Ultrasound-Engineered fabrication of immobilized molybdenum complex on Cross-Linked poly (Ionic Liquid) as a new acidic catalyst for the regioselective synthesis of pharmaceutical polysubstituted spiro compounds

Article abstract of DOI:10.1016/j.ultsonch.2021.105614

A novel supported molybdenum complex on cross-linked poly (1-Aminopropyl-3-vinylimidazolium bromide) entrapped cobalt oxide nanoparticles has been successfully fabricated through two different procedures, i.e. ultrasound (US) irradiations (100 W, 40 kHz)

Full text of DOI:10.1016/j.ultsonch.2021.105614

Ultrasonics Sonochemistry 75 (2021) 105614
Contents lists available at ScienceDirect
Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultson
Ultrasound-Engineered fabrication of immobilized molybdenum complex
on Cross-Linked poly (Ionic Liquid) as a new acidic catalyst for the
regioselective synthesis of pharmaceutical polysubstituted
spiro compounds
,b,
Zahra Elyasia, Javad Safaei Ghomia *, Gholam Reza Najafia
a Department of Chemistry, Qom Branch, Islamic Azad University, Qom, Islamic Republic of Iran
b Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, Islamic Republic of Iran
A R T I C L E I N F O
A B S T R A C T
Keywords:
A novel supported molybdenum complex on cross-linked poly (1-Aminopropyl-3-vinylimidazolium bromide)
entrapped cobalt oxide nanoparticles has been successfully fabricated through two different procedures, i.e.
ultrasound (US) irradiations (100 W, 40 kHz) and reflux. The efficiency of the two different methods was
comparatively investigated on the fundamental properties of proposed catalyst using diverse characterization
techniques. Based on the obtained results, the ultrasonication method provides controlled polymerization pro-
cess; as a result, well connected polymeric network is formed. In addition, the use of ultrasound waves turned out
to be able to increase the particles uniformity, specific surface area (from 79.19 to 223.83 m2/g), and the onset
thermal degradation temperature (Td) value (from 248 to 400 ◦C) of the prepared catalyst which intensifies the
catalytic efficiency. Besides, US-treated catalyst demonstrated high chemical stability and maintained its cross-
linked network after eight cycles recovery, while the cross-linked network of catalyst obtained under silent
condition was completely disrupted. Furthermore, the ultrafast multi-step fabrication procedure was performed
in less than 6 h under ultrasonic condition while a similar process promoted by a mechanical stirring method
came to a conclusion after 5–6 days. Accordingly, the utility of the ultrasound irradiation was proved, and US-
treated catalyst was applied for improved synthetic methodology of spiro 1,4-dihydropyridines and spiro pyr-
anopyrazoles through different acidic active sites. Due to the significant synergistic influence between the
proposed catalyst and US irradiation, a variety of novel and recognized mono-spiro compounds were fabricated
at room temperature in high regioselectivity.
Poly (ionic liquid)
Heterogeneous catalyst
Ultrasound
Molybdenum complex
Regioselective synthesis
1. Introduction
solvents, but also meets the ecological requirements more efficiently [4].
Although the interaction between ultrasound irradiation and molecules
As one of the effective and greenest techniques, sonochemistry is
interesting in the synthesis of nanomaterials and various bulks [1,2].
Ultrasound-assisted synthesis has been widely used due to its mechan-
ical, physical, or chemical effects on the process. It is obvious that
exposure of nanomaterials, various bulk, and polymer solutions to low-
frequency (20–100 kHz), high-intensity (10–1000 W/cmꢀ 2) ultrasound
induces great changes to their textural and morphological properties
such as particle size, viscosity properties, gelling property, thermal
stability, and biological activity [3]. Moreover, the synthesis of sub-
stances under ultrasonic condition not only requires fewer catalysts and
is not direct, the energy of the ultrasound waves can cause acoustic
cavitation, which provokes different physical and chemical effects.
During this process, the implosion of the bubbles leads to the release of a
large amount of mechanical and thermal energy without any significant
change in the reaction medium (in terms of pressure and temperature)
[5]. Consequently, the use of ultrasonic irradiation accelerates an
organic transformation at the synthesis pathway, and it has been
extensively employed in recent decades according to its specific
properties.
2-Oxindoles, especially those spiro-fused to other cyclic frameworks,
* Corresponding author at: Department of Chemistry, Qom Branch, Islamic Azad University, Post Box: 37491- 13191, Qom, Islamic Republic of Iran; Department of
Organic Chemistry, Faculty of Chemistry, University of Kashan, Islamic Republic of Iran.
E-mail address: safaei@kashanu.ac.ir (J.S. Ghomi).
https://doi.org/10.1016/j.ultsonch.2021.105614
Received 12 March 2021; Received in revised form 17 May 2021; Accepted 27 May 2021
Available online 1 June 2021
1350-4177/© 2021 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Z. Elyasi et al.
Ultrasonics Sonochemistry 75 (2021) 105614
Fig. 1. Biologically active 2-Oxindoles.
are structural motifs in organic chemistry due to their widespread
bioavailability and pharmacological applications such as HIV protease
inhibitor [6], anti-inflammatory [7], anti-cancer [8], antimicrobial [9],
anti-hypertensive [10], and anti-diabetic [11]. Among various drugs
with a 2-oxindole core that have already been developed, only four
marketed molecules; namely, Sunitinib proposed in pancreatic neuro-
endocrine tumors, Ropinirol utilized for Parkinson’s disease treatment,
Nintedanib known as a drug against idiopathic pulmonary fibrosis, and
HIV protease inhibitor have appeared in Fig. 1. Both functionalized spiro
1,4-dihydropyridines and spiro pyranopyrazoles are important branches
of biologically active organic compounds [12,13]. Recently, owing to
their great biological properties, some straightforward methods have
been reported for their preparation using one-pot four-component re-
actions. However, some of these protocols suffer from limitations such as
prolonged catalyst preparation, elevated temperature, and using haz-
ardous and expensive reagents besides byproducts. It is believed that an
effective general catalytic process for synthesizing both spiro 1,4-dihy-
dropyridines and spiro pyranopyrazoles can be greatly promising and
strongly desired.
limitation [23,24]. Furthermore, transition metal complexes have also
received increasing attention in the field of catalysis, and there are many
reports about their catalytic utilization. These transition metal com-
plexes, which are often in nano size, are immobilized on various sup-
ports to provide higher activity [25–27]. Although reported catalysts are
effective, each of them has some disadvantages such as low loading, long
reaction time, and harsh reaction condition. In general, designing and
preparing a new efficient catalyst with high stability, selectivity, and
recyclability is challenging in both industry and laboratory. To this end,
we can claim that supported molybdenum on cross-linked PIL can be
considered a smart way to overcome these problems due to the
numerous functionalities that can be linked to it. It is worth noting that
the immobilization of Mo (VI) Schiff base complexes into cross-linked
poly ionic liquids has not previously been reported, either. In this re-
gard, a fast and green method for the synthesis of scalable molybdenum
Schiff base complex immobilized on porous poly ionic liquid (PPIL)
framework is proposed and its efficiency in catalyzed synthesis of spiro-
pyranopyrazoles and spiro-1,4-dihydropyridines is also explored. We
develop polycyclic heterocycle framework by combining pyran, pyr-
azole, and spiro-oxindole motifs under mild condition. The proposed
process highly complements the aims of green chemistry, and shows
massive benefits both in industry and in academia.
In recent years, ionic liquids (ILs) have been increasingly taken into
consideration due to the fact that they can not only improve the catalytic
activity, but also stabilize the reaction catalytic species [14–16]. How-
ever, some properties like homogeneity, high viscosity, and both leakage
issue of ionic liquids limit their extensive use. To overcome these
problems, ILs are generally supported by various components (polymers,
metal oxides, silica, etc.) to obtain heterogeneous catalysts [17,18].
However, most IL-based catalysts need harsh conditions (high pressure/
temperature) due to lack of active sites. Poly ionic liquids (PILs) or ionic
liquid (IL) polymers are an emerging class of charged polymers having
repeating units of polymerizable ionic moieties. They possess interesting
properties of both conventional polymers (such as stiffness, tunable
macromolecular structure, and mechanical strength) and those of the ILs
(such as electrical conductivity, high thermal and chemical stability, and
wide electrochemical potential window) [19–22]. Satisfying results in
great molecular yields and weight are obtained while an oil-soluble
radical initiator like Azobisisobutyronitrile (AIBN) with a traditional
heating technology is used for radical polymerization. Although this
technique is suffering from lack of control on the polymers’ physico-
chemical attributes, employing a water-soluble initiator as 4,4′ Azobis
(4-cyanopentanoic acid) can be considered a prominent solution to this
2. Experimental
2.1. Materials
All chemicals grades were purchased from Merck and Scharlau in
excellent purity. Melting point (m.p) was carried out by Electro-Thermal
9200, and Fourier transform infrared (FT-IR) spectroscopy was operated
1
by Nicolet Magna-550 spectrometer (KBr pellets). H and 13C nuclear
magnetic resonance (NMR) spectroscopy were obtained by Bruker at
300 and 75 MHz, respectively (in DMSO, internal reference: TMS).
Philips-X’pertpro, an X-ray diffractometer utilizing Ni-filtered Cu K
α
radiation was employed for investigating X-ray diffraction (XRD) anal-
ysis, the particle size and morphological engineering were investigated
by scanning electron microscopy (model: LEO-1455VP). A transmission
electron microscope (TEM, Philips EM208S) was applied for the in-
depth examination of morphology. The compositional analysis was
done by Energy-dispersive X-ray (EDX, Kevex, Delta Class I).
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Z. Elyasi et al.
Ultrasonics Sonochemistry 75 (2021) 105614
Scheme 1. Synthetic route to obtain the Co3O4@PPIL-Mo under ultrasound irradiation.
2.2. Synthesis of vinyl functionalized Co3O4 NPs
(20 ml). Then bis (acetylacetonato) dioxomolybdenum (1 mmol) was
added to the reaction mixture and submitted to ultrasonic agitation
about 2 h (heated for 24 h at 60 ◦C). The final product was separated,
washed several times with EtOH/H2O, and then dried in a vacuum oven
and sieved.
Co3O4 NPs were synthesized through chemical co-precipitation
method according to our previous literature [28]. In short, 8.60 g of
Cobalt (II) nitrate was dispersed in EtOH (100 ml) for about 30 min.
Thereafter, 2.14 g of oxalic acid was slowly added and the solution was
stirred for 1 h at 45 ◦C. Finally, the acquired precipitate was calcined for
2.5. Typical procedure for the synthesis of mono-spiro derivatives
◦
2 h at 400 C. The vinyl functionalized Co3O4 NPs were obtained via
mixing NPs (1 g) and 3-(trimethoxysilyl) propylmethacrylate (MPS) (10
mmol) in EtOH under ultrasound condition (about 2 h). The same
preparation method was carried out for 24 h under reflux condition
according to the reported work [29]. Finally, to separate the MPS,
coated Co3O4@MPS was separated by centrifugation (6000 rpm, 5 min)
and washed with EtOH to eliminate the unreacted compounds.
Typically, isatins (1 mmol), activated methylene compounds (1.0
mmol), dimethyl acetylene dicarboxylate (DMAD), amine components
(hydrate hydrazine, phenyl hydrazine, and aromatic amines), ultra-
sound treated catalyst (10 mol%), and water (5 ml), as a green solvent,
were sonicated (ultrasonic bath) at room temperature or irradiated in a
microwave oven at 200 W for an appropriate length of time as indicated
in Tables 3 and 4. The reaction completion was checked by thin layer
chromatography technique, and then the heterogeneous catalyst was
separated. As the last step of multicomponent reaction, the crude pre-
cipitate was recrystallized from ethanol to obtain a pure product. All
products were characterized by melting point (m.p.), 1H NMR, 13C NMR,
FTIR, and elemental microanalysis. The spectral data of all compounds
are provided in Supplementary Information.
2.3. Fabrication of PPIL composite
Polymerization of aminopropyl-3-vinylimidazolium bromide
[AVIM]Br (IL), induced by ACPA in the H2O to form the porous ionic
polymer network, was conducted. Ionic liquid was prepared according
to our previous reported protocol [29]. Typically, vinyl functionalized
Co3O4 NPs (0.5 g), (IL) (0.005 mol, 0.45 g), and crosslinker (N,N’-
Methylenebis acrylamide) were dissolved into 10 ml deionized water
and then submitted to an ultrasonic agitation for 15 min. In continua-
tion, ACPA (1% mol, 0.029 g) was added as a water soluble initiator, and
the mixture was sonicated about 1 h (refluxed for 8 h). The obtained
powder was collected and treated subsequently by a drying approach to
obtain Co3O4@PPILs with unique textual properties. The probable
mechanism of the precipitation polymerization process is shown in
Scheme 1. The ACPA was decomposed by US irradiations and formed
corresponding radicals through releasing nitrogen gas that abstracted
electron from one of the terminal vinyl functional groups existing in
Co3O4@MPS, and IL to produce the corresponding macro initiators.
Mentioned macro radicals start IL grafting onto the Co3O4@MPS leading
to graft polymerization in the presence of the MBAA, and finally, poly-
meric network is obtained
2.6. Spectral data of new compounds
Methyl-6′-amino-5,7-dichloro-5′-cyano-2-oxo-2′H-spiro[indoline-3,4′-
pyrano[2,3c]pyrazole]-3′-carboxylate (5f): White solid, m.p. > 300 ℃. IR
(KBr) ν: 3426, 3275, 3251, 2955, 2275, 1782, 1736, 1660, 1537, 1446,
1200, 1086, 920, 768 cmꢀ 1; 1H NMR (300 MHz, DMSO‑d6) δ: 12.24 (s,
1H, NH), 10.55 (s, 1H, NH), 7.17 (s, 2H, NH2), 6.98 (s, 1ArH), 6.88 (s,
1ArH), 4.09 (s, 3H, OMe); 13C NMR (75 MHz, DMSO‑d6) δ: 182.5, 170.0,
158.0, 155.7, 144.2, 142.8, 127.2, 122.1, 118.7, 118.0, 113.9, 107.7,
103.4, 70.8, 28.3. Anal. calcd for C16H9Cl2N5O4: C 47.31, H 2.23, N
17.24; found C 47.34, H 2.22, N 17.23.
Methyl-6′-amino-5,7-dichloro-5′-cyano-2-oxo-1′-phenyl-1′H-spiro[indo-
line-3,4′-pyrano[2,3-c]pyrazole]-3′- carboxylate (5 l): pink solid, mp >
300 ◦C; IR (KBr)
ν: 3392, 3230, 3022, 2955, 2173, 1782, 1731, 1665,
1585, 1489, 1408, 1292, 1215, 1095, 937, 829, 779 cmꢀ 1; 1H NMR (300
MHz, DMSO‑d6): δ: 10.40 (s,1H, NH), 7.72–6.54 (m, 7 ArH, and NH2),
3.37 (s, 3H, Me); 13C NMR (75 MHz, DMSO‑d6): δ: 179.0, 167.4, 152.1,
151.9, 149.2, 142.0, 134.1, 133.7, 130.1, 124.0, 123.2, 121.7, 121.0,
118.3, 117.0, 107.3, 72.25, 35.92. Anal. Calcd. for C22H13Cl2N5O4: C,
2.4. Fabrication of PPIL-Mo composite
The prepared poly ionic liquid was subjected to a complexation re-
action. The obtained PIL (0.5 g) was ultrasonically dispersed in ethanol
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Ultrasonics Sonochemistry 75 (2021) 105614
Table 1
Comparison of the experimental conditions under US irradiation and classical
heating method.
Entry
Procedure
Condition
Time (h)
solvent
Ref.
1
Synthesis of [AVIM]
Br
Δ
>24
acetonitrile
[31]
This
work
[32]
This
work
[32]
This
work
[33]
This
work
US
less than
–
1
2
3
4
Synthesis of
NP@MPS
Δ
US
24–48
EtOH
2
–
Polymerization
process
Δ
US
6–12
MeOH
H2O
1
Immobilization of Mo
(VI)
Δ
US
24–48
MeOH
EtOH
2
Fig. 3. FT-IR spectra of b‘) Co3O4@MPS, d‘) Co3O4@PPIL, and e‘) desired
Co3O4@PPIL-Mo obtained from US irradiations.
reaction is compared with a conventional heating method to achieve the
most efficient condition for the fabrication of Co3O4@PPIL-Mo.
Furthermore, the synergistic catalytic effect is investigated between the
prepared catalyst and the ultrasonic irradiation for the synthesis of
mono-spiro derivatives. In addition, sonochemical one-pot multicom-
ponent reactions were compared with the microwave-assisted reactions
in details.
Firstly, Co3O4 NPs were prepared and sonochemically coated by
silica network (MPS) for the first time. In the following, the monomeric
IL was synthesized via quaternization of N-vinylimidazole with 3-bro-
mopropylamine hydrobromide under ultrasound irradiation. We also
introduce a straightforward method for controlled radical polymeriza-
tion of silica-coated nanoparticles, ionic monomers, and MBAA as cross-
linking agent via ultrasonic radiations. The proposed approach provides
an excellent dispersion polymerization process by choosing a water-
soluble initiator. Finally, sonochemical immobilization of molybde-
num was carried out as the main active sites for catalytic performance.
With the aim of highlighting the efficiency of the proposed multi-step
protocol, a comprehensive comparative study was done (Table 1). At
first, the choice of ultrasound method is an intelligent tactic from
various aspects (such as economic, environmental, practicality, etc.).
Acoustic cavitation causes a special interaction of matter and energy,
and ultrasonic radiation of liquids provides high energy chemical
transformations to occur (especially, the reactions involving free radi-
cals). Accordingly, these pluses will cause energy and time savings. All
of these steps were performed in less than 6 h under ultrasonic condition
while similar reported reactions promoted by a mechanical stirring
method resulted in more time. Furthermore, in order to move to more
sustainable methodologies, green and less hazardous solvents were
replaced and some steps were carried out under solvent-free conditions.
The FT-IR spectroscopy study of the NPs, vinyl functionalized NPs,
[AVIM]Br, Co3O4@PPIL, and Co3O4@PPIL-Mo was carried out to ach-
ieve more precise information. As illustrated in Fig. 2a, the peaks at 575
and 655 cmꢀ 1 are related to the spinel Co3O4 characteristic peaks [34].
Peaks at 1100, 1550, and 1740 cmꢀ 1 not only confirm successful coating
of MPS, but are also related to Si-O, C = C, and carbonyl stretching
Fig. 2. FT-IR spectra of a) Co3O4 NPs, b) Co3O4@MPS, c) IL monomers, d)
Co3O4@PPIL, and e) Desired Co3O4@PPIL-Mo obtained from reflux conditions.
54.79; H, 2.72; N, 14.07; Found: C, 54.78; H, 2.71; N, 14.07.
3. Results and discussion
3.1. Characterization of Co3O4@PPIL-Mo composite
Demonstrating the suitable conditions for nanoparticles’ surfaces is
considered one of their most significant alterations [30]. As a matter of
fact, magnetic behavior of Fe3O4 NPs can enhance their significance
because they are commonly absorbed into the magnet during the stir-
ring. As a result, magnetic NPs cannot be efficiently dispersed. There-
fore, not only are their surfaces not effectively functionalized, but also
their polymerization flow is interrupted. Subsequently, more extended
intense conditions must be applied to degrade polymer chains and core
structure. To this end, the paramagnetic Co3O4 NPs were selected and
polymerization of ionic monomers initiated and controlled by ultrasonic
agitation. In this research, the performance of ultrasonic-assisted
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Z. Elyasi et al.
Ultrasonics Sonochemistry 75 (2021) 105614
Fig. 4. XRD patterns of the US-treated Co3O4@PPIL-Mo.
Fig. 5. A, B) N2 adsorption–desorption isotherms and C) pore size distributions of Co3O4@PPIL-Mo obtained from two different methods.
vibrations, respectively (Fig. 2b). As depicted in (Fig. 2c), vinyl group’s
stretching vibration appears at 1648 cmꢀ 1. Moreover, bending vibration
of the imidazole motif is emerged at 932–1020 cmꢀ 1. Nonetheless, these
introduced peaks are not observed in the PIL spectrum, which confirms
the polymerization (Fig. 2d). Unfortunately, the presence of C = C MPS
peak (1550) reveals incomplete polymerization process under reflux
condition. N-C-N characteristic peaks at 660 and 1228 cmꢀ 1 [35] are
preserved in the spectrum after the polymerization process (Fig. 2d).
The strong absorbance band observed at 1670 cmꢀ 1 belongs to the
characteristic peak of amide C = O (Fig. 2d). Finally, incomplete and the
uncontrolled polymerization process led to partial complexation of Mo
(VI). The FT-IR spectrum of the prepared composite (Fig. 2e) confirmed
the partial complexation process with the appearance of week bands at
915 and 940 cmꢀ 1 which belong to the two cis doubly bonded oxygens at
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Ultrasonics Sonochemistry 75 (2021) 105614
Fig. 6. FESEM photographs of Co3O4@PPIL-Mo obtained under A-C) silent condition, and D-E) US irradiation.
the molybdenum core [36].
at 31.70, 37.26, 38.97, 45.17, 56.11, 59.77, and 65.62. The mentioned
peaks that appeared were consistent with Co3O4 (JCPDS No. 01–080-
1533, fcc, Fd3m) [37]. A broad peak about 2Θ = 22◦ is attributed to the
amorphous Si [38]. However, no diffraction peak characteristic of mo-
lybdenum was recorded which can be owing to its poor crystallinity and
low concentrations. In fact, XRD analysis, confirms that the Mo (VI)
loading retains the main crystalline structure of prepared catalyst [39].
The diffractograms revealed the presence of spinel structure in both
methods and the graphs were the same.
As can be seen, the peaks intensity of the determined catalyst was
well prepared via ultrasonication (Fig. 3). The FT-IR spectra of US-
treated samples exhibited a significant difference compared to clas-
sical heating method as explained in the following. According to the FT-
IR spectra, conventional heating intense condition slightly damaged the
structure of vinyl-modified Co3O4 NPs. The partial loading of MPS onto
the Co3O4 NPs leads to weak peaks (Fig. 2). While, the polymerization
process was done properly under US irradiation and as a result, the
absorption band at 1550, which belonged to C = C of MPS disappeared
(Fig. 2d‘, e‘). Two obvious peaks about 900–1020 cmꢀ 1 referred to the
successful complexation process (Fig e‘).
Qualitative analysis of the porosity and specific surface area was
determined by nitrogen sorption experiments (Fig. 5). It can be seen that
the ultrasound-treated sample is typical IV isotherm with an obvious H1
type hysteresis shape, implying the presence of micro-pores (Fig. 5A).
Moreover, as demonstrated in Fig. 5B, the sample of Co3O4@PPIL-Mo
illustrated the isotherm of type IV with a distinctive H2 type hysteresis
The prepared composite under the US and reflux methods was
investigated by the measurements of XRD analysis (Fig. 4). The XRD
graph of the Co3O4@PPIL-Mo clearly illustrated 7 diffraction angles (2θ)
Fig. 7. TEM images of the as-prepared Co3O4@PPIL-Mo obtained under A) US, and B) reflux, conditions.
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Ultrasonics Sonochemistry 75 (2021) 105614
Fig. 8. TGA curves of pure Co3O4 NPs, and Co3O4@PPIL-Mo obtained via two different methods.
loop, revealing the existence of meso-porosity under reflux condition.
The crosslinking poly ionic liquid was synthesized via ultrasonic agita-
tion, and demonstrated well-defined pore channels with a higher surface
area (223.83 m2/g) and larger pore volume (0.27 cm3/g) compared to
the sample prepared in reflux condition (disordered pores with surface
area 79.19 m2/g and 0.21 m3/g pore volume). The pore size distribution
curves (Fig. 5C) further revealed that the pore size distribution was
centered at 7 nm and 12–13 nm under reflux condition. While, the
ultrasound-treated sample provides the pore size distribution about 3–4
nm. Generally, the interaction between polymer chains can be
controlled by the pore structures. Intense shock waves of US radiations
can be employed as micro liquid jets that modify the surface of the
polymer, and the porous and cavities regions can be increased accord-
ingly. With ultrasonic treatment, the breakup of agglomerates led to the
increase in specific surface area (active sites).
The TEM and FESEM were used to study the morphology, uniformity
and size of the produced PPIL via different protocols. As it can be seen in
(Fig. 6D-F), an obvious cross-linked polymeric network including
metallic core and poly ionic liquid was formed under US irradiation. The
average size of particles was estimated via Digimizer software to be
about 200 nm. Ultrasound irradiation provides definite cross-linked
spherical shapes without any agglomeration. The results reveal that
sonochemistry has widely acted as an initiator to enhance the poly-
merization rate for the preparation of PPILs. In contrast, the agglomer-
ated particles are formed under classical heating (Fig. 6B, C). In
addition, it is properly not cross-linked under silent condition (Fig. 6A).
This occurs owing to lack of proper physico-mechanical force for the
dispersion process. The TEM images of the samples with non-ultrasonic
and ultrasonic treatments in water are shown in (Fig. 7. A, B). It is
observable on the TEM image (7A) that the use of ultrasound promotes
Fig. 9. EDX analysis and elemental mapping images of proposed catalyst.
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Ultrasonics Sonochemistry 75 (2021) 105614
Table 2
Optimization of the reaction conditions for the synthesis of 5a by Co3O4@PPIL-Mo.
Entry
Solvent
Catalyst
Condition
Time (min)
Yield b
%
1
H2O
–
US
20
5
18
68
87
73
91
98
82
98
96
93
95
90
91
62
55
88
98
2
H2O
Co3O4 NPs (10 mol%)
US
3
H2O
Co3O4@PPIL (10 mol %)
IL
US
5
4
H2O
US
5
5
H2O
Co3O4@PPIL-Mo (10 mol%)
Co3O4@PPIL-Mo (10 mol%)
Co3O4@PPIL-Mo (5 mol%)
Co3O4@PPIL-Mo (15 mol%)
Co3O4@PPIL-Mo (10 mol%)
Co3O4@PPIL-Mo (10 mol%)
Co3O4@PPIL-Mo (10 mol%)
Co3O4@PPIL-Mo (10 mol%)
Co3O4@PPIL-Mo (10 mol%)
Co3O4@PPIL-Mo (10 mol%)
Co3O4@PPIL-Mo (10 mol%)
Co3O4@PPIL-Mo (10 mol%)
Co3O4@PPIL-Mo (10 mol%)
US
5
6
H2O
US
5
7
H2O
US
5
8
H2O
US
5
9
H2O
Δ
90
10
10
10
10
20
20
5
10
11
12
13
14
15
16
17
EtOH
EtOH/H2O
CH3CN
MeOH
DMF
US
US
US
US
US
Dioxane
H2O
US
US 20 kHz
US 60 kHz
H2O
5
aReaction conditions: isatin (1 mmol), DMAD (1 mmol), malononitrile (1 mmol), and hydrazine hydrate (1 mmol) under US irradiation (40 KHz, 100 W).
bIsolated yields.
the synthesis of composite to regular cubic (Co3O4 NPs in accordance
with XRD patterns) and spherical shapes (molybdenum moieties) with
uniform sizes. The TEM image (6B) reveals that the prepared catalyst
mostly resulted in irregular shapes and sizes in silent condition.
Thermogravimetric analysis (TGA) of the Co3O4@PPIL-Mo was
investigated to determine the US radiation effect on thermal stability.
activity of the prepared Co3O4@PPIL-Mo. Different conditions utilized
to optimize the reaction and empirical results are mentioned in
(Table 2). At first, H2O was chosen as the greenest solvent to perform the
model reaction in the presence of various catalysts. According to the
data, conducting a reaction without any catalyst led to the trace yield
(entry 1). Based on the experimental results, in spite of the fact that the
Co3O4@PPIL-Mo prepared under traditional heating was more effective
(Table 2, entry 5), the ultrasound-treated composite could be considered
the optimal one (Table 2, entry 6). Moreover, the remarkable effect of
ultrasound on the structural and textural attributes (such as porosity,
surface area, etc.) resulted in better performance of the proposed cata-
lyst. An extensive set of experiments were performed to regulate the
catalyst amount. In this regard, the yield was enhanced from 82 to 98%
by enhancing the amount of Co3O4@PPIL-Mo from 5 to 10 mol% while
more catalyst did not increase the yield of the reaction (Table 2, entry
6,7,8). H2O was selected as the solvent to conduct the reaction by me-
chanical stirring under silent condition and to specify the effect of ul-
trasonic agitation (Table 2, entry 9). The experimental results revealed
that during a longer period, reaction yield is lower than sonication. As it
can be hypothesized, there is a significant synergistic effect between US
waves and active catalytic sites. From chemical aspect, the metal tran-
◦
The loss of weight at low temperature (<200 C) in the beginning is
related to the evaporation of physical adsorb water because of the hy-
drophilic nature of ionic liquid units (Fig. 8). The onset thermal degra-
dation temperature (Td) values for the US and reflux methods were
about 400 and 248 ◦C, respectively. Maximal peak shift towards higher
temperature is also related to the more thermal stability of the
ultrasound-treated sample. The Co3O4@PPIL-Mo which was obtained
using the US method revealed a 50.24% weight loss between 400 ◦C and
476 ◦C; and this can be because of the decomposition of the main bond
between ionic monomers and crosslinking. TGA curve also reveals that
Co3O4@PPIL-Mo composite is basically stable up to about 248 ◦C under
reflux condition. These observations indicate that ultrasound irradiation
has a significant treatment effect on the thermal stability of the proposed
catalyst which can definitely fit to the synthesis of spiro-pyranopyrazole
derivatives. It is assumed, well cross-linked structure leads to high
thermal stability of US-treated sample.
sition complex was integrated with the
π conjugated system (including
EDX analysis of proposed catalyst is indicated in (Fig. 9). All lines are
allocated to C, O, N, Co, Mo, Si, and Br elements for US-treated sample.
The percentage of elements are demonstrated in Fig. 9. Furthermore,
elemental mapping images clearly revealed that all elements are well
distributed throughout the Co3O4@PPIL-Mo slices (Fig. 9).
carbon–carbon double bond and N atom). Frequent irradiations of the
US waves led to acceleration in the electronic transfer, and Mo complex
changed to an activated site. Furthermore, collapse of cavitation bubbles
supplied localized hot spots with great pressures that were in charge of
the needed molecular fragmentation and bonding energy. Based on the
physical point of view, catalyst dispersion in the media was facilitated in
US irradiation and as a result, a greater surface area was created. All of
these events can help the reaction to happen quickly. Thereafter, the
influence of solvents was explored. Moreover, methanol, ethanol, and
acetonitrile generate medium yields in longer times (Table 2, entries 10,
12, and 13). The product yields were also about 55% and 62% while the
reaction was conducted in dioxane and DMF, respectively. According to
the obtained result, H2O can be considered an optimal solvent for
3.2. Application of ultrasound-treated Co3O4@PPIL-Mo catalyst for the
regioselective synthesis of mono-spiro derivatives and synergistic catalysis
effect
The one-pot multicomponent reaction between isatin, dimethyl
acetylenedicarboxylate (DMAD), malononitrile, and hydrazine hydrate
was primarily selected as a model reaction to observe the catalytic
8

Z. Elyasi et al.
Ultrasonics Sonochemistry 75 (2021) 105614
Table 3
Synthesis of spiropyrano[2,3-c]pyrazole carboxylate derivatives under ultrasound and MW irradiations a.
Entry
1
X
R
Product
5a
Time (min)
Yield b(%)
mp (◦C)
lit.mp (◦C)
268 [42]
5-H
H
US
5
98
97
98
95
97
96
97
93
92
90
91
88
92
89
90
85
94
90
95
90
94
85
80
94
267–269
MW
US
15
7
2
5-Cl
H
5b
293
293–295 [42]
>300
MW
US
20
5
3
5-Br
H
5c
>300
>300
253–254
>300
272
MW
US
20
7
4
5-Me
5-OMe
5,7-Cl
H
H
5d
304–305 [42]
251–253 [42]
NEW
MW
US
25
8
5
H
5e
MW
US
40
10
45
10
45
10
50
6
6
H
5f
MW
US
7
Ph
Ph
Ph
Ph
Ph Ph
5 g
5 h
5i
270–271[42]
262–264 [13]
258–260 [42]
255–257 [42]
270–272 [13] NEW
MW
US
8
5-Cl
261–263
258
MW
US
9
5-Br
MW
US
30
8
10
5-Me
5-OMe 5,7-Cl
5j
258
MW
US
40
6
11 12
5 k 5 l
272 > 300
MW
US
25
10
85
78
MW 45
a
Reaction conditions: US-treated Co3O4@PPIL-Mo (10 mol%) in water under US irradiation (40 KHz, 100 W) or MW (200 W).
Isolated yields.
b
Table 4
Synthesis of spiro[indoline-3,4′-pyridine] derivatives under ultrasound and MW irradiationsa.
Entry
1
X
Ar
Product
6a
Time (min)
Yield b(%)
mp (◦C)
lit.mp (◦C)
225–226 [48]
H
C6H5
US
10
30
12
30
8
90
88
88
85
92
89
89
83
92
90
91
88
224–226
MW
US
2
3
4
5
6
H
H
H
Cl
Cl
4-BrC6H4
6b
6c
6d
6e
6f
293
290–292 [48]
>250 [48]
MW
US
4-OCH3C6H4
4-CH3C6H4
4-OCH3C6H4
4-CH3C6H4
255–257
253–254
270
MW
US
20
10
25
5
>250 [48]
MW
US
270–272 [48]
232–234 [48]
MW
US
20
9
234
MW
30
aReaction conditions: US-treated Co3O4@PPIL-Mo (10 mol%) in water under US irradiation (40 KHz, 100 W) or MW (200 W).
bIsolated yields.
9

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Ultrasonics Sonochemistry 75 (2021) 105614
Scheme 2. Four-component reaction of isatins, active methylene, DMAD, and different amine components.
preparing 5a. This is because the polar intermediate has formed during
the reaction. Finally, in order to check the irradiation frequency effect,
the reaction was done in 20, 40, and 60 kHz (100 W). When the fre-
quency irradiation increased from 20 kHz to 40 kHz, the yield of 5a
changed significantly (from 88% to 98%) (Table 2, entry 6,16). How-
ever, increasing the irradiation frequency from 40 to 60 kHz (Table 2,
entry 17) did not have a considerable effect on the yield of 5a (98% in a
similar time). Therefore, the use of the ultrasound-treated Co3O4@PPIL-
Mo catalyst (10 mol%) in H2O under US agitation can be introduced as
the optimal reaction condition (40 kHz, 100 W).
Subsequently, to demonstrate the scope and applicability of this
catalyst in the one-pot four-component synthesis of spiropyranopyrazole
derivatives, the reaction was extended to other isatins which were
replaced. These findings clearly demonstrated that this catalytic
Scheme 3. The plausible mechanisms for one-pot synthesis of 5a and 6a.
10

Z. Elyasi et al.
Ultrasonics Sonochemistry 75 (2021) 105614
Scheme 4. Preparation of regioisomers through conjugate nucleophile addition.
procedure can be extended to many different substrates in order to make
a variety-oriented library of spiropyranopyrazoles (Table 3). The elec-
tronic structure of the substituents (C5 of isatins) could also be possible
with high yields. This straightforward approach was extended in a se-
ries, using phenyl hydrazine instead of hydrazine hydrate component,
which formed the desired spiro pyranopyrazole derivatives in excellent
yield. We found that reactions with hydrazine hydrate could afford the
desired products within shorter times because of its low steric hindrance
[13]. Furthermore, to gain more insight into the effect of US on the
synthetic pathway, the reactions were performed under two green pro-
tocols including microwave (MW) and ultrasound (US) irradiations
without any undesirable byproducts in good to excellent yields and short
reaction times. Clearly, US waves were found to have a remarkable ef-
fect on the preparation of spiro pyranopyrazoles, indicating its superi-
ority over the MW method with respect to the yields and reaction times.
Ultrasonic phenomena improve heterogeneous reaction rates through
increasing the mixing between reactants, controlling the distribution of
particles, accelerating the diffusion of products and reactants, and pro-
moting the generation of a new solid phase [40]. It is remarkable that
MW-accelerated chemical reactions depend on the capacity mixture to
absorb MW energy. This capacity also depends on some main factors
such as the polarity of reactants or intermediates and the nature of
solvents [41].
Table 5
Comparative study between reported catalyst and US-treated Co3O4@PPIL-Mo.
Product
Catalyst Ref.
Condition
EtOH/40 ◦
Yield%
Time
5a
[Dabco-H][AcO]13
C
96
86
98
30 min
3 h
PEG-400 42
110 ◦
C
Co3O4@PPIL-Mo
US/H2O
5 min
6b
[Dabco-H][AcO]13
EtOH/40 ◦
EtOH/25 ◦
US/H2O
C
C
86
83
90
4 h
48
N(Et)3
24 h
10 min
Co3O4@PPIL-Mo
dialkyl acetylene dicarboxylate in a regioselective manner. Ultrasound-
treated catalyst provides favorable interactions between the imidazo-
lium rings and the carbonyl groups. Apart from that, coordinated
Co3O4@PPIL-Mo to the carbonyl groups through Lewis acidic sites
(Mo6+) decreases the energy of transition state for the nucleophilic
attack of the isatin to malononitrile (and hydrazine to DMAD). Michael
addition of intermediate (A) onto isatylidene malononitrile followed by
enolization provided adduct C. In the following, the hydroxyl group
underwent fast nucleophilic addition to the CN moiety (intramolecular
cyclization) and product 5a was obtained after tautomerization. On the
whole, the asymmetric collapse form of micro liquid jet with high speed
intensified the heat and accelerated the mass transfer among the pores
and within the stationary film that was around the adsorbent [47]. These
liquid jets made the heterogeneous catalyst active and the mass transfer
better by disrupting the interfacial boundary layers. As an interesting
point, the ultrasound also accelerated the deprotonation of malononi-
trile and hydrazine as well as the thermal deprotonation. As a result, the
malononitrile and hydrazine anions were formed rapidly (Scheme 3).
With the catalyst activation by US agitations, the aniline adds on
DMAD to afford the intermediate D (β-enamino ester) which undergoes
addition with isatilidene malononitrile B to generate intermediate E. In
the following, the amino group underwent fast nucleophilic addition to
the CN moiety (intramolecular nucleophilic cyclization) and product 6a
was obtained after tautomerization (Scheme 4).
To further widen the reaction scope, we tried to apply aromatic
amines to replace hydrazines. Encouraging results were achieved,
another multicomponent reaction was obtained and a different scaffold
was produced. According to the obtained results, a library of spiro1,4-
dihydropyridines has been synthesized in good yields with no change
in the optimized conditions (Table 4). Under the same conditions,
various amine components (aromatic amine and hydrazine derivatives)
afford different product skeletons (Scheme 2). In fact, some parameters
such as the electronic and steric qualities of substituents, nature of
catalyst, etc. can influence the main product of reactions. For example, a
one-pot four-component reaction of isatin, DMAD, malononitrile, and
aromatic amines using different iodine sources as catalyst selects rout
(III) [43] While the same four-component reaction in the presence of
Dabco-based IL crosses rout (II) [13].
It is worth mentioning that the generation of isatilidenemalononitrile
(B) is noticed on thin layer chromatography, and the reaction regiose-
lectivity is controlled by the relations between stereo-electronic factors
of R‘ and R‘‘ and the carbonyl of the 2-oxindole scaffold. Addition of
pyrazolone or β-enamino ester (D) onto intermediate (B) was carried out
On the basis of our previous successful studies on the synthesis of
heterocyclic compounds using various catalysts [44–46], the proposed
reaction pathway mechanism for the synthesis of 5a is shown in (Scheme
3). At first, the catalyst facilitated Knoevenagel condensation of isatin
and malononitrile for the formation of adduct B (isatylidene malono-
nitrile) through different acidic sites which react with adduct A (pyr-
azolone) generated through the condensation of hydrazine hydrate and
through addition to α,β‘ bond in the presence of electron withdrawing
groups (EWG) (R‘,R‘‘= CN). Among mentioned regioselective mecha-
nism, US strategy also leads to improvement selectivity in organic
transformations [49].
11

Z. Elyasi et al.
Ultrasonics Sonochemistry 75 (2021) 105614
Fig. 10. Recyclability of Co3O4@PPIL-Mo obtained from two different conditions.
Fig. 11. FESEM images of the recovered Co3O4@ PPIL-Mo obtained from A) reflux, and B) US conditions.
A comparative investigation was carried out between synthesized
recovery (Fig. 11B). While, the cross-linked network of Co3O4@PPIL-Mo
obtained under silent condition completely disrupted and irregular
shape particles obtained (Fig. 11A).
Co3O4@PPIL-Mo and reported catalyst for the preparation of spiro 1,4-
dihydropyridines and spiro pyranopyrazoles. The results were summa-
rized in Table 5. Ultrasound irradiation differs from conventional energy
sources (such as heat, light, or ionizing radiation) in time, pressure, and
energy per molecule. The US radiation in the presence of Co3O4@PPIL-
Mo composite provided highest reaction yield and shortest times in H2O
at room temperature.
4. Conclusions
In conclusion, novel-supported molybdenum complex on cross-
linked poly ionic liquid entrapped cobalt oxide nanoparticles was well
fabricated via two different methods including ultrasound irradiations
and reflux. The positive impact of ultrasound irradiations on the phys-
icochemical properties (thermal stability, porosity, particle uniformity,
reusability, and catalytic activity) of the catalyst was approved through
the results of different characterization techniques. Furthermore, ul-
trasound radiation caused great dispersion of Co3O4 NPs, perfect sur-
faces functionalization, enhanced polymerization rate, and uniform
distribution of Mo (VI) Schiff-base complexes on the polymeric net-
works. Accordingly, US-treated Co3O4@PPIL-Mo introduced as a
potentially strong heterogeneous catalyst for the four-component syn-
thesis of spiro 1,4-dihydropyridines and spiro pyranopyrazoles. US wave
Reusability is known as key characteristic properties of catalysts.
Hence, the prepared catalyst was separated at the end of the reaction by
centrifugation. The recovered catalyst was washed several times with
EtOH and H2O, dried overnight, and reused with fresh substrates. The
outcomes indicated that the ultrasound-treated Co3O4@PPIL-Mo could
be reused eight cycles with no significant loss in its activity (Fig. 10).
Similarly, recoverability of Co3O4@PPIL-Mo obtained under silent
condition was also performed and found to have the ability to be reused
for five cycles. The morphology of recovered catalyst after eight cycles
was considered by FESEM (Fig. 11). The outcomes confirmed that the
US-treated catalyst structure showed no significant change after
12

Z. Elyasi et al.
Ultrasonics Sonochemistry 75 (2021) 105614
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the MW method with respect to the yields and reaction times. The fea-
tures of ultrasound-assisted organic transformations; namely, the
regioselectivity, ease of experimental manipulation, and enhanced re-
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Declaration of Competing Interest
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The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Acknowledgments
The authors acknowledge a reviewer who provided helpful insights.
The authors are grateful to the Islamic Azad University, Qom Branch,
Qom, I. R. Iran for supporting this work.
Appendix A. Supplementary data
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