Synthesis, characterization, and applications of novel Co(II)-pyridoxal phosphate-Schiff base/SBA-15 as a nanocatalyst for the green synthesis of benzothiazole heterocycles

Article abstract of DOI:10.1002/jccs.201900518

Mesoporous heterogeneous santa barbara amorphous (SBA)-15-supported cobalt complex, as a novel nanocatalyst containing N–O chelating Schiff-base ligand was successfully synthesized by the reaction of SBA-15 and Cobalt(II)-Schiff-base complex. The Co(II)-S

Full text of DOI:10.1002/jccs.201900518

Received: 2 December 2019
DOI: 10.1002/jccs.201900518
Revised: 7 March 2020
Accepted: 10 March 2020
A R T I C L E
Synthesis, characterization, and applications of novel
Co(II)-pyridoxal phosphate-Schiff base/SBA-15 as a
nanocatalyst for the green synthesis of benzothiazole
heterocycles
Hassan Yari1 | Rahebeh A. Dehkharghani1 | Ghasem R. Bardajee2
Niloufar Akbarzadeh-T3
|
1Department of Chemistry, Islamic Azad
Abstract
University, Central Tehran Branch
(IAUCTB), Tehran, Iran
Mesoporous heterogeneous santa barbara amorphous (SBA)-15-supported
cobalt complex, as a novel nanocatalyst containing N–O chelating Schiff-base
ligand was successfully synthesized by the reaction of SBA-15 and Cobalt(II)-
Schiff-base complex. The Co(II)-Schiff base complex also was prepared for the
first time, by the reaction of pyridoxal 50-phosphate or PLP (biological active
form of vitamin B6), 3-(aminopropyl)-triethoxysilane in methanol that com-
plexation with CoCl2. The subsequent grafting of entitled complex to SBA-15
afforded Co(II)-PLP-Schiff base/SBA-15 mesoporous catalyst. Characterization
of the product was carried out with powder X-ray diffraction, Brunauer–
Emmett–Teller nitrogen adsorption–desorption, transmission electron micros-
copy, scanning electron microscopy, thermogravimetric analysis, atomic
absorption spectroscopy, and inductively coupled plasma, Fourier-transform-
infrared spectroscopy. The results revealed the retention of the textural prop-
erties and hexagonally uniform structures of SBA-15 during the grafting
procedure. This nanocatalyst was applied successfully for one-pot synthesis of
various benzothiazole heterocycles under green conditions. This catalyst is an
active, reusable, and stable nanomaterial with no leaching of metal ions to the
reaction medium. It was used for the synthesis of desired benzothiazole hetero-
cycles by the cyclo-condensation of aryl-aldehydes with 2-aminothiophenol
with good to excellent yields and under green conditions.
2Department of Chemistry, Payame Noor
University (PNU), Tehran, Iran
3Department of Chemistry, University of
Sistan and Baluchestan, Zahedan, Iran
Correspondence
Rahebeh A. Dehkharghani, Department
of Chemistry, Islamic Azad University,
Central Tehran Branch (IAUCTB),
P.O. Box 1499669191, Tehran, Iran.
Email: rahebeha@gmail.com, rah.amiri@
iauctb.ac.ir
Funding information
Payame Noor University
K E Y W O R D S
cobalt Schiff base complex, mesoporous, SBA-15, nanocatalyst
1 | INTRODUCTION
nanostructure with desirable properties like noticeable
thick pore walls, large surface areas, narrow pore size dis-
The interesting, highly ordered hexagonal mesoporous
silica santa barbara amorphous (SBA)-15 is an important
tributions, and high thermal and high mechanical stabil-
ity. It has different applications in the field of catalysis,
© 2020 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
J Chin Chem Soc. 2020;1–11.
http://www.jccs.wiley-vch.de
1

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YARI ET AL.
adsorption, and separation.[1–7] This compound is also
widely used in drug delivery systems and as solid mate-
rials for supporting of the molecular catalysts in order to
introduce them as heterogeneous catalyst.[8–10] Schiff
bases are versatile organic compounds, which have
azomethine (─HC═N─) functional group. They can be
easily synthesized by the condensation reaction between
aldehydes or ketones with primary amines. They are
important ligands in the synthesis of chelating agents in
coordination chemistry, various dyes, pigments, and poly-
mer stabilizers.[11] Most of the Schiff bases which are pre-
electrophilic catalyst, thereby to stabilize different types of
carbanionic reaction intermediates. PLP also acts as a coen-
zyme in all transamination reactions, decarboxylation, deam-
ination, and racemization reactions of amino acids. The
aldehyde group of PLP forms a Schiff-base linkage (internal
aldimine) with amino groups.[35–37] Cobalt (II)-complexes of
Schiff base ligands have been demonstrated to be the efficient
catalysts for a wide range of reactions, and the covalent
anchoring of such complexes onto the SBA-15 is an efficient
way to supply an effective solid support heterogeneous
catalyst.[38–43]
This
mesoporous
catalyst
can
pared
from
aryl-amines
with
benzaldehydes,
contain advantages such as ease of separation, good
recycling ability, selectivity, and high activity in the
related applications.[44–49] This catalyst displays ordered
mesoporous hexagonal and uniform channels, implies
extensive surface area with high dispersion of cobalt com-
plex, and convenient diffusion of reactant molecules into
the pore channels of SBA-15 composition. We used this
catalyst for the synthesis of benzothiazole derivatives. Ben-
zothiazoles are privileged bicyclic ring systems with multi-
ple applications. Benzothiazole nucleus is found to possess
a number of biological activities such as anticancer,
antimicrobial, antidiabetic, anti-inflammatory, antiviral,
antileishmanial, and also antiviral component.[50,51]
salicylaldehyde, amoxicillin, pyridoxal, and sul-
phamethoxazole, act as antibacterial agents.[12,13] Schiff
bases are able to coordinate with transition metals as elec-
tron donating atoms, via nitrogen lone pare electrons, and
also the biological activities of the Schiff bases can be
enhanced by these complexes, especially with Co, Ni, Cu,
and Zn ions.[14–18] In addition, Schiff base metal complexes
are exhibiting suitable modes to stabilize them in various
oxidation states.[19–22] They are applicable in medicinal
and pharmaceutical fields due to a broad spectrum of bio-
logical and analytical activities like anti-inflammatory,
analgesic, antimicrobial, anticonvulsant, antituberculosic,
anticancer, antioxidant, anthelmintic, fungicidal, antidepres-
sants, antitumor, nematocide, and anticarcinogenic.[23–28]
Schiff bases are widely used as catalysts and many Schiff base
complexes also show excellent catalytic activity in various
reactions, and there have been many reports on their applica-
tions in homogeneous and heterogeneous catalyses.[29–33] We
used pyridoxal 50-phosphate (PLP) and 3-(aminopropyl)-
triethoxysilane (APTEOS) for the preparation of Schiff base
ligand in complexation with transition metal and anchored it
into SBA-15 (Scheme 1). PLP is water-soluble, naturally pre-
sent in many foods, and available as a dietary supplement.[34]
The versatility of PLP arises from its ability to perform cova-
lent bonding to the substrate and then to act as an
2 | RESULTS AND DISCUSSION
2.1 | Characterization of Co(II)-PLP-
Schiff base/SBA-15 catalyst
The Co(II)-PLP-Schiff base/SBA-15 mesoporous catalyst
was prepared according to Scheme 1. The fourier-trans-
form infrared (FT-IR) spectra of pure SBA-15 (a), and
Co(II)-PLP-Schiff base/SBA-15 (b) are shown in Figure 1.
As can be seen in this figure, the FT-IR spectrum of SBA-
15 (a) and Co(II)-PLP-Schiff base /SBA-15 (b), shows
bands associated with both SBA-15 (a) and the catalyst
(b). The broad band at 3,436 cm−1 attributed to hydroxyl
stretching vibrations, and it can be referred as charac-
teristics of Co(II)-PLP-Schiff base /SBA-15.[48] The
strong stretching bond at around 1,635 cm−1 represen-
ted azomethine C═N bonds. In addition, the silica
framework stretching of Si─O─Si and the bending
vibration of Si─O─Si can be detected at around 1,100
and 800 cm−1, respectively. The appearance of C─O
stretching at 1,075–1,250 cm−1 attributed to the
involvement of the phenolic OH group in coordination
during complex formation (Figure 1b).[44] The charac-
terization and textural properties of SBA-15 material
were discussed by powder X-ray diffraction (XRD) and
N2 adsorption/desorption analyses. The small-angle
XRD pattern of both SBA-15 (a), and Co(II)-PLP-Schiff-
Si (OEt ) 3
MeOH
Si (OEt ) 3
OH
OH
O
O
N
OH
P
HO
P
HO
H2N
+
O
O
O
OH
N
O
N
O
P
CoCl2 . 6 H2O
SBA-15
O
P
HO
HO
O
HO
HO
OEt
N
N
N
Si OEt
OEt
O
N
O
Co
Co
O
SBA-15
OEt
N
O
N
N
Si OEt
OEt
N
HO
HO
O
P
O
HO
HO
O
P
O
PLP-Schiff base Complex
Co (II)-PLP-Schiff base/SBA-15
SCHEME 1 Co(II)-PLP-Schiff base/SBA-15 synthesis

YARI ET AL.
3
FIGURE 1 FT-IR spectra of SBA-15 (a) and Co(II)-PLP-Schiff
base/SBA-15 (b)
FIGURE 3 TEM image of Co(II)-PLP-Schiff base/SBA-15
catalyst (a) SEM image of Co(II)-PLP-Schiff base/SBA-15 catalyst
(b) EDX image of Co(II)-PLP-Schiff base/SBA-15 catalyst (c)
FIGURE 2 XRD pattern of SBA-15 (a) and Co(II)-PLP-Schiff
base (b)
base/SBA-15 catalyst (b) is shown in Figure 2. The XRD
pattern displays three peaks in low angle, that can be inde-
xed to (100), (110), and (200) reflections in the hexagonal
two-dimensional space group for the mesoporous silica
SBA-15, and the XRD peaks of (b) shift to lower angle
than (a). This phenomenon suggests the development of
unit cell due to the connection of the complex within
SBA-15. Also, the XRD patterns of (a) and (b) in Figure 2,
showed a similar pattern, indicating that the structure of
SBA-15 was not changed with the addition of the com-
plex onto SBA-15 porous. The transmission electron
microscopy (TEM) image is in good agreement with XRD
data and is retained during grafting. The TEM image of
Co(II)-PLP-Schiff-base/SBA-15 in (Figure 3a), confirms
the ordered parallel channel structures of mesoporous
SBA-15 materials retaining of 2D hexagonal array of uni-
form linear channels after the complex anchoring. More-
over, the scanning electron microscopy (SEM) image of
the Co(II)-PLP-Schiff base/SBA-15 catalyst (Figure 3b),
also confirms the morphology and mesoporous structure
of the prepared catalyst. This catalyst displays regular
channels with the highly ordered pores, confirming the

4
YARI ET AL.
TABLE 1
EDX, semiquantitative elemental analyzing of Co(II)-PLP-Schiff base/SBA-15
Element
Line type
K series
K series
K series
K series
K series
K series
Apparent concentration
k ratio
0.00736
0.00305
0.13527
0.23492
0.00076
0.00054
wt%
7.43
wt% sigma
0.32
Atomic %
11.74
2.39
Standard label
C
0.74
1.71
C Vit
BN
N
1.76
48.15
42.38
0.18
0.23
O
40.20
29.65
0.14
0.27
57.10
28.63
0.11
SiO2
SiO2
GaP
Co
Si
0.25
P
0.05
Co
Total
0.05
0.11
0.12
0.04
100.00
100.00
(Table 2). Therefore, the presence of Co(II)-PLP-Schiff
base anchored on the SBA-15 surface, induces remark-
able decrease in the surface area and in mesoporous vol-
ume.[54] The inductively coupled plasma (ICP)-Atomic
spectrometry was also carried out to determine the
Co(II) ion contents in the catalyst which was 0.05 wt%
(Table 3). The metal leaching of the catalyst was also
studied by atomic absorption (AA) analysis before and
after the reactions. The leaching of catalyst after the
fourth cycle was about 4.18 wt% that confirms the negli-
gible metal leaching. Thermogravimetric analysis (TGA)
diagrams (Figure 5) of the pure SBA-15 (a) and Co(II)-
PLP-Schiff base/SBA-15 (b), indicated pure siliceous
SBA-15, which represented a mass loss below 100 ꢀC
through the loss of physically adsorbed water, but the
thermogram of b shows not only a mass loss due to dehy-
dration but also a more mass loss happens from 300ꢀC,
which could be attributed to loss of immobilized Schiff-
base ligand and organic materials.
FIGURE 4 BET (ADS and BJH) images of SBA-15 (a) and
Co(II)-PLP- Schiff base/SBA-15 (b)
retention of the physical structure of the siliceous mate-
rial, although Co(II)-PLP-Schiff base complex entered
into the channels of functionalized SBA-15.[52,53] The
EDX analyses were used for identifying semiquantita-
tively the constituent elements in Co(II)-PLP-Schiff base/
SBA-15 nanocatalyst compound and the results are
shown in (Table 1, and Figure 3c), the percentage of car-
bon, nitrogen, phosphorus, oxygen, and cobalt elements
have been indicated on the SBA-15-supported catalyst.
Further evidence of mesoporous nature of the prepared
catalyst was obtained by Brunauer–Emmett–Teller analy-
sis. The N2 adsorption-desorption isotherms of SBA-15
(a), and Co(II)-PLP-Schiff base/SBA-15 (b), materials are
shown in Figure 4. Both materials indicated the IV type
isotherms, according to International Union of Pure and
Applied Chemistry classification characteristic of uni-
formly sized mesoporous materials. The values of the
structural parameters obtained from the BET adsorption
((ADS) and Barrett–Joyner–Halenda) analysis are listed
in Table 2. The SBA-15 has a specific surface area
411.47 m2/g and pore volume of 0.73 cm3/g, while the
Co(II)-PLP-Schiff base/SBA-15 catalyst has a specific sur-
face area 313.72 m2/g and pore volume 0.63 cm3/g
2.2 | Catalyst efficiency
After the survey of structure and morphology of the
synthetic Co(II)-PLP-Schiff base/SBA-15 catalyst, we
intend to test the efficiency of heterogeneous catalyst, for
preparation of benzothiazole heterocycles (Scheme 2).
Also, the product 3c, 2-aminothiophenol (1a) and
4-chlorobenzaldehyde (2b) were selected as a model sub-
strate to investigate the best reaction conditions
(Scheme 3 and Table 4). Several reaction conditions
were selected and the efficiency of the synthesis was
found to be influenced by the various quantities of the
reactants, catalyst, temperature, and solvents. In the
absence of catalyst or by using PLP-Schiff base/SBA-15
or pure SBA-15 as a catalyst, we got no yield of product
at room temperature for 3 hr in water (Table 4, entries
1–3). The best yield was obtained at reflux tempera-
ture, in the presence of 0.005 g of catalyst for 1 mmol
portions of reactants (Table 4, entry 7). Although using

YARI ET AL.
5
TABLE 2
PLP-Schiff base/SBA-15 catalyst
BET, Textural properties of the SBA-15 and Co(II)–
of ethanol, methanol, and toluene as a solvent, gave
reasonable yields (Table 4, entry 9–11), the opportunity
of applying a cheap solvent such as water in a green
synthesis is an environmentally significant benefit of
the procedure.
As shown in Table 5, the optimized synthesis condi-
tions were good to excellent, and the reactivity of
2-aminothiophenol with aryl aldehydes was under control
of the electronic effects. For example, in model reaction of
2-aminothiophenol (1a) with p-chlorobenzaldehyde (2b),
the electron withdrawing group at the para-position of
aromatic ring of aldehyde, gave higher yields due to
increase in electrophilicity of the carbonyl carbon of the
aldehydes (Table 5, product 3c).
Materials ran
C (M)a
Sb BET
411
Vc BET
0.73
SBA-15
0.00
Co(II)-PLP-Schiff base/
SBA-15
0.05 (%)
313
0.63
aInitial concentration of Cobalt ion species (wt%).
bSpecific surface area (m2/g).
cPore volume (cm3/g).
TABLE 3
SBA-15 catalyst
ICP-Atomic spectrometry of Co(II)-PLP-Schiff base/
All reactions were run under the following conditions:
2-Aminothiophenol (1a, 1 mmol, 1 equivalent), and benzal-
dehyde substrates (2b-2q, 1 mmol, 1 equivalent) and cata-
lyst (0.005 g) in water (5–10 ml) were heated to reflux for
appropriate times. The mechanism of this reaction has
been shown in Scheme 4. The interaction between carbonyl
and amino groups is the key reaction in many enzymes
and other biological processes. Since, the rate of this reac-
tion shows a characteristic pH dependence,[55] conse-
quently, these condensations generally are carried out in
various concentrations of a mineral acid. The role of phos-
phoric acid in the pyridoxal phosphate is similar to other
Bronsted acids[56,57] and will accelerate the release of the
proton which is needed to advance the reaction mechanism
without adding any acid. Also, the electron interaction of
the catalyst with oxygen of the carbonyl in aldehyde groups
will accelerate the reaction. Further reusability of the cata-
lyst was examined for the model reaction (product 3j).
Thereby the catalyst was separated and reused after wash-
ing with distilled water and hot ethanol and drying at 80ꢀC
for 2 hr. The recovered catalyst was employed for five times
(Table 6).
Test result
Sample
Element
Co%
Blank
0.00%
Co(II)-PLP-Schiff base/SBA-15
0.05%
120
100
80
60
40
20
0
a %
b %
0
200
400
600
800
1000
Temperature (°C)
FIGURE 5 Thermogravimetric analysis of SBA-15 (a) and
Co(II)-PLP-Schiff base/SBA-15 (b)
SCHEME 2 Preparation of
benzothiazole derivatives
SCHEME 3 Preparation of
2-(4-chloro phenyl) benzothiazole

6
YARI ET AL.
TABLE 4
Screening of the reaction conditions of 2-aminothiophenol 1a and 4-choloro benzaldehyde 2ba
Entry
Solvent
H2O
Catalysis
Catalyst amount
0.05 g
Temperature (ꢀC)
Time (hr)
Yield (%)
1
PLP-Schiff base/SBA-15
Rt
3
3
3
3
3
3
1
2
3
3
3
4
5
—
2
H2O
SBA-15
0.05 g
Rt
—
3
H2O
Co(II)-PLP-Schiff base/SBA-15
Co(II)-PLP-Schiff base/SBA-15
Co(II)-PLP-Schiff base/SBA-15
Co(II)-PLP-Schiff base/SBA-15
Co(II)-PLP-Schiff base/SBA-15
Co(II)-PLP-Schiff base/SBA-15
Co(II)-PLP-Schiff base/SBA-15
Co(II)-PLP-Schiff base/SBA-15
Co(II)-PLP-Schiff base/SBA-15
Co(II)-PLP-Schiff base/SBA-15
Co(II)-PLP-Schiff base/SBA-15
0.0
Rt
—
2
H2O
0.01 g
Rt
30
3
H2O
0.005 g
0.005 g
0.005 g
0.005 g
0.005 g
0.01 g
Rt
30
4
H2O
60
50
5
H2O
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
60
6
H2O
80
94 (92)b,c
7
H2O
8
H2O
94
9
EtOH
MeOH
Toluene
0.005 g
0.005 g
0.005 g
93
10
11
75
70
aAll reactions were running under the following conditions: 2-aminothiophenol, (1a, 1 mmol, 1 equivalent), 4-chloro benzaldehyde (2b, 1.0 mmol,
1 equivalent) and Co(II)-PLP-Schiff base/SBA-15 nano catalyst (0.005 g) were added for appropriate time in desired Solvent (5–10 ml).
bOptimum conditions.
cIsolated yield in parentheses.
3 | EXPERIMENTAL
propylene oxide, MW = 5,800), tetraethyl orthosilicate
(TEOS [98%], Aldrich), 3-(aminopropyl)-trimethoxysilane,
pyridoxal 50-phosphate monohydrate, cobalt (II)-chloride
hexahydrate, HNO3, HCl, 2-aminothiophenol, and aro-
matic aldehyde compounds were purchased from Sigma-
Aldrich, Merck, and Across chemical companies. The
course of the synthesis of benzothiazole heterocycles was
followed by using TLC with silica gel plates (Merck, silica
gel 60 F254, ready to use), using n-hexane: ethyl acetate
(4:1) as eluent. All of the other reagents and solvents were
of analytical reagent grade and were used as received unless
otherwise noted. Double distilled water was used in all
experiments. Silica gel (Merck, grade 9385, 230–400 mesh,
60ꢀA) for column chromatography was used as received.
General procedure for the synthesis of benzothiazole het-
erocycles, using Co(II)-PLP-Schiff base/SBA-15 catalyst:
A 25 ml round-bottom flask equipped with a magnet and
condenser, was charged with 1.0 mmol, 0.125 g of ortho-
aminothiophenol (C6H7NS, MW. 125.19), and 1 mmol of
substituted benzaldehydes, then added 5–10 ml of water,
and 0.005 g optimized amount of Co(II)-PLP-Schiff base/
SBA-15 catalyst. The reaction mixture was stirred under
reflux condition for required time, and the course of the
reaction was controlled by thin layer chromatography
(TLC) tests, using silica gel sheet with (4:1) ratio of ethyl
acetate and n-hexane as mobile phase.[58,59] Finally, the
products were purified by chromatography column or by
recrystallization methods to obtain the desired and pure
products (Scheme 2). After that the purified product was
dried at 80ꢀC for 4 hr. Then according to its dry weight,
the yield (wt.%) of the product comparing to stoichiomet-
ric weight of product was calculated. The spectral data
for heterocyclic products are reported in Supporting
information.
3.2 | Characterizations
FT-IR spectra were recorded within the 4,000–400 cm−1
region on KBr pellets, using Jasco spectrum 4200 FT-IR
spectrophotometer. Nitrogen adsorption/desorption iso-
therms were obtained at 77.35 K with a Quanta chrome
Autosorb apparatus. Before measurements, the samples
were outgassed at 120ꢀC for 12 hr. The specific surface
area and the pore size distributions were obtained from
the desorption branch of the isotherms, respectively,
using the BET method and BJH analyses. TEM images
were collected in a Hitachi (Tokyo, Japan) transmis-
sion electron microscope at 200 kV electron beam
energy. XRD experiments (Bruker D8ADVANCE with
3.1 | Materials
All the chemicals used in this study were of analytical grade
and were used without further purification, unless other-
wise stated. Pluronic P123 (Aldrich) with the molecular
structure of EO20PO70EO20 (EO: ethylene oxide, PO:

YARI ET AL.
7
TABLE 5
Synthesis of required benzothiazole heterocycles, catalyzed by Co(II)-PLP-Schiff base/SBA-15

8
YARI ET AL.
TABLE 5
Continued
Ni-filtered Cu K radiation at 1.5406 Å) were recorded
using inductively coupled plasma optical emission
spectrometry 730-ES Varian, and PerkinElmer Pin-
AAcle 900T, the concentration of Co (II) in
immobilized SBA-15 was 0.05 wt%. TGA analysis was
performed at a rate of 20ꢀC/min in a temperature
range of 30–800ꢀC under N2 atmosphere using a
NETZSCH STA 409 PC/PG instrument (Selb,
1
with a speed of 2ꢀ min−1. The H NMR and 13C NMR
spectra were referenced to tetramethylsilane (0.00 ppm)
recorded at room temperature on a Bruker AC,
400 MHz spectrometer using dimethyl sulfoxide-d6 as
the NMR solvents and chemical shifts are given in
ppm. Metal content in the catalyst was determined

YARI ET AL.
9
SCHEME 4 Mechanism of
catalytic reaction
TABLE 6
2-(4-methoxyphenyl) benzothiazole 3j
Reuse of the catalyst for the synthesis of
monohydrate (C8H10N6PꢁH2O, MW. 265.16, 1 mmol,
0.26 g) in excess amount of absolute MeOH, and then
3-APTEOS (C9H23NO3Si, MW. 221.372, 1 mmol 0.221 g)
was added under vigorous stirring. The color of solution
immediately changes to yellow due to imine formation in
Schiff base ligand. The solution was stirred for 3 hr at
room temperature. Further 0.5 mmol (0.119 g)
CoCl2ꢁ6H2O was added to Schiff base solution and stirred
for 3 hr. For the activation of SBA-15, it was refluxed in
hydrochloric acid (6 M) for 6 hr, and washed thoroughly
with deionized water and then heated at 120ꢀC on a vac-
uum oven for 8 hr. The activated SBA-15 (1.5 g) was
suspended in the solution containing cobalt Schiff base
complex, and the mixture was stirred for 24 hr at room
temperature. Then the solvent was evaporated in the
rotary evaporator, and resulting green solid was dried at
80ꢀC for 8 hr. The resulting product was washed with
MeOH and deionized water until the filtrates became col-
orless. Finally, drying was carried out in oven drier at
80ꢀC for 8 hr.
Run
1
2
3
4
5
Yield (%)
Isolated yield
94
92
94
92
94
92
92
90
92
90
Germany). The weight loss was recorded as a function
of temperature. The course of the synthesis of hetero-
cycles was followed by TLC on silica gel plates (Merck
silica gel 60F254, ready to use), using n-hexane: ethyl
acetate (4:1) as eluents, for TLC, same as for chroma-
tography column. The morphologies of the catalyst
were observed further by SEM (Leo1450VP).
3.3 | Synthesis
3.3.1 | Synthesis of SBA-15 support
The ordered mesoporous silica was synthesized by the
hydrothermal method according to previously described
by Zhao et al.[60,61] First, P123, poly (ethylene oxide)-
block-poly (propylene oxide)-block-poly (ethylene oxide)
triblock copolymer 2.0 g has been dissolved in 15 ml
deionized water and then HCl solution (2 M, 60.0 ml)
was added to this mixture under vigorous stirring. In the
next step, TEOS (4.25 g) was added into the solution at
40ꢀC and mixture was stirred for 4 hr. After that, the mix-
ture was placed in an autoclave at 100ꢀC for 24 hr under
static conditions. The solid product was filtered off and
washed thoroughly with distilled water, and air-dried at
room temperature, and then calcined at 600ꢀC for 8 hr.
4 | CONCLUSIONS
To sum up, the synthesis of a novel Co(II)-PLP-Schiff
base/SBA-15 nanocatalyst was reported by the reaction of
pyridoxal phosphate and APTEOS and the resulting cata-
lyst has been characterized by different techniques
including FT-IR, XRD, TGA, BET, SEM, TEM, AA, and
ICP. The catalyst was applied for the synthesis of vitally
important benzothiazole heterocycles and good results
were obtained. This method offers several advantages
such as eco-friendly, nontoxic, mild reaction conditions,
simple experimental and work-up procedures, high con-
versions, short reaction times, recyclability of the catalyst,
and very good yields that make our methodology a valid
contribution to the existing processes in the synthesis of
benzimidazole derivatives.
3.4 | Synthesis of Co(II)-PLP-Schiff/
SBA-15
Using a similar procedure reported by the Chisem
et al.[62,63] The Co(II)-PLP-Schiff base complex was syn-
thesized by dissolving the pyridoxal phosphate
ACKNOWLEDGMENTS
Authors are thankful to the University of Central Tehran
Azad University and Payame Noor University.

10
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ORCID
Niloufar Akbarzadeh-T https://orcid.org/0000-0002-
3614-5899
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How to cite this article: Yari H,
Dehkharghani RA, Bardajee GR, Akbarzadeh-T N.
Synthesis, characterization, and applications of
novel Co(II)-pyridoxal phosphate-Schiff base/
SBA-15 as a nanocatalyst for the green synthesis of
benzothiazole heterocycles. J Chin Chem Soc. 2020;
1–11. https://doi.org/10.1002/jccs.201900518