Magnetic nanoparticles-supported tungstosilicic acid: As an efficient magnetically separable solid acid for the synthesis of benzoazoles in water

Article abstract of DOI:10.1007/s13738-013-0400-8

The magnetic nanoparticles-supported tungstosilicic acid (TSAMNP) was found to be a highly efficient solid acid for the synthesis of benzoazoles in water. TSAMNP catalyst was achieved by the immobilization of tungstosilicic acid [H₄(W₁₂SiO₄₀)] species on the silica core-shell magnetic nanoparticles (Fe₃O₄@SiO₂). A variety of aldehydes were successfully condensed with 1,2-diaminobenzene, 2-aminophenol and 2-aminothiophenol in water as a green solvent to synthesize benzoazoles in good-to-excellent yields. TSAMNP catalyst was easily separated from the reaction mixture and reused several times without any loss of efficiency.

Full text of DOI:10.1007/s13738-013-0400-8

J IRAN CHEM SOC
DOI 10.1007/s13738-013-0400-8
ORIGINAL PAPER
Magnetic nanoparticles-supported tungstosilicic acid:
as an efficient magnetically separable solid acid
for the synthesis of benzoazoles in water
Ali Khalafi-Nezhad
Reza Yousefi Sina Sarrafi
•
•
Farhad Panahi
•
•
Yasaman Gholamalipour
Received: 24 September 2013 / Accepted: 22 December 2013
Ó Iranian Chemical Society 2014
Abstract The magnetic nanoparticles-supported tung-
stosilicic acid (TSAMNP) was found to be a highly effi-
cient solid acid for the synthesis of benzoazoles in water.
TSAMNP catalyst was achieved by the immobilization of
tungstosilicic acid [H (W SiO )] species on the silica
waste [6]. One of the most important approaches to
improve their applicability in organic reactions is their
immobilization on a recyclable support. As a result, sup-
ported heteropoly acids (SHPAs) have been introduced as
economically and environmentally benign catalysts in the
recent years [7]. The immobilization of HPAs on different
type of supports has been employed [8–10]. However, the
activity and selectivity of supported catalysts are decreased
frequently, due to a significant reduction in reactant dif-
fusion rate to the surface of catalyst [11]. The aforemen-
tioned problem can be resolved to some extent by selecting
the very small size ranges of the support. Because of
nanometer size-range of nanoparticles which allow their
surface areas to increase dramatically, these materials are
reasonable potential candidate supports [12]. Moreover,
nanoparticles are dispersible in solution, forming emulsion
which further increases the diffusion rate [13]. In addition,
reactants in solution have easy access to the active sites on
the surface of nanomaterial. However, when the size of
support is decreased to nanometer scale, a simple filtration
method cannot overcome the big obstacle of catalyst sep-
aration from the reaction media. As a solution, the efforts
have been focused on magnetic recyclable supports such as
magnetic nanoparticles (MNPs) [14]. When MNPs are used
as support, both reactivity and reusability (catalyst can be
separated from reaction condition using an external mag-
netic field) could be improved. Thus, by immobilization of
HPAs on MNPs it is possible to prepare a highly efficient
solid acid based on HPAs for application in organic reac-
tions [15].
4
12
40
core–shell magnetic nanoparticles (Fe O @SiO ). A vari-
3
4
2
ety of aldehydes were successfully condensed with 1,2-
diaminobenzene, 2-aminophenol and 2-aminothiophenol in
water as a green solvent to synthesize benzoazoles in good-
to-excellent yields. TSAMNP catalyst was easily separated
from the reaction mixture and reused several times without
any loss of efficiency.
Keywords Magnetic nanoparticles Á Heteropoly acids Á
Tungstosilicic acid Á Benzoazoles Á Water
Introduction
In both academic researches and industries, heteropoly
acids (HPAs) have been widely used as catalyst in a large
number of organic reactions for fine chemical synthesis of
many materials [1–5]. The advantages of these catalysts in
organic transformations are mentioned as follows: high
catalytic performance, strong acidity, selectivity to a par-
ticular reaction product by selective stabilization of the
reaction intermediate, corrosiveness, safety, and lower
A. Khalafi-Nezhad (&) Á F. Panahi Á S. Sarrafi Á
Y. Gholamalipour
Department of Chemistry, College of Sciences, Shiraz
University, 71454 Shiraz, Iran
e-mail: khalafi@chem.susc.ac.ir
In this study, we applied a MNPs-supported tungstosil-
icic acid catalyst as a highly efficient and easy separable
solid acid for the synthesis of benzoazoles in water as a
green solvent. It is noteworthy that, the benzoazole ring
systems are important pharmacophores in medicinal
R. Yousefi
Protein Chemistry Laboratory (PCL), Department of Biology,
College of Sciences, Shiraz University, Shiraz, Iran
123

J IRAN CHEM SOC
chemistry and modern drug discovery [16–18]. A large
number of their derivatives have been found to exhibit
various biological activities such as anti inflammatory,
antifungal, antibacterial, anthelminthic, analgesic, antivi-
ral, anti trypanosomatid, anticonvulsant, cytotoxic, antidi-
abetics and antiulcer activities [19–23]. Some of the
benzoazole-based compounds have interesting photophys-
ical properties, and they are widely used in organic elec-
tronic devices [24–28]. However, some of the reported
methods for the synthesis of this class of compounds suffer
from disadvantage of use of toxic and unrecyclable cata-
lysts and solvents, prolonged reaction times, harsh reaction
conditions and difficult work-up procedures [29–43].
TSAMNP catalyst was obtained from the reaction of
H (W SiO ) and the Fe O @SiO according to the pro-
4
12
40
3
4
2
cedure in the literature [47].
To confirm the synthesis of TSAMNP catalyst its structure
was characterized using both microscopic analysis and
spectroscopic techniques. The analytical percentage of ele-
ments for TSAMNP using energy dispersive X-ray (EDS)
was obtained as Fe (42.36), W (17.44), Si (18.31) and O
(21.89). Using the EDS analysis, the amount of protons in
-1
TSAMNP was obtained about 0.225 mmol g . The com-
parison between FT-IR spectra of H (W SiO ), Fe O @-
4
12
40
3 4
SiO nanoparticles, and TSAMNP shows that TSAMNP
2
catalyst was generated according to our procedure (Fig. 1).
-1
The broad band around 1,200–1,050 cm , corresponding to
asymmetric stretching of Si–O–Si bond was seen in both
Fe O @SiO nanoparticles and TSAMNP catalyst [48]. Also
Results and discussion
3
4
2
-1
peaks at around 500 cm can be attributed to the bending
vibration of the Si–O–Si bonds [8]. The broad absorption
In the current study, TSAMNP catalyst was prepared using
immobilization of tunstosilicic acid (as a stable and reac-
tive Keggin type HPA) [44] on the Fe O -modified silica
-
band around 3500 cm is the absorption of -OH bond on the
1
-1
surface of all materials. The peaks around 1,700–1,800 cm
which are existed in the structure of H (W SiO ) can be
3
4
nanoparticles (Fe O @SiO ) as shown in Scheme 1. Fe O
3
4
2
3
4
4
12
40
nanoparticles were synthesized by a reported thermal
decomposition method [45]. The synthesized Fe O nano-
seen in the FT-IR of TSAMNP. Importantly, the character-
-1
istic bands at 1025, 995, 915, 880, and 769 cm correspond
to W=O symmetrical and asymmetrical, Si–O asymmetrical,
W–Ob–W asymmetrical, and W–Oc–W asymmetrical,
respectively [49]. The presence of these bands strongly
reveals that the primary structure of H (W SiO ) species is
3
4
particles were coated by silica via a sol–gel process to
obtain Fe O @SiO [46]. The silica shell not only prevents
3
4
2
the aggregation of MNPs during the catalyst preparation
process, it also provides an easy access to the connection of
H (W SiO ) species to the surface of MNPs. The
4
12
40
preserved even after anchoring to MNP support.
4
12
40
Scheme 1 The synthetic route
for the preparation of TSAMNP
catalyst
1
23

J IRAN CHEM SOC
3 4 2 3 4
Fig. 1 The FT-IR spectra of TSAMNP, Fe O @SiO , Fe O , and
H (W12SiO40)
4
Fig. 3 The TEM image of TSAMNP
(
311), (400), (422), (511) and (440) planes of the Fe O
3 4
nanoparticles [50].
To evaluate the catalytic performance of TSAMNP,
we checked the synthesis of benzoazoles (benzoxazoles,
benzoimidazoles and benzothiazoles) via the condensa-
tion of aldehydes with benzene1,2-diamine, 2-amino-
phenol or 2-aminothiophenol as an acid catalyzed
process. To optimize the conditions for maximum yields
of desired products, the effect of different reaction
parameters such as catalyst loading, temperature, solvent
and reaction time were investigated. So, the reaction
between 2-aminophenol (1) and benzaldehyde (2) as a
model was tested under different conditions, and the
results are depicted in Table 1.
4 3 4 2
Fig. 2 The TGA of pure H (W12SiO40), Fe O @SiO nanoparticles,
and TSAMNP
A comparison between the thermal gravimetric analysis
TGA) curves of pure H (W SiO ), Fe O @SiO nano-
(
4
12
40
3
4
2
particles, and TSAMNP catalyst is depicted in Fig. 2.
As shown in Fig. 1, the TGA of TSAMNP shows 2.7 %
weight loss within a temperature range of 150–170 °C
which is due to the loss of adsorbed water molecules.
Furthermore, it shows 6.7 % weight loss at 180–210 °C
due to the loss of water of crystallization and 13.1 %
weight loss at 300–450 °C, which is due to the decompo-
sition of anchored heteropoly acid.
The results indicated that TSAMNP catalyst can be
applied as a powerful, green and magnetically separable
catalyst for the synthesis of benzoazoles under green con-
ditions. As it is shown in Table 1 by varying the type of
solvent the yield of the desired product did not change
significantly in comparison with water (Table 1, entries
9–12). Also with increasing the amount of catalyst the
yield of product remained unchanged (Table 1, entry 13).
Furthermore, as a result of reducing the amount of catalyst
a reduction was observed in the yield of product (Table 1,
entry 14). These results show that the catalytic amount of
TSAMNP is applicable for this reaction. Thus, the simple
To further study the immobilization of the H (W SiO )
40
4
12
species into MNPs, TSAMNP catalysts were characterized
using transmission electron microscopy (TEM) and x-ray
diffraction pattern (XRD). The TEM image of TSAMNP
catalyst is depicted in Fig. 3. According to both TEM image
(
Fig. 3) and histogram, the average diameter of TSAMNP
particles is estimated to be 45 nm. TEM images of
TSAMNP catalyst show the near spherical TSAMNP par-
ticles which are produced during preparation process. To
further explore the chemically modification of the MNPs
with TSA, the morphology of the catalyst was studied using
XRD. The XRD pattern of TSAMNP catalyst (Fig. 4)
shows that the catalyst was synthesized successfully using
our methodologies. The peaks are indexed as the (220),
system, TSAMNP (0.05 g), H O as solvent, and reflux
2
temperature of water, was chosen as the optimized reaction
conditions (Table 1, entry 6). To determine the scope of
this protocol, various benzoazoles were synthesized under
the optimized conditions, and the results are summarized in
Table 2.
123

J IRAN CHEM SOC
Fig. 4 The XRD spectra of
TSAMNP
Table 1 The study of different conditions for the synthesis of
2
Table 2 The synthesis of benzoazoles in the presence of TSAMNP
as
-phenylbenzo[d]oxazole (3a) using TSAMNP as catalyst
a
magnetically separable solid acid catalyst in water
NH2
X
TSAMNP
(
0.05 g)
+
R
R
O
H
H O / reflux
N
X
2
X = O, S, NH
3a-z
a
Entry
X
R
Time (h)
Yield (%)
Entry
Catalyst
Solvent
Temp./ °C
Time
h)
Yield
a
(%)
(
3
a
O
Ph
5
3
95
97
94
93
97
95
91
93
91
90
92
89
86
84
85
91
90
92
88
87
88
91
93
93
88
90
1
2
3
4
5
6
7
8
9
–
–
–
–
–
r.t.
24
12
12
12
12
5
0
15
21
3b
3c
3d
3e
3f
S
Ph
100
NH
O
Ph
6
H
H
H
H
–
2
2
2
2
O
O
O
O
Reflux
Reflux
Reflux
Reflux
r.t.
3-OH-Ph
4-CN-Ph
5
b
Fe
3
O
4
@SiO
2
32
NH
NH
O
3
c
H
4
(W12SiO40
)
81
3-NO
2
-Ph
4
TSAMNP
TSAMNP
TSAMNP
TSAMNP
TSAMNP
TSAMNP
TSAMNP
TSAMNP
TSAMNP
95
19
61
65
76
68
84
3g
3h
3i
4-OH-Ph
4-OH-Ph
4-OMe-Ph
2-Me-Ph
4-OMe-Ph
2-Me-Ph
6
24
12
12
12
12
12
12
5
S
6
–
100
NH
S
6
EtOH
CHCl
Reflux
Reflux
100
3j
8
10
11
12
13
14
3
3k
3l
S
6
Toluene
DMSO
O
8
100
3m
3n
3o
O
Ph-CH
Et
2
-
8
d
H
2
O
O
Reflux
Reflux
96
O
10
10
8
e
H
2
84
S
Et
3
p
S
2-Cl-Ph
2-Cl-Ph
2-Cl-Ph
2,6-F-Ph
2-pyridinyl
2,6-Cl-Ph
4-Br-Ph
4-Br-Ph
4-Cl-Ph
Reaction conditions: 2-aminophenole (1.1 mmol), benzaldehyde
(
1 mmol), catalyst (0.05 g), and solvent (5 mL)
3q
3r
O
8
a
Isolated yield
NH
S
8
b
c
d
e
0
.1 g of Fe
.05 g of H
.06 g of catalyst was used
3
O
4
@SiO
2
was used
3s
3t
8
0
4
(W12SiO40) was used
NH
NH
O
8
0
3u
3v
8
0
.04 g of catalyst was used
5
3
3
3
3
w
S
5
x
y
z
NH
S
5
The results in Table 2 revealed that, TSAMNP is an
Ph-CH
2
-
6
active and efficient catalyst for the synthesis of benzoaz-
oles in water. The reaction condition is quite broad with
respect to the substrates examined, providing the desired
benzoazoles with good-to-excellent yields. As clearly
shown in Table 2, TSAMNP catalyst can be used for aro-
matic aldehydes with electron-withdrawing and electron-
NH
4-Me-Ph
6
Reaction conditions: 2-aminophenol/-thiphenol/benzene-1,2-diamine
(1.1 mmol), aldehyde (1.0 mmol), TSAMNP (0.05 g), H
under reflux conditions
2
O (5 mL)
a
Isolated yield
1
23

J IRAN CHEM SOC
1
H NMR spectra, we used a Brucker (250MHZ) Avance
DRX in pure deuterated DMSO-d and CDCl solvents
6
3
with tetramethylsilane (TMS) as the internal standard.
Mass spectra were recorded on a FINNIGAN-MAT 8430
mass spectrometer operating at 70 eV. Melting points were
determined in open capillary tubes in a Barnstead Elec-
trothermal 9100 BZ circulating oil melting point apparatus.
The reaction monitoring was accomplished by TLC on
silica gel PolyGram SILG/UV254 plates. Column chro-
matography was carried out on columns of silica gel 60
(70–230 mesh).
Fig. 5 The reusability of the TSAMNP catalyst in synthesis of
benzoazoles in water
Preparation of Fe O nanoparticles
3
4
donating groups. Moreover, aliphatic aldehydes can be
used under the same reaction conditions.
Magnetic nanoparticles were prepared via the co-precipita-
tion of Fe(III) and Fe(II) ions in the presence of sodium
hydroxide. For this purpose, in a canonical flask, a mixture of
For practical applications of a heterogeneous catalyst,
the level of reusability is a very important parameter. Thus,
the possibility of recycling the catalyst was tested using the
model reaction under optimized conditions. The recycled
catalyst could be reused at least for five times without any
treatment in its catalytic activity (Fig. 5).
FeCl
.2H
O (16 mmol, 2.6 g) and FeCl
Á6H
O (30 mmol,
2
2
2
3
8.1 g) was dissolved in 100 mL of deionized water. Then,
the 3 M aqueous solution of NaOH was added drop-wise (in
a period of 5 min) at 40 °C until the pH of the resulting
mixture increased to 11. Subsequently, the temperature of
mixture was increased to 80 °C and the solution was stirred
for 20 min. The magnetic nanoparticles as a dark solid were
isolated from the solution by magnetic separation and
washed with deionized water until pH 7 reached. Obtained
material was dried under reduced pressure for 12 h, and
Since leaching of the active species from the support
makes the catalyst unattractive, the stability study of a
heterogeneous catalyst is necessary. Thus, the leaching of
TSA species from the magnetic support was checked. After
six times of reusability we checked the W content of
TSAMNP catalyst using EDX analysis, and the results
were shown that \0.1 % of W was lost. This result was
also confirmed by ICP using hot filtration test. In an
experiment, when the reaction between benzaldehyde with
Fe
Preparation of Fe
Fe @SiO nanoparticles were prepared based on the
O
3 4
nanoparticles were obtained as a brown powder.
O
@SiO nanoparticles
3
4
2
2
-aminophenol was completed, the hot filtration had been
3
O
4
2
accomplished and the ICP analysis of the aqueous solution
showed\1 ppm of W. Considering these results, it can be
concluded that there is a small amount of TSA species
leaching from the magnetic support and the present catalyst
is truly heterogeneous in nature. These results are in good
agreements with the catalytic activity of the TSAMNP after
each recovery.
literature with some modifications. To a mixture of
cyclohexane (250 mL), 1-hexanol (50 mL), triton X-100
(80 mL) and water (25 mL), Fe
added and the mixture stirred by a mechanical stirrer under
atmosphere for 30 min. Tetraethyl orthosilicate
O nanoparticles (2 g) was
4
3
N
2
(TEOS) (20 mL) was added to the mixture and the solution
stirred for additional 12 h at 30 °C. After the specified
time, ammonia (saturated solution in water) (18 mL) was
added and the solution stirred continuously for another
12 h. The precipitate was washed with ethanol (10 mL, 3
times) and collected using an external magnetic field. The
obtained gray product was dried under reduced pressure
overnight and Fe O @SiO obtained as a gray solid.
Experimental
General
3
4
2
Chemicals were purchased from Fluka and Aldrich chem-
ical companies and used as received. FT-IR spectroscopy
Preparation of magnetic nanoparticles-supported
tungstosilicic acid (TSAMNPs)
(
Shimadzu FT-IR 8300 spectrophotometer), was employed
for characterization of the catalyst and synthesized com-
pounds. The transmission electron microscopy (TEM) was
obtained using TEM apparatus (CM-10-philips, 100 kV).
The thermogravimetry analysis (TGA) of the samples was
analyzed using a labmade TGA instrument. For recorded
The TSAMNP was prepared using an impregnation
method. For this, Fe O @SiO nanoparticles (2.0 g) were
3
4
2
mixed with a solution of tungstosilicic acid (0.57 g,
0.2 mmol) in deionized water (25 mL). The obtained
123

J IRAN CHEM SOC
mixture was stirred at 60 °C for 1 h using a mechanical
stirrer. Then the mixture was filtered and washed by dis-
tilled water (20 mL, 2 times). The filtrate was dried at
3-(1,3-Benzoxazol-2-yl)phenol (3d): Yield 93 %, white
solid; mp: 237–238 °C. IR (KBr): V = 3,125, 3,092,
1,603, 1,555, 1,454, 1,301, 750 cm . H-NMR (250 MHz,
-
1 1
80 °C for 2 h, then calcined at 150 °C for 5 h and
TSAMNP was obtained as a dark solid powder.
DMSO-d /TMS) d (ppm): 7.01 (dd, J = 7.3, 1.2 Hz, 1H),
6
7.30–7.40 (m, 3H), 7.60 (d, J = 5.8 Hz, 2H), 7.67–7.76
1
3
(
m, 2H). C-NMR (62.9 MHz, DMSO-d /TMS) d (ppm):
6
General producer for the synthesis of benzoxazoles
in the presence of TSAMNP as a solid acid catalyst
110.7, 113.6, 118.0, 119.0, 119.6, 124.7, 125.3, 127.4,
130.3, 141.4, 150.1, 157.8, 162.3.
4-(1H-1,3-benzimidazol-2-yl)benzonitrile (3e): Yield
To the suspension of aldehyde (1 mmol) and 2-amino-
97 %, white solid, mp: 262–263 °C. IR (KBr): V = 3,420,
3,050, 2,915, 2,220, 1,600, 1,450, 1,410, 840, 750 cm .
-
1
phenol/-thiphenol/benzene-1,2-diamine (1 mmol) in water
?
5 mL), TSAMNP (0.05 g, 12 mol % based on H con-
1
(
H-NMR (250 MHz, DMSO-d
6
/TMS) d (ppm): 7.23–768
(m, 4H), 8.00 (d, J = 8.1 Hz, 2H), 8.32 (d, J = 8.1 Hz,
tent) was added and the resulting mixture heated to 70 °C
for 5 h. Then the reaction was followed by TLC. After
completion of the reaction, the mixture was cooled down to
room temperature and the catalyst magnetically separated
from the reaction mixture and washed with diethyl ether
1
3
2H). C-NMR (62.9 MHz, DMSO-d /TMS) d (ppm):
6
111.7, 111.8, 118.6, 119.3, 122.2, 123.3, 127.0, 132.9,
134.2, 149.3.
2-(3-nitrophenyl)-1H-1,3-benzimidazole (3f): Yield
95 %, pale yellow solid; mp: 202.5 °C (Lit. [52] mp 200–
202 °C). IR (KBr): V = 3,440, 3,080, 1,530, 1,350,
(
10 mL, 2 times) followed by deionized and oxygen-free
water (10 mL, 2 times), dried under reduced pressure and
reused for the next run. The aqueous phase was extracted
with diethyl ether (10 mL, 2 times) and the combined
organic phases dried over Na SO . The benzoazole product
-
1
1
730 cm
.
H-NMR (250 MHz, CDCl3)
d
(ppm):
7.24–7.31 (m, 2H), 7.61–7.67 (m, 3H), 8.25 (d,
2
4
J = 8.4 Hz, 1H), 8.42 (d, J = 7.8 Hz, 1H), 8.77 (t,
1
3
was purified by column chromatography (hexane/ethyl
acetate) to obtain the desired purity.
J = 1.8 Hz, 1H). C-NMR (62.9 MHz, DMSO-d /TMS) d
6
(ppm): 116.0, 120.8, 122.7, 124.2, 130.6, 131.6, 132.4,
1
9
36.9, 148.3, 149.0.
-(3-nitrophenyl)-1H-1,3-benzimidazole (3g): Yield
1 %, white solid; mp: 259–260 °C. IR (KBr): V = 3,060,
2
Spectral data of synthesized compounds
2
-phenyl-1,3-benzoxazole (3a): Yield 95 %, white crystals,
3,000, 1,600, 1,480, 1,430, 1,280, 1,250, 1,220, 1,170, 830,
-1 1
760 cm . H-NMR (250 MHz, DMSO-d
mp: 103–104 °C (Lit. [48] mp 103 °C). IR (KBr):
V = 3,049, 1,608, 1,547, 1,483, 1,445, 1,238, 1,047, 1,013,
6
/TMS) d (ppm):
.97 (d, J = 8.7 Hz, 2H), 7.27–7.33 (m, 2H), 7.61–7.72
6
1
m, 2H), 8.01 (d, J = 8.7 Hz, 2H), 10.35 (s, 1H). C-NMR
3
-
1 1
(
9
20, 744, 692 cm . H-NMR (250 MHz, CDCl /TMS) d
3
(62.9 MHz, DMSO-d /TMS) d (ppm): 115.3, 121.3, 122.4,
(
(
ppm): 7.19–7.22 (m, 2H), 7.36–7.41 (m, 4H), 7.61–7.65
6
1
m, 1H), 8.11–8.15 (m, 2H). C-NMR (62.9 MHz, CDCl3/
3
124.5, 129.8, 34.0, 134.5, 147.0, 155.2, 166.1, 168.0.
4
-(1,3-benzothiazol-2-yl)phenol (3h): Yield 93 %, white
TMS) d (ppm): 110.6, 120.0, 124.6, 125.1, 127.1, 127.6,
28.9, 131.5, 142.1, 150.7, 163.0.
-phenyl-1,3-benzothiazole (3b): Yield 97 %, white
crystals, mp: 113–114 °C (Lit. [49] mp 112–114 °C). IR
solid, mp: 226–228 °C (Lit. [53] mp 227 °C). IR (KBr):
V = 3,090, 1,600, 1,460, 1,440, 1,290, 1,230, 1,170, 970,
1
2
-1 1
830, 746 cm . H-NMR (250 MHz, DMSO-d
/TMS) d
ppm): 6.97 (d, J = 8.5 Hz, 2H), 7.31 (t, J = 7.4 Hz, 1H),
6
-
1 1
(
(
KBr): V = 3,060, 1,472, 1,431, 960, 762, 687 cm . H-
1
.42–7.45 (m, 1H), 7.92–7.99 (m, 4H), 10.31 (s, 1H). C-
3
7
NMR (250 MHz, CDCl /TMS) d (ppm): 7.35–7.38 (m,
3
NMR (62.9 MHz, DMSO-d /TMS) d (ppm): 116.1, 121.9,
22.2, 123.5, 124.1, 126.2, 128.6, 134.2, 153.7, 160.5,
1
3
1
1
H) 7.47–7.51 (m, 4H), 7.88–7.91 (m, 1H) 8.1–8.13 (m,
1
6
3
1
H). C-NMR (62.9 MHz, CDCl /TMS) d (ppm): 121.6,
3
1
67.5.
23.2, 125.2, 126.3, 127.6, 129.0, 131.0, 133.6, 135.1,
2-(4-methoxyphenyl)benzimidazole (3i): Yield 91 %,
54.1, 168.1.
white solid, mp: 226–228 °C (Lit. [54] mp 226–227 °C).
IR (KBr): V = 3,440, 3,060, 2,950, 1,610, 1,500, 1,480,
2
-phenylbenzimidazole (3c): Yield 94 %, white crystals;
mp 295–296 °C (Lit. [51] mp 295 °C). IR (KBr):
V = 3,440, 1,620, 1,591, 1,450, 1,412, 1,315, 1,277, 1,113,
-
1
1
. H-NMR
1,450, 1,435, 1,400, 1,255, 1,180, 740 cm
-
1 1
(
250 MHz, DMSO-d /TMS) d (ppm): 3.78 (s, 3H), 7.10 (d,
7
42, 694 cm . H-NMR (250 MHz, DMSO-d /TMS) d
ppm): 7.14–7.25 (m, 2H), 7.44–7.61 (m, 5H), 8.20 (d,
1
J = 7.2 Hz, 2H), 12.94 (s, 1H). C-NMR (62.9 MHz,
6
6
J = 8.8 Hz, 2H), 7.16 (q, J = 3.0 Hz, 2H), 7.50 (m, 2H),
1
(
3
3
8.12 (d, J = 8.8 Hz, 2H), 12.76 (s, 1H).
C-NMR
(
62.9 MHz, DMSO-d /TMS) d (ppm): 55.2, 111.0, 114.3,
18.4, 121.5, 122.0, 122.6, 128.0, 151.3, 160.5.
DMSO-d /TMS) d (ppm): 122.1, 126.4, 128.4, 128.9,
6
6
1
1
29.2, 129.8, 130.1, 151.2.
1
23

J IRAN CHEM SOC
-1 1
V = 3,050, 1,480, 1,425, 1,060, 960, 750, 721 cm . H
2-(2-methylphenyl)-1,3-benzothiazole (3j): Yield 90 %,
white solid, mp: 54–55 °C (Lit. [53] mp 53–54 °C). IR
NMR (250 MHz, CDCl /TMS) d (ppm): 7.15–7.37 (m,
3
(
KBr): V = 3,060, 2,930, 1,475, 1,430, 950, 760,
-
5H), 7.73 (d, J = 7.95 Hz, 1H), 7.98 (d, J = 8.0 Hz, 1H),
13
1 1
20 cm . H-NMR (250 MHz, CDCl /TMS) d (ppm): 2.8
s, 3H), 8.26 (d, J = 8.1 Hz, 1H), 7.97 (d, J = 7.9 Hz,
7
8.05 (m, 1H). C-NMR (62.9 MHz, CDCl /TMS) d
3
3
(
(ppm): 121.4, 122.9, 125.01, 125.89, 126.3, 130.8, 131.1,
1
H), 7.90 (d, J = 7.2 Hz, 1H), 7.63–7.56 (m, 1H),
1
131.76, 132.22, 132.70, 136.12, 152.50, 164.03.
3
7
.36–7.50 (m, 4H). C-NMR (62.9 MHz, CDCl /TMS) d
2-(2-chlorophenyl)-1,3-benzoxazole (3q): Yield 90 %,
white solid, mp: 65–67 °C. IR (KBr): V = 3,060, 1,595,
1,540, 1,440, 1,425, 1,240, 1,020, 810, 730 cm . H-NMR
3
(
ppm): 21.3, 121.4, 123.5, 124.7, 126.2, 129.7, 130.4,
-
1 1
1
31.7, 133.1, 135.6, 137.3, 153.9, 168.0.
-(4-methoxyphenyl)-1,3-benzothiazole (3k): Yield
2
(250 MHz, CDCl /TMS) d (ppm): 7.13–7.23 (m, 4H),
3
9
1
1
2 %, white crystals, mp: 122–123 °C (Lit. [49] mp 1,120–
7.30–7.41 (m, 2H), 7.64–7.71 (m, 1H), 7.92–7.99 (m, 1H).
1
3
21 °C).IR (KBr): V = 3,060, 2,990, 1,600, 1,480, 1,433,
,260, 1,220, 1,170, 1,020, 960, 830, 760 cm . H-NMR
C-NMR (62.9 MHz, CDCl /TMS) d (ppm): 110.7, 120.4,
3
-
1 1
124.6, 125.5, 126.1, 126.8, 131.3, 131.5, 131.7, 133.4,
(
250 MHz, CDCl /TMS) d (ppm): 3.71 (s, 3H), 6.84 (d,
141.7, 150.5, 160.8.
3
J = 8.85 Hz, 2H), 7.16–7.36 (m, 2H), 7.71 (d, J = 7.9 Hz,
2-(2-chlorophenyl)benzimidazole (3r): Yield 92 %,
white solid, mp: 234.5 °C (Lit. [56] mp 234 °C). IR (KBr):
V = 3,445, 3,050, 1,440, 1,400, 1,050, 740 cm
1
3
1
H), 7.86–7.9 (m, 3H). C-NMR (62.9 MHz, CDCl3/
TMS) d (ppm): 55.4, 114.4, 121.5, 122.8, 124.8, 126.2,
29.1, 134.8, 154.2, 161.9, 167.9.
-(2-methylphenyl)-1,3-benzoxazole (3l): Yield 89 %,
white solid, mp: 80–82 °C (Lit. [55] mp 81–82 °C). IR
-
1
1
. H-
1
NMR (250 MHz, DMSO-d /TMS) d (ppm): 7.20–7.24 (m,
6
2
2H), 7.48–7.51 (m, 2H), 7.54–7.68 (m, 3H), 7.89–7.93 (m,
1
1H), 12.74 (s, 1H). C-NMR (62.9 MHz, DMSO-d /TMS)
3
6
(
KBr): V = 3,050, 2,960, 1,610, 1,540, 1,445, 1,240, 1,030,
-
d (ppm): 111.7, 119.0, 121.7, 122.7, 127.3, 129.9, 130.3,
131.1, 131.6, 132.0, 134.6, 143.1, 149.1.
1 1
50 cm . H-NMR (250 MHz, CDCl /TMS) d (ppm): 2.65
s, 3H), 7.12–7.18 (m, 5H), 7.37–7.42 (m, 1H), 7.61–7.67 (m,
7
3
(
2-(2,6-difluorophenyl)-1,3-benzothiazole (3 s): Yield
88 %, white solid, mp: 73–74 °C. IR (KBr): 3,070, 1,620,
1,580, 1,465, 1,240, 1,010, 960, 760, 720 cm . H-NMR
1
H), 7.99–8.03 (m, 1H). C-NMR (62.9 MHz, CDCl3/
3
1
-
1 1
TMS) d (ppm): 22.3, 110.5, 120.2, 124.4, 125.0, 126.2,
29.9, 130.9, 131.8, 138.9, 142.2, 150.3, 163.4.
-benzyl-1,3-benzoxazole (3m): Yield 86 %, colorless
liquid, IR (neat): V = 3,060, 3,030, 2,925, 1,610, 1,570,
1
(250 MHz, CDCl /TMS) d (ppm): 7.03–7.12 (m, 2H),
3
2
7.37–7.57 (m, 3H), 7.96 (d, J = 8.1 Hz, 1H), 8.19 (d,
3
1
J = 7.9 Hz, 1H). C-NMR (62.9 MHz, CDCl /TMS) d
3
1
7
4
,490, 1,455, 1,430, 1,240, 1,145, 855, 920, 845, 750,
-
(ppm): 112.2, 121.3, 123.8, 125.7, 126.3, 131.8, 135.6,
1
1
20 cm
.28 (s, 2H) 7.27–7.45 (m, 8H), 7.72–7.76 (m, 1H).
. H-NMR (250 MHz, CDCl /TMS) d (ppm):
153.0, 158.4, 162.5.
3
1
3
C
2-(2-pyridinyl)benzimidazole (3t): Yield 87 %, pale
yellow crystals, mp: 218.5 °C (Lit. [56] mp 218 °C). IR
(KBr): 3,450, 3,055, 1,590, 1,440, 1,400, 1,315, 1,280,
NMR (62.9 MHz, CDCl /TMS) d (ppm): 35.27, 110.5,
3
1
19.8, 124.2, 124.7, 127.6, 128.9, 129.0, 134.8, 141.4,
-
1 1
1
51.1, 165.2
1,120, 745 cm . H NMR (250 MHz, DMSO-d /TMS) d
6
2-ethyl-1,3-benzoxazole (3n): Yield 84 %, colorless
(ppm): 7.16–7.24 (m, 2H), 7.47–7.71 (m, 3H), 7.98 (td,
J = 7.7, 1.7 Hz, 1H), 8.30–8.34 (m, 1H), 8.71 (d,
liquid. IR (neat): V = 3,660, 2,930, 2,930, 1,610, 1,570,
-
1
J = 6.9 Hz, 1H), 13.01 (s, 1H). C-NMR (62.9 MHz,
3
1
1
1
,460, 1,240, 1,160, 750 cm
.
H-NMR (250 MHz,
DMSO-d /TMS) d (ppm): 112.0, 119.2, 121.4, 121.9,
CDCl /TMS) d (ppm): 1.38 (t, J = 7.6 Hz, 3H), 2.89 (q,
6
3
1
23.1, 124.6, 134.8, 137.5, 143.7, 148.4, 149.3, 150.7.
J = 7.6 Hz, 2H), 7.17–7.29 (m, 2H), 7.36–7.43 (m, 1H),
1
3
2-(2,6-dichlorophenyl)-1H-1,3-benzimidazole (3u):
7
.57–7.63 (m, 1H). C-NMR (62.9 MHz, CDCl /TMS) d
3
Yield 88 %, white solid, mp: 279 °C (Lit. [56] mp 218 °C).
IR (KBr): 3,430, 3,060, 1,550, 1,430, 1,330, 780,
(
ppm): 10.9, 22.1, 110.2, 119.5, 124.0, 124.4, 141.3, 150.8,
68.1.
-ethyl-1,3-benzothiazole (3o): Yield 85 %, pale yel-
lowish liquid. IR (neat): V = 3,060, 2,970, 2,930, 1,520,
1
-
1 1
7
40 cm . H-NMR (250 MHz, DMSO-d /TMS) d (ppm):
2
6
1
.11–7.30 (m, 5H), 7.54 (m, 2H). C-NMR (62.9 MHz,
3
7
-
1 1
DMSO-d /TMS) d (ppm): 115.4, 122.2, 128.3, 130.4,
1
,430, 1,120, 945, 755 cm . H-NMR (250 MHz, CDCl /
3
6
1
32.4, 135.0, 137.0, 146.6.
TMS) d (ppm): 1.17 (t, J = 7.56, 2.25 Hz, 3H), 2.85 (q,
J = 7.5, 2.3 Hz, 2H), 6.99–7.18 (m, 2H), 7.53 (d,
2-(4-bromophenyl)-1,3-benzoxazole (3v): Yield 91 %,
1
J = 8.0 Hz, 1H), 7.72 (d, J = 8.0 Hz, 1H). C-NMR
3
white solid, mp: 157–159 °C (Lit. [57] mp 157–158 °C).
IR (KBr): 3,050, 1,605, 1,590, 1,480, 1,450, 1,395, 1,240,
(
62.9 MHz, CDCl /TMS) d (ppm): 13.7, 27.7, 121.4,
3
-1 1
,070, 1,005, 829, 739 cm . H-NMR (250 MHz, CDCl /
1
1
22.4, 124.6, 125.8, 135.0, 153.2, 173.4.
-(2-chlorophenyl)-1,3-benzothiazole (3p): Yield 91 %,
white solid, mp: 82–83 °C (Lit. [53] mp 82 °C). IR (KBr):
3
TMS) d (ppm): 7.29–7.36 (m, 2H), 7.48–7.55 (m, 1H), 7.60
d, J = 8.55 Hz, 2H), 7.70–7.77 (m, 1H), 8.1 (d,
2
(
123

J IRAN CHEM SOC
1
3
J = 8.55 Hz, 2H). C-NMR (62.9 MHz, CDCl /TMS) d
(
financial supports of research councils of Shiraz University are
gratefully acknowledged.
3
ppm): 110.6, 120.1, 124.7, 125.3, 126.0, 126.2, 128.9,
32.2, 141.9, 150.7, 162.0.
-(4-bromophenyl)-1,3-benzothiazole (3w): Yield 93 %,
white solid, mp: 133–134 °C. IR (KBr): 3,050, 1,470,
1
2
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1 1
1
,430, 1,390, 1,063, 962, 827, 752, 715 cm . H NMR
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(
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3
(
1
.63–7.78 (m, 3H), 7.81 (d, J = 8.1 Hz, 1H). C-NMR
3
7
(
62.9 MHz, CDCl /TMS) d (ppm): 121.6, 123.3, 123.7,
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3
4
1
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9
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(
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1
1
1
7
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6
(
1
3
8
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8. V. Brahmkhatri, A. Patel, Ind. Eng. Chem. Res. 50, 13693 (2011)
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(
62.9 MHz, DMSO-d /TMS) d (ppm): 111.4, 118.9, 121.9,
6
1
22.7, 128.1, 129, 134.5 150.1.
-benzyl-1,3-benzothiazole (3y): Yield 88 %, pale yel-
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1
0. B. Karami, V. Ghashghaee, S. Khodabakhshi, Catal. Commun.
2
20, 71 (2012)
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-
1
1
1
,110, 760 cm
.
H-NMR (250 MHz, CDCl /TMS) d
3
1
1
(
ppm): 4.18 (s, 2H), 7.02–7.22 (m, 7H), 7.49 (d,
1
J = 7.91 Hz, 1H), 7.82 (d, J = 8.1 Hz, 1H). C-NMR
3
(
62.9 MHz, CDCl /TMS) d (ppm): 40.6, 121.6, 122.8,
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3
1
24.9, 126.0, 127.6, 128.9, 129.0, 135.7, 137.3, 153.4, 171.1.
-(4-methylphenyl)benzimidazole (3y): Yield 90 %,
white solid, mp: 276.5 °C (Lit. [59] mp 275–276 °C). IR
KBr): 3,450, 3,095, 2,980, 2,920, 1,550, 1,500, 1,460,
1
1
5. H. Hamadi, M. Kooti, M. Afshari, Z. Ghiasifar, N. Adibpour, J.
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2
(
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1
1
,430, 1,390, 1,270, 965, 822, 744. H-NMR (250 MHz,
(
2002)
DMSO-d /TMS) d (ppm): 2.35 (s, 3H) 7.15–7.20 (m, 2H),
6
1
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7
.33(d, J = 8.1 Hz, 2H), 7.46–7.56 (m, 2H), 8.07 (d,
1
3
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6
1
29.4, 139.5, 151.3.
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2
2
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(
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In conclusion, magnetic nanoparticles-supported tungsto-
silicic acid is reported as a highly efficient and reusable
solid acid catalyst for the synthesis of benzoazoles via the
reaction of aldehydes and 2-aminophenol, 2-aminothio-
phenol or benzene-1,2-diamine in water. The catalyst
showed high activity in this process and desired products
were obtained in high yields under green conditions in
relatively short reaction time. For this process, TSAMNP
acts as a heterogeneous catalyst and can be recovered from
the reaction mixture using external magnetic field.
TSAMNP was reused for 6 runs without significant lose in
its catalytic activity.
2
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(
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123