Perchloric acid-doped polyaniline as an efficient and reusable catalyst for the synthesis of 2-substituted benzothiazoles

Article abstract of DOI:10.1080/10426500802705453

2-Substituted benzothiazoles have been efficiently synthesized in good yields by the condensation reaction of o-aminothiophenol with aldehydes in the presence of a catalytic amount of perchloric acid-doped polyaniline (HClO4/PANI). The low cost, simple re

Full text of DOI:10.1080/10426500802705453

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Perchloric Acid–Doped
Polyaniline as an Efficient
and Reusable Catalyst for the
Synthesis of 2-Substituted
Benzothiazoles
Mohammad Abdollahi-Alibeik a & Safoora Poorirani a
a Department of Chemistry, Yazd University, Yazd,
Iran
Version of record first published: 18 Nov 2009
To cite this article: Mohammad Abdollahi-Alibeik & Safoora Poorirani (2009):
Perchloric Acid–Doped Polyaniline as an Efficient and Reusable Catalyst for the
Synthesis of 2-Substituted Benzothiazoles, Phosphorus, Sulfur, and Silicon and the
Related Elements, 184:12, 3182-3190
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Phosphorus, Sulfur, and Silicon, 184:3182–3190, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500802705453
Perchloric Acid–Doped Polyaniline as an Efficient and
Reusable Catalyst for the Synthesis of 2-Substituted
Benzothiazoles
Mohammad Abdollahi-Alibeik and Safoora Poorirani
Department of Chemistry, Yazd University, Yazd, Iran
2-Substituted benzothiazoles have been efficiently synthesized in good yields by
the condensation reaction of o-aminothiophenol with aldehydes in the presence of
a catalytic amount of perchloric acid–doped polyaniline (HClO4/PANI). The low
cost, simple recovery, and efficient reusability are remarkable characteristics of this
catalyst.
Keywords Benzothiazole; perchloric acid; polyaniline; polymer supported; reusability
INTRODUCTION
Compounds with a benzothiazole moiety have received considerable
attention because of their widespread occurrence in biologically ac-
tive molecules such as antitumor, antimalaria, fungicide, anti-HIV, an-
tiviral, and analgesic agents.1 Recently, radiolabeling of benzothiazole
derivatives has been developed for PET imaging in the detection of
Alzheimer diseases.2 These compounds also have many industrial ap-
plications; for example some 2-substituted benzothiazoles are utilized
as fluorescence agents in textile dyeing, antioxidants, and vulcaniza-
tion accelerators of rubber.3
Several synthetic methodologies have been developed for the syn-
thesis of 2-substituted benzothiazoles. The most common direct
methods are the condensation reaction of o-aminothiophenol with
some functional groups to provide a substituent at the 2-position
of the benzothiazole scaffold. Many acid catalysts have been used
for these condensation reactions, such as the condensation of o-
aminothiphenol with aldehydes in the presence of iodine,4 SiO2 or
Received 7 September 2008; accepted 10 December 2008.
We are thankful to the Yazd University Research Council for partial support of this
work.
Address correspondence to Mohammad Abdollahi-Alibeik, Department of Chemistry,
Yazd University, Yazd 89195-741, Iran. E-mail: abdollahi@yazduni.ac.ir
3182

Perchloric Acid–Doped Polyaniline
3183
montmorillonite/graphite,5 zirconyl chloride,6 and SiO2 under mi-
crowave irradiation,7 and also condensation with carboxylic acids
or its derivatives in the presence of iodine,8 polyphosphoric acid,9
polyphosphate,10 and ionic liquid.11 Some other methods include potas-
sium ferricyanide–mediated cyclization of thiobenzanilides (Jacobson’s
method),12 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ)–mediated cy-
clization of thiobenzanilides,13 condensation of polymer-bonded esters
with o-aminothiophenol in the presence of alkyl aluminum Lewis
acids,14 and palladium-catalyzed cyclization of o-bromophenylthioureas
and o-bromothioamides.15
However, many of these methodologies suffer from one or more dis-
advantages, such as low yields of products, expensive catalysts, pro-
longed reaction times, high temperature, need for excess amounts of
the catalysts, multistep synthesis, and non-reusability of the catalysts.
Thus, there is a need for designing a simple and efficient method for
the synthesis of benzothiazole derivatives.
In recent years, there has been an ongoing effort to replace conven-
tional acid catalysts with solid acid catalysts. This is mainly due to
some advantages of solid acid catalysts such as ease of handling, non-
toxicity, ease of recovery, and reusability.16 Among the various types
of solid acids, polymer-supported acid catalysts have attracted consid-
erable attention because of their desirable characteristics. Polyaniline
has a wide range of applications in organic synthesis as a support for
its easy preparative protocol, from inexpensive starting material, high
environmental and thermal stability, and easy doping/undoping.17
In continuation of our study on the application of solid supported
reagents in organic transformations,18 herein we report the applica-
tion of perchloric acid–doped polyaniline (HClO4/PANI) as a reusable
solid acid catalyst for the synthesis of 2-substituted benzothiazoles
by the condensation reaction of o-aminothiophenol with aldehydes
(Scheme 1).
NH2
N
HClO4/PANI
+
Ar
Ar CHO
EtOH/reflux
S
SH
3
2
1
NH
N
N
NH
PANI =
n
SCHEME 1 Synthesis of 2-substituted benzothiazoles by the reaction of 2-
aminothiophenol and aldehydes in the presence of HClO4/PANI under reflux
condition.

3184
M. Abdollahi-Alibeik and S. Poorirani
(b)
(a)
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1)
FIGURE 1 FT-IR Spectra of (a) PANI, (b) HClO4/PANI.
RESULTS AND DISCUSSION
Initially, the polyaniline was prepared by polymerization of freshly dis-
tilled aniline as reported elsewhere.19 Polyaniline was doped in 1.0 M
HClO4 solution, and HClO4/PANI was obtained with 26 wt.% of per-
chloric acid. The doped polymer was characterized by XRD and FT-IR,
and the results confirm the existence of perchlorate on the support.
The FT-IR spectra of PANI and HClO4/PANI are shown in Figure 1.
The spectrum of HClO4/PANI is similar to that of PANI base, except a
bond around 2930 cm−1 that is assigned to NH2 group and indicates
+
the formation of polyaniline salt.17e
When compared with polyaniline base, the bond at 1580 cm−1 (aris-
ing from both C = N and C = C stretching of the quinoid diimine
unit) and the bond at 1470 cm−1 (arising from C C aromatic ring
stretching of the benzenoid diimine unit) in HClO4/PANI are shifted to
lower wave numbers. The bond at 1040 cm−1, appeared in the spec-
−
trum of HClO4/PANI, is also assigned to Cl-O stretching of ClO4

Perchloric Acid–Doped Polyaniline
3185
(b)
(a)
10
20
30
40
50
60
70
2θ(°)
FIGURE 2 XRD pattern of (a) PANI (b) HClO4/PANI.
anion. Although there is not any report about exact characterization of
HClO4/PANI, these results however confirm good doping of PANI with
HClO4 with regard to literature reports for doping of polyaniline with
other Brønsted acids.17e,20
The XRD pattern of the PANI base and HClO4/PANI are shown
in Figure 2. As shown in the pattern (a), the XRD of the PANI base
indicates the amorphous nature with peak at 2θ = 19.5◦. In the XRD
pattern of HClO4/PANI, broad peaks around 2θ = 15◦, 2θ = 19.5◦, and
2θ = 25◦ were observed. The peaks at 2θ = 15◦ and 2θ = 25◦ are stronger
than that of 2θ = 19.5◦, which it similar to that of highly doped PANI
salt as reported elsewhere.20
The condensation reaction of the benzaldehyde as a model substrate
with o-aminothiophenol was investigated by using a catalytic amount
of HClO4/PANI in EtOH under reflux conditions. In a typical experi-
ment, o-aminothiophenol (1 mmol) and benzaldehyde (1 mmol) were
reacted together in the presence of HClO4/PANI (100 mg) in EtOH at
reflux. The condensation was complete after 2 h. The crude product
with high purity was achieved by filtration of the catalyst, addition
of water, and filtration of the obtained precipitate. Further purification
was achieved by recrystallization of the crude product in ethanol/water,
and 2-substituted benzothiazole was obtained in 85% yield (Table I, 3a).
To explore the generality of this reaction, various types of aromatic
aldehydes with both electron-donating and electron-withdrawing sub-
stituents were reacted with o-aminothiophenol under the same reaction

3186

3187

3188
M. Abdollahi-Alibeik and S. Poorirani
TABLE II Reusability of HClO4/PANI in the Reaction of o-
Aminothiophenol with Benzaldehyde
Entry
Time (h)
Yielda (%)
1
2
3
4
2
85
80
75
75
2:30
2:45
2:45
aIsolated yields.
conditions, and the corresponding 2-aryl benzothiazoles were obtained
in 68–86% yields (Table I, 3b–3o).
The reaction of heteroaryl aldehydes was also investigated in the
same reaction condition, and the corresponding 2-heteroaryl benzoth-
iazoles were obtained in 68% yields (Table I, 3p–3q).
All of the synthesized products are known compounds and were char-
acterized by comparing their melting points (Table I) and IR spectra.
All of the FT-IR spectra show a bond around 1560–1620 cm−1, arising
from stretching frequency of C = N in benzothiazole rings.
Catalyst reusability is one of the most important characteristics of
solid acid catalysts. To study the reusability of HClO4/PANI, the recov-
ered catalyst from the reaction of o-aminothiophenol with benzaldehyde
was applied in the same reaction four times. After each run, the cata-
lyst was washed with acetone and dried at 120◦C for 1 h. The results
show that there is no substantial change in the catalyst reactivity (Ta-
ble II), and there is only a steady decline in the yields and times of the
reactions during third time of reuse, while this moderate deactivation
is stopped in the forth run. These results suggest that the loss in cat-
alytic activity is due to the blockage of the active site of the catalyst by
coke deposition during the reaction.
In summary, we introduced HClO4/PANI as a solid acid catalyst for
efficient synthesis of 2-substituted benzothiazoles by the reaction of o-
aminothiophenol with aldehydes. The ease of the catalyst preparation,
simple workup, simple recovery, and reusability of the catalyst make
this method advantageous for organic chemistry.
EXPERIMENTAL
All of the chemicals were commercial products. Aniline from E. Merck
was distilled prior to use. High purity grade perchloric acid, reagent
grade solvents, and sodium persulfate (E. Merck) were used without
purification. o-Aminothiophenol and benzaldehyde were distilled and

Perchloric Acid–Doped Polyaniline
3189
freshly used, and other aldehydes (E. Merck and Aldrich) were used
as received. Polyaniline was synthesized by oxidative polymerization
of aniline in acidic solution, according to the method described in the
literature.19 All melting points were obtained by Buchi B-540 appa-
ratus and are uncorrected. All reactions were monitored by TLC, and
1
all yields refer to isolated products. H and 13C NMR spectra were
recorded in CDCl3 on a Bruker 500 MHz spectrometer. Infrared spec-
tra were recorded on a Bruker FT-IR Equinax-55 spectrophotometer in
KBr with absorption in cm−1. XRD patterns were recorded on a Bruker
D8 Advance X-ray diffractometer using nickel filtered Cu Kα radiation.
Synthesis of Perchloric Acid–Doped Polyaniline
Polyaniline (0.5 g) was added to a 1.0 M aqueous solution of HClO4
(50 mL) in a 100 mL round bottom flask under vigorous stirring. The
mixture was stirred for 4 h. The solid was filtered, washed with water
(100 mL) followed by acetone (50 mL), and dried at 120◦C for 1 h.
Polyaniline salt with 26 wt.% for HClO4 was obtained.
General Experimental Procedure for the Synthesis of
2-Substituted Benzothiazoles
A mixture containing o-aminothiophenol (1 mmol), ethanol (5 mL),
HClO4/PANI (100 mg), and aldehyde (1 mmol) was taken in a 10 mL
round bottom flask under reflux conditions. After completion of the
reaction (monitored by TLC, EtOAc:n-hexane, 30:70), the reaction mix-
ture was filtered, washed with EtOH (10 mL), and 50% of the sol-
vent was evaporated under vacuum. To the obtained solution, water
(5 mL) was added, and the precipitate was filtered and washed with
water (5 mL). After drying of the solid, the corresponding 2-substituted
benzothiazole was obtained with high purity. Further purification was
achieved by column chromatography on silica-gel (eluent: EtOAc:n-
hexane, 20:80). The corresponding 2-substituted benzothiazoles were
obtained in 68–86% yields.
REFERENCES
[1] (a) I. Hutchinson, S. A. Jennings, B. R. Vishnuvajjala, A. D. Westwall, and M. F.
G. Stevens, J. Med. Chem., 45, 744 (2002). (b) K. Takasu, H. Inoue, H. S. Kim,
M. Suzuki, T. Shishido, Y. Wataya, and M. Ihara, J. Med. Chem., 45, 995 (2002).
(c) T. Reemtsma, O. Fiehn, O. F. Kalnovski, and M. Jekel, Environ. Sci. Technol.,
29, 478 (1995). (d) S. R. Nagarajan, G. A. De Crescenzo, D. P. Getman, H. F. Lu, J.
A. Sikorski, J. L. Walker, J. J. McDonald, K. A. Houseman, G. P. Kocan, N. Kishore,
P. P. Mehta, C. L. Funkes-Shippy, and L. Blystone, Bioorg. & Med. Chem., 11, 4769

3190
M. Abdollahi-Alibeik and S. Poorirani
(2003). (e) A. D. Borthwick, D. E. Davies, P. F. Ertl, A. M. Exall, T. M. Haley, G. J.
Hart, D. L. Jackson, N. R. Parry, A. Patikis, N. Trivedi, G. Weingarten, and J. M.
Woolven, J. Med. Chem., 46, 4428 (2003). (f) C. Y. Jeong, J. Chio, and M. H. Yoon,
Eur. J. Pharmacol., 502, 205 (2004).
[2] G. Henriksen, B. H. Yousefi, A. Drzezga, and H. Wester, Eur. J. Nucl. Med. Mol.
Imaging, 35, 75 (2008).
[3] (a) S. P. G. Costa, J. A. Ferreira, G. Kirsch, and M. F. Oliveira Campos, J. Chem.
Res. S, 314 (1997). (b) S. K. Ivanov and V. S. Yuritsyn, Chem. Abstr., 74, 124487m
(1971). (c) R. B. Spies, B. D. Anderson, and D. W. Rice, Nature, 327, 697 (1987).
[4] F. M. Moghaddam, G. R. Bardajee, H. Ismaili, and S. M. D. Taimoory, Synth. Com-
mun., 36, 2543 (2006).
[5] S. Rostamizadeh and S. A. G. Housaini, Phosphorus, Sulfur, and Silicon, 180, 1321
(2005).
[6] F. M. Moghaddam, H. Ismaili, and G. R. Bardajee, Heteroatom Chem., 17, 136
(2006).
[7] M. Kodomari, Y. Tamaru, and T. Aoyama, Synth. Commun., 34, 3029 (2004).
[8] S. D. Gupta, P. H. Singh, and N. S. H. N. Moorthy, Synth. Commun., 37, 4327 (2007).
[9] D. W. Hein, R. J. Alheim, and J. J. Leavitt, J. Am. Chem. Soc., 79, 427 (1957).
[10] Y. Kanaoka, T. Hamada, and O. Yonemitsu, Chem. Pharm. Bull., 18, 587 (1970).
[11] R. N. Nadaf, S. A. Siddiqui, T. Daniel, R. J. Lahoti, and K. V. Srinivasan, J. Mol.
Catal. A: Chem., 214, 155 (2004).
[12] I. Hutchinson, M. G. F. Stevens, and A. D. Westwell, Tetrahedron Lett., 41, 425
(2000).
[13] D. S. Bose and M. Idrees, Tetrahedron Lett., 48, 669 (2007).
[14] H. Matsushita, S. H. Lee, M. Joung, B. Clapham, and K. D. Janda, Tetrahedron
Lett., 45, 313 (2004).
[15] C. Benedi, F. Bravo, P. Uriz, E. Fernandez, C. Claver, and S. Castillon, Tetrahedron
Lett., 44, 6073 (2003).
[16] M. A. Harmer and Q. Sun, Appl. Catal. A: General, 221, 45 (2001).
[17] (a) M. L. Kantam, M. Roy, S. Roy, M. S. Subhas, B. Sreedhar, B. M. Choudhary,
and R. L. De, J. Mol. Catal. A: Chem., 265, 243 (2006). (b) S. Palaniappan and R.
C. Shekhar, J. Mol. Catal. A: Chem., 209, 117 (2004). (c) T. Amaya, D. Saio, and T.
Hirao, Tetrahedron Lett., 48, 2729 (2007). (d) S. Palaniappan, S. Chandrasekaran,
and V. J. Rao, J. Mol. Catal. A: Chem., 229, 221 (2005). (e) S. Palaniappan, A. John,
C. A. Amarnath, and V. J. Rao, J. Mol. Catal. A: Chem., 218, 47 (2004).
[18] (a) I. Mohammadpoor-Baltork and M. Abdollahi-Alibeik, Can. J. Chem., 83, 1 (2004).
(b) M. Abdollahi-Alibeik, Z. Zaghaghi, and I. Mohammadpoor-Baltork, J. Chin.
Chem. Soc., 55, 1 (2008). (c) M. Abdollahi-Alibeik, I. Mohammadpoor-Baltork, Z.
Zaghaghi, and B. H. Yousefi, Catal. Commun., 9, 2496 (2008).
[19] (a) X. R. Zeng and T. M. Ko, Polymer, 39, 1187 (1998). (b) M. V. Kulkarni, A. K.
Viswanath, R. Marimuthu, and T. Seth, Polymer Eng. and Sci., 44, 1676 (2004).
(c) J. Anand, P. S. Rao, S. Palaniappan, and D. N. Sathyanarayana, Synth. Metals,
95, 57 (1998).
[20] T. Abdiryim, Z. X. Gang, and R. Jamal, Mater. Chem. & Phys., 90, 367 (2005).
[21] A. K. Chakraborti, S. Rudrawar, G. Kaur, and L. Sharma, Synlett, 1533 (2004).
[22] D. L. Boger, J. Org. Chem., 43, 2296 (1987).
[23] A. Cerniani and R. Passerini, J. Chem. Soc., 2261 (1954).
[24] Y. Merty, S. Michaud, and J. M. Vierfond, Heterocycles, 38, 1001 (1994).
[25] C. Rai and J. B. Braunwarth, J. Org. Chem., 26, 3434 (1961).