Covalent immobilization of Co complex on the surface of SBA-15: Green, novel and efficient catalyst for the oxidation of sulfides and synthesis of polyhydroquinoline derivatives in green condition

Article abstract of DOI:10.1016/j.poly.2018.10.054

In this work, a green and novel catalyst was prepared through immobilization of cobalt complex on the surface of mesostructured SBA-15 and characterized by TGA, SEM, FT‐IR, EDX, ICP, BET and X-ray mapping analytical methods. This mesostructural material was used as an efficient and green interphase catalyst for the oxidation reactions and synthesis of polyhydroquinoline derivatives. All reactions were performed in short times and good yields. Moreover, the prepared catalyst could be used up to six runs without significant degradation in its catalytic activity or cobalt leaching.

Full text of DOI:10.1016/j.poly.2018.10.054

Accepted Manuscript
Covalent immobilization of Co complex on the surface of SBA-15: Green, novel
and efficient catalyst for the oxidation of sulfides and synthesis of polyhydro-
quinoline derivatives in green condition
Arash Ghorbani-Choghamarani, Masoud Mohammadi, Taiebeh Tamoradi,
Mohammad Ghadermazi
PII:
S0277-5387(18)30690-9
https://doi.org/10.1016/j.poly.2018.10.054
POLY 13528
DOI:
Reference:
To appear in:
Polyhedron
Received Date:
Revised Date:
Accepted Date:
31 August 2018
12 October 2018
17 October 2018
Please cite this article as: A. Ghorbani-Choghamarani, M. Mohammadi, T. Tamoradi, M. Ghadermazi, Covalent
immobilization of Co complex on the surface of SBA-15: Green, novel and efficient catalyst for the oxidation of
sulfides and synthesis of polyhydroquinoline derivatives in green condition, Polyhedron (2018), doi: https://doi.org/
1
0.1016/j.poly.2018.10.054
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Covalent immobilization of Co complex on the
surface of SBA-15: Green, novel and efficient
catalyst for the oxidation of sulfides and synthesis
of polyhydroquinoline derivatives in green
condition
a,*
a
b
Arash Ghorbani‑ Choghamarani,
Mohammad Ghadermazi
Masoud Mohammadi, Taiebeh Tamoradi,
b
a
Department of Chemistry, Faculty of Science, Ilam University, P.O. Box, 69315516, Ilam, Iran
E-mail:arashghch58@yahoo.com or a.ghorbani@ilam.ac.ir
b
Department of Chemistry, Faculty of Science, University of Kurdistan, Sanandaj, Iran
Abstract:
In this work, a green and novel catalyst was prepared through immobilization of cobalt
complex on the surface of mesostructured SBA-15 and characterized by TGA, SEM, FT‐ IR,
EDX, ICP, BET and X-ray mapping analytical methods. This mesostructural material was
used as an efficient and green interphase catalyst for the oxidation reactions and synthesis of
polyhydroquinoline derivatives. All reactions were performed in short times and good yields.
Moreover, the prepared catalyst could be used up to six runs without significant degradation
in its catalytic activity or cobalt leaching.
Keywords: SBA-15, cobalt, heterogeneous catalyst, sulfoxide, polyhydroquinoline
1. INTRODUCTION
Over the past several decades, supported catalysts have been widely developed in organic
reactions. In this regard, some nanomaterials such as magnetic iron oxide, mesoporous silica,
molecular sieves, ionic liquids, polymers, graphene oxide, nanocomposite, etc. have been
reported to be used as support [1–9]. Nanocarrier mesoporous silica nanoparticles (MSNs),
with the exposed surface area, are of great interest to the materials community. In this sense,
it is due to the key role of this process in catalyst designing, adsorption water treatment,
extraction, drug delivery systems, preparation of SH nanoparticles and removal of heavy
metals., It is also worth noting that MSNs as support have significant advantages such as:
ease of preparation, high porosity, ease separation, high concentration of surface Si–OH

groups, excellent thermal and chemical stability, and available and exposed internal surface
area. It can also be mentioned that nanostructured mesoporous materials’ unique properties as
templates have attracted much attention in the synthesis of new shape-selective materials
[
10–16]. Indeed, SBA-15 in various fields such as those with available surface area and pore,
high surface hydroxyl density, selective adsorption and hosting properties, tunable pore
diameter, wide range of possibilities for functionalization and high mechanical stability have
become more powerful tools in catalyst designing, drug delivery systems, extraction, removal
of toxic and heavy ions. Moreover, substantial interest has been paid to the surface
functionalization of SBA-15 internal surface by post-synthetic grafting of trialkoxysilane
reagents. In this sense, the aim is to incorporate metal complexes onto the channel walls
because the siliceous SBA-15 lacks catalytic activities [3,12,14,15,17,18]. Considering the
acquired result, immobilization of transition metal complexes onto mesoporous SBA-15
materials is necessary because of various applications such as metal chelating agents [15,19–
2
2]. For example, there is reported the grafting of complexes on the surface of silica as an
efficient catalyst [23–29]. Interestingly, the metal meso-structured materials were recently
developed as catalysts in organic synthesis [30–35]. Besides, multicomponent reactions have
a wide range of important benefits such as hepatoprotective, anticancer, vasodilator,
antibacterial, antifungal, antitumor, anti-atherosclerotic, anti-tumor, anticonvulsant,
antifertility, and also as a mono amine oxidase inhibitor, anti-diabetic, geroprotective and
bronchodilator activities [31,36–39]. Polyhydroquinoline (PHQ) derivatives (six-membered
heterocyclic ring molecules-containing organic molecules) are very well-known as one of the
important multicomponent reactions [40]. Therefore, in the development of greener and
sustainable processes for the synthesis of multicomponent reactions, we attempted to
immobilize SBA-15 with Co complex (SBA-15@AMPD-Co) as a heterogeneous catalyst by
a simple procedure using expensive, green and available materials.

2
2
. Experimental
.1. General
All reagents for the synthesis of catalyst, sulfoxides, and polyhydroquinoline were obtained
from Sigma-Aldrich and Merck. Also, X-ray diffraction (XRD), SEM images,
thermogravimetric analysis (TGA), supermagnetic properties and IR spectra of samples were
recorded with Cu Kα radiation (λ= 1.54060 Å), FESEM-TESCAN MIRA3, Shimadzu
DTG‐ 60 instrument, Vibrating Sample Magnetometer (VSM) MDKFD and KBr pellets with
VERTEX 70 model BRUKER, respectively.
2
.2. General procedure for the preparation of the SBA-15@AMPD-Co
The SBA-15 mesoporous silica has been successfully prepared by sol-gel as reported by
Hajjami et al [15]. Considering the above facts, it should be mentioned that 1g of the white
powder (SBA-15) was added to 1.5 mL of 3-chloropropyltrimethoxysilane (CPTMS) in dry
toluene (20 mL) and kept under reflux conditions for 24 h. After the filtration of the final
mixture, the obtained powder was washed with hexane and dried to give the SBA-15 coated
with CPTMS (SBA-15-Cl). Organically, the functionalized SBA-15-Cl with SBA-
1
5@AMPDwith 2-Amino-2-methyl-1,3-propanediol (AMPD) was subsequently produced by
adding SBA-15-Cl (1 g), 0.21 g of AMPD and triethylamine (1.5 mmol) in dry toluene under
reflux conditions for 48 h. After the filtration of the final mixture, the obtained powder was
washed and dried to give the mesostructured SBA-15@AMPD. Covalent immobilization of
Co complex on the surface of SBA-15 was performed by adding SBA-15@AMPD (1 g) to
Co(NO
3
)
2
.6H O (0.73 g) under reflux condition for 16 h. Then, washed with ethanol (Scheme
2
1
).

Scheme 1 General scheme for the Synthesis of SBA-15@AMPD-Co.
2
.3. The preparation of polyhydroquinolines derivatives
Dimedone (1 mmol), aldehyde (1 mmol), ammonium acetate (1.2 mmol), ethyl acetoacetate (1
mmol), and SBA-15@AMPD-Co nanocatalyst (8 mg) were mixed under stirring and solvent-
free conditions at 100 °C for an appropriate time and the progress of the reaction was
monitored by TLC (acetone: n-hexane 3:7). After completion of the reaction, a solid product
was formed, then, the hot ethanol (10 mL) was added to the reaction vessel to dissolve the
solid product. Besides, the obtained solution was hotly filtered to separate the heterogeneous
catalyst and, then, the filtrate was cooled to supply the pure product as a yellow solid. In this
sense, the pure product was synthesized in high yields (86–97%).
2
.4. General procedure for the oxidation of sulfides.
Sulfide (1 mmol), H (0.4 mL) and SBA-15@AMPD-Co nanocatalyst (7 mg) were
2
O
2
vigorously stirred in a round-bottomed flask at room temperature in solvent-free conditions
for an appropriate time. To investigate the completed reaction, TLC (EtOAc/n-hexane, 1:10)
was used. When the reaction was finished, the catalyst was separated by filtration and the
products were extracted with H
2
O and CH
2
Cl . Afterward, the combined organics were dried
2

over anhydrous Na
2
SO . Evaporation of the solvent gave the pure corresponding sulfoxides
4
in good to high yield (86-97%).
2.5 Selected spectral data
Ethyl-4-(4-chlorophenyl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-
hexahydroquinoline-3-
carboxylate (entry 1, table 5): Mp: 245-247°C. H NMR (400 MHz, CDCl ): δH= 0.94 (s,
H), 1.08 (d, J = 2.0 Hz, 3H), 1.21 (t, J = 7.1 Hz, 3H), 2.14-2.35 (m, 4H), 2.37 (s, 3H), 4.08
q, J = 7.1 Hz, 2H), 5.04 (s, 1H), 7.17 (d, J = 8.4 Hz, 2H), 7.29 – 7.22 (m, 2H) ppm.
1
3
3
(
Ethyl-4-(4-methyl
carboxylate (entry 2, table 3): Mp: 260-262 °C. H NMR (CDCl
phenyl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-
hexahydroquinoline-3-
, 400 MHz) δH: 0.96 (s,
1
3
3
2
H), 1.08 (s, 3H), 1.23 (t, J = 7.1 Hz, 3H), 2.26 – 2.12 (m, 3H), 2.27 (s, 3H), 2.31 (s, 1H),
.36 (d, J = 1.4 Hz, 3H), 4.08 (q, J = 7.1 Hz, 2H), 5.03 (s, 1H), 7.02 (d, J = 7.8 Hz, 2H), 7.21
(
d, J = 8.0 Hz, 2H).
1
Methyl phenyl sulfoxide H NMR (400 MHz, DMSO, ppm): δ
H
= 2.75 (s, 3H), 7.54–
7.62 (m, 2H), 7.68–7.76 (m, 3H).
1
1
-(Propylsulfinyl) propane H NMR (400 MHz, CDCl
3
, ppm): δ = 1.21 (t, J= 6 Hz,
H
6
3
3
3
H), 1.91–1.99 (m, 4H), 2.67–2.83 (m, 4H).
. Result and discussion
.1. Catalyst characterization
.1.1. FT-IR spectrum
FTIR spectroscopy (Fig. 1a–d) represents the Fourier transform infrared (FT-IR) spectra
obtained for SBA-15, SBA-15-Cl, SBA-15@AMPD and SBA-15@AMPD-Co nanoparticles,
-1
respectively. As illustrated in Fig. 1.a, the FT-IR bands at 491, 800 and 1075 cm come from
vibrations of Si-O-Si bending vibrations, Si-O-Si symmetric stretching and Si-O-Si
asymmetric stretching, respectively (Fig. 1.a). The anchored (3-chloropropyl)
-1
trimethoxysilane group is confirmed by C-H stretching vibration appearing at 2912 cm in
the SBA-15-Cl spectrum (Fig. 1.b). The immobilized AMPD ligand to the surface of SBA-
1
5-Cl is confirmed by the presence of bands in the range of 1624 and 3132, 3385 cm-1
referring to the N–H and OH vibrations (Fig. 1.C). Also, in the FTIR spectrum of the
supported Co nanoparticles on the SBA-15@AMPD, the bending vibration of the N-H group

-1
appeared at 1705 cm (Fig. 1.D). These results suggest that Co ions coordinate on the surface
of the SBA-15@AMPD.

Fig. 1. FT-IR spectra of (A) SBA-15 (B) SBA-15-Cl, (C) SBA-15@AMPD, (D)
SBA15@AMPD-Co.
3
.1.2. TGA
Fig. 2 shows the thermo-gravimetric analysis (TGA) of the prepared catalyst. During the
process of our investigation, it was revealed that weight loss below 200 °C corresponds to the
removal of the dehydration of the surface OH groups and adsorbed solvents. At temperatures
in the range of 200-500 °C, mass loss (56.91%) was manifested that is due to the
decomposition of the organic layers such as AMPD ligand on the SBA-15 nanoparticles.
Fig. 2. TGA curve of SBA15@AMPD-Co.
3
.1.3. MAP
The dispersion of all elements of the catalyst were studied by the X-ray mapping of SBA-
5@AMPD-Co. As illustrated in fig. 3, most of the particles are quasi-spherical, and the
elemental map images indicated the good dispersion of Co on the surface of the catalyst.
1

Fig. 3. The X‐ ray map analysis of SBA-15@AMPD-Co catalyst.
3
.1.4. SEM
Fig. 4 illustrates the morphology of SBA-15 (a), immobilized SBA-15 with Co complex (b)
and recovered SBA-15@AMPD-Co (c) as probed by scanning electron microscopy (SEM)
technique. Also, the exact amount of Co loaded on modified SBA-15 mesostructured was
−
1
found to be 0.33 mmol g .

Fig. 4. SEM images of a) SBA-15, b) SBA-15@AMPD-Co and c) recovered catalyst.
.1.5. N adsorption and desorption
The N adsorption/desorption isotherms for mesostructured SBA-15 and SBA-15@AMPD-
3
2
2
Co are indicated in Fig. 5. The surface properties containing the BET surface area (SBET),
the total pore volumes (Vtotal), the pore diameters (DBJH) and the wall thickness of the
samples were investigated (Table 1). More importantly, the decrease in surface area, and pore
size was confirmed that cobalt complex was successfully immobilized on the surface of SBA-
1
5.
Table 1. Texture parameters obtained from nitrogen adsorption studies.
2
-1
Pore volume Pore diameter by
SBET (m g ) Sample
3
-1
(
cm g )
BJH method (nm)
0
0
.790
.534
3.52
2.38
643
SBA-15
238.47
SBA-15@AMPD-Co

Fig. 5. Nitrogen adsorption/desorption isotherms of (a) SBA-15 and (b) SBA-15@AMPD-Co
catalyst.
The energy-dispersive X-ray spectroscopy (EDX) of SBA-15@AMPD-Co catalyst clarified
that Si, O, C, N, Co elements verified the immobilization of Co complex on the surface of
mesostructured SBA-15. (Fig. 6).
Fig. 6. EDX pattern of SBA-15@AMPD-Co catalyst.

3
.2. Catalytic study
As a part of the present research, it was decided to explore the catalytic effect of SBA-
5@AMPD-Co in organic reactions including the synthesis of polyhydroquinoline
derivatives and oxidation of sulfides.
.2.1. Synthesis of Polyhydroquinolines:
1
3
In order to determine the optimal reaction conditions, various effective factors on the reaction
like the amount of catalyst, solvent and also the effect of temperature were applied in the
model reaction using p-Clbenzaldehyde (1 mmol), ethyl acetoacetate (1 mmol), dimedone (1
mmol) and ammonium acetate (1.2 mmol) for the synthesis of Polyhydroquinoline. The
results are shown in Table 2.
Table 2. Optimization of the Hantzsch reaction for the synthesis of ethyl 4-(4-chlorophenyl)-2-methyl-
5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate as a model catalyzed by SBA-15@AMPD-Co
under various conditions.

b
Entry
Solvent
Temperature (°C)
Catalyst (mg)
Time (mine)
Yield (%)
Solvent- free
Solvent- free
Solvent- free
Solvent- free
Solvent- free
Solvent- free
PEG-400
100
100
100
100
100
100
100
100
Reflux
100
Reflux
Reflux
80
-
600
35
35
35
35
35
35
35
35
35
35
35
35
35
35
35
35
35
35
Trace
79
87
97
97
94
64
35
52
66
75
80
31
73
79
85
87
91
97
3
5
8
10
15
8
H
2
O(reflux)
8
THF
8
DMF
8
CH
EtOH
O–EtOH (1:1)
3
CN
8
8
H
2
8
Solvent- free
Solvent- free
Solvent- free
Solvent- free
Solvent- free
Solvent- free
25(Rt)
40
10
10
10
10
10
10
60
80
90
110

a
Reaction conditions: Dimedone (1 mmol), aldehyde (1 mmol), Ammonium acetate (1.2 mmol) and Ethyl
acetoacetate (1 mmol), Catalyst and solvent (2 mL).
b
Isolated yield.
According to the results of the optimization of reaction, the optimized condition for this
reaction is 8 mg of SBA-15@AMPD-Co nanocatalyst in solvent-free condition at 100 °C
(
Table 2). To find out the scope and generality of this method, various types of aromatic
aldehydes were reacted in the optimized reaction conditions for synthesizing various
polyhydroquinoline derivatives under identical conditions. The experimental results show that
various aldehydes, having both electron withdrawing and donating groups, produced their
corresponding polyhydroquinoline derivatives in good to excellent yields. However, it is worth
mentioning that the time process of the aromatic aldehydes with electron-donating groups on
the aromatic ring reaction was longer than aromatic aldehydes with electron-withdrawing
groups on the aromatic ring (Table 3).
Table 3. Synthesis of different polyhydroquinolines via the Hantzsch reaction catalyzed by SBA-
15@AMPD-Co nanocatalyst under optimized conditions.

Time (mine) Yield M.P
%) Find
product
Entry aldehyde
(
Reported
1
3
5
4
5
0
0
97
91
94
206-247 243-245[39]
260–262 252–255 [41]
251-252 255-257 [42]
2
3
4
5
6
9
6
5
0
0
96
86
92
202–204 203–205[43]
230–232 231-234 [41]
231–233 225–227 [43]
6
7
5
0
97
252–253 249–251 [43]

8
9
4
5
92
90
233–236 231–233 [43]
180–183 180–182 [43]
35
aReactions conditions: aldehyde (1 mmol), dimedone (1 mmol), ethyl acetoacetate (1 mmol), and ammonium
acetate (1.2 mmol).
b
Isolated yield.
A plausible mechanism for the formation of polyhydroquinolines is shown in Scheme 2 [44].
Based on this mechanism the role of SBA-15@AMPD-Co catalyst comes in the Knoevenagel
coupling of aldehydes with active methylene compounds to produce an α, β‐ unsaturated
compound and in the Michael addition of intermediates to obtain the polyhydroquinoline.

Scheme 2 Proposed mechanism for the synthesis of polyhydroquinolines in the presence of
SBA-15@AMPD-Co as the catalyst.
3
.2.2. Oxidation of sulfides:
Afterward, to show the ability of SBA-15@AMPD-Co, its effect in the oxidation of sulfides
was examined. For this purpose, the oxidation of methyl phenylsulfide (1 mmol) using H O ,
2
2
in the presence of SBA-15@AMPD-Co catalyst, was considered as a model reaction and
tested by different solvent and catalytic amounts of the prepared nanoparticles to
demonstrate the best reaction condition (Table 4). During the first step, the solvent effect was
investigated, and the highest yield was obtained in the absence of the solvent. As shown in
(Table 4, entries 2-8), the n-Hexane, Ethyl acetate (EtOAc), Acetonitrile (CH
3
CN),
dichloromethane(CH Cl ), and Ethanol(EtOH) afforded low to moderate yields.
2
2
Consequently, the solvent-free condition was selected as the solvent. In the second step, the
effect of different amounts of catalyst between 2-7 mg on the reaction was studied, and it
showed that the amount of catalyst plays a crucial role in the conversion and formation of the
products. (Table 4, entries 9–12). The highest yield of the product was obtained in the
presence of 7 mg of SBA-15@AMPD-Co nanocatalyst with 94% yield. Meanwhile, in the
absence of the catalyst, the reactions were not completed even after 6 hours, and the yields
were very low (Table 4, entire 1). The optimum conditions were obtained with 7mg of SBA-
1
5@AMPD-Co under solvent-free condition. (Table 4, entry 7).
Table 4. Optimization of the oxidation of methyl phenyl sulfide for the synthesis of methyl phenyl
sulfoxide as a model catalyzed by SBA-15@AMPD-Co under various conditions.

b
Entry
Solvent
Temperature (°C)
Catalyst
mg)
Time
(mine)
360
35
Yield (%)
(
Solvent- free
Acetonitrile
n-Hexane
R.T
R.T
R.T
R.T
R.T
R.T
R.T
R.T
R.T
R.T
R.T
R.T
0
7
7
7
7
7
7
7
6
5
2
3
Trace
88
35
17
EtOAc
35
91
Dichloromethane
EtOH
35
30
35
77
H
2
O
35
Trace
94
Solvent- free
Solvent- free
Solvent- free
Solvent- free
Solvent- free
35
35
87
35
83
35
63
35
37
aReactions conditions: Sulfide (1 mmol), H
2
2
O (0.4 ml), catalyst and solvent (2ml).
b
Isolated yield.
To explore the generality of this procedure, the catalytic activities of SBA-15@AMPD-Co on
a variety of sulfides bearing various functional groups were examined under optimized
conditions. The presented results in Table 5 show that SBA-15@AMPD-Co catalyst system
worked very well, different aromatic and aliphatic sulfides showed good reaction activities
for the oxidation to corresponding sulfoxides and provided the corresponding sulfoxide with
pure products in excellent yields.
Table 5. Oxidation of various sulfides using hydrogen peroxide for the synthesis of different sulfoxides
catalyzed by SBA-15@AMPD-Co nanocatalyst under optimized conditions.

M.P
Find
product
Time (mine) Yield (%)
Entry Substrate
Reported
32-35
3
5
94
29 - 31
[
41]
1
2
3
0
93
129–131
130-133
[41]
3
4
0
94
Oil
Oil [41]
4
5
6
6
5
0
96
92
Oil
Oil
Oil [41]
Oil [41]
6
6
9
5
0
0
0
92
86
97
Oil
Oil [41]
Oil [45]
63-65
7
Oil
8
9
62–64
[
41]
4
5
92
oil
Oil [45]
aReactions conditions: Sulfide (1 mmol), H
2
2
O (0.4 ml), and catalyst (7 mg).
b
Isolated yield.
A plausible mechanism for the oxidation of sulfides to sulfoxides in the presence of SBA-
5@AMPD-Co nanocatalyst on the basis of previous reports [41]. Based on this mechanism
the role of SBA-15@AMPD-Co is to form the active oxidant substrate complex through the
1

reaction of H
2
2
O with Cobalt. After that, the transfer of oxygen to sulfur leads to the
formation of the product.
Scheme 3 Proposed mechanism for the synthesis of sulfoxide in the presence of SBA-
1
5@AMPD-Co as the catalyst.
3
.2.3. Catalyst reusability
The reusability and Stability of the presented heterogeneous catalyst in this report is one of
the most important properties of this nanocatalyst. This important feature was examined in
the four-component standard reaction of p-Clbenzaldehyde, ammonium acetate, dimedone
and ethyl acetoacetate for the synthesis of Polyhydroquinoline under optimized conditions.
After completion of the reactions, the SBA-15@AMPD-Co nanocatalyst was filtered and
washed with Et
and, then, it was dried in hot air oven at 50 °C for 4h. As shown in Fig.7, the separated SBA-
5@AMPD-Co nanocatalyst was reused for six successive runs in the synthesis of
2
O and CH
2
Cl (3*10ml) to completely remove any organic residues product
2
1
polyhydroquinoline, without any substantial loss of its catalytic activity.
In order to determine the exact amount of Co loaded on modified SBA-15, ICP-OES analysis
was performed and it was found to be 2.5 %.

Also, in order to determine the exact amount of Co loaded on modified SBA-15 for the
synthesis of ethyl-4-(4-chlorophenyl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-
3
carboxylate at least for six consecutive cycles, ICP-OES analysis was found to be 2.37%.
Fig. 7. Recovery of the catalyst in the synthesis of polyhydroquinoline.
In order to perform hot filtration experiment, the synthesis of methyl phenyl sulfoxide
catalyzed by SBA-15@AMPD-Co has been examined. Accordingly, we found that the
progress of reaction under optimized conditions in half time of the reaction was 61%. Then,
the same reaction was repeated, the SBA-15@AMPD-Co nanocatalyst was filtered and the
mixture of reaction was allowed to react more under the same reaction conditions. We found
that no more reaction occurred after the separation of the catalyst; this means that the Co
catalyst remains on the support during the reaction and the leaching of cobalt has not
occurred.
3
.2.4 Comparison of the Catalyst
In order to investigate the catalytic properties of synthesized SBA-15@AMPD-Co,
nanostructure was compared to the popular catalysts in the known literature. We investigated
the efficacy of the model reactions of the synthesis of polyhydroquinolines and oxidation of
sulfides to sulfoxides in the presence of different types of catalysts. The results are

summarized in Table 6 and 7. As it is evident from Table 6 and 7, the synthesized SBA-
5@AMPD-Co nanocatalyst showed better results than other methods in both comparisons.
1
Table 6. Comparing catalytic activity of SBA-15@AMPD-Co with previously reported methods in
the selective oxidation of sulfides.
Entry Substrate
Catalyst
Catalyst
amount
Time
mine)
Yield Ref.
(%)a
(
Methyl phenylsulfide
VO(IV)–MCM-41
20 mg
40 mg
15 mg
5 mg
480
80
70
5
95
97
97
87
98
98
96
91
90
97
92
94
[46]
Methyl phenylsulfide
Methyl phenylsulfide
Methyl phenylsulfide
Methyl phenylsulfide
Methyl phenylsulfide
Methyl phenylsulfide
Methyl phenylsulfide
Methyl phenylsulfide
Methyl phenylsulfide
Methyl phenylsulfide
Methyl phenylsulfide
MNPs-SA-PPCA
[47]
Fe
3
O
4
@PTA-VO(IV)
[48]
SSA@MNPs
[49]
Zn-2A3HP-MCM-41
15 mg
5 mg
100
80
65
60
60
55
15
35
[50]
Fe
3
O
4
@S‐ ABENZ@VO
[51]
MCM-41@creatinine@La
MCM-41@creatinine@Pr
MCM‑ 41@XA@Ni(II)
MCM‐ 41‐ Adenine‐ Zr
5 mg
[52]
5 mg
[52]
10 mg
4 mg
[45]
[11]
Fe
3
O
4
/PEG-SO
3
H
10 mg
7 mg
[53]
SBA-15@AMPD-Co
This work
Table 7. Comparing catalytic activity of SBA-15@AMPD-Co with previously reported methods in
the selective synthesis of polyhydroquinolines.

Entry Substrate
Catalyst
Catalyst
amount
Time
Yield
(%)a
Ref.
(mine)
p-Clbenzaldehyde
Co
3
O
4
-CNTs
30 mg
35
25
20
7
97
95
95
94
95
95
93
95
90
88
[54]
[55]
[56]
[57]
[58]
[59]
[60]
[61]
[62]
[63]
p-Clbenzaldehyde
p-Clbenzaldehyde
p-Clbenzaldehyde
p-Clbenzaldehyde
p-Clbenzaldehyde
p-Clbenzaldehyde
p-Clbenzaldehyde
p-Clbenzaldehyde
p-Clbenzaldehyde
Alginic acid (17.6 mg)
CSCS
17.6 mg
20 mg
ILOS@Fe/TSPP
0.6 mol %
7 mol%
10mol %
2 mol%
10 mg
[TBA]
2
[W
6
O
19
]
20
60
180
7
La
2
O
3
BiBr
3
(Bbpy)(HSO
4
)
2
SBA-15/SO
3
H
4 mol%
25 mg
25
15
Modified Mont. supported
0
Ni ‐ nanoparticles
p-Clbenzaldehyde
p-Clbenzaldehyde
p-Clbenzaldehyde
p-Clbenzaldehyde
p-Clbenzaldehyde
FeF
3
5 mol%
4 mol%
10 mol%
0.08 g
60
92
87
95
96
97
[64]
[65]
[66]
[41]
Pd‐ nanoparticles
240
180
170
35
Guanidine hydrochloride
MCM41@Serine@Cu(II)
SBA-15@AMPD-Co
7mg
This
work
4
. Conclusion:
In summary, the efficient green SBA-15@AMPD-Co catalyst was prepared as a recoverable
and efficient heterogeneous catalyst by a simple procedure and expensive materials for the

synthesis of sulfoxides and polyhydroquinoline derivatives under mild reaction conditions
with good to excellent yield. Then, the prepared catalyst was characterized using various
methods such as FT-IR, SEM, ICP-OES, BET, and TGA techniques. The designed catalyst
has significant advantages such as the use of non-toxic reagents, easy separation from
reaction media by simple filtration, available and inexpensive materials, short reaction time
and high reaction yield.
Acknowledgements: We gratefully acknowledge the support of this work by the University
of Kurdistan and the University of Ilam.
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Figures captions:
FIGURE 1 FT-IR spectra of (A) SBA-15 (B) SBA-15-Cl, (C) SBA-15@AMPD, (D)
SBA15@AMPD-Co.
FIGURE 2 TGA curve of SBA15@AMPD-Co.
FIGURE 3 The X‐ ray map analysis of SBA-15@AMPD-Co catalyst.
FIGURE 4 SEM images of a) SBA-15, b) SBA-15@AMPD-Co and c) recovered catalyst.
FIGURE 5 Nitrogen adsorption-desorption isotherms and pore size distribution curves of (a)
SBA-15 and (b) SBA-15@AMPD-Co catalyst.
FIGURE 6 EDX pattern of SBA-15@AMPD-Co catalyst.
FIGURE 7 Recovery of the catalyst in the synthesis of polyhydroquinoline.

Graphical abstract
Covalent immobilization of Co complex on surface of SBA-15:
Green, novel and efficient catalyst for the oxidation of sulfides
and synthesis of polyhydroquinoline derivatives in green
condition
Arash Ghorbani‑ Choghamarani,a,* Masoud Mohammad , Taiebeh Tamoradi,
a
b
b
Mohammad Ghadermazi
a
Department of Chemistry, Faculty of Science, Ilam University, P.O. Box, 69315516, Ilam, Iran
E-mail:arashghch58@yahoo.com or a.ghorbani@ilam.ac.ir
b
Department of Chemistry, Faculty of Science, University of Kurdistan, Sanandaj, Iran
Graphical Abstract - Synopsis
A green, new, and efficient catalyst was successfully synthesized by the immobilization of
Co as a transition metal on SBA-15 Then, this mesostructured material was characterized by
TGA, SEM, FT‐ IR, ICP, BET and X-ray mapping analytical. The prepared catalyst was
used for the oxidation of sulfides the synthesis of polyhydroquinoline derivatives. The use of

non-toxic materials, easy separation, easy operation, high yields of the products are the most
important advantages of this method.