Ultrasonic-assisted preparation of Co3O4 and Eu-doped Co3O4 nanocatalysts and their application for solvent-free synthesis of 2-amino-4H-benzochromenes under microwave irradiation

Article abstract of DOI:10.1002/aoc.6271

Co₃O₄ and Eu-doped Co₃O₄ nanocatalysts were synthesized through an ultrasonic-assisted solvothermal method and were characterized with X-ray diffraction (XRD), Fourier transform infrared (FT-IR), energy-dispersi

Full text of DOI:10.1002/aoc.6271

Received: 15 February 2021
DOI: 10.1002/aoc.6271
Revised: 5 April 2021
Accepted: 7 April 2021
F U L L P A P E R
Ultrasonic-assisted preparation of Co O and Eu-doped
3
4
Co O nanocatalysts and their application for solvent-free
3
4
synthesis of 2-amino-4H-benzochromenes under microwave
irradiation
1
2
2
Leila Kafi-Ahmadi
| Ahmad Poursattar Marjani
| Ehsan Nozad
1
Department of Inorganic Chemistry,
Faculty of Chemistry, Urmia University,
Urmia, Iran
Co O4 and Eu-doped Co O4 nanocatalysts were synthesized through an
3
3
ultrasonic-assisted solvothermal method and were characterized with X-ray
diffraction (XRD), Fourier transform infrared (FT-IR), energy-dispersive X-ray
2
Department of Organic Chemistry,
Faculty of Chemistry, Urmia University,
Urmia, Iran
(EDX), and field-emission scanning electron microscopy (FESEM) methods.
Spinel cubic crystalline system for synthesized nanocatalysts was confirmed
Correspondence
with XRD, whereas the spherical morphology of Co O changed to nanorods
3
4
Ahmad Poursattar Marjani, Department
of Organic Chemistry, Faculty of
Chemistry, Urmia University, Urmia,
Iran.
3
+
after Eu doping, which was affirmed with FESEM micrographs. Catalytic
performance of the nanomaterials was examined through the synthesis of
2-amino-4H-benzochromenes using aromatic aldehydes, malononitrile, and
Email: a.poursattar@urmia.ac.ir;
a.poursattar@gmail.com
β-naphthol condensation under solvent-free conditions and microwave
irradiation. Mild reaction conditions, short reaction times, simple setup, using
an affordable catalyst, and high-quality products were some of the advantages
of this procedure. The efficiency for Eu-doped nanocatalyst was achieved by
about 96%.
Funding information
Urmia University
K E Y W O R D S
2-amino-4H-benzochromenes, Co
3 4 3 4
O , Eu-doped Co O , nanocatalyst, solvent-free
synthesis
1
| INTRODUCTION
The simplest synthesized procedure includes a three-
component cyclocondensation reaction of aromatic
aldehydes, malononitrile (as a nucleophile), and various
enolizable C–H activated compounds. However, some
organic solvent sources used in an aforementioned proce-
2
-Amino-4H-benzochromene derivatives are outstanding
categories of oxygen heterocyclic chemicals having a
broad spectrum of interesting pharmacological and
biological attributes, for instance, cytotoxic, antitumor,
dure such as piperidine, pyridine, and triethylamine
[
1–5]
[11]
antiproliferative, and antibacterial characteristics.
may cause to several hours of reaction time.
Moreover,
Besides, cosmetics, pigments, and being parts of numer-
ous natural products are the other plus points of these
products. Therefore, the development of an efficient and
suitable methodology to synthesize these compounds is
other catalysts including methanesulfonic acid,
imidazole, porous organic polymers (POPs), potassium
phthalimide, L-proline–melamine, sodium malonate, and
Na CO3 have been utilized for this transformation.
2
[6–10]
profoundly imperative.
Some diverse 2-amino-4H-
Recently, several novel green approaches have been
reported using cetyltrimethylammonium chloride
(CTAC), KF/Al O , basic γ-alumina, MgO, CuSO Á5H O,
bezochromenes with strong pharmacological properties
are indicated in Figure 1.
2
3
4
2
Appl Organomet Chem. 2021;e6271.
wileyonlinelibrary.com/journal/aoc
© 2021 John Wiley & Sons, Ltd.
1 of 10
https://doi.org/10.1002/aoc.6271

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KAFI-AHMADI ET AL.
FIGURE 1 Representative examples of 2-amino-
4
H-benzochromene moieties with biological virtues
1
,8-diazabicyclo[5.4.0]undec-7-ene
(DBU),
CTABr/
ultrasound irradiation, nanocatalyst, bael fruit extract,
water extract of lemon fruit shell ash, and poly(ethylene
[12–26]
glycol) (PEG) in water.
One-pot, multicomponent reactions (MCRs) are
widely used and an approved method due to their atom
economy, high efficiency, and selective bond formations
for synthesizing different types of heterocyclic com-
pounds such as benzochromens, benzopyrans, and so
SCHEME 1 The synthetic pathway of 2-amino-4H-
[27–37]
many other materials with various applications.
benzochromene derivatives. MW, molecular weight
Microwave irradiation is a novel and practical tech-
nique for reagent activation in synthesis of the organic
compounds. This method has been applied successfully for
the synthesis of heterocyclic compounds under moderate
conditions, which have gained its popularity through the
less reaction duration, modified products, environmental
and commercial advantages, and simplified setup in
using field-emission scanning electron microscopy
(FESEM). The efficiency of the synthesized nanocatalysts
was investigated as efficient recyclable catalysts for the
synthesis of 2-amino-4H-benzochromenes under solvent-
free conditions and microwave irradiation (Scheme 1).
[38,39]
comparison with conventional heating reactions.
Among the metallic oxides, components including
spinel-type tricobalt tetraoxide (Co O ) have drawn
2 | EXPERIMENTAL
3
4
profound attention in as much as a pivotal role in Li-ion
rechargeable batteries, antiferromagnetic p-type semicon-
ductor, magnetic materials, and electrochemical devices.
Currently, several methods (i.e., hydrothermal, sol–gel,
chemical spray pyrolysis [CSP], microemulsion, chemical
vapor deposition [CVD], thermal decomposition of cobalt
precursors, sonochemical route, microwave irradiation,
coprecipitation, and mechanochemical processing) are
used for the synthesis of Co O . Although various
2.1 | Materials and methods
All precursors for the synthesis were purchased from
Merck (Germany), and no excess purification was carried
out. PXRD patterns of the samples were recorded by a
D5000 powder X-ray diffractometer (Siemens AG,
Munich, Germany) using Cu Kα radiation. FT-IR spectra
were provided using KBr pellets on a “Bruker Tensor”
instrument. The morphology of the products was evalu-
ated through a field-emission scanning electron micro-
scope (Hitachi FESEM, Mo. S-4160). Melting points were
determined using a finely powdered sample in a fused
3
4
morphologies of nanostructured Co O have been synthe-
3
4
sized, the producing orders need either challenging
[40–43]
technique or severe conditions.
For instance, Salehi
et al. synthesized Co O , Co NdxO , and Co3-xEuxO4
3
4
3-x
4
nanoparticles by combustion synthesis method at the
capillary with a melting point apparatus (Elico).
ꢀ
temperature of 700 C for 8 h. Co O nanoparticle had
Microwave-assisted procedures were performed at
3
4
1
cubic shape with spherical particles a few void numbers
1600 W in the Milestone microwave oven. Both H-NMR
13
on the surface but in the Co3-xNdxO and Co3-xEuxO4,
at 400 MHz and C-NMR at 100-MHz spectra were
achieved with Bruker Avance AQS 400 MHz,
ultrashield in DMSO-d as a solvent and Me Si as an
4
[44]
the particles had homogeneous structure.
The aim of this study is the synthesis of Co O (S ) and
a
3
4
1
6
4
Eu-doped Co O (S ) nanostructures by ultrasonic-assisted
internal reference, and the chemical shifts are represen-
ted by units of ppm. Mass spectra of the all compounds
were recorded using LCMS-2010A, Shimadzu. Elemental
compositions of the nanocatalysts were investigated using
energy-dispersive X-ray (EDX) spectroscopy.
3
4
2
solvothermal procedure as a novel and cost-effective
method. Characterization was conducted by Fourier trans-
form infrared (FT-IR) and X-ray powder diffraction (PXRD)
techniques. The morphology of products was evaluated

KAFI-AHMADI ET AL.
3 of 10
2.2 | Synthesis
H O. Next, 20 ml of ethanol was added to the solution
and was stirred for 15 min at 60 C. The same steps of
2
ꢀ
2
.2.1 | Synthesis of Co O (S )
reaction were accomplished to the synthesis of the Co O
3 4
3
4
1
(
yield = 89%).
A total of 2.0 mM (582 mg) of Co(NO ) Á6H O (molecu-
3
2
2
À1
lar weight [MW] = 291.03 g mol ) was dissolved in
0 ml of distilled water. Then, 20 ml of EtOH was
1
2.2.3 | General procedure for the synthesis
of 2-amino-4H-benzochromene with diverse
substituents 4a–g
added to the prepared mixture under stirring for 15 min
at 60 C. Afterward, a 4-M solution of KOH was used to
ꢀ
adjust the mixture pH at 12 and was stirred for 15 min
and kept under ultrasonic agitation for 30 min at room
temperature. A 60-ml Teflon-lined stainless steel sealed
autoclave was used to heat the solution. The heating
Substituted aromatic aldehydes (1 mmol), malononitrile
(1 mmol), β-naphthol (1 mmol), and S1 nanoparticles
(30 mg) were all mixed in a flask (50 ml) and irradiated
with microwave (500 W). The end of the reaction was
investigated with thin-layer chromatography (TLC) anal-
ysis (hexane:ethylacetate/6:4). Upon reaction completion,
the resulting product was heated in ethanol. The catalyst
was separated by filtration from the mixture and rinsed
several times with aqueous ethanol for reuse. Then, the
residue was added to crushed ice and was stirred for a
couple of minutes. The compact product was filtered off
by suction and recrystallized from aqueous ethanol to
collect the desired 2-amino-4H-benzochromenes in high
yields. The successful synthesize of the 2-amino-4H-
benzochromenes was affirmed using 1H-NMR and 13C-
NMR analysis. (see supplementary information)
ꢀ
process was continued until reaching up to 180 C
temperature for 8 h. After reaction completion, the
autoclave was cooled down by water to the room tem-
perature. The achieved powders were rinsed by distilled
ꢀ
water and dried at 90 C for 5 h in the room ambient
(yield = 81%).
2
.2.2 | Synthesis of Co2.97Eu0.03O (S )
4 2
A
total of 2.97 mM (864 mg) of Co(NO ) Á6H O
3
2
2
À1
(MW = 291.03 g mol ) and 0.03 mM (11 mg) of Eu O
2
3
À1
(MW = 351.92 g mol
)
were added to 10 ml of
FIGURE 2 X-ray diffraction (XRD)
spectrum of (a) S and (b) S
1
2

4
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KAFI-AHMADI ET AL.
3
3
| RESULTS AND DISCUSSIONS
.1 | X-ray diffraction analysis
The crystallographic information of both samples (S and
1
S2) was gathered with PXRD. Figure 2a, presents the
PXRD pattern of the S nanoparticles prepared through
1
the solvothermal method. Diffraction lines are assigned
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
to the reflections 220 , 311 , 222 , 400 , 422 , 511 , 440 ,
5
ꢀ
ꢀ
ꢀ
31 , 620 , 533 , and 622 , respectively, which corre-
spond to the spinel cubic structure of Co O with Fd3m
3
4
space group with lattice parameters of cubic structure
a = b = c = 8.081 Å. No peaks of other phases or impuri-
ties were detected, indicating the high purity of the
[45]
Co O product. (JCPDS Card No. 43-1003).
3
4
Figure 2b, displays the XRD patterns of S . There are
2
no additional XRD lines attributed to the secondary
3
+
3+
phase; hence, it is evident that Co is replaced by Eu
.
Table 1, manifests the cell parameter refinement data for
the pure and doped nanomaterial. It can be seen that the
cubic structure is not altered by doping, whereas
the changes in the intensity of the peaks exhibit that the
crystallinity is affected because of accomplished doping.
Besides, there is a marginal shift in the position of the
doped sample peak owing to the changes in lattice con-
stants. According to the Scherrer equation, D = 0.9λ/
βcosθ, whereas D is the average crystallite size, λ is the
X-ray wavelength, θ is the angle of diffraction, and β is
the full width at half maximum of the most intense peak.
The average size of nanoparticles was calculated as
outlined in Table 1.
FIGURE 3 Energy-dispersive X-ray (EDX) spectra of (a) Co
and (b) Eu-dopped Co
3 4
O
3 4
O
3.2 | Elemental analysis
3.3 | Morphology
The compositions of the synthesized nanocatalyst before
and after doping Eu were studied qualitatively through
EDX analysis. The patterns are exhibited in Figure 3.
As can be observed in Figure 3a, the spectrum confirms
the pure composition of Co O which is composed of
FESEM images were observed to determine the morphol-
ogy of nanomaterials. Figure 4a, illustrates the FESEM
images of spinel Co O . As can be seen in Figure 4a,b, S
1
3
4
has compact agglomerated spherical nanocrystals,
3
+
whereas Eu doped into Co O (S ) resulted in nanorod-
3
4
3
4
2
Co and O only. On the other hand, Eu-doped
nanocatalyst spectrum (Figure 3b) clearly shows the
appeared Eu-associated peaks; moreover, a decrease in
intensity of the Co peaks affirms the triumphantly
doped Eu within the Co O structure instead of Cobalt
shaped crystals. Therefore, the product consists of rods
with various lengths and thicknesses.
3.4 | N -physical adsorption
3
4
2
nondestructively.
measurement
TABLE 1 Average nanocrystal size and cell parameter
The physical feature of nanomaterials was taken into
account to gain in-depth insight. In this respect, the sur-
face area of the nanocatalyst, its average pore size, and
also the average pore volume of the synthesized powders
were characterized. Before conducting the measurement,
refinement data for the samples
Sample
Co
Crystallite size (nm)
a = b = c (Å)
8.081
3
O
4
30
27
Co2.97Eu0.03
O
4
8.079
ꢀ
the samples were degreased for 2 h at 150 C in a nitrogen

KAFI-AHMADI ET AL.
5 of 10
1 2
FIGURE 4 Field-emission scanning electron microscopy (FESEM) micrographs of (a) S and (b) S samples
TABLE 2 Structural properties of
2
À1
3
À1
Sample
S
BET (m g
)
Pore volume (cm g
)
Pore diameter (nm)
the catalysts
S
S
1
2
3.246
4.770
0.0154
18
23
0.1340
TABLE 3 BJH data for S
1
and S
2
and the textural properties of
bath. Next, the specific surface area (SBET) of the samples
ꢀ
the products
was calculated using the isotherms at 77 K (À196 C).
The measured physical features of the samples are shown
in Table 2. The average surface areas were approximately
Value
2
À1
3
BJH desorption property
S1
S2
3
0
.246 and 4.770 m g , though pore volumes were about
À1
.0154 and 0.1340 cm g for S and S , respectively. As
can be interpreted, doping of Eu to Co O leads to the
Cumulative surface region of pores
between 17- and 3000-Å width
4.120
5.581
1
3
2
+
3
4
expansion of the surface area, pore volume, and the
average pore diameter of the catalyst, simultaneously.
Cumulative volume of pores between
0.0159
17
0.1347
24
17- and 3000-Å width
À1
Table 3, depicts the textural properties of S and S2
Average pore width (4 V A
)
1
according to the Barrett–Joyner–Halenda (BJH) method,
which reveals that the SBET of the pores, pore width, and
volume of S are smaller than those of S . Moreover, the
Abbreviation: BJH, Barrett–Joyner–Halenda.
1
2
BET results and BJH measurements claim that the
surface area, average pore diameter sizes, and the average
pore volume of S are smaller than those of S .
obtained spectra indicate portions of two absorption
À1
bands at 574 υ ) and 667 (υ ) cm for S , plus 579 υ )
1
2
1
1
À1
and 677 υ ) cm for S , in a row. These absorptions
1
2
2
2
are signs of metal–oxygen stretching vibrations and
prove the Co O spinel oxide formations. The υ and υ
3
4
1
2
3
.5 | FT-IR spectroscopy
bands are associated with OB and ABO vibrations in
3 3
the spinel lattice, respectively, whereas B and A represent
3
+
Figure 5, illustrates the FT-IR spectra of S and S nano-
crystals. In the studied domain (4000–400 cm ), the
the Co
accordingly.
in the octahedral and tetrahedral holes
1
2
À1
[46]

6
of 10
KAFI-AHMADI ET AL.
3
.6 | Application of the prepared
nanocatalysts for the synthesis of 2-amino-
H-benzochromenes
The one-pot, three-component reaction (TCR) of benzal-
dehyde, malononitrile, and β-naphthol in a catalytic
4
amount of S was regarded as a norm. Several conditions
1
have been studied in a pilot experiment, concerning opti-
mum conditions. Then, the evaluation of the scope and
constraints of the reaction was accomplished using vari-
ous substituted aryl aldehydes as substrate compounds.
Therefore, the catalytic applicability of the S1 was
reviewed for providing the target molecule. The reaction
The activity of the synthesized catalysts for preparing the
-amino-4H-benzochromene derivatives was investigated.
2
was carried out by different amounts of S under solvent-
1
free conditions (Table 4). As indicated in Table 4, entry
4, excellent results were achieved using 30 mg of
nanocatalyst when no solvent was used. Moreover, an
increase in catalyst amount had no significant effect on
the outcome. Furthermore, no progress in the reaction
was monitored in the absence of a nanocatalyst.
The effect of various solvents on a model reaction was
investigated (Table 5). EtOH, H O, EtOH/H O (1:1),
2
2
CH Cl , CH CN, and n-hexane were used for this pur-
2
2
3
pose. Nevertheless, no significant reaction progress was
monitored even after the prolonged span. As shown in
Table 4, in the solvent-free condition, the yield of the
reaction was quite satisfying (94%).
Table 6, presents the catalytic performance of S and
1
S2 under the optimum conditions using multiple raw
material derivatives. As an outcome, electron-donating
TABLE 5 Optimization of solvent in the synthesis of 2-amino-
4H-benzochromene under 500 W
[
a]
Entry
Solvent
Yield (%)
1
2
3
4
5
6
7
—
94
H
2
O
72
EtOH
56
EtOH/H
2
O (1:1)
66
CH
CH
2
3
Cl
2
Trace
—
CN
n-Hexane
Trace
FIGURE 5 Fourier transform infrared (FT-IR) spectra of (a) S
1
a
and (b) S
2
Yield of isolated products.
[b]
TABLE 4 Catalyst amount
Entry
Amount of catalyst (mg), S
1
Time (min)
Yield (%)
optimization in the synthesis of
1
2
3
4
5
—
10
20
30
40
50
4
4
4
4
4
4
—
63
77
94
94
94
[a]
2
-amino-4H-benzochromene at
500 W
6
a
Reaction was performed with benzaldehyde (1 mM), malononitrile (1 mM), β-naphthol (1 mM), and
catalyst.
b
Isolated yield.

KAFI-AHMADI ET AL.
7 of 10
TABLE 6 Synthesis of 2-amino-4H-benzochromenes catalyzed by S
1
or S
2
nanocatalysts
[
b]
ꢀ
m.p. ( C)
[
a]
[a]
Yield (%)
Time
Yield (%)
Time
Entry
Aldehyde
CHO
Products
S
1
(min)
S
2
(min)
Obsd.
Lit.
[
[
[
[
[
[
[
47]
7]
1
2
3
4
5
6
7
C
6
H
5
4a
4b
4c
4d
4e
4f
94
95
95
96
88
87
97
4
6
5
5
4
7
7
96
97
97
97
89
89
98
6
6
4
4
7
5
6
286–287
218–220
205–208
236–238
269–271
189–190
232–234
285–287
220–222
210–212
239–241
269–271
191–193
232–235
4-BrC
4-ClC
4-FC
4-MeC
4-MeOC
3-O NC
6
H
4
CHO
48]
7]
6
H
4
CHO
6
H
4
CHO
CHO
CHO
CHO
49]
7]
6
H
4
6
H
4
50]
2
6
H
4
4g
a
Yield refers to isolated pure products.
b
Products were characterized by comparison of melting points of the known products reported in the literature.
SCHEME 2 Suggested mechanism for the
synthesis of 2-amino-4H-benzochromenes catalyzed by
1 2
S or S
groups on the aromatic aldehyde rings result in low
yields of the corresponding products, and the reaction
was slow, whereas electron-withdrawing groups result in
higher amounts of yield. After completion of the reaction,
the catalysts were readily removed by filtration, and the
products were filtered out after solvent evaporation and
easily purified by recrystallization from ethanol.
oxygen atom to C N group of intermediate II, leads to
form in situ the desired products 4. In the path of mecha-
nism, catalyst plays a pivotal role in accelerating all steps
of the reaction and is regenerated at the end of the cycle.
The catalytic performance comparison of S and S
1
2
under the optimum conditions is shown in Figure 6. As
can be seen, the efficiency of S is better than S , which
2
1
Scheme 2, exhibits the probable mechanism of reac-
tion for the synthesis 2-amino-4H-benzochromenes by
TCR, catalyzed by S /S under solvent-free conditions.
implies that the presence of both metal ions affected the
efficiency held considerably and operated cooperatively.
According to a study provided by Khademinia et al.,
cooperative catalysis accelerates some specific chemical
1
2
The reaction gets initiated by the activation of aldehyde
between the nanocatalyst and the oxygen of the carbonyl
group in the aromatic aldehyde. Simultaneously, the
Knoevenagel condensation takes place between activated
aromatic aldehydes 1 with malononitrile (2) by the loss
of one molecule of water to generate intermediate I. After
that, the Michael-type addition of β-naphthol (3) to inter-
mediate I to give intermediate II, which goes for intramo-
lecular heterocyclization by the nucleophilic attack of
[
51]
transformations.
Briefly, cooperation catalytic prop-
3+
2+
3+
erty among Co , Co , and Eu species is due to the
electron transfer by providing the activation energy to
transfer valance electron to a higher level. It is found that
the optical band gap energies of Eu O and Co O are 4.4
2
3
3 4
and 1.96 eV, respectively. However, Eu O is a photo-
2
3
luminescent material that has sharp emissions at about
550 and 620 nm that can provide the energy to pump and

8
of 10
KAFI-AHMADI ET AL.
excite the electron of Co conduction electron to the
higher level and make the electron–cavity pair. So,
the catalytic reaction can be performed more efficiently
by the cooperation of Eu and Co metal ions.
conditions using an affordable and available catalyst to
attain the expected products.
To assess the capability of the current procedure in
the obtaining the final product, as a trial chemical, the
present work was compared with some previously
reported studies (Table 7). The summarized results
clearly revealed that the method suggested in this
research could be superior to the reaction time, tempera-
ture, and in terms of yield of the target material. In addi-
tion to the aformentioned superiorities, the reaction was
carried out under mild reaction and solvent-free
3.7 | Catalyst recyclability
The reusability performance of the catalysts was investi-
gated after multiple runs. The reaction of benzaldehyde,
β-naphthol, and malononitrile under modified conditions
was regarded as a norm. After each reaction completion,
the catalysts were recycled by filtration through rinsing
with hot ethanol following by drying. Catalysts were
FIGURE 6 Catalytic performance of S
1
and S
2
at the optimum
FIGURE 7 Reusability tests for model reaction using (a) S
and (b) S as nanocatalysts
1
conditions
2
TABLE 7 Efficiency comparison of the different catalysts and conditions of previously reported studies with current research
Reaction
condition
Time
(min)
Yield
(%)
Entry Catalysts
Ref.
[
52]
1
2
FeTiO
Water extract of pomegranate peel ash
WEPPA)
3
MW
MW
9–13
4–6
87–94
86–90
Taghavi Fardood et al.
Hiremath and
[53]
(
Kamanna
[
54]
3
4
5
6
7
8
Piperazine
MW
6–8
82–95
70–90
65–95
69–86
77–95
84–90
Mobinikhaledi et al.
[55]
1-Butyl-3-methyl imidazolium ([bmim][PF
Silica tungstic acid
6
])
MW
2 h
Rao et al.
[56]
Solvent-free
Solvent-free/EtOH
Solvent-free
MW
1.5–5 h
65–220
20–45
2–8
Farahi et al.
[57]
Sodium lauryl sulfate (SLS)
MOF-5
Singh et al.
Arzehgar et al.
Kantharaju and
[58]
Water extract of lemon fruit shell ash
[25]
(WELFSA)
Khatavi
9
Water extract of banana peel ash (WEB)
MW
2–8
15–35
3
72–79
Kantharaju and
Khatavi
[59]
Grindstone/H
MW
2
O
[60]
1
0
1
NiO
76–99
94–99
Neela et al.
Present work
1
Co
3
O
4
/Eu-doped Co
3
O
4
MW
4–7
Abbreviation: MW, molecular weight.

KAFI-AHMADI ET AL.
9 of 10
reused in the next runs under comparable conditions.
Figure 7, indicates a sustained activity of the catalysts
during six runs without any significant activity loss.
[3] A. Rafinejad, A. Fallah-Tafti, R. Tiwari, A. N. Shirazi, D.
Mandal, A. Shafiee, K. Parang, A. Foroumadi, T. Akbarzadeh,
DARU J. Pharm. Sci. 2012, 20, 100.
[
[
[
[
[
[
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| CONCLUSION
The current study reports an ultrasonic-assisted
solvothermal procedure for the synthesis of S and S2
1
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of the prepared catalysts were spinel cubic with Fd3m
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3+
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3
4
also used as heterogeneous catalysts for the synthesis of
-amino-4H-benzochromenes. The prominent conclusion
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Leila Kafi-Ahmadi: Conceptualization; data curation;
investigation; methodology; project administration;
supervision; validation. Ahmad Poursattar Marjani:
Conceptualization; data curation; investigation; method-
ology; project administration; software; supervision;
validation. Ehsan Nozad: Data curation; investigation;
software; validation.
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Leila Kafi-Ahmadi https://orcid.org/0000-0001-8947-
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002-5899-4285
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