Synthesis of novel benzimidazoles at room temperature, under solvent-free condition and their biological studies

Article abstract of DOI:10.1007/s13738-020-02019-5

Abstract: An efficient and facile synthesis of substituted novel benzimidazoles (3a–3h) mediated by fruit juices viz. Cocos nucifera L. juice, Citrus limetta juice and Citrus sinensis L. juice, via condensation of substituted aldehydes (1a–1h) and o-pheny

Full text of DOI:10.1007/s13738-020-02019-5

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-020-02019-5
ORIGINAL PAPER
Synthesis of novel benzimidazoles at room temperature,
under solvent‑free condition and their biological studies
Susheel Gulati1 · Rajvir Singh1 · Suman Sangwan1 · Suprita Rana1
Received: 15 November 2019 / Accepted: 22 July 2020
© Iranian Chemical Society 2020
Abstract
An efcient and facile synthesis of substituted novel benzimidazoles (3a–3h) mediated by fruit juices viz. Cocos nucifera L.
juice, Citrus limetta juice and Citrus sinensis L. juice, via condensation of substituted aldehydes (1a–1h) and o-phenylen-
ediammine (2a) under solvent-free condition at room temperature is presented in this paper. The purity of compounds was
confrmed by melting point and thin layer chromatography. All synthesized compounds (3a–3h) were fully characterized
via NMR and FTIR spectral data and evaluated for in vitro herbicidal activity against Raphanus sativus L. (Radish) seeds.
The compounds (3a–3h) were also evaluated for their antibacterial activity against Erwinia cartovora and Xanthomonas
citri by inhibition zone method. Antifungal activity was also determined against Rhizoctonia solani and Colletotrichum
gloeosporioides by poisoned food techniques method. From activity data, it was found that compounds 3d and 3e were most
active against R. sativus L. (root) and R. sativus L. (shoot), respectively. Compound 3g has shown maximum inhibition zone
i.e. 8.00 mm against E. cartovora at 2000 µg/mL concentration. Maximum X. citrii growth was inhibited by compounds 3a
showing inhibition zone 5.20 mm at highest concentration. Compound 3f was found most active against R. solani and C.
gloeosporioides fungus at 2000 µg/mL concentration. In comparison with the conventional methods, the present method
complies with several key requirements of green chemistry principles such as the utilization of renewable feedstock, auxil-
iary aqueous conditions and reduces waste with the use of nature-derived catalyst. Therefore, the present method ofers an
attractive option because of its ecological safety, environmental acceptance, cost efective and easy workup process.
* Susheel Gulati
sgbhuna108@gmail.com
1
Department of Chemistry, Chaudhary Charan Singh Haryana
Agricultural University, Hisar 125004, India
Vol.:(0123456789)
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Journal of the Iranian Chemical Society
Graphic abstract
Keywords Benzimidazole · Cocos nucifera L. juice · Citrus limetta juice · Citrus sinensis L. juice
methods for organic transformations using low cost, natural
Introduction
feedstock extract without purifcation and characterization.
Now a days, fruit juices used in organic synthesis as homo-
geneous catalysts due to which these are highly selective
towards producing desired product. Keeping in view the
biological potential of benzimidazole nucleus, the present
research work was carried out for synthesis of substituted
benzimidazoles in the presence of Cocos nucifera L. juice,
Citrus limetta juice and Citrus sinensis L. juice at room tem-
perature. Short reaction time, excellent yields, mild reaction
conditions, simple workup, solvent-free i.e. no addition of
extra toxic reagents and cost efectiveness and are some mer-
its of this methodology.
Heterocyclic compounds are important class of organic com-
pounds which contain at least one atom other than carbon
atom in their ring. Heterocyclic compounds which having
nitrogen, sulphur and oxygen atom exhibit wide range of
biological activities and their activity depend on number of
heteroatoms, ring size and their structure. One of important
nitrogen containing heterocyclic moiety is benzimidazole
which is a bicyclic compound having imidazole ring fused to
benzene nucleus [1]. The biological properties of benzimi-
dazoles are due to their close relationship with structure of
purines. A number of benzimidazole derivatives having vari-
ous biological activities viz. antimicrobial, antiviral, antifun-
gal, antimalarial, antitumour, anticancer, antihypertensive,
anti-infammatory and antioxidant [2–10]. Many synthetic
methodologies are available for synthesis of benzimidazole
derivatives. General synthesis of benzimidazole derivatives
reported by the condensation reaction of 1,2-phenylenedi-
amine with carboxaldehydes, carboxylic acids or their deriv-
atives [11, 12] such as chlorides, nitriles and orthoesters
under strong acidic conditions with high temperature. The
major drawbacks of this procedure are lower yields, longer
reaction time, tedious workup, expensive reagents and low
atom economy. Therefore, there is still demand for efortless
synthesis of benzimidazole derivatives and replacement of
conventional methodology to develop eco-friendly synthetic
Experimental
All chemicals and solvent used were of analytical grade.
Melting points were determined on Ganson electric melt-
ing point apparatus and are uncorrected. The reaction was
monitored by thin layer chromatography. Infrared spec-
tra (4000–350 cm−1) of the synthesized compounds were
recorded in KBr pellets on Perkin Elmer FT-IR-R2X spec-
trophotometer and frequency is expressed in cm−1. The
1HNMR spectra were recorded in CDCl3 or DMSO-d6
using tetra methyl silane (TMS) as internal reference on
“Brucker Ac 400 F“(400 MHz) nuclear magnetic resonance
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Journal of the Iranian Chemical Society
spectrometer. The chemical shifts values are quoted in delta
(parts per million, ppm). The following abbreviations cor-
relate with the multiplicity of NMR signals: s = singlet,
d=doublet, t=triplet, m=multiplet and brs=broad singlet.
Coupling constant (J) values are expressed in Hz.
Antifungal activity
All synthesized compounds (3a–3h) were evaluated for
their antifungal activity against Rhizoctonia solani and
Colletotrichum gloeosporioides, respectively. Fungal
species were grown in laboratory on Potato dextrose agar
(PDA) media. The antifungal activity was determined
by poisoned food technique method [15]. The required
amount of synthesized compounds dissolved in 1 mL of
DMSO was incorporated aseptically into 99 mL aliquots
of sterilized Potato dextrose agar cooled at 45 °C after
brief shaking. Each lot of medium was poured into Petri
dishes and allowed to solidify. DMSO was used as nega-
tive control. Each dish was inoculated centrally with a
5-mm mycelial disc cut from the periphery of 2–3 days old
fungal colonies. Inoculated Petri plates were incubated in
the dark 25 2 °C for 48–72 h, and colony diameters were
measured periodically till the control dishes were nearly
completely covered with fungus growth. All observations
were made in triplicate. The degree of inhibition of growth
was calculated from the mean diferences between treat-
ments and the control as percentage of latter by using the
formula.
Bioevaluation
Herbicidal activity
Solutions of 50 µg/mL, 100 µg/mL, 150 µg/mL and 200 µg/
mL of the test compounds in DMSO were prepared. Agar
powder (5 g) was put into boiling distilled water (1 L) until
it dissolved, and then cooled down to 40–50 °C. The solution
(2 mL) containing test compounds and melting agar (18 mL)
was mixed, and this mixture was added to a Petridish with
4.5 cm diameter. The agar plate without test compound was
used as an untreated control. The 15 seeds of Raphanus sati-
vus L. (Radish) were put on the surface of the agar plate.
The Petridishes were covered with glass lids, and the cul-
tivation conditions were kept at 25 1 °C and 12 h in light
and 12 h in dark alternating for 7 days. Seven days later, the
root lengths and shoot lengths of Raphanus sativus L. were
measured. The growth inhibitory rate related to untreated
control was determined by given formula [13].
Control − Treated
% Inhibition =
× 100
Control
Control=mycelial growth in control dish, Treated=mycelial
growth in treated dish.
Control − Treated
% Inhibition =
× 100
Control
Statistical analysis
Antibacterial activity
The experiment was performed in triplicates for each treat-
ment, and the mean value was recorded and expressed as
mean SD.
Bacterial species Erwinia cartovora and Xanthomonas citri
were grown on Luria–Bertani medium in laboratory. Anti-
bacterial activity was tested using inhibition zone method
[14]. 250, 500, 1000 and 2000 µg/mL concentrations of
synthesized compounds were prepared from the stock solu-
tion by taking appropriate amount and diluting with DMSO.
DMSO was used as negative control. The circular paper
discs of 10-mm diameter were prepared from Whatman’s
Filter paper No. 1. The disc were kept in Petri plate and
autoclaved at 15 lbs pressure 20 min. Two paper discs were
used for each concentration of the synthesized compounds.
The excess of solution absorbed by paper discs was removed
by holding them vertically by sterile forecep. Such soaked
discs were transferred aseptically to Petri plates containing
media and bacterial suspension spread over the surface. The
Petri plates were kept in an incubator at 25 2 °C overnight
and then examined for inhibition zone at these diferent con-
centrations of compounds. The experiment was performed
in triplicate, and activity was determined on the basis of
inhibition zone (in mm).
Composition and preparation of biocatalyst
Extraction of Cocos nucifera L. juice
Cocos nucifera is a member of family Arecaceae (palm
family). Its juice is also called coconut water and used
for the treatment of high blood pressure, hypertension
and diarrhoea-related dehydration. The main ingredi-
ents per 100 g of coconut juice of Cocos nucifera are
water (94.99 g), carbohydrates (3.71 g), protein (0.72 g),
fat (0.2 g), ascorbic acid (2.4 mg) and pantothenic acid
(0.043 mg). Coconut juice also contains many natural
occurring bioactive enzymes such as acid phosphatase,
catalase, dehydrogenase, diastase, peroxidase, RNA-pol-
ymerase, etc. Due to the presence of ascorbic acid and
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Journal of the Iranian Chemical Society
pantothenic acid, coconut juice is weakly acidic in nature.
The coconut juice was obtained by perforating the fruit
with a knife. The coconut juice was fltered using flter
paper whatman no 1 for the elimination of residues to get
clear juice which used as a catalyst [16].
juice (10 mL) was stirred at room temperature. The progress
of reaction was followed by TLC. The solid was separated
out, then fltered and washed with ice cold water to get the
products (3a–3h), which was further recrystallized with
methanol. All compounds (3a–3h) were characterized by
1H NMR and FTIR spectroscopy.
Preparation of Citrus limetta juice
By Citrus limetta juice (Method B)
Citrus limetta is a species of citrus. Chemical composition
of sweet limes depends on the area where it grows. It con-
tains high amount of ascorbic acid due to which it acts as
acid catalyst in organic synthesis [17]. First of all, wash the
sweet limes and pat them dry. Cut them into two halves.
Then using a citrus juice squeezer, extract the juice. Then,
the juice was fltered through cotton and then through what-
man flter paper no 1 to remove solid material and to get
clear juice which as used as a catalyst.
A mixture of substituted aldehydes (20 mmol) (1a–1h),
o-phenylenediamine (20 mmol) (2a) and Citrus limetta juice
(10 mL) was stirred at room temperature. Completion of
reaction was confrmed by thin layer chromatography. The
solid was separated out, then fltered and washed with ice
cold water to get the products (3a–3h), which was further
recrystallized with methanol. All compounds (3a–3h) were
characterized by 1H NMR and FTIR spectroscopy.
Preparation of Citrus sinensis L. juice
By Citrus sinensis L. juice (Method C)
Citrus sinus is the botanical name of orange and is ever
green fruit. It is known as one of the best citrus fruits which
are rich in vitamin C. Oranges contain diferent types of
carbohydrates, fats and proteins and have a quite high nutri-
tional value than other fruits. [17] It is an excellent anti-
oxidant. Fresh orange was taken and washed it thoroughly
with water and cut by using a knife and then pieces were
pressed manually. Then, the juice was fltered through cot-
ton to remove solid material and to get clear juice which was
used as a catalyst.
To a 50-mL round-bottom fask containing substituted alde-
hydes (20 mmol) (1a–1h), o-phenylenediamine (20 mmol)
(2a) was added with the Citrus sinensis L. juice (10 mL)
and reaction mixture was stirred magnetically at room tem-
perature. The formation of products was monitored using
thin layer chromatography. The solid was separated out, then
fltered and washed with ice cold water to get the products
(3a–3h), which was further recrystallized with methanol.
All compounds (3a–3h) were characterized by 1H NMR and
FTIR spectroscopy.
All the benzimidazoles derivatives (3a–3h) were prepared
according to Method A, B and C (Scheme 1).
General method for the preparation of substituted
benzimidazole derivatives (3a–3h)
By Cocos nucifera L. juice (Method A)
A mixture of o-phenylenediamine (20 mmol) (2a), substi-
tuted aldehydes (20 mmol) (1a–1h) and Cocos nucifera L.
Scheme 1 Synthesis of substi-
tuted benzimidazole derivatives
(3a–3h)
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Journal of the Iranian Chemical Society
juice and Citrus sinensis L. juice, respectively. It was
found out that excellent yield of product i.e. 90% and
95% was obtained, respectively, when the concentration
of Citrus limetta juice and Citrus sinensis L. juice was
10 mL in reaction mixture and time of completion of
reaction was also less (Table 1, Entry 4). The physical
data of this study are presented in Table 2. After com-
pletion of the reaction, the solid products were collected
by simple fltration and then recrystallized in methanol
because of its polar and volatile nature to aford pure
benzimidazole derivatives (3a–3h) as shown in Fig. 1.
The structure of synthesized compounds was confrmed
Results and discussion
Synthesis of benzimidazole derivatives (3a–3h) were
reported by reaction between substituted aldehydes viz.
4-Methoxy benzaldehyde (1a), 2-Hydroxy benzalde-
hyde (1b), 3,4-Dihydroxy benzaldehyde (1c), 3-Nitro
benzaldehyde (1d), 3,4-Dimethoxy benzaldehyde (1e),
4-Chloro benzaldehyde (1f), 4-Methyl benzaldehyde
(1 g), 3-Hydroxy benzaldehyde (1 h) with o-phenylene-
diammine (2a) in the presence of Cocos nucifera L. juice
(10 mL)/Citrus limetta juice (10 mL)/Citrus sinensis L.
juice (10 mL) (Scheme 1). The progress of reaction was
monitored by TLC using Hexane: Ethyl acetate (80:20,
v/v) as an eluent.
1
by HNMR and FTIR analysis as well as comparison of
their melting points with those of reported compounds.
From spectral study, it was found that the compound (3a)
viz. 2-(4-Methoxyphenyl)-1H-benzo[d]imidazole showed
1H NMR spectrum in DMSO-d6, displayed a singlet at δ
3.31 integrating for three proton of aryl methoxy group,
singlet at δ 8.56 integrating for one proton of NH group,
multiplet at δ 6.55–7.95 integrating for eight proton of
aryl group and melting point 214–216 °C. The compound
(3a) viz. 2-(4-Methoxyphenyl)-1H-benzo[d]imidazole dis-
played IR absorptions at 3377.4, 1600.9, 1164.5, 3175.8
and 1274.4 cm−1 indicating the presence of NH, C=C
aromatic, C–O–C, C=CH and OCH3, respectively. The
compound (3b) viz. 2-(1H-Benzo[d]imidazol-2-yl) phe-
First, the model reaction between 4-Hydroxy-3-meth-
oxybenzaldehyde (20 mmol) and o-phenylenediammine
(20 mmol) using Cocos nucifera L. juice was carried out
for synthesis of benzimidazole derivatives at room tem-
perature. It was observed that when the amount of Cocos
nucifera L. juice was only 4.0 mL in reaction mixture
then yield of product was only 64% and time of comple-
tion of reaction was also more i.e. 10 h (Table 1, Entry
1). But when the amount of Cocos nucifera L. juice was
increased from 4.0 to 10.0 mL, then yield of product was
maximum i.e. 88% and time of completion of reaction
was also reduced (Table 1, Entry 4). Through the result
of initial possibility and optimization study under con-
sideration, we move our attention towards explored the
same model reaction in the presence of Citrus limetta
1
nol showed H NMR spectrum in DMSO-d6, displayed
a singlet at δ 8.81 integrating for one proton OH group,
singlet at δ 12.99 integrating for one proton of NH group,
multiplet at δ 6.91–8.81 integrating for eight proton of aryl
Table 1 Model reaction
Entry
Catalyst concen- Method A
Method B
Time (h)
Method C
Time (h)
of 4-hydroxy-3-
tration (mL)
methoxybenzaldehyde
(20 mmol),
Time (h)
Yield (%)
Yield (%)
Yield (%)
1
2
3
4
4.0
6.0
8.0
10
7.5
6
64
78
86
88
6
4.5
4
67
75
86
90
11
7
6
85
88
92
95
o-phenylenediammine
(20 mmol) using Cocos nucifera
L. juice, Citrus limetta juice
and Citrus sinensis L. juice as
catalyst
10.0
4.5
3
5
Table 2 Physical data of substituted benzimidazole derivatives (3a–3h)
S. nos. Product Ar Method A Method B
Time (h) Yield (%) Time (h) Yield (%) Time (h) Yield (%)
Method C
m.p. (°C)
1
2
3
4
5
6
7
8
3a
3b
3c
3d
3e
3f
Ph–OCH3
Ph–OH
Ph–(OH)2
Ph–NO2
Ph–(OCH3)2
Ph–Cl
4
8
10
4
4
9
79
86
85
92
90
89
78
92
4
4
4
2
6
9
5
4
84
82
78
86
80
81
80
83
4
6
6
4
10
6
90
92
93
89
78
76
81
82
214–216 (Lit., 216–218) [18]
270–272 (Lit., 272–274) [19]
232–234 (Lit., 236–238) [20]
298–300 (Lit., 302–304) [18]
232–234 (Lit., 228–230) [18]
285–286 (Lit., 290–292) [18]
236–238 (Lit., 240–242) [18]
270–272 (Lit., 272–274) [19]
3g
3h
Ph–CH3
Ph–OH
6
12
7
5
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Journal of the Iranian Chemical Society
Fig. 1 Substituted benzimidazole derivatives (3a–3h)
group and melting point 270–272 °C. The compound (3d)
viz. 2-(3-Nitrophenyl)-1H-benzo[d]imidazole displayed IR
absorptions at 3376.5, 1521.3, 1349.2 and 2881.8 cm−1
indicating the presence of NH, C=C aromatic, NO2 and
C=CH, respectively, and melting point 298–300 °C.
The compound (3e) viz. 2-(3,4-Dimethoxyphenyl)-1H-
benzo[d]imidazole showed 1H NMR spectrum in DMSO-
d6, displayed a singlet at δ 3.83 integrating for three
proton of aryl methoxy group, singlet at δ 3.86 integrat-
ing for three proton of aryl methoxy group, singlet at δ
8.53 integrating for one proton of NH group, multiplet
at 6.55–7.68 δ integrating for seven proton of aryl group
and melting point 232–234 °C. The compound (3f) viz.
1
2-(4-Chlorophenyl)-1H-benzo[d]imidazole showed H
NMR spectrum in DMSO-d6, displayed a singlet at 13.08
δ integrating for one proton of NH group, multiplet at δ
6.37–8.22 of aryl group and melting point 285–286 °C.
In order to show the beauty of current protocol, the previ-
ous protocols and their yields for the synthesis are sum-
marized in Table 3. We observed that Cocos nucifera L.
juice, Citrus limetta juice and Citrus sinensis L. juice cata-
lyst gives the best catalytic activity in terms of product
yield and reaction time as compared to other catalysts in
literature. Therefore, the present procedure for synthesis
Table 3 Comparison for diferent catalysts used for synthesis of benzimidazole derivatives (3a–3h)
S. nos.
Catalyst
Solvent
Temperature (°C)
Time (h)
Yield (%)
References
1
2
3
4
5
6
7
8
Zn(OAc)2
Solvent-free
H2O:CH3OH
DMF
PEG
H2O
H2O
CH3OH
Solvent-free
Solvent-free
EtOH
Ambient temperature
Ambient temperature
80 °C
50 °C
90 °C
Ambient temperature
Ambient temperature
30 °C
110 °C
Ambient temperature
Ambient temperature
RT
RT
RT
10
24
10
2
2
45
4
2
6
1.5
2
4.5
3
92
94
85
98
75
75
93
89
90
75
71
88
90
95
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
[29]
[30]
[30]
Current work
Current work
Current work
Zn2+–K10-clay
p-TsOH
CAN
Glycerol
I2/K2CO3
Cu-np/SiO2
Iron (III) sulphate-silica
PEG-400
Silica sulphuric acid
Silica sulphuric acid
Cocos nucifera L. juice
Citrus limetta Juice
Citrus sinensis L. juice
9
10
11
12
13
14
Water
Solvent-free
Solvent-free
Solvent-free
5
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Journal of the Iranian Chemical Society
Scheme 2 The plausible mechanism for synthesis of substituted benzimidazoles (3a–3h)
of benzimidazole derivatives is considered as sustainable
and eco-friendly protocol. The plausible mechanism for
the formation of substituted benzimidazoles is shown in
Scheme 2. From mechanism, it was found that carbonyl
group is activated by acidity of natural catalyst viz. Cocos
nucifera L. juice, Citrus limetta juice and Citrus sinen-
sis L. juice for nucleophilic attack that led to formation
of intermediate (I). The intermediate (I) undergo intra-
molecular cyclization proceeds to form desired products
(3a–3h).
2‑(3‑Nitrophenyl)‑1H‑benzo[d]imidazole (3d)
M.p. 298–300 °C; IR (νmax cm−1) (neat): 3376.5 (NH),
1521.3 (C=C, aromatic), 1349.2 (NO2); 2881.8 (C=CH).
2‑(3,4‑Dimethoxyphenyl)‑1H‑benzo[d]imidazole (3e)
M.p. 232–234 °C; 1H NMR (400 MHz, DMSO-d6): δ 3.83
(s, 3H, Ar-OCH3); 3.86 (s, 3H, Ar-OCH3), 6.55–7.68 (m,
7H, J=8 Hz, Ar–H); 8.53 (s, 1H, NH).
Characterization data of selected compounds
2‑(4‑Chlorophenyl)‑1H‑benzo[d]imidazole (3f)
1
2‑(4‑Methoxyphenyl)‑1H‑benzo[d]imidazole (3a)
M.p. 285–286 °C; H NMR (400 MHz, DMSO-d6): δ
6.37–8.22 (m, Ar–H, J=8 Hz); 13.08 (s, 1H, NH).
M.p. 214–216 °C; 1H NMR (400 MHz, DMSO-d6): δ 3.31
(s, 3H, OCH3); 6.55–7.95 (m, 8H, J=8 Hz, Ar–H); 8.56
(s, 1H, NH); IR (νmax cm−1) (neat): 3377.4 (NH); 1600.9
(C=C, aromatic); 1164.5 (C–O–C); 3175.8 (C=CH);
1274.4 (OCH3).
Herbicidal activity
All compounds (3a–3h) were screened for herbicidal activ-
ity against Raphanus sativus L. at various concentrations
viz. 200, 150, 100 and 50 µg/mL was shown in Table 4.
The results were quoted in the form of primary screening.
All compounds were diluted to 1000 µg/mL concentration
as a stock solution. Herbicidal activities of compounds
were evaluated against Raphanus sativus L. by inhibi-
tory efect of compounds on the growth of weed roots and
2‑(1H‑Benzo[d]imidazol‑2‑yl) phenol (3b)
M.p. 270–272 °C; 1H NMR (400 MHz, DMSO-d6): δ 8.81
(s, 1H, OH); 6.91–8.81 (m, 8H, J=8 Hz, Ar–H); 12.99 (s,
1H, NH).
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Journal of the Iranian Chemical Society
Table 4 Herbicidal activity of substituted benzimidazoles (3a–3h)
Compounds
Growth inhibition (%)
Root
Shoot
50 (µg/mL)
100 (µg/mL)
150 (µg/mL)
200 (µg/mL)
50 (µg/mL)
100 (µg/mL)
150 (µg/mL)
200 (µg/mL)
3a
3b
3c
3d
3e
3f
20.00 1.19
6.66 0.58
11.36 1.01
16.98 0.98
13.33 1.16
16.66 1.02
9.65 0.48
10.00 0.97
33.33 1.03
16.66 0.65
18.58 0.99
26.14 0.95
26.66 1.05
26.66 1.44
21.78 0.86
20.00 0.89
43.33 0.98
30.00 1.33
29.38 1.02
43.58 0.61
43.33 0.99
40.00 1.14
31.25 0.52
30.00 2.04
50.00 0.86
43.33 0.98
47.98 0.81
54.98 1.16
53.33 1.71
50.00 0.57
46.87 1.08
46.66 0.64
33.84 1.08
29.23 0.93
10.98 0.80
11.25 0.66
24.61 0.48
24.61 0.38
7.98 0.60
26.15 1.05
40.00 0.81
33.84 0.59
16.39 0.55
23.59 0.79
35.38 0.41
35.38 0.40
16.45 0.50
33.84 0.70
49.23 0.65
38.46 1.05
26.39 0.99
40.89 1.97
46.15 0.81
43.07 0.86
27.87 1.59
43.07 1.03
52.30 0.97
46.15 1.02
45.38 1.51
52.78 1.75
55.38 0.97
50.76 0.85
44.87 0.85
50.76 1.59
3g
3h
All values are mean SD
Fig. 2 Herbicidal activity of
substituted benzimidazoles
(3a–3h) against Raphanus
sativus L. (root)
shoots. The percentage of inhibition growth was calculated
from mean diferences between treated and control. From
the herbicidal activity results (Figs. 2, 3), we observed that
compound 3d was exhibited maximum percentage growth
inhibition i.e. 54.98 against Raphanus sativus L. (root)
whereas compound 3e was exhibited maximum percentage
growth inhibition i.e. 55.38 against Raphanus sativus L.
(shoot), respectively, at 200 µg/mL concentrations. The
growth inhibition may be attributed to substitution of nitro
and methoxy groups on phenyl ring.
Antibacterial activity
The favourable herbicidal activity of synthesized compounds
(3a–3h) has inspired authors to test further for antibacterial
activity. All synthesized compounds (3a–3h) were screened
for their in vitro antibacterial activity against two bacterial
strains Erwinia cartovora and Xanthomonas citri by inhi-
bition zone method using DMSO as negative control. The
results of antibacterial activity of synthesized compounds
were shown in Table 5 and Figs. 4, 5. Compound 3a and
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Journal of the Iranian Chemical Society
Fig. 3 Herbicidal activity of
substituted benzimidazoles
(3a–3h) against Raphanus
sativus L. (shoot)
Table 5 Antibacterial activity of substituted benzimidazoles (3a–3h)
Compounds
Inhibition zone (mm)
Bacteria
Erwinia Cartowora (conc.) µg/mL
Xanthomonas citrii (conc.) µg/mL
250
500
1000
2000
250
500
1000
2000
3a
3b
3c
3d
3e
3f
a
a
a
a
a
a
a
2.00 0.30
0.20 0.02
a
a
1.00 0.10
a
1.50 0.20
a
3.50 0.20
0.60 0.07
a
a
2.00 0.18
a
2.10 0.18
0.30 0.02
4.50 0.26
0.70 0.07
a
5.20 0.35
1.10 0.22
a
0.30 0.01
4.20 0.20
1.50 0.20
4.00 0.25
1.60 0.20
2.00 0.24
2.50 0.20
a
2.50 0.25
3.00 0.15
8.00 0.58
4.00 0.45
0.90 0.07
a
a
0.80 0.07
2.00 0.30
1.00 0.12
1.40 0.25
a
a
1.50 0.15
3.90 0.30
2.00 0.27
2.00 0.13
a
a
1.90 0.07
6.00 0.49
3.00 0.45
a
3.40 0.20
0.50 0.07
3.20 0.30
0.80 0.07
3g
3h
All values are mean SD. a: No inhibition zone
3d has shown no inhibition zone at all the concentrations
against Erwinia cartovora. Compound 3b has shown no
inhibition zone at lower concentrations. Compound 3b
exhibited 2.00-mm inhibition zone against Erwinia carto-
vora at 2000 µg/mL concentration. Compound 3e has shown
no inhibition zone at lower concentrations. Compound 3e
exhibited 2.50-mm inhibition zone against Erwinia carto-
vora at 2000 µg/mL concentration. Compound 3c has shown
no inhibition zone at all the concentrations against Xan-
thomonas citri. Compound 3d has shown no inhibition zone
at lower concentrations. Compound 3d exhibited 0.30-mm
inhibition zone against Xanthomonas citri at 2000 µg/mL
concentration. Compound 3f has shown no inhibition zone
at lower concentrations. Compound 3f exhibited 0.50-mm,
1.50-mm inhibition zone against Xanthomonas citri at 1000
and 2000 µg/mL concentrations, respectively. Compound 3h
has shown no inhibition zone at 250 µg/mL concentration.
Compound 3g exhibited 0.30-mm, 0.80-mm and 1.60-mm
inhibition zone against Erwinia cartovora at 500, 1000 and
2000 µg/mL concentrations, respectively. Maximum Erwinia
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Journal of the Iranian Chemical Society
Fig. 4 Antibacterial activity
of substituted benzimidazoles
(3a–3h) against Erwinia car-
towora
Fig. 5 Antibacterial activity
of substituted benzimidazoles
(3a–3h) against Xanthomonas
citrii
cartovora growth was inhibited by compounds 3g showing
inhibition zone 2.00–8.00 mm. Maximum Xanthomonas
citri growth was inhibited by compounds 3a showing inhi-
bition zone 2.00–5.20 mm. This inhibition may be due to the
presence of methyl and methoxy groups on phenyl groups.
Antifungal activity
All synthesized compounds (3a–3h) were evaluated for their
antifungal activity against 2 fungal strains viz. Rhizocto-
nia solani and Colletotrichum gloeosporioides by poisoned
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Journal of the Iranian Chemical Society
Table 6 Antifungal activity of substituted benzimidazoles (3a–3h)
Compounds
Growth inhibition (%)
Fungi
Rhizoctonia Solani (conc.) µg/mL
Collectotrichum Gleosporides (conc.) µg/mL
250
500
1000
2000
250
500
1000
2000
3a
3b
3c
3d
3e
3f
a
a
a
a
a
a
a
a
10.36 1.00
a
a
a
16.63 1.14
30.36 1.34
a
28.49 0.52
a
a
a
37.89 0.52
59.78 0.64
a
55.20 0.70
a
a
12.79 0.71
51.69 1.08
77.30 0.57
a
72.36 0.51
14.26 0.93
a
30.31 0.86
72.89 0.71
86.24 1.95
a
15.26 1.04
37.50 1.01
18.75 1.06
40.00 1.29
a
39.65 1.38
59.37 0.50
40.62 0.62
62.37 0.99
a
54.80 0.78
78.12 0.87
56.25 0.52
80.13 0.33
24.54 1.62
52.78 0.79
74.69 2.27
87.50 1.13
75.00 0.83
89.38 0.54
40.69 1.15
73.49 0.50
3g
3h
14.69 1.57
35.89 0.89
11.36 0.94
31.69 2.20
48.87 1.19
68.69 1.60
All values are mean SD. a: No growth inhibition
Fig. 6 Antifungal activity of
substituted benzimidazoles
(3a–3h) against Rhizoctonia
solani
food technique method. DMSO was used as negative con-
trol against fungal strains. The result of antifungal activ-
ity of tested compounds is shown in Table 6 and Figs. 6, 7.
Most of synthesized compounds possess a moderate to good
activity against R. solani and C. gloeosporioides, respec-
tively. Compounds 3a and 3b showed no antifungal activity
at all concentrations against R. solani. Compound 3g has
shown no growth inhibition up to 500 µg/mL concentrations
against R. solani. Compound 3g exhibited 24.54 and 40.69%
growth inhibition against R. solani fungus at 1000 µg/mL
and 2000 µg/mL concentrations, respectively. Compounds
3c and 3g showed no antifungal activity at all concentra-
tions against C. gloeosporioides. Compound 3b has shown
no growth inhibition up to 1000 µg/mL concentration against
C. gloeosporioides. Compound 3b exhibited 14.26% growth
inhibition against C. gloeosporioides fungus at 1000 µg/mL
concentration. Compound 3d has shown no growth inhibi-
tion at lower concentrations. Compound 3d exhibited 12.79
and 30.31% growth inhibition against C. gloeosporioides
fungus at 1000 µg/mL and 2000 µg/mL concentrations,
respectively. From antifungal activity results, we concluded
that compound 3f was shown to most promising against R.
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Journal of the Iranian Chemical Society
Fig. 7 Antifungal activity of
substituted benzimidazoles
(3a–3h) against Colletotrichum
gloeosporioides
solani and C. gloeosporioides. This result may be due to
substitution of chloro group on phenyl ring.
Compliance with ethical standards
Conflict of interest Authors declare that there is no confict of interest
regarding the publication of this paper.
Conclusions
References
An eco-friendly, solvent-free methodology has been devel-
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(3a–3h) were fully analysed via NMR and FTIR spectral
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no extra energy investment, no toxic by-products and inex-
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