Copper supported on functionalized MCM-41 as a novel and a powerful heterogeneous nanocatalyst for the synthesis of benzothiazoles

Article abstract of DOI:10.1016/j.poly.2018.11.005

A new functionalized mesoporous catalyst (Cu(II)-Glycerol/MCM-41) has been synthesized as a highly efficient heterogeneous nanocatalyst for the synthesis of benzothiazoles derivatives. Powder XRD, TGA, TEM, SEM, EDX, BET, FT-IR and ICP-OES techniques are

Full text of DOI:10.1016/j.poly.2018.11.005

Accepted Manuscript
Copper Supported on Functionalized MCM-41 as a Novel and a Powerful Het-
erogeneous Nanocatalyst for the Synthesis of Benzothiazoles
Nader Noroozi Pesyan, Hana Batmani, Forugh Havasi
PII:
S0277-5387(18)30723-X
https://doi.org/10.1016/j.poly.2018.11.005
POLY 13552
DOI:
Reference:
Polyhedron
To appear in:
Received Date:
Revised Date:
Accepted Date:
19 May 2018
30 October 2018
3 November 2018
Please cite this article as: N. Noroozi Pesyan, H. Batmani, F. Havasi, Copper Supported on Functionalized MCM-41
as a Novel and a Powerful Heterogeneous Nanocatalyst for the Synthesis of Benzothiazoles, Polyhedron (2018),
doi: https://doi.org/10.1016/j.poly.2018.11.005
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Copper Supported on Functionalized MCM-41 as a Novel and a Powerful
Heterogeneous Nanocatalyst for the Synthesis of Benzothiazoles
Nader Noroozi Pesyana*, Hana Batmania and Forugh Havasib
a Department of Organic Chemistry, Faculty of Chemistry, Urmia University 57159, Urmia,
IRAN
b Department of Chemistry, Faculty of Sciences, University of Kurdistan, P.O. Box 66315-
416, Sanandaj, IRAN
*E-mail address: n.noroozi@urmia.ac.ir ; nnp403@gmail.com
Abstract
A new functionalized mesoporous catalyst (Cu(II)-Glycerol/MCM-41) has been synthesized
as a highly efficient heterogeneous nanocatalyst for the synthesis of benzothiazoles
derivatives. Powder XRD, TGA, TEM, SEM, EDX, BET, FT-IR and ICP-OES techniques
are employed to characterize the prepared nanocatalyst. These one-pot reactions were carried
out under green and mild reaction conditions in EtOH as a green solvent and the catalyst can
be reused up to 5 consecutive cycles without significant change in its catalytic activity.
Keywords: mesoporous silica, copper, benzothiazoles, green reaction conditions.
1. Introduction
Benzothiazols are a most important scaffold of heteroaromatic compounds in organic
chemistry [1], and its derivatives due to their building blocks in biological and therapeutic
activities are vital core structures used to create drugs, for instance antiviral [2], antiulcer [3],
antioxidant, antibacterial [4], anti-diabetes [5], anticancer [6], enzyme inhibition [7]. Further,
benzothiazole rings are found in a myriad of natural products, for example vitamin B12 [8]
and also organic functional materials such as fluorescent dyes [9].
According to previous literatures, several approaches for the formation of benzothiazole
formatives have been reported [10] such as synthesis of 2-aryl(alkyl)benzothiazoles from 2-
1

aminothiophenol and aldehydes in air/DMSO oxidant system [11], using iron phthalocyanine
as a catalyst [12] and one of them is the condensation of 2-aminothiophenol with carbonyl
compounds [13].
However, these procedures, suffer from drawbacks or harsh reaction conditions such as high
temperature, use of toxic reagents, air-sensitive, strong acid catalysts, low yields and etc.
These factors stimulate chemists to search and develop a more effective and environmentally
friendly process [14]. In the past few decades, the use of heterogeneous catalysts as a
reusable, economic and green catalyst has attracted a much attentions in academic and
industrial purposes [15].
In continuation of our studies, on functionalizing nanoparticles with variant derivatives for
catalysis applications, we would like to report a facile procedure for the synthesis of
benzothiazoles drivatives from aminothiophenol and various aldehydes catalyzed by a novel
heterogeneous nanocatalyst (Cu(II)-Glycerol/MCM-41) as a highly efficient and reusable
o
nanocatalyst under mild conditions in green solvent (EtOH) at 25 C. Scheme 1 shows the
details of the supported catalyst preparation procedure.
1) (MeO)3Si(CH2)3Cl, n-Hexane,
Reflux, 24 hrs
2) Glycerol, Et3N, 80 oC, 24 hrs
3) CuCl2, EtOH, Reflux, 20 hrs
OH
OH
O
O
O
Si
O
O
O
OH
OH
Cu
MCM-41-Glycerol-Cu
Scheme 1. Details of process for the Synthesis of Cu(II)-Glycerol/MCM-41
2. Results and discussion
2

2.1.
Characterization of the nanocatalyst
The structure of nanocatalyst was characterized by Fourier transform infrared spectroscopy,
thermogravimetry, inductively coupled plasma-optical emission spectrometry, scanning
electron microscopy, Energy dispersive X-ray, X-ray powder diffraction and Brunauer-
Emmet-Teller techniques.
Figure 1 displays scanning electron microscopy (SEM images) of the synthesized
nanocatalyst. These images reveal spherical structure and confirm that the catalyst was
formed of uniform nanometer-sized particles, and the morphology of Cu(II)-Glycerol/MCM-
41 (Figure 1b), is similar to the particle form of MCM-41 (Figure 1a), also can be seen that
the size of the nanoparticle is 80 nm.
(a)
(b)
Figure 1. SEM of the synthesized MCM-41 (a) and Cu(II)-Glycerol/MCM-41 (b)
Figure 2 reveals the FT-IR spectra obtained for (curve a) MCM-41, (curve b) CPTMS/MCM-
41, (curve c) Glycerol/MCM-41 and (curve d) Cu(II)-Glycerol/MCM-41. Curve (a) shows
the spectrum of MCM-41 and signals appeared at 1075-800 and 450 cm-1 are corresponding
to Si-O and Si-O-Si stretching vibration respectively. Curve (b) exhibit absorption band at
2930 cm-1 which is mainly due to C–H stretching. The signals in the spectral region of 3400
and 1230 cm-1 can be assigned to O–H and C–O stretching vibrations of glycerol (Figure 2c).
3

As shown in Figure 2d, the curve displayed successful coordination of Cu within the channels
of mesoporous.
Figure 2. FT-IR spectra of, (a) MCM-41, (b) CPTMS/MCM-41, (c) Glycerol/MCM-41 and (d)
Cu(II)-Glycerol/MCM-41
The small angle powder diffraction (XRD) patterns of both MCM-41 and Cu(II)-
Glycerol/MCM-41 are displayed in Figure 3. The XRD patterns of the nano particles show
three well-resolved peaks indicative of the (100), (110) and (200) diffractions. The intensity
4

peaks of MCM-41 after functionalization became weak. This result indicates that the organic
compounds and Cu are located inside the channels of the mesoporous structure.
Figure 3. Low-angle powder XRD pattern of (a) MCM-41 and (b) Cu(II)-Glycerol/MCM-41
The EDX (Energy dispersive X-ray) data evidently shows the presence of Si, C, O, Cl, and
Cu in functionalized mesoporous MCM-41 (Figure 4).
5

2000
1500
1000
500
0
Si
C: 20.80 %
O: 28.24 %
Si: 36.86 %
Cl: 8.37 %
Cu: 5.73 %
O
Cl
Cl
Cu
Cu
C
Cu
keV
10.00
0
Figure 4. The EDX spectrum of Cu(II)-Glycerol/MCM-41
N2 adsorption-desorption isotherms of the prepared MCM-41 and Cu(II)-Glycerol/MCM-41
are reported in Figure 5. After incorporation substance in the framework of MCM-41, the
original surface area (SBET) of 1000 m2/g and total pore volume (Vtotal) of 1.3 cm3/g were
reduced to 600 and 0.7, respectively [16]. Moreover, the wall diameter of 1.1 nm was
increased to 2.9 nm. These results confirm the successful anchored of the Cu on the surface
of mesochannels.
6

Figure 5. N2 adsorption–desorption isotherms for, (a) MCM-41 and (b) Cu(II)-Glycerol/MCM-41
Figure 6 is indicative of the thermal gravimetric analysis (TGA) curves of (a) MCM-41, (b)
CPTMS/MCM-41, (c) Glycerol/MCM-41 and (d) Cu(II)-Glycerol/MCM-41 which shows a
weight loss due to the decomposition upon heating. The small amount of weight loss below
200 degrees Celsius is attributed to the removal of solvent molecules. The weight loss within
range of 200-800 degrees Celsius is associated with the decomposition of organic functional
groups located inside framework. The TGA diagrams confirmed the formation of Cu
complex.
7

Figure 6. TGA thermograms of (a) MCM-41, (b) CPTMS/MCM-41, (c) Glycerol/MCM-41 and (d)
Cu(II)-Glycerol/MCM-41
Determination of the loading exact amount of copper into the mesoporous silica MCM-41
was carried out ICP–OES analysis. The Cu content of the nanocatalyst was 4.5 %.
2.2. Application of Cu(II)-Glycerol/MCM-41 complex for the synthesis of benzothiazoles
After characterization of the nanocatalyst structure, we investigated the catalytic activity of
Cu(II)-Glycerol/MCM-41 complex as a new and recyclable nanocatalyst for the synthesis of
benzothiazoles. The parameters such as catalyst amount, reaction temperature and kind of
solvent were optimized initially in the reaction of o-aminothiophenol with benzaldehyde as a
test model (Table 1). In the first step, various amounts of the nanocatalyst was tested. Control
experiments confirmed that no desired product was obtained in the absence of a Cu(II)-
Glycerol-MCM-41 (Table 1, entry 1) and the best result was obtained in the presence 7 mg of
nanocatalyst (Table 1, entry 2). As it can be seen from Table 1, different solvents including
8

CH3CN, CH2Cl2, MeOH, EtOH, PEG and EtOAc were tested (Table 1, entries 3-8). And the
EtOH is more effective for this reaction (Table 1, entry 2). The effect of the temperature was
also examined, that the best result for the reaction was room temperature (Table 1, entry 2). It
was found that 7 mg of Cu(II)-Glycerol-MCM-41 in EtOH at 25 degrees Celsius is the best
conditions for the synthesis of benzothiazoles.
Table 1. Optimization of reaction conditions
H
O
C
NH2
SH
N
S
Cu(II)-Glycerol/MCM-41 (Cat.)
Solvent, T oC
+
3a
1
2a
Entry
Cat. (mg)
Solvent
EtOH
Temp (°C)
Time (h)
Yield (%)a
1
2
3
4
5
6
7
8
0
7
5
7
7
7
7
7
rt
rt
rt
5
3
-
EtOH
EtOH
98
65
65
40
65
80
60
5
PEG
60
60
rt
3
EtOAc
CH2Cl2
MeOH
CH3CN
5
6
rt
3.5
3
rt
Reaction conditions: o-aminothiophenol (1.0 mmol), benzaldehyde (1.0 mmol), aIsolated
yields provided.
With these results in hand, to study the utility and generality of this approach, the
catalytic activity of Cu(II)-Glycerol-MCM-41 was further explored for wide variety of
substituted benzaldehydes, and the outcomes are listed in Table 2.
Table 2. Reaction of o-aminothiophenol with different benzaldehydes in EtOH at room
temperature
Entry
Product (3) a
Time (h)
Yield (%)b
9

N
S
1
2
3
2
98 [11,17]
97 [17]
a
N
S
NO2
b
NO2
N
S
3
4
5
2.5
2.5
3
96 [11,17]
96 [11,17]
94 [17]
c
N
Cl
S
d
Cl
N
S
e
Cl
N
6
3.5
92 [11,17]
S
f
N
N
S
7
8
4
95 [17]
g
h
N
S
CH3
3.8
92 [11,17]
OMe
OMe
OMe
N
S
9
5
4
88 [17]
i
N
OCH3
S
10
89 [11,17]
j
10

HO
N
S
11
12
4.5
4.5
87 [17]
84 [17]
k
N
NH
S
l
a The products were identified and characterized by comparison of their
physical and spectral data with those of authentic samples. b Yields refer to
those purified products.
The results revealed that the reaction worked excellent for a wide range of substituted
benzaldehyde and the reaction was quite general. The results showed that benzaldehyde with
electron-withdrawing groups such as 4-nitrobenzaldehyde reacted quickly than the
benzaldehyde with the electron-donating substituents such as 4-methylbenzaldehyde (Table
2, entries 2 and 8). The sterically hindrance of the substituted benzaldehyde significantly
influenced the catalytic efficiency. For instance, the sterically hindered o-chlorobenzaldehyde
furnished the target product in lower yield and longer reaction times than p-
chlorobenzaldehydes (Table 2, entries 6 and 4). One of the important aspects of this method
is the successful reaction of indole-3-carboxaldehyde as model compounds for
heteroaldehyde with o-aminothiophenol to give the target products in high yields (Table 2,
entry 12).
According to the previous literatures, a proposed mechanism is shown in Scheme 2.
Firstly, 2-aminothiophenol (1) reacts with benzaldehyde (2a) to form an imine intermediate A
[12,18]. Then the intermediate cyclizes to heterocycle 4a. Upon formation, ready oxidation of
4a gives the desired 2-arylbenzothiazoles [17-19].
11

Cu(II)
SH
SH
N
Cu-Glycerol-MCM-41
Ar
(-H2O)
O
+
H
NH2
Ar
A
1
2
Cu(II)
[O]
S
S
Ar
Ar
N
N
H
air/O2
3
4
Scheme 2. Proposed mechanism for the synthesis of benzothiazoles in the presence of Cu(II)-
Glycerol-MCM-41
3. Experimental
3.1. Materials and apparatus
All reagents and solvents emploied in this work were obtained from Sigma-Aldrich, Fluka,
and Merck chemical companies and utilized without any purification. Proton nuclear
magnetic resonance (400 MHz) and carbon nuclear magnetic resonance (100 MHz) spectra
were measured with BRUKER NMR-Spectrometer. The FT-IR analyses were carried out
with Nexus 670 FT-IR spectrometer. TLC (Thin layer chromatography) analysis was applied
over Merck silica gel SIL G/UV254 plates. The content of Cu was measured by ICP-OES
(Model: VISTA-PRO, Varian, Australia). The catalyst pore volume, Surface area and average
pore size were determined with nitrogen adsorption–desorption isotherms at liquid N2
temperature. The crystalline structure of synthesized samples were recorded by XRD using a
Co radiation source under the conditions of 40 kV and wavelength λ = 1.78897 Å. TGA of
the samples were performed on a Shimadzu DTG-60 apparatus. SEM measurements were
performed with FESEM-TESCAN MIRA3. Finally, the catalyst component measurement
was carried out by the EDX using a FESEM-TESCAN MIRA3.
3.2.
Preparation of Cu (II)-Glycerol/MCM-41
12

The
solution
containing
480
ml
distilled
water,
1.0
cetyltrimethylammonium bromide (CTAB) and 3.5 ml NaOH (2 M) was stirred at 80 °C.
Next, 5 ml of TEOS was added drop-wise into the solution and the obtained mixture was
refluxed under continuous stirring for 2 hrs. The resulted mesoporous Si-MCM-41 was
filtered and washed by distilled water and dried in an oven at 70 °C followed by calcination
at 550 °C for 5 hrs with a ramp 2 °C min-1. The obtained MCM-41 nanoparticles (4.8 g) with
3-chloropropyltrimethoxysilane (CPTMS, 5.0 g) was added to n-hexane (96 ml). The reaction
mixture was stirred under refluxing and argon atmosphere for 24 hrs. Then, the prepared
nanoparticles (CPTMS/MCM-41) was filtered, washed with n-hexane and dried under
vacuum. Subsequently, (1 g) of CPTMS/MCM-41 was added onto the solution of (50 ml)
Glycerol and (2 mL) Et3N, and then the reaction mixture was stirred at 80 oC for 24hrs. Then,
the product (Glycerol/MCM-41) was filtered and washed by dry ethanol and dried in vacuum
oven at 60 °C. In the final step to a solution of (3 g) Glycerol-MCM-41 in (50 ml) ethanol
was added 1 g of CuCl2 and stirred under reflux for 20 hrs. The Cu(II)-Glycerol-MCM-41
was then collected by filtration and washed with ethanol and dried in vacuum at 60 °C .
3.3.
General procedure for the synthesis of benzothiazoles
In a 25-mL, round-bottom flask, a mixture of o-aminothiophenol (1.0 mmol), aldehyde (1.0
mmol) and Cu(II)-Glycerol-MCM-41 (7 mg) in EtOH (3 mL) was stirred magnetically at
room temperature for the appropriate time (Table 1). After completion of the reaction, as
indicated by TLC, the reaction mixture was filtered to isolate the nanocatalyst and the crude
product (filtrate) was purified by column chromatography on silica gel or recrystallization in
toluene to give the desired products.
4. Reusability of heterogeneous catalyst
The reusability of the nanocatalyst supported on mesoporous was investigated in the
synthesis of benzothiazole under the optimized conditions. For this study, we used the
benzaldehyde in the reaction with o-aminothiophenol for the synthesis of benzothiazole 3a.
After completion of each run, isolation of the Cu(II)-Glycerol-MCM-41 was easily performed
by centrifugation process. The solid catalyst was extensively rinsed with EtOH and ethyl
acetate to remove residual product and dried in an oven at 80 degrees Celsius and then used
directly in the next run without changing the reaction conditions. The data showed that this
13

nanocatalyst can be reused in five successive reactions without any decrease in the catalytic
efficiency (Figure 7). Also the nature of the recovered catalyst was investigated using XRD
pattern (Figure 8), EDX (Table 3) and TEM (Figure 9). According to EDS measurements the
amount of Cu was determined for unreacted catalyst (5.73%) and after fifth run (2.64%).
Figure 9 show the TEM image of representative region of Cu(II)-Glycerol-MCM-41 and
highly ordered hexagonal arrangement of pores can be clearly observed after five recycles of
Cu(II)-Glycerol-MCM-41. These results for the recovered catalyst indicate that the catalyst
can be recycled five time successfully without any significant change in its structure or
mesoporosity in silicate parent.
To examine leaching of copper in reaction mixture and heterogeneity of described catalyst,
we performed hot filtration for the synthesis of benzothiazoles derivatives from the reaction
of o-aminothiophenol and benzaldehyde. In this experiment, we obtained the yield of product
in half time of the reaction that it was 55%. Then, the reaction was repeated and in half time
of the reaction, the catalyst separated and allowed the filtrate to react further. We found that,
after this hot filtration, no further reaction was observed. The yield of reaction in this stage
was 55% that confirmed the leaching of copper is little.
14

Figure 7. Reusability of the Cu (II)-Glycerol-MCM-41 nanocatalyst
15

2000
1500
1000
500
0
Cu(II)-Glycerol/MCM-41
Recovered Cu(II)-Glycerol/MCM-41
2
4
6
8
10
2 Theta (degrees)
Figure 8. XRD pattern of recovered Cu (II)-Glycerol/MCM-41 nanocatalyst
Table 3. EDX data of recovered Cu (II)-Glycerol-MCM-41 nanocatalyst
Elt
C
Line Int
W%
A%
Ka
Ka
Ka
Ka
La
6.4
27.76
31.85
27.78
9.96
41.17
35.46
17.62
5.01
O
47.0
212.0
43.5
5.7
Si
Cl
Cu
2.64
0.74
100.00
100.00
16

Figure 9. TEM image of recovered Cu (II)-Glycerol-MCM-41 nanocatalyst
5. CONCLUSION
In conclusion, we have demonstrated a novel type of recoverable nanostructure that
was synthesized by supporting of Cu complex on MCM-41 nanoparticles (Cu(II)-Glycerol-
MCM-41) and characterized by variant techniques such as SEM, BET, XRD, TGA, EDX,
FT-IR and ICP-OES. The Cu-complex (Cu(II)-Glycerol/MCM-41) very effectively catalyzed
the formation of benzothiazoles from o-aminothiophenol and aldehydes. The significant
advantages of this catalytic procedure are: easy and inexpensive preparation, high reusability
and high air or moisture stability of nanocatalyst, green solvent, eco-friendly, room
temperature, easy workup, high functional group acceptability, short reaction times, excellent
reaction yield and simple purification methods.
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Graphical Abstract
Copper Supported on Functionalized MCM-41 as a Novel and a Powerful
Heterogeneous Nanocatalyst for the Synthesis of Benzothiazoles
Hana Batmania, Forugh Havasib and Nader Noroozi Pesyana*
NH2
SH
CHO
Ar
N
S
Cat.
+
Ar
Solvent, T oC
More than 85% yield
12 examples
O
O
O
Si
O
O
Cu
O
Cu(II)-Glycerol/MCM-41 (Cat.)
19

20