Synthesis of 1,3,5-Trisubstituted Pyrazoles and Hydrazones Using Fe3O4?CeO2 Nanocomposite as an Efficient Heterogeneous Nanocatalyst

Article abstract of DOI:10.1134/S1070428020030185

Abstract: Pyrazoles and hydrazones, as two significant kinds of potentially bioactivecompounds, were produced with good to excellent yields by condensation ofβ-dicarbonyl compounds with hydrazines in aqueous media in the presence ofFe₃O₄?CeO₂nanocomposite as an efficient heterogeneous nanocatalyst. The magneticnanocatalyst can readily be separated using an external magnet and reused atleast six times without significant loss in activity. The products werecharacterized by IR and ¹H and¹³C NMR spectra.

Full text of DOI:10.1134/S1070428020030185

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2020, Vol. 56, No. 3, pp. 485–490. © Pleiades Publishing, Ltd., 2020.
Synthesis of 1,3,5-Trisubstituted Pyrazoles and Hydrazones
Using Fe3O4@CeO2 Nanocomposite as an Efficient
Heterogeneous Nanocatalyst
H. Hassania,* and Z. Jahania
a Department of Chemistry, Payame Noor University, Tehran, 19395-4697 Iran
*e-mail: hassaniir@yahoo.com
Received October 24, 2019; revised December 29, 2019; accepted December 31, 2019
Abstract—Pyrazoles and hydrazones, as two significant kinds of potentially bioactive compounds, were
produced with good to excellent yields by condensation of β-dicarbonyl compounds with hydrazines in aqueous
media in the presence of Fe3O4@CeO2 nanocomposite as an efficient heterogeneous nanocatalyst. The magnetic
nanocatalyst can readily be separated using an external magnet and reused at least six times without significant
loss in activity. The products were characterized by IR and 1H and 13C NMR spectra.
Keywords: Fe3O4@CeO2 nanocatalyst, nanocomposite, pyrazole, hydrazone
DOI: 10.1134/S1070428020030185
Acid catalysts such as nitric, sulfuric, phosphoric,
and hydrochloric acids play an important role in
organic chemistry. However, inability to reuse, difficult
separation, and corrosive properties are disadvantages
of these homogeneous catalysts. Therefore, the design
of novel recyclable heterogeneous catalysts tolerating
a wide range of temperatures and pressures and mini-
mizing waste product is necessary [1–3]. Among het-
erogeneous catalysts, magnetic nanoparticles contain-
ing Fe3O4 are highly regarded because of their desir-
able magnetic properties, high recycling capability,
easy handling, low cytotoxicity, chemically modifiable
surface, and high commercially availability [4, 5].
tions (MCRs) were presented for merging environ-
mental aspects to economic aspects of new reactions.
Multicomponent reactions are one-pot reactions in-
volving three or more reactants to produce a favorable
product in a single flask and are characterized by mild
reaction condition, high yield, atom economy, sim-
plicity, and cost efficiency [6, 7].
One example of MCRs is the synthesis of pyrazoles.
Pyrazoles and their derivatives have gained much
attention in organic synthesis, because they have sig-
nificant therapeutic and biological values. In particular,
they are introduced as anti-inflammatory, antitumor,
antiparasitic, and antibacterial agents [8–11]. Pyrazole
derivatives are part of the core of various biologically
active compounds. Analgesic, antidiabetic, antiphlo-
Due to the increasing interest in the extension of
environmentally safe reactions, multicomponent reac-
Scheme 1.
R3
R3
R3NHNH2 (2a–2c)
N
N
N
N
or
R1
R2
R1
O
Fe3O4@CeO2 MNPs
H2O, room temp.
O
O
3a–3d, 3g, 3h
3e, 3f
R1
R2
H
N
Me
1a–1c
MeC(O)NHNH2 (4)
O
N
O
R2
R1
5a–5c
1, R1 = R2 = Me (a), R1 = Me, R2 = OEt (b), R1 = R2 = Ph (c); 2, R3 = H (a), Ph (b), 4-ClC6H4 (c); 3, R1 = R2 = Me, R3 = H (a),
Ph (b), 4-ClC6H4 (c); R1 = Me, R2 = OH, R3 = H (d); R1 = Me, R3 = Ph (e), 4-ClC6H4 (f); R1 = R2 = R3 = Ph (g), R1 = R2 = Ph,
R3 = 4-ClC6H4 (h); 5, R1 = R2 = Me (a), R1 = Me, R2 = OEt (b), R1 = R2 = Ph (c).
485

HASSANI, JAHANI
486
30
20
10
gistic, and many other modern drugs contain a pyrazole
ring as structural segment [12–14].
Imines are important intermediates in the synthesis
of biologically active N-heterocyclic compounds such
as fragrances, β-lactams, agricultural chemicals, phar-
maceuticals, and dyes [15–18]. Due to the presence of
lone electron pair on the imine nitrogen atom, partic-
ularly when this atom is located at the ortho position of
an aromatic heterocycle, imines can coordinate to
metals and the resulting complexes can be used as
catalysts [19, 20].
Magnetization, emu/g
10000 20000
–20000
–10000
0
–10
–20
–30
Field, G
In continuation of our studies of the synthesis of
recyclable and effective nanocatalysts and their use in
the preparation of biologically important compounds
[21–25], in this work we surveyed the effect of
Fe3O4@CeO2 nanocomposite in one-pot synthesis of
pyrazoles and hydrazones by the condensation of hy-
drazines/hydrazides with dicarbonyl compounds. The
proposed method does not require removal of water
and the use of any drying agent because the reaction is
carried out in aqueous solution. Eventually, pyrazole
and hydrazone derivatives were produced with good
to excellent yields (80–98 %) in aqueous medium
(Scheme 1).
Fig. 1. Vibrating sample magnetometry pattern of
Fe3O4@CeO2 magnetic nanoparticles.
The catalyst, Fe3O4@CeO2 magnetic nanoparticles,
was prepared in two steps: (1) Colloidal iron oxide
magnetite nanoparticles (Fe3O4 MNPs) were prepared
by the reaction of FeCl2·4H2O and FeCl3·6H2O with
sodium hydroxide in deionized water; (1) Cerium(IV)
oxide was incorporated as functional groups on the
surface of ferrite nanoparticles by treatment of
Fe3O4 MNPs with Ce(NO3)3·6H2O for 12 h to give
Fe3O4@CeO2 MNPs.
0
5
10
E, kEv
Fig. 2. EDS pattern of Fe3O4@CeO2 magnetic nanoparticles.
The catalyst was characterized by several tech-
niques. Figure 1 shows the magnetization plot versus
magnetic field for Fe3O4@CeO2 nanoparticles, which
was obtained by vibrating sample magnetometry
(VSM) at room temperature (300 K). The
Fe3O4@CeO2 nanoparticles exhibited superparamag-
netic behavior with a saturation magnetization (Ms) of
28.97 emu/g and without magnetic hysteresis area
coercivity and remnant magnetization.
70
30
40
50
2θ, deg
60
Fig. 3. XRD pattern of Fe3O4@CeO2 magnetic nanoparticles.
(a)
(b)
The energy-dispersive X-ray spectroscopy (EDS)
pattern of Fe3O4@CeO2 MNPs was recorded to
investigate their elemental composition (Fig. 2). It
showed peaks of cerium, oxygen, and iron of as-
prepared nanoparticles.
The X-ray powder pattern recorded for a sample of
Fe3O4@CeO2 MNPs is shown in Fig. 3. It contains
several relatively strong peaks in the region 20–80°,
which are quite similar to those observed for other
Fig. 4. (a) TEM and (b) FESEM patterns of Fe3O4@CeO2
magnetic nanoparticles.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 3 2020

SYNTHESIS OF 1,3,5-TRISUBSTITUTED PYRAZOLES AND HYDRAZONES
487
TG, mg
2.0
DTA, μV
Fe3O4 nanoparticles, 2θ = 30.1, 35.5, 43.1, 57.1, 62.7,
0
66, 74.1, and 75.4°. These peaks were assigned to the
(523), (1000), (260), (342), and (598) faces. The
pattern indicates a crystalline structure with the (184),
(144), and (157) crystallographic faces of magnetite
consistent with the standard pattern. Extra reflections
are not detected in the XRD pattern. The average
crystallite size D was estimated at 11.96–14 nm by
using Scherrer’s equation D = Kλ/(βcosθ), where K =
0.9 is a shape factor, β is the full width at half
maximum (FWHM) of the peaks of all planes in the
XRD pattern, λ = 1.5406 Å is the wavelength of Cu
target, and θ is the Bragg angle.
–2
–4
1.0
0.0
–6
–1.0
–2.0
–8
–10
0
200
400
600
800
Temperature, °C
Fig. 5. TGA Pattern of Fe3O4@CeO2 MNPs.
The TEM and FESEM images of Fe3O4@CeO2
MNPs are shown in Fig. 4. The results showed that
the average particle size of Fe3O4@CeO2 MNPs is
19–28 nm which is consistent with the XRD data.
Figure 5 shows the thermal behavior of
Fe3O4@CeO2 nanoparticles. The TGA curve showed
weight loss in the region between 0 and 800°C. Weight
loss in the region between 24 and 445°C was attributed
to decomposition of organic compounds and evapora-
tion of absorbed water. The first weight loss in the
region 24–221°C corresponds to vaporization of water
adsorbed on the surface of the composite material. The
second weight loss takes place between 221 and 445°C
due to vaporization of gaseous nitrates and ammonia
from the material. There was no weight loss above
440°C. Thus, the prepared Fe3O4/CeO2 material is
quite thermally stable above that temperature.
(a)
(b)
IR spectroscopy was used to monitor successful
loading of CeO2 on the surface of Fe3O4. As shown in
Fig. 6a, the peak about 3500 cm–1 corresponds to
vibrations of OH groups. The peak at 609 cm–1 is
attributed to Fe–O bending vibrations. The FTIR
spectrum of Fe3O4@CeO2 (Fig. 6b) showed a peak
at 431 cm–1 due to Ce–O stretching and bending
vibrations of CeO2.
3500
2500
1500
ν, cm–1
Fig. 6. FT-IR spectra of (a) Fe3O4 and (b) Fe3O4@CeO2.
Table 1. Synthesis of 3,5-dimethyl-1H-pyrazole (3a) in dif-
ferent solvents (reaction time 5 min)
Solvent
Yield, %
Water
98
95
95
90
90
85
85
80
80
75
40
To investigate the catalytic activity of Fe3O4@CeO2
nanocomposite, substituted hydrazines (acetohydra-
zide) (1 mmol) were reacted with diketones/β-keto
esters (1 mmol) in water in the presence of the nano-
composite (0.005 g) as catalyst at room temperature to
produce pyrazoles and imines (Scheme 1). To define
the optimal conditions, the synthesis of 3,5-dimethyl-
1H-pyrazole (3a) as model was carried out in various
solvents (Table 1) and in the presence of various
amounts of the catalyst (Table 2). All reactions were
stopped at 5 min, and the approximate yields were
measured by TLC. The results showed that water is the
Ethanol
Methanol
Ethyl acetate
Dimethyl sulfoxide
Dimethylformamide
1,2-Dichloroethane
Tetrahydrofuran
Chloroform
Methylene chloride
None (solvent-free)
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 3 2020

HASSANI, JAHANI
488
(5–35 min). Acetylacetone reacted with hydrazines to
afford pyrazoles 3a–3c with high yields (Table 3, entry
nos. 1–3). The reactions of hydrazines with dibenzoyl-
methane, which is a less reactive carbon electrophile
than acetylacetone, also produced pyrazoles 3g and 3h
with high yields but in a longer time (Table 3, entry
nos. 7, 8). Ethyl 3-oxobutanoate reacted with hydrazine
to give hydroxypyrazole 3d (entry no. 4), whereas its
reactions with phenyl- and 4-chlorophenylhydrazines
afforded pyrazolones 3e and 3f, respectively (entry
nos. 5, 6). In the reactions of β-dicarbonyl compounds
1a–1c with acetohydrazide (4) under the same condi-
tions (0.005 g of Fe3O4@CeO2, H2O, room tempera-
ture), we isolated the corresponding hydrazones 5a–5c
in 80 to 98% yield (Table 3, entry nos. 9–11).
Table 2. Synthesis of 3,5-dimethyl-1H-pyrazole (3a) in
water in the presence of different amounts of Fe3O4@CeO2
NPs (amounts of the reactants 1 mmol, room temperature,
reaction time 5 min)
Amount of Fe3O4@CeO2, g
Yield, %
0.001
0.005
0.007
0.010
80
98
98
98
40
No catalyst
best solvent. The optimal amount of the catalyst was
estimated at 0.005 g per mmol of the substrate.
To define the reaction scope, acetylacetone, ethyl
acetoacetate, and dibenzoylmethane were reacted with
hydrazine hydrate, arylhydrazines, and acetohydrazide
under the optimized conditions (0.005 g of the catalyst
Fe3O4@CeO2, water, room temperature; Scheme 1,
Table 3). Pyrazoles 3a–3h were produced in good to
excellent yields (80–98%) in a very short reaction time
To better demonstrate the efficiency of the proposed
catalyst, our results were compared with the reported
results for other catalysts in the synthesis of pyrazoles
(Table 4). The iron content of Fe3O4@CeO2 was
measured by ICP-OES for a 0.01-g sample which was
dissolved in a mixture of HNO3 and HF, and the op-
Table 3. Synthesis of pyrazoles and imines in the presence of Fe3O4@CeO2 nanocompositea
Entry no.
Dicarbonyl compound
Hydrazine
Product
3a
3b
3c
3d
3e
3f
3g
3h
Time, min
Yield,b %
98
1
2
3
4
5
6
7
8
9
1a
1a
1a
1b
1b
1b
1c
1c
1a
1b
1c
2a
2b
2c
2a
2b
2c
2b
2c
4
5
10
10
10
15
15
30
35
15
20
50
95
90
95
90
85
90
80
95
5a
5b
5c
10
11
4
4
98
80
a Reaction conditions: 1 mmol of hydrazine/hydrazide, 1 mmol of β-dicarbonyl compound, 0.005 g of Fe3O4@CeO2; water, room
temperature.
Isolated yield.
b
Table 4. Comparison of Fe3O4@CeO2 nanocomposite with some reported catalysts in the synthesis of 1,3,5-triphenyl-1H-
pyrazole (3g)
Catalyst and conditions
Ir(ppy)3 (2 mol %)/MeCN/hν
Fe3O4@SiO2@PDETSA (0.004 g)/H2O/r.t.
[RuCl2(p-cymene)]2 (5 mol %)/DMSO/base/1 atm O2/60–100°C
O2/activated carbon (50 mol %)/HOAc/120°C
Cellulose sulfuric acid (0.1 g)/solvent-free/r.t.
Sc(OTf)3 (2 mol %)/solvent-free/r.t.
Time, min
Yield, %
TOF, h–1
20
Reference
120
30
360
150
120
20
80
87
85
91
95
94
91
90
[27]
[28]
[29]
[30]
[31]
a
–
2.8
0.73
a
–
134
1137
200000
[32]
[33]
Sulfamic acid (1 mol %)/solvent-free/r.t.
Fe3O4@CeO2 (0.0009 mol %)/H2O/r.t.
5
30
This work
a
The catalyst amount was not given.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 3 2020

SYNTHESIS OF 1,3,5-TRISUBSTITUTED PYRAZOLES AND HYDRAZONES
489
timized concentration was found to be 0.0009 mol %.
Comparison of the turnover frequencies (TOFs)
showed that our catalyst is one of the best catalysts for
selective pyrazole synthesis.
160°C, and allowed to cool to room temperature.
The resulting magnetic catalyst was separated using
a magnet, washed several times with ethanol and
deionized water, and dried under reduced pressure
at 70°C for 10 h.
The reusability of Fe3O4@CeO2 nanocomposite
was studied in the reaction of acetylacetone with
hydrazine hydrate to produce pyrazole 3a. The catalyst
was separated using an external magnet, washed
several times with deionized water, and then used to
catalyze the reaction with fresh portions of the reactants
in six successive runs. The yield of 3a insignificantly
decreased from 98% in the first run to 97, 94, 90, 88,
and 83% in the second to sixth runs, respectively.
General procedure for the synthesis of pyrazoles
and hydrazones. A mixture of 0. 005 g of
Fe3O4@CeO2 as catalyst, hydrazine 2a–2c or hydra-
zide 4 (1.0 mmol), and β-dicarbonyl compound 1a–1c
(1 mmol) in water (2 mL) was stirred at room tempera-
ture for a time indicated in Table 3. The progress of
the reaction was monitored by TLC on Polygram
SILG/UV 254 plates. After completion of the reaction,
the catalyst was separated using an external magnet
and washed several times with ethanol and deionized
water for subsequent use. The product was extracted
with ethyl acetate (2×10 mL), the extract was dried
over Na2SO4 and evaporated, and the residue was
purified by flash column chromatography (EtOAc–
n-hexane, 1:20). Spectral characteristics of some of the
synthesized compounds are given below:
In conclusion, we have proposed a green and
efficient method for the synthesis of pyrazoles and
hydrazones in the presence of Fe3O4@CeO2 magnetic
nanoparticles as a reusable and easily separable catalyst
in water at room temperature with good to excellent
yields (80–98%) and short reaction times (5–50 min).
EXPERIMENTAL
3,5-Dimethyl-1H-pyrazole (3a). IR spectrum
The necessary reagents and solvents were purchased
from Merck (Germany) and Fluka (Switzerland) and
were used without further purification. The FT-IR
spectra were recorded in the range 400–4000 cm–1
using a Nicolet Avatar 370 spectrometer. The 1H NMR
spectra were measured on a Bruker Avance DPX-250
instrument at 300 MHz in CDCl3 using tetramethyl-
silane (TMS) internal standard. The iron content of
the catalyst was determined by inductively coupled
plasma/optical emission spectroscopy (ICP-OES) using
an Agilent 7700ce instrument.
1
(KBr), ν, cm–1: 3397, 1620, 1531, 1492. H NMR
spectrum, δ, ppm: 2.36 s (CH3), 2.69 s (CH3), 5.91 s
(4-H), 13.7 s (NH).
3,5-Dimethyl-1-phenyl-1H-pyrazole (3b). IR
(neat), ν, cm–1: 3084, 2903, 1615, 1573, 1537,
1
1459, 1395, 750, 678. H NMR spectrum: 2.24 s (3H,
CH3), 2.28 s (3H, CH3), 5.95 s (1H, 4-H), 7.31–
7.34 m (5H, Ph).
1,3,5-Triphenyl-1H-pyrazole (3h). IR spectrum
(KBr), ν, cm–1: 3147, 3082, 1639, 1565, 1515, 1473,
1491, 1388, 1227, 1193, 1088, 1043, 976, 937, 759,
Preparation of Fe3O4@CeO2 nanocomposite.
Initially, magnetic Fe3O4 nanoparticles were synthe-
sized via a modified procedure based on the previously
reported method [26]. For this purpose, a mixture of
2.0 g (10 mmol) of FeCl2·4H2O, 5.2 g (20 mmol)
FeCl3·6H2O, 25 mL deionized water, and 0.85 mL of
aqueous HCl was added dropwise to a solution of 15 g
of sodium hydroxide in 25 mL of deionized water.
The mixture was vigorously stirred, and a black solid
separated. The mixture was heated on a water bath for
4 h at 80°C, and the magnetic product was separated by
an external magnet, washed several times with ethanol
and deionized water, and dried at 110°C for 5 h.
A solution of 0.868 g (2.7 mmol) of Ce(NO3)3·6H2O in
a mixture of 17 mL of ethylene glycol and 34 mL of
ethanol was stirred for 40 min, 0.347 g of as-prepared
Fe3O4 MNPs were added, and the mixture was
sonicated for 30 min, heated on an oil bath for 5 h at
1
721. H NMR spectrum, δ, ppm: 6.88 s (1H, 4-H),
7.35–7.99 m (15H, Harom).
N′-(4-Oxopentan-2-ylidene)acetohydrazide (5a).
IR spectrum (neat), ν, cm–1: 3013, 2953, 1745, 1612,
1421, 1390, 1341, 1295, 1165, 1101, 1056, 963, 821,
1
791. H NMR spectrum, δ, ppm: 2.21 s (3H, CH3),
2.52 s (3H, CH3), 2.63 s (3H, CH3), 4.8 s (2H, CH2),
5.88 s (1H, NH).
FUNDING
This study was performed under financial support by the
Payame Noor University.
CONFLICT OF INTERESTS
The authors declare the absence of conflict of interests.
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HASSANI, JAHANI
16. Meyer, C.D., Joiner, C.S., and Stoddart, J.F., Chem. Soc.
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