Al2O3/CuI/PANI nanocomposite catalyzed green synthesis of biologically active 2-substituted benzimidazole derivatives

Article abstract of DOI:10.1039/d1dt00806d

This work is generally focused on the synthesis of an efficient, reusable and novel heterogeneous Al₂O₃/CuI/PANI nanocatalyst, which has been well synthesized by a simple self-assembly approach where aniline is oxidized into PANI and

Full text of DOI:10.1039/d1dt00806d

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Al O /CuI/PANI nanocomposite catalyzed green
2
3
synthesis of biologically active 2-substituted
Cite this: DOI: 10.1039/d1dt00806d
benzimidazole derivatives†
a,b
a
b
a
Sahil Kohli,
Garima Rathee,
Sunita Hooda* and Ramesh Chandra
*
2 3
This work is generally focused on the synthesis of an efficient, reusable and novel heterogeneous Al O /
CuI/PANI nanocatalyst, which has been well synthesized by a simple self-assembly approach where
aniline is oxidized into PANI and aniline in the presence of KI also acts as a reductant. The nanocatalyst
was well characterized by XRD, FTIR, SEM, EDX, TEM, BET and XPS techniques. In this study, the fabricated
material was employed for the catalytic one-pot synthesis of 2-substituted benzimidazoles via conden-
sation between o-phenylenediamine and aldehydes in ethanol as a green solvent. The present method is
facile and offers several advantages such as high % yield, less reaction time, and no use of additive/bases.
Also, the catalyst showed better values of green metrics including low E-factor: 0.17, high reaction mass
efficiency: 85.34%, high carbon efficiency: 94%, and high process mass intensity: 1.17.
Received 10th March 2021,
Accepted 23rd April 2021
DOI: 10.1039/d1dt00806d
rsc.li/dalton
In the past few years, nanomaterials have emerged as better
alternatives for several organic transformations as compared to
Introduction
N-Heterocycles have always been an interesting class of conventional materials. Such advanced applicability of nano-
organic compounds. Among various N-heterocycles, the benzi- materials in the field of heterogeneous catalysis and as catalyst
midazole scaffold has efficiently attracted the interest of supports is due to their higher surface area, and unique textural
1
1
researchers across the globe owing to its numerous biological and structural properties. Moreover, supported metal nano-
1
2
characteristics such as antiviral, anticancer, anti-inflamma- particles have attracted more significant attention rather than
3
4
5
6
tory, antihypertensive, antifungal and antiulcer activities.
unsupported metal nanoparticles for catalytic applications
Some of the biologically active benzimidazole molecules are because of their large surface and volume ratio. Furthermore,
shown in Fig. 1. The derivatives of benzimidazole are also the intramolecular bonding between metal–metal, surface inter-
recognized as intermediates in synthetic chemistry and as action and interaction between metal–support make the sup-
7
12
ligands in asymmetric catalysis. Moreover, they are also ported metal nanoparticles effective. Alumina is the most
advantageous in the fields of dyeing, chemosensing, fluo- commonly used ceramic material of oxide which acts as a cata-
8
rescence and corrosion science. The classical way for the fab-
rication of benzimidazole derivatives includes the reaction of
o-phenylenediamine with carboxylic acids or their derivatives
9
at high temperature under conditions of strong acidic media.
However, such traditional methods suffer from various disad-
vantages such as, usage of inorganic acids, waste production
in higher amounts, difficulty in the catalyst’s reusability and
1
0
low atom economy.
a
Drug Discovery & Development Laboratory, Department of Chemistry, University of
Delhi, Delhi-110007, India. E-mail: acbrdu@hotmail.com,
rameshchandragroup@gmail.com
b
Department of Chemistry, Acharya Narendra Dev College, University of Delhi, Delhi-
110019, India. E-mail: hooda_sunita@hotmail.com
†
Electronic supplementary information (ESI) available: SEM and XRD of the
recycled catalyst; green chemistry metric calculations, spectral data of com-
1
13
pounds, and H NMR and C NMR spectra of all compounds. See DOI: 10.1039/
d1dt00806d
Fig. 1 Biologically active molecules containing benzimidazole hetero-
cyclic scaffolds.
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lyst support because of its high thermal and chemical stability, over a water bath at 60 °C overnight for the accumulation of
1
3
2+
well-defined porous structure and high specific surface areas.
Alumina provides sites for anchoring various metallic species in Cu –Al
various applications such as Fischer–Tropsch synthesis using water. The obtained Cu –Al
Cu ions on the surface of Al O under continuous stirring.
2 3
2
+
2 3
O was collected and washed 3–4 times with distilled
2
+
2
O
3
compound was again added
into 40 mL of 0.5 M aq. solution of KI and 0.4 mL of aniline
2 3
catalysts, dry reforming of methane over the Ni–Cu/Al O cata- was added into this solution under constant stirring and the
1
4
the CoPt/Al O nanocatalyst, oxidation of benzene by Pt/Al O
2 3
2
3
15
1
6
lyst, etc. Furthermore, polyaniline is an essential conducting obtained solution was further stirred at room temperature for
polymer because of its non-toxic behaviour, high stability, low 24 hours. Lastly, the purple-black precipitate was removed by
17
cost and facile synthesis, and redox properties. It is useful as a centrifugation and washing was done with distilled water fol-
support for various metal catalysed organic reactions in modern lowed by ethanol. The nanocatalyst was dried at 60 °C over-
1
8
organic synthesis.
Copper nanoparticles are mainly attractive because of their
high abundance in nature, inexpensive cost and several methods ized by XRD, FTIR, SEM, EDAX, TEM, BET and XPS techniques.
night (Fig. 2).
The synthesized Al
2 3
O /CuI/PANI nanocatalyst was character-
1
9–22
of preparation.
Copper is a 3d transition metal which exhi-
The powder XRD pattern of the Al O /CuI/PANI nano-
2 3
bits variable oxidation states from 0 to +3 and because of this catalyst is shown in Fig. 3. The peaks at 2θ = 25.5, 29.6, 42.2,
property, copper based materials can undergo various organic 50.0, 61.2, 67.4 and 77.3 correspond to copper iodide which
23
transformations through one- and two-electron pathways.
could be confirmed by comparing it with the JCPDF file (06-
Copper based nanomaterials have a wide range of applications in 0246). The PANI peak does not appear in the pattern at 2θ = 25
24,25
organic reactions including various cross coupling,
coupling, and multicomponent reactions.
oxidative because the peak is covered by the high intensity of the CuI
26
27
30
peak [111] at 25.5.
Our research group has previously successfully reported the
2 3
Fig. 4shows the FTIR spectrum of Al O /CuI/PANI which
fabrication of multiple heterogeneous nanocatalysts for the exhibits peaks at 1591 and 1475 cm− related to the CvC
1
one-pot synthesis of various biologically significant organic stretching vibrations of quinoid and benzenoid units. The
scaffolds such as xanthenes, 1,4-dihydropyridines, polyhydro- peaks at 1331 cm− and 1296 cm are due to the defor-
quinolines, and 4H-pyrans.
1
−1
2
8,29
Herein we introduce a novel mations of the C–N bond and the stretching vibrations of the
Al O /CuI/PANI catalyst for the synthesis of 2-substituted ben-
2
3
zimidazoles from o-phenylenediamine and aldehydes as start-
ing materials at room temperature under greener conditions.
2
+
During the process of fabrication, the Cu ions get anchored
2
+
on the surface of Al
2 3 2 3
O forming an Al O –Cu complex.
2
+
Furthermore, aniline is oxidized into PANI and Cu
is
+
reduced to Cu in the presence of aniline as a reductant. The
obtained catalyst was characterized by techniques such as
XRD, FTIR, SEM, EDX, TEM, XPS and BET. The obtained
material was found to be steady under the employed reaction
conditions and was easily recovered and recycled up to five
times without any considerable loss in the yield.
Results and discussion
Development and characterization of the Al O /CuI/PANI
2
3
nanocomposites
Initially, 100 mg of Al O was added into 40 mL of water. Then
2
3
Fig. 3 XRD spectra of the nanocatalyst.
3
4 2
.04 g of CuSO ·5H O was added to this solution and heated
Fig. 2 Schematic diagram for the synthetic development of the Al
2
O
3
/CuI/PANI nanocatalyst.
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clearly indicate that CuI has been accumulated on the surface
of alumina.
2 3
The EDX spectra of Al O @CuI@PANI are presented in
Fig. 7 which shows the presence of copper, iodide, aluminium,
oxygen, nitrogen and carbon at 15.41, 23.51, 19.52, 3.48, 13.26
and 24.83 wt% respectively.
2 3
The surface composition of the synthesized Al O /CuI/PANI
samples was examined by XPS as shown in Fig. 8g. This compo-
site is mainly composed of Cu, I, Al, O, N and C. In the high
resolution spectrum the Cu 2p1/2 and Cu 2p3/2 lines appear at
9
52.3 and 932.4 eV respectively which confirms that copper
3
1
exists in the +1 oxidation state (Fig. 8a). The XPS of I 3d3/2 and
I 3d5/2 lines at 631.0 and 619.5 eV matches with the reported
data for CuI nanoparticles (Fig. 8b). The binding energy value
of the Al 2p and O 1s peaks at 74.4 and 531.0 eV corresponds to
2 3
the presence of Al O and oxide respectively as shown in Fig. 8c
and d. The carbon (N 1s) and nitrogen (C 1s) atoms of PANI are
Fig. 4 FTIR spectra of the nanocatalyst.
3
0
located at 399.6 and 284.8 eV as shown in Fig. 8e and 8f.
The N adsorption–desorption isotherm and pore radius of
C–N bond respectively. These values in the spectrum confirm the Al O /CuI/PANI nanocatalyst are shown in Fig. 9. It is
2
3
0
2
3
the presence of PANI.
The SEM pattern was analysed for studying the morphology nanocatalyst Al O /CuI/PANI has a BET surface area: 59.02 m
attributed to the H2 (b) hysteresis loop of the isotherm. The
2
2
3
−
1
3
−1
of the Al O /CuI/PANI nanocomposite. The SEM images are
g , pore radius: 7.34 nm, and pore volume: 0.22 cm g .
2
3
displayed in Fig. 5 and Fig. 6 illustrates the TEM images of the
Al /CuI/PANI nanocatalyst at 200 nm and 100 nm. For the
size determination of the nanoparticles, the size of the discrete
Al
2 3
O /CuI/PANI as the nanocatalyst for the synthesis of benzi-
2 3
O
midazole derivatives
particles was measured using TEM images and the size was Initially, the reaction of o-phenylenediamine (1) and 4-methyl-
found to be in the range of 25–40 nm. Also, these images benzaldeyde (2) using the Al O /CuI/PANI catalyst (5 mg)
2
3
2 3
Fig. 5 SEM images of the Al O /CuI/PANI nanocatalyst.
2 3
Fig. 6 TEM images of the Al O /CuI/PANI nanocatalyst.
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2 3
Fig. 7 EDX of the Al O /CuI/PANI nanocatalyst.
2 3
Fig. 8 High resolution XPS of (a) Cu; (b) I; (c) Al; (d) O; (e) N; (f) C; (g) Al O /CuI/PANI nanocomposite.
2 2 3
Fig. 9 (a) Representative isotherm of N adsorption–desorption; (b) Al O /CuI/PANI nanocatalyst pore radius.
under neat conditions and in different solvents at room temp- formed in polar aprotic solvents such as THF, DMF, aceto-
erature was carried out (Table 1). There was no formation of nitrile and DMSO. In THF and acetonitrile, the product was
the product in toluene (entry 1, Table 1). The reaction was per- formed in a trace quantity while in DMF and DMSO the pre-
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Table 1 Optimization of the Al
2
O
3
/CuI/PANI nanocatalyst for the synthesis of benzimidazole derivatives using o-phenylenediamine (1) and
a
4-methylbenzaldehyde (2c)
Entry
Catalyst (mg)
Solvent
Temp (°C)
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
Al
Al
Al
Al
Al
Al
Al
Al
Al
Al
Al
Al
Al
Al
2
2
2
2
2
2
2
2
2
2
2
2
2
2
O
O
O
O
O
O
O
O
O
O
O
O
O
O
3
3
3
3
3
3
3
3
3
3
3
3
3
3
/CuI/PANI (5)
/CuI/PANI (5)
/CuI/PANI (5)
/CuI/PANI (5)
/CuI/PANI (5)
/CuI/PANI (5)
/CuI/PANI (5)
/CuI/PANI (5)
/CuI/PANI (5)
/CuI/PANI (5)
/CuI/PANI (5)
/CuI/PANI (5)
/CuI/PANI (10)
/CuI/PANI (20)
Toluene
THF
Acetonitrile
DMF
DMSO
Neat
Water
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
50
60
rt
rt
rt
rt
24
8
8
8
8
24
24
8
1
1
1
1
1
1
1
1
—
Trace amount
Trace amount
47
61
68
—
77
71
92
92
92
92
92
35
—
EG
Methanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
1
1
1
1
1
1
1
0
1
2
3
4
5
6
CuI salt (5)
Al /CuI/PANI (5)
b
O
2 3
a
2 3
Reaction conditions: o-phenylenediamine 1 (0.5 mmol), aldehyde 2 (0.5 mmol), Al O /CuI/PANI (5–20 mg) and solvent (3 ml) were stirred at
b
2
suitable temperature. Reaction under a N atmosphere.
ferred product was 47% and 61% respectively (entries 2–5, by the catalyst followed by the formation of imine with one of
Table 1). the amino groups. The next step involves the attack of
When neat conditions and green solvents such as water, another amino group to the imine resulting in cyclization
ethylene glycol (EG), and ethanol were used to find sustainable followed by aerial oxidation resulting in 2-substitued
3
2
and green conditions of the reaction, it was observed that no benzimidazole.
reaction takes place in water (entry 7, Table 1) while upon Next we studied the recyclability of the catalyst. Once the
using EG, methanol and ethanol, the formed product was reaction was completed, the catalyst was isolated from the
7%, 71% and 92% respectively (entry 8–10, Table 1). Under reaction mixture by adding ethanol followed by centrifugation
7
neat conditions, the formed product was 68% (entry 6, and then it was washed with ethanol many times and dried
Table 1). So the best suitable solvent to afford the product was overnight in an oven. The material was used for five cycles
found to be ethanol (entry 10, Table 1). Following this, the more without any appreciable decrease in the yield which
influence of temperature was studied; an increase in the temp- shows a greener path for the synthesis of benzimidazole
erature results in the same yield in 1 h (entry 11 and 12, derivatives as shown in Fig. 11. The SEM and XRD spectra
Table 1). Then upon increasing the amount of the catalyst, the were compared for the recycled catalyst and the fresh catalyst
yield was found to be the same (entry 13 and 14, Table 1). after five consecutive cycles which shows no loss in the cata-
Then the yield was found to be 35% when the CuI salt was lytic activity (ESI S3 Fig. S1 and S2†).
used (entry 15, Table 1). The reaction does not take place when
performed in an inert atmosphere of N (entry 16, Table 1). be seen from the values of green metrics (calculations in the
Therefore, the suitable conditions for the reaction were 5 mg ESI document S4 and S5†) which are near to ideal values
of the Al /CuI/PANI nanocatalyst in ethanol as a solvent at (Table 3).
room temperature for 1 h.
-Benzimidazole derivatives were synthesized under the
The current methodology is sustainable and green as it can
2
2 3
O
2
suitable conditions for the reaction as shown in Table 2.
Different benzaldehydes were used with an excellent yield of
the preferred product in all products (3a–3n).
Experimental section
Procedure for 2-(p-methylphenyl)-benzimidazole synthesis (3a)
2 3
The plausible mechanism of the Al O /CuI/PANI nano-
composite catalyzed synthesis of 2-substituted benzimidazole In a round bottom flask, o-phenylenediamine (0.5 mmol),
is shown in Fig. 10. The first step is the activation of aldehyde 4-methyl benzimidazole (0.5 mmol) and Al O /CuI/PANI nano-
2
3
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a
2 3
Table 2 Al O /CuI/PANI nanocatalyzed synthesis of 2-benzimidazole derivatives
a
Reaction conditions: o-phenylenediamine 1 (0.5 mmol), aldehyde 2 (0.5 mmol), Al
2 3
O /CuI/PANI (5 mg) and ethanol (3 ml) were stirred at room
temperature for 1 h.
2 3
Fig. 10 Possible mechanism for the reaction catalysed by Al O /CuI/PANI.
particles (5 mg) were added in ethanol (3 mL) and stirred at pletion of the reaction, the catalyst was filtered and the residue
room temperature for an hour. The reaction was monitored by was extracted with ethyl acetate followed by column chromato-
TLC with ethyl acetate/hexane as the eluent. After the com- graphy to obtain a purified product (Table 4).
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Spectral data of the compounds
4
0
2-(p-Methylphenyl)-benzimidazole (3a)
1
Colourless solid; yield: 92%; mp = 267–269 °C; H NMR
(
DMSO-d , 400 MHz): δ 12.87 (s, 1H), 8.09–8.07 (d, J = 8.25 Hz,
6
2
2
1
H), 7.58 (s, 2H), 7.37–7.35 (d, J = 8.00 Hz, 2H), 7.21–7.18 (m,
1
3
H), 2.38 (s, 3H). C NMR (DMSO-d
6
, 100 MHz): δ 151.83,
40.02, 129.97, 127.89, 126.84, 122.39, 21.44; HRMS (ESI) calcd
+
[M + H] 209.1073; found 209.1077; Anal. Calcd for C14
H
12
N
2
:
C, 80.74; H, 5.81; N, 13.45; found C, 80.72; H, 5.79; N, 13.46.
4
5
2-(m-Methylphenyl)-benzimidazole (3b)
1
White solid; yield: 91%; mp = 213–215 °C; H NMR (CDCl
3
,
4
7
1
1
00 MHz): δ 7.88 (s, 1H), 7.83–7.82 (d, J = 7.56 Hz, 1H),
.56–7.54 (m, 2H), 7.18–7.15 (m, 3H), 7.12–7.09 (d, J = 7.70 Hz,
2 3
Fig. 11 Recyclability of the Al O /CuI/PANI nanocatalyst for compound
1
3
H), 2.15 (s, 3H). C NMR (CDCl
3
, 100 MHz): δ 152.26, 139.19,
3
a synthesis.
38.73, 131.50, 129.22, 127.94, 124.19, 123.40, 115.34, 21.50.
Anal. Calcd for C H N : C, 80.74; H, 5.81; N, 13.45; found C,
1
4
12 2
80.75; H, 5.80; N, 13.47.
4
0
2-(o-Methylphenyl)-benzimidazole (3c)
Table 3 Values of green metrics
1
Colourless solid; yield: 88%; mp = 223–225 °C; H NMR
Process mass
intensity
Reaction mass
efficiency
(
CDCl
3
, 400 MHz): δ 7.58–7.55 (m, 4H), 7.32–7.19 (m, 4H), 2.52
S. no
Catalyst
Al /CuI/PANI
E factor
0.17
13
(
s, 3H). C NMR (CDCl
3
, 100 MHz): δ 152.15, 137.15, 131.36,
1.
2
O
3
1.17
85.34%
129.82, 129.63, 126.13, 122.79, 20.91. Anal. Calcd for
: C, 80.74; H, 5.81; N, 13.45; found C, 80.74; H, 5.80;
14 12 2
C H N
N, 13.44.
4
5
2
-(m-Methoxyphenyl)-benzimidazole (3d)
White solid; yield: 90%; mp = 202–204 °C; H NMR (DMSO-d
00 MHz): δ 7.72–7.71 (d, J = 6.75 Hz, 2H), 7.58–7.56 (m, 2H),
7.45–7.41 (t, J = 8.25 Hz, 1H), 7.20–7.18 (m, 2H), 7.05–7.03 (m,
Table 4 Comparative study of various catalysts for the synthesis of 2-
1
6
,
(
p-methylPhenyl)-benzimidazole
4
Solvent/
condition
Yield
(%)
1
3
Entry Catalyst
Time
Ref.
1H). C NMR (DMSO-d
6
, 100 MHz): δ 160.01, 151.49, 131.86,
1
30.56, 122.62, 119.19, 116.35, 111.84, 55.76. Anal. Calcd for
1
2
3
4
TBN
Pt/TiO
CuI NPs
CuFe
THF, rt, O
2
2 h
1 h
1.5 h
24 h
79
75
89
53
33
34
35
36
2
Mesitylene, rt
CH CN, rt, O
Toluene,
10 °C, O
C H N O: C, 74.98; H, 5.39; N, 12.49; found C, 75.01; H,
14 12 2
3
2
5.41; N, 12.51.
2
O
4
1
2
4
0
5
6
ClSO
a-MoO
nanobelts
CuO np/silica
3
H
3
2-Propanol, rt
50° C,
t-BuOOH
2 h
40 min 90
88
37
38
2-(p-Methoxyphenyl)-benzimidazole (3e)
Colourless solid; yield: 87%; mp = 219–221 °C; H NMR
(DMSO-d , 400 MHz): δ 8.30–8.28 (d, J = 8.11 Hz, 1H),
.93–7.91 (d, J = 8.79 Hz, 1H), 7.69–7.67 (d, J = 8.25 Hz, 1H),
.42–7.39 (m, 2H), 7.11–7.08 (m, 2H), 6.70–6.68 (d, J = 8.66,
1
7
8
Methanol, rt
6 h
1 h
87
92
39
6
Al
2
O
3
/CuI/PANI Ethanol, rt
This study
7
7
1
1
1
3
H). C NMR (DMSO-d
6
, 100 MHz): δ 162.01, 150.23, 135.57,
30.26, 128.88, 125.23, 123.84, 114.39, 55.37; HRMS (ESI):
Conclusion
+
calcd [M + H] 225.1023; found 225.1025; Anal. Calcd for
O: C, 74.98; H, 5.39; N, 12.49; found C, 74.95; H,
14 12 2
C H N
In summary, we designed a novel Al O /CuI/PANI nano-
2
3
5.37; N, 12.48.
composite which is found to be an efficient and versatile nano-
catalyst for the synthesis of benzimidazole by reaction between
o-phenylenediamine and aldehydes in ethanol as a green
4
1
2-(m-Bromophenyl)-benzimidazole (3f)
1
solvent. This method is advantageous due to its simple pro- Colourless solid; yield: 93%; mp = 248–250 °C; H NMR
cedure for catalyst preparation, ambient reaction conditions (DMSO-d , 400 MHz): δ 13.05 (s, 1H), 8.39 (s, 1H), 8.21–8.19 (d,
6
1
3
and no use of additive/bases with ideal values of green J = 7.75 Hz, 1H), 7.69–7.49 (m, 4H), 7.24–7.22 (m, 2H).
C
metrics. The nanocatalyst was easily recovered and reused for NMR (DMSO-d , 100 MHz): δ 150.07, 132.87, 131.53, 129.36,
6
five constant sets of cycles without much decrease in the cata- 125.83, 122.73. Anal. Calcd for C H BrN : C, 57.17; H, 3.32; N,
1
3
9
2
lytic activity.
10.26; found C, 57.21; H, 3.34; N, 10.29.
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4
2
2
-(p-Bromophenyl)-benzimidazole (3g)
134.32, 131.54, 130.33, 126.48, 125.49, 115.67. Anal. Calcd for
C H ClN : C, 68.28; H, 3.97; N, 12.25; found C, 68.31; H, 3.98;
N, 12.26.
1
1
3
9
2
White solid; yield: 94%; mp = 293–295 °C; H NMR (DMSO-d
00 MHz): δ 8.08–8.06 (d, J = 8.75 Hz, 2H), 7.73–7.72 (d, J =
.50 Hz, 2H), 7.57–7.55 (m, 2H), 7.18–7.16 (m, 2H). C NMR
, 100 MHz): δ 150.64, 132.45, 129.76, 128.83, 123.75,
22.84. Anal. Calcd for C13 BrN : C, 57.17; H, 3.32; N, 10.26;
6
,
4
8
1
3
40
2
-(Furan-2-yl)-benzimidazole (3n)
Pale yellow solid; yield: 91%; mp = 290–292 °C; H NMR
DMSO-d , 400 MHz): δ 13.02 (s, 1H), 7.94 (d, J = 1 Hz, 1H),
.58–7.56 (m, 1H), 7.22–7.19 (m, 4H), 6.74–6.72 (m, 1H).
NMR (DMSO-d , 100 MHz): δ 146.02, 145.07, 144.09, 122.68,
112.77, 110.95; HRMS (ESI): calcd [M + H] 185.0710; found
85.0680; Anal. Calcd for C H N O: C, 71.73; H, 4.38; N,
(DMSO-d
6
1
1
H
9
2
(
7
6
found C, 57.18; H, 3.33; N, 10.27.
1
3
C
4
5
2
-(p-Chlorophenyl)-benzimidazole (3h)
6
+
1
White solid; yield: 95%; mp = 292–294 °C; H NMR (DMSO-d
00 MHz): δ 8.19–8.18 (d, J = 8.50 Hz, 2H), 7.65–7.60 (m, 4H),
.24–7.22 (m, 2H). C NMR (DMSO-d
35.01, 129.54, 128.61, 122.84. Anal. Calcd for C13
8.28; H, 3.97; N, 12.25; found C, 68.24; H, 3.94; N, 12.22.
6
,
1
1
1
8 2
4
7
1
6
1
3
15.21; found C, 71.69; H, 4.37; N, 15.19.
6
, 100 MHz): 150.59,
H
9
ClN : C,
2
Author contributions
4
2
2
-(p-Fluorophenyl)-benzimidazole (3i)
S. K., G. R., S. H., and R. C. designed the schemes. S. K. per-
formed the experiments. S. K., and G. R. evaluated the data
and prepared the figures and tables. G. R., S. K., S. H., and
R. C. revised and reviewed the manuscript.
1
6
White solid; yield: 95%; mp = 248–250 °C; H NMR (DMSO-d ,
6
, 400 MHz): δ 12.95 (s, 1H),
.26–8.23 (m, 2H), 7.68–7.54 (m, 2H), 7.43–7.38 (t, J = 8.88 Hz,
1
4
8
2
00 MHz): H NMR (DMSO-d
1
3
6
H), 7.22–7.21 (d, J = 3 Hz 2H). C NMR (DMSO-d , 100 MHz):
δ 164.75, 162.29, 150.86, 144.23, 135.49, 129.22–129.13 (d, J =
8
1
4
.72 Hz), 127.28–127.26 (d, J = 2.18 Hz), 122.99, 122.17, 119.30,
Conflicts of interest
16.56, 116.34, 111.77. Anal. Calcd for C13
9 2
H FN : C, 73.57; H,
.27; N, 13.20; found C, 73.55; H, 4.26; N, 13.20.
The authors declare no competing financial interest.
4
1
2
-(m-Nitrophenyl)-benzimidazole (3j)
1
Yellow solid; yield: 95%; mp = 282–284 °C; H NMR (DMSO-d , Acknowledgements
6
4
8
7
1
00 MHz): δ 9.02 (s, 1H), 8.63–8.61 (d, J = 7.75 Hz, 1H),
.35–8.32 (m, 1H), 7.88–7.84 (t, 1H), 7.67–7.65 (m, 2H),
.28–7.26 (m, 2H). C NMR (DMSO-d , 100 MHz): δ 149.48,
48.82, 132.96, 132.12, 131.17, 124.72, 123.21, 121.32; HRMS
S. K. acknowledges CSIR for the award of Junior Research
Fellowship (File No: 09/045(1671)/2019-EMR-I) and is also
thankful to the University of Delhi, India-110007.
1
3
6
+
(
ESI): calcd [M + H] 240.0768; found 240.0788; Anal. Calcd for
13 9 3 2
C H N O : C, 65.27; H, 3.79; N, 13.38; found C, 65.29; H,
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3
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4
7
00 MHz): δ 8.24 (s, 1H), 8.17–8.15 (m, 1H), 7.64–7.56 (m, 4H),
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