Synthesis and characterization of supramolecule grafted on modified magnetic nanoparticles: new hybrid organic–inorganic phase transfer catalyst

Article abstract of DOI:10.1007/s00706-016-1759-x

Abstract: In this study, for the first time, calix[4]resorcinarene was grafted on the silica-coated magnetic nanoparticles (MNPs-Si) which efficiently catalyze one-pot epoxide ring opening reaction in excellent yields in a very short reaction time. Variou

Full text of DOI:10.1007/s00706-016-1759-x

Monatsh Chem
DOI 10.1007/s00706-016-1759-x
ORIGINAL PAPER
Synthesis and characterization of supramolecule
grafted on modified magnetic nanoparticles: new hybrid
organic–inorganic phase transfer catalyst
Arash Mouradzadegun1 Sadjad Boroon1 Pegah Kazemian Fard1
•
•
Received: 4 December 2015 / Accepted: 11 April 2016
Ó Springer-Verlag Wien 2016
Abstract In this study, for the first time, calix[4]resor-
cinarene was grafted on the silica-coated magnetic
nanoparticles (MNPs-Si) which efficiently catalyze one-pot
epoxide ring opening reaction in excellent yields in a very
short reaction time. Various advantages associated with
this protocol include simple workup procedure, short
reaction times, and high product yields. High catalytic
activity and ease of recovery, using an external magnetic
field, are additional eco-friendly attributes of this catalytic
system.
Introduction
Nanotechnology is a multidisciplinary branch of science
which encompasses numerous applications in a variety of
fields including electronics, optics, magnetism, energy
technology, and chemistry [1–6]. The advent of nanopar-
ticles has opened up a new era in many different fields of
studies along with other nanomaterials and it should be
noted that the field of catalyst has also been influenced.
Organic/inorganic hybrid nanomaterials with controllable
chemical compositions and structures, large surface-to-
volume ratios, various surface properties, and functionali-
ties can be regarded as fascinating nanotechnological
objects with many optical, electrical, antibacterial, and
catalytic properties [7, 8]. Among these, magnetic
nanoparticles have emerged as a robust, high surface area
heterogeneous catalyst support; they are good alternatives
to filtration or centrifugation [9–13]. This strategy reduces
the loss of catalyst and enhances reusability, rendering the
catalyst cost-effective and promising for industrial
applications.
Graphical abstract
O
O
Si
O
1) NH3 / 90 C / 1 h
°
2) Tetraethyl orthosilicate
A
A
O
OH
.
FeCl3 6H2O
=A
MNP
.
O
FeCl2 4H2O
A
OMe
O
3)
MeO
MeO
HO
Si
Si
O
Cl
OH
HO
OH
OH
HO
O
O
HO
HO
4)
4
As many studies have demonstrated the potential of
supramolecular science, the cis-calix[4]resorcinarene have
been interested by many chemists in recent years. These
compounds are large cyclic tetramers with diverse appli-
cation as macrocyclic receptors, such as dendrimers in
biological systems, nanocapsules, nanoparticles, optical
chemosensors, and supramolecular tectons as components
in liquid crystals, molecular switches, selective mem-
branes, HPLC stationary phase as ion channel mimics [14–
17].
Keywords Nanostructures Á Magnetic properties Á
Heterogeneous catalysis Á Nucleophilic additions Á
Phase-transfer catalysis Á Supramolecular chemistry
Electronic supplementary material The online version of this
article (doi:10.1007/s00706-016-1759-x) contains supplementary
material, which is available to authorized users.
& Arash Mouradzadegun
arash_m@scu.ac.ir
In addition, cis-calix[4]resorcinarenes possess a cup-like
hydrophobic cavity surrounded by hydrophilic groups, and
these properties allow them to be used as phase transfer
catalyst. The possibility of modifying these structures
1
Department of Chemistry, Faculty of Science, Shahid
Chamran University of Ahvaz, Ahvaz 61357-4-3169, Iran
123

A. Mouradzadegun et al.
either via the phenol hydroxyl groups or substitutions on
the aromatic ring or even from the lower rim resulted in an
increase in their potential to form multifunctional
compounds.
Results and discussion
Scheme 1 shows the schematic representation of the
sequence synthetic pathway for MNPs-Si-resorcinarene
catalyst. Magnetite nanoparticles were prepared with lit-
erature method [22]. These particles are easily prepared by
adding a base to an aqueous mixture of Fe2? and Fe3?
chloride then silica-coated magnetite (Fe3O4/SiO2 core/
shell) nanoparticles was synthesized. Moreover, the coating
of MNPs-Si with resorcinarene can be easily accomplished
using inexpensive and routine chemicals 3-chloropropyl-
triethoxysilane (CPTES) (Scheme 1). To confirm the
coating of the magnetite surface through the silylation
reaction and verify the formation of hybrid nanocomposite,
FT-IR spectra of MNPs-Si-resorcinarene in the region of
400–4000 cm-1 (Fig. 1).
In this context and in continuation of our previous
studies [18–20], a heterogeneous catalyst has recently been
developed based on calix[4]resorcinarene immobilized on
silica-coated magnetic nanoparticles as an efficient phase-
transfer catalyst in the synthesis of azidohydrins. Although
a variety of new and mild procedures to effect this trans-
formation have been reported, most of them have some
limitations [21]. Therefore, in this report, a probable
application is introduced and described for the synthesized
nanomaterial which overcomes these limitations for the
transformation of epoxides to b-azidohydrins as a new
nanocatalyst (Scheme 1).
Scheme 1
O
O
Si
O
°
1) NH3 / 90 C / 1 h
A
A
O
OH
2) Tetraethyl orthosilicate
.
.
FeCl3 6H2O
=A
MNP
O
4H
FeCl2
2O
A
OMe
O
3)
MeO
MeO
HO
Si
Si
O
Cl
OH
HO
OH
OH
HO
O
O
HO
HO
4)
4
Fig. 1 FT-IR spectra of
calix[4]resorcinarenes
immobilized on modified
magnetic nanoparticles
123

Synthesis and characterization of supramolecule grafted on modified magnetic nanoparticles:…
Fig. 2 XRD pattern of prepared
calix[4]resorcinarenes
immobilized on modified
magnetic nanoparticles
The IR spectra of MNPs-Si-resorcinarene shows peak in
the range of 3500–3200 cm-1 attributed to the hydroxyl
stretching of internal phenol hydroxyl groups. The propyl
groups attached to the resorcinarene framework in MNPs-
Si-resorcinarene are identified by methylene stretching
bands at 2959 and 2870 cm-1. A strong peak near
1100 cm-1 is attributed to corresponding to the Si–O–Si
stretch of linker and MNPs-Si. The peaks at 1604 and
1450 cm-1 were due to the C–C skeleton vibration of
aromatic ring. Thus, FT-IR spectroscopy provides a good
evidence for the formation of MNPs-Si-resorcinarene.
X-ray diffraction shows the large-angle XRD patterns of
these samples in Fig. 2. The XRD pattern of Fe3O4 clearly
showed some reflection peaks and confirmed the formation of
a cubic spinel ferrite structure (JCPDS No. 19-0629) in
Fig. 2a. The same reflection peaks appeared in the XRD
patternsofthesynthesizedsamplesofMNPs-Si-resorcinarene
in Fig. 2b, which suggested that the Fe3O4 crystallite phase
was still maintained in the MNPs-Si-resorcinarene nanopar-
ticles. The broad peaks indicate the higher degree of
crystalline nature of the prepared material (Fig. 2a, b).
image shows the aggregation of the hollow MNPs-Si-re-
sorcinarene spheres and also indicates that the obtained
nanoparticles are composed of nearly uniform nanospheres
with some agglomerations (Fig. 3).
The nanoparticle size and morphology of MNPs-Si-re-
sorcinarene were investigated by TEM. Figure 4 shows the
TEM image of the synthesized samples MNPs-Si-resor-
cinarene, although aggregated phenomenon of some
nanoparticles was also observed, the particle diameters of
the nanoparticles have spherical morphologies and
monodispersed with less than 100 nm average diameter
range, which is in agreement with the SEM observation. It
indicated that the chemical modification of the Fe3O4 did
not cause the significant increase of the particle size, and
the advantages of magnetic nanoparticles can be main-
tained (Fig. 4).
To study the magnetic properties of magnetite nanopar-
ticles before and after silica coating, silica particles, the
hysteresis loops of magnetite nanoparticles and magnetic
silica particles and also resorcinarene-linker groups at room
temperature using vibrating-sample magnetometer were
registered shown in Fig. 5a. The inset of Fig. 5 is the
magnetization curve of magnetite nanoparticles, showing
A typical scanning electron micrograph of the prepared
MNPs-Si-resorcinarene is shown in Fig. 3. The SEM
123

A. Mouradzadegun et al.
Fig. 3 SEM image of
calix[4]resorcinarenes
immobilized on modified
magnetic nanoparticles
Fig. 4 TEM image of
calix[4]resorcinarenes
immobilized on modified
magnetic nanoparticles
Fig. 5 VSM magnetization
curve of a the Fe3O4
nanoparticles, b the silica
coated Fe3O4 nanoparticles, and
c calix[4]resorcinarenes
immobilized on modified
magnetic nanoparticles
magnetic property and saturation magnetization of about
60 emu/g of magnetite nanoparticle.
The thermal behavior of MNPs-Si-resorcinarene was
investigated by TGA analysis. Figure 6 shows the TGA
curve for the prepared MNPs-Si-resorcinarene. Four dif-
ferent slops can be observed from the TGA curve in Fig. 6
as a function of temperature. At first, the absorbed water
was heated at 147 °C, due to the hydrophobic nature of the
prepared nanocomposite material, the amount of adsorbed
water was only 4 % wt. The second weight loss step of
about 20 % started from the region of 195 °C was due to
the cleavage of the linker grafted to resorcinarene, then the
degradation at 375 °C, probably, is due to the thermal
As it could be seen in Fig. 5b, c similar to magnetite
nanoparticles, surface coating of the magnetite nanoparti-
cles with silica and MNPs-Si-resorcinarene shows super
paramagnetic behaviors, indicating that magnetite
nanoparticles remained in the composite particles. Slight
decrease of the saturation magnetization of the MNPs-Si-
resorcinarene was due to the successful grafting of
calix[4]resorcinarene on the surface of Fe3O4 nanoparticles
(Fig. 5).
123

Synthesis and characterization of supramolecule grafted on modified magnetic nanoparticles:…
Fig. 6 TGA curve of prepared
calix[4]resorcinarenes
immobilized on modified
magnetic nanoparticles
decomposition of resorcinarene units. When temperature is
up to 600 °C, organics are completely denatured and only
magnetic nanoparticles remain. Thus, the TGA curves also
confirm the excellent chemical stability of this compound
in high temperature (Fig. 6).
With cyclic epoxides, the ring opening completely took
place via a trans-stereospecific pathway and giving only the
trans isomers (Table 2, entry 6). This reaction was per-
formed in short time with excellent yield. In case of acyclic
terminal olefins (Table 1, entries 3–5), the major product
results from the attack of nucleophile at the less substituted
carbon to give 1,2-azidoalcohol in good to excellent yields.
The catalytic performances of this reusable catalyst were
compared with some of the other literatures for the model
reaction under optimized conditions (Table 1, entry 1). The
results show a greater superiority of catalyst. It can be seen
that the heterogeneous catalyst exhibited a significantly
higher turnover number and turnover frequency than those
reported for other catalytic systems (Table 1, entries 2-5).
The structure of all the products was settled from their
Epoxides are widely used in organic synthesis reactions
of the fine chemicals and pharmaceutical industries [22].
The azidolysis of phenyl glycidyl ether (1 mmol), sodium
azide as a test reaction was carried out to investigate the
catalytic properties of the prepared MNPs-Si-resorcinarene
(Scheme 2).
TLC analysis of the reaction mixture shows the com-
pletion of the reaction after 75 min and produced 1-azido-
3-phenoxy-2-propanol in quantitative yield (Table 2, entry
1). To show the general applicability of the method and
also ability of MNPs-Si-resorcinarene as nanomagnetic
phase-transfer catalyst and molecular host system, the ring
opening epoxide with this catalyst was applicable for a
wide range of epoxides in Table 2.
1
analytical and spectral (IR, H NMR) data and by direct
comparison with authentic samples. Obviously, in the
absence of MNPs-Si-resorcinarene or in the presence of the
initial resorcinarene, the reaction was found to exhibit very
negligible activity and even after prolonged reaction time a
considerable amount of starting material was remained.
It is presumable that, the catalytic activity of MNPs-Si-
resorcinarene as a phase transfer catalyst in ring opening
epoxides reaction could be attributed to formation inclu-
sion complex epoxide with hydrophobic porous of
functionalize resorcinarene, and via hydrogen bonding of
the epoxide oxygen to the outer OH of resorcinarene. In
addition, bare azide anion transfer and react with immo-
bilized epoxide. Therefore, the high selectivity and shorter
reaction time could be explained by this method.
Because of the predominant attack of azide ion on the
less hindered carbon of the epoxide, all the terminal
epoxides gave highly regioselective azidohydrins in quan-
titative yields. Due to formation of the stabilized benzylic
cation during the reaction, ring opening of styrene oxide
with NaN3 resulted in 2-azido-2-phenylethanol as the
major product with selectivity 80:20 (Table 2, entry 2).
Scheme 2
N3
OH
O
NaN3 (3 mmol)
Cat
+
N3
OH
It is worthy to note that reusability of the catalyst was an
important character and a performance criterion of any
industrial process. In this method, the catalyst can be
Ph
Ph
Ph
I
II
123

A. Mouradzadegun et al.
Table 1 Comparison of the catalytic performance of catalyst with other literatures
Entry
Reactant
Catalyst
Solvent
Temp.
Time/min
Yield/%
References
1
2
3
4
5
6
NaN3
Nanocatalyst
b-cyclodextrine
PEG-300
H2O
80 °C
r.t
75
93
45
90
85
86
85
Present work
[23]
TMSN3
NaN3
H2O
300
60
Solvent free
H2O
60 °C
Reflux
r.t
[24]
NaN3
MPTC
30
[25]
TMSN3
NaN3
Er(OTf)3
Solvent free
H2O
400
75
[26]
[pbmim](fecl4)2
Reflux
[27]
Fig. 7 Recyclability of catalyst
Recyclability of catalyst
100
89
88
85
90
80
70
60
50
40
30
20
10
0
83
0
1
2
3
4
Number of cycle
separated by simple magnetic decantation using a perma-
nent magnet at the end of reaction, and reused after
washing with ethanol and then drying in vacuum at 60 °C
for 8 h. The nanocatalyst could be reactivated in a very
easy way. No addition of acid, base, and special reagent,
were needed during the reactivation. In every cycle, the
nanocatalyst recovery was almost quantitative. After the
third cycle, the yield was slightly decreased, indicating that
the catalyst possessed an excellent reusability under the
reaction conditions. The drop of product yield at the 4th
catalytic cycle may be due to the clogging of some of
effective nanoporous sites by reagents or even eluent
(Fig. 7).
part is isolated and protected by the dense silica shell; thus,
making its use under harsh reaction conditions possible.
The high surface area of the mesoporous shell means that it
can accommodate large amounts of the resorcinarene
which can increase acidity, making the catalyst highly
active. In addition, magnetic core can be readily utilized
for the easy recovery and recycling of the catalyst with no
significant loss of catalytic activity.
Experimental
Iron(II) chloride tetrahydrate (99 %), iron(III) chloride
hexahydrate (98 %), epoxides, and other chemical materi-
als were purchased from Fluka and Merck and used
without further purification. The products were character-
ized by the comparison of their physical data, FT-IR and
1H NMR and 13C NMR spectra with known samples. NMR
spectra were recorded in CDCl3 on a Bruker Avance DPX
400 MHz spectrometer using TMS as internal standard.
The purity determination of the products and reaction
monitoring were accomplished by TLC on silica gel
polygram SILG/UV 254 plates. The TGA curve was
recorded on a BAHR, SPA 503 at heating rates of 10 °C
Conclusion
The novel design and synthesis of calix[4]resorcinarene
was immobilized on modified magnetic nanoparticle. In
addition, some characterizations and one of the probable
application of this nanomaterial as a new magnetically
recyclable and efficient nano-phase transfer catalyst was
investigated. This catalyst exhibits several attractive fea-
tures for the synthesis of fine chemicals. The magnetic core
123

Synthesis and characterization of supramolecule grafted on modified magnetic nanoparticles:…
min-1. The thermal behavior was studied by heating
1–3 mg of samples in aluminum-crimped pans under
nitrogen gas flow, over the temperature range of
25–500 °C.
mixture of ethanol and deionized water (1:1) by sonication
and heated to reflux, then 1 mmol of the 3-chloropropyltri-
ethoxysilane was added to the mixture. After mechanical
agitation of mixture for 24 h, for immobilizing resorcinarene
with 3-chloropropyltriethoxysilane grafted surface of MNPs-
Si, 0.2 g of the calix[4]resorcinarene was added to a mag-
Preparation of magnetic nanoparticles grafted resor-
cinarene (MNPs-Si-resorcinarene)
netically
stirred
mixture
of
1.0 g
MNPs-Si-resorcinarene involved some steps. First, mag-
netic nanoparticles (MNPs) were prepared via improved
chemical coprecipitation method [28]. Silica coating of
iron oxide nanoparticle was carried out using modified
reported methods [29, 30], tetramethylcalix[4]resor-
cinarene was obtained by the condensation of resorcinol
with acetaldehyde [30], dried at 70 °C for 6 h before using.
3-chloropropyltriethoxysilane grafted on MNPs-Si in
50 cm3 toluene, 0.5 g potassium carbonate, and 0.02 g
tetrabutylammonium bromide, and then heated to reflux and
stir vigorously in nitrogen atmosphere for 24 h.
The mixture was then filtered, washed with 60 cm3
ethanol then dried at room temperature to give the mag-
netic nanoparticles grafted on the upper rim of
calix[4]resorcinarenes. The precipitation was separated by
magnetic decantation and washed with ether several times.
Product was dried in vacuum at 50 °C for 12 h.
In the second step, for introducing of 3-chloropropyltri-
ethoxysilane onto the surface of the magnetic nanoparticles,
0.4 g MNPs-Si powder was dispersed in 50 cm3 of a
Table 2 Reaction of various
epoxides with sodium azide in
the presence of the
representative catalyst in water
Time Yield
Product
Entry
1
Substrate
/min
/% a
93
75
2
3
4
30
35
20
89
85
83
5
6
15
25
87
82
7
20
84
Products were identified by comparison of their physical and spectral data with those of authentic samples
a
Isolated yields
123

A. Mouradzadegun et al.
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NaN3
MNPs-Si-resorcinarene (0.03 g) was added to a mixture of
the epoxide (1.0 mmol) and NaN3 (3 mmol) in 3 cm3
water. The reaction mixture was magnetically stirred at
80 °C as much as the time shown in Table 2. After
complete consumption of starting material as judged by
TLC [using n-hexane:ethyl acetate (5:1) as eluent], the
catalyst was concentrated on the sidewall of the reaction
vessel using an external magnet, the aqueous phase was
separated by decantation and extracted with diethyl ether
(2 9 10 cm3).
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The extract was dried with calcium chloride (CaCl2) and
evaporated in vacuum to give corresponding product. For
styrene oxide, further purification was achieved by
preparative TLC or by silica gel column chromatography.
The residual catalyst in the reaction vessel was washed and
dried and then subjected to the next run directly.
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Acknowledgments We are grateful to the Research Council of
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