Magnetic starch nanocomposite as a green heterogeneous support for immobilization of large amounts of copper ions: Heterogeneous catalyst for click synthesis of 1,2,3-triazoles

Article abstract of DOI:10.1039/c5ra25519h

A new magnetic heterogeneous copper catalyst was prepared by immobilization of copper ions onto a cross-linked polymeric nanocomposite composed of starch grafted polyacrylamide and functionalized Fe₃O₄ magnetic nanoparticles. The resulting support was loaded with large amounts of copper ions (1.6 mmol g^-1). The prepared catalyst is highly active in Huisgen 1,3-dipolar cycloaddition reactions of different azides and alkynes at low catalyst amounts. Various corresponding 1,2,3-triazoles were produced with high yields in mild conditions. The catalyst was easily recovered and reused for ten cycles of reaction and no significant loss of catalytic activity was observed.

Full text of DOI:10.1039/c5ra25519h

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Magnetic Starch Nanocomposite as a Green Heterogeneous Support for
Immobilization of Large Amounts of Copper Ions: Heterogeneous Catalyst
for Click Synthesis of 1,2,3-triazoles
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Ali Pourjavadi*, Anahita Motamedi, Seyed Hassan Hosseini, Mojtaba Nazari
Polymer Research Laboratory, Department of Chemistry, Sharif University of Technology, Tehran, Iran
Eꢀmail address: purjavad@sharif.edu; Phone/fax: (982)166165311
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Abstract
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A new magnetic heterogeneous copper catalyst was prepared by immobilization of copper
ions onto a crossꢀlinked polymeric nanocomposite composed of starch grafted
polyacrylamide and functionalized Fe3O4 magnetic nanoparticles. The resulting support was
loaded with large amounts of copper ions (1.6 mmol gꢀ1). The prepared catalyst is highly
active in Huisgen 1,3ꢀdipolar cycloaddition reaction of different azides and alkynes at low
catalyst amount. Various corresponding 1,2,3ꢀtriazoles were produced with high yields in
mild condition. The catalyst was easily recovered and reused for ten cycles of reaction and no
significant loss of catalytic activity was observed.
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Keywords: Huisgen cycloaddition, copper catalysis, magnetic nanoparticles, polymeric
supports, green catalytic system
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Introduction
The concept of click chemistry, first introduced by Sharpless et al., refers to the reactions that
are modular, wide in scope and highly efficient, performing with high regioꢀ and sterioꢀ
selectivity under mild conditions.1 In recent years, these kinds of reactions have attracted
much attention in different fields of organic chemistry, material science and drug discovery.2ꢀ
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The most wellꢀknown example of click reactions is catalytic 1,3ꢀdipolar cycloaddition of
organic alkynes and azides.5,6 This reaction is very attractive since it can be used for synthesis
of 1,2,3ꢀtriazole derivatives, a class of compounds that have been recognized possessing
biological and pharmaceutical activities.7,8
However the original nonꢀcatalyzed form of this reaction, known as Huisgen cycloaddition
reaction, has slow rate and low yield at room temperature due to high kinetic energy barrier
of the reaction.9,10 It has been recognized that Cu(I) is an appropriate catalyst for Huisgen
reaction since it accelerates the rate of the reaction and significantly improves its
regioselectivity.11,12 Although both homogeneous and heterogeneous catalysts were used in
this reaction, heterogeneous catalysts have more advantages than homogenous ones, because
of facile separation and reusability of the catalyst and simple isolation of the product.13ꢀ16
These properties are especially very important for pharmaceutical purposes since it is
essential to remove trace amount of catalysts remained in the final product. Moreover, in
drugs synthesis process the supported materials, used for immobilization of copper, should be
biocompatible to prevent the possible leached contamination from solid catalysts to final
products.
A variety of heterogeneous catalytic systems were prepared by immobilization of copper ions
onto different solid supports such as magnetic nanoparticles,17 silica,18 zeolite,19 alumina,20
and polymers21, and were used for click synthesis of 1,2,3ꢀtriazoles. In these systems, the
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catalyst can be separated from the reaction medium by simple filtration or centrifugation.
However, using magnetic nanoparticles makes separation and recovery of the catalyst faster
and more convenient in comparison with nonꢀmagnetic catalysts. The catalyst can be easily
removed after the completion of the reaction by using a magnet.22ꢀ24
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In spite of the great advantageous of heterogeneous catalytic systems, loading amounts of the
active spices (copper ions) in these systems is usually low and thus a large amount of solid
catalyst is required to perform the reaction. This resulted to using large amounts of solvent
for reaction mixing and catalyst separation. Plus, increasing in the amount of used catalyst
leads to an increase in the contamination of final products. In many cases, the activity of the
catalyst also decreases after immobilization on solid supports. High catalyst leaching and low
thermal stability of the catalyst are other drawbacks of heterogeneous catalytic systems. As a
consequence, it is still demanded to develop an efficient heterogeneous catalytic system with
high loading, high stability and easy separation.
Polymeric materials with different structures, compositions and functionalities have been
prepared and employed as supports in heterogeneous catalytic systems.25ꢀ27 However, natural
polymers, especially polysaccharides, are more attractive since they are easily available,
inexpensive, nontoxic, and biodegradable.28ꢀ30 There are also many functional groups in the
structure of natural polymers being able to interact with metal ions and nanoparticles. These
properties make polysaccharides and other natural polymers excellent candidates for being
used as supports in heterogeneous catalytic systems.
Herein, we report preparation of copper immobilized magnetic starchꢀbased heterogeneous
catalytic system for 1,4ꢀdisubstituted 1,2,3ꢀtriazols. The catalyst is easily prepared by
simultaneous polymerization, grafting and crosslinking of acrylamide onto the starch in the
presence of magnetic nanoparticles.
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Experimental
Materials
Acrylamide was purified by recrystallization in methanol. Starch, tetraethylorthosilicate
(TEOS), 3ꢀ(trimethoxysilyl) propylmethacrylate (MPS), sodium ascorbate, sodium azide
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(NaN3),
FeCl2.4H2O,
FeCl3.6H2O,
ammonium
persulfate
(APS),
N,N`ꢀ
methylenebisacrylamide (MBA), CuCl2, ammonia solution (25%) and ethanol all were
obtained from Merck and Aldrich and used without further purification.
Fourier transform infrared (FTIR) spectra were recorded on ABB Bomem MB 100
spectrophotometer. Xꢀray diffraction (XRD) patterns were obtained by a Siemens D5000
diffractometer with Cu Kα radiation in 2θ range of 5ꢀ80°. Scanning electron microscopy
(SEM) images were taken on Mira3 Tescan microscope. Thermogravimetric analysis (TGA)
was performed at heating rate of 10 °C under nitrogen atmosphere using PerkinꢀElmer Pyris1
instrument. Transmission electron microscopy (TEM) experiments were carried out by a
Philips CM30 electron microscope. Nuclear magnetic resonance (NMR) spectra were
recorded on Bruker (Avance DRXꢀ400) spectrometer using CDCl3 as solvent and
tetramethylsilane (TMS) as internal standard. The magnetic properties of samples were
measured with a vibrating sample magnetometer (VSM, PPMSꢀ9T) in Kashan University,
Iran.
Synthesis of MPS functionalized silica-coated Fe3O4 nanoparticles (MNPs)
Fe3O4 magnetic nanoparticles were prepared by coprecipitation of Fe (II) and Fe (III) salts.
Typically, 200 mL distilled water was poured in a roundꢀbottom flask equipped with a
mechanical stirrer. 5 mmol (1.0 g) FeCl2.4H2O and 10 mmol (2.7 g) FeCl3.6H2O were added
and stirred to dissolve. Then, ammonia solution was added to the flask dropwise until the pH
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of the solution reached to 10. The mixture was stirred vigorously at 60 °C for 1 h. The black
precipitate was collected by a magnet and washed with water (5×50 mL) and dried at 60 °C.
In order to prepare silicaꢀcoated Fe3O4 nanoparticles, 1.0 g of the prepared magnetic
nanoparticles were dispersed in 80 mL 4:1 ethanol/water solution in a roundꢀbottom flask and
sonicated for 20 min. Then, 0.5 mL tetraethylorthosilicate (TEOS) was added and the pH of
the solution was adjusted to 10 using ammonia solution. The mixture was refluxed for 12 h.
Afterward, the flask was cooled to room temperature and the resulting particles were washed
with water (3×50 mL) and ethanol (2×25 mL) and dried in an oven at 60 °C.
Fe3O4@SiO2 nanoparticles were then functionalized with MPS using the same procedure
mentioned above for synthesis of Fe3O4@SiO2. 0.7 g Fe3O4@SiO2, 3 mL MPS and 1 mL
ammonia were refluxed in 100 mL 4:1 ethanol/water solution. After 12 h, the prepared
particles were washed with water (3×20 mL) and ethanol (2×20 mL) and dried at 60 °C
(MNPs).
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Preparation of the catalyst (MNP@SPAAm/Cu)
Magnetic polymeric support was prepared according to the following procedure: 0.5 g MNPs
were dispersed in 20 mL water in a roundꢀbottom flask and sonicated for 20 min. Then, 0.5 g
starch was added to flask. After all starch was dissolved, 0.05 g APS was added to solution
and mixture was put in an oil bath at 70 °C. Then, a mixture of 2.0 g acrylamide and 0.4 g
MBA in 10 mL water was added to flask and polymerization was performed for 1 h. The
prepared hydrogels were washed with ethanol, dried at 50 °C and sieved through an 80ꢀmesh
sieve for further use.
For loading of copper, 0.5 g of the prepared polymeric nanocomposite was added to an
aqueous solution of CuCl2 (0.3 g in 25 mL). The mixture was stirred for 24 h at 50 °C and the
solid particles were then magnetically separated, washed with water (5×25 mL) and ethanol
(2×25 mL) and dried at 60 °C.
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General procedure for synthesis of 1,2,3-triazoles
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Alkyne (1 mmol), alkyl halide (1 mmol) and NaN3 (1.3 mmol) were added to 3 mL water in a
roundꢀbottom flask. 3.1 mg of the prepared catalyst and 0.02 g sodium ascorbate (10 mol%)
were added and the flask content was stirred at room temperature. The completion of the
reaction was monitored by thin layer chromatography (TLC). After completion of the
reaction, the catalyst was separated magnetically and the flask content was extracted with
ethyl acetate. The catalyst was washed with ethanol three times and dried at 60 °C and used
for next runs. All the products are known compounds and the spectral data and melting points
were identical to those reported in the literature.17ꢀ24
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Results and discussion
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Preparation of the Catalyst
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The heterogeneous catalyst was prepared by immobilization of Cu (II) ions in the structure of
crossꢀlinked solid polymeric nanocomposite. The polymeric support was prepared by
simultaneous polymerization, grafting and crossꢀlinking of acrylamide onto starch as a
biodegradable backbone. Using starch makes the prepared catalyst more biodegradable and
environmentally friendly. The polymerization was performed in the presence of APS as
initiator and MBA as crossꢀlinking agent. While crossꢀlinking polymerization was performed,
MNPs were entrapped into the polymeric matrix. The presence of acrylate groups on the
surface of MNPs causes the covalent attachment of MNPs to polymer. Moreover, acrylate
functionalized MNP acts as a second crossꢀlinker and improves the stability of solid support.
The presence of magnetic nanoparticles into the polymeric support facilitates the separation
and recyclability of the catalyst. The copper ions were then loaded onto the surface of
magnetic nanocomposite by complextion with numerous amide groups of MNP@SPAAm.
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This leads to high loading and low leaching of copper ions in the prepared catalyst. The
synthetic route of the prepared catalyst is illustrated in Fig. 1.
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Fig. 1 The synthetic route of MNP@SPAAm/Cu catalyst.
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Characterization
FTIR spectra of Fe3O4, Fe3O4@SiO2, Fe3O4@SiO2@MPS and MNP@SPAAm are shown in
Fig. 2. The peak appeared at 570 cmꢀ1 is characteristic peak of FeꢀO stretching vibrations of
Fe3O4. The strong peak appeared at 1100 cmꢀ1 is attributed to SiꢀO stretching vibrations of
silica layer coated on Fe3O4. In the spectrum of Fe3O4@SiO2@MPS (Fig. 1c), the extra weak
peak appeared at 1725 cmꢀ1 is related to C=O stretching band and confirms that MPS was
successfully coated onto Fe3O4@SiO2 nanoparticles. The peaks appeared in the spectrum of
MNP@SPAAm are due to different functional groups present in the structure of starch and
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polyamide. The peaks appeared at 3500, 2950 and 1670 cmꢀ1 are related to OꢀH, CꢀH and
C=O amide stretching bands of polymer matrix, respectively.
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Fig. 2 FTIR spectra of Fe3O4 (a), Fe3O4@SiO2 (b), Fe3O4@SiO2@MPS (c) and MNP@SPAAm (d).
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Fig. 3a shows the TEM image of Fe3O4 nanoparticle, synthesized by coprecipitation method
with size of 5ꢀ9 nm. These sizes of MNPs are suitable for catalytic application, due to high
magnetization and fast separation. The TEM image of MNP@SPAAm/Cu (Fig. 3b) shows
that magnetic nanoparticles (dark spots) are wellꢀdispersed in the polymeric matrix (gray
shell). The SEM image of MNP@SPAAm/Cu (Fig. 3c) also shows that the prepared particles
have semispherical morphology with rough surface. Such rough structure of the catalyst
increases surface area of catalyst and improves its catalytic activity. The presence of copper
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as well as iron and silica in the structure of the catalyst was also confirmed by EDX analysis
(Fig. 3d).
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Fig. 3 HRTEM images of Fe3O4 (a) and MNP@SPAAm/Cu (b) and SEM (c) image and EDX analysis
(d) of MNP@SPAAm/Cu.
The loading of copper on the surface of support was calculated using ICPꢀOES and the value
of 1.6 mmol gꢀ1 was obtained. The high loading of copper obtained here is due to the
polymeric nature of support surface with large chelating groups on the surface of support.
The loading level of catalytically active species on the surface of solid supports is an
important feature of catalysts since high loadings reduce weight percent of catalyst required
for the reaction. This feature is especially more prominent for large scale applications.
The XRD pattern of MNP@SPAAm/Cu is shown in Fig 4. Six peaks appeared at 2θ values
about 30, 36, 43, 53, 57, and 62° are characteristic peaks of Fe3O4 particles, indicating the
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crystalline phase of Fe3O4 nanoparticles did not changed during the catalyst preparation. The
broad peak at 2θ range of 20ꢀ30° is related to amorphous silica layer in MNPs.
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Fig. 4 XRD pattern of MNP@SPAAm/Cu.
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Magnetic properties of bare Fe3O4 and MNP@SPAAm/Cu were investigated by VSM and
the related magnetization curves are depicted in Fig. 5. It is observed that magnetic hysteresis
loop of both samples exhibits superparamagnetic characteristic at room temperature.
Saturation magnetizations of MNPs and MNP@SPAAm/Cu are 64 and 22 emu gꢀ1,
respectively. Although saturation magnetization decreases after embedment of MNPs into the
structure of polymeric network, it is still high enough to be readily separated by an external
magnetic field.
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Fig. 5 Magnetization curve of MNPs (a) and MNP@SPAAm/Cu (b).
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TGA curves of Fe3O4@SiO2, Fe3O4@SiO2@MPS, pure starch and MNP@SPAAm/Cu are
shown in Fig. 6aꢀd. The weight loss observed at about 100 °C in all curves is related to
removal of physically adsorbed water molecules. The weight loss occurred at 250ꢀ450 °C in
TGA curve of Fe3O4@SiO2@MPS is due to degradation of propylmethacrylate groups
grafted onto Fe3O4@SiO2. The main thermal degradation of pure starch occurs at 200 °C and
about 90 wt% of starch is degraded up to 700 °C. TGA curve of MNP@SPAAm/Cu shows a
twoꢀstep degradation behavior, the first of which occurs at 250 °C and is related to
degradation of starch. The second degradation step of MNP@SPAM/Cu starts at 320 °C and
about 40 wt% of the sample is lost in this step due to decomposition of grafted
polyacrylamide.
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Fig. 6 TGA curves of Fe3O4@SiO2 (a), Fe3O4@SiO2@MPS (b), pure starch (c) and
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MNP@SPAAm/Cu (d).
Catalytic performance of MNP@SPAAm/Cu
The catalytic activity of the prepared catalyst in multicomponent cycloaddition of alkyl
halides, sodium azide and terminal alkynes was then examined. The reaction of phenyl
acetylene, benzyl bromide and sodium azide was chosen as the control reaction and the effect
of different experimental conditions on yield of the reaction was investigated.
The results of optimization experiments are listed in Table 1. It can be seen that in the
absence of any catalyst, no significant amount of product was obtained even at 70 °C (Entries
1,2). The same result was observed in the case of using just MNPs or MNP@SPAAm, and
the reaction yield was very low, indicating MNPs and MNP@SPAAm do not have any
catalytic activity in this reaction (Entries 3,4). In the presence of 5 mg (0.8 mol%) of
MNP@SPAAm/Cu, the reaction yield was increased to 99% in 30 min at 50 °C (Entry 5).
However, the reaction was slower at room temperature and only 80% yield was obtained after
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2 h (Entry 6). Completion of the reaction at room temperature required longer times up to 8 h
(Entry 7). The effect of the amount of the catalyst on yield of the reaction was also
investigated. Decreasing the amount of MNP@SPAAm/Cu to 0.5 mol% did not change the
yield of the reaction (Entry 8). However, further decreasing of the amount of
MNP@SPAAm/Cu to 0.3 and 0.1 mol% reduced rate of the reaction, and only 73 and 66%
yield were obtained after 1 h (Entries 9,10). Thus, 0.5 mol% was chosen as the optimum
amount of MNP@SPAAmCu. In other experiments, the reaction performed in the presence
of small amounts of catalyst and the results showed that in longer reaction times only 0.01
mol% of catalyst gave 89% yield (Entries 11,12). The reaction was also performed in
different solvents such as H2O/tꢀBuOH (3:1), tꢀBuOH, CH3CN, CH3OH and toluene (Entries
13ꢀ17). However, the best result was obtained in pure water or water/alcohol mixture due to
NaN3 dissolves in water. Based on the results obtained here, the reaction of alkyl halides,
sodium azide and alkynes in H2O at 50 °C in the presence of 0.5 mol% MNP@SPAAm/Cu
was considered as optimum experimental condition for further experiments.
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Table 1 Optimization of the reaction conditions for the synthesis of 1,4ꢀdisubstituted 1,2,3ꢀ
triazolesa
Entry
Catalyst
Cat. Amount
T
(°C)
50
70
50
50
50
r.t
Time
(h)
7
8
7
7
0.5
2
8
0.5
1
Solvent
Yield
(%)b
ꢀ
12
27c
7
99
80
97
99
73
66
94
89
99
46
32
68
10
(mol%)
1
2
3
4
5
6
7
8
9
ꢀ
ꢀ
ꢀ
ꢀ
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
MNPs
100 mg
100 mg
0.8
MNP@SPAAm
MNP@SPAAm/Cu
MNP@SPAAm/Cu
MNP@SPAAm/Cu
MNP@SPAAm/Cu
MNP@SPAAm/Cu
MNP@SPAAm/Cu
MNP@SPAAm/Cu
MNP@SPAAm/Cu
MNP@SPAAm/Cu
MNP@SPAAm/Cu
MNP@SPAAm/Cu
MNP@SPAAm/Cu
MNP@SPAAm/Cu
0.8
0.8
0.5
0.3
0.1
0.1
0.01
0.5
0.5
r.t
50
50
50
50
50
50
50
50
50
50
10
11
12
13
14
15
16
17
1
H2O
H2O
H2O
10
24
0.5
1
1
2
H2O/tꢀBuOH
tꢀBuOH
CH3CN
CH3OH
Toluene
0.5
0.5
0.5
3
a
Reaction condition: Phenyl acetylene (1 mmol), benzyl bromide (1 mmol), sodium azide
(1.3 mmol), sodium ascorbate (10 mol%), solvent (2 ml).
b Isolated yield
c A mixture of isomers.
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The activity of the catalyst in multicomponent cycloaddition reaction of sodium azide and
various alkyl halides and alkynes were then investigated using optimized experimental
conditions obtained previously. The structure of the alkyl halides and alkynes used as
substrates and the results of the experiments are shown in Table 2. All reactions were
proceeded easily and the corresponding 1,2,3ꢀtriazoles were produced with satisfactory
yields. The results show that the prepared catalyst is very efficient in synthesis of various
1,2,3ꢀtriazole compounds.
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Table 2 Cycloaddition reaction of different alkyl halides and alkynes catalyzed with
MNP@SPAAm/Cua
.
a Reaction condition: alkyl halide (1 mmol), NaN3 (1.3 mmol), alkyne (1 mmol), H2O (2 mL).
bIsolated yield.
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Reusability of the catalyst
Reusability is an important feature of the catalyst which should be examined in catalytic
reactions. The reaction of phenyl acetylene, benzyl bromide and sodium azide was chosen as
model reaction and the reusability of MNP@SPAAm/Cu in this reaction was tested. After
completion of the reaction, the catalyst was readily separated by using a magnet, washed with
ethanol (2×25 mL) and dried at 50 °C and used for next run. This process was repeated for
ten runs of reactions and the results are shown in Fig. 7. It can be seen that high yields of the
reactions were obtained even after ten cycles of reaction. However, the time required for
completion of the reaction was slightly increased. It is also observed that turnover number
(TON) of the catalyst did not changed significantly. However, turnover frequency (TOF) of
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the catalyst decreased after 6 cycles which resulted from increasing in reaction times. It is
notable, that the increasing of the reaction time is attributed to loss of catalyst mass during
the separation process. High catalytic activity and high loading of the catalyst along with
simple separation, recyclability and reusability of MNP@SPAAm/Cu make it cost effective
and environmentally friendly.
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Fig. 7 Recycling experiment.
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The structure of the recycled catalyst was investigated by FTIR spectroscopy and was
compared with that of the fresh catalyst. Fig. S1 shows that FTIR spectra of both fresh and
recycled catalyst are almost similar. Moreover, ICPꢀOES shows that there are no significant
changes in copper content of the recycled catalyst and loading of copper after 10 cycles was
1.46 mmol gꢀ1. The results confirm that the catalyst is stable and its structure and composition
did not change even after ten times recycling.
In order to investigate the leaching of the catalyst, the reaction of phenyl acetylene, benzyl
bromide and sodium azide was chosen as the model reaction and performed under optimized
condition given in Table 1. The reaction was stopped after half of the reaction time and the
catalyst was separated from the reaction mixture by using a magnet. The remaining mixture
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(without catalyst) was left to stir for another period of half the reaction time. As is shown in
Fig. 8, no more products were produced after removal of the catalyst indicating there is no
significant leaching of copper ions. Moreover, based on the results of ICPꢀOES, no free
copper ions were detected in the reaction mixture which confirms that the leaching of catalyst
is negligible.
299
300
301
302
303
304
305
Fig. 8 Leaching experiment.
306
307
308
309
310
311
312
313
314
315
316
317
Comparison with other catalysts
The catalytic performance of MNP@SPAAm/Cu was then compared with that of some other
catalysts used for Huisgen cycloaddition of azides and alkynes. The reaction of phenyl
acetylene, benzyl bromide and sodium azide was chosen as the model reaction and the data
obtained from some catalysts reported recently are summarized in Table 3. It is observed that
in most cases the yield of the reactions is high. However the process introduced in this study,
is a green approach in which the reaction is performed in water at mild temperature and is
completed in short time. The catalyst is partly composed of starch which as a nonꢀtoxic
natural polymer makes the catalyst more biodegradable and environmentally friendly.
Because of its magnetic properties, the catalyst can also be easily and rapidly separated from
the reaction mixture by using a magnet. Moreover, the loading of the catalyst prepared here is
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very high which in turn decreases the amount of catalyst required for the reaction. Due to
high loading of the catalyst, only a small amount of catalyst can precede the reaction
effectively.
318
319
320
Table 3 The comparison of MNP@SPAAm/Cu with other catalysts reported for Huisgen
cycloaddition.
Cu loading Cat. Amount
(mmol gꢀ1) (mg(mol%))
T
(°C)
r.t
r.t 12
70 12
50
70
r.t 0.17
Time Yield
Catalyst
Chitosan/Cu
Solvent
H2O
CH2Cl2
H2O
H2O
H2O
Ref
(h)
(%)
99
92
95
97
98
98
99
95
91
0.80
Chitosanꢀcoated Fe3O4/Cu 0.77
50(0.4)
20(1.54)
38.5(10)
200(2)
4
28
22
31
32
33
34
17
24
Cu/SiO2
2.59
0.1
Hydroxyapatite/Cu (II)
Cu NPs/Activated carbon
Silica PEI/CuNPs
MNP@Triazole/Cu
MNP@PILCu
8
3
0.3
17(0.5)
2(0.05)
10(0.5)
4(0.7)
0.24
0.51
1.87
0.77
DMSO
H2O/tꢀBuOH 55
2
H2O
H2O/CH3OH
50 2.5
70 12
Cu NPs/Graphite
6.5(0.05)
35
This
study
MNP@SPAAm/Cu
1.6
3.1(0.5)
H2O
50 0.5
99
321
322
323
324
325
326
327
328
329
330
331
332
333
Conclusion
We have successfully developed a green heterogeneous catalytic system for Huisgen
cycloaddition by immobilization of copper ions on magnetic polymeric supports. The solid
support was prepared by polymerization and grafting of AAm onto starch in the presence of
functionalized Fe3O4 magnetic nanoparticles. The presence of starch makes the prepared
catalyst more cost effective and ecoꢀfriendly. The loading level of copper ions on the crossꢀ
linked polymeric supports was 1.6 mmol gꢀ1 and no significant loss of catalyst activity was
observed. The prepared catalyst exhibits high catalytic activity in Huisgen cycloaddition of
various azides and alkynes. 1,2,3ꢀtriazoles with good to excellent yields were synthesized by
using the prepared catalyst. The catalyst was separated magnetically and reused for ten cycles
of reaction without any significant loss of catalytic activity. Finlay, comparison of this
protocol with other reported methods showed that the presented catalyst is used in lower
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weight percent. This aspect of catalyst is especially useful in large scale where a small
amount of catalyst can produce large amounts of products.
334
335
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Graphical Abstract
Magnetic Starch Nanocomposite as a Green Heterogeneous Support for
Immobilization of Large Amounts of Copper Ions
Ali Pourjavadi*, Anahita Motamedi, Seyed Hassan Hosseini, Mojtaba Nazari
Polymer Research Laboratory, Department of Chemistry, Sharif University of Technology, Tehran, Iran
E-mail address: purjavad@sharif.edu; Phone/fax: (982)166165311