, 3H, J
¼ 5.8 Hz, ArH), 7.80 (s, 1H, ArH), 8.16 (d, 4H, J ¼ 8.4 Hz, ArH);
13C NMR (100 MHz, CDCl3): d 123.2, 123.4, 123.7, 124.4, 124.6,
125.5, 127.6, 127.7, 128.9, 129.5, 132.7, 133.2, 134.3, 136.4,
143.2, 152.6; MS: m/z ¼ 518 [M]+.
1-(4-Chlorophenyl)-2-(4-nitrophenyl)-4,5-diphenyl-ꢁ1H-imid-
azole (Table 4, entry 2). Yellow solid; M.p: 218–220 C; yield:
(method A: 97%, method B: 95%); IR (KBr): n 1624, 1597, 1515,
1343 cmꢀ1; 1H NMR (400 MHz, CDCl3): d 7.25 (t, 3H, J ¼ 7.2 Hz,
ArH), 7.43 (t, 3H, J ¼ 8.8 Hz, ArH), 8.10 (d, 6H, J ¼ 8.8 Hz, ArH),
8.36 (d, 6H, J ¼ 8.8 Hz, ArH); 13C NMR (100 MHz, CDCl3): d
112.0, 112.6, 112.7, 112.9, 113.4, 128.3, 128.4, 136.3, 136.7,
144.6, 149.0, 149.2, 151.2, 151.3; MS: m/z ¼ 451 [M]+.
1-(4-Chlorophenyl)-4,5-diphenyl-2-p-tolyl-1H-imidazole (Table 4,
entry 9). Yellow solid; M.p: 221–223 ꢁC; yield: (method A: 92%,
method B: 91%); IR (KBr): n 1623, 1598, 1516, 1338, 1106 cmꢀ1; 1H
NMR (400 MHz, CDCl3): d 2.42 (s, 3H, –CH3), 7.23 (t, 3H, J ¼ 8.4 Hz,
ArH), 7.27 (t, 3H, J ¼ 8.4 Hz, ArH), 8.11 (d, 6H, J ¼ 8.8 Hz, ArH), 8.36
(d, 6H, J ¼ 8.8 Hz, ArH); 13C NMR (100 MHz, CDCl3): d 21.1, 113.4,
114.0, 115.0, 118.0, 118.1, 134.7, 137.0, 151.8, 152.6, 152.8, 152.9,
153.1, 160.1, 164.6.
1-(4-Bromophenyl)-2-(4-nitrophenyl)-4,5-diphenyl-ꢁ1H-imid-
azole (Table 4, entry 3). Yellow solid; M.p: 262–264 C; yield:
(method A: 98%, method B: 96%); IR (KBr): n 1624, 1596, 1513,
1340 cmꢀ1; 1H NMR (400 MHz, CDCl3): d 7.18 (t, 3H, J ¼ 5.8 Hz,
ArH), 7.58 (t, 3H, J ¼ 5.6 Hz, ArH), 8.11 (d, 6H, J ¼ 8.8 Hz, ArH),
8.36 (d, 6H, J ¼ 8.8 Hz, ArH); 13C NMR (100 MHz, CDCl3): d
124.8, 124.9, 126.3, 128.1, 128.2, 128.5, 128.6, 129.1, 138.5,
142.2, 145.6, 152.1, 152.6, 167.6; MS: m/z ¼ 495 [M]+.
1-(4-Bromophenyl)-4,5-diphenyl-2-p-tolyl-1H-imidazole (Table 4,
ꢁ
entry 10). White solid; M.p: 228–230 C; yield: (method A: 93%,
method B: 92%); IR (KBr): n 1622, 1605, 1474, 1165 cmꢀ1; 1H NMR
(400 MHz, CDCl3): d 2.45 (s, 3H, –CH3), 7.11 (t, 3H, J ¼ 8.8 Hz, ArH),
7.32 (d, 6H, J ¼ 8.0 Hz, ArH), 7.53 (t, 3H, J ¼ 8.4 Hz, ArH), 7.81 (d,
6H, J ¼ 8.0 Hz, ArH); 13C NMR (100 MHz, CDCl3): d 21.7, 127.5,
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127.6, 128.3, 128.8, 129.3, 129.5, 137.6, 138.2, 140.7, 140.8, 145.0,
145.9, 147.3, 152.0; MS: m/z ¼ 464 [M]+.
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(method A: 93%, method B: 92%); IR (KBr): n 1620, 1605, 1572,
1508, 1254, 1167 cmꢀ1; 1H NMR (400 MHz, CDCl3): d 3.90 (s, 3H,
–OCH3), 7.02 (d, 6H, J ¼ 8.8 Hz, ArH), 7.10 (t, 3H, J ¼ 8.8 Hz, ArH),
7.52 (t, 3H, J ¼ 8.8 Hz, ArH), 7.87 (d, 6H, J ¼ 8.8 Hz, ArH); 13C NMR
(100 MHz, CDCl3): d 55.5, 110.0, 115.3, 115.4, 115.5, 123.3, 126.2,
126.3, 126.4, 128.1, 129.3, 133.8, 141.3, 144.4, 144.8; MS: m/z ¼ 480
[M]+.
1-(4-Bromophenyl)-2-(4-chloro-3-nitrophenyl)-4,5-diphenyl-1H-
imidazole (Table 4, entry 12). Yellow solid; M.p: 223–225 ꢁC; yield:
(method A: 94%, method B: 93%); IR (KBr): n 1622, 1599, 1557,
1528, 1353 cmꢀ1; 1H NMR (400 MHz, CDCl3): d 7.16 (t, 3H, J ¼ 7.2
Hz, ArH), 7.57 (t, 3H, J ¼ 5.6 Hz, ArH), 7.70 (d, 6H, J ¼ 8.4 Hz,
ArH), 8.08 (d, 4H, J ¼ 5.2 Hz, ArH), 8.43 (s, 1H, ArH); 13C NMR (100
MHz, CDCl3): d 104.6, 112.7, 112.9, 113.5, 120.7, 122.6, 125.3,
129.6, 132.4, 132.5, 132.6, 135.9, 149.5, 156.2, 167.6, 174.8; MS: m/
z ¼ 529 [M]+.
2-(Biphenyl-4-yl)-1-(4-bromophenyl)-4,5-diphenyl-1H-imid-
azole (Table 4, entry 13). Yellow solid; M.p: 281–283 ꢁC; yield: 11 A. P. Philips, H. L. White and S. Rosen, Eur. Pat. Appl., 1983,
(method A: 96%, method B: 95%); IR (KBr): n 1620, 1604, 1485,
58, 890.
1
1166 cmꢀ1; H NMR (400 MHz, CDCl3): d 7.16 (t, 3H, J ¼ 7.2 12 T. Welton, Chem. Rev., 1999, 99, 2071.
Hz, ArH), 7.44 (t, 3H, J ¼ 7.8 Hz, ArH), 7.50 (d, 2H, J ¼ 8.0 Hz, 13 K. R. Seddon, A. Stark and M. J. Torres, Pure Appl. Chem.,
ArH), 7.56 (t, 3H, J ¼ 8.4 Hz, ArH), 7.69 (d, 4H, J ¼ 8.4 Hz, ArH),
2000, 72, 2275.
7.75 (d, 4H, J ¼ 8.4 Hz, ArH), 8.00 (d, 4H, J ¼ 8.4 Hz, ArH); 13
C
14 J. Dupont, R. F. de Souza and P. A. Z. Suarez, Chem. Rev.,
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NMR (100 MHz, CDCl3): d 116.1, 116.2, 116.3, 116.4, 117.2,
117.4, 123.2, 124.6, 125.5, 129.6, 132.8, 134.2, 143.3, 152.5, 15 J. G. Huddleston, H. D. Willauer, R. P. Swatloski, A. E. Visser
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and R. D. Rogers, Chem. Commun., 1998, 1765.
1-(4-Bromophenyl)-2-(naphthalen-2-yl)-4,5-diphenyl-ꢁ1H-imid- 16 A. E. Visser, R. P. Swatloski and R. D. Rogers, Green Chem.,
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(method A: 95%, method B: 94%); IR (KBr): n 1617, 1574, 1484, 17 M. L. Dietz and J. A. Dzielawa, Chem. Commun., 2001, 2124.
1331, 1068 cmꢀ1; 1H NMR (400 MHz, CDCl3): d 7.19 (d, 4H, J ¼ 18 A. E. Visser, J. D. Holbrey and R. D. Rogers, Chem. Commun.,
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1H, ArH); 13C NMR (100 MHz, CDCl3): d 123.1, 123.2, 123.8, 20 Polymer Electrolytes Reviews, ed. J. R. MacCallum and C. A.
123.9, 124.0, 126.1, 126.8, 126.9, 127.1, 127.9, 128.9, 129.6, 129.7, Vincent, Elsevier, London, 1989, vol. 2.
129.8, 132.9, 134.2, 134.7, 134.8, 138.1, 143.5; MS: m/z ¼ 500 21 N. Gokon, Y. Oku, H. Kaneko and Y. Tamaura, Sol. Energy,
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Acknowledgements
The authors gratefully acknowledge the Bu-Ali Sina University
Research Council and Center of Excellence in Development of
Environmentally Friendly Methods for Chemical Synthesis
(CEDEFMCS) for providing support to this work.
Notes and references
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A. Zare and V. Khakyzadeh, Appl. Catal., A, 2011, 400, 70;
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32940 | RSC Adv., 2015, 5, 32933–32940
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