Fabrication of a new heterogeneous tungstate-based on the amino-functionalized metal-organic framework as an efficient catalyst towards sonochemical oxidation of alcohols under green condition

Article abstract of DOI:10.1016/j.jorganchem.2020.121483

Ultrasonic-assisted reactions, as a green technique, are often more efficient compared to those traditional protocols. To this end, the selective and solvent-free oxidation of aromatic alcohols to the corresponding aldehydes and ketones were investigated in the presence of Co-ABDC/W at room temperature under ultrasonic irradiation conditions for the first time in this paper. The structure, particle size, thermal stability, and morphology of the fabricated heterogeneous catalyst and the products were characterized by FT-IR, EDS, FE-SEM, XRD, TGA, and GC analyses. In this regard, immobilization of tungstate had a significant effect on thermal stability (around 450 °C for 40percent weight loss) and catalytic performance. Moreover, the efficiency of two different oxidation methods, including ultrasound irradiations and reflux, were comparatively investigated by GC spectrometry. Obtained sonoxidation results presented higher conversions ranging (84 to 100percent) than reflux condition via shorter reaction times. The influences of the reaction parameters, such as hydrogen peroxide concentration, and catalyst loading, were also investigated. The proposed method offers several advantages, such as excellent conversions, selective oxidations, environmentally-benign procedure, short reaction times, and easy workup. Notably, this is the first report that focuses on using amino-functionalized MOFs with ultrasonic irradiation for selective oxidation reactions.

Full text of DOI:10.1016/j.jorganchem.2020.121483

Journal of Organometallic Chemistry 925 (2020) 121483
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Fabrication of a new heterogeneous tungstate-based on the
amino-functionalized metal-organic framework as an efficient catalyst
towards sonochemical oxidation of alcohols under green condition
Maryam Sabaghi, Zahra Aghajani∗, Gholam Reza Najafi
Department of Chemistry, Qom Branch, Islamic Azad University, Qom, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Ultrasonic-assisted reactions, as a green technique, are often more efficient compared to those traditional
protocols. To this end, the selective and solvent-free oxidation of aromatic alcohols to the corresponding
aldehydes and ketones were investigated in the presence of Co-ABDC/W at room temperature under ul-
trasonic irradiation conditions for the first time in this paper. The structure, particle size, thermal stability,
and morphology of the fabricated heterogeneous catalyst and the products were characterized by FT-IR,
EDS, FE-SEM, XRD, TGA, and GC analyses. In this regard, immobilization of tungstate had a significant
effect on thermal stability (around 450 °C for 40% weight loss) and catalytic performance. Moreover, the
efficiency of two different oxidation methods, including ultrasound irradiations and reflux, were compara-
tively investigated by GC spectrometry. Obtained sonoxidation results presented higher conversions rang-
ing (84 to 100%) than reflux condition via shorter reaction times. The influences of the reaction parame-
ters, such as hydrogen peroxide concentration, and catalyst loading, were also investigated. The proposed
method offers several advantages, such as excellent conversions, selective oxidations, environmentally-
benign procedure, short reaction times, and easy workup. Notably, this is the first report that focuses on
using amino-functionalized MOFs with ultrasonic irradiation for selective oxidation reactions.
Received 15 May 2020
Revised 12 August 2020
Accepted 17 August 2020
Available online 19 August 2020
Keywords:
Alcohols oxidation
Amino-functionalized metal-organic
framework
solvent-free
Tungstate
ultrasonic-assisted oxidation
© 2020 Elsevier B.V. All rights reserved.
1. Introduction
sidered as an excellent reaction media for economical and green
approaches in organic functional group transformations, including
The oxidation of alcohols to carbonyl compounds is known as
a pivotal functional group transformation which is basically impor-
tant for the environment, life, and synthetic chemistry [1]. Tradi-
tional alcohol oxidation methods involve transition metals, such
as stoichiometric oxidants, that are not only toxic but also re-
lease considerable amounts of side products [2]. Therefore, de-
veloping an alternative methodology using a clean energy source
and green oxidants is really essential. Ultrasonic irradiation has
attracted considerable attention by researchers for its diverse ap-
plications. In comparison with traditional protocols, ultrasonic ac-
celerated reactions are faster, more convenient, simple, and eas-
ily controlled. In addition to accelerating organic reactions, it is
also possible to decrease the number of required stages for these
types of techniques. The acceleration of ultrasonic-assisted reac-
tions can be described by the cage effects phenomenon and acous-
tic cavitation that is performed at high pressures and temperatures
within a few seconds. Thus, this powerful technique can be con-
conversions of alcohols to chemically important aldehydes [3-9].
In recent years, organic-inorganic hybrid porous coordination poly-
mers, called Metal-Organic Frameworks (MOFs), have attracted sig-
nificant attention as favorable materials owing to their potential
applications in sensors [10,11], drug delivery [12–15], gas separa-
tion [16], catalysis [17–21], and photocatalysis [22–26]. MOF-based
structures exhibit some special properties of both inorganic and
organic materials, such as tunable pore sizes, high surface areas,
flexibility, exposed active sites, the ease of process ability, and
structural diversity. As an approach to improve the selectivity, po-
lar functional groups, namely basic nitrogen-bearing groups in-
cluding aromatic amines, heterocycles, and alkylamines, have been
broadly incorporated into MOFs [27,28]. 2-Aminoterephthalic acid
(H2ABDC) has been widely used as an efficient organic building
block for making open frameworks, such as NH2−MIL-53, IRMOF-
3, NH2-UiO(Zr)-66, etc [29-34]. In such complex compounds, car-
boxylate groups of the deprotonated ABDC2− ligand are the only
participants in metal bonding. Whereas the replaced amino groups
are not coordinators of the metal centers, they possibly function
as binding sites [35]. Building unsaturated metal centers (or OMSs)
∗
Corresponding author:
E-mail address: haj_aghajani@yahoo.com (Z. Aghajani).
https://doi.org/10.1016/j.jorganchem.2020.121483
0022-328X/© 2020 Elsevier B.V. All rights reserved.

2
M. Sabaghi, Z. Aghajani and G.R. Najafi / Journal of Organometallic Chemistry 925 (2020) 121483
Fig. 1. Synthesis route of Co-ABDC/W MOF.
Fig. 2. FT-IR spectra of a) pure 2-Aminoterephthalic acid, and b) Co-ABDC and c) Co-ABDC/W MOF.
in the frameworks is another common approach for improving the
selectivity and affinity of MOFs. These open metal sites are usu-
ally obtained upon the desolvation of MOFs, where the solvent
molecules in the coordination of the metal centers are removed
under vacuum and/or at the elevated temperatures [36-38]. Appli-
cation of tungsten moiety aims to convert cyclohexene to adipic
acid using sodium tungstate (Na2WO4). Diverse types of W-base
systems have been extremely used due to the fact that they have
high selectivity and activity in most oxidation processes, such as
oxidation of sulfides to sulfoxide, halogenation of olefins, isomer-
ization of alkenes, and oxidation of alcohols to aldehydes [39,40].
W-base systems are actuated by hydrogen peroxide as a green ox-
idant owing to the co-formation of water and large quantity of
active oxygen. Homogenous W-based catalysts are associated with
few notable weaknesses, such as reusability, recovery, the use of
phase transfer catalysts, etc. Heterogenization of W-species onto
the solid support has gained ground to surmount the mentioned
challenges in recent years [41].
Taking the mentioned content into account, an affordable cat-
alyst was prepared based on amino-functionalized MOF that was
immobilized by tungsten aiming to oxidize alcohols to aldehydes
and ketones under eco-friendly condition. Amino-functionalized
MOF was synthesized using
a solvothermal technique. Subse-
quently, it was mixed with Na2WO4•2H2O and stirred for 24 h at
40˚C until the solid violet precipitate was obtained which was de-
noted as an Amino-functionalized MOF/tungstate. In addition, se-
lective and solvent-free oxidation of aromatic alcohols to the cor-
responding aldehydes were reported in the presence of H2O2 as an
oxidant agent and Co(ABDC)/W catalyst under ultrasonic irradia-
tion conditions at room temperature. To the best of our knowledge,
this selective approach is the first report aiming to use MOF-based
structure in conjunction with ultrasonic irradiation in the oxidation
of alcohols.

M. Sabaghi, Z. Aghajani and G.R. Najafi / Journal of Organometallic Chemistry 925 (2020) 121483
3
Fig. 3. EDS analysis of the Co-ABDC/W MOF.
Fig. 4. EDS analysis of the Co-ABDC MOF.
2. Experimental
2.2. Synthesis of Co-ABDC/W
2.1. General
The catalyst was obtained according to the previously men-
tioned procedure [42]. The MOF was prepared through solvother-
mal reactions of 2-Aminoterephthalic acid (0.4 mmol) and cobalt
nitrate hexahydrate (Co(NO3)2•6H2O) (0.8 mmol) in the ethanol-
DMF solution that was mixed in a 50 ml beaker. The reagents were
stirred for 15 min and then transferred to a 40 mL Teflon-lined au-
toclave, and heated at 125 °C under autogenous pressure for 48 h.
Dark violet solid was collected by centrifuge, washed three times
with DMF, rinsed twice by methanol over 24 h, and dried at 80 °C
in a vacuum oven. Finally, the resulting dark violet solid was added
to 25 mL of saturated Na2WO4•2H2O. The mixture was stirred for
24 h at 40 ˚C. The precipitated violet solid was collected by cen-
trifuge, washed by methanol/DMF, and dried in a vacuum oven at
60 °C.
All solvents and reagents were purchased from Sigma Aldrich
and Merck and utilized without further purification. FT-IR sam-
ples were prepared as KBr pellets and spectra were recorded on a
PerkinElmer 1600 FTIR spectrometer. All products were confirmed
by a GC manufactured by Teif Gostar Faraz Co., Iran. The powder
diffractometer patterns were collected by ADVANCEX-ray with CuK
radiation. Elemental analyses were obtained using a PerkinElmer
analyzer. Thermal stability of heterogeneous MOFs was measured
with a heating rate of 5 °C min−1 from 50 to 600 °C on a Perkin
Elmer STA 6000 TGA. Field Emission Scanning Electron Microscopy
(FE-SEM) imaging was performed on a Zeiss microscope with an
attached camera. Ultrasonic irradiation was generated by a Digital
Sonifier S-250D from Branson.

4
M. Sabaghi, Z. Aghajani and G.R. Najafi / Journal of Organometallic Chemistry 925 (2020) 121483
ligand to produce a two-dimensional structure. The Co-ABDC was
produced after removing coordinated DMF molecules and then
tungsten was immobilized on MOF support. The MOF was then
characterized using different techniques.
3.1. Characterization of Co-ABDC/W MOF
FT-IR spectroscopy is a powerful tool to identify the functional
group of organic compounds. FT-IR spectra of amino-functionalized
metal-organic framework (Fig. 2b) exhibited a significant differ-
ence compared to that of pure 2-Aminoterephthalic acid (Fig. 2a).
Two dominant peaks that are appeared between 3300–3600 con-
firmed the existence of symmetric and asymmetric stretching vi-
brations of the NH2 group that are shown in Fig. 2a. The peaks
in the range of 1400 cm−1 and 1600 -1500 cm−1 can be respec-
tively ascribed to the asymmetric and symmetric stretches of the
carboxylate group (Fig. 2a). The deprotonation of COOH groups
in 2-Aminoterephthalic acid after reacting with metal ions was
validated as strong absorption bands that are present at 1650
cm−1 and at the same time the absorption bands that are ab-
sent at around 1700 cm−1. The C-N stretching band of Co-ABDC
(Fig. 2b) appears at 1340 cm−1. The mentioned band for Co-
ABDC/W (Fig. 2c) is shifted to a lower frequency (1275 cm−1) ow-
ing to complexation with the tungstate. Lastly, a peak emerging at
890 cm−1 in c spectrum can be ascribed to W=O (Fig. 2c) [43].
EDS analysis identifies the purity of materials by qualitative de-
tection of elements. EDS spectrum of Co-ABDC/W (Fig. 3) presents
the presence of Co, N, O, C, and W elements in their specified en-
ergy which confirms the purity of the product.
As shown in Fig. 4, all mentioned elements exist in EDS analysis
of the Co-ABDC except W.
The crystalline phase purity of the synthesized Co-ABDC/W
MOF was analyzed by X-Ray Powder Diffraction (XRD). As shown
in Fig. 5, the characteristic diffraction peaks of the prepared sam-
ple are in good agreement with the theoretical patterns (Fig. 5a).
Moreover, the crystalline structure of the as-prepared Co-ABDC is
similar to the pattern reported by Ying Yang et. Al [42]. The pow-
der XRD patterns of Co-ABDC/W confirm that this material has
isoreticular frameworks. As can be observed from Fig. 5, the pow-
der XRD patterns of both Co-ABDC (5b) and Co-ABDC/W (5c) have
identical characteristics which confirm that the complexation with
tungstate has no effect on the crystalline structure.
Fig. 5. Comparison of XRD patterns of synthesized a) Co-ABDC (green), b) Co-
ABDC/W (blue), and simulation (red).
2.3. Ultrasonic oxidation procedure
A mixture of benzyl alcohol (1 mmol), aqueous hydrogen perox-
ide, and Co-ABDC/W as heterogeneous catalysis (0.01 g) was soni-
cated in an ultrasonic bath (constant frequency) at 25 °C by circu-
lating water. At the end of the oxidation, the mixture was diluted
by adding ethyl acetate (3 × 15) to separate the product from the
catalyst. The MOF was then washed and to be reused directly for a
new procedure, without further purification.
To study the morphology of Co-ABDC/W MOF and how to con-
nect tungstate to MOF, the FE-SEM was applied. As expected, the
SEM micrograph confirms the achievement of crystalline material
(similar to rhombus shape) (Fig. 6). The FE-SEM graphs reveal the
The catalytic performance of the catalyst was calculated in
terms of conversion of benzylic alcohols (%) and yield/selectivity
(%) to the product according to the following equations:
Initial moles of benzylic alcohol − remaining moles of benzylic alcohols × 100
Conversion %
=
( )
Initial moles of benzylic alcohols
as-prepared catalyst in different magnificent. As it can be seen
Aldehyde yield
%
( )
= Moles of formed aldehydes
× 100/ Initial moles of alcohols
from Fig. 6C, the particle size of the as-prepared catalyst was mea-
sured to be between 24.84 to 63.53.
The comparative study on the TGA plots of the Co-ABDC/W
(blue) and Co-ABDC (green) are shown in Fig. 7. All two sam-
ples were thermally stable up to 300 °C. A first weight losses
of ≈ 1–3% are observed at below 200 °C, suggesting the evap-
oration of surface-adsorbed solvents and coordinated DMF. Co-
ABDC shows a fast weight loss of up to 300 °C (around 350 °C
for 60% weight loss), indicating the rapid decomposition of struc-
ture. While the Co-ABDC/W weight loss (>40%) occurred between
400 °C to 450 °C, the decomposition of Co-ABDC/W happened at
a higher temperature. It was assumed that a difference in the net-
work forces of the MOFs or morphology may explain the difference
between the obtained thermal stability of samples.
Aldehyde selectivity
%
( )
= Aldehyde yield × 100 /conversion
3. Results and discussion
In this work, [Co3(ABDC)3(DMF)4] was first synthesized from
the reaction of 2-Aminoterephthalic acid and cobalt nitrate hex-
ahydrate by a solvothermal method according to the previously
mentioned procedure. According to literature, Co-ABDC coordina-
tion polymer is not only isostructural but also based on a trin-
uclear cobalt cluster [37]. As it can be seen in Fig. 1, the trinu-
clear [Co3(CO2)6] secondary building unit is connected to six ABDC

M. Sabaghi, Z. Aghajani and G.R. Najafi / Journal of Organometallic Chemistry 925 (2020) 121483
5
Fig. 6. FE-SEM micrograph of the Co-ABDC/W MOF in different magnificent.
Fig. 7. TGA curves of Co-ABDC/W and Co-ABDC measured in air.
3.2. Catalytic sonochemical oxidation of benzylic alcohols
alent of oxidant, the limited concentration of oxidizing moieties
seems to promote high selectivity by limiting the over-oxidation
phenomena [44]. Increasing the amount of catalyst and oxidant led
to an increase in the conversion of benzylic alcohols, while a de-
crease occurred in the selectivity because of a little over-oxidation
to yield by-products, such as carboxylic acids.
Direct sonochemical oxidation of alcohol under solvent-free
condition as a green process requires an efficient catalyst to pro-
vide the activation of alcohol and oxygen molecules. Therefore, we
checked the activity of the prepared catalyst for selective oxida-
tion of benzyl alcohol using H2O2 as the oxidant under mild con-
ditions. The conditions in solvent-free oxidation reactions were op-
timized to explore the performance of the catalyst. A pilot test was
conducted with benzyl alcohol in the presence of various amounts
of Co-ABDC/W MOF catalyst under ultrasonic irradiation to afford
benzaldehyde. It is worth mentioning, sonoxidation of benzyl alco-
hols could not proceed in the absence of either catalyst or H2O2
(Fig. 8). It was found that the optimum amount of catalyst was
about 0.01 g to afford 100% yield at 25˚C after 5 min based on
the results of gas chromatography analysis. Then, the influence of
hydrogen peroxide concentrations was investigated on the ultra-
sonoxidation. Benzaldehyde (model substrate) yield increased from
25% to 100% when the H2O2/ substrate molar ratio increased from
0.5 to 1 under solvent-free sonication irradiation and decreased to
65% at 3 molar equivalents of H2O2 (Fig. 8). Below 1 molar equiv-
The catalytic performance of Co-ABDC/W was compared with
other catalysts to investigate the need for the present catalyst for
the oxidation of alcohols. To this end, a pilot reaction was done in
the presence of different catalysts, such as Lewis acids, Co3O4 NPs,
MWCNTs/TiO2, Co-ABDC, and Co-ABDC/W (Table 1). The yields of
conversions in the rest of the cases were lower or contained side
products. An experiment was also carried out in the absence of
a catalyst. The yield of the reaction in this case was very traced
after 45 min. A comparison between the last two rows (Table 1)
clearly demonstrates the power of activated tungstate anion dur-
ing sonochemical oxidation protocol. Sonication conditions had a
significant role in this process. In the absence of ultrasonic irradi-
ation, (stirring/ grinding/ classical heating) no considerable yields
were observed. The optimization of the ultrasonic instrument was
done within the power of 100–300 W and the frequency range of

6
M. Sabaghi, Z. Aghajani and G.R. Najafi / Journal of Organometallic Chemistry 925 (2020) 121483
Fig. 8. Oxidation of PhCH2OH as a function of catalyst amount (g) and H2O2/PhCH2OH molar ratio under US irradiation (40 kHz, 100 W) at 5 min.
Table 1
Optimization of various reaction conditions on the model reactiona.
b
Entry
Conditions
Time (min)
Yield (%)
Ref.
1
2
3
4
5
6
7
8
9
Stirring, r.t.
45
5
Trace
15
This work
This work
This work
This work
This work
This work
[45]
Ultrasound, r.t.
Co-ABDC/W, stirring, r.t.
H2SO4, ultrasound, r.t.
HCl, ultrasound, r.t.
30
30
30
30
15
20
5
55
38
32
Co3O4 NPs, ultrasound, r.t.
MWCNTs/TiO2, ultrasound, r.t.
Co-ABDC, ultrasound, r.t.
Co-ABDC/W, ultrasound, r.t.
68
100
100
100
This work
This work
a
Benzyl alcohol (1 mmol), H2O2 (15% Wt.), catalyst (0.01 g), ultrasonic: 40 kHz,
100 W.
b
Conversion yield
Scheme 1. A possible reaction mechanism.

M. Sabaghi, Z. Aghajani and G.R. Najafi / Journal of Organometallic Chemistry 925 (2020) 121483
7
Table 2
Solvent-free sonoxidation of various alcoholsa.
b
Entry
1
R
R1
H
Time (min)
Yield (%)
Selectivity (%)
2-Methoxyphenyl
))))US
࢞
9
96
90
100
93
98
92
100
97
96
88
95
89
92
75
100
98
90
85
90
87
90
89
85
83
84
79
91
89
92
92
100
95
180
7
2
4-Methoxyphenyl
2-Chlorophenyl
4-Chlorophenyl
4-Nitrophenyl
2-Nitrophenyl
4-Bromophenyl
Phenyl
H
))))US
࢞
100
96
165
6
3
H
))))US
࢞
99
155
5
97
4
H
))))US
࢞
100
100
100
96
140
7
5
H
))))US
࢞
150
8
6
H
))))US
࢞
100
99
160
12
230
5
7
H
))))US
࢞
98
97
8
H
))))US
࢞
100
100
100
100
100
99
200
8
9
Phenyl
Methyl
))))US
࢞
185
8
10
11
12
13
14
15
Phenyl
Ethyl
))))US
࢞
160
10
205
15
210
20
225
10
190
9
Phenyl
Phenyl
))))US
࢞
100
97
4-Chlorophenyl
4-Chlorophenyl
4-Methoxyphenyl
4-Methoxyphenyl
Phenyl
))))US
࢞
99
96
4-Chlorophenyl
Phenyl
))))US
࢞
99
97
))))US
࢞
100
99
4-Methoxyphenyl
))))US
࢞
100
100
190
a
Reaction conditions: alcohol (1 mmol), H2O2 (15% wt), and catalyst (0.01 g). Ultrasonic irradiation:
40 kHz, 100 W at room temperature or under the conventional heating condition at 60 ˚C.
b
The conversion yield was based on GC analyses.
30–70 kHz. As a result, the best data were obtained in 40 kHz fre-
quency and 100 W power. Moreover, it can be concluded that the
existence of the MOF catalyst and ultrasonic irradiation could syn-
ergistically affect one another for selective and significant promo-
tion of the oxidation reactions.
examined cases in the presence of the catalyst is presented in
Table 2.
To investigate the domains and limitations of Co-ABDC/W MOF,
various substituted benzyl alcohols with both electron-donating
(OCH3) and electron-withdrawing (Cl, Br, NO2) were oxidized un-
der optimized conditions. The preadsorption of the various sub-
strates on the surface of Co-ABDC/W MOF was modified by the
steric arrangement of functional group and substitution. The men-
tioned hypothesis was partially confirmed by the presence of a
steric effect in the ortho and para isomers of chlorobenzyl alco-
hols, methoxybenzyl alcohols, and nitrobenzyl alcohols with a re-
activity trend of ortho < para (Table 2). To expand the applica-
bility of the fabricated Co-ABDC/W MOF for selective oxidation,
sonocatalytic oxidation of various alcohols other than primary ben-
zyl alcohols was examined. As shown in Table 2, prepared MOF
was also effective in oxidation of the secondary aromatic alcohols
(Table 2, entry 9–15) to corresponding ketones. In most oxidations
cases, secondary aromatic alcohols had lower yields and longer re-
action times compared to that of the primary benzylic substrate.
It might due to the larger steric hindrance of the aryl groups. Be-
sides, the secondary benzylic alcohols possessing electron-donating
substituents (methoxy-) on the aromatic ring were oxidized to the
corresponding ketones with higher conversions (Entries 14,15). This
method proceeded quite cleanly under mild conditions, without
undesirable side reactions under ultrasonic irradiation (40 kHz,
100 W). The efficient advancement of the reaction in all of the
In summary, based on the empirical results, it can be stated
that the ultrasound irradiation can remarkably improve the yield
of the reactions as well as decreasing the reaction times in the
presence of H2O2 and Co-ABDC/W MOF as a catalyst compared to
a conventional heating method. It should be mentioned that the
Co-ABDC/W MOF is nontoxic, stable to moisture or air, and very
active. Another advantage of this efficient catalyst is its high selec-
tivity. Furthermore, it can be recovered by simple separation and
reused in reactions for at least five runs (Fig. 10) with only a bit at-
tenuation of activity. According to the XRD pattern of Co-ABDC/W
MOF (Fig. 9), the crystalline structure was maintained after 5 cy-
cles of reuse. Therefore, the slight attenuation is mainly because of
the loss of Co-ABDC/W MOF after centrifugation.
According to the successful studies of the plausible mecha-
nism for the oxidation process in the presence of transition metals
[38,46], procreation of W(O2) O3 from the reaction of tungstate an-
ion of the catalyst with H2O2 is the proposed reaction mechanism.
The activated catalyst can transfer an oxygen molecule to the sub-
strate. The oxidation procedure occurs and then the aldehyde prod-
uct is produced from the benzylic alcohol substrate. After this step
and passing the active oxygen molecule, the WO4 anion regener-
ates (Scheme 1).

8
M. Sabaghi, Z. Aghajani and G.R. Najafi / Journal of Organometallic Chemistry 925 (2020) 121483
dation of synthetic compounds presented some significant advan-
tages, such as easy workup procedure, readily available precursors,
recyclability of the heterogeneous catalyst, high atom economy,
short reaction times, and excellent conversion yields according to
the green chemistry principles.
Declaration of competing interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared to
influence the work reported in this paper.
Acknowledgments
The Authors acknowledge the kind financial supports of the Re-
search Council of Qom Branch, Islamic Azad University, Qom, Iran.
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