CoFe2O4/Cu(OH)2 magnetic nanocomposite: An efficient and reusable heterogeneous catalyst for one-pot synthesis of β-hydroxy-1,4-disubstituted-1,2,3-triazoles from epoxides

Article abstract of DOI:10.1039/c9ra06038c

A magnetically separable CoFe₂O₄/Cu(OH)₂ nanocomposite was prepared and characterized by various techniques such as FESEM, EDS, TEM, XRD, VSM and FT-IR. This novel composite was used as a heterogeneous catalyst for the reg

Full text of DOI:10.1039/c9ra06038c

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CoFe2O4/Cu(OH)2 magnetic nanocomposite: an
efficient and reusable heterogeneous catalyst for
one-pot synthesis of b-hydroxy-1,4-disubstituted-
1,2,3-triazoles from epoxides†
Cite this: RSC Adv., 2019, 9, 29873
*
Ronak Eisavi
and Asmar Karimi
A magnetically separable CoFe2O4/Cu(OH)2 nanocomposite was prepared and characterized by various
techniques such as FESEM, EDS, TEM, XRD, VSM and FT-IR. This novel composite was used as
a heterogeneous catalyst for the regioselective synthesis of b-hydroxy-1,4-disubstituted-1,2,3-triazoles
from sodium azide, terminal alkynes and structurally different epoxides in water at 60 ꢀC. The formation
of the product proceeds in one pot through a mechanism that involves an in situ generated organic
azide intermediate, followed by rapid ring closure with the alkyne component. The simple procedure,
short reaction times, perfect regioselectivity, high product yields, and use of a benign solvent and
nontoxic catalyst are among the considerable advantages of this protocol. Furthermore, the catalyst was
easily separated using an external magnet and reused several times without any significant loss of
catalytic activity or magnetic properties.
Received 3rd August 2019
Accepted 13th September 2019
DOI: 10.1039/c9ra06038c
rsc.li/rsc-advances
CuI37 and NiFe2O4-glutamate-Cu.38 Ramachary–Bressy–Wang
cycloaddition of enolate intermediates and organic azides is the
1. Introduction
other basic method for one-pot preparation of 1,4-disubsti-
tuted-1,2,3-triazoles.39–43
1,2,3-Triazoles are signicant heterocyclic intermediates for the
manufacture of important compounds such as pharmaceuti-
cals, agrochemicals, dyes and corrosion retarding agents.1–4
They also show vital biological activities such as anticancer,5
anti HIV,6 antiviral, antiallergic,7 antifungal,8 antibacterial,9
antitubercular,10 anti-inammatory,11 antimalarial,12 and anti-
oxidant activities.13
The Huisgen 1,3-dipolar cycloaddition of alkynes and
organic azides has been developed as the principal method for
synthesis of 1,2,3-triazoles.14–22 Recently, multicomponent one-
pot synthesis of b-hydroxy-1,2,3-triazoles has been carried out
through in situ click reaction of azides, alkynes and epoxides in
the presence of heterogeneous copper catalysts such as carbon
supported copper nanoparticles,23,24 porphyrinatocopper nano-
particles,25 CuSO4$5H2O/sodium ascorbate,26 copper(I)-zeolite,27
Cu[N2,N6-bis(2-hydroxyphenyl)pyridine-2,6-dicarboxamidate]/
ascorbic acid,28 copper ferrite nanoparticles,29 copper(I)@phos-
phorated SiO2,30 Cu(OAc)2$H2O,31 (Cu/Cu2O) nanoparticles,32
Cu(II)-azide complexes,33 Cu(II)-DA@nano AlPO4,34 1,4-dihy-
droxyanthraquinone-copper(II) nanoparticles immobilized on
silica gel,35 40-phenyl-2,20:60,200-terpyridine copper(II) complex
immobilized on activated multiwalled carbon nanotubes,36
The reduction of work-up procedures and purication steps,
high purity of desired products, short reaction times, high to
excellent yields are among the signicant benets of multi-
component one-pot reactions.44,45 Furthermore, the reaction
involving ring opening of epoxides with organic azides in water
solvent occurs with perfect regioselectivity and takes advantage
of green and benign conditions.
In recent years, magnetic nanoparticles (MNPs) due to their
facile preparation, easy separation using an external simple
magnet leading to avoid traditional ltration processes, recov-
erability and reusability,46,47 high catalytic activity,48 thermal
and chemical stability49,50 have been widely utilized as green and
efficient nanocatalysts in the synthesis of organic compounds.
Nevertheless, the nano-ferrites oen suffer from high tendency
of self-aggregation and low quantity of functional groups on the
surface.51,52 The coating of nano-ferrites with a functionalized
shell, not only reduces the aggregation of the nanoparticles in
the solution, but also improves the efficiency of the catalyst by
increasing the amount of functional groups on the surface.53
Recently, these coated nanostructures have received special
attention as air-stable materials and easy separable catalysts in
organic transformations, drug targeting, and magnetic cell
separation.54–57
Department of Chemistry, Payame Noor University, PO BOX 19395-3697, Tehran, Iran.
E-mail: roonak.isavi@gmail.com
In connection with our recent works on nano-ferrites,58–63
herein we wish to report an efficient one-pot three-component
† Electronic supplementary information (ESI) available: Spectral data for
b-hydroxy-1,2,3-triazoles. See DOI: 10.1039/c9ra06038c
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protocol for the synthesis of b-hydroxy-1,2,3-triazoles from 4 min. Next, in order to remove the additional salts, the
sodium azide, terminal alkynes, and various epoxides in the produced mixture was washed with distilled water for several
ꢀ
presence of CoFe2O4/Cu(OH)2 magnetic nanoparticles as times. The product was dried at 80 C for 2 h and it was then
a novel and green heterogeneous catalyst in water (Scheme 1). calcined at 900 ꢀC for 2 h to obtain the nal cobalt nanoferrite
as a dark brown powder.
2. Experimental
2.3. Synthesis of CoFe2O4/Cu(OH)2 nanocomposite
2.1. Instruments and materials
In a round-bottomed ask equipped with a magnetic stirrer,
a solution of CuCl2$2H2O (0.8 g, 4.7 mmol) in distilled water (30
mL) was prepared and then CoFe2O4 (1.01 g, 4.31 mmol) was
added. The mixture was stirred vigorously for 10 min at room
All materials were purchased from the Merck and Aldrich
Chemical Companies with the best quality and they were used
without further purication. The synthesized nanocatalyst was
characterized by XRD on a Bruker D8-Advanced diffractometer
temperature and followed by dropping of NaOH solution (6 mL,
with graphite-monochromatized Cu Ka radiation (l ¼ 1.54056
1 M) in order to basify the mixture up to pH ꢁ 13. The stirring of
alkali mixture was continued at room temperature for 24 h. The
black nanoparticles of CoFe2O4/Cu(OH)2 were separated using
a magnet, washed with distilled water and then dried under air
atmosphere within two days.
Aꢀ) at room temperature. Magnetic property of synthesized
nanocatalyst was measured using a VSM (Meghnatis Daghigh
Kavir Co., Kashan Kavir, Iran) at room temperature. TEM image
was recorded using an EM10C-100 kV series microscope from
the Zeiss Company, Germany. FESEM images were determined
using FESEM-TESCAN. The energy dispersive X-ray spectrom-
eter (EDS) analysis was taken on a MIRA3 FE-SEM microscope
(TESCAN, Czech Republic) equipped with an EDS detector
(Oxford Instruments, UK). IR and 1H/13C NMR spectra were
recorded on Thermo Nicolet Nexus 670 FT-IR and 400 MHz
Bruker Avance spectrometers, respectively. The products were
characterized by their spectra data and comparison with the
reported data in literature. All yields refer to isolated pure
products.
2.4. One-pot synthesis of b-hydroxytriazoles from epoxides
catalyzed by CoFe2O4/Cu(OH)2 in water: a general procedure
In a round-bottomed ask equipped with a magnetic stirrer and
condenser, a solution of the epoxide (1 mmol), alkyne (1 mmol)
and sodium azide (0.078 g, 1.2 mmol) in H2O (5 mL) was
prepared. CoFe2O4/Cu(OH)2 nanocomposite (0.032 g, 0.1 mmol)
was then added to the solution and the resulting mixture was
stirred magnetically for 3–6.5 h at 60 ꢀC. The progress of the
reaction was monitored by TLC using CCl4 : Et2O (10 : 2) as an
eluent. Aer completion of the reaction, the magnetic nano-
2.2. Preparation of CoFe2O4 nanoparticles
CoFe2O4 nanoparticles were prepared by a solid-state procedure catalyst was separated using an external magnet and collected
according to our previous research.58 Briey, in a mortar, CoCl2, for the next run. The reaction mixture was extracted with EtOAc
Fe(NO3)3$9H2O, NaOH, and NaCl were mixed with the desired (3 ꢂ 10 mL) and then dried over anhydrous Na2SO4. Aer
molar ratio (1 : 2 : 8 : 2) and ground together for 55 min. The evaporating the organic solvent, the crude b-hydroxytriazoles
reaction started quickly along with the release of heat. The were obtained. Removal of the solvent under vacuum, followed
mixture color changed from yellow to chocolate brown aer by recrystallization with EtOH/H2O (3 : 1) or purication on
Scheme 1 One-pot synthesis of triazoles from epoxides catalyzed by CoFe2O4/Cu(OH)2 nanoparticles.
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silica gel using CCl4 : Et2O (10 : 2) as the eluent afforded the room temperature using vibrating sample magnetometer. The
pure b-hydroxytriazoles derivatives in 75–95% yield (Table 2). hysteresis loops of CoFe2O4 and CoFe2O4/Cu(OH)2 nano-
The collected CoFe2O4/Cu(OH)2 nanoparticles were washed particles are shown in Fig. 1. The wide cycles and the hysteresis
with distilled water and dried for the next cycle. All products are loops show the behavior of hard ferromagnetic particles with
known compounds and were characterized by comparison of high coercivity. CoFe2O4/Cu(OH)2 nanoparticles show lower
their spectra (FT-IR, 1H NMR and 13C NMR) with those of valid magnetization saturation (18 emu gꢃ1) than the uncoated cobalt
samples;23,25,26,29,30,38,45 these data are given in the ESI.†
ferrite nanoparticles (128 emu gꢃ1). This is due to the effect of
Cu(OH)2 shell coating where each particle was separated from
its neighbors by the coated layer leading to decrease the
magnetostatic coupling between the particles.
3. Results and discussion
3.1.2. Fourier transform infra-red (FT-IR) spectrum. The
FT-IR spectrum of synthesized CoFe2O4, Cu(OH)2 and CoFe2O4/
Cu(OH)2 nanoparticles are shown in Fig. 2. A strong absorption
band at 596 cmꢃ1 is corresponded to the stretching vibration of
metal–oxygen (M–O) indicating the formation of spinel ferrite
structure. The absorption peaks at 1608 cmꢃ1 and 3390 cmꢃ1
are related to bending and stretching vibrations of O–H group
in surface absorbed H2O in the sample, respectively.65 A sharp
and intense absorption band at 3568 cmꢃ1 is related to the O–H
stretching vibrations in crystal structure of Cu(OH)2 and the
peak at 941 cmꢃ1 indicates Cu–O–H bending vibrations.66
3.1.3. X-ray diffraction (XRD). Fig. 3 displays the X-ray
diffraction (XRD) patterns of CoFe2O4, Cu(OH)2 and CoFe2O4/
Cu(OH)2 nanoparticles. In the XRD pattern of CoFe2O4/
Cu(OH)2, all the peaks of CoFe2O4 and Cu(OH)2 are detectable.
The lines (111), (220), (311), (222), (400), (422), (511), (440),
(620), (533) and (622) related to 2q ¼ 18.36ꢀ, 30.18ꢀ, 35.54ꢀ,
37.18ꢀ, 43.17ꢀ, 53.55ꢀ, 57.09ꢀ, 62.68ꢀ, 71.13ꢀ, 74.13ꢀ and 75.20ꢀ
respectively, are assigned to the diffraction of CoFe2O4 crystals
and indicate that the synthesized CoFe2O4 nanoparticles are
pure and high crystalline. These peaks are consistent with the
standard data (JCPDS card no. 22-1086).67 The peaks at 2q ¼
16.81ꢀ, 23.89ꢀ, 34.09ꢀ, 38.24ꢀ, and 39.77ꢀ correspond to ortho-
rhombic Cu(OH)2 which are in good agreement with JCPDS no.
(13-420).68 The peak at 53.52ꢀ for copper hydroxide overlaps with
the 53.55ꢀ peak of CoFe2O4. The average crystallite size of
CoFe2O4/Cu(OH)2 nanoparticles is calculated using the Scher-
rer's formula (40 nm).
3.1. Synthesis and characterization of CoFe2O4/Cu(OH)2
magnetic nanocatalyst
The coating of CoFe2O4 nanoparticles was carried out with
Cu(OH)2 in order to reduce the self-aggregation and also
increase the amount of hydroxyl functional groups on the
surface of nano-ferrite which makes the catalyst more active
than the bare cobalt ferrite. The use of CoFe2O4 nanoparticles as
catalyst support not only donated sufficient magnetic property
for the easy separation of nanocatalyst, but also enhanced the
efficiency of the catalyst by increasing the recoverability and
reusability of the novel nanocomposite.
The magnetic nanoparticles of CoFe2O4/Cu(OH)2 was
synthesized in a two-step process. CoFe2O4 was prepared using
solid-state reaction of CoCl2, Fe(NO3)3$9H2O, NaCl and NaOH
in an agate mortar (Scheme 2). Aer calcination of crude
powder at 900 ꢀC, the CoFe2O4 nanoparticles were obtained
with high crystallinity, phase purity and increased saturation
magnetization (Ms). The calcination process at high tempera-
tures improves the efficiency of CoFe2O4, and also leads to
decompose the excess salts used in the preparation of these
nanoparticles.64 Aerwards, the collected pure CoFe2O4 nano-
particles were added to an aqueous solution of CuCl2 and fol-
lowed by dropping of the NaOH solution under intense stirring.
Eventually, the black precipitate was accumulated through
magnetic separation, washed with deionized water, and dried at
room temperature (Scheme 3). The prepared CoFe2O4/Cu(OH)2
nanocatalyst was characterized by vibration sample magne-
tometer (VSM), FT-IR, X-ray diffraction (XRD), transmission
electron microscopy (TEM), eld emission scanning electron
microscope (FESEM), and energy dispersive X-ray spectrometer
(EDS) techniques.
3.1.4. TEM, FESEM and EDS of CoFe2O4/Cu(OH)2 nano-
composite. The morphology and size distribution of the
synthesized nanocatalyst have been investigated by TEM and
FESEM techniques. Fig. 4 shows the TEM images of the
CoFe2O4/Cu(OH)2 nanocomposite. The TEM images with
different magnications clearly reveal the wire shape of the
3.1.1. Vibration sample magnetometer (VSM). The hyster-
esis loops, saturation magnetization (Ms) and switching eld
(Hc) of the prepared magnetic nanoparticles were measured at
Scheme 2 Synthesis of CoFe2O4 nanoparticles.
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Scheme 3 Synthesis of CoFe2O4/Cu(OH)2 nanocomposite.
Cu(OH)2 nanoparticles, and also show that many nanowires
The chemical composition of CoFe2O4/Cu(OH)2 was
come together to form a bundle-like morphology. The CoFe2O4 approved with EDS analysis. In this analysis, Cu, Co, Fe, and O
nanoparticles are spherical and have been uniformly sur- signals are detectable (Fig. 6).
rounded by Cu(OH)2 nanowires, indicating the successful
3.1.5. Structure of CoFe2O4/Cu(OH)2 nanocomposite. The
coating of CoFe2O4 surface with Cu(OH)2. The images also possible structure of CoFe2O4/Cu(OH)2 nanocomposite was
demonstrated that the agglomeration of CoFe2O4 nanoparticles proposed based on the characterization results (Scheme 4). In
has not occurred. The cobalt ferrite particles are clearly distin- the presented catalytic system, copper plays the key role in the
guishable as black spherical segments with diameter 40 nm. [3 + 2] cycloaddition between alkyne and azide components, and
The gray particles of Cu(OH)2 are also obviously detectable in the use of nano-CoFe2O4 as a magnetic support facilitates the
TEM images.
separation, accumulation and recycling of nanoparticles.
The FESEM images conrm the nanowire structure of the
catalyst containing the spherical cobalt ferrite nanoparticles,
and show that the diameter of wires lies in the range of 28 to
40 nm. Each nanobelt with an average diameter of 32 nm is
composed of tiny nanostructured grains that were created
during the reaction in solution but has a uniform shape (Fig. 5).
The obtained results are in good agreement with TEM and XRD
data.
3.2. Catalytic activity of CoFe2O4/Cu(OH)2 for the synthesis
of 1,4-disubstituted b-hydroxy-1,2,3-triazoles
The optimization of reaction conditions was conducted with
styrene oxide, phenylacetylene and sodium azide as a model
reaction. The quantity of catalyst, temperature, time and
solvents were investigated as the main optimization factors
Fig. 1 Magnetization curves of (a) CoFe2O4 (b) CoFe2O4/Cu(OH)2 nanoparticles.
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Fig. 2 FT-IR (KBr) spectrum of (a) Cu(OH)2, (b) CoFe2O4 and (c) CoFe2O4/Cu(OH)2.
(Table 1). The desired result was obtained using styrene oxide (1
In order to determine the effect of temperature, the reaction
mmol), phenylacetylene (1 mmol) and sodium azide (1.2 mmol) was repeated at different temperatures (25 ꢀC, 40 ꢀC and 60 ꢀC).
in the presence of CoFe2O4/Cu(OH)2 (0.032 g, 0.10 mmol, At room temperature (25 ꢀC), the reaction was carried out in 8 h
10 mol%) in water at 60 ꢀC (entry 5). As can be seen, the use of affording the moderate yield of product (entry 14). But
catalytic amount of nanocatalyst was essential to perform the increasing the temperature encouragingly raised both the
reaction and in the absence of catalyst, no cyclization product product yield and reaction speed, and the corresponding tri-
ꢀ
was generated aer 10 h (entry 1). The model reaction was azole was prepared in 65% yield aer 5 h at 40 C (entry 15).
tested using the various amounts of CoFe2O4/Cu(OH)2 (0.01, With further increase in temperature to 60 ꢀC the yield
0.02, 0.025, 0.032 and 0.045 g), and the best result was achieved increased to 94% aer 3.3 h (entry 5).
using (0.032 g) of catalyst (entries 2–6). The enhancement of
Performing the mentioned reaction under the optimized
catalyst amount from 0.01 to 0.032 g, not only increased the conditions but in the presence of CoFe2O4 (without the copper
reaction speed, but also led to raise the product yield signi- hydroxide) produced a trace of the corresponding triazole aer
cantly. Applying the more amounts of nanocatalyst did not 5 h (entry 16). Cobalt ferrite without Cu(OH)2 was not capable of
ameliorate the product yield (entry 6).
conducting the reaction. The reaction was also investigated
The effect of solvents was also studied by performing the using bare Cu(OH)2 nanoparticles under the same conditions
cyclization reaction in various solvents. It was observed that the (entry 17). The reaction was carried out within 3.5 h giving 90%
reaction was carried out in polar solvents, such as water, yield of product. The presence of copper hydroxide signicantly
ethanol, acetonitrile, ethyl acetate, methanol and dime- enhanced the catalytic capability. These results approved the
thylformamide whereas no reaction took place in nonpolar essential catalytic role of copper hydroxide particles. It also
solvents (entries 7–13). The reaction was accomplished effi- showed that the interactions between the Cu(OH)2 and CoFe2O4
ciently in H2O and in comparison with water, the product yields nanoparticles may increase the catalytic activity of CoFe2O4/
were lower in all other solvents; hence, this solvent was selected Cu(OH)2 composite. Cobalt ferrite plays the role of a magnetic
as a green and eco-friendly option for synthesis of triazoles.
support that enhances the effectiveness of the catalyst by
increasing the contact surface and easy separability.
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Fig. 3 The X-ray diffraction patterns of (a) nano-Cu(OH)2, (b) nano-CoFe2O4 and (c) CoFe2O4/Cu(OH)2 nanocomposite.
Fig. 4 TEM images of CoFe2O4/Cu(OH)2.
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Fig. 5 FESEM images of CoFe2O4/Cu(OH)2.
In order to exhibit the diversity of the CoFe2O4/Cu(OH)2
catalyst, the optimized conditions were applied to epoxides
containing either electron-donating or -withdrawing substitu-
ents, and cyclic epoxides as shown in Table 2. In addition, the
reaction of aliphatic terminal alkynes with styrene oxide was
also considered under mentioned conditions (entries 18–21).
All reactions were carried out successfully within 3–6.5 h to give
1,2,3-triazoles in 75–95% yields.
3.3. Recycling of CoFe2O4/Cu(OH)2 nanoparticles
The recyclability of nano-CoFe2O4/Cu(OH)2 was investigated in
the synthesis of 3-chloro-1-(4-phenyl-1H-1,2,3-triazol-1-yl)
propan-2-ol as halogen containing sample (Table 2, entry 15)
and 2-hydroxy-3-(4-phenyl-1H-1,2,3-triazol-1-yl)propyl methac-
rylate with the lowest yield in the rst run (Table 2, entry 7).
Aer completion of the reaction, the reaction mixture was
cooled to room temperature and the nanoparticles were easily
Fig. 6 EDS of CoFe2O4/Cu(OH)2.
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Scheme 4 Structure of CoFe2O4/Cu(OH)2 as a surface modified nanocatalyst.
collected by an external magnet, washed several times with catalyst and the freshly prepared nanoparticles revealed that the
distilled water and ethanol and dried at 70 ꢀC for 1 h. The magnetic properties, original structure and morphology of the
recovered catalyst was reused 6 times without any signicant catalyst remained unchanged aer several reuses.
loss of activity, under the same conditions (Fig. 7). The structure
The hot ltration test was used for conrming the hetero-
of the recovered CoFe2O4/Cu(OH)2 nanocatalyst was conrmed geneity of as-prepared catalyst. Accordingly, the ltration of the
using VSM, XRD, FESEM and TEM analyses aer ve runs catalyst was carried out aer 30 min at 80 ꢀC and the ltrate was
(Fig. 8). Comparison of the results obtained from the recycled allowed to react for additional 2 hours, but the reaction due to
Table 1 Nano-CoFe2O4/Cu(OH)2-catalysed reaction of styrene oxide with phenylacetylene and sodium azide under different conditionsa
Temperature
Entry
CoFe2O4/Cu(OH)2 (g)
Solvent
Time (h)
(ꢀC)
Yieldb (%)
1
2
3
4
5
6
7
8
—
0.01
0.02
0.025
0.032
0.04
0.032
0.032
0.032
0.032
0.032
0.032
0.032
0.032
0.032
0.032
0.032
H2O
H2O
H2O
H2O
H2O
H2O
EtOH
CH3CN
EtOAc
MeOH
DMF
THF
n-Hexane
H2O
H2O
10
8
8
6
3.3
3
4
4
4
4
60
60
60
60
60
60
78
82
77
65
100
60
68
25
40
100
60
0
25
55
85
94
94
50
35
60
50
45
0
9
10
11
12
13
14
15
16c
17d
4
24
24
8
5
5
0
50
65
Trace
90
H2O
H2O
3.5
a
All reactions were carried out with styrene oxide (1 mmol), phenylacetylene (1 mmol) and sodium azide (1.2 mmol). b Isolated yields. c Catalysed by
CoFe2O4. d Catalysed by Cu(OH)2.
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a
Table 2 One-pot synthesis of b-hydroxy-1,2,3-triazoles from epoxides catalyzed by nano-CoFe2O4/Cu(OH)2
Entry
Epoxide (a)
Alkyne
Triazole (b)
Time (h)
3.3
Yieldb (%)
1
94
2
3
95
3
4
5
3.3
4.3
4.5
90
88
85
6
7
4.5
5.5
87
75
8
9
4.3
4.2
80
85
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Table 2 (Contd.)
Entry
Epoxide (a)
Alkyne
Triazole (b)
Time (h)
6.3
Yieldb (%)
10
84
11
5
82
12
13
14
15
6
85
87
88
80
6
6.5
5
16
17
5
6
90
92
18
5.5
85
19
4
90
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Table 2 (Contd.)
Entry
20
Epoxide (a)
Alkyne
Triazole (b)
Time (h)
Yieldb (%)
5
88
21
6.5
84
a
All reactions were carried out with 1 mmol of epoxide in the presence of alkyne (1 mmol), sodium azide (1.2 mmol) and nano-CoFe2O4/Cu(OH)2
(0.032 g, 0.1 mmol, 10 mol%) in water at 60 ꢀC. b Yields refer to isolated pure products.
the absence of copper did not take place, and no cycloaddition is more efficient than the other methods in terms of product
reaction was occurred.
yield, and it is also comparable to the most of them from
viewpoints of reaction time and temperature. The study of re-
ported literature shows that magnetic nanocatalysts have been
rarely used for one-pot synthesis of 1,2,3-triazoles from epox-
ides (entries 2 and 3), and the overwhelming majority of the
reported cases have been carried out in the presence of non-
magnetic catalysts (entries 4–11). On the other hand, in some
cases, the use of acid or base alongside the catalyst is essential
for the reaction progress (entries 10 and 11). Therefore, our
3.4. Comparison of CoFe2O4/Cu(OH)2 catalytic activity with
other catalysts
The comparison of the catalytic activity of the prepared
CoFe2O4/Cu(OH)2 nanocomposite with various catalysts in the
reaction of styrene oxide, phenylacetylene and sodium azide is
summarized in Table 3. As can be seen, our proposed procedure
Fig. 7 Recycling of nano-CoFe2O4/Cu(OH)2 in the synthesis of 3-chloro-1-(4-phenyl-1H-1,2,3-triazol-1-yl)propan-2-ol and 2-hydroxy-3-(4-
phenyl-1H-1,2,3-triazol-1-yl)propyl methacrylate.
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Fig. 8 (a) Magnetization curve, (b) XRD pattern, (c) FESEM and (d) TEM images of CoFe2O4/Cu(OH)2 after five runs in the synthesis of 3-chloro-1-
(4-phenyl-1H-1,2,3-triazol-1-yl)propan-2-ol.
method, due to the use of ferromagnetic nanocatalyst, takes recovering, reusability aer several cycles without loss of cata-
advantage of both heterogeneity benets and magnetic prop- lytic activity or magnetic property and subsequently facilitating
erties. In addition, performing of reaction in a green solvent the achievement to the goals of green chemistry are among the
under neutral conditions is really important privilege. Easy remarkable advantages of CoFe2O4/Cu(OH)2 catalytic system,
preparation and utilization of surface modied nanoparticles, which highlight its importance in comparison with the most
simple separation just by an external magnet, convenient reported catalysts. Furthermore, the one-pot reaction due to the
Table 3 Comparison of CoFe2O4/Cu(OH)2 catalytic activity with various catalysts reported for the one-pot synthesis of 2-phenyl-2-(4-phenyl-
1H-1,2,3-triazol-1-yl)ethanol from styrene oxide, phenylacetylene and sodium azidea
Yield
Entry
Catalyst system
NaN3 (mmol)
Conditions
Time (h)
(%)
Ref.
1
2
3
4
5
6
7
8
CoFe2O4/Cu(OH)2 (10 mol%)
Nano CuFe2O4 (10 mol%)
Nano Fe2O3 (10 mol%)
Cu nanoparticles/C (0.5 mol%)
Cu(I)@phosphorated SiO2 (0.64 mol%)
Copper(I)–zeolite (8 mol%)
CuI (5 mol%)
1.2
1.1
1.2
1.1
1.1
1.2
1.1
1
H2O/60 ꢀ
H2O/60 ꢀ
C
C
C
C
C
3.3
6
5
8
1
20
16
5
5
2
94
87
81
93
93
77
83
35
36.8
90
92
This work
29
45
23
30
27
37
31
31
28
26
H2O/100 ꢀ
H2O/70 ꢀ
H2O/60 ꢀ
H2O/r.t.
PEG-400/r.t.
H2O/r.t.
H2O/r.t.
Ascorbic acid/H2O/r.t.
Sodium ascorbate/H2O/r.t.
CuCl2 (10 mol%)
9
10
11
Cu(NO3)2$3H2O (10 mol%)
[Cu(bhppda)H2O]b (5 mol%)
CuSO4$5H2O (10 mol%)
1
1.2
1.2
4
a
b
All reactions were carried out with styrene oxide (1 mmol) and phenylacetylene (1 mmol). bhppda ¼ N2,N6-bis(2-hydroxyphenyl)pyridine-2,6-
dicarboxamidato dianion.
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Scheme 5 Reaction mechanism proposed for the one-pot synthesis of 1,4-disubstituted b-hydroxy-1,2,3-triazole catalyzed by CoFe2O4/
Cu(OH)2 bifunctional catalyst.
reduction of work-up procedures and purication steps phenylacetylene and produce the intermediate (I), which facil-
required compared to a more stepwise approach was used in itates the [3 + 2] cycloaddition between carbon–carbon triple
order to conduct synthesis in a greener fashion.
bond of the 2-azido-2-arylethanol and in situ generated inter-
mediate (II), to give the Cu–C-triazole (IV). The alkyne
consumption and also the generation and the disappearance of
the 2-azido-2-alkylethanol intermediate, were monitored by gas
chromatography (GC) analysis and thin layer chromatography
(TLC) runs of the reaction mixture. Finally, protonolysis of the
Cu–C bond of intermediate (IV) by aqueous media affords the
corresponding b-hydroxy-1,2,3-triazole (V) (Scheme 5).
3.5. The proposed mechanism for synthesis of 1,4-
disubstituted b-hydroxy-1,2,3-triazoles catalyzed by CoFe2O4/
Cu(OH)2 nanocomposite
The proposed mechanism for the formation of b-hydroxy-1,4-
disubstituted-1,2,3-triazoles includes two pathways (A and B)
in which CoFe2O4/Cu(OH)2 catalyzes both ring opening and 1,3-
dipolar cycloaddition reactions.28 The pathway A demonstrates
the formation of metal azide which is followed by epoxide
4. Conclusions
activation via CoFe2O4/Cu(OH)2 catalyst. Ring opening of In summary, the magnetic nanocatalyst of CoFe2O4/Cu(OH)2
epoxide takes place through azide delivery from the catalyst and has been successfully prepared through a simple method and it
leads to the formation of 2-azido-2-arylethanol. The regiose- was then characterized using various techniques such as
lective cleavage of oxiranes carrying alkyl and allyl substituents FESEM, EDS, TEM, XRD, VSM and FT-IR. This novel composite
by azide ion is strongly favored from less hindered carbon of the has been demonstrated to be an efficient catalyst for one-pot
epoxide ring via SN2 type of mechanism (b-cleavage); however, synthesis of a wide variety of 1,4-disubstituted-1,2,3-triazoles
aryl-substituted epoxides prefer to be opened from the more via three component reactions of sodium azide, terminal
sterically hindered position via SN1 type of mechanism (a- alkyne, and different epoxides in water. The simple procedure,
cleavage).
short reaction times, perfect regioselectivity, high product
The pathway B displays the insertion of copper catalyst to the yields, the use of benign solvent, easy separation of catalyst
C–H bond of terminal alkyne in order to activate the using an external magnet and efficient recycling are remarkable
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aspects of this proposed protocol that make it to be an impor- 17 C. S. Radatz, L. d. A. Soares, E. F. Vieira, D. Alves,
tant addition to the existing methodologies for synthesis of 1,4-
disubstituted-1,2,3-triazoles.
D. Russowsky and P. H. Schneider, New J. Chem., 2014, 38,
1410.
18 M. I. Mangione, R. A. Spanevello and M. B. Anzardi, RSC
Adv., 2017, 7, 47681.
Conflicts of interest
19 H. X. Siyang, H. L. Liu, X. Y. Wu and P. N. Liu, RSC Adv., 2015,
5, 4693.
20 W. D. Castro-Godoy, A. A. Heredia, L. C. Schmidt and
J. E. Arguello, RSC Adv., 2017, 7, 33967.
21 N. V. Sokolova and V. G. Nenajdenko, RSC Adv., 2013, 3,
16212.
There are no conicts to declare.
Acknowledgements
22 W. Yang, T. Miao, P. Li and L. Wang, RSC Adv., 2015, 5,
95833.
23 F. Alonso, Y. Moglie, G. Radivoy and M. Yus, J. Org. Chem.,
2011, 76, 8394.
The nancial support of this work by the Research Council of
Payame Noor University is gratefully acknowledged.
24 F. Alonso, Y. Moglie, G. Radivoy and M. Yus, Adv. Synth.
Catal., 2010, 352, 3208.
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