A highly efficient one-pot multicomponent synthesis of 3,4-dihydropyrimidin-2-(1H)-ones/thiones catalyzed by strontium pyroarsenate nano-plates

Article abstract of DOI:10.1016/j.molstruc.2020.128124

The present work describes the one-pot multicomponent synthesis of heterocyclic 3,4-dihydropyrimidin-2-(1H)-ones and thiones (DHPMs) under solvent-free conditions by Sr₂As₂O₇ nanocatalyst. Sr₂As₂O

Full text of DOI:10.1016/j.molstruc.2020.128124

Journal Pre-proof
A highly efficient one-pot multicomponent synthesis of 3,4-dihydropyrimidin-2-(1H)-
ones/thiones catalyzed by strontium pyroarsenate nano-plates
Rozhin Esmaeili, Leila Kafi-Ahmadi, Shahin Khademinia
PII:
S0022-2860(20)30449-X
DOI:
https://doi.org/10.1016/j.molstruc.2020.128124
MOLSTR 128124
Reference:
To appear in: Journal of Molecular Structure
Received Date: 9 February 2020
Revised Date: 21 March 2020
Accepted Date: 22 March 2020
Please cite this article as: R. Esmaeili, L. Kafi-Ahmadi, S. Khademinia, A highly efficient one-pot
multicomponent synthesis of 3,4-dihydropyrimidin-2-(1H)-ones/thiones catalyzed by strontium
pyroarsenate nano-plates, Journal of Molecular Structure (2020), doi: https://doi.org/10.1016/
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Rozhin Esmaeili: Investigation, Software, Methodology.
Leila Kafi-Ahmadi: Conceptualization, Supervision, Writing - Original Draft, Formal analysis, Software,
Methodology.
Shahin Khademinia: Writing - Review & Editing, Writing - Original Draft, Formal analysis, Software,
Methodology.

A highly efficient one-pot multicomponent synthesis of 3,4-dihydropyrimidin-2-(1H)-ones/thiones catalyzed by
strontium pyroarsenate nano-plates
Rozhin Esmaeili
Department of Inorganic Chemistry, Faculty of Chemistry, Urmia University, Urmia, Iran
Email Address: Roshna.Esmaili@gmail.com
*
Leila Kafi-Ahmadi
Department of Inorganic Chemistry, Faculty of Chemistry, Urmia University, Urmia, Iran
Shahin Khademinia
Department of Inorganic Chemistry, Faculty of Chemistry Semnan University, Semnan 35351-19111, Iran
Email Address: Shahinkhademinia@alum.semnan.ac.ir
*
Corresponding Author’s E-mail Address: L.kafiahmadi@urmia.ac.ir
Tel. and Fax Number: +98443255294
Abstract
The present work describes the one-pot multicomponent synthesis of heterocyclic 3,4-dihydropyrimidin-2-(1H)-
ones and thiones (DHPMs) under solvent-free conditions by Sr As O nanocatalyst. Sr As O nanocatalyst was
2
2
7
2
2
7
synthesized by solvothermal reactions at stoichiometric molar ratio. The characterizations of the as-prepared
nanomaterials were performed by X-ray powder diffraction (XRPD) and fourier-transform infrared (FTIR)
techniques. According to Rietveld analysis data, it was found that reaction time had a considerable effect on crystal
phase change from monoclinic to tetragonal crystal system. Field emission scanning electron microscope (FESEM)
images showed that the morphology of the obtained materials was changed by increasing the reaction time, from 24
to 120 h, from long-length rods to multigonal plates. Catalytic activity of the nanomaterials was investigated in
Biginelli reactions for the synthesis of heterocyclic DHPMs compounds. The synthesis yields at optimum
conditions were 94% and 96% for S and S , respectively. Langmuir–Hinshelwood kinetic model revealed that the
1
5
reactions followed a pseudo-first order kinetic model.
Keywords: Solvothermal, Sr As O , nanocatalyst, Biginelli Reaction, DHPMs.
2
2
7
1

1
. Introduction
Mixed metal oxides are of interest because of their interesting applications [1] such as immobilization of fission products [2],
catalysis [3-9], and solid electrolytes [10]. A B O is a mixed metal oxide in which A is a medium-large cation and B is an
2
2
7
octahedrally coordinated cation. The oxidation state charge ratio of A/B is +3/+4 or +2/+5 [11-13]. A B O is interested due
2
2
7
II
V
to its ability to form substituted and defective structures [14,15]. Among A As O materials (A is the alkaline earth element),
Sr As O has been studied more in several works [16-18]. It had been reported that Sr As O is crystallized in tetragonal
2
2
7
2
2
7
crystal system with the space group P4 and P4 [19]. However, we have recently reported a new monoclinic crystal system
3
1
with the space group of P2 and the lattice parameters of a=5.34918 Å, b=11.32062 Å and c=8.20518 Å with β=91.313 º
1
[
20]. Sr As O has been synthesized previously by solid state [21-23] (tetragonal crystal system was achieved) and
2 2 7
hydrothermal (monoclinic crystal system was achieved) [20] methods. The solid state synthesis method mentioned in ref.
21] used As O and SrCO raw materials, the reaction temperature was 700 ºC and the reaction time was 36 h. The solid
[
2
5
3
state method mentioned in ref. [22] used As O and SrCO raw materials, the reaction parameter was 900 ºC and the reaction
2
3
3
time was 48 h. The XRD data showed that the obtained materials reported in the solid state methods were crystallized in
tetragonal crystal system. As mentioned above, the data revealed that solid state methods prepared Sr As O in single crystal
2
2
7
system and nano sized material was not synthesized. However, the hydrothermal method reported in ref. [20] produced
Sr As O nanomaterial in a new crystal system. The advantages of the hydrothermal method compared to the solid state
2
2
7
methods were the lower reaction temperature (180 ºC), mild reaction condition and nano sized obtained materials. The
obvious difference in the obtained crystal system type by changing the reaction method can be due to the different reaction
conditions including time, temperature, pressure, solvent and raw materials type. The Biginelli reaction is a method for the
synthesis of DHPMs in one-step process. Several metal oxides as nanocatalysts have been used in Biginelli reactions
summarized in ref. [24-30].
The aim of the present work is the introduction of a novel synthesis procedure for the synthesis of Sr As O nanomaterials.
2
2
7
So, solvothermal method is applied for the synthesis of nanostructured Sr As O powders using As O and Sr(NO ) .
2
2
7
2
3
3 2
Rietveld analysis is used to study the effect of the reaction conditions on the crystallographic parameters of the as-
synthesized nanomaterials. Catalytic activity of the synthesized Sr As O nanomaterials is studied for the synthesis of
2
2
7
DHPMs in the Biginelli reactions. Factors such as catalyst amount, reaction time and temperature are optimized using
experimental design method.
2

2
2
. Experimental
.1. Materials and instruments
All chemicals including As O , Sr(NO ) , C H OH and KOH were of analytical grade, obtained from commercial source
2
3
3 2
2
5
(
Merck Company) and used without further purifications. Phase identifications were performed on an X-ray powder
diffractometer D5000 (Siemens AG, Munich, Germany) using CuKα radiation. The XRD apparatus used for the
crystallographic study had monochromator. FullProf software was used to perform Rietveld analysis. Several
crystallographic data including lattice parameter, residual factor (R ), Bragg residual factor (RBragg), goodness of refinement
F
2
(
χ ), crystal phase type and purity values were obtained by the analysis. Hitachi FE-SEM model S-4160 was used to study
the morphology of the obtained materials. UV-visible spectrophotometer model-UV-1650 PC (Shimadzu, Japan) was used to
record the absorption spectra. Tensor 27 spectrometer (Bruker Corporation, Germany) was used to take FTIR spectra. The
purity of the Biginelli reactions products was checked by thin layer chromatography (TLC) on glass plates coated with silica
gel 60 F254 using n-hexane/ethyl acetate mixture as mobile phase. Thermo scientific 9100 apparatus was used to record the
melting points of the DHPMs compounds.
2
.2. Solvothermal synthesis of Sr As O
2 2 7
−1
Sr As O is synthesized as follow: 0.212 g (1.0 mmol) of Sr(NO ) .5H O (Mw = 211.62 g mol ) and 0.198 g (1.0 mmol) of
2
2
7
3 2
2
−1
As O (Mw = 197.87 g mol ) were added to 10 mL of distilled water. Then, 20 mL of ethanol was added to the resultant
2
3
mixture. The pH value of the solution is 5. The solution was stirred for 15 min at 60 °C. Certain volume of 4M KOH was
added to the solution while stirring until the pH value was reached to 12. The resultant solution was stirred more for 15 min
and then ultrasonicated for 30 min at room temperature. After transferring the solution into a 60-mL Teflon lined stainless
steel autoclave, it was sealed and heated at 200 °C for 24 h (S ), 48 h (S ), 72 h (S ), 96 h (S ) and 120 h (S ). The autoclave
1
2
3
4
5
was cooled immediately by water to room temperature when the certain reaction time was finished. A white - colored
powder was obtained, washed by distilled water and dried at 120 °C for 20 min under normal atmospheric condition.
2
.3. General procedure to synthesize of DHPMs
In a typical procedure, a mixture of benzaldehyde, ethyl acetoacetate, and urea with the molar ratio of 1:1:1.2, respectively,
and certain amount of catalyst (Sr As O ) were poured into a round bottom flask. The suspension was stirred at desired
2
2
7
reaction temperature which was designed by the design expert software. At the certain designed time, the solid product was
separated and washed by distilled water to separate the unreacted raw materials. Then, the obtained crude DHPM was
dissolved in ethanol to separate Sr As O and crystallized at room temperature to obtain the pure DHPM. The experimental
2
2
7
3

designed procedure summarized in table 3 was performed by changing the reaction parameters simultaneously. The reaction
yield for each designed test was calculated by measuring the mmole fraction of the final product.
3
3
. Results and discussions
.1. Characterization
The X-ray dꢀffractꢀon patterns of the as-synthesꢀzed Sr As O samples ꢀs reported ꢀn fꢀgure 1 a-e. Structural analysis was
2
2
7
performed by FullProf program, employꢀng profꢀle matchꢀng wꢀth constant scale factor. Fꢀgure 1 a ꢀndꢀcates that the pattern
has a main Sr As O monoclꢀnꢀc crystal system with space group P2 for S . However, with increasing the reaction time to
2
2
7
1
1
4
8 h (Figure 1 b), the proportion of the monoclinic crystal system is decreased. In the case, the material is composed of both
tetragonal and monoclinic crystals with almost equal proportions. Also, the data reveal that SrCO impurity amount is
3
increased by increasing the reaction time to 48 h. But, by increasing more the reaction time to 72 h, the impurity amount is
decreased until a homogeneous tetragonal crystal phase is obtained. So, when the reaction time is increased to 120 h, it is
found that the purity of the tetragonal crystal system is increased more until a nearly pure tetragonal crystal system is
obtained. The data indicate that the monoclinic crystal system is stable at low reaction time in the solvothermal method.
Besꢀdes, we found that when the reactꢀon condꢀtꢀon ꢀs changed from hydrothermal [20] to solvothermal method, the stabꢀlꢀty
of monoclꢀnꢀc crystal system ꢀs changed. It was found that the monoclꢀnꢀc crystal system was more stable at lower reactꢀon
tꢀme and the tetragonal crystal system was more stable at hꢀgher reactꢀon tꢀme ꢀn the solvothermal method. However, only
the monoclꢀnꢀc crystal system was obtaꢀned by hydrothermal method. The data ꢀndꢀcate that the reactꢀon solvent type ꢀs also
an ꢀmportant parameter on the fꢀnal crystal system.
4

Fꢀgure 1. XRPD patterns and the rꢀetveld analyses of a) S , b) S and c) S , d) S and e) S .
1
2
3
4
5
2
Table 1 presents the rietveld refinement (R , RBragg, χ ) and cell parameters (a, b and c) data for S to S . The quantitative
F
1
5
phase analysis was investigated for the synthesized nanomaterials by direct comparison method [31]. For the purpose, the
intensity of two peaks in the XRD pattern with the highest intensity related to the SrCO and the Sr As O (monoclinic or
3
2
2
7
tetragonal crystal system) were compared. So, the peaks at about 29.7˚, 30.9˚ and 27.5˚ for SrCO , monoclinic and tetragonal
3
crystal phases, respectively, were used. The data indicate that the monoclinic crystal system proportion is more than the
tetragonal one when the reaction time is 24 h. The data show that the proportion of tetragonal, monoclinic and SrCO are 90,
3
6
and 4 %, respectively, for S . The count data reveal that the crystal phase growth of S is more than the other synthesized
5 5
samples. It is clear that increasing the reaction time has a positive effect on the crystal phase growth of the obtained
materials.
The volume of unit cell (V) is calculated by the following formulas for monoclinic and tetragonal crystal systems,
respectively:
5

ꢀ
= ꢁ. ꢂ. ꢃ. ꢄꢅꢆꢇꢈꢉ
And
ꢀ
= ꢁ. ꢂ. ꢃ
The grain size (D) data of the obtained nanomaterials are calculated by the following equation using the parameters obtained
from rietveld analysis (Table 2):
ꢋꢌ
ꢊ =
ꢍ
ꢎ
ꢏ
ꢃꢐꢄꢑ
Dislocation density (δ) is also calculated by the following formula:
1
ꢒ =
ꢊꢏ
The parameter is related to the number of defects in the crystal. The data showed that δ was decreased when the purity of the
monoclinic and/or tetragonal crystal system was improved.
To calculate strain (ε) value, the following formula is used:
ꢈꢔꢕꢖ ꢃꢐꢄꢑ
ꢓ =
4
Decrease in the strain value with increase in the purity of the crystal system is due to improve in the degree of crystallite of
the synthesized material. So, the data in table 2 indicate that the reaction time affect considerably on the D, δ and ε values.
The interplanar spacing data of the obtained materials were calculated by Bragg equation and compared to the calculated
data for monoclinic and tetragonal crystal systems, respectively, by the following formulas:
ꢏ
ꢏ
ꢚꢏ
ꢃꢏ
1
1
ꢏ
ℎꢏ ꢙ ꢄꢅꢆ ꢈ
2ℎꢚ cos ꢈ
ꢁꢃ
=
ꢘ
+
+
−
ꢛ
ꢗꢏ ꢄꢅꢆ ꢈ ꢁ
ꢏ
ꢂꢏ
And
1
ꢗꢏ
ℎꢏ ꢙꢏ
ꢘ +
ꢚꢏ
=
+
ꢛ
ꢁꢏ ꢂꢏ ꢃꢏ
The value of 2θ ≈ 27.80 ᵒ, the (h k l) value of (1 0 2), and β = 91.30 ᵒ for monoclinic crystal system; and 2θ ≈ 44.80 º, the (h
k l) value of (0 1 12) for tetragonal crystal system were used in the above equation. As we know, sin (91.30) is about 0.9997
and cos (91.30) is -0.023.
So, the formulas can be rewritten for monoclinic and tetragonal crystal systems, respectively.
1
ꢗꢏ
1
4
0.184
ꢁꢃ
=
ꢜ
+
+
ꢝ
ꢁꢏ ꢃꢏ
And
6

1
ꢗꢏ
1
ꢂꢏ
144
ꢃꢏ
=
ꢜ
+
ꢝ
Table 1. Rietveld analysis and unit cell parameters data of the obtained nanomaterials.
2
Sample
a
b
c
V
Β
R
F
R
B
χ
Counts
1045
307
Tetragonal (%)
Monoclinic %
3
SrCO %
S
1
S
2
S
3
S
4
S
5
5.32131
6.89515
7.08658
7.08040
7.00587
11.24496
6.89515
7.08658
7.08040
7.00587
8.17577
25.34752
25.34782
25.23535
25.32477
489
91.3
90.0
90.0
90.0
90.0
1.06
0.89
2.15 2.58
2.38 3.34
6
88
30
26
15
6
6
1205
1273
1265
1243
36
55
75
90
34
19
10
4
0.541 1.39 1.52
0.930 2.92 3.92
463
864
1.45
2.95 4.23
2355
Table 2. Crystallite size, dislocation density, strain and interplanar spacing data of the obtained nanomaterials.
2
Sample
2θ
B(˚)
B(rad)
Cosθ
sinθ
D (nm)
δ(lines/m )
ε
dBragg(Å)
dhkl(Å)
S1
S2
S3
S4
S5
27.7996
44.8041
44.7166
44.8811
44.8210
0.27988
0.51304
0.51295
0.51312
0.29681
0.004882
0.008950
0.008948
0.008951
0.005136
0.971
0.925
0.925
0.924
0.924
0.240
0.381
0.380
0.382
0.382
29
17
17
17
29
0.001189
0.0035
1.185106
2.06969
3.208
2.020
2.026
2.016
2.016
3.284401
2.019649
2.024304
2.015908
2.020707
0.00346
0.00346
0.00119
2.069225
2.067681
1.186416
3
.2. Morphology analysꢀs
Fꢀgures 2 a-e’ shows typꢀcal FESEM ꢀmages of S to S , respectꢀvely. As could be seen from fꢀgure 2 a and a’, the product ꢀs
1
5
composed of long-length rods. Fꢀgure 2 b and b’ shows that when the reactꢀon tꢀme ꢀs ꢀncreased, the morphology of the
obtaꢀned materꢀal ꢀs changed to multꢀgonal partꢀcles and short-length rods. The observatꢀon can confꢀrm the mꢀxture of
monoclꢀnꢀc and tetragonal crystal phases. Accordꢀng to fꢀgure 2c and c’, the morphology of the obtaꢀned materꢀal ꢀs almost
multꢀgonal plates. Besꢀdes, a few rod lꢀke partꢀcles are seen ꢀn the mꢀxture. Wꢀth ꢀncreasꢀng the reactꢀon tꢀme to 96 h (fꢀgure 2
d and d’) and 120 h (fꢀgure 2 e and e’) , ꢀt ꢀs found that the morphology of the obtaꢀned materꢀal ꢀs a pure multꢀgonal plate
lꢀke structure.
7

Fꢀgure 2. FESEM ꢀmages of a,a’) S , b,b’) S and c,c’) S ; d,d’) S and e,e’) S .
1
2
3
4
5
3
.3. Optical properties
UV-Vis absorption spectra associated with the direct optical band gap energies (Eg) of the as-synthesized samples are shown
in figure 3 a and b, respectively. Figure 3 a shows a visible absorption edge at about 375 nm for the as-synthesized samples.
However, the figure reveals that there is another absorption peak as a shoulder at 425 nm. The Eg plots are also shown in
2
figure 3 b. The direct band gap energy can be obtained by (αhν) = A(hν - Eg) where A is constant [32]. It was found that the
Eg values were in the range of 2.80-3.02 eV. The Eg values are about 2.92 and 3.02 eV for S and S , respectively.
1
5
1
.3
0.02
S1
S2
S3
S4
S5
a
S1
S2
S3
S4
S5
b
0
0
2
00
250
300
350
400
450
500
2
2.5
3
3.5
Wavelength (nm)
Eg (eV)
2
Figure 3. Plots of a) UV-Vis absorption and b) (αhν) versus hν for S to S .
1
5
-
Figure 4 presents the FTIR spectra of the obtained samples. The peaks at 432, 647, 802, 852, 1033, 1080, 1465 and 3400 cm
1
-1
are observed in the spectra. The strong band at 432 cm is assigned to the As–Obridging stretching vibration [21]. The
8

-1
–1
absorption at 647 cm is assigned to Sr–O stretching vibration [33]. The bands at 802 and 1033 cm are related to
-1
As–O vibration modes [34]. The band at 802 cm is assigned to stretching vibrations of As–O bonds [23,35]. The peaks at
-1
1
465 and 3400 cm are related to the H-O vibration modes of free H O [36].
2
1
9
8
00
0
0
S1
S2
S3
S4
S5
70
60
5
4
3
2
1
0
0
0
0
0
0
3
400
2900
2400
1900
1400
900
400
-1
Wavenumber (cm )
Figure 4. FTIR spectra of the as-synthesized nanomaterials.
3
.4. Experimental design procedure to obtain optimum conditions
Full factorial design is used to obtain the optimum conditions in the Biginelli reactions by combinations of all factors and
their settings [37]. To analyze the experimental design, response surface methodology (RSM) is used by applying an
empirical model [38]. The analysis of variance (ANOVA) was used to check the adequacy of the applied model. For the
purpose, some replicated experiments are needed in the model.
The goal of the present experimental design study is determining the values of nanocatalyst, reaction time and temperature in
which the maximum response (yield (%)) is achieved. All the probably combinations of the three factors associated with the
response values are presented in table 3. All of the experiments are done at two days randomly. Four replicates at the center
of the factors are considered to validate the applied model by ANOVA (Table 4). The low and high levels of the above
mentioned factors were coded to -1 and +1, respectively (Table 5). The observed data of the factorial design was fitted to a
linear response model. The relation between the three factors (catalyst, time and temperature) and the yield of the Biginelli
reaction, Y%, is shown below based on the first order model:
2
Y%=-87.14746+5.18178×Catalyst+1.24024×time+0.19943×temperature-0.027500×Catalyst×time-0.037460×Catalyst
(
Equation 1)
9

The effects of the parameters are shown by their coefficients in the above equation. It is clear that the effect of catalyst is
higher than the other factors. However, the effects of catalyst and time on the reaction yield are close to each other.
Table 4 displays the analysis of variance for suggested first-order model. The data indicate that the p-value of the regression
is smaller than 0.05. So, it reveals that the model is significant at a high confidence level (95%) [38]. Besides, it is found that
the p-value of lack of fit is greater than 0.05 confirming the significance of the model. Also, two other parameters (R-square
and adjusted–R-square) obtained by the ANOVA are used to express the quality of fit of the linear model equation. It was
2
found that the value of variation fitting (R ) is 0.92 indicating a high degree of correlation between the response and the
independent factors. Besides, high significance of the proposed model was confirmed by the high values of adjusted
2
2
regression coefficient (R -adj = 0.89) and predicted regression coefficient (R -prd = 0.79).
Counter and three–dimensional response surface plots of Y% (using equation (1) when the amount of temperature was
maintained constant at optimum value and the other two factors were allowed to vary) is presented in figure 5 to illustrate the
effects in the mentioned factors.
3
.5. Catalytic studies
The as-described experimental design methodology in this work was used to find the optimum conditions for the
Biginelli reaction with small number of experiments rather than one-at-a-time method. By means of RSM method
to analyze the procedure, it was found that the factors (catalyst, time and temperature) were independent
parameters. Their effects on the reaction response (Y%) was depicted and interpreted with RSM method. The
optimization results obtained by the full factorial design showed that the optimum condition for the synthesis of the
DHPMs was 0.031 g of catalyst, 90 ºC reaction temperature, and 100 min reaction time (Table 3). The optimized
condition was used for the synthesis of other derivatives. Schematic image is presented below to shows a summary
of the Biginelli reaction pathway (Scheme 1).
Table 3. Three-level full factorial design in Biginelli reaction*.
Catalyst (mg)
Time (min)
Temperature (ºC)
Yield %
4
2
4
3
0
0
0
0
100
100
50
40
40
90
65
86
79
79
83
75
1
0

3
2
4
3
2
2
3
4
3
3
3
4
1
3
3
3
0
0
0
0
0
0
0
0
0
0
0
6
3
0
0
0
75
50
65
40
90
65
90
90
65
40
107
65
65
65
65
65
23
65
79
40
89
80
50
85
82
77
94
94
65
83
58
71
66
81
100
75
50
100
75
50
75
117
33
75
75
75
75
75
*
Benzaldehyde: Ethyl acetoacetate: Urea molar ratios is as follows: 1:1:1.2.
Table 4. Analysis of variance for suggested first-order model.
Source
Sum of Squares
2.7
df
1
Mean Square
2.7
F Value
p-value Prob > F
Block
Model
3432.851
1037.696
1471.737
339.4834
378.125
205.8087
307.3995
247.3995
60
5
686.5701
1037.696
1471.737
339.4834
378.125
205.8087
23.64611
27.48883
15
29.03522
43.88444
62.24013
14.35684
15.991
< 0.0001
< 0.0001
< 0.0001
0.0023
significant
A-Catalyst
B-time
1
1
C-temperature
AB
1
1
0.0015
2
A
1
8.7037
0.0113
Residual
13
9
Lack of Fit
Pure Error
Cor. Total
1.832589
0.2930
not significant
4
3742.95
19
1
1

*
For detailed explanation of the table, refer to [36].
Table 5 presents the experimental range and levels of the three factors used in the experimental design method. The central
composite design (CCD) is chosen to model the proposed procedure described in table 3. The variables (catalyst amount (A)
and reaction time (B) and reaction temperature (C)) are given in coded form (-α, -1, 0, +1, +α).
Table 5. The experimental range and levels of independent variables in CCD.
Factor
Name
Low Actual
High Actual
Low Coded
High Coded
A
B
C
Catalyst
time
20
50
40
40
100
90
-1
-1
-1
1
1
1
temperature
Scheme 1. Schematic representation of the reaction pathway for the synthesis of DHPMs.
The effect of the three independent factors on the response of the proposed process presented by experimental design method
was studied by RSM. Figure 5 represents the 2D and 3D plots related to the interaction of AB. The semi-curvature of the plot
indicates the interaction between the variables. The data presented in the figure reveal that the DHPMs production
percentage is enhanced when the catalyst amount and reaction time are increased at a certain reaction temperature. This is
because of the availability of high surface area of catalyst for the raw materials molecules to produce the targets.
1
2

Figure 5. 2D and 3D surface plots of the production of DHPMs.
The normal plot of residuals and predicted versus the experimental production efficiency plots are shown in figure 6. The
data presented in the figure display a good agreement between the predicted and experimental efficiency and represents the
adequacy and significance of the model. Also, the normal plots of the internally studentized residuals versus probability and
predicted versus actual data are presented in the figure. As it is evident in this figure, the data appear on a straight trend line
demonstrating that there is no considerable dispersal.
Figure 6. Dispersal residuals and normal plots for the Biginelli reaction.
1
3

The optimum values of the three factors (using in range option for the factors and maximum value for response (R)) obtained
by RSM are presented in figure 7. It is found that the optimum values for catalyst amount, reaction time and temperature are
3
1 mg, 100 min and 90 ºC, respectively.
Figure 7. The optimum values of the factors in the Biginelli reaction.
The catalytic activity values of the synthesized nanomaterials and the raw materials at the optimized conditions and the
reusability performance of the nanocatalysts are presented in figure 8 a and b. As could be seen from figure 8 a, Sr As O
2
2
7
catalytic activity was higher than the two raw materials showing the fact that the presence of the both metal ions (Sr and As)
is important and the two ions have acted cooperatively. Several researches have focused on the cooperative properties of
metal ions on the catalytic reactions. The data revealed that cooperative catalysis accelerates some especial chemical
transformations [39-41]. In this approach, the presence of at least two different ions with different hardness/softness is
2
+
5+
necessary to activate substrates simultaneously. In the present work, Sr is the softer metal ion while As is the harder one.
In Biginelli reactions, the substrates with different hardness/softness are presented in the reaction mixture. So, the presence
of the two different metal ions with different carbophilicity will interact better with a broader range of such substrates. The
reusability of the synthesized nanocatalysts in the Biginelli reactions is shown in figure 8 b. As could be seen from the
figures, S can maintain active more than S in the same reaction condition.
5
1
1
4

9
6
1
00
95
96
a
92
b
93
1
00
90
9
2
92
8
6
83
1
S1
S5
8
8
6
4
2
0
0
0
0
0
74
8
6
4
2
0
0
0
0
0
69
6
2
51
4
6
44
4
1
39
S1
S2
S3
S4
S5
Sr(NO3)2
As2O3
Run 1 Run 2 Run 3 Run 4 Run 5 Run 6 Run 7
Run number
Sample
Figure 8. a) Catalytic performance of the synthesized nanomaterials and the raw materials at the optimum conditions using
ethyl acetate, benzaldehyde, and urea at 1:1:1.2 molar ratios and b) Reusability tests for the obtained nanocatalysts.
Table 6 presents a comparative study on the catalytic performance of S and S . As could be seen from the data
1
5
included in the table, it is clear that the efficiency of S is more than S at the same reaction conditions. Also, the
5
1
data indicate that the best synthesis yield was achieved when benzaldehyde, urea and ethyl acetate were used as the
DHPM raw materials. However, the data reveal that the yield value of the Biginelli reactions was lowest when
methyl acetate was used as raw material.
Table 6. Comparative study on the catalytic performance of S and S .
1
5
Sample
R1
R2
R3
Y%
92
S1
S1
S1
S1
Benzaldehyde
Benzaldehyde
Benzaldehyde
Benzaldehyde
Ethyl acetate
Methyl acetate
Methyl acetate
Ethyl acetate
Urea
Urea
88
Thiourea
Thiourea
90
93
S5
S5
S5
S5
Benzaldehyde
Benzaldehyde
Benzaldehyde
Benzaldehyde
Ethyl acetate
Methyl acetate
Methyl acetate
Ethyl acetate
Urea
Urea
96
92
93
98
Thiourea
Thiourea
1
5

Table 7 shows the catalytic activity of S and S at the optimized conditions using different raw materials
1
5
derivatives associated with the obtained melting points of the synthesized DHPMs compounds. As could be found
from the data, it is clear that the catalytic performance of S is more than S for almost all of the derivatives.
5
1
Table 7. Catalytic activity of S and S at the optimized conditions using different raw materials derivatives.
1
5
R1
H
R2
Y% (S1)
Y% (S5)
Found Melting Point (ºC) (S1)
Found Melting Point (ºC) (S ) [24]
5
OEt
OEt
92
87
85
81
95
75
46
59
66
88
84
90
61
93
27
57
36
96
88
84
82
94
80
59
61
67
92
89
93
76
92
38
66
44
197-199
208-210
214-217
211-214
224-226
261-263
256-258
165-167
252-255
203-205
201-203
226-229
238-241
277-280
282-285
191-193
238-240
200-202
210-212
216-219
211-213
225-227
263-265
255-258
166-168
254-256
202-204
203-206
227-229
240-242
276-279
284-286
195-197
240-242
4
2
4
3
2
3
3
4
-Cl
-Cl
OEt
-Br
OEt
-NO2
-OMe
-OMe
-OH
-OH
OEt
OEt
OEt
OEt
OEt
H
OMet
OMet
OMet
OMet
OMet
OMet
OMet
OMet
4
2
4
3
2
3
4
-Cl
-Cl
-Br
-NO2
-OMe
-OMe
-OH
1
6

Table 8 represents a comparison study of the catalytic performance for the synthesis of DHPMs with the H, 4-Cl and 2-Cl
derivatives among S and S with other previously reported catalysts to confirm the merit of the present work. As could be
1
5
seen from the table, the catalytic efficiency of the present work is in compatible with the other reported catalysts. In the
catalytic reaction, the catalyst amount, and reaction time and temperature are the important parameters affect the conversion
yield. The data show that the catalytic reaction conditions including nanocatalyst amount, and reaction time and temperature
are comparable to the other reported works. The data indicate that some of the works in table 8 report the yields when the
reaction time and temperature are higher than the present work. The data reveal that composite materials [42, 43, 45, 46]
show lower yield compared to the other works. Besides, the data indicate that mixed metal oxides (Bi V O and Sr As O )
2
2
7
2
2
7
present higher efficiency than a simple metal oxide (ZnO) that can be due to the cooperative property of the metal ions in the
A B O crystal system.
2
2
7
Table 8. Comparison study of the catalytic ability of the synthesized Sr As O with other catalysts.
2
2
7
Catalyst
S1
R1
H
Catalyst amount
30 mg
Reaction Condition
solvent-free, 90 °C
Yield %
92
Time (min)
100
Ref.
Present work
4
-Cl
-Cl
87
2
85
S5
H
30 mg
solvent-free, 90 °C
solvent-free, 90 °C
96
88
84
100
Present work
4
2
-Cl
-Cl
-
2
Bi V O
7
H
3.1 × 10 mmol
89
92
98
60
[41]
2
2
4
2
-Cl
-Cl
Bi O /ZrO
2
H
20 mol%
solvent-free, 80-85 °C
85
85
82
120
120
165
[42]
2
3
4
2
-Cl
-Cl
ZrO –Al O –Fe O
4
H
0.05 g
Ethanol, reflux, 140 °C
82
66
40
300
[43]
2
2
3
3
4
2
-Cl
-Cl
1
7

ZnO
H
-Cl
H
25 mol%
0.1 g
solvent-free conditions at 90 °C
acetonitrile solvent at 80 °C
solvent free condition
92
95
80
50
[44]
[45]
[46]
4
AlTiTUD
360
calcium
H
H
8 mole%
98
97
1440
hydroxyapatite
TiO -CNT
0.03 g
Ethanol solvent at 100 ºC
60
[47]
2
3
.6. Reaction kinetic study
The influence of the parameters on the reaction rate is studied by the reaction kinetic study. The Langmuir–Hinshelwood (L–
H) kinetic model (Eq. (2)) is used to study the kinetic of several catalytic processes in which the heterogeneous catalytic
procedure is considered.
ln [C ]/[C] =kapp
t
(2)
0
Where C is ethyl acetoacetate concentration in the reaction mixture at time t; C is the initial ethyl acetoacetate
0
concentration; and k is the first-order rate constant.
The graphs in figure 9 show the catalytic behavior of S and S . The data indicate that the linear dependence of the graphs at
1
5
2
the time intervals among 0 to 100 min follows a first-order kinetic model for the two samples. The amount of kapp and R
-1
-1
values are 0.025 min and 0.978, and 0.035 min and 0.989, for S and S , respectively. It is clear that the rate of the
1
5
catalytic reaction for S is more than S .
5
1
1
8

3
2
1
0
.5
3
y = 0.0352x - 0.2535
R² = 0.9895
S1
S5
.5
2
y = 0.025x - 0.2559
R² = 0.9784
.5
1
.5
0
0
20
40
60
80
100
Time (min)
Figure 9. Plots of ln (C /C) versus reaction time for the synthesis of DHPMs.
0
4
. Conclusion
The present work reported a systematic study of the reaction time influence on the crystal phase growth, purity and
type of Sr As O materials. Ultrasonic assisted solvothermal method was used for the synthesis of Sr As O
2
2
7
2
2
7
materials. The rietveld analysis data revealed that increasing the reaction time from 24 h to 120 h lead to changing
the crystal phase type from monoclinic to tetragonal structure. FESEM images indicated that the reaction time had a
considerable effect on the morphology of the obtained materials. It was found that the morphology of the obtained
targets was changed from long - length rods to multigonal plates when the reaction time was increased from 24 h to
1
20 h. The obtained nanomaterials were used as high efficient nanocatalyst for the synthesis of DHPMs. The
optimum conditions were obtained by experimental design methodology. It was found that the optimum conditions
obtained by RSM analysis were 31 mg of catalyst, 90 ºC temperature and 100 min time. The synthesis yields at the
optimum conditions were 94 % and 96 % for S and S , respectively. The Langmuir–Hinshelwood (L–H) kinetic
1
5
model data revealed that the Biginelli reaction followed a pseudo-first order kinetic model. The apparent rate
constant (kapp) values indicated that the rate of Biginelli reaction using S was faster than that of S . The catalytic
5
1
performance data indicated that the efficiency for S (tetragonal crystal system) was more than that of S
5
1
(
monoclinic crystal system). This may be due to the higher surface energy of the tetragonal crystal system than the
monoclinic crystal system.
1
9

Conflict of interest
The authors Rozhin Esmaeili, Leila Kafi-Ahmadi and Shahin Khademinia declare that they have no conflict of
interest.
Reference
[
1] Kasinathan K, Kennedy J, Elayaperumal M, Henini M, Malik M (2016) Photodegradation of organic pollutants RhB dye
using UV simulated sunlight on ceria based TiO nanomaterials for antibacterial applications. Sci Rep. 6: 38064-38075.
2
https://doi.org/10.1038/srep38064.
[
2] Pirzada M, Grimes RW, Maguire J, Sickafus K (2002) Predictions of strontium accommodation in A B O pyrochlores.
2 2 7
J Mater Res. 17: 2041-2047. https://doi.org/10.1557/JMR.2002.0302.
[
3] Cheng J, Li J, Ma C, Hao Z (2009) Catalytic combustion of methane over La TM Zr O (TM=Mn, Fe, and Co)
2 0.3 1.7 7−δ
pyrochlore oxides. Catal. Commun. 10: 1170-1173. https://doi.org/10.1016/j.catcom.2009.01.006.
[
4] Christopher J, Swamy C.S (1991) Surface characterization and catalytic activity of Ln Ti O (Ln=Y, Sm, Gd and Tb),
2 2 7
J. Mater. Sci. 26: 4966-4970. https://doi.org/10.1007/BF00549878.
[
5] Hakimyfard A, Khademinia S, Rahimkhani M (2018) Solid state synthesis, crystal structure, evaluation of direct and
indirect band gap energies and optimization of reaction parameters for As Ni O nanomaterials. J. Nanoanalysis. 5: 91-98.
2
3
8
https://doi.org/10.22034/JNA.2018.541865.
6] Haynes D.J, Berry D.A, Shekhawat D. Spivey J.J (2009) Catalytic partial oxidation of n-tetradecane using Rh and Sr
substituted pyrochlores: Effects of sulfur. Catal. Today. 145: 121-126. https://doi.org/10.1016/j.cattod.2008.05.014.
7] Park S, Hwang H.J, Moon J (2003) Catalytic Combustion of Methane over Rare Earth Stannate Pyrochlore. Catal. Lett.
7: 219-223. https://doi.org/10.1023/A:1023626226464.
8] Sohn J.M, Kim M.R, Woo S.I (2003) The catalytic activity and surface characterization of Ln B O (Ln=Sm, Eu, Gd and
[
[
8
[
2
2
7
Tb; B=Ti or Zr) with pyrochlore structure as novel CH combustion catalyst. Catal. Today. 83: 289-297.
4
https://doi.org/10.1016/S0920-5861(03)00249-9.
[
9] Jiang Z, Su J, Han Y, Alshahrani F, Hao Z, Xiao T (2005) The effect of transition metal in Sn-based pyrochlores on the
methane catalytic combustion. Prog. Nat. Sci. 15: 134-138. https://doi.org/10.1080/10020070512330020.
[
(
10] Wuensch B.J, Eberman K.W, Heremans C, Ku E.M, Onnerud P, Yeo E.M.E, Haile S.M, Stalick J.K, Jorgensen J.D
2000) Connection between oxygen-ion conductivity of pyrochlore fuel-cell materials and structural change with
composition and temperature. Solid State Ionics. 129: 111-133. https://doi.org/10.1016/S0167-2738(99)00320-3.
2
0

[
11] Sellami M, Caignaert V, Hamdad M, Belarbi A, Sari-Mohamed I, Bahmani A, Bettahar N (2011) Synthesis and
characterization of the new pyrochlore Bi Sb Nb MnO7 solid solution. C. R. Chim. 14: 887-890.
1.5
1.5-x
x
https://doi.org/10.1016/j.crci.2011.05.010.
12] Khademinia S, Behzad M (2015) Catalytic performance of bismuth pyromanganate nanocatalyst for Biginelli reactions.
RSC Adv. 5: 24313-24318. https://doi.org/10.1039/C5RA11432B.
13] Khademinia S, Behzad M (2015) Low temperature hydrothermal synthesis, characterization and optical properties of
strontium pyroniobate. Adv. Powder Technol. 26: 644-649. https://doi.org/10.1016/j.apt.2015.01.016.
14] Khademinia S, Behzad M (2015) Lanthanum cerate (La Ce O ): hydrothermal synthesis, characterization and optical
[
[
[
2
2
7
properties. Int. Nano Lett. 5: 101-107. https://doi.org/10.1007/s40089-015-0143-x.
15] Khademinia S, Behzad M (2015) Bismuth Pyromangenate: Hydrothermal and solid state synthesis, characterization and
optical properties. J. Adv. Mater. Pro. 3: 77-84.
16] Weil (2001) Cadmium(II)
https://doi.org/10.1107/S1600536801004342.
17] Harvey C.F, Ashfaque K.N, Yu W, Badruzzaman A.B.M, Ali M.A, Oates P.M, Michael H.A, Neumann R.B, Beckie R,
[
[
M
diarsenate(V),
Cd As O ,
Acta Cryst. E.
57:
28-29.
2
2
7
[
Islam S, Ahmed M.F (2006) Groundwater dynamics and arsenic contamination in Bangladesh. Chem. Geol. 228: 112-136.
https://doi.org/10.1016/j.chemgeo.2005.11.025.
[
18] Raicevic S, Stanic V, Kaludjerovic-Radoicic T (2007) Theoretical Assessment of Calcium Arsenates Stability:
Application in the Treatment of Arsenic Contaminated Waste. Mater. Sci. Forum. 555: 131-136.
https://doi.org/10.4028/www.scientific.net/MSF.555.131.
[
19] Weil M, Kolitsch U (2005) Crystal structures of the triclinic low-temperature modifications of Co As O and Ni As O .
2 2 7 2 2 7
Poster, Annual Meeting of the DGK, Köln, Germany, February 28 - March 4,; Abstract in Z. Kristallogr., Suppl. No. 22:
83.
20] Khademinia S, Behzad M, Kafi-Ahmadi L, Hadilou S (2018) Solar Light Photocatalytic Degradation of Malachite
1
[
Green by Hydrothermally Synthesized Strontium Arsenate Nanomaterial through Response Surface Methodology. Z. Anorg.
Allg. Chem. 644: 221–227. https://doi.org/10.1002/zaac.201800004.
[
21] Weil M, drdevic´T, Lengauer CL, Kolitsch U (2009) Investigations in the systems Sr–As–O–X (X= H, Cl): Preparation
and crystal structure refinements of the anhydrous arsenates(V) Sr (AsO ) , Sr As O , α- and β-SrAs O , and of the apatite-
3
4 2
2
2
7
2
6
type
https://doi.org/10.1016/j.solidstatesciences.2009.08.019.
22] Mbarek A, Edhokkar (2013), The P43 enantiomorph of Sr As O . Acta Cryst. E. 69: 84-86.
https://doi.org/10.1107/S1600536813031619.
phases
Sr (AsO ) OH
and
Sr (AsO ) Cl.
Solid
State
Sci.
11:
2111-2117.
5
4 3
5
4 3
[
F
2
2
7
2
1

[
23] Gmelins Handbuch der Anorganischen Chemie 29 Strontium. Supplement, eighth ed. Verlag Chemie, Weinheim,
Germany, 1960, p. 290.
24] Khademinia S, Behzad M, Alemi A, Dolatyari M, Sajjadi SM (2015) Catalytic performance of bismuth pyromanganate
nanocatalyst for Biginelli reactions. RSC Adv. 5: 71109-71114. https://doi.org/10.1039/C5RA11432B.
25] Siddiqui ZN (2013) Bis[(L)prolinato-N,O]Zn–water: A green catalytic system for the synthesis of 3,4-
dihydropyrimidin-2 (1H)-ones via the Biginelli reaction. C. R. Chim. 16: 183-188.
https://doi.org/10.1016/j.crci.2012.10.008.
[
[
[
26] Sheykhan M, Yahyazadeh A, Ramezani L (2017) A novel cooperative Lewis acid/Brønsted base catalyst Fe O @SiO -
3 4 2
APTMS-Fe(OH)2:
An
efficient
catalyst
for
the Biginelli reaction.
Mol.
Catal. 435: 166-173.
https://doi.org/10.1016/j.mcat.2017.03.032.
27] Barthelemy AL. , Magnier E (2018) Recent trends in perfluorinated sulfoximines Développements récents de la chimie
des sulfoximines perfluorées. C. R. Chim. 21: 711-722. https://doi.org/10.1016/j.crci.2018.01.004.
28] Kolvari E Koukabi N Hosseini MM (2015) Perlite: A cheap natural support for immobilization of sulfonic acid as a
[
[
heterogeneous solid acid catalyst for the heterocyclic multicomponent reaction. Mol. Catal. 397: 68-75.
https://doi.org/10.1016/j.molcata.2014.10.026.
[
29] Sanchez LM, Sathicq ÁG, Romanelli GP, González LM, Villa AL (2017) Activity of immobilized metallic
phthalocyanines in the multicomponent synthesis of dihydropyridine derivatives and their subsequent aromatization. Mol.
Catal. 435: 1-12. https://doi.org/10.1016/j.mcat.2017.03.010.
[
30] Atashkar B, Zolfigol MA, Mallakpour S (2018) Applications of biological urea-based catalysts in chemical processes.
Mol. Catal. 452: 192-246. https://doi.org/10.1016/j.mcat.2018.03.009.
31] Yousefzadeh F, Kafi-Ahmadi L, Khademinia S (2019) Visible light induced photocatalytic degradation of malachite
[
4
+
2+
2+
3+
3+
3+
green by solid state synthesized MgFeO –MgFe M O (M=None, Mn , Ni , Zn , Eu , Dy , Yb ) nanocomposites.
3
2
x
4+δ
Catal. Lett. 149: 1660-1679. https://doi.org/10.1007/s10562-019-02733-7.
32] Pascual J, Camassel J, Mathieu M (1978) Fine structure in the intrinsic absorption edge of TiO . Phys. Rev. B. 18:
[
2
5
606-5614. https://doi.org/10.1103/PhysRevB.18.5606.
[
33] Angel J, Greena M, Karuppasamy K, Antony R, Shajan XS, Kumaresan S (2013) Effect of magnesium doping on the
physicochemical properties of strontium formate dihydrate crystals.
https://doi.org/10.7598/cst2013.333.
Chem. Sci. Trans. 2: 141-146.
[
34] Bishay A, Maghrabi C (1969) Properties of Bismuth Glasses in Relation to Structure. Phys. Chem. glasses. 10: 1-11.
2
2

[
35] Srinivisa Rao G, Veeraiah N (2001) Study on various physical properties of PbO–As O glasses containing manganese
2 3
ions. J. alloys compd. 327: 52-56. https://doi.org/10.1016/S0925-8388(01)01559-6.
[
36] Khademinia S, Behzad M (2015) Low temperature hydrothermal synthesis, characterization and optical properties of
strontium pyroniobate. Adv. Powder Technol. 26: 644-649. https://doi.org/10.1016/j.apt.2015.01.016.
37] Sarabia LA, Ortiz MC (2009) Comprehensive Chemometrics Chemical and Biochemical Data Analyses, 1, chapter 12,
page 345.
[
[
[
38] Box GEP, Draper NR (1987) Empirical Model-Building and Response Surfaces, Wiley, New York.
39] Masaya S, Masaki S, Ito Y (1996) An Enantioselective Two-Component Catalyst System:ꢁ Rh−Pd-Catalyzed Allylic
Alkylation of Activated Nitriles. J. Amer. Chem. Soc. 118: 3309-3310. https://doi.org/10.1021/ja954223e.
40] Cai YF, Yang HM, Li L, Jiang KZ, Lai GQ, Jiang JX, Xu LW (2010) Cooperative and Enantioselective NbCl5/Primary
Amine Catalyzed Biginelli Reaction. Eur. J. Org. Chem. 4986-4990. https://doi.org/10.1002/ejoc.201000894.
41] Khademinia S, Behzad M, Jahromi HS (2015) Solid state synthesis, characterization, optical properties and cooperative
[
[
catalytic performance of bismuth vanadate nanocatalyst for Biginelli reactions. RSC Adv. 5: 24313-24318.
https://doi.org/10.1039/C5RA00368G.
[
42] Safari J, Ravandi SG (2014) Fe O –CNTs nanocomposites: a novel and excellent catalyst in the synthesis of
3 4
diarylpyrimidinones using grindstone chemistry. RSC Adv. 4: 11486-11492. https://doi.org/10.1039/C3RA47827K.
43] Safari J, Ravandi SG (2014) Titanium dioxide supported on MWCNTs as an eco-friendly catalyst in the synthesis of
,4-dihydropyrimidin-2-(1H)-ones accelerated under microwave irradiation. New J. Chem. 38: 3514-3521.
https://doi.org/10.1039/C3NJ01618H.
44] Pourshamsian K (2015) ZnO-NPs as an efficient reusable heterogeneous catalyst for synthesis of 1, 4-
Dihydropyrimidine derivatives in solvent-free conditions. Int. J. Nano Dimens. 6: 99-
04. https://doi.org/10.1080/00397911.2014.987350.
45] Pasupathi M, Santhi N, Pachamuthu MP, Alamelu Mangai G, Ragupathi C (2018) Aluminium and titanium modified
mesoporous TUD-1: A bimetal acid catalyst for Biginelli reaction. J. Mol. Struct. 1160:161-166.
46] Moussa SB, Mehri A, Badraoui B (2020) Magnesium modified calcium hydroxyapatite: An efficient and recyclable
catalyst for the one-pot Biginelli condensation. J. Mol. Struct. 1200: 127111.
47] Safari J, Gandomi-Ravandi S (2014) Carbon nanotubes supported by titanium dioxide nanoparticles as recyclable and
green catalyst for mild synthesis of dihydropyrimidinones/thiones. J. Mol. Struct. 1065-1066: 241-247.
[
3
[
1
[
[
[
2
3

Figure Captions
Fꢀgure 1. XRPD patterns and the rꢀetveld analyses of a) S , b) S and c) S , d) S and e) S .
1
2
3
4
5
Fꢀgure 2. FESEM ꢀmages of a,a’) S , b,b’) S and c,c’) S ; d,d’) S and e,e’) S .
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Figure 3. Plots of a) UV-Vis absorption and b) (αhν) versus hν for S to S .
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Figure 4. FTIR spectra of the as-synthesized nanomaterials.
Scheme 1. Schematic representation of the reaction pathway for the synthesis of DHPMs.
Figure 5. 2D and 3D surface plots of the production of DHPMs.
Figure 6. Dispersal residuals and normal plots for the Biginelli reaction.
Figure 7. The optimum values of the factors in the Biginelli reaction.
Figure 8. a) Catalytic performance of the synthesized nanomaterials and the raw materials at the optimum conditions using
ethyl acetate, benzaldehyde, and urea at 1:1:1.2 molar ratios and b) Reusability tests for the obtained nanocatalysts.
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Ultrasonic assisted solvothermal method was used for the first time to synthesize of Sr
2 2 7
As O .
Monoclinic and tetragonal crystal systems were achieved by changing the reaction condition.
High efficient catalytic performance was obtained to synthesize of DHPMs in Biginelli reactions.
Langmuir–Hinshelwood (L–H) kinetic model was used to study the kinetic behavior of the
catalyst.

Declaration of interests
☒
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.