Nano-Titania-Supported Sulfonic-Acid-Catalyzed Synthesis of 2-Arylbenzothiazole Derivatives under Solvent Free Conditions

Article abstract of DOI:10.1080/10426507.2015.1031753

Nano-titania-supported sulfonic acid (n-TSA) has been used as an efficient, inexpensive and reusable heterogeneous nano catalyst for synthesis of 2-arylbenzothiazole derivatives under solvent free condition. The reaction works very well, with good to exce

Full text of DOI:10.1080/10426507.2015.1031753

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Nano-titania-supported sulfonic acid catalyzed
synthesis of 2-arylbenzothiazole derivatives under
solvent free conditions
a
a
a
a
b
Ali Amoozadeh , Rahmat Allah Azadeh , Salman Rahmani , Mehdi Salehi , Maciej Kubicki &
b
Grzegorz Dutkiewicz
a
Department of Chemistry, Semnan University, Semnan, Zip Code: 35131-19111, Iran
b
Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, 61-614 Poznan, Poland
Accepted author version posted online: 16 Apr 2015.
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To cite this article: Ali Amoozadeh, Rahmat Allah Azadeh, Salman Rahmani, Mehdi Salehi, Maciej Kubicki & Grzegorz
Dutkiewicz (2015): Nano-titania-supported sulfonic acid catalyzed synthesis of 2-arylbenzothiazole derivatives under solvent
free conditions, Phosphorus, Sulfur, and Silicon and the Related Elements, DOI: 10.1080/10426507.2015.1031753
To link to this article: http://dx.doi.org/10.1080/10426507.2015.1031753
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NANO-TITANIA-SUPPORTED SULFONIC ACID CATALYZED SYNTHESIS OF 2-
ARYLBENZOTHIAZOLE DERIVATIVES UNDER SOLVENT FREE CONDITIONS
a
a
a
a
b
Ali Amoozadeh *, Rahmat Allah Azadeh , Salman Rahmani *, Mehdi Salehi , Maciej Kubicki ,
b
Grzegorz Dutkiewicz
a
Department of Chemistry, Semnan University, Semnan, Semnan, Zip Code: 35131-19111, Iran,
Fax: +98 (233) 3354110, Tel.: +98 (233) 3366177, e-mail: aamozadeh@semnan.ac.ir,
s_rahmani@semnan.ac.ir
b
Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, 61-614 Poznan, Poland
Abstract: Nano-titania-supported sulfonic acid (n-TSA) has been used as an efficient,
inexpensive and reusable heterogeneous nano catalyst for synthesis of 2-arylbenzothiazole
derivatives under solvent free condition. The reaction works very well, with good to excellent
yields, for different aromatic aldehydes with both electron withdrawing and electron donating
groups. Easy preparation and separation of catalyst, simply workup procedure, clean reaction and
reusability of the catalyst up to 7 times without appreciable loss of its catalytic activity are
undoubtful advantages of this work.
1
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Keywords: Nano-titania-supported sulfonic acid; 2-arylbenzothiazole; heterogeneous nano
catalyst; solvent free
2
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INTRODUCTION
In recent years, heterogeneous solid acid catalysts have gained importance in organic
synthesis due to several advantages such as operational simplicity, no toxicity, reusability and
1
ease of isolation after completion of the reaction. In this context the use of nanoparticles as
heterogeneous catalysts have attracted considerable attention because of the interesting structural
2
,3
features and high levels of catalytic activity associated with these materials.
2
-Arylbenzothiazole and their derivatives compose a very important group of heterocyclic
4
compounds. They are well known for their biological and pharmaceutical activities such as
5
6
7
8
9
antitumor, anticancer, antimicrobial, antimalarial, antiglutamate/antiparkinson. In addition
1
0
11
12
some of these compound exhibit nonlinear optical, luminescent and fluorescent properties.
Numerous methods have already been reported for the synthesis of 2-arylbenzothiazoles. The
classical one involves condensation of 2-aminothiophenol with substituted aldehydes, carboxylic
1
3
14
acids, acyl chlorides, estersor nitriles. On the other hand, the most common method for such
synthesis involves condensation of aldehydes with 2-aminothiophenol in the presence of various
1
5
16
catalysts such as I
2
/DMF, O
2
or H
2
O
2
in the presence of scandium triphtalate (Sc(OTf)
3
),
1
7
18
MnO
2
/SiO
2
, p-TsOH or graphite supported on solid mineral under microwave irradiation, 1-
1
9
phenyl-3-methylimidazoliumbromide [PmIm]Br under microwave irradiation, solid hetero poly
2
0
21
acid supported on silica gel, cerium (IV) ammonium nitrate (CAN), activated carbon
®
22
23
(
shirasagi KL or DARCO KB) under oxygen atomosphere and dowex 50W.
2
4
We have recently reported nano-titania-supported sulfonic acid (n-TSA) as a new and
efficient solid acid catalyst in organic reactions.
3
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RESULTS AND DISCUSSION
In continuation of our studies on developing inexpensive and environmentally benign
2
5,26
methodologies for synthesis of heterocyclic compounds and organic reactions
and to extend
our knowledge about the applicability of our new catalyst, we have decided to investigate the
possibility of synthesizing 2-arylbenzothiazole derivatives by one-pot condensation reaction
strategy in presence of n-TSA under solvent free conditions. In order to examine the catalytic
activity of n-TSA, we have begun with the condensation of 2-aminothiophenol (1) with
benzaldehyde (2) (Scheme 1).
To optimize the reaction conditions, amount of the n-TSA, different temperatures and
solvents were screened. Initially, the limitation of catalyst amount was examined.
The obtained results showed that by increasing the catalytic load of n-TSA from 0.00 to 0.099
mmol, the yield has improved from 25% to 92%, but further increasing of the catalyst amount
did not improve the yield (Table 1). In order to evaluate the effect of the catalyst particle size and
acidity on the catalytic activity, the obtained results were compared with those obtained using
other titanium dioxide bases such as unmodified nano-TiO
2
, unmodified bulk TiO
(prepared by procedure reported earlier ). The obtained yields were 8, 4 and
5%, respectively. These results showed clearly that n-TSA worked very well for this reaction,
2
and
2
7
modified-bulk TiO
2
6
so we have selected it.
In the next step, the effect of temperature in presence of 0.099 mmol of n-TSA was
investigated. The results showed that the best temperature is 70 ºC. By increasing the
o
temperature to 90 C, the achieved yields decreased. So the further experiments were performed
o
at 70 C.
4
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Eventually, to making sure that the solvent free condition is appropriate, we investigated the
o
effect of different solvents such as H
2
O, PEG, Toluene, Et-OH and CH
3
CN at 70 C (Table 2).
The results showed that by using of these solvents caused significantly lower yields, and longer
reaction times did not improve the yields. It seems that among these solvents, Et-OH provided
the best yield but as solvent free conditions are more valuable (also from the point of view of so-
called green chemistry), so we chose this possibility.
Now, with optimized conditions (n-TSA (0.099 mmol) as catalyst in solvent free at 70 ºC), we
have performed some experiments to develop the scope of this procedure. For this purpose, the
condensation between 2-aminothiophenol and various aromatic aldehydes (including aromatic
aldehydes with electron-releasing, electron-withdrawing and halogen substituents) were carried
out to provide corresponding products in good to excellent yields. Entertainingly, by present
procedure the synthesized 2-arylbenzothiazole derivatives were prepared purely without any
byproducts. The results are summarized in Table 3.
As indicated in Table 3, the reaction works easily for a variety of aldehydes with both
electron-donating and electron-withdrawing groups to give corresponding 2-arylbenzothiazole
derivatives in good to excellent yields (85-96%). In almost all cases, the reactions proceeded
smoothly within 15-50 min. It seems that the reaction for aldehydes with strong withdrawing
groups like 4-fluoro, 4-bromo and nitro is very fast (Table 3, products 3f, 3g and 3j-3l). This
2
8
could be justified by regarding the proposed mechanism (Figure. 1). It seems that the rate
determining step must be the nucleophilic attack of sulfur ion pair on to carbonyl group of
aldehydes.
5
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Various methods have been reported for the synthesis of 2-arylbenzothiazoles, including,
condensation of aromatic aldehydes and 2-aminothiophenol in presence of different catalysts. A
comparison between the result of the proposed catalyst and some of the recently used catalysts
for synthesis of 2-arylbenzothiazole derivatives is summarized in Table 2.
Although, some of these methods have convenient protocols with good to high yields, the
majority of these methods suffer at least from one of the following disadvantages such as the use
of toxic organic solvents, excess reagents, long reaction time and harsh reaction conditions.
Table 2 shows that the heterogeneous solid acid catalyst of nano-TiO
2
-SO H is the best in
3
comparison to the other mentioned catalysts. The proposed new catalyst has some advantages in
comparison with the other catalyst including shorter reaction time, easy separation and low
consumption of organic solvents, reusability and ability to perform reactions in solvent free
conditions. It is a stable solid acid catalyst with high densities of sulfuric acid groups that can be
easily synthesized in the laboratory and can be reused for several times.
To test the reusability of catalyst and green chemistry aspects, the reaction mixture was
washed with hot ethanol, catalyst was separated with centrifuge and dried at 50 ºC for 2h. The
condensation of 1 (1 mmol) and 2 (1 mmol) was repeated with recovered catalyst without any
loss of activity. The catalyst could be efficiently recovered and recycled up to seven times
without suffering any significant drop in its catalytic activity or the yield for the reaction (90-
9
2%) (Figure S 1, Supplemental Materials)
The characterization of the nano-TiO -SO
particle size by scanning electron microscopy (Fig. 2b)
2
3
H before and after reuse 7 times showed the same
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Crystal Structure Description of Compound 3c
The asymmetric part of the unit cell of 3c contains four symmetry-independent molecules;
their geometrical features differ only slightly. Figure 3 shows a perspective view of one of the
molecules and an overlay comparison is provided in Figure S 2 (Supplemental Materials). The
lengths of two C-S bonds differ, and the difference is statistically important: for the S1-C9 bond
the mean value for the four molecules is 1.728(3) Å, while for S1-C2 it is 1.753(4) Å. The mean
value of the C-S-C angle is 89.32(13)° (Table S 1, Supplemental Materials). These values
2
9,30
compare well with those found for instance in arylbenzothiazole derivatives.
Benzothiazole
and phenyl groups are planar within the experimental errors and the dihedral angles between
appropriate planes are small, ranging from 0.62(8)° in molecule D to 5.96(7)° in molecule A.
The title compound has no other intermolecular contacts of structural significance than weak
π···π (centroid-to-centroid distances longer than 3.57Å) and van der Waals contacts.
EXPERIMENTAL SECTION
Materials and Instruments: Chemicals were purchased from the Merck chemical companies.
Thin-Layer Chromatography (TLC) on commercial plates of silica gel 60 F254 was used to
1
monitor the progress of reactions. The products were characterized by FT-IR spectra, H NMR,
1
3
1
13
C NMR. FT-IR spectra were recorded on Shimadzu FT-IR 8400 instrument. H and C NMR
spectra were recorded on Bruker Advance Spectrometer 400 MHz using CDCl as solvent. The
3
chemical shifts are expressed in parts per million (ppm) and tetramethylsilane (TMS) was used
as an internal reference. Elemental analyses were performed by Perkin Elmer CHN analyzer,
2400 series II. Melting points were recorded on a THERMO SCIENTIFIC 9100 apparatus. The
1
13
Supplemental Materials contains sample H and C NMR spectra for 3m (Figures S 3 – S 4)
7
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2 3
Preparation of nano-TiO -SO H (n-TSA): A suction flask equipped with a constant-pressure
dropping funnel and a gas inlet tube for conducting HCl gas over an adsorbing solution (i.e.,
water) was used, charged with the titania nanoparticles (4 g). Chlorosulfonic acid (1 mL, 15
mmol) was added drop wise over a period of 30 min at room temperature. HCl gas immediately
evolved from the reaction vessel. Stirring was continued HCl evolution was seized. After the
addition was completed, the mixture was shaken for 30 min. A gray solid of nano-titania-
supported sulfonic acid was obtained.
The prepared n-TSA stored in vacuum desiccator over anhydrous silica gel, then, was dried in
+
1
20 °C for 6 hours. The mmol of H per gram of catalyst (4.5 mmol/g of n-TSA) was determined
2
6
by the titration of 0.1 gram of sample with a standard solution of NaOH (0.1 N).
General Procedure for preparation of benzothiazole derivatives: In a typical experiment, 2-
aminothiophenole (1 mmol), aromatic aldehyde (1 mmol) and catalyst (0.099 mmol) in solvent
o
free condition were taken in a 25 ml round bottomed flask and was stirred at 70 C for an
appropriate time. The reaction mixture was cooled, eluted with hot ethanol (5 mL) and was
centrifuged and filtrated to collect the formed precipitate. The crude product was recrystallized
from ethanol to yield pure benzothiazole derivatives.
Spectral data of 2-(naphthalen-3-yl)benzo[d]thiazole (3m)
-1
Colorless Crystal (yield 91%), M.P: 127-130 °C; IR (KBr) ν Cm : 3065,1496,1427, 1357,
1
1
118, 979, 732; H NMR (400 MHz, CDCl
3
): δ 8.59-8.60 (d, J= 0.8 Hz, 1H, Ar), 8.23-8.26 (dd,
J= 8.6 and 1.6 Hz, 1H, Ar), 8.13-8.16 (dq, J= 8.2 and 0.4 Hz, 1H, Ar), 7.96-8.02 (m, J= 0.4-6 Hz,
H, Ar), 7.90-7.93 (m, J= 1.2-5.2 Hz, 1H, Ar), 7.58-7.61 (m, J= 1.2-4.8 Hz, 2H, Ar), 7.52-7.58
3
1
3
(
dd, J= 7.8 and 1.2 Hz, 1H, Ar) 7.42-7.46 (td, J= 7.6 and 1.2 Hz, 1H, Ar). C NMR (100 MHz,
8
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CDCl
3
): δ 121.7 (C 13, C 14), 123.2 (C 17), 124.4 (C 12), 125.3 (C 16), 126.4 (C 11), 126.9 (C
), 127.5 (C 7), 127.6 (C 9), 127.9 (C 6), 128.8 (C 10), 130.9 (C 5), 133.2 (C 4), 134.6 (C 15),
35.1 (C 3), 154.2 (C 2), 168.1 (C 1). Anal. Calc. for C17 11NS, C, 78.13; H, 4.24: N, 5.36;
8
1
H
Found: C, 78.26, H, 4.36, N, 5.48.
Crystallographic Data Collection and Structure Determination
Diffraction data of the compounds1(3c) were collected at room temperature by the ω-scan
technique on an Agilent Technologies Xcalibur four-circle diffractometer with Eos CCD-
detector and graphite-monochromatized MoK radiation source (λ = 0.71073 Å). The data were
α
3
1
corrected for Lorentz-polarization as well as for absorption effects. Precise unit-cell parameters
were determined by a least-squares fit of 5846 reflections of the highest intensity, chosen from
3
2
the whole experiment. The structure was solved with SIR92 and refined with the full-matrix
2
33
least-squares procedure on F by SHELXL97. Hydrogen atoms were placed geometrically and
refined as riding model with Uiso set at 1.2 times Ueq for appropriate carrier atoms. Relevant
crystal data are listed in Table 5, together with refinement details.
CONCLUSIONS
In summary, nano-titania-supported sulfonic acid has been used as a heterogeneous nano catalyst
for the synthesis of 2-arylbenzothiazole derivatives in solvent-free conditions. This reaction leads
to appropriate products in good to excellent yields. This new reported method has some
advantages such as easy preparation and high efficiency of catalyst, operational simplicity, mild
reaction conditions, easy purification, high yields of products, no environmental hazards and
reusability of the catalyst for at least 7 times.
ACKNOWLEDGMENTS
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We gratefully acknowledge the department of chemistry of Semnan University for supporting
this work.
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REFERENCES
1
2
3
4
5
. Niralawd, K. S.; Shingate, B. B.; Shingare, M. S. Bull. Korean Chem. Soc. 2010, 31, 981-983.
. Schatz, A.; Reiser, O.; Stark, W. J. Chem. Eur. J. 2010, 16, 625-638.
. Yan, N.; Xiao, C. X.; Kou, Y. Coord. Chem. Rev. 2010, 254, 1179-1218.
. Horton, D. A.; Bourne, G. T.; Smythe, M. L. Chem. Rev. 2003, 103(3), 893-930.
. Hotchinson, I.; Bradshaw, T. D.; Matthews, C. S.; Stevens, M. F. G.; Westwell, A. D. Bioorg.
J. Med. Chem. Lett. 2003, 13, 472-474.
6
7
8
9
. Huang, S. T.; Hesi, I. J.; Chen, C. Bioorg. J. Med. Chem. 2006, 14, 6106-6119.
. Palmer, P. J.; Trigg, R. B.; Warrington, J. V. J. Med. Chem. 1971, 14, 248-251.
. Burger, A.; Sawhey, S. N. J. Med. Chem. 1968, 11, 270-273.
. Benazzouz, A.; Boraud, T.; Dubedat, P.; Boireau, A.; Stutzmann, J.-M.; Gross, C. Eur. J.
Pharmacol. 1995, 284, 299-307.
1
2
1
1
1
1
1
1
1
0. Costa, S. P. G.; Batista, R. M. F.; Cardoso, P.; Belsely, M.; Raposo, M. M. M. Eur. J. Chem.
006, 2006, 3938-3946.
1. Day, J. C.; Tisi, L. C.; Bailey, M. J. Luminescence 2004, 19, 8-20.
2. Batista, R. M. F.; Costa, S. P. G.; Raposo, M. M. M. Tetrahedron Lett. 2004, 45, 2825-2828.
3. Ben-Alloum, A.; Bakkas, S.; Soufiaoui, M. Tetrahedron Lett. 1997, 38, 6395-6396.
4. Tale, R. H. Org. Lett. 2002, 4(10), 1641-1642.
5. Li, Y.; Wang, G. Y.; Wang, J. Y.; Jacquline, L. Chem. Lett. 2006, 35, 460-461.
6. Ioth, T.; Nagata, K.; Ishikawa, H.; Ohsawa, A. Heterocycles 2004, 62, 197-201.
7. Bougrin, K.; Loupy, A.; Soufiaoui, M. Tetrahedron Lett. 1998, 54, 8055-8064.
1
1
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
8. Rostamizadeh, S.; Housaini, S. A. G. Phosph, Sulfur and Silicon. 2005, 180, 1321-1326.
9. Ranu, B. C.; Jana, R.; Day, S. Chem. Lett. 2004, 33, 274-275.
0. Fazaeli, R.; Aliyan, H. Appl. Catal. A: General 2009, 353, 74-79.
1. Al Qalaf, F.; Mekheimer, R. R.; Sadek, K. U. Molecules 2008, 13, 2098-2914.
2. Kawashita, Y.; Ueba, C.; Hayashi, M. Tetrahedron Lett. 2006, 47, 4231-4233.
3. Mukhopahyay, C.; Datta, A. J. Heterocycl. Chem. 2009, 46, 91-95.
4. Rahmani, S.; Amoozadeh, A.; Kolvari, E. Catal. Commun. 2014, 56, 184-188.
5. Amoozadeh, A.; Rahmani, S.; Nemati, F. Heterocycl. Commun. 2013, 19, 69-73.
6. Amoozadeh, A.; Tabrizian, E.; S., R. C. R. Chimie 2015, In Press.
7. Kolvari, E., Bu-Ali Sina University, 2008.
8. Maleki, B.; Salehabadi, H. Eur. J. Chem. 2010, 1, 377‐380.
9. Rudd, S.; Barany, G. Acta Cryst. 1984, C40, 2118-2120.
0. Zobel, D.; Rltban, G. Acta Cryst. 1981, B37, 1867-1871.
1. Agilent Technologies, CRYSALIS PRO: Oxford Diffraction Ltd, 2010.
2. Altomare, A.; Cascarano, G.; Giacovazzo, C.; Gualardi, A. J. Appl. Crystallogr. 1993, 26,
43-350.
3. Sheldrick, G. M. Acta, Part A. 2008, 64, 112-122.
4. Khosravi, K.; Kazemi, S. Chin. Chem. Lett. 2010, 23, 61-64.
5. Maleki, B.; Salehabadi, H.; Moghadam, M. K. Acta Chim. Solv. 2010, 57, 741-745.
6. Pratap, U. R.; Mali, J. R.; Jawale, D. V.; Mane, R. A. Tetrahedron Lett. 2009, 50, 1352-1354.
7. Lim, H.-J.; Myung, D.; Lee, I. Y.-C.; Jung, M. H. J. Comb. Chem. 2008, 10, 501-503.
8. Naeimi, H.; Heidarnezhad, A. J. Sulfur Chem. 2014, 35, 493-501.
1
2
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ACCEPTED MANUSCRIPT
39. Prajapati, N. P.; Vekariya, R. H.; Borad, M. A.; Patel, H. D. RSC Adv. 2014, 4, 60176-60208.
1
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a
Table 1 The effect of different conditions on synthesis of 2-phenylbenzothiazoles .
b
Entr
y
1
2
3
4
5
6
7
Time
(min)
60
30
30
30
30
30
30
Yield
(%)
25
43
51
68
85
92
91
8
Catalyst (mmol)
Catalyst Free
Nano-TiO
Nano-TiO
Nano-TiO
Nano-TiO
Nano-TiO
Nano-TiO
2
2
2
2
2
2
SO
SO
SO
SO
SO
SO
3
3
3
3
3
3
H (0.012)
H (0.025)
H (0.050)
H (0.074)
H (0.099)
H (0.124)
8
9
Nano TiO
Bulk TiO
Bulk-TiO SO
2
(0.099)
(0.099)
60
60
60
2
4
65
10
2
3
H (0.099)
a
Reaction Condition: 1 (1 mmol), 2 (2 mmol) at 90 ºC under solvent free condition.
b
Isolated yield.
1
4
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a
Table 2 The effect of different conditions on synthesis of 2-phenylbenzothiazole .
o
b
Entry Temp. ( C) Solvent Time (min) Yield (%)
1
2
3
4
5
6
7
RT
50
60
70
80
90
-
-
-
-
-
30
30
30
30
30
30
60
32
63
76
92
91
90
35
-
70 Toluene
PEG-
8
70
60
45
400
9
0
1
70
70 CH
70
H
2
O
60
60
60
55
75
85
1
1
3
CN
EtOH
a
reaction condition: 1 (1 mmol), 2 (1 mmol) and n-TSA (0.099 mmol).
1
5
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a
Table 3 Synthesis of 2-arylbenzothiazoles by n-TSA as a reusable nano catalyst.
Entr
y
1
2
3
4
5
6
Time
(min)
30
40
40
20
15
15
20
45
35
20
15
b
Melting Point (ºC)
2
Product
Yield (%)
Found
111-114
73-77
Reported
3
4
-C
6
H
5
3a
3b
3c
3d
3e
3f
3g
3h
3i
92
87
91
86
87
90
90
93
96
85
89
93
112-115
1
2-Cl-C
4-Cl-C
6
H
H
4
72-74
1
6
4
114-116
129-131
225-227
101-103
130-132
86-88
116-117
3
5
2-HO-C
4-HO-C
4-F-C
4-Br-C
4-H C-C
4-H CO-C
6
H
H
4
126-128
226-227
3
5
6
4
1
6
H
4
102-103
3
5
7
6
H
4
130-131
85-87
c
1
8
3
6
H
4
1
9
3
6
H
4
119-121
132-134
184-186
223-226
120-122
3
4
5
1
1
1
0
1
2
2-O
3-O
4-O
2
2
2
N-C
N-C
N-C
6
6
6
H
H
H
4
4
4
3j
3k
3l
132-135
180-183
3
1
10
226-228
Not
Reported
d
13
2-Naphtaldehyde
3m
3n
20
20
91
80
127-130
102-104
Thiophen-2-
Carbaldehyde
34
14
102-103
a
o
Reaction condition: 1 (1 mmol) 2 (1 mmol) and n-TSA (0.099 mmol) in solvent-free at 70 C.
b
Isolated yield.
c
New single crystal: characterized by Xcalibur four-circle diffractometer.
d
1
13
New compound: characterized by FT-IR, H NMR, C NMR and elemental analysis.
1
6
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Table 4 Comparison of the characteristic of new reported method with other methods for
synthesis of 2-arylbenzothiazoles.
Amount of
Catalyst
2 g
10 mol%
70 mol%
Time
(min)
1440
360
Yield
(%)
75
85
84
Entry
Catalyst
Condition
Solvent
CH Cl
3
6
1
2
3
Baker's Yeast
RT
RT
RT
2
2
3
4
HMTA-Bromine
CH CN
3
2
8
NH
SSA
SO .SiO
CH -SO
Nano BF /SiO
4
Cl
30
MeOH/H
2
O
1
Microwave
4
5
6
100 mg
5 mg
12
25
30
-
90
80
93
(
45 W)
RT
3
5
H
2
4
2
EtOH
1,2-
3
7
Microwave
3
3
H
15 mol%
(
230 ºC)
RT
Cl
2
C
6
H
4
3
8
7
8
9
3
2
25 mol%
10%/weight
0.016 g
30
240
30
EtOH
EtOH
-
85
90
92
3
9
Indion-190 Resin
Present method
70 ºC
70 ºC
1
7
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Table 5 Crystal information of 3c
.
Crystal structure and data refinement parameters for
3c
Formula
Formula Weight
Crystal System
Space group
a (Å)
C
13
H
8
ClNS
245.72
Triclinic
P-1
11.1540(6)
14.3104(8)
15.0501(7)
95.626(4)
106.740(5)
100.092(5)
2236.6(2)
1.46
b (Å)
c (Å)
α (°)
β (°)
γ (°)
3
V (Å )
3
D
x
(g/cm )
F(000)
1008
µ (/mm)
0.50
θ range (°)
3.0-25.0
-
12 ≤ h ≤ 13
hkl range
-17 ≤ k ≤ 17
-
17 ≤ I ≤ 15
Reflection
Collected
18271
Unique (Rint
)
7862 (0.029)
6091
With I> 2σ(I)
No. of parameters
R (F) [I> 2σ(I)]
577
0.039
2
wR (F ) [I> 2σ(I)]
0.097
R (F) [all data]
0.057
2
wR (F ) [all data]
0.104
1
8
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Goodness of fit
1.08
3
Min/Max ∆ρ (e/Å )
0.30/-0.34
1021332
CCDC No.
1
9
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NH2
N
n-TSA (0.099 mmol)
Ar-CHO
Ar
o
Solvent free, 70 C
S
SH
2
1
3
a-n
Scheme 1
2
0
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Figure 1: Possible mechanism for synthesis of 2-arylbenzothiazoles derivatives.
2
1
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Figure 2: The SEM images of n-TSA before use (a) and after reuse 7 times (b).
2
2
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Figure 3: Perspective view of molecule A found in the structure of 3c; the ellipsoids are drawn
at 50% probability level, hydrogen atoms are shown as spheres of arbitrary radii.
2
3
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