CuI nanoparticles mediated expeditious synthesis of 2-substituted benzimidazoles using molecular oxygen as the oxidant

Article abstract of DOI:10.1039/c6ra11678g

A general and easy method for the synthesis of several 2-substituted benzimidazoles from cyclization of o-diaminobenzenes and various aldehydes using CuI nanoparticles as a heterogeneous catalyst is described. Short reaction times, easy and quick isolation of the products and excellent yields are the main advantages of this procedure. This CuI nanoparticles catalyst system was found to be air/O₂ stable and also used for large scale cyclization reaction with recoverable and reusable properties without loss of catalytic activity for upto six cycles.

Full text of DOI:10.1039/c6ra11678g

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CuI nanoparticles mediated expeditious synthesis of 2-substituted
benzimidazoles using molecular oxygen as oxidant
P. Linga Reddy,a R. Arundhathi,b Mohit Tripathia and Diwan S. Rawat*a
Received 00th January 20xx,
Accepted 00th January 20xx
A
general and easy method for the synthesis of several 2-substituted benzimidazoles from cyclization of o-
DOI: 10.1039/x0xx00000x
diaminobenzenes and various aldehydes using CuI nanoparticles as a heterogeneous catalyst is described. Short reaction
times, easy and quick isolation of the products and excellent yields are the main advantages of this procedure. This CuI
nanoparticles catalyst system was found to be air/O2 stable and also used for large scale cyclization reaction with
recoverable and reusable properties without loss of catalytic activity for upto six cycles.
www.rsc.org/
Introduction
Nitrogen containing heterocyclic compounds are pivotal
building blocks in natural products, pharmaceuticals and
materials chemistry. In particular, benzimidazoles have been
found to possess a broad spectrum of biological activities such
as anti-bacterial,1 anti-fungal,2 anti-inflammatory,3 anti-viral4
and anti-cancer5,6 activities. Owing to their significance,
numerous methods have been reported for benzimidazole
synthesis and the increasing demands for green and
sustainable protocols have revived the focus on their synthesis
in recent years.7
Fig.1 General routes for the synthesis of 2-substituted benzimidazoles
disadvantages like prolonged reaction times, high cost of the
catalysts, formation of side products, difficulties in separation
of the products and generation of highly hazardous metallic
and organic wastes. The above mentioned limitations warrant
the development of a green and recyclable, environmentally
benign catalytic system for the synthesis of 2-substituted
benzimidazoles preferably employing a greener oxidant.
The traditional method for the synthesis of benzimidazoles
involves the condensation of o-phenylenediamines with
carboxylic acids and their derivatives in the presence of strong
o
acids at high temperatures (~200 C).8,9 Various catalysts have
been employed and use of microwave irradiation has also
shortened the reaction time but the conditions remain harsh,
hence hampering the synthetic applicability of these
protocols.7,10 Oxidative cyclization of Schiff-base derivatives
from o-phenylenediamine and aldehydes also give the
corresponding 2-substituted benzimidazoles which is a more
acceptable route (Fig. 1). Use of different catalysts has
improved this strategy for the generation of benzimidazoles,
notable examples being H2O2-CAN,11 oxone,12 DDQ,13
PhI(OAc)2,14 copper-triflate,15 4-Methoxy-TEMPO,16 Yb(OTf)3,17
In recent times, various heterogeneous catalysts, including
highly active nano-catalysts have been developed for the
synthesis of benzimidazoles via condensation of o-
phenylenediamines with aromatic aldehydes. Examples
include CuFe2O4-nanoparticles,20 Mesoporous Titania-Iron(III)
Oxide,21 Pt-TiO2,22 SBA-15 supported Cobalt Nanocatalysts,23 β-
cyclodextrin,24
Fe3O4/SiO2/(CH2)3N+Me3Br-3
core-shell
nanoparticles,25 nano zinc oxide/nano-crystalline sulfated
zirconia,26 Fe3O4-SiO2-(NH4)6Mo7O24 magnetic coreshell
nanocomposite,27 Cu(II)-nanosilica triazine dendrimer,28 α-
MoO3 nanobelts,29 CuO/Silica,30 Co(III)-salen on activated
carbon31 etc. However, most of these methods use
stoichiometric amounts of hazardous oxidants, employ
expensive metal catalysts and generate toxic by-products
which solicit the development of a greener protocol.
19
In(OTf)3,18 and I2/KI/K2CO3 as oxidising agents at relatively
mild conditions. Although most of these homogeneous
reaction conditions are milder, they still suffer from some
a.Department of Chemistry, University of Delhi, Delhi-110007, India. E-mail:
dsrawat@chemistry.du.ac.in; Fax: +91-11-27667501; Tel: +91-11-27662683.
b.Corporate Research & Development Centre, Bharat Petroleum Corporation
Limited, Greater Noida, Uttar Pradesh-201306, India.
In continuation of our efforts towards the development of
novel catalysts for important synthetic transformations,32-42
herein we report CuI nanoparticles (CuI-np) catalysed synthesis
of 2-aryl/alkyl- benzimidazoles using molecular oxygen as the
Electronic Supplementary Information (ESI) available: 1H and 13C NMR spectra for
the synthesised benzimidazoles. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
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oxidant. The CuI-nps were prepared as described previously41
and characterized by XRD, XPS, TEM and EDX. It was then
evaluated for its catalytic activity for the synthesis of 2-
substituted benzimidazoles by using o-phenylediamines and
various aromatic aldehydes as starting materials using
air/oxygen as a green oxidant under ambient conditions. The
prepared CuI nps were found to be stable under the employed
reaction conditions and were easily recovered and recycled
upto five times without showing any appreciable loss in yield.
Table 1 Optimization of the reaction conditions for benzimidazole synthesis a
NH2
N
Catalyst
O
+
Solvent, air/O2
N
H
NH2
Entry
1
Catalyst
CuI salt
CuI salt
TiO2
Solvent
CH3CN
Time (h)
Yieldb (%)
25
6
6
2
EtOH
16
3
CH3CN
6
38
4
Fe3O4
CH3CN
6
27
5
CuFe2O4
CoFe2O4
CoFe2O4
CuI np
CuI np
CuI np
CuI np
CuI np
CuI np
-
CH3CN
6
54
6
CH3CN
6
65
Results and discussion
7
CH3CN
12
3
82
In an effort to devise a heterogeneous catalyst for the
benzimidazole synthesis, initially we screened various catalysts
and solvents for the model coupling between o-
phenylediamine and benzaldehyde to yield 2-phenyl-1H-
benzimidazole, including ferrites, TiO2, CuI and CuI nps (Table
1). The CuI nps were prepared by the ‘sodium citrate assisted
hydrothermal method’ as previously reported.41 The TEM
images and EDX spectrum for the prepared catalyst is shown in
Fig.1. As shown in table 1, in the case of ferrites, the yields
were increased by doping the ferrite nanoparticles with copper
and cobalt metals (entries 5-7, Table 1). Among the various
catalysts screened, the prepared CuI nps gave the best yield of
the corresponding benzimidazole when acetonitrile was used
8
CH3CN
92
9
MeOH
3
40
10
11
12
13
14
15
Toluene
H2O
6
30
50, 66c
6
Ethylene glycol
CH3CN
6
25
1
97d
15d
18e
CH3CN
12
6
CuI np
CH3CN (degassed)
a Reaction conditions: o-phenylenediamine (1.0 mmol), benzaldehyde (1.1 mmol),
b
c
catalyst (10 mol%) and solvent (2 mL) were stirred at rt; Isolated yields. at
reflux conditions; d under O2-balloon; e under inert (Ar) atmosphere.
oxygen as the oxidant for this reaction under the ambient
conditions.
as the solvent (entry 8, Table 1). Even though water gave
moderate yield at room temperature, unfortunately there was
no further increase in the yield even at reflux temperature of
water. On the other hand, we found acetonitrile as a solvent of
choice with no base or additional heat required to give the
desired cyclized product in excellent yield at room
temperature maintaining the selectivity. Subsequently, we
performed the reaction with an O2-filled balloon and found a
To test the general scope and versatility of this procedure
for the synthesis of a variety of 2-substituted benzimidazoles,
we examined a number of aldehydes (Table 2) and different o-
substituted diamines (Table 3). We were pleased to find that
the optimized set of conditions afforded moderate to excellent
Table 2 Cyclization of o-phenylenediamine with substituted aldehydes using
remarkable increase in yield with the shortening of reaction CuI nanoparticles as catalyst a
time (entry 13, Table 1). Control experiments without catalyst
(entry 14, Table 1) and without O2 (using degassed solvent and
Argon atmosphere; entry 15, Table 1) were performed which
ascertained the necessity of the CuI np catalyst and molecular
Entry
2a
2b
2c
R
Time (h)
Yield* (%)
55
m.p. (oC)
148-150
158-160
196-198
291-293
233-235
264-266
275-276
221-223
277-279
295-297
222-224
259-261
264-266
340-341
-
Ref.
[43]
[44]
[43]
[45]
[46]
[44]
[47]
[44]
[44]
[48]
[44]
[44]
[49]
[44]
C3H7
2
1.5
1
C5H11
76
C6H5-CH=CH
C6H5
88
97b
2d
2e
2f
1
2-ClC6H4
4-ClC6H4
2,6-ClC6H3
2-MeC6H4
4-MeC6H4
2,6-MeC6H3
4-MeOC6H4
4-NO2C6H4
2-NO2C6H4
Thiolyl
1
90
1
95
2g
2h
2i
2
78
1.5
1.5
2
84
89
2j
72
2k
2l
2
82
1
95
2m
2n
2o
2
83
2
88
Cyclohexyl
4
nr
aReaction conditions: O-phenylenediamine (1.0 mmol), aldehyde (1.1 mmol),
b
catalyst (10 mol%), CH3CN (2 mL) were stirred at rt; kept at 10mmol scale; nr:
No reaction; * Isolated yield
Fig.2 TEM images of A) fresh and B) re-used CuI nps; C) EDX spectrum for synthesised
CuI nps.
2 | J. Name., 2012, 00, 1-3
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Table 3 Cyclization of substituted O-phenylenediamine with benzaldehyde using CuI
nanoparticles as catalyst a
Entry
R1
R2
Time Yield *
m.p.
( oC)
Ref.
(h)
1
(%)
91
95
65
76
87
92
67
72
80
3a
3b
3c
3d
3e
3f
4-Me
4,5-Me
4-NO2
4,5-Cl
4-Me
H
H
244-246
[43]
[50]
[43]
[51]
[43]
[52]
-
1
235-237
154-156
224-226
168-170
195-197
197-199
185-186
236-238
H
2
H
1
4-OMe
4-OMe
2-OMe
4-n-Bu
4-Me
1
4,5-Me
4,5-Cl
4-NO2
4,5-Cl
1
Fig. 3 Recyclability of CuI nps for synthesis of 2d
3g
3h
3i
2
2
-
2
-
a
Reaction conditions: o-phenylenediamine (1.0 mmol), aldehyde (1.1 mmol),
catalyst (10 mol%), CH3CN (2 mL), reactions stirred at rt; * isolated yields.
yields in the condensation of o-phenylenediamine with
aliphatic, aromatic and hetero-aromatic aldehydes as shown in
table 2. In case of aliphatic aldehydes, hexanal gave good yield
than butanal (entries 2a and 2b, Table 2). We also observed
that cinnamaldehyde, an α,β-unsaturated aldehyde, also gave
the corresponding benzimidazole in excellent yield (entry 2c
,
Table 2). For aryl aldehydes, those with electron-withdrawing
substituents gave better yields when compared to those
having electron-donating groups (entries 2e-g and 2l-m vs 2h-
k, Table 2). Para-substituted benzaldehydes resulted in higher
Fig. 4 XRD spectra of A) fresh CuI nps and B) CuI nps after sixth cycle.
yields than the ortho-substituted ones and the low yields can
be explained due to steric hindrance caused at the ortho
position (entry 2e vs 2f and 2h vs 2i, Table 2). For di-ortho-
substitutions, the effect was even more pronounced (2g and
2j, Table 2). Heteroaryl aldehyde (entry 2n, Table 2) also gave
the acceptable yield, whereas no product was obtained when
characterized by XRD. According to the diffraction data card
(JCPDS, 06-0246); all of the peaks can be perfectly indexed to
CuI in peak position as shown in Fig. 4.
XPS survey scan of CuI nanoparticles showed the presence
of copper, Cu 2p (at 933.37 eV), and iodine, I 3d (at 620 eV).
The XPS high resolution narrow scans of Cu 2p for the fresh
and used CuI nanoparticles are shown in Fig. 5 A and B. The
observed Cu 2p binding energy peaks could be deconvoluted
into two peaks, 933.379, 954.721 and 933.395, 953.059 eV for
the fresh and used CuI nanoparticles, which are characteristic
of 2p3/2 and 2p1/2 core levels. These observed binding energy
alicyclic aldehyde was used (entry 2o
, Table 2). 2-
Phenylbenzimidazole (2d) was also synthesised at a 10 mmol
scale, in excellent yield.
In the case of synthesis of benzimidazoles from different
substituted o-phenylenediamines and aldehydes, it was
observed that o-phenylenediamines with electron-donating
substituents at para position yielded benzimidazoles with
increasing yields (entries 3a-b vs 3c-d, Table 3). The yields
were lower with the combination of electron-withdrawing
diamines and benzaldehydes containing electron-donating
groups (entries 3g-i, Table 3).
Having checked the generality of this protocol for the
synthesis of variety of benzimidazoles, next we studied the
recyclability of the CuI nps. CuI nanoparticles were easily
separated from the reaction mixture by centrifugation. The
recovered catalyst was washed with acetone and then dried at
65 oC. It was then used for the next cycle and consistent
catalytic activity was observed (see Fig. 3 and Table 2, entry
2d: 1st cycle 97 %; 6th cycle 93 %). TEM image (Fig. 1B)
showed no changes in the morphology of the recycled catalyst.
Both the used and fresh CuI np catalysts were also
Fig. 5 XPS high resolution narrow scan of Cu 2p for CuI nanoparticles [A] fresh and [B]
used (after 6th cycle).
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Fig. 6 XPS high resolution narrow scan of I 3d for CuI nanoparticles [A] fresh and [B]
used (after 6th cycle)
peaks can be attributed to the Cu in +1 oxidation state.
Similarly, the observed peak of I 3d peak at 620 eV could be
deconvoluted into two peaks 3d5/2 and 3d3/2 at
619.313,629.724 and 619.808, 630.017 eV for the fresh and
used CuI nanoparticles, respectively as shown in Fig. 6.
Next, to confirm the heterogeneity of the CuI
nanoparticles, a reaction between o-phenylenediamine and
benzaldehyde was terminated after a small conversion (20
min, 30% conversion), the catalyst was filtered-off and the
reaction was continued with the filtrate for next 2 h. Almost no
change in the conversion of o-phenylenediamine was
observed. These studies and the non-activity in the absence of
CuI nanoparticles in cyclization of o-phenylenediamine and
benzaldehyde clearly prove that the reaction occurs
heterogeneously.
Fig. 7 Plausible reaction mechanism for CuI nps catalysed condensation of benzaldeyde
with o-phenylenediamine.
require higher temperatures to exhibit their catalytic activity,
the present CuI nps were active at ambient temperature. Two
catalysts (entries
7 and 8, Table-4) yield the desired
benzimidazole in less time, but require the use of hazardous
oxidants, while in our case environmentally benign molecular
oxygen is used as the oxidant. Furthermore, the use of
molecular oxygen as the oxidant leads to a higher atom
economy (84.35%) for the synthesis of benzimidazole (2d) than
with the use of hydrogen peroxide or tert-butyl peroxide
which render lower atom economies to the reaction having
the values of 78.23% and 63.81%, respectively (calculations of
atom economies can be found in the ESI). This further
elucidates the ‘greenness’ of this protocol.
Table 4 compares the catalytic activity of the prepared CuI
nps with other recently reported heterogeneous nanocatalysts
for the synthesis of 2-substituted benzimidazole (2d or 2f). It
can be clearly observed that while most of the catalysts
A plausible mechanism for the CuI nps catalysed formation
of 2-substituted benzimidazoles via the condensation of
benzaldehyde with o-phenylenediamine is proposed (Fig. 7).
The reaction generally proceeds via condensation mechanism,
which involves the formation of Schiff’s base and followed by
oxidative cyclization. CuI has been recognized as a Lewis acid
catalyst for important organic reactions.53,54 So, in this catalytic
process, the Cu(I) may be acting as a Lewis acid, forming a
complex with the benzaldehyde and increasing the
electrophilicity of its carbonyl group thereby facilitating imine
formation with one of the amino group of the diamine. The
other amino group (ortho) then proceeds with a nucleophilic
attack on the imine and subsequent oxidative aromatization by
dioxygen leads to the formation of the desired 2-substituted
benzimidazole through removal of a water molecule.
Table 4: Comparison of CuI nps with reported nano-catalysts for the synthesis of 2-
phenyl benzimidazole (2d).
S.
No
1.
Catalysta/solvent/oxidant
T
Time
(h)
Yield
(%)
89b
Ref.
[19]
[20]
(oC)
CuFe2O4-nps (20 mol%),
Toluene, O2
110
24
2.
Mesoporous TiO2-Fe2O3
(20 mg), H2O, O2
40
3
97
3.
4.
5.
Pt-TiO2 (1 mol%), mesitylene
Co/SBA-15 (0.4 mol%), EtOH
Fe3O4/SiO2/(CH2)3N+Me3Br-3 nps
(7 mg)
165
60
1
4
78
98
92
[21]
[22]
[24]
80
0.3
6.
7.
Nano-ZnO (10 mol%), EtOH
Fe3O4-SiO2-(NH4)6Mo7O24
nanocomposite (220 mg), EtOH,
H2O2
80
rt
1.67
0.5
88
90
[25]
[26]
Conclusions
8.
α-MoO3 nanobelts
50
0.5
93
[28]
In conclusion, we report nanostructured Copper Iodide as a
simple and highly efficient catalytic system for the oxidative
cyclization of various o-phenylenediamines with substituted
benzaldehydes/aldehydes at room temperature to generate 2-
substituted benzimidazoles. CuI nps were found to be stable
under the employed reaction conditions and well-
(2 mol%), t-BuOOH
9.
CuO np/Silica (10 mol%), MeOH
CuI nps, acetonitrile, O2
rt
rt
4
1
93
97
[29]
This
10.
work
acatalyst loading per 1mmol reaction scale; b for 2f.
4 | J. Name., 2012, 00, 1-3
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characterized by various spectroscopic analyses. The
ARTICLE
developed catalytic system was also employed at large scale 5,6-dichloro-2-(2-methoxyphenyl)-1H-benzo[d]imidazole (3g):
cyclization reaction with recoverable and reusable properties 1H NMR (400 MHz, DMSO-d6): δ = 12.29 (s, 1H), 8.32-8.27 (m,
without loss of catalytic activity for several cycles in the 1H), 7.90 (s, 1H), 7.78 (s, 1H), 7.50 (t, J = 8.39 Hz, 1H), 7.24 (d, J
synthesis of benzimidazoles. The developed protocol is =8.39 Hz, 1H), 7.11 (t, J =7.63 Hz, 1H), 4.02 (s, 3H); 13C NMR
environmentally benign, does not involve the use of any toxic (100 MHz, DMSO-d6): δ = 156.94, 151.48, 142.40, 134.28,
oxidants and devoid of generation of any toxic/hazardous by- 132.05, 129.88, 124.14, 124.10, 121.00, 119.53, 117.13,
products.
113.22, 112.25, 55.90; ESI-HRMS (m/z) calcd for C14H10Cl2N2O:
293.0243 (MH)+; found: 293.0241 (MH)+.
Experimental
2-(4-butylphenyl)-6-nitro-1H-benzo[d]imidazole (3h):
1H NMR (400 MHz, DMSO-d6): δ = 13.52 (s, 1H), 8.60-8.27 (m,
1H), 8.11 (d, J = 7.63 Hz, 3H), 7.86-7.59 (m, 1H), 7.41 (d, J =
7.63 2H), 2.65 (t, J = 7.63 Hz, 2H), 1.63-1.54 (m, 2H), 1.37-1.27
(m, 2H), 0.90 (t, J = 7.63 Hz, 3H); 13C NMR (100 MHz, DMSO-
d6): δ = 145.78, 142.60, 129.06, 126.97, 126.53, 117.98, 34.72,
32.83, 21.79, 13.78. ESI-HRMS (m/z) calcd for C17H18N3O2:
296.1394 (MH)+; found: 296.1373 (MH)+.
All reagents were purchased from commercial sources and
were used as such. The reaction progress was monitored using
pre-coated TLC plates (E. Merck Kieselgel 60 F254) and spots
were visualised under UV light and also by exposing TLC plates
to iodine vapour. 1H NMR and 13C NMR spectra were recorded
on a JEOL Spectrospin spectrometer at 400 MHz and 100 MHz,
respectively, using TMS as an internal standard. Melting points
were recorded in open capillary tubes on an ERS automated
melting point apparatus and are uncorrected. Mass spectra
were recorded on an Agilent Accurate Mass Q-TOF MS system
or micromass LCT Mass Spectrometer/Data system. IR spectra
were recorded using Bruker FT-IR in the range of 4000–400 cm-
5,6-dichloro-2-(p-tolyl)-1H-benzo[d]imidazole (3i):
1H NMR (400 MHz, DMSO-d6): δ = 13.16 (s, 1H), 8.04 (d, J =
8.39 Hz, 2H), 7.89 (s, 1H), 7.71 (s, 1H), 7.35 (d, J = 7.63 Hz, 2H),
2.36 (s, 3H); 13C NMR (100 MHz, DMSO-d6): δ = 153.97, 140.43,
129.63, 126.68, 126.51, 124.25, 21.01; ESI-HRMS (m/z) calcd
for C14H11Cl2N2: 277.0294 (MH)+; found: 277.0300 (MH)+.
1
and only characteristic frequencies are expressed. CuI
nanoparticles were synthesized as reported previously.40
General procedure for the synthesis of 2-substituted
benzimidazoles
Acknowledgements
A mixture of o-phenylenediamine (1 mmol) and aldehyde (1.1 DSR thanks DST-SERB (File No. EMR/2014/001127) and R & D
mmol) was well stirred with CuI nps (10 mol%) and acetonitrile grant, University of Delhi for the financial support. PLR, MT
(2 mL) at room temperature for appropriate time. At the end and RA thank UGC for the award of senior research fellowship,
of the reaction, as observed by TLC, the reaction mixture was DST for INSPIRE-senior research fellowship and BPCL for their
then diluted with 2-3 mL of EtOAc, and centrifuged to remove encouragement, respectively. We would also like to thank
the catalyst, and the catalyst was further washed with 5-10 mL USIC–CIF, University of Delhi for analytical support.
of EtOAc to make it free from organic matter. To this reaction
mixture, EtOAc (25 mL) was added and washed with water and
Notes and references
then with brine. The organic phase was separated, dried over
sodium sulfate and concentrated under vacuum to get the
crude products. The crude products were purified by silica gel
column chromatography using Hexane:EtOAc (80:20) as
eluent.
1
P. S. Hameed, A. Raichurkar, P. Madhavapeddi, S. Menasinakai,
S. Sharma, P. Kaur, R. Nandishaiah, V. Panduga, J. Reddy, V. K.
Sambandamurthy and D. Sriram, ACS Med. Chem. Lett., 2014,
5, 820-825.
2
3
4
B. Fang, C. H. Zhou and X. C. Rao, Eur. J. Med. Chem., 2010, 45,
4388-4398.
G. Kaur, M. Kaur and O. Silakari, Mini Rev. Med. Chem., 2014,
14, 747-767.
Spectral data for representative compounds
2-(2,6-dichlorophenyl)-1H-benzo[d]imidazole (2g):
1H NMR (400 MHz, DMSO-d6): δ = 12.87 (brs, 1H), 7.72-7.51
(m, 5H), 7.30-7.17 (m, 2H); 13C NMR (100 MHz, DMSO-d6): δ =
146.72, 143.21, 135.08, 134.09, 132.40, 130.61, 128.36,
122.79, 121.60, 119.30, 111.61; anal. calcd for C13H8Cl2N2: C,
59.34; H, 3.06; N, 10.65, found: C, 59.52; H, 3.14; N, 10.55.
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5
6
2-(thiophen-2-yl)-1H-benzo[d]imidazole (2n):
1H NMR (400 MHz, DMSO-d6): δ = 12.95 (s, 1H), 7.82 (d, J =
3.05 Hz, 1H), 7.71 (d, J = 5.34 Hz, 1H), 7.63-7.44 (m, 2H), 7.24-
7.12 (m, 3H); 13C NMR (100 MHz, CDCl3): δ = 147.04, 143.66,
134.67, 133.73, 128.75, 128.28, 126.68, 122.39, 121.73,
118.59, 110.99., anal. calcd for C11H8N2S: C, 65.97; H, 4.03; N,
13.99, found: C, 66.08; H, 4.09; N, 13.94.
7
8
9
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DOI: 10.1039/C6RA11678G
CuI nanoparticles mediated expeditious synthesis of 2-substituted
benzimidazoles using molecular oxygen as oxidant
P. Linga Reddy,a R. Arundhathi,b Mohit Tripathia and Diwan S. Rawat*a
2-substituted benzimidazoles from o-diaminobenzenes and aldehydes using CuI nanoparticles as a
heterogeneous nano-catalyst and O2 as an oxidant were synthesised in excellent yields.