A one-pot synthesis of benzimidazoles via aerobic oxidative condensation of benzyl alcohols with o-phenylenediamines catalyzed by [MIMPs]+Cl-/NaNO2/TEMPO

Article abstract of DOI:10.1177/1747519820912163

The ionic liquid 1-methyl-3-(3-sulfopropyl)imidazolium chloride ([MIMPs]⁺Cl^-) in combination with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and sodium nitrite (NaNO₂) as a catalytic system demonstrates high efficiency in the one-pot two-step aerobic oxidative condensation of benzyl alcohols with 1,2-phenylenediamines to give benzimidazoles. Various benzimidazoles are obtained in good to excellent yields by this strategy.

Full text of DOI:10.1177/1747519820912163

912163CHL0010.1177/1747519820912163Journal of Chemical ResearchGeng et al.
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Journal of Chemical Research
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A one-pot synthesis of benzimidazoles via
aerobic oxidative condensation of benzyl
alcohols with o-phenylenediamines
https://doi.org/10.1177/1747519820912163
DOI: 10.1177/1747519820912163
journals.sagepub.com/home/chl
catalyzed by [MIMPs]+Cl-/NaNO2/TEMPO
Zhenzhen Geng1, Hong-yu Zhang1, Guohui Yin1,
Yuecheng Zhang1,2 and Jiquan Zhao1
Abstract
The ionic liquid 1-methyl-3-(3-sulfopropyl)imidazolium chloride ([MIMPs]+Cl-) in combination with 2,2,6,6-
tetramethylpiperidine-1-oxyl (TEMPO) and sodium nitrite (NaNO2) as a catalytic system demonstrates high efficiency
in the one-pot two-step aerobic oxidative condensation of benzyl alcohols with 1,2-phenylenediamines to give
benzimidazoles. Various benzimidazoles are obtained in good to excellent yields by this strategy.
Keywords
1-methyl-3-(3-sulfopropyl)imidazolium chloride, acidic ionic liquids, benzimidazoles, benzyl alcohols,
o-phenylenediamines
Date received: 9 December 2019; accepted: 19 February 2020
generally required in the reported oxidative condensation
Introduction
of alcohols with o-phenylenediamines to give benzimida-
Benzimidazole is an important structural motif found in a
zoles,22–25,28–31 which represents a big obstacle in large-
wide range of natural and bioactive compounds. The ben-
scale applications. At the same time, metal-based oxidative
zimidazole nucleus has been employed as a privileged
condensation processes may leave traces of poisonous
scaffold to synthesize various therapeutic drugs such as
heavy metals in drugs, which are harmful to patients.
anti-HIV, antifungal, antitumor, anti-ulcer, anticancer, and
anti-inflammatory agents.1–11 Therefore, many protocols
have been developed to synthesize benzimidazoles. The
traditional methods to synthesize benzimidazoles include
1School of Chemical Engineering and Technology, Hebei University of
Technology, Tianjin, P.R. China
the condensation of o-phenylenediamines with aldehydes, 2Hebei Provincial Key Lab of Green Chemical Technology and High
Efficient Energy Saving, Hebei University of Technology, Tianjin, P.R.
China
carboxylic acids, amides, acid chlorides, esters, and nitriles
in strong acid mediums at high temperature.12–20
Benzimidazoles can also be obtained by the oxidative con-
densation of alcohols or amines with o-phenylenedi-
amines.21–27 Compared to other protocols, the oxidative
condensation of alcohols with o-phenylenediamines has
the advantages of easy availability, low toxicity, low cost
of the starting materials, and mild reaction conditions.
However, transition metals, especially noble metals, are
Corresponding authors:
Yuecheng Zhang, School of Chemical Engineering and Technology,
Hebei University of Technology, Tianjin 300401, P.R. China.
Email: yczhang@hebut.edu.cn
Jiquan Zhao, School of Chemical Engineering and Technology, Hebei
University of Technology, Tianjin 300401, P.R. China.
Email: zhaojq@hebut.edu.cn

2
Journal of Chemical Research 00(0)
Therefore, it is still necessary to develop efficient, transi- particular, some ILs as catalysts exhibit good performances
tion metal-free, economic, and environmentally friendly in the oxidative condensation of aldehydes or benzylamines
protocols for the synthesis of benzimidazoles via oxidative with o-phenylenediamine to give benzimidazoles.46–49
condensation of alcohols with o-phenylenediamines.
More particularly, some Brönsted acid ILs as catalysts per-
As disclosed in the literature,13,30 the oxidative con- formed well in condensation reactions to afford benzimida-
densation of an alcohol with a o-phenylenediamine to zoles and bis(arylidene)cycloalkanones.50,51
give a benzimidazole is accomplished via three elemen-
Inspired by the above-reported results that acidic ILs in
tary steps, which are catalytic oxidation of the alcohol combination with TEMPO and NaNO2 to form a transition
to an aldehyde, condensation of the aldehyde with metal-free catalytic system might be effective in one-pot,
o-phenylenediamine to afford an imine being in equilib- two-step synthesis of benzimidazoles from alcohols and
rium with a dihydrobenzazole, and catalytic oxidative o-phenylenediamines in an environmentally friendly man-
dehydrogenation of the dihydrobenzazole to the benzi- ner, we prepared several 1-propylsulfonic acid-functional-
midazole. In the transformation, the aerobic oxidation ized ILs. These acidic ILs in combination with TEMPO and
of the alcohol to the aldehyde is an independent step, NaNO2 were then tested in the one-pot, two-step aerobic
but the condensation and dehydrogenation cyclization oxidative condensation of alcohols with o-phenylenedi-
(CDHC) processes are inseparable, being called the sec- amines to give benzimidazoles.
ond step.
The aerobic oxidation of alcohols to carbonyl com-
pounds has been intensively investigated. Several TEMPO
Results and discussion
(2,2,6,6-tetramethylpiperidineoxy)-based transition metal-
free catalytic systems have proved to be very efficient for
the oxidation of alcohols to aldehydes or ketones with
molecular oxygen as the terminal oxidant,32–43 among
which those consisting of acid, nitrite sources, and TEMPO,
such as HCl/sodium nitrite (NaNO2)/TEMPO and [Imim-
TEMPO]+X/[Imim-COOH]+X/NaNO2, are the most
attractive due to their high efficiency, easy availability, and
mild reaction conditions.36,39 Either HCl or [Imim-COOH]
is necessary to convert nitrite into nitrous acid in situ in the
catalytic cycles. Besides, using [Imim-COOH] instead of
HCl has the advantage of avoiding corrosion to equipment
caused by chloride in the large-scale practice.
Several ILs, as shown in Scheme 1, were synthesized and
characterized. The results were in agreement with those in
the literature.52–54
First, [MIMPs]+Cl−/NaNO2/TEMPO was evaluated in
the aerobic oxidation of benzyl alcohol to benzaldehyde in a
CH3CN/H2O mixture with a volume ratio of 10:1 and a tem-
perature range of 30°C–50°C. As shown in Table 1, the
reaction proceeded slowly at 30°C, and the conversion of
benzyl alcohol was only 11% in 7h (Table 1, entry 1). When
the reaction temperature was raised from 30°C to 45°C, the
On the contrary, ionic liquids (ILs) are substances with
special properties, such as exceptional thermal and chemi-
cal stability and negligible vapor pressure. Because of these
important features, ILs have been increasingly applied in
catalytic synthesis, either as solvents or as catalysts.44–47 In
Scheme 1. The structures of the ILs.
Table 1. Reaction conditions for the oxidation of benzyl alcohol to benzaldehyde.a
Entry
T1 (°C)b
Solvent
t1 (h)b
Conversion (%)c
Selectivity (%)c
1
2
3
4
5
6
7
8
30
35
40
45
50
45
45
45
45
45
45
CH3CN/H2O
CH3CN/H2O
CH3CN/H2O
CH3CN/H2O
CH3CN/H2O
Dioxane/H2O
EtOAc/H2O
Toluene/H2O
DMF/H2O
7
7
7
5
5
7
7
7
7
7
7
11
36
>99
>99
>99
12
21
5
9
9
>99
>99
>99
>99
94
98
96
97
96
9
10
11
DCM/H2O
DME/H2O
97
98
8
EtOAc: ethyl acetate; DMF: dimethylformamide; DCM: dichloromethane; DME: dimethyl ether.
aUnless noted otherwise, the reaction conditions are as follows: benzyl alcohol (2mmol), [MIMPs]+Cl− (20mol%), TEMPO (5mol%), NaNO2
(8mol%), CH3CN/H2O (2.0mL/0.2mL), and atmospheric O2.
bT1: reaction temperature during oxidation of the alcohol to the aldehyde; t1: reaction time for the oxidation of the alcohol to the aldehyde.
cConversions and selectivity were based on the gas chromatography (GC) analysis with area normalization.

Geng et al.
3
Table 2. Acidic ILs catalyzed aerobic oxidative condensation of benzyl alcohol with o-phenylenediamine to give
2-phenylbenzimidazole.a
Entry
IL
t1 (h)b
Conversion (%)c
Selectivity (%)c
t2 (h)b
Yield (%)d
1
2
3
4
5
6
7
8
[MIMPs]+Cl−
[PyPs]+Cl−
5
1.5
7
2
2
2
7
7
>99
>99
78
>99
>99
>99
>99
62
>99
>99
99
>99
>99
>99
>99
98
8
6
5
6
10
7
85
49
49
38
42
42
41
35
[MIMPs]+HSO−4
[PyPs]+HSO−4
[MIMPs]+H2PO−4
[PyPs]+H2PO−4
[MIMPs]+PF6−
4
4
[PyPs]+PF6−
IL: ionic liquid.
aUnless noted otherwise, the reaction conditions are as follows: benzyl alcohol (2mmol), o-phenylenediamine (2mmol), IL (20mol%), TEMPO
(5mol%), NaNO2 (8mol%), CH3CN/H2O (2.0mL/0.2mL), T1 =45°C, T2 =45°C, and atmospheric O2.
bt1: reaction time in step 1; t2: reaction time in step 2.
cConversions and selectivity, referring to the alcohol oxidation step, were based on the gas chromatography (GC) analysis with area normalization.
dIsolated yields of 2-phenylbenzimidazole from benzyl alcohol and o-phenylenediamine.
conversion of benzyl alcohol increased gradually, and the
With these results in hand, the IL/NaNO2/TEMPO cata-
reaction time was also reduced (Table 1, entries 1–4). When lytic systems were then applied to the one-pot, two-step
the reaction was conducted at 45°C for 5h, the benzyl alco- aerobic oxidative condensation of benzyl alcohol with
hol was converted into benzaldehyde quantitatively. A fur- o-phenylenediamine to give 2-phenylbenzimidazole at
ther increase in the reaction temperature to 50°C led to a 45°C in both steps. To our delight, an isolated yield of 85%
decrease in the selectivity for benzaldehyde due to over oxi- of 2-phenylbenzimidazole was obtained after the CDHC
dation of benzaldehyde to benzoic acid (Table 1, entry 5). reaction lasting for 8h under the catalysis of [MIMPs]+Cl−/
Next, the reaction was also performed in other solvent/water NaNO2/TEMPO (Table 2, entry 1). However, much lower
mixtures; however, poor results were obtained in all the yields of 2-phenylbenzimidazole were obtained under the
cases (Table 1, entries 6–11). The influence of the amount of catalysis of other IL/NaNO2/TEMPO catalytic systems
water on the whole reaction was also investigated, and the (Table 2, entries 2–8). The results indicated that the aerobic
results are given in Supporting Information (Table S4). At oxidative condensation of benzyl alcohol with o-phenylen-
lower water loading, longer reaction time was required to ediamine to give 2-phenylbenzimidazole was mainly
finish the oxidation of benzyl alcohol to give benzaldehyde, affected by the second step, that is, the CDHC reaction.
and the yield of 2-phenylbenzimidazole was lower. With the Obviously, the CDHC reaction was related to both the cati-
increase in CH3CN/H2O ratio to 2.0mL/0.2mL, the oxida- onic and anionic moieties of the ILs. Except for the ILs
tion rate increased and the yield of 2-phenylbenzimidazole with an H2PO-4 anion, the IL with a methylimidazolium
reached a maximum of 95%. A further increase in the cation generally gave a higher yield of benzimidazole than
amount of water did not affect the oxidation rate, but led to that with a pyridinium cation under the reaction conditions
low yield of 2-phenylbenzimidazole. It is assumed that (see footnote a in Table 2). Whether the cationic moiety
water is beneficial for [MIMPs]+Cl− to dissolve in acetoni- was methylimidazolium or pyridinium, the IL with a Cl−
trile. However, the high concentration of water will hinder anion gave good results, while that with a PF- anion
6
the dehydration in the condensation reaction.
showed poor results.Among all the eight ILs, [MIMPs]+Cl−
The other acidic ILs were then compared with performed best in the transformation. From these results, it
[MIMPs]+Cl− in the aerobic oxidation of benzyl alcohol to can be concluded that the CDHC of benzaldehyde with
benzaldehyde under the same conditions (step 1), followed o-phenylenediamine was catalyzed by the cationic moiety
by evaluation in the condensation of benzaldehyde gener- instead of H+ in the ILs, similar to the IL-catalyzed synthe-
ated in situ with o-phenylenediamine to give 2-phenylben- sis of benzimidazoles from alcohols and o-phenylenedi-
zimidazole. As shown in conversion and selectivity amines reported in the literature.47
columns in Table 2, the catalytic systems from all the ILs
Next, the effect of the catalyst loading on the whole reac-
in combination with TEMPO and NaNO2 were efficient in tion was investigated, and the results are given in Table S1
the aerobic oxidation of benzyl alcohol to benzaldehyde, (see the Supporting Information). In the case of 15mol% of
and benzaldehyde was achieved quantitatively except for [MIMPs]+Cl−, 5mol% of TEMPO, and 8mol% of NaNO2,
+
+
the cases of MIMPs HSO− and PyPs PF− , which the conversion of benzyl alcohol was only 26%, which was
[
]
[
]
4
6
could be ascribed to the acidities of the ILs being strong not enough to support the second-step reaction. With an
enough to convert NaNO2 into HNO2 smoothly, thus pro- increase in the [MIMPs]+Cl− loading, and keeping the
moting the aerobic oxidation of benzyl alcohol.34–36
amounts of TEMPO and NaNO2 constant, the time to finish

4
Journal of Chemical Research 00(0)
Table 3. Synthesis of benzimidazoles from alcohols and
the transformation of benzyl alcohol into benzaldehyde
always decreased (Table S1, entries 1–5). However, the yield
of benzimidazole reached a maximum of 85% at the
[MIMPs]+Cl− loading of 20mol% (Table S1, entry 3). A fur-
ther increase in the catalyst loading to 25mol% led to a
decrease in the yield of 2-phenylbenzimidazole to 72%,
whichmightbeduetothecombinationofacidic[MIMPs]+Cl−
with basic o-phenylenediamine, preventing the condensation
reaction of benzaldehyde with o-phenylenediamine. The
optimum loadings of [MIMPs]+Cl−, NaNO2, and TEMPO
were determined to be 20, 8, and 5mol%, respectively.
After determination of the optimum catalytic system,
the effect of the molar ratio of benzyl alcohol to o-phe-
nylenediamine was investigated by maintaining the reac-
tion conditions constant. As shown in Table S2 (see the
Supporting Information), the yield of 2-phenylbenzimida-
zole initially increased with an increase in the molar ratio of
o-phenylenediamine to benzyl alcohol, and then decreased
slightly with a further increase in the molar ratio. The high-
est yield of 90% was obtained when the molar ratio of
o-phenylenediamine to benzyl alcohol was 1:1.1. A higher
amount of o-phenylenediamine could suppress the forma-
tion of 1-benzyl-2-phenylbenzimidazole, which is a major
by-product in the synthesis of 2-phenylbenzimidazole.
However, a much higher quantity of o-phenylenediamine
will also lead to combination of [MIMPs]+Cl− with the
basic o-phenylenediamine, which will decrease the cataly-
sis of [MIMPs]+Cl− in the CDHC of the aldehyde with
o-phenylenediamine to form 2-phenylbenzimidazole.
Finally, the effect of temperature on the CDHC reaction
was studied by maintaining the other reaction conditions
constant. As shown in Table S3 (see the Supporting
Information), the yield of 2-phenylbenzimidazole increased
gradually with an increase in the reaction temperature and
reached a maximum of 95% at 55°C (Table S3, entries
1–3). A further increase in the reaction temperature led to a
decrease in the yield of 2-phenylbenzimidazole due to the
preferred formation of 1-benzyl-2-phenylbenzimidazole at
high temperature (Table S3, entries 4 and 5).
diamines.a,b
For further confirmation of the catalysis by the
[MIMPs]+Cl−/NaNO2/TEMPO system on the CDHC reac-
tion, the condensation of benzaldehyde with o-phenylene-
diamine to give 2-phenylbenzimidazole was performed in
the absence of [MIMPs]+Cl−/NaNO2/TEMPO. The reac-
tion proceeded very slowly, and 2-phenylbenzimidazole
was obtained in a yield of only 7% after reaction for 5h
(Table S3, entry 6).
aUnless noted otherwise, the reaction conditions are as follows:
alcohol (2mmol), diamine (2.2mmol), [MIMPs]+Cl− (20mol%), TEMPO
(5mol%), NaNO2 (8mol%), CH3CN/H2O (2.0mL/0.2mL), T1 =45°C,
t1 =5h, T2 =55°C, t2 =5h, and atmospheric O2.
bIsolated yields.
Based on the above results, the optimum reaction condi-
tions for the synthesis of 2-phenylbenzimidazole from aer- cThe reaction time (t1) in the first step is 30h.
obic oxidative condensation of benzyl alcohol with
o-phenylenediamine were obtained, which were as follows:
CH3CN/H2O (10:1) as the solvent; the molar ratio of benzyl
Having optimized the reaction condition, the substrate
alcohol to o-phenylenediamine is 1:1.1; the loadings of scope was studied to demonstrate the generality of this
[MIMPs]+Cl−, TEMPO, and NaNO2 are 20, 5, and 8mol%, strategy. As shown in Table 3, a series of substituted ben-
respectively; the reaction temperature and time in the first zyl alcohols could be condensed with o-phenylenediamine
step are 45°C and 5h, respectively; and the reaction tem- to give the corresponding benzimidazoles (3a–s) in good
perature and time in the second step are 55°C and 5h, to excellent yields. Electron-donating groups (Me, OMe;
respectively. Under these conditions, the yield of 2-phe- 3b–g) and electron-withdrawing groups (F, Cl, Br, NO2;
nylbenzimidazole was 95%, which is higher than the results 3h–s) on the aromatic ring of the alcohol substrates had
in the literature.28–30
little effect on the yields of the benzimidazoles. Since the

Geng et al.
5
substituted benzyl alcohols and substituted o-phenylene-
diamines, and various benzimidazoles can be synthe-
sized in good to excellent yields. The acid IL
[MIMPs]+Cl− acts both as an acid to transform NaNO2
into HNO2 and as a catalyst to promote condensation of
the aldehyde with the o-phenylenediamine followed by
intramolecular cyclization. TEMPO, which can be
regenerated in the catalytic cycles, not only oxidizes the
alcohol to the aldehyde in the first step but also converts
the dihydrobenzazole into the benzimidazole via oxida-
tive dehydrogenation in the second step.
Scheme 2. Gram-scale experiment.
formation of conjugated systems was more beneficial for
the reaction, ortho- and para-substituted benzyl alcohols
generally gave high yields of the corresponding benzimi-
dazoles compared to the meta-substituted counterparts
(3b–s). The reactions of heteroaryl carbinols such as furfu-
ryl alcohol and thenyl alcohol, and naphthyl carbinol also
proceeded smoothly to afford the desired products with
fairly high yields (3t, 3u, 3ae). It is worth noting that
cyclohexylmethanol and geraniol, being representatives of
cycloaliphatic carbinols and long-chain allyl alcohols,
were also compatible with the reaction, although the yields
of the target products were not so encouraging (3af, 3ag).
Unfortunately, no benzimidazole was received in the case
of n-hexanol as the alcohol substrate; instead, 1-hexyl-
2-pentylbenzimidazole was obtained in a yield of 19%
(3ah). In order to further explore the applicability of the
strategy, various substituted o-phenylenediamines were
then tested in the reaction. Generally, both mono- and di-
substituted o-phenylenediamines reacted well with benzyl
alcohol to afford the corresponding benzimidazoles with
good to excellent yields, but o-phenylenediamines with
electron-donating groups gave higher yields than those
with electron-withdrawing groups (3v–ad). The ortho-
substituted o-phenylenediamine gave a lower yield of the
target product compared to the meta-substituted counter-
part (3v, 3w). The results fully demonstrate that the strat-
egy to synthesize benzimidazoles from aerobic oxidative
condensation of alcohols with o-phenylenediamines cata-
lyzed by [MIMPs]+Cl−/NaNO2/TEMPO tolerates a wide
range of substrates.
In order to illustrate the usefulness of this reaction in the
synthesis of benzimidazoles, a gram-scale experiment was
carried out (Scheme 2). This reaction could be readily
scaled up to 20mmol, and the target product 3a was
obtained in a satisfactory isolated yield of 95% (3.7020g).
The above experimental results manifest the following
three facts: (1) all the catalytic systems from the eight
acidic ILs can catalyze the aerobic oxidation of benzyl
alcohol to benzaldehyde, (2) [MIMPs]+Cl− demonstrates
the best catalyst performance in the conversion of benzal-
dehyde and o-phenylenediamine into 2-phenylbenzimida-
zole, and (3) almost no 2-phenylbenzimidazole is obtained
from benzaldehyde with o-phenylenediamine in the absence
of [MIMPs]+Cl−/NaNO2/TEMPO.
Experimental
Preparation of acidic ILs
The acidic ILs were prepared as described in the litera-
ture,52–54 and the procedures are given in the Supporting
Information.
General experimental details
The starting materials were obtained from the Macklin
Biochemical Technology Co., Ltd or Aladdin Chemical and
1
used as received, without further purification. H and 13C
nuclear magnetic resonance (NMR) spectra were recorded
1
on a Bruker AC-P 400 spectrometer (400MHz for H and
101MHz for 13C) in dimethyl sulfoxide (DMSO)-d6 and
CDCl3 with tetramethylsilane (TMS) as the internal stand-
ard or D2O. The data are reported as follows: chemical shift,
multiplicity (s=singlet, d=doublet, t=triplet, q=quartet,
m=multiplet), and coupling constant, J, which is reported in
hertz. The Fourier-transform infrared spectroscopy (FTIR)
spectra were recorded on a Bruker Vector 22 type instru-
ment as KBr pellets. Melting points were measured on a
Shanghai Inesa WRS-3 melting-point apparatus without
calibration. The thin-layer chromatography (TLC) was per-
formed using 60 mesh silica gel plates visualized with short-
wavelength ultraviolet (UV) light (254nm).
General catalytic procedures
TEMPO (5mol%), NaNO2 (8mol%), and the IL (20mol%)
were added successively into a 5-mL round-bottom flask
that was purged with oxygen five times. Subsequently, ben-
zyl alcohol (2mmol) and CH3CN/H2O (10:1; 2.2mL) were
added in turn via a syringe. Then, the mixture was stirred at
45°C in an oil bath under atmospheric oxygen. When the
benzyl alcohol had been consumed (monitored by TLC),
o-phenylenediamine (2.2mmol) was added. The mixture
was further stirred at 55°C under atmospheric oxygen until
completion of the reaction (monitored by TLC). The reac-
tion mixture was extracted with dichloromethane
(4×15mL), and the combined extract was evaporated
under vacuum. The crude product was purified by column
chromatography on silica gel to afford product 3.
Conclusion
In conclusion, a catalytic system, [MIMPs]+Cl−/NaNO2/
TEMPO, has been proved to be very efficient for the
aerobic oxidative condensation of benzyl alcohols with
o-phenylenediamines to give the corresponding benzi-
midazoles. This strategy tolerates a wide scope of both
2-Phenyl-1H-benzo[d]imidazole (3a): The crude prod-
uct was purified by flash column chromatography on silica
gel (petroleum ether/ethyl acetate/dichloromethane=20:5:1
as eluent) to afford the product 3a (95% yield, 0.3681g) as

6
Journal of Chemical Research 00(0)
a white solid, m.p.292–293°C. 1H NMR (400MHz,
2-(4-Fluorophenyl)-1H-benzo[d]imidazole (3h): The
DMSO-d6) δ: 12.92 (s, 1H), 8.18 (d, J=7.4Hz, 2H), 7.66 crude product was purified by flash column chromatogra-
(s, 1H), 7.57-7.47 (m, 4H), 7.20 (d, J=4.3Hz, 2H). NMR phy on silica gel (petroleum ether/ethyl acetate/dichlo-
data matched previously reported values.55
romethane=20:5:1 as eluent) to afford the product 3h (96%
2-(p-Tolyl)-1H-benzo[d]imidazole (3b): The crude yield, 0.4057g) as a white solid, m.p.254–255°C. 1H NMR
product was purified by flash column chromatography on (400MHz, DMSO-d6) δ: 12.93 (s, 1H), 8.24-8.21 (m, 2H),
silica gel (petroleum ether/ethyl acetate/dichlorometh- 7.66 (d, J=7.3Hz, 1H), 7.53 (d, J=7.3Hz, 1H), 7.40 (t,
ane=20:5:1 as eluent) to afford the product 3b (94% J=8.8Hz, 2H), 7.24-7.17 (m, 2H). NMR data matched pre-
1
yield, 0.3919g) as a white solid, m.p. 275–277°C. H viously reported values.55
NMR (400MHz, DMSO-d6) δ: 12.82 (br s, 1H), 8.07 (d,
2-(3-Fluorophenyl)-1H-benzo[d]imidazole (3i): The
J=8.1Hz, 2H), 7.57 (s, 2H), 7.35 (d, J=8.1Hz, 2H), 7.20- crude product was purified by flash column chromatogra-
7.17 (m, 2H), 2.37 (s, 3H). NMR data matched previously phy on silica gel (petroleum ether/ethyl acetate/dichlo-
reported values.55
romethane=20:5:1 as eluent) to afford the product 3i (90%
2-(m-Tolyl)-1H-benzo[d]imidazole (3c): The crude prod- yield, 0.3798g) as a white solid, m.p.255–256°C. 1H NMR
uct was purified by flash column chromatography on silica (400MHz, DMSO-d6) δ: 13.03 (s, 1H), 8.03 (d, J=7.7Hz,
gel (petroleum ether/ethyl acetate/dichloromethane=20:5:1 1H), 7.97 (d, J=10.1Hz, 1H), 7.69 (d, J=7.5Hz, 1H), 7.63-
as eluent) to afford the product 3c (91% yield, 0.3798g) as a 7.55 (m, 2H), 7.36-7.32 (m, 1H), 7.27-7.19 (m, 2H). NMR
white solid, m.p.212–214°C. 1H NMR (400MHz, data matched previously reported values.55
DMSO-d6) δ: 12.90 (s, 1H), 8.04 (s, 1H), 7.99 (d, J=7.8Hz,
2-(2-Fluorophenyl)-1H-benzo[d]imidazole (3j): The
1H), 7.62 (d, J=7.6Hz, 2H), 7.43 (t, J=7.6Hz, 1H), 7.29 (d, crude product was purified by flash column chromatogra-
J=7.5Hz, 1H), 7.21-7.19 (m, 2H), 2.41 (s, 3H). NMR data phy on silica gel (petroleum ether/ethyl acetate/dichlo-
matched previously reported values.55
romethane=20:5:1 as eluent) to afford the product 3j (95%
2-(o-Tolyl)-1H-benzo[d]imidazole (3d): The crude yield, 0.4024g) as a white solid, m.p.254–255°C. 1H NMR
product was purified by flash column chromatography on (400MHz, DMSO-d6) δ: 13.03 (s, 1H), 8.05 (d, J=7.8Hz,
silica gel (petroleum ether/ethyl acetate/dichlorometh- 1H), 7.99 (d, J=10.2Hz, 1H), 7.70 (d, J=6.2Hz, 1H), 7.63-
ane=20:5:1 as eluent) to afford the product 3d (95% 7.55 (m, 2H), 7.35-7.31 (m, 1H), 7.23 (s, 2H). NMR data
1
yield, 0.3965g) as a white solid, m.p. 213–216°C. H matched previously reported values.58
NMR (400MHz, DMSO-d6) δ: 12.65 (s, 1H), 7.76 (d,
2-(4-Chlorophenyl)-1H-benzo[d]imidazole (3k): The
J=6.8Hz, 1H), 7.61 (s, 2H), 7.38-7.34 (m, 3H), 7.22-7.20 crude product was purified by flash column chromatogra-
(m, 2H), 2.62 (s, 3H). NMR data matched previously phy on silica gel (petroleum ether/ethyl acetate/dichlo-
reported values.55
romethane=20:5:1 as eluent) to afford the product 3k (95%
1
2-(4-Methoxyphenyl)-1H-benzo[d]imidazole (3e): The yield, 0.4353mg) as a white solid, m.p.290–292°C. H
crude product was purified by flash column chromatogra- NMR (400MHz, DMSO-d6) δ: 12.98 (s, 1H), 8.19 (d,
phy on silica gel (petroleum ether/ethyl acetate/dichlo- J=8.5Hz, 2H), 7.67 (d, J=7.7Hz, 1H), 7.63 (d, J=8.4Hz,
romethane=20:5:1 as eluent) to afford the product 3e (93% 2H), 7.54 (d, J=7.4Hz, 1H), 7.25-7.18 (m, 2H). NMR data
yield, 0.4184g) as a white solid, m.p.216–218°C. 1H NMR matched previously reported values.55
(400MHz, DMSO-d6) δ: 12.76 (br s, 1H), 8.14 (d, J=8.8Hz,
2-(3-Chlorophenyl)-1H-benzo[d]imidazole (3l): The
2H), 7.57 (s, 2H), 7.19-7.15 (m, 2H), 7.11 (d, J=8.8Hz, crude product was purified by flash column chromatogra-
2H), 3.83 (s, 3H). NMR data matched previously reported phy on silica gel (petroleum ether/ethyl acetate/dichlo-
values.56
romethane=20:5:1 as eluent) to afford the product 3l (88%
2-(3-Methoxyphenyl)-1H-benzo[d]imidazole (3f): The yield, 0.4029g) as a white solid, m.p.228–229°C. 1H NMR
crude product was purified by flash column chromatogra- (400MHz, DMSO-d6) δ: 13.06 (s, 1H), 8.24 (s, 1H), 8.16
phy on silica gel (petroleum ether/ethyl acetate/dichlo- (d, J=7.3Hz, 1H), 7.68 (s, 1H), 7.59-7.53 (m, 3H), 7.23 (d,
romethane=20:5:1 as eluent) to afford the product 3f (91% J=4.1Hz, 2H). NMR data matched previously reported
yield, 0.4064g) as a white solid, m.p.201–203°C. 1H NMR values.55
(400MHz, DMSO-d6) δ: 12.91 (s, 1H), 7.77 (d, J=7.9Hz,
2-(2-Chlorophenyl)-1H-benzo[d]imidazole (3m): The
2H), 7.68 (d, J=7.2Hz, 1H), 7.54 (d, J=7.2Hz, 1H), 7.46 crude product was purified by flash column chromatogra-
(t, J=8.1Hz, 1H), 7.21 (t, J=7.6Hz, 2H), 7.07-7.04 (m, phy on silica gel (petroleum ether/ethyl acetate/dichlo-
1H), 3.86 (s, 3H). NMR data matched previously reported romethane=20:5:1 as eluent) to afford the product 3m
values.49
(94% yield, 0.4296g) as a white solid, m.p.213–216°C. 1H
2-(2-Methoxyphenyl)-1H-benzo[d]imidazole (3g): The NMR (400MHz, DMSO-d6) δ: 12.73 (s, 1H), 7.92-7.89 (m,
crude product was purified by flash column chromatogra- 1H), 7.71 (d, J=7.6Hz, 1H), 7.67-7.64 (m, 1H), 7.58-7.51
phy on silica gel (petroleum ether/ethyl acetate/dichlo- (m, 3H), 7.27-7.20 (m, 2H). NMR data matched previously
romethane=20:5:1 as eluent) to afford the product 3g (94% reported values.56
yield, 0.4192g) as a white solid, m.p.217–219°C. 1H NMR
2-(4-Bromophenyl)-1H-benzo[d]imidazole (3n): The
(400MHz, DMSO-d6) δ: 12.64 (s, 1H), 7.75 (d, J=6.8Hz, crude product was purified by flash column chromatogra-
1H), 7.68 (s, 1H), 7.54 (s, 1H), 7.39-7.34 (m, 3H), 7.21 (d, phy on silica gel (petroleum ether/ethyl acetate/dichlo-
J=4.2Hz, 2H), 2.62 (s, 3H). NMR data matched previously romethane = 20:5:1 as eluent) to afford the product 3n
reported values.57
(95% yield, 0.5192 g) as a white solid, m.p. 286–288 °C.

Geng et al.
7
1H NMR (400 MHz, DMSO-d6) δ: 13.01 (br s, 1H), 8.13 δ: 12.94 (s, 1H), 7.83 (d, J=3.6Hz, 1H), 7.72 (d, J=5.0Hz,
(d, J = 8.5 Hz, 2H), 7.75 (d, J = 8.5 Hz, 2H), 7.61 (s, 2H), 1H), 7.61 (d, J=7.6Hz, 1H), 7.50 (d, J=7.5Hz, 1H),
7.22-7.20 (m, 2H). NMR data matched previously 7.24-7.15 (m, 3H). NMR data matched previously reported
reported values.55
values.56
4-Methyl-2-phenyl-1H-benzo[d]imidazole (3v): The
2-(3-Bromophenyl)-1H-benzo[d]imidazole (3o): The
crude product was purified by flash column chromatogra- crude product was purified by flash column chromatogra-
phy on silica gel (petroleum ether/ethyl acetate/dichlo- phy on silica gel (petroleum ether/ethyl acetate/dichlo-
romethane = 20:5:1 as eluent) to afford the product 3o romethane=20:5:1 as eluent) to afford the product 3v (86%
(88% yield, 0.4785 g) as a white solid, m.p. 241–243 °C. yield, 0.3586g) as a white solid, m.p.248–249°C. 1H NMR
1H NMR (400 MHz, DMSO-d6) δ: 13.06 (s, 1H), 8.39 (s, (400MHz, DMSO-d6) δ: 12.71 (d, J=105.8Hz, 1H), 8.24-
1H), 8.20 (d, J = 7.8 Hz, 1H), 7.67 (d, J = 8.4 Hz, 2H), 8.18 (m, 2H), 7.57-7.46 (m, 3H), 7.34 (d, J=6.8Hz, 1H),
7.56 (d, J = 4.6 Hz, 1H), 7.50 (t, J = 7.92 Hz, 1H), 7.23 (s, 7.10 (s, 1H), 6.99 (d, J=7.12Hz, 1H), 2.58 (s, 3H). NMR
2H). NMR data matched previously reported values.59
data matched previously reported values.56
2-(2-Bromophenyl)-1H-benzo[d]imidazole (3p): The
5-Methyl-2-phenyl-1H-benzo[d]imidazole (3w): The
crude product was purified by flash column chromatogra- crude product was purified by flash column chromatogra-
phy on silica gel (petroleum ether/ethyl acetate/dichlo- phy on silica gel (petroleum ether/ethyl acetate/dichlo-
romethane=20:5:1 as eluent) to afford the product 3p (92% romethane=20:5:1 as eluent) to afford the product 3w
yield, 0.5031g) as a white solid, m.p.229–231°C. 1H NMR (95% yield, 0.3953g) as a white solid, m.p.241–242°C. 1H
(400MHz, DMSO-d6) δ: 13.01 (br s, 1H), 8.12 (d, J=8.6Hz, NMR (400MHz, DMSO-d6) δ: 12.76 (d, J=15.0Hz, 1H),
2H), 7.77 (d, J=8.6Hz, 2H), 7.60 (s, 2H), 7.24-7.19 (m, 8.16 (d, J=7.5Hz, 2H), 7.56-7.45 (m, 4H), 7.42-7.31 (m,
2H). NMR data matched previously reported values.58
2-(4-Nitrophenyl)-1H-benzo[d]imidazole (3q): The crude matched previously reported values.56
1H), 7.05-7.00 (m, 1H), 2.42 (d, J=7.8Hz, 3H). NMR data
product was purified by flash column chromatography on
2-Phenyl-5-(trifluoromethyl)-1H-benzo[d]imidazole
silica gel (petroleum ether/ethyl acetate/dichlorometh- (3x): The crude product was purified by flash column chro-
ane=20:5:1 as eluent) to afford the product 3q (92% yield, matography on silica gel (petroleum ether/ethyl acetate/
0.4412g) as a faint yellow solid, m.p.315–317°C. 1H NMR dichloromethane=25:5:1 as eluent) to afford the product
(400MHz, DMSO-d6) δ: 13.28 (s, 1H), 8.43-8.38 (m, 4H), 3x (90% yield, 0.4735g) as a white solid, m.p.184–186°C.
7.73 (d, J=7.8Hz, 1H), 7.59 (d, J=7.7Hz, 1H), 7.31-7.22 1H NMR (400MHz, DMSO-d6) δ: 13.37 (s, 1H), 8.21 (d,
(m, 2H). NMR data matched previously reported values.55
J=7.3Hz, 2H), 8.04-7.72 (m, 2H), 7.61-7.50 (m, 4H).
2-(2-Nitrophenyl)-1H-benzo[d]imidazole (3r): The crude NMR data matched previously reported values.55
product was purified by flash column chromatography on 5-Fluoro-2-phenyl-1H-benzo[d]imidazole (3y): The
silica gel (petroleum ether/ethyl acetate/dichlorometh- crude product was purified by flash column chromatogra-
ane=20:5:1 as eluent) to afford the product 3r (92% yield, phy on silica gel (petroleum ether/ethyl acetate/dichlo-
0.4378g) as a faint yellow solid, m.p.264–266°C. 1H NMR romethane=20:5:1 as eluent) to afford the product 3y (85%
(400MHz, DMSO-d6) δ: 13.09 (s, 1H), 8.01 (dd, J1 =8.0Hz, yield, 0.3616g) as a white solid, m.p.240–241°C. 1H NMR
J2 =17.5Hz, 2H), 7.87-7.84 (m, 1H), 7.76-7.72 (m, 1H), (400MHz, DMSO-d6) δ: 13.07 (s, 1H), 8.18 (d, J=7.4Hz,
7.63 (s, 2H), 7.25 (s, 2H). NMR data matched previously 2H), 7.67-7.34 (m, 5H), 7.07 (s, 1H). NMR data matched
reported values.60
previously reported values.55
2-(3,5-Difluorophenyl)-1H-benzo[d]imidazole (3s): The
5-Chloro-2-phenyl-1H-benzo[d]imidazole (3z): The crude
crude product was purified by flash column chromatogra- product was purified by flash column chromatography
phy on silica gel (petroleum ether/ethyl acetate/dichlo- on silica gel (petroleum ether/ethyl acetate/dichlorometh-
romethane=20:5:1 as eluent) to afford the product 3s (89% ane=20:5:1 as eluent) to afford the product 3z (85%
yield, 0.4097g) as a white solid, m.p.222–224°C. 1H NMR yield, 0.3879g) as a white solid, m.p.208–210°C. H
1
(400MHz, DMSO-d6) δ: 13.09 (s, 1H), 7.86 (d, J=6.7Hz, NMR (400MHz, DMSO-d6) δ: 13.13 (s, 1H), 8.17 (d,
2H), 7.70 (d, J=6.0Hz, 1H), 7.56 (d, J=6.0Hz, 1H), 7.35 J=7.4Hz, 2H), 7.73-7.66 (m, 1H), 7.58-7.49 (m, 4H), 7.24
(t, J=9.2Hz, 1H), 7.24 (s, 2H). NMR data matched previ- (d, J=8.3Hz, 1H). NMR data matched previously reported
ously reported values.57
values.55
5-Nitro-2-phenyl-1H-benzo[d]imidazole (3aa): The crude
2-(Furan-2-yl)-1H-benzo[d]imidazole (3t): The crude
product was purified by flash column chromatography on product was purified by flash column chromatography
silica gel (petroleum ether/ethyl acetate=3:1 as eluent) to on silica gel (petroleum ether/ethyl acetate/dichlo-
afford the product 3t (88% yield, 0.3222g) as a white solid, romethane=20:5:1 as eluent) to afford the product 3aa
m.p.286–287°C. 1H NMR (400MHz, DMSO-d6) δ: 12.93 (81% yield, 0.3877g) as a white solid, m.p.146–148°C. 1H
(s, 1H), 7.93 (s, 1H), 7.54 (s, 2H), 7.20 (d, J=3.4Hz, 3H), NMR (400MHz, DMSO-d6) δ: 13.52 (br s, 1H), 8.40
6.73-6.72 (m, 1H). NMR data matched previously reported (s, 1H), 8.17 (d, J=7.2Hz, 2H), 8.05 (d, J=8.8Hz, 1H), 7.68
values.56
(d, J=4.8Hz, 1H), 7.57-7.51 (m, 3H). NMR data matched
2-(Thiophen-2-yl)-1H-benzo[d]imidazole (3u): SCHEThe previously reported values.56
crude product was purified by flash column chromatogra-
5,6-Dimethyl-2-phenyl-1H-benzo[d]imidazole (3ab): The
phy on silica gel (petroleum ether/ethyl acetate=3:1 as elu- crude product was purified by flash column chromatogra-
ent) to afford the product 3u (89% yield, 0.3551g) as a faint phy on silica gel (petroleum ether/ethyl acetate/dichlo-
yellowsolid, m.p.>320°C. 1HNMR(400MHz, DMSO-d6) romethane=25:5:1 as eluent) to afford the product 3ab

8
Journal of Chemical Research 00(0)
(95% yield, 0.4243g) as a white solid, m.p.249–251°C. 1H Declaration of conflicting interests
NMR (400MHz, DMSO-d6) δ: 12.66 (br s, 1H), 8.15 (d,
J=7.7Hz, 2H), 7.52 (t, J=7.5Hz, 2H), 7.45 (t, J=7.3Hz,
2H), 7.32 (s, 1H), 2.32 (s, 6H). NMR data matched previ-
ously reported values.56
The author(s) declared no potential conflicts of interest with
respect to the research, authorship, and/or publication of this
article.
5,6-Difluoro-2-phenyl-1H-benzo[d]imidazole (3ac): The
crude product was purified by flash column chromatogra-
phy on silica gel (petroleum ether/ethyl acetate/dichlo-
romethane=20:5:1 as eluent) to afford the product 3ac
(89% yield, 0.4074g) as a white solid, m.p.205–207°C. 1H
Funding
The author(s) disclosed receipt of the following financial support
for the research, authorship, and/or publication of this article: The
authors appreciate the financial support from the National Natural
Science Foundation of China (grant no. 21776056) and the Natural
NMR (400MHz, DMSO-d6) δ: 13.15 (s, 1H), 8.15 (d, Science Foundation of Hebei Province (CN) (grant no.
B2018202253).
J=7.2Hz, 2H), 7.71 (s, 1H), 7.55-7.45 (m, 4H). NMR data
matched previously reported values.61
ORCID iD
5,6-Dichloro-2-phenyl-1H-benzo[d]imidazole (3ad): The
crude product was purified by flash column chromatogra- Jiquan Zhao
phy on silica gel (petroleum ether/ethyl acetate/dichlo-
https://orcid.org/0000-0003-0913-6011
Supplemental material
romethane=20:5:1 as eluent) to afford the product 3ad
(94% yield, 0.4953g) as a white solid, m.p.217–218°C. 1H
NMR (400MHz, DMSO-d6) δ: 13.24 (s, 1H), 8.16 (d,
J=6.9Hz, 2H), 7.91 (s, 1H), 7.73 (s, 1H), 7.57-7.49 (m,
3H). NMR data matched previously reported values.56
2-(Naphthalen-2-yl)-1H-benzo[d]imidazole (3ae): The
crude product was purified by flash column chromatogra-
phy on silica gel (petroleum ether/ethyl acetate/dichlo-
romethane=20:5:1 as eluent) to afford the product 3ae
(89% yield, 0.4367g) as a white solid, m.p.215–216°C. 1H
NMR (400MHz, DMSO-d6) δ: 13.11 (s, 1H), 8.76 (s, 1H),
8.33 (d, J=8.5Hz, 1H), 8.09-8.04 (m, 2H), 7.99 (d,
J=7.1Hz, 1H), 7.71 (d, J=7.1Hz, 1H), 7.61-7.57 (m, 3H),
7.23 (d, J=6.9Hz, 2H). NMR data matched previously
reported values.55
Supplemental material for this article is available online.
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