Synthesis of 2-arylbenzothiazoles using nano BF3/SiO2 as a reusable and efficient heterogeneous catalyst under mild conditions

Article abstract of DOI:10.1080/17415993.2014.917377

2-Arylbenzothiazoles were synthesized via condensation of 2-aminothiophenol and different aldehydes catalyzed by nano silica-supported boron trifluoride (nano BF₃/SiO₂) as an efficient and reusable catalyst in high yields and short r

Full text of DOI:10.1080/17415993.2014.917377

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Synthesis of 2-arylbenzothiazoles
using nano BF /SiO as a reusable and
3
2
efficient heterogeneous catalyst under
mild conditions
a
a
Hossein Naeimi & Arash Heidarnezhad
a
Department of Organic Chemistry, Faculty of Chemistry,
University of Kashan, Kashan, 87317, I.R. Iran
Published online: 14 May 2014.
To cite this article: Hossein Naeimi & Arash Heidarnezhad (2014) Synthesis of 2-arylbenzothiazoles
using nano BF /SiO as a reusable and efficient heterogeneous catalyst under mild conditions,
3
2
Journal of Sulfur Chemistry, 35:5, 493-501, DOI: 10.1080/17415993.2014.917377
To link to this article: http://dx.doi.org/10.1080/17415993.2014.917377
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Journal of Sulfur Chemistry, 2014
Vol. 35, No. 5, 493–501, http://dx.doi.org/10.1080/17415993.2014.917377
Synthesis of 2-arylbenzothiazoles using nano BF /SiO as a
3
2
reusable and efficient heterogeneous catalyst under mild
conditions
∗
Hossein Naeimi and Arash Heidarnezhad
Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, 87317, I.R. Iran
(Received 28 October 2013; accepted 18 April 2014)
2-Arylbenzothiazoles were synthesized via condensation of 2-aminothiophenol and different aldehydes
catalyzed by nano silica-supported boron trifluoride (nano BF3/SiO2) as an efficient and reusable catalyst
in high yields and short reaction times. The reactions proceeded at room temperature under mild conditions
to afford 2-arylbenzothiazole derivatives. The pure products were identified and characterized by physical
1
13
and spectroscopic data such as IR, H NMR, C NMR and Mass spectroscopy.
Keywords: 2-arylbenzothiazoles; nano-BF3/SiO2; synthesis; 2-aminothiophenol; aldehydes
1
.
Introduction
The synthesis, reactions and biological properties of benzothiazoles and compounds contain-
ing the benzothiazole nucleus constitute a significant part of modern heterocyclic chemistry.[1]
They are well known for their biological and pharmaceutical activities such as antitumor,
antiparkinsonism,[2] antimalarial, anticonvulsant, antihemintic, antifungal and analgesic. Several
methods for the synthesis of 2-arylbenzothiazoles have been developed.[3,4] In general, benzoth-
iazoles have been synthesized by the condensation of 2-aminothiophenol with carboxylic acid
derivatives.[5] On the other hand, the most general approaches for 2-arylbenzothiazoles include
the following; (1) oxidative cyclization of phenolic Schiff bases derived from the condensation
of 2-aminothiophenols and aldehydes using various oxidants such as Sc(OTf)3-molecular oxygen
[
6] and pyridinium chlorochromate,[7] and (2) the condensation of 2-aminothiophenols with car-
boxylic acids under microwave irradiation in the presence of a Lewis acid.[8–11] Despite their
∗
Corresponding author. Email: naeimi@kashanu.ac.ir
©
2014 Taylor & Francis

4
94 H. Naeimi and A. Heidarnezhad
potential utility, these methods are not environmentally friendly and suffer from one or more disad-
vantages for example hazardous reaction conditions, complex work-up and purification, strongly
acidic conditions, high temperatures, use of toxic metal catalysts and long reaction times. There-
fore, the development of a facile and mild general method to overcome these shortcomings remains
a challenge for organic chemists in the synthesis of 2-arylbenzothiazoles.[12,13]
In this study, in continuation of our interest on the synthesis of 2-arylbenzothiazoles,[14]
and using BF3 as a catalyst in organic reactions,[15] we decided to explore the ability of nano
BF3/SiO2 as a mild and non-toxic Lewis acid catalyst for the synthesis of 2-arylbenzothiazoles.
Therefore, nano BF3/SiO2 was used as a new catalyst for the synthesis of 2-arylbenzothiazoles
by the condensation reaction of 2-aminothiophenol with aromatic aldehydes at room temperature
under mild conditions.
2
. Results and discussion
Inthisresearch, wehavedevelopedasyntheticmethodusingnanoBF3/SiO2 asareusable, efficient
and eco-friendly solid acid catalyst for synthesis of 2-arylbenzothiazoles from 2-aminothiophenol
and aldehydes in excellent yields at room temperature (Scheme 1).
Scheme 1. Synthesis of 2-arylbenzothiazoles.
The dimension of nano catalyst was observed with the scanning electron microscope (SEM).
The size of the synthesized BF3/SiO2 nanoparticles was confirmed to be about 18–39 nm by
scanning electron microscopy (Figure 1).
We first screened a number of different catalysts in the reaction of 4-nitrobenzaldehyde with
2
-aminothiophenol (reaction model) such as different Lewis acids, different reagents supported
on solid materials, nano crystalline TiO2 and acidic alumina. The results are shown in Table 1.
When the reaction was carried out in the presence of nano BF3/SiO2 as a catalyst, the product
was obtained in excellent yields and short reaction times (Table 1, Entry 8). On the other hand, the
same reaction using other catalysts gave the products in low yields even after prolonged reaction
time.
In order to optimize the reaction in terms of yield and reaction time, we examined the
efficiency of different reaction media and catalyst amounts in the condensation reaction of
4-nitrobenzaldehyde (1 mmol) with 2-aminothiophenol in ethanol solution. The results are given
in Table 2.
In order to ascertain the scope and limitation of this method, the reaction of 2-aminothiophenol
and several substituted aromatic aldehydes using the optimized method was examined at room
temperature. By considering the above results, conversion of different aromatic aldehydes to the
corresponding 2-arylbenzothiazoles using nano BF3/SiO2 as a catalyst was investigated. The
results of these reactions are summarized in Table 3.

Journal of Sulfur Chemistry 495
Figure 1. SEM image of nano BF3/SiO2.
Table 1. Screening of catalyst in the reaction of
-nitrobenzaldehyde with 2-aminothiophenol.
4
a
Entry
Catalyst
AlCl3
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
15
15
15
15
15
15
15
15
48
62
25
85
7
70
35
92
FeCl3
Al2O3
b
SSA
Nano TiO2
BF3(Et2O)
Nano SiO2
Nano BF3/SiO2
a
Isolated yield.
Silica sulphuric acid.
b
Table 2. Synthesis of 2-arylbenzothiazoles catalyzed by nano BF3/SiO2 under
various conditions.
a
Entry
Nano BF3/SiO2(g)
Catalyst (mol% BF3)
Solvent
Yield (%)
1
2
3
4
5
6
7
8
9
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.04
0.05
0.06
15
15
15
15
15
15
15
15
15
20
25
30
CH3CN
CH3CN
CH3CN
EtOH
EtOH
EtOH
CH2Cl2
CH2Cl2
CH2Cl2
EtOH
EtOH
EtOH
48
70
76
55
82
85
50
72
80
92
95
95
1
1
1
0
1
2
aIsolated yields based on starting materials.

4
96 H. Naeimi and A. Heidarnezhad
Table 3. Synthesis of 2-arylbenzothiazoles using nano BF3/SiO2 as a catalyst (0.05 g, 25 mol % BF3) in EtOH
at room temperature.
Time Yielda
M.P. ( C) (min) (%)
◦
Entry
1
Substrate
Product
N
CHO
S
111–112
30
85
N
CHO
OH
S
HO
2
3
127–128
120–122
35
35
87
95
N
S
e
OM
e
M O
CHO
CHO
N
S
e
e
M
M
4
5
53–55
82–84
40
25
62
80
N
S
e
M
e
M
CHO
N
S
CHO
Cl
Cl
6
7
72–74
30
25
85
90
N
S
Cl
Cl
CHO
114–116
N
S
CHO
NO2
O N
2
8
9
94–96
40
20
78
95
N
NO2
O N
CHO
2
S
227–229
N
S
CHO
Cl
Cl
Cl
Cl
10
118–120
30
73
N
CHO
S
O N
NO2
N CH
2
1
1
1
2
181–183
160–162
30
45
91
84
N
(
3
)
2
H C N
CHO
(
3
)
2
S
aIsolated yields.

Journal of Sulfur Chemistry 497
Table 4. Synthesis of 2-(4-Nitrophenyl)-benzothiazole with recovered catalyst.
a
Entry
Time (min)
Yield (%)
1
2
3
4
5
20
20
20
20
20
95
92
90
85
82
aIsolated yields.
This reaction was also carried out with BF3.Et2O as a Lewis acid for comparison with nano
BF3/SiO2 as a catalyst. Unfortunately, BF3.Et2O is a liquid that fumes in the air and reacts with
moisture to form hydrofluoric acid making its use inconvenient and laborious. In addition, the
yields of products using nano BF3/SiO2 as a catalyst are considerably higher than BF3.Et2O
and it is clear that it is the preferred catalyst. As can be seen from Table 3, the products were
obtained in 62–95% yields and in reaction times of 20–45 min. In this reaction, the Lewis acid
nano BF3/SiO2 catalyst activates the carbonyl group via coordination with the oxygen atom to
accelerate the nucleophilic attack of the amino group at the carbon atom of the carbonyl group.
1
13
The structure of the products was confirmed by spectroscopic methods such as IR, H NMR, C
NMR and Mass spectroscopy. In the IR spectra, the stretching frequency of aromatic C=C bonds
−
1
1
is observed in the region between 1475 and 1600 cm . In the H NMR spectra, the proton of −OH
group in 2-(2-hydroxyphenyl)-benzothiazole appeared at 12.54 ppm. The signals at 6.95–8.94 are
assigned to CH=CH of the aromatic rings. The hydrogen atoms of the methoxy group have a
chemical shift of 3.89 ppm, and the signal around 6.77–6.79 ppm is assigned to the −N(CH3)2
1
3
group. In the C NMR spectra, the aromatic carbons absorb at 110–169 ppm and the signal of
5
5.47 is assigned to the −OCH3 group. The mass spectra (Electron Impact (EI)) of products have
shown the corresponding molecular ion peak.
Reusability of the nano BF3/SiO2 catalyst: In the next step of our study, our attention was
directed toward evaluating the reusability and recycling potential of nano BF3/SiO2 in these reac-
tions. After each run, conducted for the 20 min indicated in Table 4, the catalyst was filtered from
◦
the product and washed with acetone, then dried at 90 C for 2 hours and reused in the next reaction
cycle using the optimized conditions for an additional 20 min. The recovered catalyst was active
although a gradual decline was observed in its activity as its time of use was increased (Table 4).
3
. Conclusion
In summary, a facile and mild procedure for the synthesis of 2-arylbenzothiazoles has been devel-
oped using the condensation reaction of 2-aminothiophenol and aromatic aldehydes with nano
BF3/SiO2 as an efficient, eco-friendly and reusable heterogeneous catalyst. The main advantages
of the present synthetic protocol are mild conditions, high yields, short reaction times and easy
reaction work up procedure.
4
4
.
Experimental section
.1. Chemicals
Chemicals were purchased from the Merck, Fluka and Aldrich Chemical Companies in high
purity. All of the materials were of commercial reagent grade. The solvents were purified by
standard procedure.

4
98 H. Naeimi and A. Heidarnezhad
4
.2. Apparatus
−
1
The FT-IR spectra were obtained with potassium bromide pellets in the range 400–4000 cm
with a Perkin Elmer 550 spectrometer. Melting points were determined in open capillaries using
1
13
an Elactrothermal MK3 apparatus and are uncorrected. All H NMR and C NMR spectra were
recorded with a Bruker DRX-400 spectrometer at 400 MHz. The NMR spectra were obtained in
CDCl3 solutions and are reported as parts per million (ppm) downfield from tetramethylsilane as
an internal standard. The abbreviations used are: singlet(s), doublet (d), triplet (t) and multiplet
(
m). Mass spectra were recorded on an Agilent Technology (HP) MS Model: 5973 Network
Mass Selective Detector, instrument by EI ionization mode with an ionization voltage of 70 eV.
The SEM of nano catalyst was performed on a KYKY EM 3200 SEM instrument. The purity
determination of the substrates and reaction monitoring were accomplished by TLC on silica-gel
polygram SILG/UV 254 plates (from Merck Company).
4
.2.1. Preparation of nano BF3/SiO2 as catalyst
For preparation of nano BF3/SiO2, to a mixture of 0.65 g nano-silicagel and 5 ml chloroform,
0
7
.35 g BF3(0.65 ml of BF3.Et2O) was added drop-wise to the reaction mixture over a period of
0 min at room temperature with stirring. Then after completion of the reaction, Et2O and CHCl3
were evaporated from the reaction mixture by heating to obtain dry nano BF3/SiO2.[16–18]
4
.2.2. General procedure for the synthesis of 2-arylbenzothiazoles catalyzed by nano
BF3/SiO2
To a mixture of 2-aminothiophenol (1 mmol, 0.995 g) and aldehyde (1 mmol) in ethanol (10 ml),
nano BF3/SiO2 (0.05 g, 25 mol% BF3) was added in a beaker and the reaction mixture was mixed
properly with the help of a glass rod and stirred in ambient temperature for the time indicated
in Table 3. The progress of the reaction was monitored by TLC (ethylacetate:hexane, 6:4), after
completion of the reaction the solvent was removed under reduced pressure, then the mixture
was cooled and dichloromethane (15 ml) was added to the mixture and filtered to remove the
catalyst. Then the filtrate was evaporated under reduced pressure to isolate a solid residue, and
recrystallized from ethanol (10 ml) to afford the corresponding products and the catalyst residue
was washed with acetone and reused. All of the 2-arylbenzothiazole products were identified by
physical and spectroscopic data as follows.
◦
4
1
.2.2.1. 2-(2-Hydroxyphenyl)-benzothiazole. Yellow solid; m.p. = 127–128 C (m.p. = 126–
◦
−1
1
28 C) [19]; IR (KBr)/υ(cm ): 3285, 3090, 2900, 1619, 1590, 1490, 1423, 874, 751; H NMR
(
7
(
400 MHz, CDCl3)/δ ppm: 6.95–699 (t, 1H, J = 8.0 Hz, Ar-H) 7.12 (d, 1H, J = 8.0 Hz, Ar-H),
.38–7.44 (m, 2H,Ar-H) 7.50–7.54 (t, 1H, J = 8.4 Hz,Ar-H) 7.71 (d, 1H, J = 8.0 Hz,Ar-H) 7.92
1
3
d, 1H, J = 8.4 Hz,Ar-H) 8.01 (d, 1H, J = 8.0 Hz,Ar-H) 12.54 (s, 1H, OH); C NMR/(100 MHz,
CDCl3)/δ ppm: 116.80, 117.88, 119.54, 121.52, 122.19, 125.56, 126.70, 128.43, 132.60, 132.77,
1
1
51.84, 157,96, 169.39. MS (EI, m/z): 217 (M+, 1.8), 200 (37), 183 (5.7), 167 (16.5), 136 (100),
24 (81), 107 (78), 97 (13), 77 (50), 65 (30), 51 (18), 41(3).
◦
◦
4
.2.2.2. 2-Phenyl-benzothiazole. White solid; m.p. = 110–112 C (m.p. = 111–112 C) [19];
−
1
1
IR (KBr)/υ(cm ): 3066, 3017, 2835, 1608, 1587, 1476,1430, 830, 763; H NMR (400 MHz,
CDCl3)/δ ppm: 7.02–7.06 (t, 1H, J = 7.6 Hz,Ar-H) 7.25 (t, 1H, J = 8.4 Hz,Ar-H), 7.56–7.70 (m,
1
3
5
H, Ar-H) 7.93(d, 1H, J = 7.6 Hz, Ar-H) 8.41(d, 1H, J = 8.4 Hz, Ar-H); C NMR/(100 MHz,
CDCl3)/δ ppm: 121.50, 123.38, 125.07, 126.36, 127.58, 128.91, 130.77, 133.89, 135.11, 155.05,

Journal of Sulfur Chemistry 499
1
8
67.98. MS (EI, m/z): 211 (M+, 42), 197 (8), 182 (40), 171 (6), 143 (11.9), 125 (100), 108 (18),
7 (83), 79 (44), 69 (9.4), 58 (70), 47(51).
◦
4
1
.2.2.3. 2-(4-Metoxyphenyl)-benzothiazole. White solid; m.p. = 120–122 C (m.p. = 120–
◦
−1
1
22 C) [20]; IR (KBr)/υ(cm ): 3021, 3048, 2837, 1609, 1590, 1483, 830; H NMR (400 MHz,
CDCl3)/δ ppm: 3.89 (s, 3H, OCH3) 7.015 (d, 2H, J = 10.0 Hz, Ar-H) 7.36 (t, 1H, J = 8.0 Hz,
Ar-H) 7.48 (t, 1H, J = 8.0 Hz, Ar-H) 7.89 (d, 1H, J = 8.0 Hz, Ar-H) 8.04–8.06 (d, 3H, J = 10.0
1
3
Hz, Ar-H); C NMR/(100 MHz, CDCl3)/δ ppm: 55.47, 114.38, 121.53, 122.83, 124.81, 126.23,
1
1
26.42, 129.13, 134.86, 154.21, 161.94, 167.89. MS (EI, m/z): 243 (12.5), 242 (38), 241 (M+,
00), 226 (15.8), 198 (23), 171 (3.5), 154 (5.4), 139 (0.8), 127 (1.6), 108 (2.8), 82 (2.8), 69 (6.9).
◦
4
2
.2.2.4. 2-(4-Nitrophenyl)-benzothiazole. Yellow solid; m.p. = 227–229 C (m.p. = 226–
◦
−1
1
28 C) [20]; IR (KBr)/υ(cm ): 3042, 2937, 1520, 1461, 1342, 1106, 851, 762; H NMR
(
400 MHz, CDCl3)/δ ppm: 7.45–7.49 (t, 1H, J = 7.2 Hz, Ar-H) 7.54–7.58 (t, 1H, J = 7.2 Hz,
Ar-H) 7.97 (d, 1H, J = 7.6 Hz, Ar-H) 8.14 (d, 1H, J = 7.6 Hz, Ar-H) 8.27 (d, 2H, J = 8.0 Hz,
13
Ar-H) 8.36 (d, 2H, J = 8.0 Hz, Ar-H); C NMR/(100 MHz, DMSO)/δ ppm: 121.85, 123.94,
1
24.32, 126.24, 126.94, 128.23, 133.1, 135.40, 148.8, 154.0, 164.90.
◦
4
[
.2.2.5. 2-(2,3-Dichlorophenyl)-benzothiazole. White solid; m.p. = 118–120 C (119–121)
−
1
1
19]; IR (KBr)/υ(cm ): 3020, 2900, 1635, 1512, 1470,1432, 1348, 780; H NMR (400 MHz,
CDCl3)/δ ppm: 7.35–7.39 (t, 1H, J = 8.0 Hz, Ar-H) 7.45–7.49 (t, 1H, J = 8.0 Hz, Ar-H) 7.54–
.58 (t, 1H, J = 8.0 Hz,Ar-H) 7.62 (d, 1H, J = 8.0 Hz,Ar-H) 7.98 (d, 1H, J = 8.0 Hz,Ar-H) 8.07
7
(
1
1
1
3
d, 1H, J = 8.0 Hz, Ar-H) 8.15 (d, 1H, J = 8.0 Hz, Ar-H); C NMR/(100 MHz, CDCl3)/δ ppm:
17.77, 118.13, 123.30, 124.54, 127.10, 128.11, 128.73, 129.27, 129.95, 130.91, 131.67, 146.01,
49.00. MS (EI, m/z): 281 (0.7), 280 (M+, 1.2), 244 (3.9), 230 (100), 212 (31), 199 (16.7), 171
(
4.3), 157 (1.6), 143 (1.3), 125 (14), 87 (30), 58 (22), 44 (9.6).
◦
4
1
.2.2.6. 2-(3-Nitrophenyl)-benzothiazole. Colorless solid; m.p. = 181–183 C (m.p. = 181–
◦
−
1
1
82 C) [20]; IR (KBr)/υ(cm ): 3039, 2936, 1522, 1460, 1345, 1103, 1041, 851, 750; H NMR
(
(
8
1
400 MHz, CDCl3)/δ ppm: 7.47 (m, 1H, Ar-H) 7.56 (m, 1H, Ar-H) 7.71–7.79 (m, 1H, Ar-H) 7.97
d, 1H, J = 7.6 Hz, Ar-H) 8.14 (m, 1H, Ar-H) 8.36 (m, 1H, Ar-H) 8.44 (d, 1H, J = 7.6 Hz, Ar-H)
.95 (s, 1H, Ar-H); 13C NMR/(100 MHz, DMSO)/δ ppm: 121.90, 122.4, 123.32, 125.24, 126.11,
26.80, 128.75, 131.1, 133.63,134.40, 147.8, 153.0, 162.23.
◦
◦
4
[
.2.2.7. 2-(2-Nitrophenyl)-benzothiazole. Brown solid; m.p. = 94–96 C (m.p. = 95–97 C)
−
1
1
19]; IR (KBr)/υ(cm ): 3033, 2930, 1545, 1466, 1349, 1111, 880, 851, 762; H NMR (400 MHz,
CDCl3)/δ ppm: 7.44–7.56 (m, 2H,Ar-H) 7.64–7.73 (m, 2H,Ar-H) 7.81 (d, 1H, J = 7.6 Hz,Ar-H)
1
3
7
1
1
.93–7.96 (m, 2H, Ar-H) 8.09 (d, 1H, J = 7.6 Hz, Ar-H); C NMR/(100 MHz, DMSO)/δ ppm:
20.85, 122.18, 124.30, 124.98, 126.03, 126.94, 128.88, 133.12, 136.14, 138.90, 143.8, 157.0,
64.09.
◦
◦
4
[
(
7
.2.2.8. 2-(4-Methylphenyl)-benzothiazole. White solid; m.p. = 82–84 C (m.p. = 83–85 C)
−
1
1
19]; IR (KBr)/υ(cm ): 3024, 2905, 1610, 1519, 1480, 1435, 1383, 1312, 821, 759; H NMR
400 MHz, CDCl3)/δ ppm: 2.45 (s, 3H, CH3) 7.34–736 (m, 4H, Ar-H) 7.54–759 (m, 1H, Ar-H)
.75–7.78 (m, 1H, Ar-H) 8.14–8.16 (m, 2H, Ar-H); C NMR/(100 MHz, CDCl3)/δ ppm: 23.6,
1
3
1
10.42, 120.33, 121.76, 123.34, 128.56, 132.67, 143.15, 155.63, 160.83, 165.11.
◦
4
.2.2.9. 2-(4-Chlorophenyl)-benzothiazole. Yellow solid; m.p. = 114–116 C (116–118) [20];
−
1
1
IR (KBr)/υ(cm ): 3055, 2358, 1560, 1455, 1430, 1317, 1275, 1060, 965, 750, 725; H NMR
(
400 MHz, CDCl3)/δ ppm: 7.37–739 (m, 2H, Ar-H) 7.51–753 (d, 2H, J = 7.6 Hz, Ar-H)

5
00 H. Naeimi and A. Heidarnezhad
7
.58–7.61 (m, 1H, Ar-H) 7.77–7.79 (m, 1H, Ar-H) 8.19–8.22 (d, 2H, J = 7.6 Hz, Ar-H); 13C
NMR/(100 MHz, CDCl3)/δ ppm: 121.8, 123.13, 125.17, 126.80, 129.10, 129.78, 132.67, 135.2,
1
37.1, 154.4, 166.21.
◦
4
1
.2.2.10. 2-(4-N, N-dimethylphenyl)- benzothiazole. Brown solid; m.p. = 160–162 C (160–
−
1
1
62) [19]; IR (KBr)/υ(cm ): 3355, 2358, 1598, 1478, 1210, 1017, 965, 743; H NMR (400 MHz,
CDCl3)/δ ppm:3.08(s, 6H, N(CH3)2)6.77–6.79(d, 2H, J = 8 Hz,Ar-H)7.27–7.31(m, 2H,Ar-H)
7
.52–7.54 (d, 1H, J = 8.2 Hz, Ar-H) 7.70 (d, 1H, J = 8.2 Hz, Ar-H) 8.11–8.13(d, 2H, J = 8 Hz,
1
3
Ar-H); C NMR/(100 MHz, CDCl3)/δ ppm: 39.8, 111.13, 121.1, 122.0, 124.1, 126.78, 128.67,
1
35.2, 152.1, 154.4, 168.2.
◦
4
.2.2.11. 2-(2-Chlorophenyl)-benzothiazole. Colorless solid; m.p. = 72–74 C (72–74) [20];
−
1
1
IR (KBr)/υ(cm ): 2955, 1538, 1502, 1421, 1242, 1117, 965, 750, 733; H NMR (400 MHz,
CDCl3)/δ ppm: 7.38–7.49 (m, 4H, Ar-H) 7.58–760 (m, 1H, Ar-H) 7.63–7.65 (m, 1H, Ar-H)
.66–7.68 (m, 1H, Ar-H) 8.15–8.18 (m, 1H, Ar-H); C NMR/(100 MHz, CDCl3)/δ ppm: 111.8,
1
3
7
1
23.13, 124.17, 125.80, 128.19, 129.88, 131.67, 134.21, 137.1,143.51, 154.4, 162.21.
◦
4
5
.2.2.12. 2-(2-Methylphenyl)-benzothiazole. Yellow solid; m.p. = 53–55 C (m.p. = 54–
◦
−1
1
6 C) [19]; IR (KBr)/υ(cm ): 3040, 2980, 1598, 1550, 1451, 1244,1115, 862, 754; H NMR
(
400 MHz, CDCl3)/δ ppm: 2.47 (s, 3H, CH3) 7.35–737 (m, 3H, Ar-H) 7.41–745 (t, 1H, J = 8 Hz,
Ar-H) 7.58–7.60 (m, 1H, Ar-H) 7.77–7.79 (m, 1H, Ar-H) 8.05–8.07 (d, 1H, J = 8 Hz, Ar-H) 8.08
13
(
1
d, 1H, J = 8 Hz, Ar-H); C NMR/(100 MHz, CDCl3)/δ ppm: 22.6, 112.13, 119.38, 120.53,
22.34, 126.17, 130.67, 144.15, 152.68, 159.93, 162.17.
Funding
The authors are grateful to University of Kashan for supporting this work by [Grant No. 159148/18].
Supplemental data
Supplemental data for this article can be accessed at http://dx.doi.org/10.1080/17415993.2014.917377.
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