A ternary hybrid system based on combination of mesoporous silica, heteropolyacid and double-layered clay: an efficient catalyst for the synthesis of 2,4-dihydro-3H-pyrazol-3-ones and pyranopyrazoles in aqueous medium: studying the effect of the synthetic

Article abstract of DOI:10.1007/s11164-018-3521-y

SBA/hydrotalcite/heteropolyacid nanocomposite is synthesized via a novel procedure in which the as-prepared heteropolyacid-loaded SBA-15 was impregnated with calcined hydrotalcite. The ternary hybrid system was characterized by using SEM/EDS, XRD, BET, TP

Full text of DOI:10.1007/s11164-018-3521-y

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-018-3521-y(0123456789(). -, vo Vl
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A ternary hybrid system based on combination
of mesoporous silica, heteropolyacid and double-layered
clay: an efficient catalyst for the synthesis of 2,4-dihydro-
3H-pyrazol-3-ones and pyranopyrazoles in aqueous
medium: studying the effect of the synthetic procedure
on the catalytic activity
Samahe Sadjadi1 Majid M. Heravi2 Vahideh Zadsirjan2
Vahid Farzaneh1
•
•
•
Received: 16 October 2017 / Accepted: 2 July 2018
Ó Springer Nature B.V. 2018
Abstract
SBA/hydrotalcite/heteropolyacid nanocomposite is synthesized via a novel proce-
dure in which the as-prepared heteropolyacid-loaded SBA-15 was impregnated with
calcined hydrotalcite. The ternary hybrid system was characterized by using SEM/
EDS, XRD, BET, TPD, TGA, FTIR and ICP-AES and also used as an efficient
catalyst for the synthesis of 2,4-dihydro-3H-pyrazol-3-one derivatives via the
reaction of arylaldehydes and 5-methyl-1H-pyrazol-3(2H)-one under reflux condi-
tion. Moreover, the catalytic activity of this catalyst was confirmed for the one-pot
four-component reaction of aryl aldehydes, ethylacetoacetate, malononitrile and
hydrazine hydrate/phenyl hydrazine in aqueous media for the synthesis of pyra-
nopyroles. The investigation of the effect of the synthetic procedure and calcination
of the hydrotalcite on the catalytic activity of the catalyst established that this factor
does not exert a marked effect on the catalytic activity. The present procedures
benefit from diverse advantages, including high yields, simplicity, mild reaction
conditions and short reaction times. Moreover, this catalyst was reusable for up to
five reaction runs and the HPA leaching was suppressed.
Keywords 2,4-Dihydro-3H-pyrazol-3-ones Á Pyranopyrazoles Á Catalyst Á Hybrid Á
Heteropolyacid Á SBA Á Hydrotalcite
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11164-
018-3521-y) contains supplementary material, which is available to authorized users.
Extended author information available on the last page of the article
123

S. Sadjadi et al.
Introduction
Mesoporous silica materials such as SBA-15 exhibit outstanding properties,
including non-toxicity, good mechanical properties, thermal stability and tunability.
The utility of these compounds for a broad range of applications [1, 2] such as
catalysis [3], gas storage and waste treatment has been proved. Among various uses,
catalysis is of great importance. There are numerous reports on the catalytic
activities of mesoporous compounds [4–8]. In the last decade, functionalization of
mesoporous silica materials as well as designing hybrid catalytic systems based on
functionalized compounds has attracted growing attention and various catalytic
species such as complexes [9, 10], nanoparticles [11, 12] and heteropolyacids [13]
have been incorporated in mesoporous silica material hybrid catalysts. For this
purpose, heteropolyacids (HPAs) are considered as promising candidates due to
their unique features such as non-toxicity, Bronsted acidity, redox potentiality and
non-corrosive nature [14]. Moreover, these catalysts exhibit high catalytic activities
for various photochemical, organic [15], electrochemical [16] and petrochemical
[17] reactions. The merit of incorporating HPA into the mesoporous silica materials
is transforming homogenous HPAs [14] into heterogeneous catalyst and improving
the catalyst surface area.
Layered double hydroxides (LDHs) are two-dimensional layered materials in
which the layers are composed of two types of metallic cations and the interlayer
space hosts anionic species. The general formula of an LDH is [M2?
M
(OH)2]x?
3?
x
1-x
Anx=ÀnÁmH2O, where M2? and M3? are di- and trivalent metal ions, An- is the
interlayer anion and x is the fraction of M2?, i.e. x = M2?/(M2? ? M3?) [18, 19].
These layered materials have various applications, including catalysis [20–22],
polymer science and designing carrier systems [23], emerged from their unique
properties such as ion exchange ability, tunable element compositions, and acid–
base properties.
One-pot multicomponent reactions (MCRs) provide a potent class of synthetic
procedures because of their excellent efficiencies, short reaction times and
distinctive selectivity [24–26]. These reactions create one of the best pathways
for modern organic chemistry since they can employ most of the component atoms
of diverse reactant compounds to provide a target product [27, 28]. Green chemistry
processes follow to develop alternative methods which help to protect properties
and decrease costs. The replacement of usual solvents with H2O that is harmless to
health and is accessible in large amounts is a significant basic method [29, 30]. Also,
organic synthesis in water gives main benefits, involving rate improvement and
insolubility of the target molecules that assists their separation through simple
filtration [26].
Heterocycles bearing pyrazole rings are remarkable target products in synthetic
and medicinal chemistry since this ring is a vital scaffold in numerous biologically
active molecules. Pyrazole is an essential heterocycle analogue that demonstrates a
significant role in various pharmaceutical and agrochemical industries [31]. Among
this group of molecules, 2,4-dihydro-3H-pyrazol-3-one derivatives have a wide
range of biological properties involving antibacterial, antipyretic, antidepressant and
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A ternary hybrid system based on combination of mesoporous…
anti-inflammatory activities [32]. Furthermore, they are imperative intermediates in
organic chemistry [33]. The treatment of aldehydes with 3-methyl-1-phenyl-5-
pyrazolone is a useful pathway to make 4,40-(arylmethylene)bis(1H-pyrazol-5-ols).
Diverse catalysts have been applied for the synthesis of these products through the
condensation reaction. These catalysts contain sodium dodecyl sulfate [34],
piperidine or acetic acid [35] silica-bonded S-sulfonic acid [36], ETBA [37] and
CAN [38].
Pyranopyrazoles are fused heterocyclic molecules that contain various biological
activities, including bactericidal [39], fungicidal [40] and vasodilatory activities
[41], and act as anticancer agents [42]. Pyranopyrazole was first provided by the
treatment between 3-methyl-1-phenylpyrazolin-5-one and tetracyanoethylene [43].
Sharanin and co-workers demonstrated a one-pot and three-component reaction
between aromatic aldehyde, pyrazolone and malononitrilein under Et3N as a
catalyst in EtOH to provide pyranopyrazoles [44]. Also, in this route, Vasuki and
Kandhasamy and co-workers reported a four-component reaction of aldehydes,
ethyl acetoacetate, malononitrile and hydrazine hydrate in H2O and catalytic b-
cyclodextrin [45].
In the following of our research on developing new catalysts for improving
organic transformations under green and eco-friendly condition [46, 47], we
recently reported the catalytic utility of SBA-15/hydrotalcite nanocomposite for
immobilization of HPA [48]. The hybrid system was prepared through formation
and functionalization SBA-15 followed by incorporation of HPA and subsequent
synthesis of un-calcined LDH in the presence of HPA-loaded SBA-15. To expand
our research on the catalytic potency of ternary hybrid of SBA/LDH/HPA and
because of the significance of pyrazolone derivatives, herein we disclose a novel
procedure for the synthesis of SBA/LDH/HPA nanocomposite through impregna-
tion of HPA-loaded SBA-15 and calcined LDH and studied its catalytic activity for
the synthesis of 2,4-dihydro-3H-pyrazol-3-ones and pyranopyrazole derivatives.
Furthermore, to provide more insight into the effect of the synthetic procedure and
use of calcined LDH on the catalytic activity, the catalytic activity of this catalyst is
compared with that prepared via our previously reported methodology, synthesis of
un-calcined LDH in the presence of HPA-loaded SBA-15 [48]. Noteworthy, the
catalyst reusability and HPA leaching are investigated too.
Results and discussion
Catalyst characterization
The FTIR spectrum of the catalyst is illustrated in Fig. 1. This spectrum shows two
main characteristic bands. One, the bands related to the SBA-15 structure, i.e. the
bands at 3450 and 1631 cm-1 that can be representative of SiO–H and the adsorbed
water respectively as well as the bands at 1084, 797, 950 and 454 cm-1, which are
assigned to stretching of Si–O–Si. Notably, the three mentioned peaks can also be
assigned to the symmetric stretching of P–O, W–Oc–W, W–Oe–W and W–Ot,
respectively [50].
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S. Sadjadi et al.
Fig. 1 FTIR spectrum of the catalyst
Noteworthy, the band at 2927 cm-1 is representative of the –CH2 stretching and
clearly establish the conjugation of APTES to SBA-15. The second characteristic
band is the band observed at 1366 cm-1 which is representative of LDH scaffold
[51].
The SEM/EDX images of the hybrid catalyst are depicted in Fig. 2. As depicted,
the SEM images of the hybrid system are distinguished from those of pure SBA-15
(Fig. 2). The hybrid system exhibited less compact morphology in which the rod-
like morphology of pure SBA-15 is observable to some extent. This observation
confirmed that incorporation of calcined LDH can alter the morphology of the SBA-
15. Notably, the SEM images of SBA/LDH/HPA and SBA/LDH/HPA/P (Fig. 1 in
supporting information) [48] are distinguished, indicating that the synthetic
procedure and use of calcined LDH affect the morphology of final composite.
The catalyst prepared by using calcined LDH exhibited more packed morphology.
Although the EDX analysis cannot prove the formation of LDH, SBA-15 and
incorporation of HPA, it can be considered as a useful tool for confirming the results
obtained from other analyses. As shown in Fig. 2, the Si and O atoms are present in
the structure. This may indicate the formation of SBA-15 structure. Besides, the C
and N atoms can be assigned to the attachment of APTES. Furthermore, the
observation of Al, Mg and O atoms can be representative of LDH framework. The
presence of P and W atoms can prove the immobilization of HPA.
The low-angle and wide-angle XRD patterns of the nanocomposite are shown in
Fig. 3. This pattern which contained three peaks at 0.9°, 1.5° and 1.8° established
100, 110 and 200 reflections of the highly ordered periodic arrangement of
hexagonal channels and also is in good accordance with previously reported XRD
patterns for SBA-15 [52]. This observation confirmed that upon formation of
nanocomposite, the ordered structure of SBA-15 was not destroyed. The peaks
observed in the wide-angle XRD pattern of the catalyst are in good agreement with
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A ternary hybrid system based on combination of mesoporous…
Fig. 2 a SEM/EDX images of the catalyst, b SEM images of pure SBA-15 [48]
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S. Sadjadi et al.
Fig. 3 The low-angle (top) and wide-angle (bottom) XRD patterns of the catalyst
the previous reports and clearly indicate the formation of LDH framework [53, 54].
Comparing with SBA/LDH/HPA/P [48], the wide-angle XRD pattern of SBA/LDH/
HPA is completely different (Fig. 2 in supporting information). The XRD pattern of
the former, un-calcined LDH showed only the layered structure, while the SBA/
LDH/HPA XRD pattern exhibited sharp and symmetric reflections for (003), (006),
(110) and (113) planes with broad and asymmetric reflections for (012), (015) and
(018) planes [55]. It is worth mentioning that no distinguished peak was observed in
the XRD pattern for HPA. Based on a previous report, this can be attributed to
uniform and high dispersion of the HPA as well as its low amount [56].
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A ternary hybrid system based on combination of mesoporous…
Fig. 4 Nitrogen adsorption–
desorption isotherm of the LDH/
SBA/HPA
Next, to study the textural properties of LDH/SBA/HPA, a nitrogen adsorption–
desorption isotherm of the LDH/SBA/HPA was recorded (Fig. 4). The shape of the
obtained isotherm confirmed the porous structure of the catalyst and belonged to the
type IV isotherms with a H2-type hysteresis loop. Notably, the nitrogen adsorption–
desorption isotherms of the LDH/SBA/HPA and LDH/SBA/HPA/P were similar
and indicative of porous structures (Fig. 3 in supporting information). The BET
surface area of the hybrid system (* 200 m2 g-1) was lower that of free SBA-15
(* 700 m2 g-1) and higher than that of LDH (* 100 m2 g-1).
To estimate the value of HPA in the ternary hybrid system, LDH/SBA/HPA was
digested in concentrated HCl and HNO3 solution and the obtained extract was
analyzed by using ICP-AES analysis. Using this procedure, the content of HPA was
measured to be about 5.5 w/w%.
Fig. 5 TGA analysis of the catalyst
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S. Sadjadi et al.
A TGA thermogram of LDH/SBA/HPA is illustrated in Fig. 5. As depicted, two
degradation stages can be observed over the range of 25–700 °C. The first
degradation step which occurred at about 100 °C is attributed to the loss of adsorbed
water molecules. The next degradation step was observed at about 400 °C
(* 3 wt%) and can be assigned to the loss of silane functionality of SBA-15.
The acidity of the catalyst was studied by measuring the temperature-
programmed desorption of NH3 (NH3-TPD, Fig. 6). As shown, the catalyst
exhibited two broad peaks distributed in the region of * 100, 200 to 400 °C,
implying two types of acid sites in the catalyst.
According to the literature, the low-temperature desorption peak observed at
* 100 °C indicates the presence of weak acidic sites on the catalyst. The high-
temperature desorption peak (detected at 400 °C), on the other hand, can confirm
the strong acidic sites on the catalyst. These sites can be due to the incorporation of
HPA [57, 58].
Catalytic activity
The catalytic activity of the novel hybrid catalyst was examined for the
development of 4,40-alkylmethylene-bis(3-methyl-5-pyrazolones) via the treatment
of 5-methyl-1H-pyrazol-3(2H)-one and aldehyde in aqueous media under reflux
condition (Scheme 1). At first, the reaction of 5-methyl-1H-pyrazol-3(2H)-one and
bezaldehyde was considered as a model reaction to examine the catalytic potential
of the designed catalyst and determine the optimum reaction condition. Initially, the
model reaction was performed in the absence of the catalyst. The result established
that the yield of the desired product in this condition was low, indicating the
necessity of using catalyst for this organic transformation. Secondly, the catalytic
activity of the hybrid system was compared with each component individually, i.e.
SBA, HPA and LDH. The results demonstrated that the ternary nanocomposite
exhibited superior catalytic activity compared to each component. Next, to study
whether the synthetic procedure of SBA/LDH/HPA and using calcined LDH can
affect the catalytic activity, the model reaction was performed in the presence of
SBA/LDH/HPA and SBA/LDH/HPA/P. Interestingly, the results established that
Fig. 6 NH3-TPD of the catalyst
123

A ternary hybrid system based on combination of mesoporous…
Scheme 1 Synthesis of 4,40-alkylmethylene-bis(3-methyl-5-pyrazolones) derivatives 3 under LDH/SBA/
HPA as an efficient catalyst
despite different physical characteristics, both catalysts exhibited similar catalytic
activity. This observation can confirm that in the nanocomposite, the catalytic
activity of the LDH component is independent of its calcined or un-calcined nature
and both of them exhibited similar catalytic activities.
Next, to optimize the reaction conditions, a series of experiments with diverse
solvents and quantities of the catalyst was accomplished. As shown, the best yield of
the desired product was achieved in water as solvent and in the presence of 5 mg of
catalyst under reflux condition in water after 15 min (Table 1). Then, to establish
the generality of the method, the optimum reaction condition was applied for the
synthesis of various derivatives of 4,40-alkylmethylene-bis(3-methyl-5-pyra-
zolones). As demonstrated in Table 2, this procedure exhibited broad substrate
scope in which diverse aldehydes with electron-withdrawing and electron-donating
groups can be employed effectively to furnish the target products in high yields. As
anticipated, the aldehydes containing electron-withdrawing groups led to the desired
products in slightly higher yields.
Table 1 Optimizing the reaction conditions for the synthesis of 3aa
Entry
Catalyst amount (mg)
Solvent
Temperature
Yield (%)
1
2
–
5
5
5
5
5
5
2
3
7
Water
Water
Water
CH3CN
DMF
Reflux
r.t.
Trace
20
3
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
85
4
60
5
55
6
EtOH
80
7
Toluene
Water
Water
Water
50
8
70
9
78
10
85
aIsolated yield
123

S. Sadjadi et al.
Table 2 LDH/SBA/HPA-mediated synthesis of 4,40-alkylmethylene-bis(3-methyl-5-pyrazolones)
derivatives
Entry
Product
Ar
Yield (%)a
mp (°C) found
mp (°C) from lit. [34]
1
2
3
4
5
3a
3b
3c
3d
3e
C6H5
85
79
82
87
90
229–231
263–265
225–227
270–273
299–302
230–232
262–264
224–226
271–272
300–302
4-HOC6H4
4-ClC6H4
3-NO2C6H4
4-NO2C6H4
aYields refer to isolated products
Scheme 2 Plausible mechanism for the synthesis of 4,40-(arylmethylene)bis(3-methyl-1H-pyrazol-5-ols)
Reaction mechanism for the synthesis of 4,40-alkylmethylene-bis(3-methyl-5-
pyrazolones)
A probable mechanism for the synthesis of 4,40-(arylmethylene)bis(3-methyl-1H-
pyrazol-5-ols) is exhibited in Scheme 2. The catalyst showed an important role in
improving the electrophilic character of the electrophiles in the reaction. The
reaction happens through initial construction of the intermediate I, produced by
Knoevenagel condensation reaction of the first equivalent of an enolic form of
123

A ternary hybrid system based on combination of mesoporous…
3-methyl-1H-pyrazol-5(4H)-one, 2, and aryl aldehydes, 1, that reacted successively
with a second equivalent of an enolic form of 2 to give the corresponding products
3.
Motivated by the gratifying results for the synthesis of 2,4-dihydro-3H-pyrazol-
3-ones derivatives and with the aim of expanding the catalytic utility of the ternary
hybrid system, we studied the catalytic activity of novel catalyst for promoting the
four-component reaction of aromatic aldehydes, ethylacetoacetate, malononitrile
and hydrazine hydrate/phenylhydrazine for the synthesis of pyranopyrazoles
(Scheme 3). Again, the comparison of the catalytic activities of SBA/LDH/HPA
and SBA/LDH/HPA/P confirmed their equal catalytic activity. For a detailed
exploration, the reaction between ethyl acetoacetate, hydrazine hydrate, benzalde-
hyde and malononitrile was considered as a model reaction and applied for the
optimization of reaction conditions; for this purpose, various solvents and catalyst
amounts were tested. Noteworthy, the reaction was not accomplished in the absence
of the catalyst. The results demonstrated the water was the solvent of choice.
Furthermore, the optimum amount of the catalyst was found to be 5 mg (Table 3).
In order to establish the generality of this procedure, the catalyst was employed
for the treatment of diverse aryaldehydes with ethylacetoacetate, malononitrile and
hydrazine hydrate/phenylhydrazine (Table 4). The method displayed good substrate
tolerance and the application of different electron-deficient and electron-rich
aldehydes resulted in the desired products in excellent yields.
To further generalize this protocol, biologically active spiro compounds were
also synthesized from four-component reaction of isatin, malononitrile and
3-methyl-1H-pyrazol-5(4H)-one (Scheme 4). The result established that the spiro
derivative can also be synthesized in high yield and short reaction time (Table 4,
entry 13).
Reaction mechanism for the synthesis of pyranopyrazoles
A probable mechanism can be reasonably suggested for the development of
pyranopyrazole 6 from the reaction of benzaldehyde, hydrazine hydrate, malonon-
itrile and ethyl acetoacetate (Scheme 5). In this pathway, the basic site of LDH/
SBA/HPA, i.e. LDH, plays a key role in the improving the activity of the reagents
for the synthesis of ylidenemalononitrile I from Knoevenagel reaction of
benzaldehyde and malononitrile. Then, the 3-methyl-1H-pyrazol-5 (4 H)-one II
was provided from the treatment of ethyl acetoacetate and hydrazine that would be
transformed into its expected enolate form III under LDH/SBA/HPA catalysis.
Also, the intermediated I can be activated by both acidic sites of the catalyst, HPA
Scheme 3 Synthesis of pyranopyrazoles 7 under LDH/SBA/HPA as an extremely effective catalyst
123

S. Sadjadi et al.
Table 3 Optimizing the reaction conditions for the synthesis of 7a
Entry
Catalyst amount (mg)
Solvent
Temperature
Yield (%)
1
2
–
5
5
5
5
5
5
2
3
7
Water
Water
Water
CH3CN
DMF
Reflux
r.t.
Trace
10
3
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
95
4
50
5
50
6
EtOH
85
7
Toluene
Water
Water
Water
45
8
83
9
90
10
95
Table 4 [59–62]: LDH/SBA/HPA as an extremely significant heterogeneous catalyst for the formation of
pyranopyrazoles
Entry Product
R
Ar/isatin
C6H5
Yield (%)a Time (min) Mp (°C) found Mp (°C) from lit.
95
1
7a
7b
7c
7d
7e
7f
H
H
H
H
H
H
H
15
15
15
15
15
15
15
20
20
20
20
20
15
242–245
206–209
219–223
245–247
231–234
250–253
223–225
167–169
170–172
175–179
143–148
183–186
284–287
243–245 [59]
208–210 [59]
220–222 [59]
246–248 [59]
233–235 [59]
249–252 [59]
224–226 [59]
166–168 [60]
169–170 [60]
176–178 [60]
144–146 [60]
184–185 [61]
285–286 [62]
2
4-CH3OC6H4 87
3
3-BrC6H4
2-ClC6H4
4-ClC6H4
4-NO2C6H4
4-OHC6H4
89
92
95
89
88
93
4
5
6
7
7g
7h
7i
8
Ph C6H5
9
Ph 4-CH3OC6H4 88
10
11
12
13
7j
Ph 4-CH3C6H4
Ph 4-ClC6H4
Ph 4-Br-C6H4
91
90
85
80
7k
7l
7m
H
Isatin
Scheme 4 Four-component reaction for the synthesis of spiro compounds
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A ternary hybrid system based on combination of mesoporous…
Scheme 5 Plausible mechanism for the synthesis of pyranopyrazole derivatives
and SBA-15. In the following, Michael-type reaction of III with the intermediate
I provide intermediated IV, that experienced intramolecular cyclization by using the
nucleophilic addition of enolate oxygen to the nitrile group to provide intermediate
V. Lastly, the tautomerization of intermediate V afforded the corresponding
pyranopyrazole 6 [62].
To demonstrate the merits of the new synthesized catalyst, its activity for the
four-component reaction of benzaldehyde, ethylacetoacetate, malononitrile and
hydrazine hydrate for the development of the model pyranopyrazole was compared
with those reported previously (Table 5). As tabulated, compared to c-alumina,
meglumine, imidazole and phase transfer catalyst HDBAC, the ternary hybrid of
LDH/SBA/HPA can mediate the reaction in shorter reaction time to furnish the
desired product in higher yields. Although piperidine and isonicotinic acid led to the
formation of the product in slightly lower reaction times, the yields of the product
were lower than the hybrid catalyst. Additionally, the homogeneous nature of these
catalysts hindered their recovery and reuse. Similarly, per-6-amino-b-cyclodextrine,
which exhibited high catalytic activity, is homogeneous. Some other catalyst
including nanosized magnesium oxide and magnetic Fe3O4 nanoparticles furnished
the product in slightly higher yields. This comparison established that the hybrid
system shows superior or comparative catalytic activity for a model organic
transformation compared to previous reports.
Reusability of the catalyst
As simple recovery and high reusability are requisites for a heterogeneous catalyst
with potential application in industry, the recyclability of the catalyst was also
investigated. To this end, the yield of model pyranopyrazole was obtained in the
presence of fresh catalysts. Subsequently, the catalyst was filtrated, washed with
123

S. Sadjadi et al.
Table 5 The comparison of the catalytic activity of LDH/SBA/HPA with formerly reported catalysts
Entry Catalyst
Condition Time
Solvent Catalyst
amount
Yield Ref.
(%)
1
Per-6-amino-b-
cyclodextrin
Mixing,
r.t.
1 min
–
0.008 mmol [ 99
[63]
2
3
4
Imidazole
80 °C
r.t.
20 min
5–10 min
1 min
H2O
–
0.5 mmol
5 mol%
6 mol%
89
83
97
[64]
[45]
[65]
Piperidine
Magnetic Fe3O4
nanoparticles
r.t.
H2O
5
Phase transfer catalyst
(hexadecyl dimethyl
benzyl ammonium
chloride: HDBAC)
Reflux
30 min
EtOH
30 mol%
80
[66]
6
Nano-sized magnesium
oxide
r.t.
10 min
MeCN
H2O
50 mg
97
[67]
7
8
c-Alumina
Reflux
r.t.
50 min
15
30 mol%
10 mol%
80
90
[68]
[69]
Meglumine
EtOH/
H2O
(9:1)
9
Isonicotinic acid
LDH/SBA/HPA
85 °C
10 min
15 min
Solvent- 10 mol%
free
90
95
[40]
This
10
Reflux
H2O
5 mg
work
EtOH and dried. Then, the reused catalyst was subjected to the next run of the same
reaction. The results of the catalytic activity of the fresh and the reused catalyst up
to five reaction runs are depicted in Fig. 7. As shown in Fig. 7, the catalyst could be
recovered and reused for five successive reaction cycles without remarkable loss of
catalytic activity. Motivated by this promising result, we also studied the leaching of
HPA after five reaction runs to elucidate whether the preservation of the catalytic
activity is due to the heterogeneous nature of the catalyst and low leaching of HPA.
The results of ICP-AES experiments demonstrated low leaching of HPA upon reuse.
Fig. 7 Recyclability of catalyst for the synthesis of pyranopyrazoles
123

A ternary hybrid system based on combination of mesoporous…
Fig. 8 SEM image of reused
catalyst
This result indicated that the catalytic process does not involve leaching of HPA in
the course of reaction and its re-deposition at the end of the catalytic process.
To further characterize the reused catalyst and investigate the effect of reusing on
the morphology of the catalyst, the SEM image of the reused catalyst was recorded
(Fig. 8) and compared with that of the fresh catalyst (Fig. 2). As depicted, the
Fig. 9 FTIR spectra of fresh and recycled catalysts
123

S. Sadjadi et al.
reused catalyst showed more compact and aggregated morphology compared to the
fresh catalyst.
The comparison of the FTIR spectra of fresh and recycled catalysts (Fig. 9)
established that the recycled catalyst still showed the catalyst characteristic bands,
confirming the fact that recycling did not destroy the structure of the catalyst.
Experimental
Materials
The chemicals used for the synthesis of the hybrid catalyst include Na2CO3 (99.9%),
NaOH (ACS reagent, 98%), Al(NO3)3.6H2O (99%), Mg(NO3)2.6H2O (ACS
reagent, 99%), triblock copolymer surfactant (P123), (3-aminopropyl)triethoxysi-
lane (APTES), HCl, tetraethoxysilane (TEOS) and phosphotungstic acid
(H3PW12O40). The chemicals applied for studying the catalytic performance were
phenyl hydrazine, hydrazine hydrate, malononitrile, ethylacetoacetate, isatin and
aldehydes derivatives; all materials were obtained from Merck and used as received.
Synthesis of SBA-15
The silica mesoporous material SBA-15 was synthesized according to the procedure
reported in the literature [49]. Typically, P123 (4.1 g) was added to deionized water
(32 mL). Subsequently, a solution of 123 mL of HCl (2 M) was added to dissolve
P123. After complete solvation, TEOS (10 g) was added drop-wise and the resulting
mixture was stirred at 45 °C for 12 h. Finally, the solution was transferred into a
Teflon-lined stain-less steel autoclave and subjected to hydrothermal treatment at
103 °C for 21 h. Upon completion and cooling, the white precipitate was filtered,
washed repeatedly with deionized water and calcined at 600 °C for 6 h.
Functionalization of the SBA-15
To functionalize SBA-15, 1 g of SBA-15 was added to 100 mL of 0.01 mol L-1-
APTES in dry toluene. The mixture was then refluxed for 24 h, after the end of the
reaction; the white precipitate was filtered, washed with deionized water and dried
overnight at 100 °C.
Incorporation of HPA
To incorporate HPA onto the SBA-15, a wet impregnation method was exploited.
Briefly, a solution of HPA, H3PW12O40, (20 wt%) in acetonitrile was added drop-
wise to a solution of functionalized SBA in acetonitrile. The resulting mixture was
subsequently stirred vigorously overnight. Finally, the precipitate was filtered,
washed with deionized water and dried overnight at 100 °C.
123

A ternary hybrid system based on combination of mesoporous…
Synthesis of LDH
To obtain the LDH, an aqueous mixture of Mg(NO3)2.6H2O and Al(NO3)3.9H2O
with an Mg-to-Al molar ratio of 2 was prepared and stirred vigorously at ambient
temperature. Subsequently, a basic solution of Na2CO3 (0.943 mol) and NaOH
(3.5 mol) was added drop-wise. Upon reaching a pH of 13, the slurry was heated at
65 °C for 18 h. Finally, the obtained precipitate was filtered, washed with deionized
water and calcined at 600 °C for 8 h.
Synthesis of SBA-LDH hybrid
To a suspension of synthesized LDH in deionized water the SBA-15 (1:1 wt%) was
added and the mixture was stirred vigorously for 24 h. The obtained white
precipitate was dried overnight at 75 °C and subsequently dried overnight at
100 °C.
Synthesis of SBA/LDH/HPA via previous method
The previously reported synthetic procedure for SBA/LDH/HPA nanocomposite
was to some extent similar to the present work. Typically, HPA-loaded SBA was
synthesized according to Sections 2-2 to 2-4. The synthesis and incorporation of
LDH, however, was performed in the presence of HPA-loaded SBA [48]. This
catalyst is denoted as SBA/LDH/HPA/P.
Synthesis of 2,4-dihydro-3H-pyrazol-3-one derivatives 3a–e
A mixture of an appropriate aldehyde (1 mmol), 5-methyl-1H-pyrazol-3(2H)-one
(2 mmol) in the presence of catalytic amount of LDH/SBA/HPA as catalyst (5 mg)
was refluxed in (3 ml) water for an appropriate reaction time. The progress of the
reaction was monitored by TLC; upon completion, the mixture was cooled to room
temperature, filtered off and the obtained solid residue was washed with H2O. The
crude products were purified by recrystallization from EtOH and H2O.
Synthesis of pyranopyrazole derivatives 7a–m
A mixture of hydrazine hydrate or phenylhydrazine (1 mmol), ethyl acetoacetate
(1 mmol), aldehyde (1 mmol) and malononitrile (1 mmol) in the presence of a
catalytic amount of LDH/SBA/HPA as catalyst (5 mg) was refluxed in water for an
appropriate reaction time. The progress of the reaction was monitored by TLC; then
the mixture was cooled to room temperature, filtered off and the obtained solid
residue was washed with H2O. The crude products were purified by recrystallization
from EtOH and H2O. A spiro derivative was synthesized through the similar
procedure in which aldehyde was replaced with isatin.
123

S. Sadjadi et al.
Catalyst and product characterization
The synthesized catalyst was characterized by employing SEM/EDS, XRD, BET,
elemental mapping analysis and FTIR techniques. SEM/EDS images as well as
elemental mapping were recorded by a Tescan instrument, using Au-coated samples
and an acceleration voltage of 20 kV. FTIR analyses were performed by using
PERKIN-ELMER-Spectrum 65 instrument. Room temperature powder X-ray
diffraction patterns were collected using a Siemens, D5000. CuKa radiation was
used from a sealed tube. The BET analyses were carried out using BELSORP Mini
II instrument. Before analysis, the SBA or the catalyst was degassed at 423 K for
4 h. Thermo-gravimetric analysis (TGA) was conducted with a METTLER
TOLEDO thermo gravimetric instrument under N2 atmosphere at a heating rate
of 10 °C min-1 from 25 to 700 °C.
Melting points of the synthesized pyrazole derivatives were measured by using
the capillary tube method with an electro thermal 9200 apparatus and FTIR
spectroscopy. All known products were identified by comparison of their physical
data with those of already reported authentic samples. For some selected samples,
1H-NMR and 13C-NMR spectra were also obtained.
Conclusion
In conclusion, a ternary hybrid catalyst comprising three active catalytic species
including HPA, LDH and SBA-15 has been synthesized through a novel procedure.
The catalytic activity of this novel catalyst was examined for the development of
2,4-dihydro-3H-pyrazol-3-one and pyranopyrazole derivatives as pharmacologically
and biologically attractive molecules. Additionally, to disclose the effect of the
synthetic procedure and calcination of the LDH on the catalytic activity of the
catalyst, the catalytic activities of SBA/LDH/HPA and SBA/LDH/HPA/P were
compared. The results demonstrated that both catalysts exhibited similar catalytic
activity. The excellent catalytic performance of this catalyst was obtained in
aqueous media. Some advantageous of theses procedure are cleaner reaction
profiles, mild reaction conditions, excellent yields of the products, wide substrate
scope, recyclability of the catalyst as well as facile experiment and separation
approaches that make it a very beneficial and stimulating method for the synthesis
of these compounds. Significantly, water has been considered as an eco-friendly
solvent for these reactions.
Physical and spectral data for selected organic compounds
To confirm the formation of the final products, spectral data were obtained for
selected products, as presented below, showing results in good agreement with
previous reports [34, 63, 70], thereby proving the formation of the final products.
1. 4,40-(Phenylmethylene)bis(3-methyl-1H-pyrazol-5-ol)
(3a):
1H-NMR
(400 MHz, d6-DMSO): d 2.08 (s, 6H), 4.83 (s, 1H), 7.08–7.17 (m, 3H),
7.19–7.25 (m, 2H), 11.24 (br. 4H); 13C-NMR (100 MHz, d6-DMSO): d 10.8,
123

A ternary hybrid system based on combination of mesoporous…
33.2, 104.7, 125.9, 127.9, 128.2, 140.2, 143.8, 161.5; IR (KBr): mmax: 3296,
2971, 2500–3500, 1614, 1522, 1492, 1380, 1275, 1214, 1050, 774, 718 cm-1
.
2. 4,40-((4-Hydroxyphenyl)methylene)bis(3-methyl-1H-pyrazol-5-ol) (3b): 1H-
NMR (DMSO-d6): d: 2.06 (s, 6H, CH3), 4.71 (m, 1H, CH), 6.58–6.60 (d,
2H, ArH), 6.90–6.92 (d, 2H, ArH); IR (KBr): mmax: 3266, 1561, 1514, 1466,
1400, 1174, 872, 786, 731 cm-1
.
3. 4,40-((4-Chlorophenyl)methylene)bis(3-methyl-1H-pyrazol-5-ol) (3c): 1H-
NMR (400 MHz, d6-DMSO): d: 2.08 (s, 6H), 4.82 (s, 1H), 7.13 (d,
J = 8.4 Hz, 2H), 7.27 (d, J = 8.4 Hz, 2H), 11.33 (br. 4H); 13C-NMR
(100 MHz, d6-DMSO): d 10.8, 32.6, 104.3, 128.1, 129.8, 130.4, 140.1,
142.8, 161.4; IR (KBr): mmax: 2400–3500, 1601, 1532, 1491, 1203, 1172, 1091,
1015, 852, 799, 767 cm-1
.
1
4. 4,40-((3-Nitrophenyl)methylene)bis(3-methyl-1H-pyrazol-5-ol) (3d): H-NMR
(DMSO-d6): d: 2.11 (s, 6H, CH3), 4.99 (ms, 1H, CH), 7.54–7.57 (d, 2H, ArH),
7.96 (s, 1H, ArH), 8.03–8.04 (s, 1H, Ar H).IR (KBr): mmax: 3419, 2961, 1599,
1447, 1390, 1182, 837, 795, 764 cm-1
.
1
5. 4,40-((4-Nitrophenyl)methylene)bis(3-methyl-1H-pyrazol-5-ol) (3e): H-NMR
(DMSO-d6): d: 2.10 (s, 6H, CH3), 4.98 (s, 1H, CH), 7.36–7.39 (d, 2H, ArH),
8.11–8.13 (d, 2H, ArH); IR (KBr): mmax: 3419, 2961, 1603, 1510, 1442, 1346,
1178, 880, 800, 772 cm-1
.
6. 6-Amino-2,4-dihydro-3-methyl-4-phenylpyrano[2,3-c]pyrazole-5-carbonitrile
1
(7a): H-NMR (DMSO-d6): d: 2.08 (s, 3H); 4.44 (s,1H); 6.94 (s br, 2H);
7.17–7.44 (m, 5H); 13C-NMR: d 11.4, 24.8, 70.4, 112.2, 126.3, 127.2, 129.3,
130.9, 140. 2, 143.9, 152.3, 160.0; IR (KBr): mmax: 3372, 2190.74 cm-1
.
7. 6-Amino-4-(4-methoxyphenyl)-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5-
carbonitrile (7b): 1H-NMR (DMSO-d6): d: 2.07 (s, 3H); 3.70 (s, 3H); 4.61 (s,
1H); 7.16 (d, J = 8.7 Hz, 2H); 7.95 (d, J = 8.4 Hz, 2H); 8.61 (s br, 2H); 13C-
NMR: d 11.5, 24.5, 55.4, 70.4, 114.7, 115.2, 127.8, 129.2, 14 0.5, 143.8, 153.3,
159.9, 160.0; IR (KBr): mmax: 3483.78, 3255.25, 2191.7 cm-1
.
8. 6-Amino-4-(4-chlorophenyl)-2,4-dihydro-3-methylpyrano[2,3-c]pyrazole-5-
carbonitrile (7e): 1H-NMR (DMSO-d6); d: 11.82 (s, 3H); 4.58 (s, 1H); 6.69 (s
br, 2H); 7.18 (d, J = 8.1 Hz, 2H); 7.31 (d, J = 8.1 Hz, 2H); 13C-NMR: 111.7,
24.4, 70.4, 112.1, 126.7, 127.6, 130.1, 134.2, 141.4, 142.1, 153.6, 159.3; IR
(KBr): mmax: 3380, 3281, 2193, 1622, 1454 cm-1
9. 6-Amino-3-methyl-4-(4-nitrophenyl)-2,4-dihydropyrano[2,3-c]
.
pyrazole-5-
1
carbonitrile (7f): H-NMR (DMSO-d6); d: 2.04 (s, 3H); 4.73 (s, 1H); 6.22
(sbr, 2H); 7.48 (d, J = 8.1 Hz, 2H); 8.17 (d, J = 8.1 Hz, 2H); 13C-NMR: 11.4,
23.3, 70.7, 112.8, 127.9, 126.0, 130.0, 135.5,141.9, 150.4, 154.2, 160.4; IR
(KBr): mmax: 3383, 3272, 2198, 1620, 1451 cm-1
.
10. 6-Amino-4-(4-hydroxyphenyl)-3-methyl-2,4-dihydropyrano [2,3-c]pyrazole-5-
carbonitrile (7g): 1H-NMR: d: 2.00 (s, 3H); 4.46 (s, 1H); 6.44 (s br, 2H); 7.01
(d, J = 8.4 Hz, 2H); 6.07 (d, J = 8.1 Hz, 2H); 13C-NMR: 12.0, 25.0, 71.0,
113.6, 119.5, 127.0, 130.2, 141.5, 143.8, 153.4, 154.5, 159.1; IR (KBr): mmax
:
878, 1271, 1368, 1583, 1645, 2222, 3056, 3350, 3410 cm-1
.
11. 60-Amino-30-methyl-2-oxo-10H-spiro[indoline-3,40-pyrano[2,3-c]pyrazole]-50-
carbonitrile (7m): 1H-NMR (DMSO-d6, 500 MHz) d: 1.52 (s, 3H, CH3), 6.90
123

S. Sadjadi et al.
(d, J = 7.5 Hz, 1H, HAr), 6.98–7.04 (m, 2H, HAr), 7.22–7.25 (m, 3H, HAr,
NH2), 10.6 (s, 1H,NH), 12.3 (s, 1H, NH) ppm.
Acknowledgements The authors appreciate partial financial supports from Alzahra University and Iran
Polymer and Petrochemical Institute. MMH is also thankful to the Iran National Science Foundation for
the individual given grant.
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Affiliations
Samahe Sadjadi1 Majid M. Heravi2 Vahideh Zadsirjan2 Vahid Farzaneh1
•
•
•
&
&
1
Samahe Sadjadi
samahesadjadi@yahoo.com; S.Sadjadi@ippi.ac.ir
Majid M. Heravi
mmheravi@alzahra.ac.ir
Gas Conversion Department, Faculty of Petrochemicals, Iran Polymer and Petrochemical
Institute, PO Box 14975-112, Tehran, Iran
2
Department of Chemistry, School of Science, Alzahra University,
PO Box 1993891176, Vanak, Tehran, Iran
123