Novel green procedure for the synthesis of 2-arylbenzothiazoles under microwave irradiation in Peg 200 or Peg 400

Article abstract of DOI:10.1080/10426501003598648

An improved green procedure for the synthesis of 2-aryl- and 2-hetarylbenzothiazoles by condensation of equivalent amounts of 2,2'-diaminodiphenyldisulfides or 2-aminothiophenols and various aromatic aldehydes in PEG 200/400 under microwave irradiation has been developed. This method allows the synthesis of 2-arylbenzothiazoles in high yields and with high purity regardless of the state of the starting compounds (liquid or solid) or the nature of the substituents in the aromatic ring. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/10426501003598648

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Novel Green Procedure for the
Synthesis of 2-Arylbenzothiazoles Under
Microwave Irradiation in Peg 200 Or Peg
400
Todor G. Deligeorgiev a , Stefka Kaloyanova a , Aleksey Vasilev a &
Juan J. Vaquero b
a Faculty of Chemistry , University of Sofia , Sofia , Bulgaria
b Facultad de Farmacia, Universidad de Alcalá , Alcalá de Henares ,
Madrid , Spain
Published online: 05 Nov 2010.
To cite this article: Todor G. Deligeorgiev , Stefka Kaloyanova , Aleksey Vasilev & Juan J. Vaquero
(2010) Novel Green Procedure for the Synthesis of 2-Arylbenzothiazoles Under Microwave Irradiation
in Peg 200 Or Peg 400, Phosphorus, Sulfur, and Silicon and the Related Elements, 185:11, 2292-2302,
DOI: 10.1080/10426501003598648
To link to this article: http://dx.doi.org/10.1080/10426501003598648
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Phosphorus, Sulfur, and Silicon, 185:2292–2302, 2010
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426501003598648
NOVEL GREEN PROCEDURE FOR THE SYNTHESIS OF
2-ARYLBENZOTHIAZOLES UNDER MICROWAVE
IRRADIATION IN PEG 200 OR PEG 400
Todor G. Deligeorgiev,1 Stefka Kaloyanova,1 Aleksey Vasilev,1
and Juan J. Vaquero2
1Faculty of Chemistry, University of Sofia, Sofia, Bulgaria
2Facultad de Farmacia, Universidad de Alcala´, Alcala´ de Henares, Madrid, Spain
An improved green procedure for the synthesis of 2-aryl- and 2-hetarylbenzothiazoles by con-
densation of equivalent amounts of 2,2ꢀ-diaminodiphenyldisulfides or 2-aminothiophenols
and various aromatic aldehydes in PEG 200/400 under microwave irradiation has been
developed. This method allows the synthesis of 2-arylbenzothiazoles in high yields and with
high purity regardless of the state of the starting compounds (liquid or solid) or the nature
of the substituents in the aromatic ring.
Keywords 2-Aminothiophenols; arylbenzothiazoles; 2,2ꢁ-diaminodiphenyldisulfides; green
chemistry; microwave
INTRODUCTION
Benzothiazoles are an important group of heterocyclic compounds that have nu-
merous applications based on their wide spectrum of biological and biophysical prop-
erties.1–4 2-Arylbenzothiazoles are known as antifungal,5 antimicrobial, and antitumor
agents.6 The presence of a benzothiazolyl moiety in these compounds, including 2-
hetarylbenzothiazoles, determines the fluorescence properties and their potential use as
fluorescent markers for biostructures,7 e.g., thioflavine T8 and the well-known DNA inter-
calator TOTO-1 (Figure 1), and as intermediates for the preparation of other derivatives
and dyes.9,10
The known methods for the synthesis of benzothiazoles include two main routes: (i)
condensation of o-aminothiophenols or derivatives such as 2,2ꢁ-diaminodiphenyldisulfides
with aldehydes, carboxylic acids, or their derivatives in the presence of different catalysts
and solvents11–20 and (ii) oxidative cyclization of thioanilides under basic conditions.9,21–24
The intermediate Schiff bases formed by 2-aminothiophenol and benzaldehydes cyclize
spontaneously to give the corresponding dihydrobenzothiazoles. These compounds are
then oxidized by air to give benzothiazoles.20,25,26 The reaction conditions often involve
Received 9 November 2009; accepted 6 January 2010.
The authors acknowledge financial support (in part) of this work from the Spanish Ministerio de Ciencia e
Innovacio´n (project CTQ2008/04313).
Address correspondence to Stefka Kaloyanova, University of Sofia, Faculty of Chemistry, 1164 Sofia,
Bulgaria. E-mail: ohtsk@chem.uni-sofia.bg
2292

GREEN SYNTHESIS OF 2-ARYLBENZOTHIAZOLES
2293
H3C
CH3
CH3
S
N
N
CH3
Cl
Thioflavine T (Basic Yellow 1)
I
CH3
N
CH3
S
N
N
N CH3
N CH3
CH3
S
I
N
CH3
TOTO-1
Figure 1 Chemical structures of thioflavine T and TOTO-1, a fluorescent DNA intercalator that contains the
benzothiazole heterocycle as an end group.
relatively high temperatures and long reaction times.11,15,17,22,27 In some cases the exper-
imental procedures for the isolation of the product require laborious techniques such as
extraction and distillation.9,19,23,24
The advantages offered by the use of microwave irradiation in heterocyclic synthesis28
have been applied to some of the methods described above in an effort to simplify and
improve the procedures. In recent years, a wide range of practical applications has been
identified for microwave irradiation in the synthesis of 2-substituted benzothiazoles. Most
of the reported methods that involve the use of microwaves concern the condensation
of o-aminothiophenol with various aromatic aldehydes and derivatives in short reaction
times. These procedures tend to give higher product yields and proceed under solvent-
free conditions.29–36 However, some limitations are associated with this approach; these
include elevated temperatures, the use of toxic metallic compounds, and laborious isolation
techniques.
A literature survey reveals that the synthesis of the benzothiazole moiety from
diphenyldisulfides under microwave irradiation has not been reported to date. The methods
in which disulfides are used as starting materials include (i) direct reaction with sub-
stituted benzaldehydes in the presence of a catalytic amount of p-toluenesulfonic acid,
triphenylphosphine as a reducing agent, and toluene as a solvent18–20,22 under reflux for
14–24 hours, and (ii) oxidative cyclization of the corresponding benzanilides.15–17
RESULTS AND DISCUSSION
We report in this article a general and environmentally friendly procedure for the
synthesis of benzothiazoles by reaction of 2,2ꢁ-diaminodiphenyldisulfides 1a–1c (Method

2294
T. G. DELIGEORGIEV ET AL.
A) or 2-aminothiophenols 3a and 3b (Method B) with different benzaldehydes in polyethy-
lene glycol (PEG) 200 or PEG 400 (known as an ecofriendly reaction medium) under
microwave irradiation (Scheme 1). The application of PEGs in synthetic organic chemistry
represents both an opportunity and a challenge, and the wide availability of PEGs at low
cost may give such processes a promising future in green chemistry.37 These methods can
be applied to the synthesis of a variety of 2-aryl- and 2-hetarylbenzothiazoles with different
substituents in the aromatic nucleus. This approach gives products with high purity and in
short reaction times, typically 3–15 min.
Method A
MW
R
S
450-560 watts
Ar-CHO
+
PEG-200/400
10-15 min
p-TsOH
NH2
2
2a - 2w
1a: R = H
(R1)R
S
N
1b: R = Cl
1c: R = OCH3
R2
Method B
4 - 34
MW
R1
SH
560 watts
+
Ar-CHO
PEG-200/400
3-10min
NH2
p-TsOH
3a: R = H
3b: R = Cl
2a - 2w
Scheme 1 Preparation of 2-aryl and 2-hetarylbenzothiazoles under microwave irradiation.
The methods reported for the synthesis of arylbenzothiazoles under microwave irra-
diation give low yields for some substituted aryl systems.24,29 These results are attributed
to the nature and the position of the substituents. For example, similar procedures un-
der solvent-free conditions show lower yields for 2-arylbenzothiazoles bearing a hydroxyl
(yield 53%) or nitro (yield 61%) group in the para-position of the aryl ring.24
During our investigations to find the optimal conditions for the condensation reac-
tion, we discovered a significant restriction for the use of microwaves under solvent-free
conditions. This approach only works well if the starting materials are liquids or low-
melting compounds (i.e., below 100◦C). If one of the starting materials is a solid with
melting point over 100◦C, the method either does not proceed at all or proceeds only par-
tially upon prolonged microwave irradiation, even at higher power. The reaction between
2,2ꢁ-diaminodiphenyldisulfide (1a) and p-nitrobenzaldehyde (2h) using PEG-200/400 as
solvent or in solvent-free conditions was carried out in the presence of either p-TsOH or
SnCl2·2H2O·19,20 The progress of the reaction was monitored by TLC in each case. In the
reactions under solvent-free conditions, starting materials were still present as a mixture
with the product even when using microwave irradiation at the highest power and for pro-
longed reaction times (over 20 min). The use of SnCl2 as a catalyst under solvent-free
conditions did not increase the purity of the products for the same irradiation time.
Studies aimed at optimizing the condensation reaction according to Method A were
carried out with 2,2ꢁ-diaminodiphenyldisulfide and aldehyde 2a (Table I). The best yield of
4 was obtained by irradiating the reaction mixture for 15 (3 × 5) minutes at 560 W (Table I,
entry 17) in the presence of the green solvent PEG 200/400 and p-toluenesulfonic acid as a

GREEN SYNTHESIS OF 2-ARYLBENZOTHIAZOLES
2295
Table I Optimization of conditions for the microwave synthesis of product 4 by Methods A and B
Entry
MW (Watts)
Irradiation time (min)
Method A yield (%)a
Method B yield (%)a
1
2
80
80
2
4
No reaction
No reaction
No reaction
No reaction
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
290
290
480
480
480
560
560
560
560
560
560
560
560
560
560
800
800
2
No reaction
No reaction
No reaction
No reaction
4 (2 × 2)
2
4
10
29
45
24.5
28
30
32
34
56
58
67
89
93
22
23
30
59
26
67
89
87
70
67
68
—
—
—
43
8 (2 × 4)
2
4
5
6
6 (2 × 3)
8 (2 × 4)
10
10 (2 × 5)
12 (2 × 6)
15 (3 × 5)
1
3
Decomposition
Decomposition
catalyst. Complete consumption of the starting materials (i.e., they were no longer detected
by TLC) was considered to represent the end of the reaction. Irradiation at lower power did
not lead to a high enough temperature for the two solids to react (Table I, entries 1–4) and
irradiation at higher power led to decomposition (Table I, entries 18 and 19).
Bearing in mind the results described above, we also optimized the conditions used
for the synthesis by Method B. These studies were carried out with 2-aminothiophenol
(3a) and benzaldehyde (2a) (Table I). Of the conditions tested (Table I), the best results
were obtained by irradiation of the reaction mixture for 5 min at 560 W in the presence of
p-toluenesulfonic acid and using the green solvent PEG 200/400, which is easily recovered
when working with larger amounts (Table I, entry 10). Microwave irradiation at lower
(Table I, entries 1–7) or higher (Table I, entries 18 and 19) power did not improve the yield
of 4. Lower yields were also obtained when attempting the condensation by irradiation of
the mixture in two separate periods of 2 × 3 and 2 × 4 minutes (Table I, entries 12 and
13). The same yield of 4 was obtained when the reaction was conducted in PEG 200 as the
solvent.
The optimal conditions found for the condensation of 1a–c or 3a with the given
aldehydes to obtain 4 were successfully applied to the reactions of 1a–c, 3a, 3b and
different aromatic aldehydes bearing strong electron-donating and electron-withdrawing
substituents (Table II). However, in some cases it was observed that the optimal irradiation
time found for 4 led to decomposition of the condensation product, as was the case for
compounds 11 and 14 (Table II). Consequently, the irradiation time had to be reduced to 3
min to obtain a good yield of the arylbenzothiazole derivatives. In contrast, longer reaction
times were needed to complete the reaction of some aldehydes, such as 2r and 2t, with two
periods of 5 min being the best choice for compounds 21 and 23 (Table II). These changes
in the reaction times enabled the benzothiazole derivative to be obtained with high purity
and in good-to-excellent yield, regardless of the nature of the substituent on the aromatic

2296
T. G. DELIGEORGIEV ET AL.
Table II Starting materials, benzothiazoles 4–34 isolated yields, and melting points
MW
Starting (time,
material min) Method
Benzo-thiazole
product
Benzothiazole
product
structure
Aldehydes
2a–2w
Yield Mp/mp(lit.)
no.
(%)a
(◦C)
1a
5
A
4
5
89
102–104/
OHC
S
N
10214
;
113–11410
2a
3a
1a
15
10
B
A
93
89
118–120/
120–12117
S
OHC
N
HO
HO
2b
3a
1a
5
15
B
A
86
82
6
7
90–92/
S
OHC
OCH3
OCH3
10117
;
N
2c
121–12223
3a
1a
5
10
B
A
92
92
154–156/
174–17510
S
OHC
N(CH3)2
N(CH3)2
N
2d
3a
3a
10
10
B
B
93
97
8
9
124–126/
125–12610
S
OHC
N
N
N
2e
3a
10
B
89
74–75
OHC
S
N
2f
3a
1a
5
B
A
10
11
12
S
83
84
115–117
OHC
OHC
CN
CN
N
2g
15
224–226/
229–23025
S
NO2
NO2
N
3a
3a
3
3
B
B
86
92
2h
177–178
NO2
S
N
OHC
NO2
Br
2i
2j
3a
3a
10
3
B
B
13
14
88
83
156–158
149–151
OHC
HO
Br
Br
S
N
HO
OHC
HO
Br
Br
S
N
Br
HO
Cl
2k
3a
10
B
15
82
76–78/
S
OHC
84–8525
12517
;
N
Cl
2l

GREEN SYNTHESIS OF 2-ARYLBENZOTHIAZOLES
2297
Table II Starting materials, benzothiazoles 4–34 isolated yields, and melting points (Continued)
MW
Starting (time,
material min) Method
Benzo-thiazole
product
Benzothiazole
product
structure
Aldehydes
2a–2w
Yield Mp/mp(lit.)
no.
(%)a
(◦C)
3a
10
5
B
16
S
N
93
106–108/
OHC
Cl
119–12117
Cl
2m
2n
2o
3a
B
17
94
89
94
166–168
273–275
220–222
OHC
OHC
S
N
N
N
3a
3a
5
5
B
B
18
19
S
N
N
O
N
O
S
OHC
NHCOCH3
N
NHCOCH3
2p
2q
3a
3a
5
B
B
20
97
77
257–259
105–107
S
N
S
N
OHC
CHO
2 × 5
21 b
OHC
HO
S
N
HO
2r
3a
3a
1b
10
2 × 5
10
B
B
B
22 b
92
62
85
219–220/
CHO
212–21310
S
N
2s
23
141–142
144–146
OHC
S
N
N
N
C2H5
C2H5
2t
2b
24
Cl
S
N
HO
3b
1b
15
15
B
B
2c
2t
25
26
78
58
136–138
148–150
Cl
S
N
OCH3
Cl
S
N
N
C2H5
(Continued on next page)

2298
T. G. DELIGEORGIEV ET AL.
Table II Starting materials, benzothiazoles 4–34 isolated yields, and melting points (Continued)
MW
Starting (time,
material min) Method
Benzo-thiazole
product
Benzothiazole
product
structure
Aldehydes
2a–2w
Yield Mp/mp(lit.)
no.
(%)a
(◦C)
3b
1b
10
5
B
B
2d
2h
27
28
92
199–201
Cl
CH3
CH3
S
N
N
S
85
208–210
Cl
NO2
NO2
N
S
1c
1c
15
15
B
B
2h
2b
29
30
69
71
156–158
132–134
H3CO
N
S
H3CO
N
HO
1a
10
A
31
32
33
34
96
135–136/
S
OHC
OHC
N
N
133–13410
N
3a
1a
10
10
B
A
80
95
2u
2v
137–138/
12710
S
N
N
N
3a
1a
10
10
B
A
90
93
136–137/
137–13810
S
N
OHC
N
N
3a
1a
10
10
B
B
85
92
2w
103/10510
S
OHC
O
O
N
2x
aIsolated yields.
bReactions were carried out with addition of DMSO (1 mL).
ring.24 An excellent yield was also obtained in the double condensation reaction to give
dibenzothiazole 20 (Table II). The use of the carbazole derivative 2t as a heteroaromatic
aldehyde produced benzothiazole 23 as the condensation product, albeit in moderate yield.
It is worth noting that for some compounds, such as 21 and 22, which were obtained from
the 2-naphthol analog (2r) and 9-anthranylaldehyde (2s), respectively (Table II), better
yields were achieved by adding DMSO (1 mL) as a co-solvent. This behavior is related to
the ability of DMSO to act as an oxidant, which leads to a significant improvement in the
yields.11
The condensation reaction was also attempted with 2-amino-5-chlorothiophenol 3b
and arylaldehydes bearing strong electron-donating or electron-withdrawing substituents
(2c, 2d, and 2h). In all cases, the reaction gave excellent yields of the corresponding
condensation products 25, 27, and 28 (Table II).
In the reactions involving heteroaryl aldehydes 2u–2w, we observed that
the yields of the corresponding benzothiazoles 31–33 were higher on using 2,2ꢁ-
diaminodiphenyldisulfide 1a as the starting material (Table II).
In summary, we report a simple and general experimental procedure for the prepa-
ration of 2-aryl- and 2-hetarylbenzothiazoles under microwave irradiation (Table II). This

GREEN SYNTHESIS OF 2-ARYLBENZOTHIAZOLES
2299
approach requires short reaction times, has an easy workup procedure, and ensures reduced
environmental impact. The method also gives products in excellent yields and with high
purity regardless of the substituents in the arylaldehydes and the state (solid or liquid) of
the starting compounds used.
CONCLUSIONS
The synthetic procedure reported here is a reliable, simple, highly reproducible pro-
cess. The procedure is also very energy efficient as it involves very short reaction times
(3–15 min). The green solvent PEG 200 or PEG 400 is used, and this ensures reduced
environmental impact. The proposed method is very versatile, as a variety of different
starting materials can be used. The use of 2,2ꢁ-diaminodiphenyldisulfides as starting mate-
rials does not require the addition of reducing agents to the reaction mixture. The reaction
products are obtained in high yields and with high purity. In most cases, the yields are
higher than those obtained using similar methods reported in the literature. Furthermore,
column chromatography was not necessary for product purification.
EXPERIMENTAL
1H NMR spectra were recorded on Varian 200 MHz and Bruker Avance II+ 600
spectrometers in DMSO-d6 as solvent. The reactions were monitored by TLC (Merck F
254 silica gel; dichloromethane:n-heptane, 3:2). Melting points were obtained on a Kofler
apparatus and are uncorrected. 2-Aminothiophenol (3a) and aldehydes 2a–2x were com-
mercial products; 2-amino-5-chlorothiophenol (3b) and 2,2-diaminodiphenyldisulphides
(1a–1c) were synthesized by known procedures.38,39 A Neo MWO-M8205 commercial
microwave oven operating at a frequency of 2450 MHz with a power ranging from 80 to
800 Watts was used.
The analytical data for all known compounds were compared with those reported in
the literature. The compounds that have not been reported previously were characterized
by NMR spectroscopy and elemental analysis (Table III).
Method A
The appropriate 2,2ꢁ-diaminodiphenyldisulfide 3a–3c (2.5 mmol), the corresponding
aldehyde 2a–2x (5 mmol), PEG 200/400 (5 mL), and p-TsOH (0.1 mmol) were placed in a
25 mL Erlenmeyer flask. The reaction mixture was irradiated for 10–15 min at 560 W (450
W for compounds 31, 32, 33, 34) in a microwave oven. The mixture was allowed to cool
to room temperature, and ethanol (10 mL) was added. In some cases the products 3–34
crystallized, and in other cases they were precipitated by dilution with cold water (50 mL).
The compounds were isolated by filtration.
Method B
o-Aminothiophenol 1a or 1b (5 mmol), the corresponding aldehyde 2a–2x (5 mmol),
PEG 200/400 (5 mL), and p-TsOH (0.1 mmol) were placed in a 25 mL Erlenmeyer flask.
The reaction mixture was irradiated for 3–10 min at 560 W in a microwave oven. The
mixture was allowed to cool down to room temperature, and EtOH (10 mL) was added.

2300
T. G. DELIGEORGIEV ET AL.
Table III Elemental analysis and 1H NMR data of the unknown compounds
Analysis
Molecular
formula
(mw)
C% Calc.
found
H% Calc.
found
N% Calc.
found
Product
1H NMR [DMSO-d6, δ(ppm)]
9
C16H15NS
(253.36)
75.85
75.39
5.97
5.84
5.53
5.52
1H NMR (200 MHz): 1.23 d (6H, CH(CH3)2); 3.05 h (1H,
CH(CH3)2); 7.43–7.55 m (4H, ArH); 7.99–8.05 m (3H,
ArH); 8.12 d (1H, ArH)
10
12
13
14
17
C14H8N2S
(236.29)
71.16
70.66
3.41
3.32
11.86
11.36
1H NMR (200 MHz): 7.48–7.61 m (3H, ArH); 8.03 d (1H,
ArH); 8.11 d (1H, ArH); 8.19 d (1H, ArH); 8.26–8.29 m
(2H, ArH)
1H NMR (200 MHz): 7.48–7.63 m (2H, ArH); 7.83–7.87
m (1H, ArH); 8.12–8.23 m (2H, ArH); 8.39–8.51 m
(2H, ArH); 8.82 s (1H, ArH)
1H NMR (200 MHz): 7.04 d (1H, ArH); 7.39–7.59 m (3H,
ArH); 8.06 d (1H, ArH); 8.13 d (1H, ArH); 8.37 d (1H,
ArH); 11.7 br s (1H, OH)
1H NMR (200 MHz): 7.04 d (1H, ArH); 7.40–7.57 m (2H,
ArH); 8.06 d (1H, ArH); 8.13 d (1H, ArH); 8.38 s (1H,
ArH); 11.70 s (1H, OH)
C13H8N2O2S
(256.28)
60.93
60.42
3.15
3.23
10.93
10.62
C13H8BrNOS
(306.18)
51.00
50.59
2.63
2.59
4.57
4.72
C13H7Br2NOS
40.55
41.01
1.83
2.32
3.64
4.12
(385.07)
C18H18N2S
(294.41)
73.43
74.01
6.16
5.90
9.51
9.50
1H NMR (200 MHz): 1.59 brs (6H, CH2CH2CH2); 3.23 d
(4H, CH2NCH2); 7.03 d (2H, ArH); 7.33–7.38 m (1H,
ArH); 7.44–7.49 m (1H, ArH); 7.86–7.94 m (3H, ArH);
8.04 d (1H, ArH)
18
19
C17H16N2OS
(296.39)
68.89
69.31
5.44
5.79
9.45
9.46
1H NMR (200 MHz): 3.41 d (4H, CH2OCH2); 3.74 d (4H,
N(CH2)2); 7.07 d (2H, ArH); 7.35–7.40 m (1H, ArH);
7.45–7.50 m (1H, ArH); 7.91–7.96 m (3H, ArH); 8.05 d
(1H, ArH)
1H NMR (200 MHz): 2.08 s (3H, CH3); 7.39–7.83 m (2H,
ArH); 7.89 d (2H, ArH); 7.99–8.09 m (3H, ArH); 8.13 d
(1H, ArH); 10.26 s (1H, NH)
C15H12N2OS
(268.33)
67.14
66.86
4.51
4.23
10.44
10.03
20
21
C20H12N2S2
(344.45)
C17H11NOS
(277.34)
69.74
69.21
73.62
73.12
3.51
3.12
4.00
4.00
8.13
7.86
5.05
5.39
1H NMR (200 MHz): 7.47–7.64 m (4H, ArH); 8.12 d (2H,
ArH); 8.20 d (2H, ArH); 8.28–8.34 m (4H, ArH)
1H NMR (200 MHz): 7.3–7.6 m (5H, ArH); 7.89 d (1H,
ArH); 7.97 d (1H, ArH); 8.10–8.18 m (2H, ArH); 8.25 d
(1H, ArH)
23
C21H16N2S
(328.43)
76.80
76.27
4.91
4.67
8.53
8.54
1H NMR (200 MHz): 1.16 t (3H, NCH2CH3); 4.50 q (2H,
NCH2CH3); 7.27–7.32 m (1H, ArH); 7.39–7.47 m (1H,
ArH); 7.49–7.58 m (2H, ArH); 7.68 d (1H, ArH); 7.78 d
(1H, ArH); 8.03 d (1H, ArH); 8.12 d (1H, ArH); 8.18 d
(1H, ArH); 8.37 d (1H, ArH); 8.91 s (1H, ArH)
1H NMR (600 MHz): 7.05 t (1H, ArH); 7.12 d (1H, ArH);
7.18 d (1H, ArH); 7.40 t (1H, ArH); 7.70 d (1H, ArH);
7.89 d (1H, ArH); 8.12 d (1H, ArH); 11.52 s (1H, OH)
1H NMR (600 MHz): 3.87 s (3H, CH3); 7.13 d (2H, ArH);
7.55 dd (1H, ArH); 8.00 d (1H, ArH); 8.04 d (2H, ArH);
8.28 d (1H, ArH)
1H NMR (600 MHz): 1.31 t (3H, NCH2CH3); 4.45 q (2H,
NCH2CH3); 7.20 t (2H, ArH); 7.46 t (2H, ArH); 7.56 d
(2H, ArH); 7.60 d (2H, ArH); 8.15 d (2H, ArH)
1H NMR (200 MHz): 3.04 s (6H, N(CH3)2); 6.83 d (2H,
ArH); 7.48–7.53 m (1H, ArH); 7.87–7.93 m (3H ArH);
8.21 d (1H, ArH)
24
25
26
27
C13H8ClNOS
(261.73)
59.66
59.19
3.08
2.89
5.35
4.92
C14H10ClNOS
(275.75)
60.98
60.79
3.66
3.11
5.08
4.82
C21H15ClN2S
(362.88)
69.51
69.75
3.08
3.43
5.35
5.61
C15H13ClN2S.
H2O(306.81)
58.72
58.43
4.93
4.24
9.13
9.01
28
29
C13H7ClN2O2S
(290.72)
C14H10N2O3S
(286.31)
53.71
54.15
58.73
58.49
2.43
2.86
3.52
3.24
9.64
9.75
9.78
9.31
1H NMR (200 MHz): 7.93 d (1H, ArH); 7.41–7.45 m (1H,
ArH); 8.12–8.21 m (5H, ArH)
1H NMR (600 MHz): 3.80 s (3H, CH3); 7. 20 d (1H, ArH);
7.53 d (2H, ArH); 7.79 d (1H, ArH); 8.03 d (1H, ArH);
8.16 d (2H, ArH)
30
C14H11NO2S
(257.31)
65.35
64.91
4.31
4.11
5.44
5.08
1H NMR (600 MHz): 3.86 s (3H, CH3); 7.01 t (1H, ArH);
7.07 d (1H, ArH); 7.14 dd (1H, ArH); 7.39 t (1H, ArH);
7.72 d (1H, ArH); 7.95 d (1H, ArH); 8.09 d (1H, ArH);
11.56 s (1H, OH)

GREEN SYNTHESIS OF 2-ARYLBENZOTHIAZOLES
2301
In some cases the products 3–34 crystallized, and in other cases they were precipitated by
dilution with cold water (50 mL). The compounds were isolated by filtration.
Analytical samples of the products were obtained by recrystallization from ethanol.
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