Tungstic acid (H4WO5) immobilized on magnetic-based zirconium amino acid metal–organic framework: An efficient heterogeneous Br?nsted acid catalyst for l-(4-phenyl)-2,4-dihydropyrano[2,3c]pyrazole derivatives preparation

Article abstract of DOI:10.1002/aoc.6192

A new magnetic nanocatalyst based on the immobilization of tungstic acid onto new design robust, cost-effective, green, and scalable zirconium-L-aspartate amino acid metal–organic framework (MOF)-grafted L-(+)-tartaric acid stabilized magnetite nanopartic

Full text of DOI:10.1002/aoc.6192

Received: 20 September 2020
DOI: 10.1002/aoc.6192
Revised: 20 January 2021
Accepted: 22 January 2021
F U L L P A P E R
Tungstic acid (H4WO5) immobilized on magnetic-based
zirconium amino acid metal–organic framework:
An efficient heterogeneous Brønsted acid catalyst for
l-(4-phenyl)-2,4-dihydropyrano[2,3c]pyrazole derivatives
preparation
Shima Khademi1,2
Rashid Badri1,2
| Saeed Zahmatkesh2,3
| Alireza Aghili4
|
1Department of Chemistry, Islamic Azad
University, Khouzestan Science and
Research Branch, Ahvaz, Iran
2Department of Chemistry, Islamic Azad
University, Ahvaz Branch, Ahvaz, Iran
3Department of Science, Payame Noor
University, Tehran, Iran
4Department of Polymer Engineering,
Islamic Azad University, Shiraz Branch,
Shiraz, Iran
A new magnetic nanocatalyst based on the immobilization of tungstic acid
onto new design robust, cost-effective, green, and scalable zirconium-
L-aspartate amino acid metal–organic framework (MOF)-grafted L-(+)-tartaric
acid stabilized magnetite nanoparticles (Fe3O4/tart-NPs) was synthesized by
two successive solvo (hydro)-thermal methods. This catalyst was characterized
by Fourier-transform infrared (FT-IR), energy-dispersive X-ray spectroscopy
(EDS), X-ray diffraction (XRD), field-emission scanning electron microscopy
(FESEM), Brunauer–Emmett–Teller (BET), Barrett–Joyner–Halenda (BJH),
zeta potential, Thermogravimetry Analysis-Differential Thermal Analysis
(TGA–DTA), and vibrating sample magnetometer (VSM) analyses. This cata-
lyst is outstanding to prepare l-(4-phenyl)-2,4-dihydropyrano[2,3-c] pyrazole
derivatives in aqueous media due to the open metal sites, high and steady pro-
ton conductivity in the zirconium-MOF, MIP-202(Zr), and MOF and also due
to Brønsted acid properties of tungstic acid. This acidic catalyst can easily be
extracted by an outward magnetic field after completion of the reaction with-
out any deactivation or selectivity loss. The products were characterized by
Correspondence
Saeed Zahmatkesh, Department of
Science, Payame Noor University,
19395-4697, Tehran, Iran.
Email: zahmatkesh1355@pnu.ac.ir
spectroscopic analysis (FT-IR, H-NMR, and 13C-NMR). The optimized reac-
1
tion conditions and a possible reaction mechanism are outlined.
K E Y W O R D S
nanocatalyst, pyrazole derivatives, tungstic acid
1 | INTRODUCTION
of anti-inflammatory,[3] anticancer,[4] biodegradable
agrochemicals,[5] and antimicrobial agents.[6] Also, they
Pyranopyrazoles as a type of heterocyclic compounds
have very desirable potential in pigment industries[1]
and medicinal chemistry comprising pharmaceutical
and biological industries.[2] They have the main role
of essential synthetic intermediates for the production
are applied as anti-disinfectant like Alzheimer's,
Parkinson's disease, and Huntington's disease.[7] There-
fore, synthesis and purification of pyranopyrazoles are
important cases for researchers. In the past decade, mul-
ticomponent reactions (MCRs) were developed as the
Appl Organomet Chem. 2021;35:e6192.
wileyonlinelibrary.com/journal/aoc
© 2021 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.6192

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KHADEMI ET AL.
most straightforward method in the presence of a rele-
vant catalyst for the pyranopyrazoles synthesis.[8] Gener-
ally, MCR avoids the setbacks such as time-consuming
reaction, low yields, toxicity of the chemicals and solvents,
dynamic reaction conditions and tedious workup.[7]
Recently, to improve the efficiency of pyranopyrazoles and
its derivatives production, several catalysts such as
SO3H@carbon powder,[8] MIL-53 (Fe) metal–organic
frameworks (MOFs),[9] iron-doped calcium oxalates,[10]
structure.[21,23] However, these compounds themselves
have moderate catalytic properties, though suitable sites for
the growth of other reactive catalysts such as SO3H, Lewis
acid, and noble metal NPs and Brønsted acid, while so far,
there are no reports for tungstic acid as Brønsted acid
catalyst.[24–27] We decide to load tungstic acid (H2WO4.
H2O) on amino group of as-proposed MIP-202 (Zr), which
benefit from high acidity, high thermal stability, and desir-
able hydrophobicity, in comparison with the other.[28] Also,
use of magnetite material and tungstic acid refines the low
recovery chance of tungstic acid.[29] Briefly, in this work,
we designed a new magnetic nanocatalyst based on the
immobilization of tungstic acid onto Zr-L-aspartate amino
acid MOF grafted L-(+)-tartaric acid stabilized Fe3O4 NPs
and characterized by Fourier-transform infrared (FT-IR),
energy-dispersive X-ray spectroscopy (EDS), X-ray diffrac-
tion (XRD), field-emission scanning electron microscopy
(FESEM), Brunauer–Emmett–Teller (BET), Barrett–
Joyner–Halenda (BJH), zeta potential, TGA–DTA, and
vibrating sample magnetometer (VSM) analyses. This
heterogeneous catalyst was applied for the preparation of
biologically potent l-(4-phenyl)-2,4-dihydropyrano[2,3-c]
pyrazole derivatives in aqueous media via MCRs (see
Scheme 1).[30,31] The catalytically synthesized derivatives
were confirmed by 1H-NMR and 13C-NMR and FT-IR
analyses. Possible reaction mechanisms and optimize
conditions for the l-4-phenyl-2,4-dihydropyrano[2,3-c]
pyrazole derivatives preparation were outlined.
poly (ethylene imine)-modified magnetic hallo site
nanotubes,[11] and nano-Al2O3/BF3/Fe3O4
have been
[12]
developed. All of these catalysts suffer from several draw-
backs: difficult separation from the reaction medium, high
costs, low surface area, middle electronic and thermal sta-
bility, and the use of toxic organic solvents. On the other
hand, heterogeneous catalytic methods that are used tradi-
tionally in bulk chemical synthesis are not generally appli-
cable for the production of pyranopyrazoles. The unique
combination of magnetic nanoparticles (NPs), high surface
area materials containing catalytic reactive sites such as
MOFs[13] and graphene,[14] and other catalytically active
species such as SO3H, Lewis acid, and noble metal NPs
presents the opportunity to refine a range of catalyst
challenges.[15,16] For this purpose, one-pot capping, stabiliz-
ing, and functionalization of Fe3O4 NPs open a new path
for researchers, which till now citric acid, ascorbic acid,
tartaric acid, and so forth was used for simultaneous
decreasing of NPs sizes and create a cross-linker for
simple modifications.[17] Besides, due to the low surface
area of Fe3O4 and its stabilized NP use of high
surface area materials with chemical growth capability
is an important issue.[18,19] Among, MOFs as organic–
inorganic-coordinated materials have been reported as a
promising class of solids for such applications.[20]
Nevertheless, so far, the reported MOFs are low
environmental-friendly, due to its involvement of either
toxic metal ions or time and effort-consuming organic
linker synthesis.[21] In this context, the design of highly sur-
face area and biocompatible, thermal and electronic
stable, robust, cost-effective, low toxicity, and scalable prep-
aration MOF based zirconium as metal cluster and L-
aspartic acid as green L-α-amino acid was developed
as MIP-202 (MIP stands for the Materials of the Institute
of porous materials from Paris).[21,22] In MIP-202,
the 12-connected Zr6(μ3-O)4(μ3-OH)4 node and the L-
aspartate amino acid spacer are assembled in water gener-
ating a 3-D microporous framework with a UiO-66 type
2 | EXPERIMENT
2.1 | Materials and physical
measurements
Tartaric acid (tart), iron (III) chloride hexahydrate
(FeCl3Á6H2O), L-(+)-tartaric acid, urea, diethylene
glycol, ethanol, zirconium chloride (ZrCl4), L-aspartate
(LA) amino acid, sodium tungstate dihydrate
(Na2WO4.2H2O), n-hexane, HCl, malononitrile and ethyl
acetoacetate, and other compounds were purchased from
different commercial sources (Sigma-Aldrich and Merck
Company). Double distilled water was used for the entire
synthesis. Reactions were monitored by thin-layer chro-
matography (TLC) using silica gel 60 F254 coated alumi-
num sheets with ethyl acetate/hexane (3:7) mixture as
the eluting medium. Melting points are uncorrected and
SCHEME 1 Synthesis of dihydropyrano
[2,3c]pyrazoles using Fe3O4/MIP-202-H4WO5

KHADEMI ET AL.
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were determined using an electrothermal apparatus by
the open capillary method.
(1.80 g, 30 mmol) were completely dissolved in
diethylene glycol (30 ml) by vigorous mechanical stirring.
The obtained solution was sealed in a Teflon lined stain-
less steel autoclave and then heated at 200ꢀC for 8 h.
After cooling to room temperature, the black magnetite
was separated magnetically and washed with ethanol sev-
eral times to eliminate organic and inorganic impurities,
and then dried at 60ꢀC for 6 h.
The EDS spectra of as-prepared catalyst confirm the
presence of major elements of Fe, W, O, C, and Zr
(Figure 6). Thus, the approximate molecular weight for
the proposed catalyst (FeZr1.6C2W7.8O1.5) was found to be
1684 g mol−1. FT-IR spectra were recorded on a JASCO-
680 instrument (Jasco Company, Tokyo, Japan) using
KBr optics. XRD pattern was tested by an automated
Philips X'Pert X-ray diffractometer from Netherlands
(40 kV and 30 mA). Morphological analysis was investi-
gated by FESEM (ZEISS SUPRATM 50 VP, Germany).
High-resolution transmission electron microscopy
(HRTEM) studies were carried out on a JEOL JEM 2010
transmission electron microscope with an accelerating
voltage of 200 kV. The specific surface area (SBET), pore
size, and pore volume of the samples were determined by
N2 physisorption studies on the BET instrument (BET,
PHS-1020, PHS CHINA). The magnetic properties were
analyzed with a VSM (LDJ 9600-1, USA. TGA measure-
ments were recorded by DTG-60 Shimadzu instrument.
Nuclear magnetic resonance (NMR) spectra were
recorded on a BRUKER AVANCE III HD Nanobay
400-MHz spectrometer in DMSO-d6, and δ values are
expressed in ppm using tetramethyl silane (TMS) as an
internal standard. Zeta potential was analyzed via
Zetasizer instrument (Nano ZS, Malvern-90 Plus
instrument).
2.2.3 | Fe3O4/tart-MIP-202
Fe3O4/tart-MIP-202 was synthesized as follows: Typically,
0.25 g of Fe3O4/tart was dispersed in 10-ml deionized
water under ultrasound irradiation for 2 h. A mixture of
ZrCl4 (1.15 g, 4.93 mmol) and L-aspartate (LA) amino
acid (1.4 g, 10.52 mmol) was completely dissolved in
10-ml deionized water and added in Fe3O4/tart suspen-
sion. Subsequently, the solution was transferred into a
Teflon lined stainless steel autoclave and then heated at
120ꢀC for 24 h. After cooling down to room temperature,
the resulting precipitate was isolated by an external mag-
net and washed with EtOH for several times. After that,
the precipitate was immersed in EtOH (80 ml) for 12 h,
during which EtOH was refreshed every 3 h. Finally, the
precipitated powder was collected by an external magnet
and dried in a vacuum oven at room temperature for
24 h.
2.2 | General procedure
2.2.1 | Synthesis of Fe3O4
2.2.4 | Fe3O4/tart-MIP-202-tungstic acid
(H4WO5)
Tungstic acid-functionalized Fe3O4/tart-MIP-202 was pre-
pared by reaction between Fe3O4/tart-MIP-202 and
sodium tungstate dihydrate. The amount of 0.5 g of
Fe3O4/tart-MIP-202 in 15-ml of n-hexane was placed in a
50-ml round bottom flask. Then 0.658 g of sodium tung-
state dihydrate was added to the dispersed Fe3O4/tart-
MIP-202 solution, and then it was refluxed for 12 h under
a nitrogen atmosphere. After completion of the reaction,
it was cooled to room temperature and filtered through
suction followed by washing thoroughly with n-hexane
(10 ml) and distilled water (10 ml), respectively. The sam-
ple was dried and then stirred in the presence of a 15-ml
aqueous HCl medium so that the pH of the solution
comes down to ꢁ4.0 in 1 h. Finally, the mixture was fil-
tered, washed with distilled water, and dried at room
temperature. Chemical structures and mechanism of for-
mation for Fe3O4/tart and Fe3O4/tart-MIP-202 and
Fe3O4/tart-MIP-202-tungstic acid are illustrated in
Scheme 2, and all steps for Fe3O4/tart-MIP-202-tungstic
acid preparation were graphically illustrated in Figure 1.
Magnetic Fe3O4 particles were synthesized based on a
modified coprecipitation method.[35–37] Briefly, the mix-
ture of FeCl3.6H2O (1.3 g, 4.8 mmol), FeCl2.4H2O (0.9 g,
4.5 mmol), and polyvinyl alcohol (PVA 15000) (1 g) as a
surfactant was dissolved in water (30 ml) with vigorous
stirring. Afterward, as the temperature of the mixture
was elevated to 80ꢀC, a proper amount of hexamethy-
lenetetramine (HMTA) (1.0 mol L−1) was added dropwise
until reaction media reaches pH 10. The black magnetic
particles were collected with the help of a magnetic field,
followed by washing with ethanol and deionized water
three times. The product was then dried at 80ꢀC for 10 h.
2.2.2 | Synthesis of Fe3O4/tart-NPs
Fe3O4 NPs stabilized with chiral tartaric acid (tart) was
synthesized as follows: Typically, FeCl3Á6H2O (0.81 g,
3 mmol), L-(+)-tartaric acid (0.075 g, 0.5 mmol), and urea

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KHADEMI ET AL.
SCHEME 2 Schematic preparation of Fe3O4/tart and Fe3O4/tart-MIP-202 and Fe3O4/tart-MIP-202-tungstic acid
FIGURE 1 Schematically for all steps of Fe3O4/tart-MIP-202-tungstic acid preparation
2.2.5 | General procedure for the
preparation of l-(4-phenyl)-
2,4-dihydropyrano[2,3-c] pyrazole
derivatives
hydrazine hydrate (1 mmol) in a round bottom flask,
40 mg of Fe3O4/MIP-202-H4WO5 (0.0237 mol%) was
added, and the resulting mixture was vigorously stirred
long enough in water solvent at 60ꢀC. After completion
of the reaction as observed by TLC (n-hexane/ethyl
acetate: 7/3), the catalyst was separated magnetically.
The Fe3O4/MIP-202-H4WO5 was washed with ethanol
To a mixture of an aromatic aldehyde (1 mmol),
malononitrile (1 mmol), ethyl acetoacetate (1 mmol), and

KHADEMI ET AL.
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and then dried at 50ꢀC for 3 h in order to preserve cata-
lyst, and it was used for the alternative reaction.[32] Sub-
sequently, the products in the aqueous layer were filtered
and separated, and then the crude product was purified
by washing with acetone. The purity of products was
studied by TLC and 1H-NMR, 13C-NMR, and FT-IR
spectroscopy.
127.5, 129.8, 130.5, 130.9, 131.3, 138.0, 144.4, 145.6, 146.9,
and 160.0.
Spectral data for 6-Amino-3-methyl-4-(4-methylphenyl)-
1-phenyl-1,4-dihydropyrano[2,3-c] pyrazole-5-carbonitrile (5f)
IR (KBr, cm−1): 3415, 3399, 3319, 3079, 3027, 2939,
2216, 1522, 1498, 1225, 1116, and 803. 1H-NMR
(400 MHz, DMSO-d6,): δ (ppm): 1.78 (s, 3H), 2.32 (s, 3H),
4.65 (s, 1H), 6.86 (s, 2H), 7.12–7.14 (d, 2H), 7.33–7.35
(d, 2H), and 12.20 (s, 1H). 13C NMR (100 MHz, DMSO-
d6) δ (ppm): 10.03, 22.60, 35.54, 56.71, 113.14, 117.66,
125.44, 128.09, 132.36, 135.72, 139.00, 154.64, and 161.88.
Spectral data for 6-Amino-3-methyl-4-(3-Ethoxy-4-
hydroxyphenyl)-1-phenyl-1,4-dihydropyrano[2,3-c] pyrazole
e-5-carbonitrile (5g)
The data that support the findings of this study are
available in the supporting information of this article.
Spectral data for 6-Amino-5-cyano-3-methyl-1,4-diphenyl-
1,4-dihydropyrano[2,3-c]pyrazole (5a)
IR (KBr, cm−1): 3472, 3320, 2195, 1660, 1590, 1264,
1
1125, 1027, and 753. H-NMR (400 MHz, DMSO-d6,): δ
(ppm):1.93 (s, 3H, CH3), 4.68 (s, 1H, 4-H), 4.75 (s, 2H,
NH2), and 7.16–7.32 (m, 10H, ArH) ppm.
IR (KBr, cm−1): 3420, 3329, 2195, 1653, 1590, 1519,
1477, 1449, 1393, 1131, 1061, and 869; 1H-NMR
(400 MHz, DMSO-d6,): δ (ppm): 1.29–1.32 (t, 3H), 1.84
(s, 3H), 3.95–4.01 (q, 2H), 4.59 (s, 1H), 6.62–7.80 (m, NH2
and Ar), and 8.86 (s, 1H).
Spectral data for 6-Amino-4-(4-cyanophenyl)-3-methyl-
1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile (5h)
IR (KBr, cm−1): 3402, 3394 (NH2), 3314 (–NH–), 3067,
3020 (aromatic), 2931 (–CH3), 2213 (Ar–CN), 1486
(–NH–), and 817 (Para-CN). 1H-NMR (400 MHz,
DMSO-d6,): δ (ppm): 1.79 (s, 3H, CH3), 4.76 (s, 1H, 4H),
7.04 (s, 2H, NH2), 7.38–7.40 (d, 2H, J = 8.12 Hz, Ar–H),
7.79–7.81 (d, 2H, J = 8.08 Hz, Ar–H), and 12.20 (s, 1H,
NH). 13C-NMR (100 MHz, DMSO-d6) δ (ppm): 9.69,
36.10, 55.97, 96.61, 109.60, 118.76, 120.52, 128.56, 132.57,
135.77, 150.02, 154.66, and 161.10.
Spectral data for 6-Amino-3-methyl-4-(4-methoxyyphenyl)-
1-phenyl-1,4-dihydropyrano[2,3-c] pyrazole-5-carbonitrile (5b)
IR (KBr, cm−1): 3390, 3321, 3204, 3022, 2191, 1660,
1583, 1513, 1391, 1259, 11,249, 1128, 1109, 1026, 839, 759,
1
692, and 573. H-NMR (400 MHz, DMSO-d6,): δ (ppm):
1.78 (s, 3H, CH3), 3.74 (s, 3H, CH3), 4.62 (s, 1H, CH), and
6.84–7.82 (m, 11H, H–Ar, NH2) ppm. 13C NMR
(100 MHz, DMSO-d6) δ (ppm): 12.4, 36.1, 54.6, 59.1, 98.3,
113.4, 119.8, 125.5, 128.4, 128.7, 135.0, 137.4, 143.6, 145.2,
158.0, and 158.9.
Spectral data for 6-Amino-3-methyl-4-(2-cholorophenyl)-
1-phenyl-1,4-dihydropyrano[2,3-c] pyrazole-5-carbonitrile (5c)
1H-NMR (400 MHz, DMSO-d6,):
δ (ppm):12.13
(s, 1H), 7.44 (m, 1H), 7.33 (m, 1H), 7.29 (s, 1H), 7.20
(m, 1H), 6.95 (s, 2H) 5.08 (s, 1H), and 1.78 (s, 3H); 13C
NMR (100 MHz, DMSO-d6) δ (ppm): 161.78, 155.45,
141.41, 135.85, 132.45, 131.19, 129.96, 128.24, 120.85,
97.34, 56.26, and 9.99.
Spectral data for 6-Amino-3-methyl-4-(3-nitrophenyl)-
1-phenyl-1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile (5i)
IR (KBr, cm−1): 3438, 3298, 2194, 1652, 1517, 1352,
1
Spectral data for 6-Amino-3-methyl-4-(2,4-dicholorophenyl)-
1-phenyl-1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile (5d)
IR (KBr, cm−1): 3455, 3332 (NH2), 3056 (=C–H),
2954 (C–H), 2193 (CN), 1574, 1482 (C=C), 1130 (C–O),
1068, and 755; H-NMR (400 MHz, DMSO-d6,): δ (ppm):
1.89 (s, 3H, CH3), 4.78 (s, 1H, C–H), 4.81 (s, 2H, NH2),
7.26–8.19 (m, 9H, ArH) ppm.
Spectral data for 6-Amino-4-(4-nitrophenyl)-3-methyl-
1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile (5j)
IR (KBr, cm−1): 3414, 3389 (NH2), 3323 (–NH–), 3073,
3025 (aromatic), 2936 (–CH3), 2209 (–CN), 1485 (–NH–),
1354, 1563 (Ar–NO2), and 818 (Para-NO2). 1H-NMR
(400 MHz, DMSO-d6,): δ (ppm): 1.82 (s, 3H, CH3), 4.84
(s, 1H, 4H), 7.08 (s, 2H, NH2), 7.46–7.48 (d, 2H,
J = 8.48 Hz, Ar–H), 8.20–8.22 (d, 2H, J = 8.48 Hz, Ar–H),
and 12.22 (s, 1H, NH). 13C-NMR (100 MHz, DMSO-d6) δ
(ppm): 9.71, 35.84, 55.84, 96.52, 120.47, 123.87, 128.81,
135.84, 146.34, 152.08, 154.63, and 161.11.
1
and 752; H-NMR (400 MHz, DMSO-d6,): δ (ppm):1.79
(s, 3H), 5.16 (s, 1H), 7.32–7.35 (d, 3H, J = 8.0 Hz),
7.38–7.39 (d, 1H), 7.43–7.44 (d, 1H), 7.49–7.52 (t, 2H,
J = 8.0 Hz), 7.56 (s, 1H), 7.63 (s, 1H), and 7.80 (s, 2H).
13C-NMR (100 MHz, DMSO-d6) δ (ppm): 12.82, 56.67,
97.77, 119.98, 120.53, 126.76, 128.58, 129.42, 129.81,
132.96, 133.00, 133.56, 137.91, 144.75, 145.30, 145.30,
and 160.41.
Spectral data for 6-Amino-3-methyl-4-(3-boromophenyl)-
1-phenyl-1,4-dihydropyrano[2,3-c] pyrazole-5-carbonitrile (6e)
IR (KBr, cm−1): 3450, 3324, 3195, 2199, 1660, 1593,
1518, 1487, 1456, 1391, 1126, 1065, 859, 751, and 686.
1H-NMR (400 MHz, DMSO-d6,): δ (ppm):1.81 (s, 3H),
4.75 (s, 1H), 7.29–7.35 (m, 5H), 7.47–7.52 (m, 4H), and
7.79–7.81 (m, 2H) ppm. 13C NMR (100 MHz, DMSO-d6) δ
(ppm): 13.1, 36.8, 58.0, 98.5, 120.4, 120.6, 122.3, 126.7,
2.3 | Measuring heterogeneity
Fe3O4/MIP-202-H4WO5 nanocatalyst (0.004 g [0.0237
mol%]) was added to a mixture of aromatic aldehydes

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KHADEMI ET AL.
(1 mmol), malononitrile (1 mmol), ethyl acetoacetate
(1 mmol), and hydrazine hydrate (1 mmol) in aqueous
media and stirred at 60ꢀC for 20 min. Then Fe3O4/MIP-
202-H4WO5 nanocatalyst was removed by an external
magnet; the reaction was progressed catalyst freely and
was monitored by TLC (n-hexane: EtOAc, 6:4), and the
reaction yield was recorded at different times.
Fe3O4/MIP-202-H4WO5 samples are shown in Figure 2.
The Fe3O4 NPs spectrum shows two broad peaks at 1600
and 3365 cm−1 attributed to O–H bending and stretching
mode of Fe–OH, respectively. The characteristic lattice
vibration of the magnetite peak for Fe–O band was
observed at 560 cm−1 (Figure 2a). In Fe3O4/tart spec-
trum, a dominant peak at 1730 cm−1, resulting from the
carbonyl stretch (C=O) associated with protonated car-
boxyl groups, confirmed adsorption/chemisorption of
tartaric acid on Fe3O4 NPS as the carboxyl groups. The
appeared peaks at 1550 and 1420 cm−1 represent the
asymmetric and symmetric COO carbon–oxygen
stretches of carboxylate groups, respectively.[17] Results
confirmed that tart as monotartrate species was
chemisorbed on the Fe3O4-NPs surface as a carboxylate
as reactive organic cross-linker for MOF grafting. The
FTIR spectrum of MIP-202 (Zr) MOF (Figure 2c) displays
vibration mode at 660 and 470 cm−1, which is due to
stretching vibrations of the Zr-OH and Zr-COO frame-
works, whereas the small band at 530 cm−1 is ascribed to
Zr-(OC) asymmetric stretching vibrations. Bands
3 | RESULTS AND DISCUSSION
3.1 | Characterization of as-prepared
samples
The Fe3O4/MIP-202-H4WO5 material was in nanosized
amorphous, and it can be more effective as a catalyst due
to the large acidic density of H4WO5 groups presented in
the high surface area of Fe3O4/MIP-202 surface. Our part
of interest was in exploring the catalytic activity of
Fe3O4/MIP-202-H4WO5 for the preparation of l-(4-phe-
nyl)-2,4-dihydropyrano[2,3-c] pyrazole derivatives in
aqueous media via MCRs. This catalyst was characterized
by FT-IR, XRD, FESEM, BET, BJH, zeta potential, TGA–
DTA, and VSM analyses.
The FT-IR spectra of the Fe3O4 (as-comparison),
Fe3O4/tart, MIP-202(Zr), Fe3O4-MIP-202(Zr), and
FIGURE 2 Fourier-transform infrared (FT-IR) spectra of
Fe3O4 nanoparticles (a), Fe3O4/tart (b), MIP-202(Zr) (c), Fe3O4-
MIP-202(Zr) (d), and Fe3O4/MIP-202-H4WO5 (e) samples
FIGURE 3 X-ray diffraction (XRD) patterns of Fe3O4
nanoparticles, Fe3O4/tart, MIP-202(Zr), Fe3O4-MIP-202(Zr), and
Fe3O4/MIP-202-H4WO5 samples

KHADEMI ET AL.
7 of 14
indicating the occurrence of asymmetric and symmetric
(OCO) stretching's in the linker are visible at 1550 and
1420 cm−1, respectively. Absence of free–COOH groups
in 1673 cm−1 implies successful coordination of Zr to
COO group and makes the MIP-202(Zr) (Figure 2c).
When Fe3O4-MIP-202(Zr) nanostructures were synthe-
sized, the position of absorption bands of Fe3O4/tart NP,
and MIP-202(Zr) nanostructure in the final structure
(Figure 2d) does not change, which confirmed the
successful formation of Fe3O4-MIP-202(Zr) sample
(Figure 2d) as well as not appeared no new peak. The
presence of tart on Fe3O4-NPs helps the formation of the
same Zr–O–C complex on the Fe3O4 surface and grafted
by L-aspartic acid for better construction of MIP-202
(Zr) MOF. After H4WO5 loading, corresponded FTIR
spectra show the characteristic peak of W–O species in
the range of 800–960 cm−1, and the characteristic bands
of other parts of composite were stable and appeared at
final FTIR spectrum (Figure 2e).
characteristic peaks at 2θ of 30.3ꢀ, 35.4ꢀ, 43.2ꢀ, 53.5ꢀ, 57.2ꢀ,
and 62.9ꢀ corresponding to the (220), (311), (400), (422),
(511), and (440) crystal planes of cubic inverse spinel.
When Fe3O4 was synthesized in the presence of L-tartaric
acid, the intensity of the as mention peaks decreases, while
the positions of all diffraction peaks for both Fe3O4-NPs
and Fe3O4/tart-NPs well match (Figure 3b).[17] XRD pat-
tern of as-synthesized MIP-202(Zr) MOF is identical to the
simulated XRD results calculated based on single-crystal
structure for MIP-202 as well as confirms the high phase
purity.[23] After MOF grafting on Fe3O4-tart NPs, no
appearance of new peaks corresponds to MIP-202 and
Fe3O4-NPs peaks. After H4WO5 loading on high surface
area of Fe3O4/MIP-202, the corresponded XRD pattern in
addition to the MIP-202 and Fe3O4 peaks shows new dif-
fraction peaks related to those in the standard database
(PDF: 00-018-1420) of H4WO5 (Figure 3).[33]
The size, shape, and size distribution of the
Fe3O4/tart, MIP-202(Zr), Fe3O4-MIP-202(Zr), and
Fe3O4/MIP-202-H4WO5 were examined by FESEM tech-
nique (Figure 4). The FESEM images of Fe3O4/tart
(Figure 4a) show that in the presence of L-(+)-tartaric
The crystallinity of the as-prepared samples was
recorded by wide angle X-ray powder diffraction (XRD).
The XRD patterns of Fe3O4 (Figure 3a) show six
FIGURE 4 The field-emission scanning electron microscopy (FESEM) image of Fe3O4/tart (a), MIP-202(Zr) (b), Fe3O4-MIP-202(Zr) (c),
and Fe3O4-MIP-202(Zr)-H4WO5 (d) samples

8 of 14
KHADEMI ET AL.
acid, the Fe3O4 particles have a uniform smooth spherical
shape in nanosize distribution. The carboxylic acid as
stabilizing and capping agent causes to the becoming
uniform and dramatically reducing its diameter. For
comparison, pure MIP-202(Zr) was synthesized in the
absence of Fe3O4/tart and the FESEM images (Figure 4b)
apparent that it had clean and smooth surface sheets,
which were nicely interlinked through thin and delicate
three-dimensional networks, resulting in a porous, loose
sponge-like structure. Although after MIP-202(Zr) MOF
grafted on Fe3O4/tart, the corresponded FESEM image
(Figure 4d) clearly indicates the growth of MIP-202
(Zr) MOF on Fe3O4/tart surface. Finally, smooth and uni-
form cubic shapes of H4WO5 in the presence of Fe3O4-
MIP-202(Zr) are clearly visible and confirm the successful
preparation of Fe3O4/MIP-202-H4WO5 catalyst by self-
assembly and grafting reactions. The diameters of the
magnetic core and its sell were about 50 nm (Figure 5).
The EDS spectra of as-prepared catalyst confirm the pres-
ence of major elements of Fe, W, O, C, and Zr (Figure 6.).
The magnetic features of Fe3O4/tart, Fe3O4-MIP-202
(Zr), and Fe3O4-MIP-202(Zr)-H4WO5 nanocomposites
were studied with the VSM method (Figure 7) and rev-
ealed that saturation magnetization was found to be
60, 40, and 28 emu g−1, respectively, which is suitable for
magnetic-based catalyst (Figure 7). Also, the S like shape
and absence of any hysteresis loop in these VSM curves
showed the superparamagnetic behavior of as-prepared
samples (Figure 7).
Nitrogen adsorption isotherms for Fe3O4-MIP-202
(Zr) and Fe3O4-MIP-202(Zr)-H4WO5 were recorded to
study their textural properties and pore size distributions.
FIGURE 5 The high-resolution transmission electron microscopy (HRTEM) image of Fe3O4-MIP-202(Zr)-H4WO5
FIGURE 6 The energy-
dispersive X-ray spectroscopy
(EDS) spectra of Fe3O4-MIP-202
(Zr)-H4WO5

KHADEMI ET AL.
9 of 14
The Fe3O4-MIP-202(Zr) nanocomposite resembles a type
V isotherm and H3 IUPAC classification, which may
result from slit-shaped pores of MIP-202(Zr). Also, this
sample at low relative pressures shows the high absorp-
tion volume and the plateau at medium relative pres-
sures, demonstrating V isotherms type for mesoporous
matter (see Figure 8a). After H4WO5 loading, the meso-
pores pore was filling and surface area and pore volume
were decreased, while the textural properties and pore
size distribution type remain stable. This observation is
in excellent agreement with high BET levels and a large
pore volume of Fe3O4-MIP-202(Zr) and Fe3O4-MIP-202
(Zr)-H4WO5 (800 and 390 m2 g−1). Besides, a larger
total pore volume of 0.531 and 0.289 cm3 g−1 was found
to be for Fe3O4-MIP-202(Zr) and Fe3O4-MIP-202(Zr)-
H4WO5, respectively (see Figure 8b). The results con-
firm that the synthesized Fe3O4-MIP-202(Zr)-H4WO5
as a high surface area sample has a high ability to
catalyze MCRs.
FIGURE 7 Vibrating sample magnetometer (VSM) analysis of
Fe3O4/tart, Fe3O4-MIP-202(Zr), and Fe3O4-MIP-202(Zr)-H4WO5
samples
FIGURE 8 N2 adsorption–desorption isotherms (a) and pore size distributions (b) of Fe3O4-MIP-202(Zr) and Fe3O4/MIP-202-H4WO5 samples
FIGURE 9 Thermal analysis TGA–DTA (a) and zeta potential of Fe3O4/MIP-202-H4WO5 sample

10 of 14
KHADEMI ET AL.
DTA–DTG analysis (Figure 9a) shows three strong exo-
L-aspartic acid in MIP-202 (Zr) structure while H4WO5,
complexation with NH2 group of L-aspartic acid will cause
the more stability of MIP-202 (Zr). The thermal stability of
the Fe3O4/MIP-202-H4WO5 catalyst is assertively well in
the range of 0–420ꢀC, which covers the temperature range
for the synthesis of l-(4-phenyl)-2,4-dihydropyrano[2,3-c]
pyrazole derivatives.
thermic transformations: The first is the peak between at
35ꢀC and 160ꢀC with a maximum at 95ꢀC attributed to the
surface adsorbed of distilled water and another solvent on
Fe3O4/MIP-202-H4WO5 structure. The second peak ranges
between 195ꢀC and 320ꢀC with a maximum at 220ꢀC is
related to the tartaric acid group on the Fe3O4 surface. The
third peak occurred between 460ꢀC and 610ꢀC with a
maximum at 585ꢀC, which corresponds to the losing of
Electronic stability as a potential for good dispersion of
the Fe3O4/MIP-202-H4WO5 sample in reaction media was
SCHEME 3 Synthesis of dihydropyrano
[2,3c]pyrazoles using Fe3O4/MIP-202-H4WO5
TABLE 1 Optimization of conditions in the synthesis of dihydropyrano[2,3c]pyrazolesa
Entry
1
Solvent
Catalyst (g)
0.005
T (ꢀC)
r.t.
Time (min)
Yield (%)
EtOH/H2O (1:1)
90
60
210
50
45
55
230
230
65
65
55
50
48
50
60
60
50
65
60
50
2
EtOH/H2O (2:1)
0.005
65
75
3
H2O
-
70
55
4
H2O
0.005
70
80
5
H2O
0.004(0.0237 mol%)
0.003
60
92 (TOF = 51.76)b
6
H2O
50
83
40
42
40
47
53
60
47
70
70
75
85
68
75
7
CH2Cl2
0.004
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
90
8
CCl4
0.004
9
CHCl3
0.004
10
11
12
13
14
15
16
17
18
19
THF
0.004
CH3CN
0.004
MeOH
0.004
EtOH
0.004
EtOH
0.004
Reflux
r.t.
EtOH/H2O (1:1)
0.006
EtOH/H2O (1:1)
0.004
Reflux
Reflux
Reflux
60
EtOH/H2O (1:2)
0.004
-
-
0.004
0.004
aReaction condition: ethyl acetoacetate (1 mmol), phenylhydrazine (1 mmol), malononitrile (1 mmol), and a solvent. Catalyst: Fe3O4/MIP-202-H4WO5.
bTON = (mmol product/mmol catalyst) × 100; TOF = TON/time (h).
Abbreviation: r.t. = room temperature.
Bold show the optimized conditions which is used.

KHADEMI ET AL.
11 of 14
tested by zeta potential at different potential (Figure 9b). It
can be seen that natural surface charge of Fe3O4/MIP-
202-H4WO5 is negative due to the presence of acidic struc-
ture of H4WO5 on the Fe3O4/MIP-202 surface. On the other
hand, higher positive or negative zeta potential (greater
than +30 mV or less than −30 mV) refers to the strong
repulsion force between particles in reaction media and
prevents aggregation and agglomeration of particles. In his
work, the negative surface charge and the suspension of
Fe3O4/MIP-202-H4WO5 powder is satisfactory stable.
To optimize the reaction conditions, the reaction of
ethyl acetoacetate, phenylhydrazine, malononitrile, and
benzaldehyde was selected, and the effect of various
parameters such as temperature, Fe3O4/MIP-202-H4WO5
catalyst mass, and solvent type was investigated and opti-
mized (see Table 1). It can be seen that, under solvent-
free conditions, lower yields of the product were obtained
due to aggregation of magnetite catalyst in the absence of
solvation (Table 1, Entries 18 and 19).
In order to evaluate the optimum amount of
Fe3O4/MIP-202-H4WO5 nanocatalyst required for the
multi-component condensation reaction, the reaction
was performed in the presence of varying amounts of cat-
alyst from 0.003 to 0.006 g. As can be seen, in the absence
of the catalyst, this reaction takes a long time (210 min),
and this indicates that the presence of Fe3O4/MIP-
202-H4WO5 heterogeneous acidic catalyst is not
preventable for this reaction and 0.002 g of Fe3O4/MIP-
202-H4WO5 was selected as desirable mass. In higher of
Fe3O4/MIP-202-H4WO5 nanocatalyst mass, no increase
in yield is seen because of the agglomeration of catalyst
particles. Also, the efficiency and condensation reaction
speed was decreased with decreasing in the catalyst mass,
which is due to the not available of desired number of
active catalyst sites.
3.2 | Catalytic activity and optimization
After synthesis and characterization, the catalytic perfor-
mance of pure Fe3O4/tart, pure Fe3O4/MIP-202, and
Fe3O4/MIP-202-H4WO5 for comparison was conducted
and results showed that Fe3O4/MIP-202-H4WO5 catalyst
was higher catalytic activity than the others, which is
due to the synergistic effects between catalyst sepsis. A
typical reaction model for dihydropyrano[2,3c]pyrazoles
derivatives synthesis via a MCR of ethyl acetoacetate,
phenylhydrazine, malononitrile, and an aldehyde, in dis-
tilled water at 60ꢀC in the presence of Fe3O4/MIP-
202-H4WO5 is illustrated in Scheme 3.
TABLE 2 Preparation of dihydropyrano[2,3c]pyrazoles derivatives in the presence of Fe3O4/MIP-202-H4WO5
Mp (ꢀC)
Entry
Ar
Product
Time (min)
Yield[a] (%)
Found
Reported
1
2
C6H5
5a
5b
5c
5d
5e
5f
45
38
40
35
45
40
55
45
40
38
92
90
91
92
89
89
86
90
92
91
167–169
169–171
143–145
181–183
164–166
173–175
166–169
194–196
189–191
191–193
165–167 (Mandha et al.[34]
)
4-OMe-C6H5
2-Cl-C6H4
2,4-Cl2-C6H4
3-Br-C6H4
4-Me-C6H4
3-OEt-4-OH-C6H4
4-CN-C6H4
3-NO2-C6H4
4-NO2-C6H4
171–172 (Armesto et al.[35]
145–146 (Armesto et al.[35]
)
3
)
4
182–184 (Heravi et al.[36]
163–165 (Vekariya et al.[37]
176–178 (Heravi et al.[36]
170–171 (Vekariya et al.[37]
197–199 (Heravi et al.[36]
)
5
)
)
6
)
7
5g
5h
5i
8
)
9
188–190 (Vekariya et al.[37]
194–196 (Vekariya et al.[37]
)
)
10
5j
aReaction condition: ethyl acetoacetate (1 mmol), phenylhydrazine (1 mmol), malononitrile (1 mmol), and H2O. Catalyst mass: Fe3O4/MIP-202-H4WO5
(0.004 g [0.0237 mol%]).

12 of 14
KHADEMI ET AL.
To determine the best reaction conditions, we have
Fe3O4/MIP-202-H4WO5 catalyst in the synthesis of
dihydropyrano[2,3c]pyrazoles derivatives.
carried out the condensation reaction in the solvent free
and in the presence of various solvents such as water,
ethanol, CH2Cl2, and CH3Cl (see Table 1). According to
Table 1 in H2O as solvent, high yield of product was
obtained due to the better dispersion of Fe3O4/MIP-
202-H4WO5 nanocatalyst than in other solvents, which is
related to the middle zeta potential results for Fe3O4/
MIP-202-H4WO5 nanocatalyst. Although when the reac-
tion was carried out in nonpolar solvents such as CH2Cl2
and CCl4, the yield of the desired product was
increased in very long time, which it is not satisfactory
due to their toxicity and probable destroying of Fe3O4/
MIP-202-H4WO5 structure.
The reaction temperature was also studied for
selecting the appropriate temperature of reaction, 25ꢀC,
50ꢀC, 60ꢀC, 65ꢀC, 70ꢀC, and 90ꢀC, and the results showed
that the best yield is seen at 60ꢀC, which is due to the
well dispersion and mass transfer rate in reaction
section for migrating and transferring on Fe3O4/MIP-
202-H4WO5. Attractively, establishing the same condi-
tions as above (60ꢀC, H2O solvent, 0.004 g (0.0237 mol%)
of Fe3O4/MIP-202-H4WO5 catalyst) gave best yield at a
shorter time, 45 min (Table 1, Entry 5).
3.3 | Heterogeneity measuring
This test was performed to examine the durability and
stability of the heterogeneous catalyst during reaction
process. For this purpose, the reaction mixture was con-
tinued for 20 min, then the nanocatalyst was magneti-
cally recovered, and the reaction was continued under
catalyst-free conditions. The results showed that after
45 min, only a trace amount of product is obtained
which proving heterogeneity, high stability, and durabil-
ity of Fe3O4/MIP-202-H4WO5 as a designed catalyst for
After than at optimized condition, some of the
dihydropyrano[2,3c]pyrazoles derivatives were prepared
in presence of different aldehydes with electron-donating
or electron-withdrawing groups. Results indicate that the
excellent yields for all aldehydes were obtained in short
reaction times, so it can be said that this method is
applicable in the presence of both electron-donating
and electron-withdrawing groups (Table 2). This
means that position and substitution type does not
have any effect on the reaction process, which
shows very good and effective performance of new
FIGURE 10 Recoverability and reusability of Fe3O4/
MIP-202-H4WO5
SCHEME 4 The suggested mechanism for the catalyzed synthesis of 1,4-dihydropyrano [2,3c]pyrazole using Fe3O4/MIP-202-H4WO5

KHADEMI ET AL.
13 of 14
TABLE 3 Comparison of Fe3O4/MIP-202-H4WO5 with other catalysts reported in the literature for the synthesis of dihydropyrano[2,3c]
pyrazole
Entry
Catalyst
Conditions
Time (min)
Yield (%)
References
1
2
3
4
5
InCl3 (10 mol%)
EtOH-H2O (2: 1), reflux
H2O, reflux
150
50
60
60
45
91
80
85
94
92
Chavan et al.[31]
Mecadon et al.[39]
Kiyani et al.[40]
Heravi et al.[36]
This work
γ-alumina (30 mol%)
Sodium benzoate (15 mol%)
H14[NaP5W30O110] (1 mol%)
Water, r.t.
H2O, reflux
Fe3O4/MIP-202-H4WO5
(0.004 g [0.0237 mol%])
H2O solvent, 60ꢀC
Abbreviation: r.t. = room temperature.
reaction under applied conditions. This result also
confirms no leaching of active Fe3O4/MIP-202-H4WO5
catalytic sites during reaction process.
3.6 | Comparison with literature
The comparison of our proposed catalyst efficiency for
synthesis of 1,4-dihydropyrano [2,3c]pyrazoles with other
reported catalysts was also evaluated (Table 3). Results
showed that Fe3O4/MIP-202-H4WO5 has much higher
catalytic reactivity than others in terms of reaction tem-
perature, product yield, reaction time, and catalyst reus-
ability, which are due to the satisfactory surface area and
surface charge of as-prepared catalyst and also it was
thermal and chemical stable.
3.4 | Proposed mechanism
A possible mechanism for the synthesis of dihydropyrano
[2,3c] pyrazoles is shown in Scheme 4. In this
mechanism, the role of Fe3O4/MIP-202-H4WO5 as an
acidic catalyst is showing in electrophilic activation for
nucleophilic attack of amino group. Fe3O4/MIP-
202-H4WO5 as an acidic catalyst initially activates
malononitrile for nucleophilic attack, while the presence
of an Fe3O4/MIP-202-H4WO5 as acidic catalyst in the
enol–keto equilibrium in 3-methyl-1-phenyl-5-pyrazolone
8 is furthered in the form of analysis, which then
undergoes activated Michael addition to the Knoevenagel
product formed between aldehydes and malononitrile.
Finally, intramolecular nucleophilic cyclization and
tautomerization afford the 1,4-dihydropyrano [2,3-c]
pyrazoles.[38]
4 | CONCLUSION
In conclusion, a Brönsted acidic, tungstic acid-supported
zirconium-L-aspartate amino acid MOF grafted
L-(+)-tartaric acid that is stabilized on magnetite NPs
was successfully prepared, fully characterized, and
subsequently applied as an effective heterogeneous,
robust, cost-effective, green, chemical, thermal and
electronic stable, and scalable catalyst for the synthesis of
l-(4-phenyl)-2,4-dihydropyrano[2,3-c] pyrazole deriva-
tives by one-pot condensation reaction. This method ben-
efits from clean work-up and easy reusability of the
catalyst, satisfactory reaction time, and high efficiency
under distilled water as green media. It is expected that
this catalyst and proposed method would be extensively
used in the combinatorial chemistry, diversity-oriented
organic synthesis, and drug discovery, while this catalyst
can be used in photocatalytic system for ORR and water
splitting reactions.
3.5 | Reusability of catalyst
The recovery test is a simple and easy method to prove
the performance of a magnetite separable catalyst. For
this purpose, after separating the Fe3O4/MIP-202-H4WO5
catalyst by external magnet, it was washed several
times with H2O or ethanol and dried at 70ꢀC. The
recovered Fe3O4/MIP-202-H4WO5 was used six cycles for
1,4-dihydropyrano [2,3c]pyrazole preparation at opti-
mized conditions in which the results showed not-
significant variation in reaction yields due to the high
electric, thermal and chemical stability of Fe3O4/MIP-
202-H4WO5 catalyst (Figure 10).
ACKNOWLEDGMENT
This work was supported by Ahvaz branch of Islamic
Azad University of Iran.
Furthermore, the amount of catalyst leaching after
the first run was determined by ICP analysis to be only
0.19% and after sixth run was 2.00%, respectively.
AUTHOR CONTRIBUTIONS
Saeed Zahmatkesh: Project administration. Alireza
Aghili: Visualization.

14 of 14
KHADEMI ET AL.
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DATA AVAILABILITY STATEMENT
The data that support the findings of this study are
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ORCID
Shima Khademi https://orcid.org/0000-0003-4618-4581
Saeed Zahmatkesh https://orcid.org/0000-0002-3054-
2842
[27] Y. Zhang, Y. Zhou, Y. Zhao, C.-j. Liu, Catal. Today 2016,
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Rashid Badri https://orcid.org/0000-0002-7474-9888
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