Fe3O4@PEG-SO3H rod-like morphology along with the spherical nanoparticles: Novel green nanocomposite design, preparation, characterization and catalytic application

Article abstract of DOI:10.1039/c6ra24029a

The design and preparation of polyethylene glycol sulfonic acid surface coated magnetic nanoparticles (Fe₃O₄@PEG-SO₃H) is described. The morphology of the prepared nanocomposite was rod-like along with spherical nanopartic

Full text of DOI:10.1039/c6ra24029a

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Fe3O4@PEG-SO3H rod-like morphology along with
the spherical nanoparticles: novel green
nanocomposite design, preparation,
Cite this: RSC Adv., 2016, 6, 110928
characterization and catalytic application†
*
Ali Maleki, Pedram Zand and Zahra Mohseni
The design and preparation of polyethylene glycol sulfonic acid surface coated magnetic nanoparticles
(Fe3O4@PEG-SO3H) is described. The morphology of the prepared nanocomposite was rod-like along
with spherical nanoparticles. It was characterized by Fourier transform infrared (FT-IR) spectroscopy,
field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), energy-dispersive X-ray
(EDX), vibrating sample magnetometry (VSM), N2 adsorption–desorption by Brunauer–Emmett–Teller
(BET) and inductively coupled plasma (ICP) analysis. Furthermore, this novel heterogeneous catalyst was
Received 27th September 2016
Accepted 16th November 2016
successfully used in
a multicomponent one-pot reaction for the synthesis of dihydropyrimidine
derivatives. This efficient protocol includes some other advantages such as using ethanol as a green
solvent, no significant decrease in the activity of the nanocatalyst during the recovery process, relatively
short reaction times and high-to-excellent yields of the products.
DOI: 10.1039/c6ra24029a
www.rsc.org/advances
the synthesis of PEG-coated MNPs is of prime importance.
Although, a few strategies have been reported in the literature
Introduction
for the modication of PEG-based MNPs, the synthetic pathway
was remained almost complicated up to now. In other words,
most of them suffer from harsh reaction conditions.8 For
example, in a typical work, reuxing temperature (above 200 ꢀC)
has been applied for the synthesis of PEG-coated MNPs.9
Dihydropyrimidines (DHPMs) are well-known scaffolds that
are easily prepared through the condensation reaction of urea/
thiourea, b-ketoesters and aryl aldehydes.10 DHPMs have
a signicant role in medicinal chemistry because of their
various pharmacological activities such as anticancer, antibac-
terial, antifungal, antihypertensive, antitubercular, antima-
larial, antiviral and anti-inammatory.11–13 Therefore, design
and development of inexpensive, general, and reusable catalysts
in conjunction with multicomponent reactions strategy for the
synthesis of DHPMs is of prime importance.
In continuation of our research on the introduction of new
recoverable nanocatalysts and their applications in organic
synthesis,14–18 herein, we wish to report a convenient and facile
multicomponent one-pot synthesis of DHPMs 4a–l via the
condensation of b-ketoesters 1, aldehydes 2 and urea or thiourea
3 in the presence of Fe3O4@PEG-SO3H as a superparamagnetic
heterogeneous nanocatalyst (Scheme 1).
Recently, due to importance of catalysts and catalytic reactions
in chemical research and industry, the catalytic performances
of heterogeneous catalysts compared to their counterpart
homogeneous ones have been widely improved by bringing the
catalysts to the nanoscale to provide higher surface area and
enhance the contact frequency between them and the reaction
components.1–4 Supported magnetic nanoparticles (MNPs) are
important in the eld of green chemistry. MNPs are typically
surface-modied or coated with biocompatible polymers which
improve their colloidal stability in physiological media and
reduce toxicity. MNPs have found various applications in
different disciplines such as biomedicine, catalysis, biosepara-
tion, data storage, magnetic resonance imaging, etc. Fe3O4
nanoparticles are attractive because of their low cost, reactive
surfaces, high specic surface area and easy separation.
Recently, a few functionalized Fe3O4 MNPs have been employed
in a wide variety of organic reactions.5,6
Polyethylene glycol (PEG) is an important biocompatible
synthetic polymer that could be used as a coating agent for
nanoparticles. Due to its unique properties such as extremely
hydrophilic nature (hydrophilicity), exibility, non-toxicity and
nonimmunogenicity,7 the introduction of any new protocol for
To the best of our knowledge, this is the rst report on design,
preparation and characterization of Fe3O4@PEG-SO3H nano-
composite and its application as a novel, efficient, eco-friendly
catalyst in chemical reactions, especially in organic synthesis
such as DHPMs. Furthermore, the surface modication procedure
Catalysts and Organic Synthesis Research Laboratory, Department of Chemistry, Iran
University of Science and Technology, Tehran 16846-13114, Iran. E-mail: maleki@
iust.ac.ir; Fax: +98 21 73021584; Tel: +98 21 77240540
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c6ra24029a
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Results and discussion
Characterization of the prepared Fe3O4@PEG-SO3H
nanocatalyst
Fe3O4@PEG-SO3H nanocatalyst was prepared by in situ co-
precipitation method. As can be seen in Fig. 1, the FT-IR spec-
trum of the Fe3O4@PEG-SO3H magnetic nanocatalyst can verify
the preparation of the expected product. The bending vibration
band at 584 cmꢁ1 and stretching vibration band at 1627 cmꢁ1 is
induced by structure Fe–O vibration. A broad O–H stretch
around 3419 cmꢁ1 was observed in both Fe3O4 and the PEG
coated MNPs. The C–H stretching vibrations observed at 2852
and 2923 cmꢁ1 indicate that the PEG was successfully
composed onto the surfaces of Fe3O4 nanoparticles. The func-
tionalization of SO3H groups on Fe3O4@PEG surface was
approved by the absorption band at 1124 cmꢁ1 of the S]O
stretching vibrations.
To clarify the morphology of the nanocatalyst, FE-SEM
images of Fe3O4@PEG-SO3H were provided (Fig. 2). It can be
seen that the nanocatalyst was uniformly prepared and the
main structure of nanocatalyst was rod-like morphology along
with the spherical iron oxide (II, III) nanoparticles. In addition,
the nanosized structure and morphology of the catalyst was
proved by FE-SEM images.
Scheme 1 Fe3O4@PEG-SO3H catalyzed synthesis of DHPMs 4a–l.
The result of the EDX analysis of the Fe3O4@PEG-SO3H
magnetic nanoparticles was illustrated in Fig. 3. It conrms
the presence of carbon, oxygen and sulfur elements in the
nanocatalyst.
Fig. 4 shows the XRD measurements were performed with
the dried powder samples of bare and PEG coated MNPs to
identify the crystal phases present in the samples. The XRD
pattern of a representative Fe3O4@PEG-SO3H (curve a) along
with bare Fe3O4 NPs (curve b). The pattern of the Fe3O4@PEG-
SO3H showed all the major peaks corresponding to Fe3O4. The
diffraction angles (2q) of 30.28, 35.64, 43.28, 57.24, 62.87 and
74.42 can be assigned to 2 2 0, 3 1 1, 4 0 0, 5 1 1, 4 4 0, and 5 3 3
planes, respectively; which are in accordance with Fe3O4 refer-
ence pattern (JCPDS#19-0629). Additionally, one peak around 2q
¼ 25ꢀ along with small peaks due to the PEG-SO3H polymer are
observed in the case of the Fe3O4@PEG-SO3H. These results
Fig. 1 The comparative FT-IR spectra of: (a) Fe3O4, (b) Fe3O4@PEG
and (c) Fe3O4@PEG-SO3H.
described in this work can be classied as a green protocol
because of using water and ethanol as solvents, room temperature
reactions, and safe and simple reaction conditions.
Fig. 2 FE-SEM images of Fe3O4@PEG-SO3H rod-like nanocatalyst with different magnifications: (a) 10 mm and (b) 200 nm.
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Fig. 3 EDX analysis of Fe3O4@PEG-SO3H nanocatalyst.
Fig. 5 VSM magnetization curves of: (a) Fe3O4, (b) Fe3O4@PEG and (c)
Fe3O4@PEG-SO3H.
conrmed the surface modication of the Fe3O4 NPs with PEG-
SO3H.
The magnetic properties of Fe3O4, Fe3O4@PEG and Fe3O4@-
PEG-SO3H were measured by VSM curves at room temperature.
As can be seen in Fig. 5, the hysteresis loops of the super-
paramagnetic behavior can be clearly observed for all the nano-
particles. The superparamagnetism is responsible to an applied
magnetic eld without retaining any magnetism aer removal of
the applied magnetic eld. From M versus H curves, the saturation
magnetization value (Ms) of uncoated MNPs was found to be 56
emu gꢁ1. For Fe3O4@PEG and Fe3O4@PEG-SO3H the magneti-
consequence/conrmation of immobilization of PEG-OSO3H on
Fe3O4 nanoparticles.
Catalytic application of Fe3O4@PEG-SO3H in the synthesis of
DHPMs
Initially, to optimize the reaction conditions for the synthesis of
DHPMs, various parameters were studied on the reaction of b-
zations obtained at the same eld were 38 and 27 emu gꢁ1
,
respectively, those were lower than neat Fe3O4 nanoparticles. This
is mainly attributed to the existence of materials on the surface of
the nanoparticles. The photograph of the magnetic separation of
catalyst from the organic reactions mixture was shown in Fig. 5.
Furthermore, inductively coupled plasma (ICP) analyses of
the catalysts revealed that the metal (Fe) content of the catalyst
(ꢂ0.4%) were close to target metal content (12.24 wt%).
Table 1 Optimizing of the reaction conditions
Nano-Fe3O4@PEG-SO3H
(g)
Time
(min)
Yield
(%)
Entry
Solvent
1
2
3
4
5
6
7
8
9
0.005
0.010
0.015
0.020
0.010
0.010
0.010
0.010
0.010
EtOH
EtOH
EtOH
EtOH
MeOH
H2O
MeCN
DMF
70
20
70
95
75
60
65
40
43
55
35
100
110
125
90
130
100
90
The specic surface area of Fe3O4@PEG-SO3H was measured
by using Brunauer–Emmett–Teller (BET) analysis with N2
adsorption–desorption. BET surface area of Fe3O4@PEG-SO3H
was 43.86 m2 gꢁ1. The reduced amount of surface area in
comparison with iron oxide (II, III) nanoparticles may be the
Solvent-free
Fig. 4 The XRD pattern of: (a) Fe3O4@PEG-SO3H and (b) Fe3O4. The symbol ‘*’ represents the PEG-SO3H peak.
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Table 2 A comparison of some catalysts effects with the present nanocatalyst on the model reaction
Entry
Catalyst
Temperature (ꢀC)
Time
Yield (%)
Ref.
1
2
3
4
5
6
7
8
9
10
Nano-Fe3O4@PEG-SO3H
Nano-Fe3O4@PEG
Nano-Fe3O4
PEG-SO3H
PEG
r.t.
r.t.
r.t.
r.t.
20 min
45 min
50 min
60 min
48 h
8 h
48 h
6 h
5 h
95
90
85
80
75
15
77
91
80
56
This work
This work
This work
This work
This work
This work
19
20
21
22
r.t.
—
100
130
Reux
Reux
100
Montmorillonite KSF
Silica–sulfuric acid
H3PMo12O40
ZrOCl2$8H2O
2 h
diketone (2 mmol), aromatic aldehyde (2 mmol) and urea or
thiourea (2.4 mmol), as a pilot test. First, the effect of the
catalyst amount on the reaction yield was studied. It was found
that using 0.010 g of the Fe3O4@PEG-SO3H nanocatalyst is
sufficient to complete the reaction and give 4a aer 20 min in
95% yield in 4 mL of EtOH as a green solvent at room temper-
ature. The results summarized in Table 1. To compare the
efficiency of ethanol, several solvents with different polarities
were tested using the model reaction in the presence Fe3O4@-
PEG-SO3H. As it obvious from the results, it was found that
ethanol is the superior solvent for this study than MeOH, H2O,
MeCN and DMF in the presence of 0.010 g of Fe3O4@PEG-SO3H
catalyst at room temperature.
Finally, a comparison was done between the present work
and others earlier reports for the synthesis of 4a. The results
summarized in Table 2 clearly demonstrate the superiority of
the present work in saving energy, high yields of the products
and the reusability of the nanocatalyst.
In order to investigate the scope and limitations of the
present protocol and to show the application of Fe3O4@PEG-
SO3H in the synthesis of DHPMs, a variety of products were
synthesized under the optimized conditions. The results
summarized in Table 3 shows that all products were obtained in
good-to-excellent yields aer appropriate reaction times. The
Table 4 Calculated values of turnover number (TON) and turnover
frequency (TOF) for DHPMs
Entry
Product
TON
TOF/hꢁ1
1
2
3
4
5
6
7
8
4a
4b
4c
4d
4e
4f
4g
4h
4i
67.857
57.142
60
57.142
60
65.714
67.857
60.714
65.714
63.571
64.285
60.714
3.392
0.816
1.333
0.952
1.333
1.877
2.261
1.214
1.194
1.558
1.607
1.103
9
10
11
12
4j
4k
4l
corresponding reaction yields, TON and TOF values are also
listed in Table 4.
The suggested possible mechanism for the formation of
DHPMs 4a–l is shown in Scheme 2. On the basis of the
literature and substrates chemistry, the rst step is believed
to be the condensation between an aldehyde and urea or
thiourea in the presence of Fe3O4@PEG-SO3H, similar to the
Table 3 Synthesis of DHPMs 4a–l by using Fe3O4@PEG-SO3H nanocatalyst
Mp (ꢀC)
Found
Entry
R1
R2
X
Product
Time (min)
Yielda (%)
Reported
1
2
3
4
5
6
7
8
Et
4-Cl
O
S
4a
4b
4c
4d
4e
4f
4g
4h
4i
20
70
45
60
45
35
30
50
30
55
40
55
95
80
84
80
84
92
95
85
92
84
90
85
213
153
222
195
221
213
180
201
243
182
180
203
212–214 (ref. 23)
153–155 (ref. 24)
220–222 (ref. 25)
194–195 (ref. 26)
221–222 (ref. 27)
213–214 (ref. 28)
179–180 (ref. 29)
201–203 (ref. 30)
241–243 (ref. 31)
181–185 (ref. 32)
178–180 (ref. 33)
204–206 (ref. 34)
Me
Me
Me
Et
Et
Et
Et
Me
Et
Et
Et
4-OMe
3-OH
4-OMe
3-OH
4-Br
4-Cl
H
4-Cl
3-OH
4-Br
H
O
O
O
O
S
O
S
S
9
10
11
12
4j
4k
4l
S
S
a
Isolated yield.
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Scheme 2 The proposed mechanism for the formation of DHPMs in the presence of Fe3O4@PEG-SO3H nanocatalyst.
Mannich condensation reaction. The produced iminium 5
acts as an electrophile for the nucleophilic addition of the
Conclusions
ketoester carbanion 6 (obtained from 1 attached by anion
form of the nanocatalyst) to yield intermediate 7. Then, the
carbonyl group of ketone of the resulting adduct undergoes
condensation with the NH2 of urea part to give the compound
8. Finally, an imine–enamine tautomerization of 8 leads to
the formation of the products 4.10
In summary, Fe3O4@PEG-SO3H as a novel, highly efficient,
simple, green and cost-effective, environmentally-friendly and
reusable superparamagnetic nanocatalyst was described. It was
prepared through a facile process and completely characterized
by FT-IR spectroscopy, FE-SEM images, XRD pattern, EDX, VSM,
BET and ICP analyses. Then, the catalytic property of the
nanocomposite was investigated in the synthesis of DHPMs.
The products were obtained in high-to-excellent yields at room
temperature under simple reaction conditions. The nano-
catalyst was easily recovered by an external magnet and reused
efficiently for the several runs without signicant decrease in
activity. This is the rst report on design, in situ synthesis,
functionalization and characterization of the present nano-
composite and also performance as a heterogeneous catalyst in
organic reactions.
Recyclability of Fe3O4@PEG-SO3H nanocatalyst
The reusability of Fe3O4@PEG-SO3H catalyst was studied in the
model reaction. In this regard, aer completion of the reaction,
the nanocatalyst were separated by an external magnet and
washed with ethanol and water, dried and reused in subsequent
reactions. It was observed that the catalyst can be reused at least
six times without any signicant decrease in yield of the prod-
ucts (Fig. 6).
Experimental
General
All the solvents, chemicals and reagents were purchased from
Merck, Sigma and Aldrich. Melting points were measured on
an Electrothermal 9100 apparatus and are uncorrected. Fourier
transforms infrared spectroscopy (FT-IR) spectra were recorded on
a Shimadzu IR-470 spectrometer by the method of KBr pellet. 1H
and 13C NMR spectra were recorded on a Bruker DRX-300 Avance
spectrometer at 300 and 75 MHz, respectively. Field-emission
scanning electron micrograph (FE-SEM) images were taken
with Sigma-Zeiss microscope with attached camera. Magnetic
measurements of the solid samples were performed using Lake-
shore 7407 and Meghnatis Kavir Kashan Co., Iran vibrating sample
magnetometers (VSMs). Elemental analysis of the nanocatalyst was
carried out by energy-dispersive X-ray (EDX) analysis recorded
Numerix DXP-X10P. X-ray diffraction patterns of the solid powders
Fig. 6 Recycling of Fe3O4@PEG-SO3H nanocatalyst in the synthesis of
4a.
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were recorded with a X' Pert Pro X-ray diffractometer operating at
40 mA, 40 kV. The specic surface area was measured via BET N2
adsorption–desorption method by using a Nansord92 instrument.
Inductively coupled plasma (ICP) analysis was provided on a Shi-
madzu ICPS-7000.
Acknowledgements
The authors gratefully acknowledge the partial support from
the Research Council of the Iran University of Science and
Technology.
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