Mild and efficient synthesis of benzimidazole using lead peroxide under solvent-free conditions

Article abstract of DOI:10.1080/00397910903531789

Benzimidazole derivatives have been synthesized using a catalytic amount of lead peroxide (PbO₂) at room temperature with excellent yields. The remarkable selectivities under mild, neutral and solvent-free conditions and use of a commercially available, inexpensive catalyst are attractive features of this method. Copyright

Full text of DOI:10.1080/00397910903531789

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Mild and Efficient Synthesis of
Benzimidazole Using Lead Peroxide
Under Solvent-Free Conditions
Vishvanath D. Patil a , Jaymala Patil a , Priyanka Rege a & Ganesh
Dere a
a Organic Chemistry Research Laboratory, Department of Chemistry,
C. K. Thakur A. C. S. College, New Panvel, Raigad, Maharashtra,
India
Version of record first published: 14 Dec 2010
To cite this article: Vishvanath D. Patil, Jaymala Patil, Priyanka Rege & Ganesh Dere (2010): Mild and
Efficient Synthesis of Benzimidazole Using Lead Peroxide Under Solvent-Free Conditions, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
41:1, 58-62
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Synthetic Communications1, 41: 58–62, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910903531789
MILD AND EFFICIENT SYNTHESIS OF BENZIMIDAZOLE
USING LEAD PEROXIDE UNDER SOLVENT-FREE
CONDITIONS
Vishvanath D. Patil, Jaymala Patil, Priyanka Rege, and
Ganesh Dere
Organic Chemistry Research Laboratory, Department of Chemistry,
C. K. Thakur A. C. S. College, New Panvel, Raigad, Maharashtra, India
Benzimidazole derivatives have been synthesized using a catalytic amount of lead peroxide
(PbO2) at room temperature with excellent yields. The remarkable selectivities under mild,
neutral and solvent-free conditions and use of a commercially available, inexpensive catalyst
are attractive features of this method.
Keywords: Benzimidazoles; lead peroxide; solvent free
INTRODUCTION
The development of simple, efficient, environmentally benign, and econo-
mically viable chemical processes or methodologies for widely used organic com-
pounds is in great demand.[1] Benzimidazoles are present in various bioactive
compounds possessing antiviral, antihypertension, and anticancer properties.[2,3]
Compounds possessing the benzimidazole moiety express significant activity against
several viruses such as HIV,[4] Herpes (HSV-1),[5] and influenza.[6] Bis-benzimidazole
is a DNA minor-grove binding agent possessing antitumor activity.[7]
The condensation of o-phenylenediamine with carbonyl compounds in the
presence of strong acids such as polyphosphoric acid or mineral acids[8] and other
reagents such as I2=KI=K2CO3,[9] N-halosuccinamide (X Cl, Br, I),[10]
=
Yb(OTf)3,[11] polyethelene glycol (PEG-100),[12] (NH4)H2PW12O40,[13] and palladium
as well as microwave-irradiated reaction[14] and solid-phase reactions[15] have been
reported in the literature. However, many of the synthetic protocols reported so
far suffer from disadvantages, such as a requirement for anhydrous conditions,
use of organic solvents, harsh reaction conditions, prolonged reaction times, expens-
ive reagents, and poor to moderate yields. Almost all the reported methods make use
of an acid catalyst, giving rise to tedious working procedures. Therefore, the devel-
opment of a cost-effective, safe, and environmentally friendly reagent is still needed.
Received September 2, 2009.
Address correspondence to Vishvanath D. Patil, Organic Chemistry Research Laboratory,
Department of Chemistry, C. K. Thakur A. C. S. College, New Panvel, Raigad, Maharastra, India.
E-mail: patilvd148@yahoo.in
58

SYNTHESIS OF BENZIMIDAZOLE
59
Scheme 1. Synthesis of benzimidazole with lead peroxide.
In this communication, we report a simple and efficient method for synthesis of
benzimidazole derivatives using lead peroxide as a catalyst under mild conditions.
RESULTS AND DISCUSSION
A wide variety of compounds were applied under optimal reaction conditions
to prepare benzimidazoles. The results are summarized in Table 1. A variety of alde-
hydes and aliphatic, heterocyclic and aromatic compounds possessing both
electron-donating and electron-withdrawing groups were employed for benzimida-
zole formation, and in all cases, the yields were excellent (Table 1, entries 1–18). Four
different types of o-phenylenediamines were employed, and all of them reacted
smoothly under the reaction conditions. The aliphatic aldehydes, which were reacted
under similar conditions, gave considerable yields (Table 1, entries 12 and 13).
General Procedure for Synthesis of Benzimidazole Derivatives
A mixture of o-phenyldiamine (2 mmol), p-nitrobenzaldehyde (2 mmol), and
lead peroxide (0.1 mmol) was stirred magnetically at room temperature, and the
progress of the reaction was monitored by thin-layer chromatography (TLC).
The reaction mixture was filtered and extracted with ethyl acetates (3 ꢀ 30 ml). The
combined ethyl acetate extracts were dried with Na2SO4 and concentrated under
reduced pressure. In all the cases, the product obtained after the usual workup gave
satisfactory spectral data.
Entry 2
IR (KBr): 840, 1342, 1525, 1619, 2987, 3474 cmꢁ1 1H NMR (300 MHz,
.
CDCl3): d ¼ 6.9 (m, 2H, J ¼ 7.2 Hz), 7.3 (d, 2H, J ¼ 7.2 Hz), 8.2 (d, 2H, J ¼ 7.2 Hz),
8.4 (d, 2H, J ¼ 7.8 Hz), 8.6 (s, br, 1H, NH).
Entry 4
IR (KBr): 833, 1035, 1125, 1342, 1536, 1628, 2988, 3478 cmꢁ1 1H NMR
.
(300 MHz, DMSO): d ¼ 3.25 (s, 3H), 7.52 (s, broad, 2H), 7.68 (d, 2H, J ¼ 7.6 Hz,
2H), 7.93 (m, 2H), 8.12 (d, J ¼ 7.6 Hz, 2H), 11.92 (s, 1H).
Entry 5
1
IR (KBr): 837, 925, 1045, 1109, 1129, 1355, 1544, 1629, 2988, 3479 cmꢁ1. H
NMR (300 MHz, DMSO): d ¼ 7.2 (m, 2H), 7.55 (d, broad, J ¼ 7.5 Hz, 1H), 7.62

60
V. D. PATIL ET AL.
Table 1. Synthesis of benzimidazole in the presence of PbO2 at room temperature
Time Yieldc
Entry
1
1,2-Diaminea
Aldehyde
Productb
(min)
(%)
10
94
2
3
4
10
10
15
95
92
90
5
20
91
6
7
15
10
94
90
8
20
91
9
10
11
12
13
25
40
40
40
50
87
87
92
86
87
(Continued )

SYNTHESIS OF BENZIMIDAZOLE
61
Table 1. Continued
Time Yieldc
Entry
14
1,2-Diaminea
Aldehyde
Productb
(min)
(%)
50
89
15
16
17
10
10
10
95
92
96
18
20
93
aThe substrate was treated with benzaldehyde (2 mmol) using 0.1 mmol of PbO2 in solvent-free
conditions and at room temperature.
bAll products were identified by their IR and 1H NMR spectra.
cIsolated yields.
(d, broad, J ¼ 7.5 Hz, 1H), 8.21 (d, J ¼ 6.8 Hz, 1H), 8.55 (d, J ¼ 7.8 Hz, 1H), 9.12 (s,
1H), 12.5 (s, 1H).
Entry 9
IR (KBr): 732, 815, 1036, 1537, 1627, 2929, 3329, 3478 cmꢁ1 1H NMR
.
(300 MHz, DMSO): d ¼ 5.2 (s, 1H), 7.3 (s, broad, 2H), 7.5 (d, 2H, J ¼ 7.6 Hz, 2H),
7.8 (m, 2H), 8.2 (d, J ¼ 7.6 Hz, 2H), 12.1 (s, 1H).
CONCLUSIONS
In conclusion, this article describes a method in which PbO2 is a highly efficient
catalyst for the synthesis of benzimidazole derivatives. The advantages include low
cost, ease of catalyst handling, mild reaction conditions, and reactions carried out
at room temperature with excellent yields.
ACKNOWLEDGMENT
The authors acknowledge the partial support of this work by Prof. B. P.
Bandgar, Vice Chancellor, University of Solapur, India.

62
V. D. PATIL ET AL.
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