Urea-functionalized silica-coated Fe3?xTixO4magnetic nanoparticles: as highly efficient and recyclable heterogeneous nanocatalyst for synthesis of 4H-chromene and 1H-pyrazolo[1,2-b]phthalazine-5,10-dione derivatives

Article abstract of DOI:10.1007/s13738-016-0989-5

Novel urea-functionalized silica-coated magnetic core–shell Fe_3?xTi_xO₄nanoparticles were prepared and fully characterized by different methods such as Fourier transform infrared spectroscopy, energy-dispersive X-ray spectr

Full text of DOI:10.1007/s13738-016-0989-5

J IRAN CHEM SOC
DOI 10.1007/s13738-016-0989-5
ORIGINAL PAPER
Urea‑functionalized silica‑coated Fe3−xTixO4 magnetic
nanoparticles: as highly efficient and recyclable
heterogeneous nanocatalyst for synthesis of 4H‑chromene
and 1H‑pyrazolo[1,2‑b]phthalazine‑5,10‑dione derivatives
Davood Azarifar1 · Omolbanin Badalkhani1 · Younes Abbasi1 · Morteza Hasanabadi1
Received: 13 June 2016 / Accepted: 30 September 2016
© Iranian Chemical Society 2016
Abstract Novel urea-functionalized silica-coated magnetic
core–shell Fe3−xTixO4 nanoparticles were prepared and
fully characterized by different methods such as Fourier
transform infrared spectroscopy, energy-dispersive X-ray
spectroscopy, field emission scanning electron microscopy,
high-resolution transmission electron microscopy, vibrating
sample magnetometer, X-ray diffraction, and thermogravi-
metric analyses. These magnetic nanoparticles have been
explored as highly efficient and recoverable heterogeneous
nanocatalyst for one-pot three-component reactions under
mild conditions for the synthesis of diverse range of 5-oxo-
dihydropyrano[3,2-c]chromenes known as coumarins and
1H-pyrazolo[1,2-b] phthalazine-5,10-diones in high yields.
Simple isolation of the products, use of green solvent, and
magnetically easy isolation and reusability of the catalyst
with no significant loss of activity are the main advantages
of the present method.
and bioorganic chemistry. Their importance stems from
their amazing level of catalytic performance and improved
selectivity [1–3]. On the other hand, the issue of green
chemistry has emerged as major concern for the scientists
in organic chemistry who have taken considerable efforts
for development and application of green approaches, more
selective, and environmentally benign heterogeneous nano-
catalysts in industrial and synthetic organic chemistry [4–
8]. In this context, various nanoparticles (NPs), especially
nanometal oxides such as Fe2O3, Fe3O4, TiO2, Al2O3, ZnO,
have recently been developed and applied as nanocatalysts
in different research and technological areas [9–13]. These
nanoparticles offer many advantages due to their unique
size and extraordinary physical and chemical properties
such as high surface area, oxidizing, reducing, and acid–
base characters on their surfaces [14, 15]. Moreover, nano-
metal oxides serve as excellent adsorbents or supports for
immobilization of a wide variety of homogeneous organic
and inorganic catalysts [16, 17]. Usually, immobilization
of homogeneous catalysts on nanosupports enhances their
stability and catalytic power in chemical transformations
due to their interesting properties like high ratio of surface
area to volume, high selectivity, long-term stability, and
reusability [18–21]. However, many of these nanocatalysts
are subject to tedious process of isolation and recycliza-
tion via filtration or centrifugation [22]. Such problem has
prompted the application of magnetically separable and
reusable magnetic nanoparticles (MNPs) as excellent sup-
ports for various catalysts [2, 23–28]. Nevertheless, these
magnetic nanoparticles suffer from quick aggregation into
large bunch and thereby loss of their unique properties. In
order to prevent the aggregation of magnetic nanoparticles
and preserve their nanoscale properties, their surface is
coated with organic or inorganic components such as silica
to form core–shell structures [29]. The surface-modified
Keywords Titanomagnetite nanoparticles · Urea-
functionalized Fe3−xTixO4@SiO2 MNPs · Nanocatalyst ·
4H-Chromene · 1H-Pyrazolo[1,2-b] phthalazine-5,10-dione
Introduction
The last few years have witnessed much advancement in
developments and applications of nanoparticles (NPs) as
heterogeneous nanocatalysts or supports for various homo-
geneous catalysts in different fields of synthetic organic
* Davood Azarifar
azarifar@basu.ac.ir
1
Department of Chemistry, Bu-Ali Sina University,
Hamedan 65178, Iran
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J IRAN CHEM SOC
Scheme 1 Synthesis of
dihydropyrano[2,3-c]chromenes
2a‑j and 1H-pyrazolo[1,2-b]
phthalazine-5,10-diones 3a‑j
catalyzed by Fe3−xTixO4@
SiO2@urea MNPs
magnetic nanoparticles contain reactive sites with high
mobility which can be grafted with different functional
groups with oxidizing, acidic, basic, and ionic liquid prop-
erties and widely employed as selective heterogeneous
catalysts in various organic transformations [30–33]. In
recent years, magnetic nanoparticles (MNPs) have shown a
rapid growth in their developments and applications in vari-
ous industrial and biological areas such as drug delivery,
hyperthermia, bioseparations, magnetic resonance imaging
(MRI), and catalytic processes [23, 25, 28, 34].
The presence of chromene scaffold in the framework of
various pharmacologically active compounds possessing
spasmolytic [35], diuretic [36], anti-HIV [37], antitumor
[38], antimalarial [39], anti-Alzheimer [40], and antileuke-
mic [41, 42] properties continues to spur synthetic efforts
regarding their acquisition. In addition, different derivatives
of chromenes are known as valuable synthones used for
potential biodegradable agrochemicals [43] and as cosmet-
ics and pigments [35]. Chromenes are also used as antimi-
crobial and antituberculosis agents [44].
The broad range utility of chromenes and phthalazine
derivatives as useful precursors in synthetic organic and
medicinal chemistry has accentuated the need to develop
more improved synthetic approaches for scaffold manipula-
tion of heterocycles containing chromene and phthalazine
moieties.
In continuation of our efforts for the development of ver-
satile and efficient catalysts for the synthesis of various het-
erocyclic compounds including the chromenes and phthala-
zines and other organic transformations [61–64], we were
encouraged to initiate for the first time the synthesis of hith-
erto unreported urea-functionalized silica-modified titano-
magnetite nanoparticles and explore its catalytic activity
as a novel and highly efficient heterogeneous basic nano-
catalyst toward the synthesis of dihydropyranochromenes
2a‑j and 1H-pyrazolo[1,2-b]phthalazine-5,10-diones 3a‑j
(Scheme 1). It is to mention that the catalytic activity of
urea-grafted nanoparticles such as Fe3O4/SiO2 magnetic
NPs has been previously explored for one-pot synthesis of
other heterocyclic compounds [65].
A number of methods have been reported in the litera-
ture for the preparation of chromenes which utilize differ-
ent catalytic systems including diammonium hydrogen
phosphate (DAHP) [45], H6P2W18O62.18H2O [46], MgO
[47], ionic liquids [48], hexadecyltrimethyl ammonium
bromide [49], SiO2PrSO3H [50], Mg/La mixed metal
oxides [51], nanosilica [52], α-Fe2O3 nanoparticles [53],
and silica-grafted ionic liquid [54].
Experimental setup
Materials and instrumentation
Chemicals were purchased from Merck Chemical Com-
1
pany. H NMR and 13C NMR spectra were measured for
In addition, pyrazolo-fused phthalazine derivatives,
constituting a bridgehead hydrazine, are reported to pos-
sessing multiplicity of pharmacological properties includ-
ing anticonvulsant [55], vasorelaxant [56], and cardiotonic
[57] activities. Albeit, there are several methods available
for the synthesis of different phthalazine derivatives [58,
59]. Raghuvanshi and Singh [60] have recently reported
a highly efficient green synthesis of 1H-pyrazolo[1,2-b]
phthalazine-5,10-diones of photophysical importance.
samples in CDCl3 or DSMO-d6 using a 400 MHz Bruker
AVANCE instrument at 400 and 100 MHz, respectively,
using Me4Si as internal standard. Fourier transform infra-
red (FT-IR) spectra were recorded on a Shimadzu 435-U-
04 FT spectrophotometer from KBr pellets. Melting points
were measured on a BUCHI 510 apparatus in open capil-
lary tubes. Qualitative analysis of Fe3−xTixO4@SiO2@
urea MNPs was performed by field emission scanning
electron microscopy (FE-SEM) on a MIRA3 FE-SEM
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J IRAN CHEM SOC
instrument (TESCAN company) operated at 15 kV accel-
erating voltage. High-resolution transmission electron
microscopy (HRTEM) images of the catalyst were pro-
vided by a Philips CM30 TEM (300 kV) instrument. The
energy-dispersive X-ray (EDX) analysis was performed
using an SAMX model instrument. The X-ray diffraction
measurements of the synthesized Fe3−xTixO4, Fe3−xTixO4@
SiO2 and Fe3−xTixO4@SiO2@urea samples were carried
out using an XRD Model D500 Ziemence instrument from
2θ 10° to 120° at room temperature. The vibrating sam-
ple magnetometry (VSM) measurement was performed
on a MDKFT instrument. Thermal stability of the nano-
catalyst was studied by thermogravimetric analysis (TGA)
performed on a PerkinElmer, Pay Rise Diamond, USA,
TG/DTG at the heating rate of 5 °C/min in the range of
25–700 °C under N2 flow. Ultrasonication was performed
in a 2200 ETH-SONICA ultrasound cleaner with a fre-
quency of 45 kHz. The pH measurement of the catalyst was
performed using a pH meter Model Metrohm 827 (Herisan,
Switzerland) with a combined glass electrode.
Preparation of the urea‑functionalized Fe3−xTixO4@
SiO2@urea nanoparticles
A dispersion of Fe3−xTixO4@SiO2 MNPs (1 g) in dry xylene
(30 mL) was ultrasonicated for 1 h. Then, 3-(trimethoxysi-
lyl)propyl urea (1.93 mL, 10 mmol) was added dropwise to
the resulted dispersion under N2 atmosphere and refluxed
for 24 h with vigorous stirring. The resulted black powders
were then isolated by an external magnetic field, succes-
sively washed with xylene and ethanol, and dried in an oven
to obtain the Fe3−xTixO4@SiO2@urea NPs (3.1 g).
Typical procedure for the synthesis
of dihydropyrano[3,2‑c]chromen‑2‑ones
To a mixture of aldehyde 1 (1 mmol), malononitrile
(0.08 g, 1.2 mmol), and 4-hydroxycoumarin (0.162 g,
1 mmol) in H2O (1 mL) and EtOH (4 mL) was added the
catalyst Fe3−xTixO4@SiO2@urea (0.01 g), and the mixture
was refluxed for an appropriate time (Table 2). After com-
pletion of the reaction as monitored by TLC, the resulted
reaction mixture was diluted with hot ethanol (5 mL) and
stirred for 10 min. Then, the catalyst was isolated by an
external magnetic field, and the remaining supernatant was
diluted with water (50 mL) and let to stir for 20 min. The
precipitated crude product was filtered, washed with water,
dried in oven, and recrystallized from ethanol to obtain the
pure product. All the synthesized products 2a‑j are known
compounds which are characterized by their melting points
and spectral (FT-IR, 1H NMR, and 13C NMR) analysis and
compared with the corresponding reported data (Table 2).
Preparation of the Fe3−xTixO4 MNPs
Titanomagnetite nanoparticles were prepared accord-
ing to our previously reported procedure [64] based on
almost a similar procedure as reported by Yang et al. [66].
FeSO4.7H2O (1.903 g, 6.8 mmol) was dissolved in deion-
ised water (10 mL). The pH of the solution was reduced
to <1 by addition of HCl solution. Then, TiCl4 (1.3 g,
6.8 mmol) and hydrazine monohydrate (2 mL) were suc-
cessively added to the reaction mixture. The resulted
mixture was refluxed at 90 °C under N2 atmosphere for
30 min followed by dropwise addition of aqueous solutions
of NaOH (1.6 g) and NaNO3 (0.77 g) in deionised water
(10 mL) under vigorous stirring at a rate of 500 rpm for 1 h.
Finally, the resulting reaction mixture was cooled to room
temperature. The precipitated titanomagnetite nanoparticles
were isolated simply by using a magnet bar, washed with
water several times, and dried in air.
Typical procedure for the synthesis
of 1H‑pyrazolo[1,2‑b]phthalazine‑5,10‑dione derivatives
To the mixture of aryl aldehyde (1 mmol), malononi-
trile (1 mmol), and phthalhydrazide (1 mmol) was added
the catalyst Fe3−xTixO4@SiO2@urea (0.03 g), and the
resulted mixture was stirred at 100 °C for an appropri-
ate time (Table 4). After the completion of the reaction as
monitored by thin-layer chromatography (TLC), the reac-
tion mixture was cooled to room temperature, diluted with
ethanol (10 mL), and stirred for 10 min. The catalyst was
isolated in an external magnetic field. The remaining insol-
uble phthalhydrazide was removed by filtration, and the
supernatant liquid was evaporated under reduced pressure
to leave the crude product which was washed with acetone
and 10 % NaHCO3 solution and finally recrystallized from
ethyl acetate/n-hexane (5:7) to yield the reasonably pure
product. All the synthesized products 3a‑j are known com-
pounds which are characterized by their melting points and
Synthesis of silica‑coated magnetite Fe3−xTixO4 @SiO2
The prepared magnetic Fe3−xTixO4 nanoparticles (1 g)
were placed in the mixture of EtOH (10 mL) and deionized
water (30 mL), and the mixture was sonicated for 30 min.
Then, a 25 % aqueous solution of NH4OH (20 mL) and
tetraethyl orthosilicate (TEOS) (1.2 mL) was successfully
added dropwise to the resulted mixture followed by sonica-
tion for an additional 15 min. Finally, the mixture was vig-
orously stirred at room temperature for 24 h. The resulted
nanoparticles were magnetically separated by a magnet bar,
successively washed with deionized water and ethanol, and
dried in air.
1
spectral (FT-IR, H NMR, and 13C NMR) analyses and
compared with the corresponding reported data (Table 4).
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J IRAN CHEM SOC
Selected data
56.9 (=C–CN), 102.9, 112.8 (C=C), 116.4 (C–HAr), 119.0
(C≡N), 122.5, 123.7, 124.5, 132.9, 135.4, 138.7, 146.2 (C–
HAr), 149.0 (C=N), 152.1 (=C–NH2), 153.7, 158.0 (=C–
O), 159.5 (O=C–O) ppm.
2‑Amino‑4‑(phenyl)‑5‑oxo‑4,5‑dihydropyrano[3,2‑c]chrom-
ene‑3‑carbonitrile (2a) Cream solid, m.p. 254–256 °C;
FT-IR (KBr) ν (cm−1): 3380, 3285, 3179 (NH2), 3096 (CAr
–H), 2198 (C≡N), 1709 (C=O), 1674, 1604,1568 (C=C),
1211, 1056 (C–O), 1493, 1380 (C–N); 1H NMR (400 MHz,
DMSO-d6) δ: 4.45 (s, 1H, CH), 7.5–8.2 (m, 11H, Ar–H and
NH2) ppm; 13C NMR (100 MHz, DMSO-d6) δ: 13C NMR
(125 MHz, CDCl3): δ 39.1(C–H), 57.9 (=C–CN), 103.9,
112.7 (C=C), 116.4 (C–HAr), 120.2 (C≡N), 122.3, 125.6,
128.0, 127.5, 128.4, 133.8 (C–HAr), 143.2 (C=C), 153.1
(=C–O),, 154.3 (=C–NH2), 157.9 (=C–O), 159.4 (O=C–O)
ppm.
3‑Amino‑1‑phenyl‑5,10‑dioxo‑5,10‑dihydro‑1H‑pyrazolo[1,2‑
b]phthalazine‑2‑carbonitrile (3a) Yellow solid, m.p. 274–
276 °C; FT-IR (KBr) ν (cm−1): 3362, 3261, 3192 (NH2), 3035
(CAr–H), 2198 (C≡N), 1681 (C=O), 1660, 1605 1568 (C=C),
1439, 1383 (C–N); 1H NMR (90 MHz, DMSO-d6): δ 6.12 (s, 1H,
CH), 7.37–8.05 (m, 11H, Ar–H and NH2). 13C NMR (75 MHz,
DMSO-d6,): δ 61.4 (HC–N), 62.9 (=C–CN), 116.0 (C≡N),
126.6, 126.7, 127.2, 128.2, 128.5, 128.6, 128.7 (CHAr), 129.1,
(=C–CO), 133.7, 134.6 (CHAr), 138.4 (=C–CH), 150.6 (C=O),
153.6 (=C–NH2), 156.6 (C=O) ppm.
2‑Amino‑4‑(2,4‑dichlorophenyl)‑5‑oxo‑4,5‑dihydropyran
o[3,2‑c]chromene‑3‑carbonitrile (2e) Cream solid, m.p.
255–258 °C; FT-IR (KBr) ν (cm−1): 3463, 3297,3164
(NH2), 3069 (CAr–H), 2200 (C≡N), 1716 (C=O), 1674,
3‑Amino‑1‑(2,3‑dichlorophenyl)‑5,10‑dioxo‑5,10‑dihydro‑1H‑
pyrazolo[1,2‑b]phthalazine‑2‑carbonitrile (3e) Yellow solid,
m.p. 262–264 °C; FT-IR (KBr) ν (cm−1): 3373, 3238, 3178
(NH2), 2211 (C≡N), 1683 (C=O), 1659, 1603, 1566 (C=C),
1
1631, 1590 (C=C), 1376 (C–N), 1062 (C–O); H NMR
1
(400 MHz, DMSO-d6): δ 4.98 (1H, s, CH), 7.35–7.92 (m,
9H, Ar–H and NH2) ppm; 13C NMR (100 MHz, DMSO-
d6): δ 34.3 (C–H), 56.4 (=C–CN), 102.9, 113.3 (C=C),
117.1 (C–HAr), 119.1 (C≡N), 123.0, 125.2, 128.3, 129.3,
132.5, 132.9 (C–HAr), 133.6, 133.8 (C–Cl), 139.9 (C=C),
152.7 (=C–O), 158.5 (=C–NH2), 158.6 (=C–O), 159.9
(O=C–O) ppm.
1415, 1380 (C–N); H NMR (400 MHz, DMSO-d6): 6.30
(1H, s, CH), 7.63–8.37 (m, 9H, Ar–H and NH2) ppm. 13C
NMR (100 MHz, DMSO-d6): δ 60.6 (HC–N), 62.5 (=C–CN),
116.3 (C≡N), 122.2, 123.8, 127.1 (CHAr), 127.7 (=C–Cl),
128.7, 129.3 (CHAr), 130.7 (=C–CO), 134.2, 134.3 (CHAr),
135.1 (=C–Cl), 148.3 (=C–CH), 151.5 (C=O), 154.3 (=C–
NH2), 157.2 (C=O) ppm.
2‑Amino‑4‑(3‑nitrophenyl)‑5‑oxo‑4,5‑dihydropyrano[3,2
‑c]chromene‑3‑carbonitrile (2h) Cream solid, m.p. 260–
263 °C; FT-IR (KBr) ν (cm−1): 3398, 3323, 3190 (NH2),
3087 (CAr –H), 2194 (C≡N), 1712 (C=O), 1674, 1603
3‑Amino‑1‑(4‑methoxyphenyl)‑5,10‑dioxo‑5,10‑dihydro‑1H‑
pyrazolo[1,2‑b]phthalazine‑2‑carbonitrile
(3g) Yellow
solid, m.p. 238–240 °C; FT-IR (KBr) ν (cm−1): 3373, 3267
(NH2), 2192 (C≡N), 1665 (C=O), 1603, 1584 (C=C),
1
1
(C=C), 1532, 1379 (C–N), 1212, 1063 (C–O); H NMR
1417,1382 (C–N); H NMR (400 MHz, DMSO-d6): δ 3.80
(400 MHz, DMSO-d6) δ: 4.70 (s, 1H, CH), 7.2–7.9 (m,
10H, Ar–H and NH2) ppm; 13C NMR (100 MHz, CDCl3):
δ 38.0 (C–H), 59.8 (=C–CN), 102.7, 112.8 (C=C), 116.4
(C–HAr), 119.8 (C≡N), 122.1, 124.3, 123.5, 125.5, 130.0,
133.0, 134.6 (C–HAr), 145.4 (C=C), 148.7 (=C–NO2),
152.2 (=C–NH2), 153.7, 159.1 (=C–O), 159.5 (O=C–O)
ppm.
(s, 3H, OCH3), 6.15 (s, 1H, CH), 6.95–8.31 (m, 10H, Ar–H
and NH2) ppm. 13C NMR (100 MHz, DMSO-d6): δ 55.1
(CH3), 61.3 (HC–N), 62.6 (=C–CN), 113.8 (CHAr), 116.1
2‑Amino‑5‑oxo‑4‑(pyridin‑3‑yl)‑4,5‑dihydropyrano[3,2
‑c]chromene‑3‑carbonitrile (2i) Cream solid, m.p. 257–
260 °C; FT-IR (KBr) ν (cm−1): 3365, 3282, 3177 (NH2),
3029 (CAr–H), 2202 (C≡N), 1707 (C=O), 1673, 1605
1
(C=C), 1377 (C–N), 1060 (C–O); H NMR (400 MHz,
DMSO-d6) δ: 4.57 (s, 1H, CH), 7.4–8.5 (m, 10H, Ar–H and
NH2) ppm; 13C NMR (100 MHz, CDCl3): δ 37.8 (C–H),
Scheme 2 Steps for the synthesis of the catalyst Fe3−xTixO4@SiO2@
urea MNPs
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J IRAN CHEM SOC
Fig. 1 FT-IR spectra of
synthesized Fe3−xTixO4 (a),
Fe3−xTixO4@SiO2 (b), and
Fe3−xTixO4@SiO2@urea NPs
(c)
Fig. 2 EDX spectra of Fe3−xTixO4 (a) and Fe3O4@SiO2@urea (b) NPs
(C≡N), 125.1, 126.6, 127.2, 128.5 128.7 (CHAr), 130.1
(=C–CO), 132.5, 133.7 (CHAr), 134.6 (=C–CH), 150.6
(C=O), 153.6 (=C–NH2), 156.6 (=C–OMe), 159.2 (C=O)
ppm.
3‑Amino‑5,10‑dioxo‑1‑(pyridin‑4‑yl)‑5,10‑dihy-
dro‑1H‑pyrazolo[1,2‑b]phthalazine‑2‑carbonitrile
(3j) Yellow solid, m.p. 264–267 °C; FT-IR (KBr) ν
(cm−1): 3388, 3285 (NH2), 2198 (C≡N), 1681 (C=O),
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J IRAN CHEM SOC
Fig. 3 FE-SEM images of Fe3−xTixO4 (a) and Fe3−xTixO4@SiO2@urea (b) NPs
1
1664, 1604, 1579 (C=C), 1441, 1384 (C–N); H NMR
(400 MHz, DMSO-d6): δ 6.21 (s, 1H, CH), 7.57–8.64 (m,
10H, Ar–H and NH2) ppm. 13C NMR (100 MHz, DMSO-
d6): δ 60.1 (HC–N), 61.7 (=C–CN), 115.7 (C≡N), 121.3,
126.7, 127.2, (CHAr), 128.3, 128.9 (=C–CO), 133.8, 134.6
(CHAr), 147.1 (=C–CH), 149.9 (CHAr), 150.9 (C=O),
153.7 (=C–NH2), 156.7 (C=O) ppm.
SiO2@urea) as a new basic nanocatalyst and examine its
catalytic activity in the synthesis of the titled products.
It is has been shown that the presence of Ti+4 cations in
the structure of nanoparticles can increase the number of
superficial hydroxyl groups [67]. Such a structural qual-
ity can improve the loading capacity of sulfonic acid
groups on the surface of the titanomagnetite nanoparticles
(4.0–5.5 mmol/g) compared with the magnetite Fe3O4 NPs
(1.76 mmol/g) [68] and magnetite silica-coated Fe3O4 NPs
(0.32 mmol/g) [69].
Result and discussion
As illustrated in Scheme 2, this heterogeneous nano-
catalyst is synthesized following our previously reported
procedure [64]. Initially, a mixture of equimolar amounts
of FeSO4.7H2O and TiCl4 in acidic solution is treated with
hydrazine hydrochloride in deionized water while reflux-
ing under nitrogen atmosphere. The resulting Fe3−xTixO4
MNPs are separated from the reaction mixture simply
by using a magnetic bar. In the second step, in order to
protect the Fe3−xTixO4 MNPs from possible oxidation
Characterization of the catalyst Fe3−xTixO4@SiO2@
urea MNPs
In continuation of our efforts to develop green and recov-
erable heterogeneous catalysts, herein, we are encouraged
to synthesize the hitherto unreported urea-functionalized
silica-modified Fe3−xTixO4 nanoparticles (Fe3−xTixO4@
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J IRAN CHEM SOC
or aggregation, the nanoparticles are modified on their
external surface by treating with tetraethyl orthosilicate
(TEOS) in aqueous NH4OH solution under sonication.
Then, the hydroxyl groups on the resulted Fe3−xTixO4@
SiO2 MNPs are reacted with 3-(trimethoxysilyl)propylu-
rea in dry xylene under sonication and nitrogen atmosphere
to produce the urea-functionalized magnetic nanoparticles
Fe3−xTixO4@SiO2@urea.
Fe, Ti, Si, C, O, N in these nanoparticles, respectively. The
EDX pattern shown in Fig. 2 obviously approves the well
dispersion of Fe3−xTixO4 nanoparticles.
As illustrated in Figs. 3 and 4, the morphology and
particle sizes of the Fe3−xTixO4 and Fe3−xTixO4@SiO2@
urea MNPs are studied by field emission scanning elec-
tron microscopy (FE-SEM) and high-resolution transmis-
sion electron microscopy (HRTEM). As can be seen in the
SEM images (Fig. 3), the Fe3−xTixO4 and Fe3−xTixO4@
SiO2@urea nanoparticles exhibit a regularly spherical
morphology which are made up of nanometer-sized par-
ticles with an average diameter of 23 and 31 nm, respec-
tively. In addition, based on the HRTEM analysis (Fig. 4),
the core–shell structure and the nanometer-sized particles
(~70 nm) of Fe3−xTixO4@SiO2@urea nanoparticles are
verified.
The structure of the prepared catalyst was established
by performing different analytical methods such as Fourier
transform infrared (FT-IR) spectroscopy, X-ray diffraction
(XRD) analysis, field emission scanning electron micros-
copy (FE-SEM), high-resolution transmission electron
microscopy (HRTEM), thermogravimetric analysis (TGA),
energy-dispersive X-ray (EDX) spectroscopy, and vibrating
sample magnetometric (VSM) analysis as described below.
The FT-IR spectra of the Fe3−xTixO4, Fe3−xTixO4@SiO2
and Fe3−xTixO4@SiO2@urea MNPs are presented in Fig. 1.
As shown in Fig. 1a, the FT-IR spectrum of the Fe3−xTixO4
MNPs as prepared in the first step (Scheme 2) performs
the characteristic broad absorption bands centered at 3418
and 1630 cm−1 which are attributed to the symmetrical and
asymmetrical vibrational modes of the O–H bonds attached
to the surface metal atoms. In addition, the absorption band
at 470 cm−1 is due to the introduction of titanium into mag-
netite structure and also the bands appearing at 735 and
587 cm−1 are assigned to the symmetric stretching vibra-
tions of the Ti–O and Fe–O bonds, respectively. The appear-
ance of the band at 1095 cm−1 in the infrared spectrum of
Fe3−xTixO4@SiO2 MNPs as shown in Fig. 1b underlines
the covalent bond between silane and titanomagnetite sur-
face characteristic for Si–O groups. In addition, the absorp-
tion bands at 951 and 715 cm−1 are likely associated with
the stretching vibrations of Si–O–Si groups. These results
confirm the successful formation of SiO2 layer on the sur-
face of Fe3−xTixO4. The bands appeared at 2841–2943 cm−1
(C–H stretching vibrations) in the FT-IR spectrum of
Fe3−xTixO4@SiO2 (Fig. 1c) substantiate the presence of
the propyl groups which are successfully anchored on the
Fe3−xTixO4@SiO2 MNPs. Moreover, the signals appeared at
3307 and 1549 cm−1 regions are attributed to the stretching
and bending vibrations of N–H groups, respectively. Also,
appearance of the absorption band at 1689 cm−1 is assigned
to the amidyl C=O stretching of urea moiety grafted on the
surface of Fe3−xTixO4@SiO2 MNPs.
Figure 5a exhibits the crystalline structure of Fe3−xTixO4
nanoparticles identified by X-ray diffraction (XRD) tech-
nique. The diffraction peaks are appeared at 2θ° values of
18.5, 30.2, 35.6, 37.2, 43.2, 53.6, 57.1, 62.7, 74.1, 89.9,
106. The broad peak observed at 2θ° region between 20°
and 28° in the XRD pattern of the Fe3−xTixO4@SiO2 nano-
particles as shown in Fig. 5b confirms the successful coat-
ing of Fe3−xTixO4 nanoparticles with amorphous SiO2
layers. Also, as seen in the XRD pattern obtained for the
Fe3−xTixO4@SiO2@urea nanoparticles (Fig. 5c), the posi-
tions and relative intensities of the corresponding peaks
are almost in accord with those shown for the non-grafted
Fe3−xTixO4@SiO2 nanoparticles and no significant changes
are observed.
The spectra obtained from the energy-dispersive X-ray
(EDX) analysis of Fe3−xTixO4 and Fe3−xTixO4@SiO2@
urea MNPs are illustrated in Fig. 2a, b. As shown in this
figure, the expected elemental compositions of these nano-
particles are clearly demonstrated by the spectra 2a and 2b,
respectively. Based on these spectra, the elemental analy-
sis performed on the Fe3−xTixO4 and Fe3−xTixO4@SiO2@
urea MNPs clearly indicates the presence of Fe, Ti, O and
Fig. 4 HRTEM image of Fe3−xTixO4@SiO2@urea NPs
1 3

J IRAN CHEM SOC
Fig. 5 X-ray diffraction (XRD)
patterns of Fe3−xTixO4 (a),
Fe3−xTixO4@SiO2 (b), and
Fe3−xTixO4@SiO2@ urea NPs
(c)
The magnetic measurements of the Fe3−xTixO4,
Fe3−xTixO4@SiO2, and Fe3−xTixO4@SiO2@urea nano-
particles were registered by using vibrating sample mag-
netometer (VSM) at 300 k. The magnetization curves
determined for these nanoparticles are compared and
shown in Fig. 6. As shown in this figure, the values of
the saturation magnetization were found to be 33.85,
22.92, and 13.22 emu/g for Fe3−xTixO4 nanoparticles,
Fe3−xTixO4@SiO2 core–shell, and Fe3−xTixO4@SiO2@
urea, respectively, in 20,000 Oe. The reduction in the
saturation magnetization values (Ms) of the Fe3−xTixO4@
SiO2 and Fe3−xTixO4@SiO2@urea in comparison to the
Fe3−xTixO4 NPs proposes the successful coating of SiO2
and grafting the trimethoxysilylpropyl urea moiety for the
formation of Fe3−xTixO4@SiO2@urea. However, despite
the considerable decrease in the magnetization value, the
catalyst could still be separated from the solution by using
an external magnetic field.
1 3

J IRAN CHEM SOC
derivative thermogravimetric (D-TG) thermogram performs
three major peaks centered at about 100, 246, and 393 °C
which correspond to the aforementioned major decomposi-
tion steps shown by the TG thermogram.
In order to determine the pH value of the catalyst, we
used a simple and rapid procedure in this paper. First,
0.05 g of the catalyst (Fe3−xTixO4@SiO2@urea NPs) in dis-
tilled water (10 mL) was stirred for 5 min. Subsequently,
the pH measurement of the mixture was performed at room
temperature using a pH meter instrument. As expected, the
measured pH value of 9.24 confirms that the synthesized
catalyst is basic in nature. This result could be explained by
the presence of the grafted urea moiety and the remaining
hydroxyl groups on the surface of the catalyst.
Fig. 6 VSM curve of the Fe3−xTixO4 (A), Fe3−xTixO4@SiO2 (B), and
Fe3−xTixO4@SiO2@urea NPs (C)
Catalytic activity of the Fe3−xTixO4@SiO2@urea MNPs
for the synthesis of dihydropyranochromen‑2‑ones
Thermogravimetric (TG) and derivative thermogravi-
metric (DTG) analyses were performed on the prepared
Fe3−xTixO4@SiO2@urea MNPs to monitor its thermal
decomposition profile (Fig. 7). According to the TG ther-
mogram, the weight loss process of the catalyst could be
divided into three stages. The first weight loss of 10.70 mg
around 100 °C was due to surface physisorbed water. The
second weight loss of 9.80 mg centered at about 240 °C
can be attributed to the immobilized urea moiety followed
by third decomposition weight loss of 8.85 mg centered
at about 390 °C likely due to the complete removal of
the organic residue. Accordingly, as shown in Fig. 7b, the
In order to evaluate the catalytic potential of the newly
prepared Fe3−xTixO4@SiO2@urea MNPs as hetero-
geneous nanocatalyst in organic transformations, we
decided to examine its activity in one-pot synthesis
of dihydropyrano[3,2-c]chromen-2-ones from three-
component reaction of aromatic aldehydes, malon-
onitrile, 4-hydroxycoumarin, and one-pot synthesis of
1H-pyrazolo[1,2-b]phthalazine-5,10-diones from three-
component reaction between aromatic aldehydes, malononi-
trile, and phthalhydrazide. Preliminarily, we carried out the
reaction of benzaldehyde with malononitrile and 4-hydroxy-
coumarin as model reaction for optimization of the reaction
Fig. 7 TG (a) and DTG (b)
curves of Fe3−xTixO4@SiO2@
urea NPs
1 3

J IRAN CHEM SOC
conditions. The effects of different reaction parameters like
the catalyst loading, solvent, and temperature were screened
on the model reaction. According to the experimental results
summarized in Table 1, the best results in terms of the reac-
tion rate and yield of the product 2-amino-5-oxo-4-phenyl-
4H,5H-dihydropyrano[3,2-c]chromene-3‑carbonitrile were
obtained when the reaction was carried out in the mixture of
EtOH and H2O (4:1) as the solvent of choice with using the
catalyst loading of 0.01 g under reflux conditions (entry 9).
In addition, the important role of the catalyst in the reaction
was substantiated by conducting the reaction in the absence
of the catalyst under optimized conditions which resulted in
a very low yield of the expected product after a prolonged
reaction time (entry 15). Finally, it was noted that when the
reaction is conducted under ultrasonication at 35 and 50 °C
no improvement of the reaction rates and yields is observed
(entries 13 and 14).
Similarly, to establish the conditions for the synthesis
of 1H-pyrazolo[1,2-b]phthalazine-5,10-diones, we chose
the one-pot condensation reaction between benzaldehyde,
malononitrile, and phthalhydrazide as model reaction.
The effects of the reaction parameters like solvents, cata-
lyst loading, and reaction temperature on the reaction were
screened. Based on the experimental results summarized in
Table 2, the optimal results were obtained for the reaction
under solvent-free condition using the catalyst loading of
0.03 g at 100 °C (entry 13). The necessary involvement of
the catalyst in the reaction was substantiated by conducting
the reaction in the absence of the catalyst for a prolonged
reaction time that resulted in only a trace amount of the
expected product with almost full recovery of the starting
materials (entry 15).
Table 1 Screening the reaction parameters for the synthesis of
2-amino-5-oxo-4-phenyl-4H,5H-dihydropyrano[3,2-c]chromene-
3‑carbonitrilea
To establish the scope and general applicability of
these reactions, a series of variously substituted aldehydes
were reacted under the aforementioned optimized condi-
tions to furnish the corresponding chromenes 2a‑j and
1H-pyrazolo[1,2-b] phthalazine-5,10-diones 3a‑j. Accord-
ing to the experimental results summarized in Tables 3
and 4, all the reactions proceeded smoothly to yield the
respected products in relatively low reaction times and high
yields. Generally, as seen in these tables, the aldehydes
bearing electron-withdrawing substituent groups react
more rapidly in comparison with those carrying electron-
donating groups. This can be attributed to the inductive
and resonance electronic effects of the electron-withdraw-
ing groups which activate the carbonyl group toward the
nucleophilic addition reaction with malononitrile. All the
products are known compounds which are characterized
Entry Catalyst
(g)
Solvent
Tempera- Time
Yield (%)b
ture (°C)
(min)
1
2
3
4
5
0.01
0.01
0.01
0.01
0.01
No solvent 25
120
90
60
90
90
30
32
52
51
65
H2O
25
25
25
EtOH
CH3CN
EtOH/H2O 25
(1:1)
6
0.01
0.01
0.01
0.01
0.03
0.05
0.007
0.01
0.01
EtOH/H2O 25
(4:1)
90
80
60
40
40
40
90
90
90
180
72
7
EtOH/H2O 50
(4:1)
76
8
EtOH/H2O 80
(4:1)
85
1
by their melting points and spectral (FT-IR, H NMR, 13C
9
EtOH/H2O Reflux
(4:1)
98
NMR) analysis and compared with the reported data. The
characteristic data for some selected products are presented
in the experimental section.
10
11
12
13c
14c
15
EtOH/H2O Reflux
(4:1)
96
EtOH/H2O Reflux
(4:1)
92
The superiority and efficiency of the present method
to a number of other reported works are compared for the
synthesis of 4H,5H-dihydropyrano[3,2-c]chromene-3-car-
bonitriles and 1H-pyrazolo[1,2-b]phthalazine-2-carbon-
itriles as summarized in Table 5. Although each of these
methods has their own advantages, they suffer from some
drawbacks such as the use of organic solvent, long reac-
tion time, low yield, and use of non-recyclable catalyst. As
seen in Table 5, the ungrafted Fe3−xTixO4 MNPs exhibited
a very low catalytic activity in comparison with the cata-
lyst Fe3−xTixO4@SiO2@urea and the products were pro-
duced in lower yields and higher reaction times (entries 2
and 10).
EtOH/H2O Reflux
(4:1)
85
EtOH/H2O 35
(4:1)
75
EtOH/H2O 50
(4:1)
86
No cata-
lyst
EtOH/H2O Reflux
(4:1)
Trace
a
Conditions: benzaldehyde (1 mmol), malononitrile (1.2 mmol),
4-hydroxycoumarin (1 mmol), solvent (5 mL)
b
Isolated pure yield
c
Under ultrasonication
1 3

J IRAN CHEM SOC
Table 2 Screening the reaction
parameters for the synthesis
of 3-amino-5,10-dioxo-1-
phenyl-5,10-dihydro-1H-
pyrazolo[1,2-b]phthalazine-2-
carbonitrilea
Entry
Catalyst (g)
Solvent
Temperature (°C)
Time (min)
Yield (%)b
1
0.01
H2O
60
120
120
120
120
120
120
120
120
120
80
20
2
0.01
EtOH
60
38
3
0.01
EtOH/H2O (1:1)
CH3CN
60
32
4
0.01
60
Trace
5
0.01
H2O
Reflux
Reflux
Reflux
Reflux
60
30
6
0.01
EtOH
42
7
0.01
EtOH/H2O (1:1)
CH3CN
37
8
0.01
Trace
9
0.01
No solvent
No solvent
No solvent
No solvent
No solvent
No solvent
No solvent
35
10
11
12
13
14
15
0.01
80
50
0.01
100
100
100
100
100
60
65
0.02
25
83
0.03
10
98
0.05
10
85
No catalyst
180
No reaction
a
Conditions: benzaldehyde (1 mmol), malononitrile (1 mmol), phthalhydrazide (1 mmol), solvent (5 mL)
Isolated pure yield
b
Table 3 Synthesis of
dihydropyranochromenes
catalyzed by Fe3−xTixO4@
SiO2@urea MNPs in EtOH/
H2O under reflux conditionsa
Entry
Ar
Product
Time (min)
Yield (%)b
Mp (°C)
Found
Reported [70–73]
1
2
3
4
5
6
7
8
9
10
C6H5
2a
2b
2c
2d
2e
2f
40
60
35
15
25
15
80
20
10
20
98
86
92
98
95
96
90
96
92
92
254–256
252–254
263–265
250–252
255–258
254–257
264–267
260–263
258–260
264–267
256–257
253–255
265–267
250–251
256–258
252–254
266–268
261–263
256–258
266–268
4-MeC6H4
2-ClC6H4
4-ClC6H4
2,4-Cl2C6H3
4-BrC6H4
4-HOC6H4
3-O2NC6H4
4-O2NC6H4
3-C5H4N
2g
2h
2i
2j
a
Conditions: aldehyde (1 mmol), malononitrile (1.2 mmol), 4-hydroxycoumarin (1 mmol), EtOH/H2O
(4:1) (5 mL), catalyst (0.01 g), reflux temperature
b
Isolated pure yield
1 3

J IRAN CHEM SOC
Table 4 Synthesis of
1H-pyrazolo[1,2-b]phthalazine-
5,10-dione catalyzed by
Fe3−xTixO4@SiO2@urea MNPs
under solvent-free conditions at
100 °Ca
Entry
Ar
Product
Time (min)
Yield (%)b
Mp (°C)
Found
Reported [74–77]
1
2
C6H5
3a
3b
3c
3d
3e
3f
10
10
25
15
20
15
25
10
10
20
95
96
89
94
91
90
87
98
96
90
274–276
269–271
253–255
250–252
262–264
264–267
238–240
269–271
263–265
263–265
276–278
270–272
255–256
259–262
261–263
265–267
240–242
269–271
265–266
260–262
4-ClC6H4
4-MeC6H4
2-ClC6H4
2,3-Cl2C6H3
4-BrC6H4
4-MeOC6H4
3-O2NC6H4
2-O2NC6H4
4-C5H4N
3
4
5
6
7
3g
3h
3i
8
9
10
3j
a
Conditions: benzaldehyde (1 mmol), malononitrile (1 mmol), phthalhydrazide (1 mmol), catalyst
(0.03 g), 100 °C
b
Isolated pure yield
Table 5 Comparison of results
using Fe3−xTixO4@SiO2@urea
MNPs with results obtained by
other works for the synthesis of
2-amino-4-(4-chlorophenyl)-5-
oxo-4,5-dihydropyrano[2,3-c]
chromene-3-carbonitrile
(product A) and 3-amino-1-(3-
nitrophenyl)-5,10-dioxo-5,10-
dihydro-1H-pyrazolo[1,2-b]
phthalazine-2-carbonitrile
(product B)
Entry Catalyst
Condition
Product Yield (%)a Ref.
1
Fe3−xTixO4@SiO2@urea MNPs EtOH/H2O (4:1), reflux, 15 min
A
A
A
A
A
A
A
A
B
B
B
B
B
B
B
B
98
42
80
78
71
35
55
62
98
34
84
92
86
97
89
90
Current
Current
[78]
2
Fe3−xTixO4 MNPs
Nano-Al2O3
S-proline
EtOH/H2O (4:1), reflux, 180 min
EtOH, r.t., 5 h
3
4
H2O/EtOH (1:1), reflux, 3 h
EtOH, reflux, 2 h
[45]
5
Nano-Al(OH)3
p-TSA
[79]
6
H2O/EtOH (1:1), reflux, 60 min
H2O/EtOH (1:1), reflux, 60 min
H2O/EtOH (1:1), reflux, 42 min
[79]
7
Fe3O4/SiO2/Met
SBPPSP
[80]
8
[74]
9
Fe3−xTixO4@SiO2@urea MNPs Solvent-free, 100 °C, 10 min
Current
Current
[81]
10
11
12
13
14
15
16
Fe3−xTixO4 MNPs
Al-KIT-6 (33)
PTSA
Solvent-free, 100 °C, 80 min
EtOH, reflux, 4 h
[bmim]Br, 100 °C, 3.8 h
PEG 400, 70 min
[74]
CAN
[82]
Et3N
Ultrasonication, EtOH, 60 min
80 °C, 50 min
[75]
Glycerol
[77]
NZF@HAP-Cs
Solvent-free, 110 °C, 20 min
[83]
a
Isolated yield
Proposed catalytic reaction mechanisms
NH2 group to produce the intermediate arylidenemalon-
onitrile (I). Subsequently, the catalyst-activated 4-hydrox-
A plausible mechanism to explain the three-component
condensation reactions between aldehydes, malononitrile,
and 4-hydroxycoumarin is depicted in Scheme 3. Likely,
the initial step involves the condensation reaction between
the aldehyde and malononitrile under the catalytic effect
of Fe3−xTixO4@SiO2@urea as a basic nanocatalyst via its
ycoumarin undergoes a Michael-type addition reac-
tion with the intermediate (I) to produce the adduct (II).
Finally, under the catalytic acceleration, intramolecular
nucleophilic cyclization of the intermediate (II) followed
by a 1,3-proton rearrangement to furnish the expected
1,4-dihydropyranochromen-2-ones.
1 3

J IRAN CHEM SOC
Scheme 3 Possible mecha-
nism for the synthesis of
4H-chromenes catalyzed by
Fe3−xTixO4@SiO2@urea
A similar pathway can be suggested for the synthesis of
1H-pyrazolo[1,2-b]phthalazine-5,10-diones as illustrated in
Scheme 4. Likewise, the initial step in this reaction involves
the condensation of aromatic aldehydes with malononitrile
under the catalytic effect of the nanocatalyst Fe3−xTixO4@
SiO2@urea to produce the intermediate arylidenemalo-
nonitrile (I). Subsequently, the catalyst-activated phthal-
hydrazide undergoes the Michael-type addition to the
intermediate (I) followed by successive intramolecular
cyclization and tautomerization steps to afford the respec-
tive 1H-pyrazolo[1,2-b]phthalazine-5,10-dione products.
Catalyst recyclability
Recycling experiments were performed on the model
reaction between 3-nitrobenzaldehyde, malononitrile,
1 3

J IRAN CHEM SOC
Scheme 4 Possible mecha-
nism for the synthesis of
1H-pyrazolo[1,2-b] phthala-
zine-5,10-dione catalyzed by
Fe3−xTixO4@SiO2@urea
and 4-hydroxycoumarin under the optimized conditions.
After completion of the reaction, the catalyst was mag-
netically separated from the reaction mixture, washed with
hot ethanol, and reused for at least five fresh runs without
significant loss of its catalytic activity (Fig. 8). Based on
the IR analysis, the integrity of the recovered catalyst was
examined and proved to be as active as the originally used
sample.
Conclusion
In conclusion, we have successfully prepared the magnetic
nanocatalyst Fe3−xTixO4@SiO2@urea and fully charac-
terized by FT-IR, SEM, HRTEM, EDX, TGA, VSM, and
XRD analytical techniques. This newly prepared nano-
catalyst has been explored as an efficient, versatile, and
selective heterogeneous nanocatalyst with basic nature
1 3

J IRAN CHEM SOC
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