Epichlorohydrin cross-linked β -cyclodextrin: An environmental method for the synthesis of 2-arylbenzothiazoles derivatives in water

Article abstract of DOI:10.1080/17415993.2015.1089874

In the present study, we report an environmentally benign synthesis of 2-arylbenzothiazoles derivatives from o-aminothiophenol and aldehydes in aqueous medium using β-cyclodextrin polymer as a catalyst and air as an oxidant. The polymer showed excellent c

Full text of DOI:10.1080/17415993.2015.1089874

Journal of Sulfur Chemistry
ISSN: 1741-5993 (Print) 1741-6000 (Online) Journal homepage: http://www.tandfonline.com/loi/gsrp20
Epichlorohydrin cross-linked β-cyclodextrin:
an environmental method for the synthesis of 2-
arylbenzothiazoles derivatives in water
Mahmoud Abd El Aleem Ali Ali El-Remaily & Ahmed M. M. Soliman
To cite this article: Mahmoud Abd El Aleem Ali Ali El-Remaily & Ahmed M. M. Soliman
(2015): Epichlorohydrin cross-linked β-cyclodextrin: an environmental method for the
synthesis of 2-arylbenzothiazoles derivatives in water, Journal of Sulfur Chemistry, DOI:
10.1080/17415993.2015.1089874
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Date: 07 November 2015, At: 10:14

JOURNAL OF SULFUR CHEMISTRY, 2015
http://dx.doi.org/10.1080/17415993.2015.1089874
Epichlorohydrin cross-linked β-cyclodextrin:
an environmental method for the synthesis of
2-arylbenzothiazoles derivatives in water
Mahmoud Abd El Aleem Ali Ali El-Remaily and Ahmed M. M. Soliman
Department of Chemistry, Faculty of Science, Sohag University, Sohag, Egypt
ABSTRACT
ARTICLE HISTORY
Received 10 July 2015
Accepted 30 August 2015
In the present study, we report an environmentally benign syn-
thesis of 2-arylbenzothiazoles derivatives from o-aminothiophenol
and aldehydes in aqueous medium using β-cyclodextrin polymer
as a catalyst and air as an oxidant. The polymer showed excellent
catalytic activity, recovered, reused six times, and the catalyst effi-
ciency remained unchanged. This suggests that the catalyst is an
efficient and green catalyst for the synthesis of 2-arylbenzothiazoles
derivatives and the obtained results could be promising for industrial
synthesis of 2-arylbenzothiazoles derivatives.
KEYWORDS
β-Cyclodextrin polymer;
2-arylbenzothiazoles;
environmental; water
chemistry; air oxidant and
industry
1. Introduction
Cyclodextrins (CDs) are cyclic oligosaccharides composed of 6–8 glucopiranose units
(namely α-, β- and γ -CDs) linked by glycosidic bonds. CDs have been introduced into
many organic reactions in aqueous solution.[1–8] They are water soluble, non-toxic and
hydrophobic in the central cavity. The most significant characteristic of the CDs is their
ability to form inclusion complexes with different guest molecules in aqueous solution or
in the solid state through host–guest interactions.[9–11] β-CD is the cheapest among the
CD family and has been widely used in separation, catalysis and in organic reactions.[12–
15] It has played a vital role in activating substrate and improving its selectivity.[16–19]
Although β-CD exhibits good catalytic activity in liquid-phase oxidation, the separation
of β-CD from the homogeneous system is very difficult. Therefore, β-CD was immo-
bilized on appropriate supports, for example, organic, polymeric and mineral materials
CONTACT Mahmoud Abd El Aleem Ali Ali El-Remaily
msremaily@yahoo.com
© 2015 Taylor & Francis

2
M. A. A. EL-REMAILY AND A. M. M. SOLIMAN
in order to improve recyclability, easy recovery and cost-effectiveness.[20] Immobilized
β-CD not only shows good mechanical properties but also completely retains molecular
recognition and catalytic properties of cyclodextrins. One way for producing immobilized
β-CD (abbreviated as β-CDP) is through the reaction ofβ-CD molecules with bifunctional
cross-linking agents such as epichlorohydrin (EPI).[21–24]
Over the last few years, we are constantly working on development of new tools and
methodologies for synthesized bio active compounds by green catalyst.[25–34] On the
basis of exhaustive literature review, it has been found that 2-substituted benzothiazole
have good potential to exhibit anticancer activity.[35–46] Accordingly, in the present study,
we report the synthesis of 2-arylbenzothiazoles derivatives using β-cyclodextrin polymer
as a catalyst in an environmentally benign method which includes water as a solvent and
air as an oxidant.
2. Results and discussion
In this paper, we have screened β-cyclodextrin polymer as a catalyst in an environmental-
friendly synthesis of 2-arylbenzothiazoles derivatives 3a–p from o-aminothiophenol 1 and
aldehydes in water using air as an oxidant (Scheme 1). The use of β-CDP in water not only
gave high yield, selectivity and lower reaction time but also the whole process turned out
to be cheap, speedy, facile and eco-friendly (Table 1).
2.1. Infrared spectroscopy (FTIR) characterization
FTIR spectra of β-CD (a) and β-CDP (b) are shown in Figure 1. FTIR spectrum of β-CDP
is similar to that of β-CD, indicating that the frame of β-CD does not change during
Scheme 1. Synthesis of 2-arylbenzothiazoles 3a–p
.
Table 1. β-CDP as catalyst for the synthesis of 2-arylbenzothiazolesa 3a–p
.
Entry
No
R
Time (hour)
Yield (%)b
Entry
No
R
Time (hour)
Yield (%)b
1
2
3
4
5
6
7
8
3a
3b
3c
3d
3e
3f
H
4-Cl
4-Br
4-F
3-CH3
4-NMe2
4-NO2
4-MeO
2
2
2
2
3
2
2
2
98
97
96
96
95
94
98
97
9
10
11
12
13
14
15
16
3i
3j
3k
3l
3m
3n
3o
3p
4-OH
2-OH
2-Cl
2-NO2
2-MeO
2-pyridyl
2-Furyl
2-thienyl
2
3
3
3
3
4
4
4
92
90
93
96
95
92
91
90
3g
3h
aReaction conditions: 1(1 mmol), 2a (1.2 mmol) and catalyst (1 g) in 25 ml water.
bIsolated yields.

JOURNAL OF SULFUR CHEMISTRY
3
(a)
(b)
Figure 1. FTIR spectra of β-CD (a) and β-CDP (b).
Table 2. The effect of the reaction temperature for synthesis 2-phenylbenzothiazolea 3a.
Entry
Temperature
Conversionb (%)
Yieldc (%)
1
2
3
4
40
50
60
70
66
71
95
95
50
56
98
98
aReaction conditions: 1(1 mmol), 2a (1.2 mmol) and catalyst (1 g) in 25 ml water.
bConsumption of o-aminothiophenol.
cNMR yield.
the course of immobilization. The peaks of β-CDP at 3423 and 2874 cm−1 are stronger
than those of β-CD, and the increased intensity may be attributed to the presence of
more −OH and −CH2 groups in the β-CDP. The FTIR spectrum of β-CDP showed the
characteristic peaks at 1260 and 721 cm−1, indicating the presence of the expoxy group
in β-CDP. The peak at 1033 cm−1 in the β-CDP was assigned to the C−O or C−O−C
stretching in the β-CDP. The increase in the band intensity at around 1033 cm−1 might
be β-CD. In addition, the peak at 892 cm−1 in the β-CDP was the characteristic bands of
α-(1,4)-glucopyranose in β-CD.[47] Therefore, it could be concluded that β-CD had been
immobilized successfully onto β-CDP.
2.2. The effect of reaction temperature
The effects of the reaction temperatures on the yield of 2-phenylbenzothiazole and the
conversion of o-aminothiophenol are shown in Table 2.
As shown in Table 2, the synthesis of 2-phenylbenzothiazole promoted by β-CDP is
highly sensitive to the reaction temperature. At 50°C, both the conversion and the yield
were low. As the reaction temperature was increased to 60°C, both the conversion and
yield increased. Further increase in the reaction temperature was not beneficial to the yield
anymore and 60°C was chosen as the optimal reaction temperature.

4
M. A. A. EL-REMAILY AND A. M. M. SOLIMAN
Table 3. The effect of the amount of β-CDP for synthesis 2-phenylbenzothiazolea 3a.
Entry
Amount of β-CDP (g)
Conversion (%)b
Time (h)
Yield (%)
1
2
3
4
5
6
0
56
68
77
95
95
95
2
2
2
2
2
2
12
31
65
98
98
98
0.2
0.5
1
2
3
aReaction conditions: 1(1 mmol), 2a (1.2 mmol) and catalyst (1 g) in 25 ml water.
bConsumption of o-aminothiophenol.
2.3. The effect of the amount β-CDP
The effect of amount of the catalyst, that is, β-CDP on the yield of 2-phenylbenzothiazole
3a and the conversion of o-aminothiophenol were investigated by varying the catalyst
loading from 0 to 3 g. As shown in Table 3, β-CDP exhibited higher catalytic activity
for synthesis of 2-phenylbenzothiazole compared with that in blank experiment, where
no catalyst was used. The conversion of o-aminothiophenol increased with the amount
of catalyst, which might be attributed to the increased number of hydrophobic cavity
in β-CDP. Maximum conversion (ca. 95%) was obtained using 1.0 g of β-CDP, further
increase in the catalyst amount negatively affects the yield of 2-phenylbenzothiazole.
This is the first example to use β-CDP as a catalyst in water to restrain the conversion
while improving the selectivity and this method is particularly effective to enhance the
selectivity for those reactions in which the side reactions can happen smoothly with-
out β-CDP. The optimal amount of β-CDP used in the reaction is 1.0 g is shown in
Table 3.
2.4. Effect of stirring speed
Stirring speed has a great influence on the synthesis 2-phenylbenzothiazole by β-CDP
catalysis. The effect of stirring speed was investigated in the range of 100–800 rpm. The
results showed that the conversion of o-aminothiophenol significantly increased with an
increase in stirring speed. The conversion corresponding to a stirring speed of 500 rpm
was up to 94%, much higher than 45% at a stirring speed of 100 rpm. Beyond this point
(500 rpm), an increase in stirring speed had no significant influence on the conversion
of o-aminothiophenol. These results indicated that the conversion of o-aminothiophenol
was strongly dependent on the dispersion extent of the organic phase in aqueous phase,
which promoted the mass transfer between the two phases to improve the selectivity of
2-phenylbenzthiazole.
2.4.1. Scale-up experiment
Besides, in order to verify the efficiency of the catalytic system, a scale-up experiment for
the synthesis of 2-phenylbenzothiazole catalyzed by β-CDP in water under the above opti-
mum reaction conditions was carried out as shown in Scheme 1. The isolated yield of
2-phenylbenzthiazole was 98%. In comparison with the prior reports, the current pro-
cess realized the clean synthesis of 2-phenylbenzothiazole and provided high yield to

JOURNAL OF SULFUR CHEMISTRY
5
Figure 2. The possible reaction mechanism.
the product under mild reaction conditions, which is very important to preserve natural
essence of 2-phenylbenzothiazole during the reaction process.
2.5. Reaction mechanism
The mechanism for β-CDP catalysed synthesis 2-phenylbenzothiazole based on above
experimental results has been proposed in Figure 2. β-CD in the β-CDP and
o-aminothiophenol can form the inclusion complex via intermolecular hydrogen bonding
O—H O at the second rim of β-CD still retained in the cavity. Then, benzaldehyde entered
into the cavity from the primary side, with the aldehyde group pointed towards the sec-
ondary side to react with amidine resulting in the formation of a Schiff’s base. The oxidative
cyclodehydrogenation of reaction intermediate, that is, the Schiff’s base using air as an oxi-
dant occurred inside the β-CD cavity and finally resulted in the 2-phenylbenzothiazole
formation.[17,18]
2.6. Reusability of the catalyst
The insoluble β-CDP could be easily recycled by centrifugation after the reaction. The
recovered β-CDP was washed successively with ethanol and deionised water. After drying,
the catalyst was reused for the next run under the same condition. The results indicated that
the catalytic activity was not affected significantly over the consecutive cycles. The catalyst

6
M. A. A. EL-REMAILY AND A. M. M. SOLIMAN
Figure 3. Recyclability of β-CDP in the model reaction.
was reused for six cycles and it retains the catalytic activity and the selectivity during
recycling experiments (cf. Figure 3).
3. Conclusion
This work provides an easy access to efficient synthesis of 2-arylbenzothiazoles derivatives
under mild reaction conditions with easy recovery of the catalyst β-CDP. This water-
mediated reaction is mild, easy to handle, economic and eco-friendly. This method is
bestowed with merits such as high yield, cost-effectiveness, biomimetic, neutral aqueous-
phase conditions and environmentally benign nature. These advantages of the catalyst
made it preferential for the synthesis of 2-arylbenzothiazoles derivatives in the industrial
process.
4. Experimental
4.1. Catalyst preparation
According to the previous report,[48–51] a typical procedure for the preparation of β-CDP
was described as follows: β-CD (5 g, 0.44 mmol) was mixed with 8 mL NaOH (50%, w/w)
solution and mechanically stirred for 20 min till β-CD was completely dissolved. Then,
15 mL epichlorohydrin (EPI) was slowly added to the reaction mixture. The reaction mix-
ture was polymerized at 65°C under vigorous stirring (200 r.min−1). After stirring for
about 1–2 h, precipitate could be observed, and the viscosity of the solution was also
increased. The solution was mixed with 100 ml acetone, and the insoluble polymers were
poured into water. The resultant product was filtrated, and further washed with acetone in a
Soxhlet extractor for 24 h. After drying in oven at 80°C for 12 h under vacuum, the polymer
product was crushed and granulated to 160–250 μm in diameter. The content of β-CDP in
immobilized β-CDP, measured by the phenolphtalein decoloration method according to
the literature report,[52] was found to be 50%.
4.2. Catalyst characterization
The FTIR spectra of samples were measured by KBr pellet. All the infrared spectra were
recorded on a Shimadzu DR-8001 spectrometer with wave numbers ranging from 400 to
4000 cm−1
.

JOURNAL OF SULFUR CHEMISTRY
7
4.3. General procedure for the synthesis of 2-arylbenzothiazole
For a typical reaction run, o-aminothiophenol (1 mmol, 125 mg) was dissolved in
deionised water (25 mL) at 60°C in a 100 mL 3-necked round bottom flask fitted with a
reflux condenser and magnetic stirrer. β-CDP (1 g) was added to the vessel and the mixture
was heated to 60°C in an oil bath with electric heater. Substituted aldehyde (1.2 mmol) was
added to the reaction system and it was stirred for 2 h at 60°C. The progress of the reaction
was monitored by TLC. When the reaction was finished, the mixture was extracted with
ethyl acetate and dried over anhydrous sodium sulfate. Then, ethyl acetate was removed in
vacuum. All of the products are known compounds and characterized easily by comparison
with melting point, IR and 1H NMR spectral data reported in literature.[53–56]
4.4. Scale-up experiment
The large-scale reaction experiment was performed under the following optimum reac-
tion conditions: a mixture of β-CDP (100 g) and 250 ml deionised water was stirred at
60°C. Subsequently, o-aminothiophenol (100 mmol) was added. After 1 h, 120 mmol of
benzaldehyde was added, the reaction system was then stirred for 2 h. After the reaction,
the solution was extracted by ethyl acetate, and crude product was obtained in 98% yield.
Acknowledgement
The authors are deeply gratitude to both of Sohag University in Egypt for supporting and facilitating
this study.
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