Magnetic Co-doped NiFe2O4 Nanocomposite: A Heterogeneous and Recyclable Catalyst for the One-Pot Synthesis of Benzimidazoles, Benzoxazoles and Benzothiazoles under Solvent-Free Conditions

Article abstract of DOI:10.1002/jccs.201700060

A simple and efficient procedure for the synthesis of benzimidazoles, benzoxazoles, and benzothiazoles via the condensation of o-phenylenediamine, o-aminophenol, and o-aminothiophenol with various benzaldehydes by using magnetic Co-doped NiFe₂O₄ nanoparticles has been developed. This nanocatalyst has advantages such as excellent product yields, solvent-free conditions, and very short reaction times. After any experiment, the magnetic nanocatalyst could be easily separated with the aid of an external magnet and reused at least four times without any loss of its catalytic performance.

Full text of DOI:10.1002/jccs.201700060

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
Magnetic Co-doped NiFe O Nanocomposite: A Heterogeneous and Recyclable
2
4
Catalyst for the One-Pot Synthesis of Benzimidazoles, Benzoxazoles and
Benzothiazoles under Solvent-Free Conditions
*
Azam Karimian , Roya Mohammadzadeh Kakhki and Hamideh Kargar Beidokhti
Department of Chemistry, Faculty of Sciences, University of Gonabad, Gonabad, Iran
(Received: February 22, 2017; Accepted: August 7, 2017; DOI: 10.1002/jccs.201700060)
A simple and efficient procedure for the synthesis of benzimidazoles, benzoxazoles, and benzothia-
zoles via the condensation of o-phenylenediamine, o-aminophenol, and o-aminothiophenol with
various benzaldehydes by using magnetic Co-doped NiFe O nanoparticles has been developed.
2
4
This nanocatalyst has advantages such as excellent product yields, solvent-free conditions, and
very short reaction times. After any experiment, the magnetic nanocatalyst could be easily sepa-
rated with the aid of an external magnet and reused at least four times without any loss of its cata-
lytic performance.
Keywords: Benzimidazoles; Benzoxazoles; Benzothiazoles; Magnetic; Nanocatalyst.
2
7
28
29
30
INTRODUCTION
carbon,
MnO2,
Fe(HSO4)3,
Sc(OTf )3
and
31
1
,3-Benzazoles such as benzimidazoles, benzoxa-
CoCl2. Some of these methods have problems such as
poor yield, long reaction times, difficult work-up, efflu-
ent pollution, harsh reaction conditions, occurrence of
several side reactions, difficulty in separation of the pro-
ducts from the reaction mixture, and the application of
expensive catalysts and hazardous solvents. On the
other hand, in chemical processes, solvents are usually
used as the reaction medium and in the separation of
products and work-up. Because solvents, especially
toxic and nonvolatile solvents, cause pollution in the
environment, a solvent-free chemical medium is highly
desired in chemical processes.
zoles, and benzothiazoles are utilized in numerous syn-
thetic studies. These compounds are used for the
synthesis of many clinically useful drugs.
1
–3
They are
4
5
well known as antihypertensive, antitumor, anti-
6
7
8
Parkinson, anti-inflammatory, antimicrobial, antivi-
9
10
ral and antibacterial agents. These molecules are
well-known inhibitors of the chemokine receptor
11
12
(
CXCR3) and the lymphocyte tyrosine kinase (Lck).
Because of the wide range of medicinal applications
and synthetic use of these benzo-fused heterocyclic sys-
tems, many synthetic procedures have been reported.
The commonly employed methods for the synthesis of
Therefore, because of environmental concerns,
reduction of cost, and the simplicity of processes, recent
investigations are toward using green solvents or
solvent-free reactions with high yields, recyclable cata-
1,3-benzazoles involve the condensation of o-phenylene-
diamine, o-aminophenol, and o-aminothiophenol with
13
14–16
carboxylic acid or their derivatives
under strong
32
acidic conditions and sometimes combined with high
temperature or microwave irradiation.
lysts, and mild conditions.
1
7,18
Another
Furthermore, recently heterogeneous catalysts,
route for synthesis of these fused-ring compounds is the
condensation of aldehydes with o-phenylenediamines,
o-aminothiophenol, and o-aminophenol in the presence
of various oxidative and catalytic reagents such as
especially magnetic nanoparticles, have aroused consid-
33–38
erable interest in organic synthesis.
These magnetic
nanoparticles can be easily separated and recycled from
the reaction medium by an external magnet.
19
20
21
22
CeCl3,
Cu(OTf )3,
Ce(NO ) Á6H O,
In(OTf )3,
Co(OH)2,
LaCl3,
A magnetic Co-doped NiFe O4 nanocomposite
3 3
2
2
23
24
25
26
NiEuFe O ,
TiCl OTf,
was synthesized in our previous work that showed high
photocatalytic activity for the degradation of some
2
4
3
cobalt(III)–salen complex supported on activated
*Corresponding author. Email: a_karimian87@yahoo.com, a-karimian@gonabad.ac.ir
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1

Article
Karimian et al.
39
textile dyes. Therefore, we have sought its application
as catalyst for organic reactions. In view of the afore-
mentioned facts and also in continuation of our
research program, we now report an effective, conven-
ient, one-pot multicomponent reaction of the aldehyde
derivatives with o-phenylenediamines, o-aminothiophe-
nol, and o-aminophenol in the presence of a magnetic
Co-doped NiFe O nanocatalyst for the synthesis of
2
4
benzimidazoles, benzoxazoles, and benzothiazoles
under solvent-free conditions.
Fig. 2. FTIR spectrum of the pure Ni0.6Co0.4Fe
2 4
O
nanocatalyst.
RESULTS AND DISCUSSION
Characterization of magnetic Co-doped NiFe O
2
4
−
1
absorption band at 3300 cm belongs to the stretching
vibration of the absorbed hydroxyl groups on the sur-
face and O–H groups in absorbed water. The vibra-
nanocatalyst
The magnetic Co-doped NiFe O nanocatalyst
2
4
was synthesized according to our previously published
−1
39
tional band at v = 1500 cm is assigned to the H–O–H
bending vibration of water molecules or the O–H defor-
mation due to surface hydroxyls.
method. The crystal structure and phase purity of the
as-prepared samples were studied by X-ray powder dif-
fraction (XRD) patterns of Ni1–xCo Fe O (x = 0.4)
x
2
4
The low-magnification and high-magnification
field-emission scanning electron microscopy (FESEM)
images of pure Ni0.6Co0.4Fe O4 nanocomposites are
(Figure 1). The average crystal sizes of the nanoparti-
cles were determined from the XRD data with the
Debye–Scherrer formula
2
shown in Figure 3. The SEM images show that the pre-
pared magnetic nanoparticles are constructed from a
random agglomeration of particles and are spherical
with an average size of <50 nm in diameter, which is
larger than the results of XRD analysis, indicating that
these nanoparticles are polycrystalline.
D = 0:9λ=βcos θ
where λ is the X-ray wavelength, β is the full width at
half-maximum (FWHM) of the considered peak, and θ
is the Bragg angle. This gave D = 33.25 nm for pure
The prepared Ni0.6Co0.4Fe O nanocatalysts can
2
4
39
be separated from the solvent or reaction mixture by
the application of an external magnetic field (Figure 4).
These magnetic nanoparticles have main advantage of
ensuring product purity and simple work-up.
Ni0.6Co0.4Fe O .
2
4
Figure 2 shows Fourier transform infrared (FT-
IR) spectrum of the nanoparticles. In general, the
Catalytic application of magnetic Co-doped NiFe O4
2
nanoparticles for the synthesis of benzimidazoles,
benzoxazoles, and benzothiazoles
Our previous published study on the synthesis and
39
use of Co-doped NiFe O4 prompted us to explore
2
another aspect of the Co-doped NiFe O as magnetic
2
4
nanocatalysts for the synthesis of benzimidazoles, ben-
zoxazoles, and benzothiazoles from the reaction
between o-phenylenediamine, o-aminophenol, o-
aminothiophenol and a variety of substituted benzalde-
ꢀ
hydes under solvent-free conditions at 70 C (Scheme 1).
At first, in order to study the optimum conditions
Fig. 1. XRD pattern of the Ni0.6Co0.4Fe O4
2
nanocatalyst.
for the synthesis of benzimidazoles, benzoxazoles, and
2
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Synthesis of Benzimidazoles, Benzoxazoles and Benzothiazoles
O
H
R
NH2
XH
N
Co doped NiFe2O4
70 °C, Solvent free
+
X
R
R= H, Me, OMe, Cl,
NO2, (CH3)2N
X= NH, O, S
Scheme 1. Synthesis of benzimidazoles, benzoxa-
zoles, and benzothiazoles.
The effect of reaction temperature on the yield of
the product is another important factor that was stud-
ied (Table 2, entry 1). The rate of reaction increased
ꢀ
when it was carried out at 70 C, producing 97% iso-
lated yield of 2-phenyl-benzimidazole (Table 2, entry
1
); the yield of product decreased when the reaction
Fig. 3. Low-magnification (a, b) and high-
magnification (c, d) images of Ni0.6Co0.4-
was carried out at lower temperatures (Table 2,
entry 1).
The optimal conditions were then used for the
preparation of derivatives of benzimidazoles, benzoxa-
zoles, and benzothiazoles (Table 2).
As can be seen from Table 2, in these reactions no
side product was observed. All reactions on a wide
range of aromatic aldehydes bearing both electron-
2 4
Fe O nanocomposites.
benzothiazoles, the reaction of o-phenylenediamine and
benzaldehyde was chosen as a model reaction. This
reaction was investigated using various amounts of the
ꢀ
nanocatalyst at 70 C. In the absence of the nanocata-
lyst, the yield of the reaction was low. With the addi-
tion of the catalyst (2 mol%, 0.004 g) to the reaction
mixture, the reaction occurred with 60% yield. Further
study showed that the best results were obtained with
0 mol% catalyst, with 97% yield under similar condi-
tions (Table 1).
donating
afforded excellent yields with short reaction times
Table 2.). According to the results, o-aminophenol
and electron-withdrawing substituents
(
showed lower reactivity than o-phenylenediamine and
o-aminothiophenol with aldehydes, and the reaction
took longer for completion in comparison with the
reactions involving the two other nucleophiles (NH and
1
SH
groups)
in
o-phenylenediamine
and
o-
(
a)
(b)
aminothiophenol.
In our experiments, performance of the reaction
was monitored by the disappearance of the benzalde-
hyde peak on TLC, followed by the appearance of the
Table 1. Effect of the amount of nanocatalyst on the yield of
ꢀ
a
the reaction at 70 C
b
Entry
Catalyst% (g)
Time (min)
Yield (%)
1
2
3
4
5
None
55
55
55
55
55
55
Trace
60
89
97
97
2(0.004 g)
5(0.012 g)
10(0.023 g)
15(0.035 g)
20(0.047 g)
6
a
98
Fig. 4. (a, b) Magnetic separation property of the
o-Phenylenediamine (1 mmol) and benzaldehyde (1.2 mmol).
Isolated yields.
synthesized Ni0.6Co0.4Fe
temperature.
2
O
4
catalyst at room
b
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Article
Karimian et al.
Table 2. Synthesis of different benzimidazoles, benzoxazoles and benzothiazoles using the magnetic Co-doped NiFe
2
O
4
a
nanocatalyst
b
ꢀ
Ref
Entry
1
Substrate
Product
Time (h)/isolated yield (%)
M.p. ( C)/
.
40
55(min)/97 X = NH (1a)
293–294
293–294
293–294
102–103
113–294
307–308
270–272
226–227
c
40
40
1
1
2
1
/25 X = NH (1a)
/36 X = NH (1a)
/97 X = O (1b)
d
4
4
4
4
1
0
1
2
3
7
5(min)/98 X = S (1c)
2
1.15/88 X = NH(2a)
3
1
/90 X = O (2b)
/85 X = S (2c)
4
4
4
4
5
6
3
4
1.15/85 X = NH (3a)
204–206
206–207
186–188
5
1
/85 X = O (3b)
.15/80 X = S (3c)
4
4
4
7
3
1
45(min)/98 X = NH (4a)
283–284
152–153
114–115
1
1
/95 X = O (4b)
0(min)/92 X = S (4c)
4
2
5
6
1/90 X = NH (5a)
229–230
48
1
1
.30/85 X = O (5b)
5(min)/85 X = S (5c)
68–69
83–84
41
4
4
4
4
9
1
1.25/95 X = NH (6a)
223–225
105–106
123–124
2
5
/85 X = O (6b)
5(min)/83 X = S (6c)
1
7
7
8
1.25/85 X = NH (7a)
264–265
50
5
1
/90 X = O (7b)
(min)/80 X = S (7c)
92–93
83–84
44
5
2
4
1
3
1
1/90 X = NH (8a)
294–295
180–181
179–180
2
1
/80 X = O (8b)
/83 X = S (8c)
a
ꢀ
o-Phenylenediamine (1 mmol) and benzaldehyde (1.2 mmol) at 70 C under solvent-free conditions.
b
1
All obtained products are known compounds and were characterized on the basic of spectral data ( H NMR, FT-IR, and mass
spectra) and were identified by comparing their melting points with those of authentic samples.
c,d
ꢀ
o-Phenylenediamine (1 mmol) and benzaldehyde (1.2 mmol) at room temperature and 40 C respectively, under solvent-free
conditions.
4
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Synthesis of Benzimidazoles, Benzoxazoles and Benzothiazoles
new product. The resulting compounds, after purifica-
conditions to produce the desired benzimidazoles, ben-
zoxazoles, and benzothiazoles and release Ni0.6Co0.4-
Fe O for the next catalytic cycle.
tion via crystallization, were characterized using FT-IR,
1
H NMR, and mass spectrometry (MS). For example,
2
4
the FT-IR spectrum of benzimidazoles exhibits highly
In order to show the ability of the novel magnetic
intense absorption peaks at 3140–3435 and
nanocatalyst in comparison with those of the other
reported ones, we compared the results and reaction
conditions of this work with some other methods
reported in the literature used in the synthesis of 2-
phenyl-1H-benzo[d]imidazole, 2-phenyl benzo[d]oxa-
zole, and 2-Phenyl benzo[d]thiazole (Table 3).
As shown in Table 3, this novel magnetic nanoca-
talyst is an effective and green one with high catalytic
activity for the synthesis of 1,3-benzazoles such as ben-
zimidazoles, benzoxazoles, and benzothiazoles with
short reaction times.
The most important advantages of this novel mag-
netic nanocatalyst are its ability to be separated from
the reaction mixture by the application of an external
magnetic field and its recyclability. In all the reactions,
the obtained products were isolated by a very simple
work-up.
−1
1605–1650 cm , corresponding to NH and C=N
groups of benzimidazoles, respectively.
The formation of benzoxazoles was also confirmed
by the presence of absorption bands at 1597–1625 and
−1
1
225–1255 cm , which correspond to the C=N and C–
O groups of benzoxazoles, respectively. The absorption
−1
bands at 1580–1650 cm are also identified as charac-
teristic of the C=N group of benzothiazoles.
1
The H NMR spectrum of benzimidazoles shows
a downfield shift at 12.70–13.21 ppm corresponding to
the NH proton. All products were also identified by
their mass spectra. The melting points of the products
were compared with their reported values.
Based on the similar mechanisms published in the
22,52
literature,
a plausible reaction mechanism for the
Ni0.6Co0.4Fe O -catalyzed synthesis of benzimidazoles,
2
4
benzoxazoles, and benzothiazoles is shown in Scheme 2.
First, the aldehyde is activated by the magnetic nano-
composite to give I. The nucleophilic attack of o-pheny-
lenediamines, o-aminothiophenol, or o-aminophenol on
I affords II followed by formation of imine III. This
resulting imine, which in turn is activated by Ni0.6Co0.4-
Fe O , provides intramolecular nucleophilic attack of
Recycling of magnetic nanocatalyst
One more advantage of this magnetic nanocata-
lyst is its ability to be recycled from the reaction
medium. Therefore, the reusability of the catalyst was
also investigated. For this purpose, the same model
reaction for synthesis as for the 2-phenyl-1H-benzo[d]
imidazole was again studied under optimized condi-
tions. After completion of the reaction, ethyl acetate
2
4
the XH (X = NH, S, O) group to afford IV, which sub-
sequently undergoes aromatization under oxidative
(
EtOAc) was added to the reaction mixture to dissolve
the product. With the aid of an external magnet, the
catalyst could be separated easily. The catalyst was
ꢀ
washed with diethyl ether, dried at 60–80 C under
vacuum for 2 h, and then reused for a similar reaction.
As shown in Figure 5, the nanocatalyst could be
reused at least four times without significant loss of
activity.
EXPERIMENTAL
Materials and instrumentation
All reagents were purchased from Merck and used
without further purification. The melting points of pro-
ducts were determined with an Electrothermal Type
9
200 melting point apparatus. The FTIR spectra were
Scheme 2. A plausible mechanism for the synthesis
of benzimidazoles, benzoxazoles and
benzothiazoles.
recorded on an Avatar 370 FT-IR Thermal Nicolet
spectrometer. The NMR spectra were recorded on a
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Article
Karimian et al.
Table 3. Comparison of conditions for the synthesis of 2-phenyl-1H-benzo[d]imidazole, 2-phenyl benzo[d]oxazole, and 2-phenyl
benzo[d]thiazole with some other methods reported in the literature
Compound
Conditions
Time (h)
Yield (%)
Present work
55 min
1.5
1.5
4
6/4
4
13 min
4
97
93
90
81
93/96
95
89
98
90
77
95
85
92
70
83
90
97
86
85
82
87
97
90
73
98
92
91
87
90
91
85
85
ꢀ
20
Ce(NO ) .6H O/DMF, 80 C
3
3
2
ꢀ
53
Iodine/water, 90 C
CoCl .6H O(10 mol%)/ CH
3
1
2
2
3
CN, rt
2
2
Co(OH) /CoO(II)(10 mol%)/ Ethanol, air, rt
2
5
4
AlKIT-5/CH
Ionic liquid, 90 C
Cu(OH) / CH OH, rt
3
CN, reflux
ꢀ
55
5
6
2
3
5
7
Triphenylphosphine/trichloroisocyanuric acid, 1, 4-dioxane, reflux
T3P (in AcOEt), DIPEA/MW, 160 C
FHS/ EtOH, rt
HMTA-Bromine(10 mol%)/ MeCN, rt or MW
1
ꢀ
58
30 min
25 min
4
5
2
9
4
4
ꢀ
42
WOx -ZrO
2
/ 1,4-dioxane, 100 C
ꢀ
40
Glycerol:H O/ 90 C
3
2
59
H
2
2
O ,HCl/ CH
3
CN, heating
44 min
10 min
2
50 min
12
6
0
MCM-41-SO
Present work
3
2
H/ H O, rt
2
4
NiEuFe
Fe/150 C, argon
2
O
4
/water, reflux
ꢀ
61
ꢀ
62
DCM, NEt / MW, 40 C
2
3
ꢀ
63
PIFA/ EtOH, MW, 80 C
Triphenylphosphine/trichloroisocyanuric acid, 1, 4-dioxane, reflux
15 min
4
4
57
ꢀ
40
Glycerol:H O/ 90 C
2
ꢀ
43
CeCl
3
(15 mol%), NaI (10 mol%), toluene/O
2
, 100 C
36
Present work
15 min
45 min
10 min
15 min
5 min
20 min
6
6
4
VOSO /EtOH, rt
4
ꢀ
58
T P (in AcOEt), DIPEA/MW, 100 C
3
ꢀ
63
PIFA/ EtOH, MW, 80 C
Triphenylphosphine/trichloroisocyanuric acid, 1, 4-dioxane, reflux
FHS/EtOH, reflux
HMTA-bromine(10 mol%) MeCN, rt or MW
57
2
9
4
4
41
FeCl /montmorillonite K-10, air, CH OH
1
3
3
Brucker Avance 400 MHz instrument in [d ]DMSO
CoCl (0.8 mmol), and FeCl (4 mmol) were dissolved
2 3
6
and CDCl . All products were known compounds and
characterized by the FT-IR and H NMR, as well as
comparison of their melting points with those of known
compounds. Mass spectra were recorded with a
CH7AV aria mat Bremen instrument at 70 eV.
in distilled water (30 mL), then isoamyl alcohol
(10 mL) was added to it, and the volume of solution
was made up to 50 mL with distilled water. Then KOH
(16 mmol dissolved in a small quantity of water) was
added to the solution under vigorous stirring at room
temperature. The stirring of the solution was continued
for 1 h. After completion of the reaction, the product
was washed three times with distilled water and once
with absolute ethanol, and finally annealed in oven at
3
1
Preparation of the magnetic Co-doped NiFe O
2
4
nanocatalysts
Co-doped NiFe O magnetic nanocomposite was
2
4
ꢀ
ꢀ
synthesized according to
method. In a typical experiment, NiCl (1.2 mmol),
a
previous published
80 C for 3 h and then calcined at 300 C for 2 h to form
the Ni0.6Co0.4Fe O nanocatalyst.
39
2
2
4
6
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Synthesis of Benzimidazoles, Benzoxazoles and Benzothiazoles
(
1H, m, Ar), 7.54–7.50 (3H, m, Ph), 7.41–7.34 (2H, m,
+
Ar). m/z 195 [M] .
2
-Phenylbenzo[d]thiazole (1c)
Light yellow solid, mp 113–114 C. IR (KBr,
ꢀ
−1
cm ): 3060, 3019, 2925, 2847, 1580, 1511, 1433, 1313,
1
1
8
281, 1158, 962, 764. H NMR (CDCl , 400 MHz) δ:
3
.14–8.11 (1H, m, Ph), 8.11–8.08 (2H, m, Ar), 7.93
(
1H, d, J 8.0, Ar), 7.54–7.51 (4H, m, Ph),7.42 (1H, td,
+
J 8.4, 1.4, Ar). m/z 211 [M] .
Fig. 5. Recycling performance of the Co-doped
NiFe nanocatalyst in the synthesis of
2
O
4
2
-(4-Nitrophenyl)-1H–benzo[d]imidazole (2a)
benzimidazole (1a).
ꢀ
−1
Light yellow, mp 307–308 C. IR (KBr, cm ):
3
1
4
140, 2900, 2400, 1629, 1609, 1525, 1490, 1401, 1281,
1
229, 1110, 866, 774, 617, 540. H NMR (DMSO-d ,
6
General procedure for the preparation of benzimidazoles,
benzoxazoles, and benzthiazoles
A mixture of o-phenylenediamines, o-aminothio-
phenol, or o-aminophenol (1 mmol), benzaldehyde deri-
00 MHz) δ: 12.25 (br, 1H, s, −NH), 8.45 (2H, d,
J 8.8, Ph), 8.15 (2H, d, J 8.8, Ph), 7.65 (2H, dd, J 6.4,
+
3
.2, Ar), 7.34 (2H, dd, J 6.0, 3.2, Ar). m/z 239 [M] .
vatives
(1.2 mmol),
and
Co-doped
NiFe O
2-(4-Nitrophenyl)benzo[d]oxazole (2b)
2
ꢀ
4
ꢀ
−1
nanoparticles (10% mol, 0.023 g) was stirred at 70 C.
The progress of the reaction was monitored by thin-
layer chromatography; TLC, hexane/ethyl acetate, 10:2.
After completion of the reaction, hot ethyl acetate
White solid, mp 270–272 C. IR (KBr, cm ):
3113, 3092, 1597, 1521, 1450, 1347, 1225, 1056,
1
855, 752, 706. H NMR (CDCl , 400 MHz) δ: 8.46
3
(2H, dt, J 9.2, 2.0, Ph), 8.41(2H, dt, J 9.2, 2.0, Ph),
7.86–7.84 (1H, m, Ar), 7.67–7.65 (1H, m, Ar),
(5 mL) was added to the mixture, and the nanomag-
+
netic catalyst was separated from the reaction mixture
using an external magnet. After that, the solvent was
removed under reduced pressure and the precipitated
solid was collected, which was purified by recrystalliza-
tion from ethyl acetate and n-hexane to afford the pure
benzimidazole, benzoxazole, and benzthiazole deriva-
tives. The isolated compounds were characterized by
7.49–7.42 (2H, m, Ar). m/z 195 [M] .
2
-(4-Nitrophenyl)benzo[d]thiazole (2c)
ꢀ
−1
Yellow solid, mp 226–227 C. IR (KBr, cm ):
3
9
8
065, 1600, 1556, 1521, 1425, 1343, 1313, 1108,
70, 855, 766, 728. H NMR (CDCl , 400 MHz) δ:
.35 (2H, dt, J 8.6, 2.1, Ph), 8.27 (2H, dt, J 8.8, 2.0,
1
3
1
Ph), 8.09 (1H, d, J 7.8, Ar), 7.97 (1H, d, J 7.8, Ar),
.55 (1H, td, J 7.0, 1.2, Ar), 7.48 (1H, td, J 7.0, 1.2,
their melting points, FT-IR, H NMR, and mass spec-
trometry (MS).
7
+
Ar). m/z 256 [M] .
2
-Phenyl-1H-benzo[d]imidazole (1a)
2
-(3-Nitrophenyl)-1H–benzo[d]imidazole (3a)
ꢀ
−1
Pale yellow solid, mp 293–294 C. IR (KBr, cm ):
ꢀ
−1
Yellow solid, mp 204–206 C. IR (KBr, cm ):
3
8
1
390, 3160, 1625, 1585, 1512, 1460, 1287, 1231,
72, 752, 698, 622. H NMR (DMSO-d , 400 MHz) δ:
3
1
4
8
350, 3050, 2900, 1634, 1609, 1530, 1490, 1401, 1340,
281, 1123, 811, 739, 620, 540. H NMR (DMSO-d ,
00 MHz) δ:13.21 (br, 1H, s, −NH),8.98 (1H, s, Ph),
.61 (1H, d, J 7.2, Ph), 8.30 (1H, d, J 8.4, Ph), 7.84
1
6
1
6
2.90 (1H, s, NH), 8.18–8.12 (2H, m, Ar), 7.75–7.71
(2H, m, Ph), 7.67–7.60 (3H, m, Ph), 7.30–7.22 (2H, m,
+
Ar). m/z 194 [M] .
(
(
1H, t, J 8.0, Ph), 7.65 (2H, dd, J 6.1, 3.2, Ar), 7.22
2H, dd, J 4.6, 3.2, Ar). m/z 239 [M] .
+
2
-Phenylbenzo[d]oxazole (1b)
ꢀ
−1
White solid, mp 102–103 C. IR (KBr, cm ):
2-(3-Nitrophenyl)benzo[d]oxazole (3b)
ꢀ
−1
3
8
060, 2960, 1617, 1552, 1472, 1445, 1240, 1052,
04, 745, 683. H NMR (CDCl , 400 MHz) δ: 8.30
Yellow solid, mp 206–207 C. IR (KBr, cm ):
1
3096, 2921, 2859, 1609 1528, 1472, 1451, 1351, 1245,
1098, 1053, 807, 765, 743, 705, 665. H NMR (CDCl ,
3
1
(2H, dd, J 6.4, 4, Ph), 7.86–7.80 (1H, m, Ar), 7.61–7.55
3
J. Chin. Chem. Soc. 2017
© 2017 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.jccs.wiley-vch.de
7

Article
Karimian et al.
4
1
00 MHz) δ: 9.12 (1H, t, J 1.6, Ph), 8.61 (1H, dt, J 7.6,
.2, Ph), 8.40 (1H, dt, J 7.2, 1.2, Ph), 7.85–7.83 (1H, m,
2-(2-Chlorophenyl) benzo[d]oxazole (5b)
ꢀ
−1
White solid, mp 68–69 C. IR (KBr, cm ): 3068,
Ar), 7.76 (1H, t, J 8.0, Ph), 7.67–7.65 (1H, m, Ar),
1609, 1568, 1535, 1452, 1430, 1343, 1311, 1249, 1086,
+
1
7.47–7.41 (2H, m, Ar). m/z 240 [M] .
1021, 918, 813, 761, 746, 729, 461. H NMR (CDCl ,
3
4
00 MHz) δ: 8.17 (1H, dd, J 7.4, 2.0, Ph), 7.89–7.86
(
1H, m, Ph), 7.65–7.62 (1H, m, Ph), 7.59 (1H, dd,
2
-(3-Nitrophenyl)benzo[d]thiazole (3c)
+
ꢀ
J 8.0, 1.6, Ph), 7.49–7.38 (4H, m, Ar). m/z 225 [M] ,
2
Light yellow crystals, mp 186–188 C. IR (KBr,
+
−1
27 [M + 2] .
cm ): 3091, 1623, 1580, 1558, 1529,1432, 1345, 1315,
1
1
4
1
7
7
288, 1225, 1101, 984, 888, 761. H NMR (CDCl ,
3
2
-(2-Chlorophenyl)benzo[d]thiazole (5c)
00 MHz) δ: 8.94 (1H, t, J 2.1, Ph), 8.42 (1H, dt, J 7.6,
.4,Ph), 8.37–8.34 (1H, m, Ph), 8.13 (1H, d, J 8.0, Ar),
.97 (1H, dd, J 4.6, 0.4, Ar), 7.70 (1H, t, J 8.2, Ph),
ꢀ
−1
White solid, mp 83–84 C. IR (KBr, cm ): 3055,
1
9
590, 1556, 1479, 1431,1315, 1271, 1221, 1059, 1016,
1
67, 758, 729. H NMR (CDCl3, 400 MHz) δ: 8.25
.57 (1H, td, J 8.0, 1.2, Ar), 7.47 (1H, td, J 8.0, 1.2,
+
(1H, dd, J 5.8, 3.6, Ph), 8.17 (1H, d, J 8.4, Ar), 7.98
(
(
Ar). m/z 256 [M] .
1H, d, J 8.0, Ar), 7.57–7.54 (2H, m, Ar), 7.48–7.43
+
+
3H, m, Ph). m/z 245 [M] , 247 [M + 2] .
2
-(4-Chlorophenyl)-1H-benzo[d]imidazole (4a)
ꢀ
−1
Light yellow, mp 283–284 C. IR (KBr, cm ):
2
-(4-Methoxyphenyl)-1H–benzo[d]imidazole (6a)
−1
3
8
421, 2925, 1627, 1602, 1596, 1489, 1375, 1232, 1012,
36, 748, 616. H NMR (DMSO-d , 400 MHz) δ: 12.98
ꢀ
Light yellow, mp 223–225 C. IR (KBr, cm ):
1
6
3339, 3019, 2928, 1634, 1608, 1506, 1306, 1263, 1189,
1
(br, 1H, s, −NH), 8.23 (2H, dd, J 4.6, 2.0, Ph),
1
1
7
023, 835, 750. H NMR (DMSO-d , 400 MHz) δ:
6
7.64–7.58 (4H, m, Ph, Ar) 7.31 (2H, dd, J 6.4, 2.8, Ar).
2.73 (1H, br s, NH), 8.09 (2H, dd, J 6.4, 2.0, Ar),
+
+
m/z 228 [M] , 230 [M + 2] .
.61–7.59 (2H, m, Ph), 7.45–7.40 (2H, m, Ar), 7.12
+
(
2H, d, J 9.6, Ph), 3.84 (3H, s, OMe). m/z 224 [M] .
2
-(4-Chlorophenyl) benzo[d]oxazole (4b)
ꢀ
−1
2-(4-Methoxyphenyl)benzo[d]oxazole (6b)
White crystals, mp 152–153 C. IR (KBr, cm ):
ꢀ
−1
White solid, mp 105–106 C. IR (KBr, cm ):
3
9
055, 3060, 1613, 1481, 1452, 1343, 1089, 1056, 1011,
27832, 739. H NMR (CDCl , 400 MHz) δ: 8.22 (2H,
1
3
1
051, 2982, 2840, 1615, 1605, 1589, 1503, 1454, 1327,
255, 1242, 1169, 1061, 1017, 923, 831, 741, 729. H
3
1
dt, J 8.6, 2.2, Ar), 7.81–7.77 (1H, m, Ph), 7.60–7.58
NMR (CDCl , 400 MHz) δ: 8.23 (2H, dd, J 7.2, 2.0,
(
(
1H, m, Ph), 7.52 (2H, dt, J 8.6, 2.2, Ar), 7.41–7.38
2H, m, Ph). m/z 229 [M] , 231 [M + 2] .
3
+
+
Ph), 7.77–7.75 (1H, m, Ar), 7.58–7.56 (1H, m, Ar),
7
3
.37–7.29 (2H, m, Ar), 7.06 (2H, dd, J 6.8, 2.0, Ph),
.91 (3H, s, OMe). m/z 225 [M] .
+
2-(4-Chlorophenyl)benzo[d]thiazole (4c)
−1
White solid, mp 114–115. IR (KBr, cm ): 3054,
2
-(4-Methoxyphenyl)benzo[d]thiazole (6c)
2
1
930, 2851, 1589, 1474, 1434, 1398, 1315, 1285, 1090,
008, 969, 828756, 730. H NMR (CDCl , 400 MHz)
ꢀ
Light yellow solid, mp 123–124 C. IR (KBr,
cm ): 3064, 2990, 2937, 2835, 1608, 1591, 1518, 1484,
1
3
−1
δ: 8.09 (1H, d, J 8.1, Ar), 8.05 (2H, dt, J 8.6, 2.0, Ph),
.93 (1H, d, J 8.0, Ar), 7.51–7.54(1H, m, Ar), 7.49 (2H,
dt, J 8.8, 2.0, Ph), 7.43 (1H, td, J 8.0, 1.2, Ar). m/z
1
9
8
7
466, 1434, 1308, 1287, 1253, 1225, 1171, 1122, 1074,
7
1
67, 832, 791. H NMR (CDCl , 400 MHz) δ:
3
.07–8.05 (3H, d, J 8.4, Ar, Ph), 8.01 (1H, d, J 8.0, Ph),
.48 (1H, t, J 7.6, Ar), 7.39 (1H, t, J 7.2, Ar), 7.12 (2H,
+
+
245 [M] , 247 [M + 2] .
+
d, J 8.4, Ph), 3.91 (3H, s, OMe). m/z 241 [M] .
2-(2-Chlorophenyl)-1H–benzo[d]imidazole (5a)
ꢀ
−1
White solid, mp 229–230 C. IR (KBr, cm ):
2-p-Tolyl-1H-benzo[d]imidazole (7a)
ꢀ
−1
3
1
1
2
396, 3100, 2885, 1630, 1590, 1443, 1373, 1316, 1274,
054, 974, 756, 731. H NMR (DMSO-d , 400 MHz) δ
2.7 (1H, br s, NH), 7.80–7.25 (8H, m, Ph, Ar). m/z
28 [M] , 230 [M + 2] .
White solid, mp 264–265 C. IR (KBr, cm ):
1
3435, 3065, 2853, 1625, 1500, 1447, 1398, 1369, 1274,
6
1
966, 823, 746, 726. H NMR (DMSO-d , 400 MHz) δ:
6
+
+
12.81 (1H, br s, NH), 8.23 (2H, d, J 8.2, Ph), 7.61 (2H,
8
www.jccs.wiley-vch.de
© 2017 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
J. Chin. Chem. Soc. 2017

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Synthesis of Benzimidazoles, Benzoxazoles and Benzothiazoles
m, Ar), 7.32 (2H, d, J 8.0, Ph), 7.20 (2H, dd, J 6.3, 2.6,
Ar), 2.38 (3H, s, Me). m/z 208 [M] .
o-phenylenediamine,
aminothiophenol with various benzaldehydes by using
o-aminophenol,
and
o-
+
the magnetic Co-doped NiFe O4 nanoparticles as a
2
2
-p-Tolylbenzo[d]oxazole (7b)
White solid, mp 92–93 C. IR (KBr, cm ): 3049,
917, 2851, 1621, 1550, 1485, 1445, 1348, 1243, 1172,
115, 1059, 1016, 820, 757, 726. H NMR (CDCl ,
00 MHz) δ: 8.23 (2H, d, J 8.4, Ph), 7.78–7.75 (1H, m,
reusable and efficient nanocatalyst. The advantages of
this magnetic nanocatalyst, such as excellent product
yields, mild reaction conditions, very short reaction
times, and convenient work-up procedures, make this
method practical. Solvent-free condition also is an
interesting improvement in terms of green chemistry. In
addition, this nanocatalyst could be reused at least four
times without significant loss of its activity.
ꢀ
−1
2
1
4
1
3
Ph), 7.60–7.58 (1H, m, Ph), 7.35–7.32 (4H, m, Ar), 2.70
+
(3H, s, Me). m/z 209 [M] .
2
-p-Tolylbenzo[d]thiazole (7c)
−1
White solid, mp 83–84. IR (KBr, cm ): 3060,
3
1
8
023, 2906, 1609, 1527, 1484, 1434, 1312, 1286, 1226,
1
122, 959, 817, 760. H NMR (CDCl , 400 MHz) δ:
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1
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+
4
5
6
4-(1Hbenzo[d]imidazol-2-yl)-N,N-dimethylaniline (8a)
ꢀ
Light yellow solid, mp 294–295 C. IR (KBr,
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−1
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2
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7
+
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ꢀ
−1
White solid, m.p 181–182 C; IR (KBr, cm ):
9
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3
1
051, 2909, 1619, 1606, 1554, 1447, 1376, 1246, 1230,
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1
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3
1
+
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1
1
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2
-(4-N,N-Dimethylphenyl)benzothiazole (8c)
ꢀ
−1
Pale yellow solid, mp 179–180 C. IR (KBr, cm ):
2
016, 2, 20.
3
1
052, 2895, 2802, 1609, 1576, 1545, 1479, 1456, 1370,
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1
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4
CONCLUSIONS
In summary, we have developed a mild and green
1
5
procedure for the synthesis of benzimidazoles, benzoxa-
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