Direct Oxidative Conversion of Benzoyl Chlorides to 2-Imidazoles Using Heteropolyacids

Article abstract of DOI:10.1080/00397910902730978

The reaction of benzoyl chlorides with ethylenediamine in the presence of catalytic amounts of Keggin-type heteropolyacids led to oxidative conversion of benzoyl chlorides to the corresponding 2-imidazoles in good yields.

Full text of DOI:10.1080/00397910902730978

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Direct Oxidative Conversion
of Benzoyl Chlorides
to 2-Imidazoles Using
Heteropolyacids
Samaheh Sadjadi a , Majid M. Heravi a , Nargess
Poormohammad a , Hossein A. Oskooie a , Yahya. Sh.
Beheshtiha a & Fatemeh F. Bamoharram b
a Department of Chemistry, School of Sciences,
Azzahra University, Vanak, Tehran, Iran
b Department of Chemistry, School of Sciences,
Islamic Azad University, Mashhad Branch, Mashad,
Iran
Version of record first published: 03 Aug 2009.
To cite this article: Samaheh Sadjadi , Majid M. Heravi , Nargess Poormohammad ,
Hossein A. Oskooie , Yahya. Sh. Beheshtiha & Fatemeh F. Bamoharram (2009): Direct
Oxidative Conversion of Benzoyl Chlorides to 2-Imidazoles Using Heteropolyacids,
Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 39:17, 3119-3125
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Synthetic Communications1, 39: 3119–3125, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910902730978
Direct Oxidative Conversion of Benzoyl
Chlorides to 2-Imidazoles Using Heteropolyacids
Samaheh Sadjadi,1 Majid M. Heravi,1 Nargess Poormohammad,1
Hossein A. Oskooie,1 Yahya. Sh. Beheshtiha,1
and Fatemeh F. Bamoharram2
1Department of Chemistry, School of Sciences, Azzahra University,
Vanak, Tehran, Iran
2Department of Chemistry, School of Sciences, Islamic Azad University,
Mashhad Branch, Mashad, Iran
Abstract: The reaction of benzoyl chlorides with ethylenediamine in the presence
of catalytic amounts of Keggin-type heteropolyacids led to oxidative conversion
of benzoyl chlorides to the corresponding 2-imidazoles in good yields.
Keywords: Heteropolyacids, imidazole, recyclable catalysts
INTRODUCTION
The imidazole ring is a crucial pharmacophore in drug discovery.
Imidazole derivatives are unique and broad-spectrum class of antirhino=
enteroviral agents. They exhibit significant activity against several
viruses.[1–4]
A number of synthetic methods have been developed in recent
years to uncover a variety of new reagents for the synthesis of imidazole
derivatives.[5,6] However, the reported yields in these methods are moder-
ate to poor. In addition, more than one step is involved in the synthesis of
Received November 11, 2008.
Address correspondence to Majid M. Heravi, Department of Chemistry,
School of Sciences, Azzahra University, Vanak, Tehran, Iran. E-mail:
mmh1331@yahoo.com
3119

3120
S. Sadjadi et al.
these compounds. Recently, the oxidative conversion of imidazolines to
imidazoles using activated carbon–O2 has been reported.[7]
We have recently reported new routes for the synthesis of
heterocyclic compounds using heteropolyacids as green and recyclable
catalysts.[8–12] In our previous work, we reported a successful oxidative
aromatization of Hantzsch 1,4-dihydropyridines using catalytic amounts
of heteropolyacids.[13]
Considering the ability of heteropolyacids to oxidize hydro-aromatic
compounds to aromatic ones, and with the fact that the oxidative conver-
sion of imidazolines to imidazoles can be performed in relatively good
yields, we contemplated a one-pot oxidative reaction of benzoyl chlorides
with ethylenediamine for the synthesis of imidazole compounds.
In our new method, the synthesis of imidazolins and their oxidative
conversion to the corresponding imidazoles have been performed in the
one-pot reaction, catalyzed by Keggin types of heteropolyacids including
H6[PMo9V3O40], H5[PMo10V2O40], H4[PMo11VO40], and H3[PMo12O40]
as multifunctional catalysts with no need for a co- oxidative agent or
severe reaction conditions (Scheme 1).
Various reaction conditions such as different amounts and types of
catalyst were examined to obtain the optimum reaction conditions. The
results of the synthesis of imidazole derivatives in the presence of a
catalytic amount of H6[PMo9V3O40] are summarized in Table 1.
The suggested mechanism is patterned in Scheme 2. Heteropolyacids
are multifunctional catalysts. They have both acidic and oxidative pro-
perties. In our proposed reaction, both oxidative and acidic characteris-
tics of heteropolyacids are in action and catalyzed the reaction.
For studying the effect of catalyst type on this reaction, the syntheses of
two imidazole derivatives were selected as model reactions, and the yields of
these reactions, using four Keggin-types of heteropolyacids including
H5[PMo10V2O40], H4[PMo11VO40], H6[PMo9V3O40], and H3[PMo12O40],
were obtained. The results are reported in Table 2. The order of efficiency
of these catalysts is as follows: H6[PMo9V3O40] > H5[PMo10V2O40] >
H4[PMo11VO40] > H3[PMo12O40].
As shown in Table 2, H6[PMo9V3O40] gave the best yields for this
reaction and was selected as the catalyst of choice for the synthesis of
imidazole derivatives.
Scheme 1.

Direct Oxidative Conversion
3121
Table 1. Synthesis of imidazole derivatives using H6[PMo9V3O40], under
refluxing conditions
Yield Mp
(%)a
Lit. mp
(ꢀC)[7]
Entry
1
R
Product
(ꢀC)
Ph
90
143
140–142
2
3
4-CH3Ph
88
88
223
153
223
4-OCH3Ph
152–154
248
4
4-ClPh
90
248
5
6
3-ClPh
92
85
134
311
133
4-NO2Ph
310–312
7
4-BrPh
83
249
247–249
aYields are related to isolated pure products.
To optimize the amount of catalyst, the yields of reactions using
various amounts of catalyst (0.1, 0.3, 0.5 mol%) were obtained. The
results for the synthesis of imidazole derivatives using different amounts
of H6[PMo9V3O40] are shown in Table 3. As shown in Table 3, the good
yields of the products can be obtained using very small amounts of

3122
S. Sadjadi et al.
Scheme 2.
catalysts. The optimum amount of catalyst was as little as 0.3 mol% for
all reactions.
In summary, imidazole derivatives were obtained from the one-pot
oxidative reaction of benzoyl chlorides with ethylenediamine, catalyzed
by H6[PMo9V3O40], a multifunctional, inexpensive, reusable, easy-
to-handle, and noncorrosive catalyst. This catalyst offers advantages,
including simplicity of operation due to the heterogeneous nature of reac-
tion, easy workup procedure, good yields of products, good selectivity,
and the reusability of the catalyst.
EXPERIMENTAL
All the chemicals were purchased from Merck Company. Keggin-type
heteropolyacids were prepared according to the literatures.[14] Melting
points were measured using a Barnstead electrothermal instrument.
Gas chromatography (GC)=mass analysis was performed using an
Agilent 6890 GC system Hp-5 capillary (30 m ꢁ 530 mm ꢁ 1.5 mm
nominal). All compounds were known, and their physical data were
compared with those of authentic compounds and found to be
identical.
Table 2. Effect of various types of Keggin heteropolyacids on
imidazole derivative yields
Entry
R
Catalyst
Yield (%)a
1
2
3
4
5
6
7
8
Ph
Ph
Ph
Ph
H6[PMo9V3O40]
H5[PMo10V2O40]
H4[PMo11VO40]
H3[PMo12O40]
90
88
85
82
90
88
87.7
85
4-ClPh H6[PMo9V3O40]
4-ClPh H5[PMo10V2O40]
4-ClPh H4[PMo11VO40]
4-ClPh H3[PMo12O40]
aYields refer to isolated products.

Direct Oxidative Conversion
3123
Table 3. Results of using different amounts of H6[PMo9V3O40]
in synthesis of two derivatives of imidazole under refluxing
conditions
Entry
R
Catalyst amount (mol%)
Yield (%)a
1
2
3
4
5
6
Ph
Ph
Ph
4-ClPh
4-ClPh
4-ClPh
0.1
0.3
0.5
0.1
0.3
0.5
85
90
90
86
90
90.1
aYields refer to isolated products.
Synthesis of Imidazole Derivatives: General Procedure
A mixture of benzoyl chloride (10 mmol), ethylenediamine (10 mmol), and
appropriate heteropolyacid (0.03 mmol) was refluxed in CH3CN at 90ꢀC
for 2 h. The progress of the reaction was monitored by thin-layer chroma-
tography (TLC). After completion of the reaction, the catalyst was filtered
off, and the pure products were obtained by column chromatography.
All products were identified by comparison of their physical and
spectroscopic data with those of reported samples.[7]
Recycling of the Catalyst
After filtration of the products, the catalyst could be recycled by
evaporating the solution and washing the residue with diethyl ether.
Table 4. Comparison of efficiency of H6[PMo9V3O40] in synthesis of imidazoles
after five times
Yield (%)a (after each use)
Entry
R
First
Second
Third
Fourth
Fifth
1
2
3
4
5
6
7
Ph
90
88
88
90
92
85
83
88
88
86
86.7
87
90.4
83
82
87
85.3
86
85.5
89
83
80.7
87
85
85.6
84
89
82.5
80.5
4-CH3Ph
4-OCH3Ph
4-ClPh
3-ClPh
4-NO2Ph
4-BrPh
86.5
87.5
89
91
84
82
aYields refer to isolated products.

3124
S. Sadjadi et al.
The recovered catalyst could be dried and reused for the next reaction
with only a modest loss in activity. The catalyst has been recovered
and reused five times in reactions. The obtained results are summarized
in Table 4.
ACKNOWLEDGMENTS
The authors are thankful to Azzahra University Research Council for
the partial financial support.
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