Sulfated tin oxide: A reusable and highly efficient heterogeneous catalyst for the synthesis of 2,4,5-triaryl-1H-imidazole derivatives

Article abstract of DOI:10.1080/00397911.2010.541744

One-pot, three-component condensation of benzil/benzoin, substituted aromatic aldehydes, and ammonium acetate in an ethanol-water (1:1, v/v) solvent system using sulfated tin oxide catalyst under reflux condition afforded corresponding 2,4,5-triaryl-1H-imidazoles in excellent yield. The remarkable advantages offered by this method include green and reusable catalyst, mild reaction conditions, fast reaction rate, and excellent yield of products. This novel methodology maintains atom economy and an environmentally friendly approach. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397911.2010.541744

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Sulfated Tin Oxide: A Reusable and
Highly Efficient Heterogeneous Catalyst
for the Synthesis of 2,4,5-Triaryl-1H-
imidazole Derivatives
Satish A. Dake a , Mahesh B. Khedkar a , Ghanshyam S. Irmale a
,
Suhas J. Ukalgaonkar a , Vinod V. Thorat b , Suhas A. Shintre b
Rajendra P. Pawar b
&
a Organic Synthesis Laboratory, Department of Chemistry,
Dnyanopasak College, Parbhani, India
b Department of Chemistry, Deogiri College, Aurgangabad, India
Accepted author version posted online: 21 Oct 2011.Version of
record first published: 25 Jan 2012.
To cite this article: Satish A. Dake , Mahesh B. Khedkar , Ghanshyam S. Irmale , Suhas J.
Ukalgaonkar , Vinod V. Thorat , Suhas A. Shintre & Rajendra P. Pawar (2012): Sulfated Tin Oxide: A
Reusable and Highly Efficient Heterogeneous Catalyst for the Synthesis of 2,4,5-Triaryl-1H-imidazole
Derivatives, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 42:10, 1509-1520
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Synthetic Communications1, 42: 1509–1520, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.541744
SULFATED TIN OXIDE: A REUSABLE AND HIGHLY
EFFICIENT HETEROGENEOUS CATALYST FOR THE
SYNTHESIS OF 2,4,5-TRIARYL-1H-IMIDAZOLE
DERIVATIVES
Satish A. Dake,1 Mahesh B. Khedkar,1 Ghanshyam S. Irmale,1
Suhas J. Ukalgaonkar,1 Vinod V. Thorat,2 Suhas A. Shintre,2
and Rajendra P. Pawar2
1Organic Synthesis Laboratory, Department of Chemistry, Dnyanopasak
College, Parbhani, India
2Department of Chemistry, Deogiri College, Aurgangabad, India
GRAPHICAL ABSTRACT
Abstract One-pot, three-component condensation of benzil/benzoin, substituted aromatic
aldehydes, and ammonium acetate in an ethanol–water (1:1, v=v) solvent system using sul-
fated tin oxide catalyst under reflux condition afforded corresponding 2,4,5-triaryl-1H-imi-
dazoles in excellent yield. The remarkable advantages offered by this method include green
and reusable catalyst, mild reaction conditions, fast reaction rate, and excellent yield of pro-
ducts. This novel methodology maintains atom economy and an environmentally friendly
approach.
Keywords Benzil=benzoin; ethanol; sulfated tin oxide; 2,4,5-triaryl-1H-imidazole; water
INTRODUCTION
2,4,5-Triaryl-1H-imidazole compounds have gained remarkable importance
because of their widespread biological activities. The heterocyclic imidazole ring is
one of the most important structures found in a large number of natural products
and pharmacologically active compounds such as antiulcerative agent cimetidine,
the proton pump inhibitor omeprazole, and the benzodiazepine antagonist flumaze-
nil. Trifenagrel, a 2,4,5-triaryl-1H-imidazole, reduces the platelet aggregation in
several animal species and humans.
Received October 17, 2010.
Address correspondence to Rajendra P. Pawar, Department of Chemistry, Deogiri College, Station
Road, Aurgangabad 431 005, India. E-mail: rppawar@yahoo.com
1509

1510
S. A. DAKE ET AL.
These compounds also play an important role in biochemical processes.[1] Imi-
dazole derivatives show estrogen receptor and cytotoxic inhibitory activities of
cyclooxygenase,[2] antifungal,[3] antihelmitic,[4] and pesticidal and herbicidal proper-
ties. Substituted imidazole possesses potentially novel therapeutic activities[5] and
absolute controlled processes.[6] In addition, they also show analgesic,[7] fungicidal,[8]
anti-inflammatory,[9] and antithrombotic activities.[10] Despite their importance from
pharmacological and synthetic points of view, few methods for the preparation of
trisubstituted imidazoles have been reported. These include the condensation of
1,2-diketone, aldehydes, and ammonium acetate in the presence of H3PO4,[11]
H2SO4,[12] AcOH,[13] silica sulfuric acid,[14] para-toluenesulfonic acid (p-TSA),[15]
boric acid,[16] and room-temperature ionic liquid,[17] as well as palladium-catalyzed
multicomponent coupling,[18] palladium-catalyzed cyclization,[19] organocatalysis,[20]
and solid-support synthesis.[21] Recently, substituted imidazoles have been synthe-
sized using catalyst L-proline[22] and InCl3 ꢀ H2O.[23]
Sulfated tin oxide was found to be efficient and suitable in aldol condensation
reactions, particularly for benzoylation.[24] In continuation of our work by grinding
[25a]
with I2
and microwave irradiation using solvent polyethylene glycol,[25b] herein
we report a new methodology for the synthesis of 2,4,5-triaryl-1H-imidazole using
sulfated tin oxide (STO) catalyst and inexpensive starting materials benzil=benzoin,
aromatic aldehydes, and ammonium acetate in a ethanol–water (1:1, v=v) system
(Scheme 1).
RESULTS AND DISCUSSION
In this protocol, benzil=benzoin and ammonium acetate were refluxed with
substituted aromatic aldehydes in the presence of sulfated tin oxide catalyst for an
appropriate time (30–55 min) to afford substituted 2,4,5-triaryl-1H-imidazoles
(Tables 1 and 2). More important, it can be recovered and reused several times with-
out any change in its efficiency. The reaction was carried out using 1:1.2:4 molar
ratios of reactants in ethanol–water (1:1, v=v) medium. In a similar fashion, a variety
of substituted 2,4,5-triaryl-1H-imidazoles were also synthesized using different alde-
hydes. The time required for the condensation was considerably reduced, and yields
of the products were excellent as compared to the reported methods. This evidence
indicates that the catalyst efficiently makes the condensation reaction much faster
with good yield of products.
To determine the role of the catalyst, the same reaction was carried out in the
absence of catalyst. The desired product was not obtained in 4–5 h. It indicates that
the catalyst exhibits high catalytic activity in this transformation. The reaction
Scheme 1. Synthesis of 2,4,5-triaryl-1H-imidazole derivatives. (Figure is provided in color online.)

SULFATED TIN OXIDE
1511
Table 1. One-pot synthesis of 2,4,5-triaryl-1H-imidazoles using benzil, aromatic aldehydes, and
ammonium acetate in ethanol–water (1:1, v=v) system using sulfated tin oxide (10 mol%)
Solvent
system
(1:1, v=v)
Reaction
time
(min)
MP
Yields (ꢁC)
Entries
Reactants (2)
Products (4)
(%)a
[lit.]
Ethanol–
water
(1:1, v=v)
276 ꢁC
[276–
278]16
a
30
92
Ethanol–
water
(1:1, v=v)
269 ꢁC
[268–
b
35
30
40
95
89
92
270]16
Ethanol–
water
(1:1, v=v)
229 ꢁC
[230–
233]15
c
Ethanol–
water
(1:1, v=v)
d
260 ꢁC
Ethanol–
water
(1:1, v=v)
201 ꢁC
[200–
e
45
30
89
90
203]15
Ethanol–
water
(1:1, v=v)
f
220 ꢁC
(Continued )

1512
S. A. DAKE ET AL.
Table 1. Continued
Solvent
system
(1:1, v=v)
Reaction
time
(min)
MP
Yields (ꢁC)
Entries
Reactants (2)
Products (4)
(%)a
[lit.]
Ethanol–
water
(1:1, v=v)
g
30
91
261 ꢁC
Ethanol–
water
(1:1, v=v)
263 ꢁC
[260–
h
30
35
30
94
86
89
262]16
Ethanol–
water
(1:1, v=v)
220 ꢁC
[220–
221]16
i
Ethanol–
water (1:1,
v=v)
195 ꢁC
[195–
196]16
j
Ethanol–
water
(1:1, v=v)
k
40
35
84
82
230 ꢁC
Ethanol–
water
(1:1, v=v)
l
262 ꢁC
aYield of isolated products.
proceeds in solvent water, which is nontoxic, imflammable, inexpensive, and abun-
dantly available. However, the use of only water in this reaction gave moderate yield
of products (73%). Therefore, we studied the effects of different organic solvents on
the synthesis of 2,4,5-triaryl-1H-imidazole derivatives, and the results are summarized

SULFATED TIN OXIDE
1513
Table 2. One-pot synthesis of 2,4,5-triaryl-1H-imidazoles using benzoin, aromatic aldehydes, and
ammonium acetate in ethanol–water (1:1, v=v) system using sulfated tin oxide (10 mol%)
Solvent
system
(1:1, v=v)
Reaction
time
(min)
MP
Yields (ꢁC)
Entries
Reactants (2)
Products (4)
(%)a
[lit.]
Ethanol–
water
(1:1, v=v)
201 ꢁC
[200–
a
35
30
30
35
40
85
203]15
Ethanol–
water
(1:1, v=v)
b
87
90
98
91
261 ꢁC
Ethanol–
water
(1:1, v=v)
195 ꢁC
[195–
196]16
c
Ethanol–
water
(1:1, v=v)
d
203 ꢁC
Ethanol–
water
(1:1, v=v)
255 ꢁC
[256–
257]15
e
(Continued )

1514
S. A. DAKE ET AL.
Table 2. Continued
Solvent
system
(1:1, v=v)
Reaction
time
(min)
MP
Yields (ꢁC)
Entries
Reactants (2)
Products (4)
(%)a
[lit.]
Ethanol–
water
(1:1, v=v)
f
45
55
40
35
96
185 ꢁC
Ethanol–
water
(1:1, v=v)
g
85
86
93
157 ꢁC
215 ꢁC
207 ꢁC
170 ꢁC
Ethanol–
water
(1:1, v=v)
i
Ethanol–
water
(1:1, v=v)
j
Ethanol–
water
(1:1, v=v)
k
50
30
89
92
Ethanol–
water
(1:1, v=v)
231 ꢁC
[230–
233]15
l
aYield of isolated products.
in Table 3. Among them, ethanol–water (1:1, v=v) was most efficient with respect to
reaction time and yield of products. Both electron-donating and electron-withdrawing
aromatic aldehydes offered 2,4,5-triaryl-1H-imidazole derivatives in good to excellent
yields.

SULFATED TIN OXIDE
1515
Table 3. Effect of various solvents for synthesis of 2,4,5-triaryl-1H-imidazolea
Entries
Solvents
Temperature (ꢁC)
Yieldsb (%)
Time
1
2
3
4
5
6
7
Dichloromethane
Toluene
DMF
40
75
75
65
75
75
80
75
80
12 h
4.0 h
78
80
4.5 h
3.0 h
MeOH
EtOH
95
97
2.0 h
2.0 h
CH3CN
Ethanol–water (1:1, v=v)
80–98
30–55 min
aReaction conditions: 4-hydroxy benzalaldehyde (12 mmol), benzil (10 mmol), ammonium acetate
(40 mmol), and sulfated tin oxide (10 mol%).
bYield of isolated products.
The catalyst was separated and reused after washing with n-hexane, drying at
60 ꢁC, and activating at 500 ꢁC for 1 h before each catalytic run. The reusability of
catalyst was investigated in the reaction of 4-hydroxybenzaldehyde with benzoin
and ammonium acetate in the presence of sulfated tin oxide (10 mol%) as catalyst,
which showed that the catalyst can be used three times without any loss in activity
(Table 4).
EXPERIMENTAL
Synthesis of Sulfated Tin Oxide as Catalyst
Sulfated tin oxide was synthesized using following literature procedure.[26]
To a solution of 100 g stannous chloride (SnCl2 nH2O) in 300 ml water, 25%
ammonia solution was added dropwise with constant stirring untill the pH of the sol-
ution was adjusted to 8. The precipitated product was collected by filtration and
poured on 500 ml cold ammonium acetate solution (0.5 to 4%). The precipitated
solid was filtered and dried at 100 ꢁC for 24 h. Tin oxide gel obtained was taken in
glass suction funnel, 30 ml of concentrated sulfuric acid was added slowly to it,
and the mixture was allowed to stand for 1 h. The solid obtained was filtered and
dried at 100 ꢁC for 2 h. Further, the solid was heated in air at 500 ꢁC for 3 h and
stored in a sealed sample bottle until use.
General Experimental Procedure for 2,4,5-Triaryl-1H-imidazoles
Aromatic aldehyde (12 mmol) was added to a mixture of benzil or benzoin
(10 mmol), ammonium acetate (40 mmol), and sulfated tin oxide (10 mol %) in
Table 4. Recovery of sulfated tin oxide in the synthesis of 2,4,5-triaryl-1H-imidazole from Table 1
Yields %
Entry
Product
Time (min)
Run 1
Run 2
Run 3
1
2
4b
4c
35
40
95
97
92
94
89
91

1516
S. A. DAKE ET AL.
ethanol–water (20 ml, 1:1, v=v). The reaction mixture was heated at 80 ꢁC under
refluxed condition for appropriate times (Tables 1 and 2). After completion of
reaction as confirmed by thin-layer chromatography (TLC) using eluent petroleum
ether–ethyl acetate (7:3), the reaction mixture was cooled to room temperature
and poured onto ice water (50 ml) to get precipitate the solid. The catalyst, sulfated
tin oxide, was recovered as a residue, washed with ethanol, dried, and reused.
The product was collected by filtration, washed with water, and dried to give the
corresponding 2,4,5-triaryl-1H-imidazole derivatives.
Synthesis of 4-(4,5-diphenyl-1H-imidazol-2-yl)phenol (4b). A mixture of
4-hydroxybenzalaldehyde (1.46 g, 12 mmol), benzil (2.10 g, 10 mmol), ammonium
acetate (3.08 g, 40 mmol), sulfated tin oxide (10 mol%), and 2 ml ethanol–water sys-
tem (1:1, v=v) were taken in a round-bottom flask. The reaction mixture was heated
at 80 ꢁC under refluxed condition for an appropriate time (Table 1). After com-
pletion of the reaction as confirmed on thin-layer chromatography (TLC) using elu-
ent (7:3 ml, petroleum ether–ethyl acetate), the reaction mixture was cooled at room
temperature and poured onto ice water (50 ml) to precipitate the solid. The catalyst,
sulfated tin oxide, was recovered as a residue, washed with ethanol, dried, and
reused. The product was collected by filtration, washed with water, and dried to give
the corresponding 4-(4,5-diphenyl-1H-imidazol-2-yl)phenol.
Spectral Data of Selected Compounds
1
FT-IR (KBr), H NMR, and 13C NMR spectra were recorded at room tem-
perature on a Varian Inova spectrometer in CDCl3=dimethylsulfoixde (DMSO-d6)
using tetramethylsilane (TMS) as internal standard.
2-Methoxy-4-(4,5-diphenyl-1H-imidazol-2-yl)phenol (Table 1, 4d). IR
(KBr, cmꢂ1): 3475 (N-H), 3360 (Ar-OH), 2923 (C-H), 1646 (C¼N), 1620 (C¼C),
1
1355 (C-N), 1237 (C-O); H NMR (CDCl3=DMSO-d6, 400 MHz, d ppm): 3.67 (s,
3H, -OCH3), 5.01 (s, 1H, -OH), 6.61 (dd, 1H, Ar-H), 6.85 (s, 1H, Ar-H), 7.06 (dd,
1H, Ar-H), 7.05–7.25 (m, 10H, Ar-H), 12.24 (brs, 1H, -NH); 13C NMR (100 MHz,
CDCl3=DMSO-d6): 55.7, 111.5, 115.9, 121.4, 123.9, 125.5, 127.5, 128.9, 129.1,
129.7, 132.7, 146.1, 152.1; LCMS: 344.15 [Mþ], 345.29 [M þ 1].
2-Iodo-6-methoxy-4-(4,5-diphenyl-1H-imidazol-2-yl)phenol (Table 1,
4f). IR (KBr, cmꢂ1): 3478 (N-H), 3345 (br, O-H), 2965 (C-H), 1590 (C¼C), 1655
(C¼N), 1250(C-O), 545 (C-I); 1H NMR (CDCl3=DMSO-d6, 400 MHz, d ppm):
3.67 (s, 3H, -OCH3), 5.01 (s, 1H, -OH), 6.75 (s, 1H, Ar-H), 7.35 (s, 1H, Ar-H),
7.05–7.15 (m, 10H, Ar-H), 12.27 (brs, s, 1H, -NH); 13C NMR (100 MHz, CDCl3=
DMSO-d6): 56.2. 88.0, 110.9, 126.0, 127.2, 128.9, 129.1, 129.7, 130.2, 132.8, 148.0,
151.8, 154.1; LCMS: 368.03 [Mþ], 369.05 [M þ 1].
2-(3-Chlorophenyl)-4,5-diphenyl-1H-imidazole (Table 1, 4g). IR (KBr,
cmꢂ1): 3465 (N-H), 2950 (C-H), 1669 (C¼N), 1345 (C-N), 1590 (C¼C),1085
1
(C-Cl); H NMR (CDCl3=DMSO-d6, 400 MHz, d ppm): 7.19 (dd, 1H, Ar-H), 7.30
(dd, 1H, Ar-H), 7.40 (dd, 1H, Ar-H), 7.43 (s, 1H, Ar-H), 7.05–7.19 (m, 10H,
Ar-H), 12.25 (brs, s, 1H, -NH); 13C NMR (100 MHz, CDCl3=DMSO-d6): 125.9,

SULFATED TIN OXIDE
1517
127.2, 132.8, 128.9, 129.0, 129.1, 129.7, 131.0, 132.7, 132.8, 133.0, 148.0; LCMS:
330.81, [Mþ], 331.21, isotopic peak-333.16, 334.21.
2-(4-Chlorophenyl)-4,5-diphenyl-1H-imidazole (Table 1, 4h). IR (KBr,
cmꢂ1): 3465 (N-H), 2950 (C-H), 1670 (C¼N), 1345 (C-N), 1593 (C¼C), 1082
(C-Cl); 1H NMR (CDCl3=DMSO-d6, 400 MHz, d ppm): 7.25 (dd, 2H, Ar-H),
7.07–7.25 (m, 10H, Ar-H), 7.60 (dd, 2H, Ar-H), 12.24 (brs, s, 1H, -NH); 13C
NMR (100 MHz, CDCl3=DMSO-d6): 127.2, 128.9, 129.1, 129.3, 129.7, 130.1,
132.8, 135.0, 148.1; LCMS: 330.81 [Mþ], 331.12 [M þ 1], [M þ 1], isotopic peaks
333.14, 334.18.
2-(3-Nitrophenyl)-4,5-diphenyl-1H-imidazole (Table 1, 4k). IR (KBr,
cmꢂ1): 3424 (N-H), 2955 (C-H), 1659 (C¼N), 1385 (C-N), 1535 (C¼C), 1520
1
(Ar-N-O); H NMR (CDCl3=DMSO-d6, 400 MHz, d ppm): 7.62 (dd, 1H, Ar-H),
7.75 (dd, 1H, Ar-H), 7.02–7.20 (m, 10H, Ar-H), 8.05 (dd, 1H, Ar-H), 8.45 (s, 1H,
Ar-H), 12.30 (brs, s, 1H, -NH).
2-Bromo-6-methoxy-4-(4,5-diphenyl-1H-imidazol-2-yl)phenol (Table 1,
4l). IR (KBr, cmꢂ1): 3479 (N-H), 3357 (br, Ar-OH), 2972 (C-H), 1556 (C¼C),
1
1637 (C¼N), 1265 (C-O), 1078 (C-Br); H NMR (CDCl3=DMSO-d6, 400 MHz, d
ppm): 3.63 (s, 3H, -OCH3), 5.07 (s, 1H, -OH), 6.80 (s, 1H, Ar-H), 7.00 (s, 1H,
Ar-H), 7.30–7.55 (m, 10H, Ar-H), 12.35 (brs, s, 1H, -NH).
3-(4,5-Diphenyl-1H-imidazol-2-yl)phenol (Table 2, 4d). IR (KBr, cmꢂ1):
3492 (N-H), 3378 (Ar-OH), 2945 (C-H), 1633 (C¼N), 1554 (C¼C), 1380 (C-N),
1
1242 (C-O); H NMR (CDCl3=DMSO-d6, 400 MHz, d ppm): 6.57 (dd, 1H, Ar-H),
6.75 (s, 1H, Ar-H), 7.00 (dd, 1H, Ar-H), 7.10 (dd, 1H, Ar-H), 7.05–7.17 (m, 10H,
Ar-H), 12.21 (brs, s, 1H, -NH); 13C NMR (100 MHz, CDCl3=DMSO-d6): 113.1,
116.2, 119.4, 127.2, 128.9, 129.1, 129.7, 130.3, 131.8, 132.8, 148.1, 158.5.
4-(4,5-Diphenyl-1H-imidazol-2-yl)benzonitrile (Table 2, 4f). IR (KBr,
cmꢂ1): 3407 (N-H), 2921 (C-H), 2240 (Ar-CN), 1649 (C¼N), 1555 (C¼C), 1675
1
(C ¼ N), 1240 (C-N); H NMR (CDCl3=DMSO-d6, 400 MHz, d ppm): 7.01–7.31
(m, 10H, Ar-H), 7.47 (dd, 2H, Ar-H), 7.95 (dd, 2H, Ar-H), 12.10 (brs, s, 1H,
-NH); 13C NMR (100 MHz, CDCl3=DMSO-d6): 113.1, 116.0, 127.2, 127.6, 128.4,
128.9, 129.1, 129.7, 131.0, 132.8, 133.5, 137.0, 148.1; LCMS: 321.13 [Mþ], 322.13
[M þ 1].
2-(2-Methyl-1H-imidazol-4-yl)-4,5-diphenyl-1H-imidazole
(Table
2,
4g). IR (KBr, cmꢂ1): 3436 (N-H), 2922 (C-H), 1659 (C¼N), 1540 (C¼C), 1384
(C-N); 1H NMR (CDCl3=DMSO-d6, 400 MHz, d ppm): 2.40 (s, 3H, -CH3),
7.09–7.95 (m, 10H, Ar-H), 6.91 (s, 1H), 12.05 (brs, s, 1H, -NH), 13.57 (s, 1H,
-NH); 13C NMR (100 MHz, CDCl3=DMSO-d6): 17.9, 120.0, 121.1, 127.2, 128.9,
129.1, 129.7, 132.8, 144.0, 165.5; LCMS: 300.36 [Mþ], 301.36 [M þ 1].
2-(4-Chloro-3-fluorophenyl)-4,5-diphenyl-1H-imidazole (Table 2, 4i). IR
(KBr, cmꢂ1): 3445 (N-H), 2920 (C-H), 1659 (C¼N), 1639 (C-N), 1540 (C¼C),
1170 (C-F), 1075 (C-Cl); 1H NMR (CDCl3=DMSO-d6, 400 MHz, d ppm): 6.08
(dd, 1H, Ar-H), 7.20 (s, 1H, Ar-H), 7.50 (dd, 1H, Ar-H), 7.09–7.73 (m, 10H,
Ar-H), 12.47 (s, 1H, -NH); 13C NMR (100 MHz, CDCl3=DMSO-d6): 116.9, 121.2,

1518
S. A. DAKE ET AL.
125.0, 127.2, 128.9, 129.1, 129.7, 130.7, 132.0, 132.8, 148.1, 164.0; LCMS: 348.80
[Mþ], 349.80 [M þ 1].
2-(3,4-Difluorophenyl)-4,5-diphenyl-1H-imidazole (Table 2, 4j). IR (KBr,
1
cmꢂ1): 3465 (N-H), 2985 (C-H), 1615 (C¼N), 1575 (C¼C), 1175 (C-F); H NMR
(CDCl3=DMSO-d6, 400 MHz, d ppm): 7.01 (dd, 1H, Ar-H), 7.12 (s, 1H, Ar-H),
7.47 (dd, 1H, Ar-H), 7.09–7.72 (m, 10H, Ar-H), 12.45 (s, 1H, -NH).
2-(4,5-Diphenyl-1H-imidazol-2-yl)-6-meyhoxy phenol (Table 2, 4k). IR
(KBr, cmꢂ1): 3412 (N-H), 3350 (-OH), 2925 (C-H), 1654 (C¼C), 1565 (C¼N),
1
1335 (C-N); H NMR (CDCl3=DMSO-d6, 400 MHz, d ppm): 3.68 (s, 3H, -OCH3),
5.01 (s, 1H, -OH), 6.59 (dd, 1H, Ar-H), 6.77 (dd, 1H, Ar-H), 6.80 (dd, 1H, Ar-H),
7.05–7.25 (m, 10H, Ar-H), 12.21 (brs, 1H, -NH); 13C NMR (100 MHz, CDCl3=
DMSO-d6): 54.7, 110.9, 112.1, 115.6, 117.1 121.1, 126.2, 127.3, 127.4, 129.8, 145.1,
146.1, 147.3; LCMS: 342.14 [Mþ], 343.14 [M þ 1].
CONCLUSION
In summary, we developed a simple, efficient, clean methodology and mild
protocol for the synthesis of 2,4,5-triary-1H-imidazole derivatives by condensation
of benzoin=benzil, substituted aromatic aldehydes, and ammonium acetate in the
presence of sulfated tin oxide (STO) solid heterogeneous catalyst. In this procedure,
ethanol–water (1:1, v=v) is used as solvent and therefore is relatively ecofriendly. The
notable merits of this method are short reaction times, simple workup procedure,
excellent yield of products, nontoxicity, cost-efficiency, and reusability of the
catalyst.
ACKNOWLEDGMENT
The authors are thankful to Dr. P. L. More, Dnyanopasak College, Parbhani,
for the encouragement during this research.
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