Magnetically recoverable chitosan-stabilised copper-iron oxide nanocomposite material as an efficient heterogeneous catalyst for azide-alkyne cycloaddition reactions

Article abstract of DOI:10.1039/c5nj00754b

Chitosan-stabilised copper-iron oxide nanocomposite material is found to be a very efficient recyclable/reusable heterogeneous catalyst for azide-alkyne cycloaddition reaction under mild conditions. The as-synthesized nanocomposite material is magneticall

Full text of DOI:10.1039/c5nj00754b

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Magnetically recoverable chitosan stabilised copper-iron oxide
nanocomposite material as efficient heterogeneous catalyst for
azide-alkyne cycloaddition reactions
Received 00th January 20xx,
Accepted 00th January 20xx
Mitali Chetia,a Abdul Aziz Ali,a Diganta Bhuyan,b Lakshi Saikia,b* and Diganta Sarmaa*
DOI: 10.1039/x0xx00000x
Chitosan stabilised copper-iron oxide nanocomposite material is found to be a very efficient recyclable/reusable
heterogeneous catalyst for azide-alkyne cycloaddition reaction under mild condition. The as-synthesized nanocomposite
material is magnetically recoverable and reusable at least up to four times without significant loss in their catalytic activity.
The catalytic system is found to be highly useful for the regioselective synthesis of a wide range of 1,2,3-triazoles from
various azides and alkynes.
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usually generated from copper (II) salts with reducing agents (e.g.
sodium ascorbate) or added directly as cuprous salts, usually with
stabilizing ligands.[8] Sometimes metallic copper or clusters are also
Introduction
The Huisgen[1] 1,3-dipolar cycloaddition of alkynes and azides is the
most convenient and straightforward approach for synthesis of
1,2,3-triazoles. This classical reaction usually requires higher
temperatures and provides a mixture of 1,4- and 1,5-disubstituted
1,2,3- triazoles (Scheme 1). Sharpless et al.[2] and Meldal et al.[3] in
2002 independently published their pioneering work on Cu
catalyzed azide alkyne cycloaddition (CuAAC) reaction leading to a
employed. But these catalytic systems sometimes require oxidative
agents. The reactions are relatively slow and a significant amount of
catalyst is necessary. In some cases formation of diacetylenes and
bistriazoles are also observed.[9] In order to overcome these
drawbacks, systems with heterogeneous catalyst have been
developed. Heterogeneous catalyst exhibits possible advantages[10]
mild and efficient synthesis of 1,4-disubstituted 1,2,3-triazoles. For such as easy separation, reusability, the potential for incorporation
reactions to be considered “click” they must fulfill a number of basic
requirements: (i) they must demonstrate no sensitivity towards
moisture or oxygen, (ii) they must afford products in high yields and
with stereospecificity, and (iii) they must proceed in the absence of
a solvent (or the use of a benign one) and led themselves to simple
product isolation. CuAAC reaction satisfies the basic criteria of click
chemistry and is increasingly used in diverse applications ranging
from chemical and combinatorial synthesis, bioconjugation, and
biology to materials science.[4-7]
in continuous reactors and microreactors and are becoming a trade
in the present research works in chemistry. These days, works on
click-compatible heterogeneous catalyst system is gaining more
attention among the scientific community. In an effort to find
efficient heterogeneous catalyst system, Cu (I) catalysts have been
immobilized on polymers or zeolite, Cu (0) on charcoal, Cu (0)
nanoparticles as well as CuO nanostructures, have also been
successfully employed in azide-alkyne cycloaddition.[11-15]
R1
N
R1
N
Chitosan is
a natural, nontoxic, renewable biopolymer and
N
N
N
N
R1
+
N
R2
+
N
N
possesses a great quantity of hydroxyl and amine groups, which can
be coordinated with metal ions through chelate mechanism.[16] It is
widely used in many industrial and manufacturing processes and is
commonly used for metal extraction and catalysis.[17-22] Recently,
functionalized magnetic nanoparticles represent as feasible
alternatives to conventional materials as robust, easily available,
high-surface-area heterogeneous catalyst supports. They offer an
environmentally benign advantage of being magnetically separable
and reduce the requirement of catalyst filtration after completion
of the reaction.[23] Magnetite is an ideal oxide support, having a
very active surface for adsorptions or immobilization of metals and
ligands with easy preparation system. It can be separated by simple
magnetic decantation after the reaction which makes it a more
sustainable catalyst.[24] Catalysts with various metals like Pd, Ru, Co,
Mo supported on magnetite have been developed for use in various
R2
R2
1,4-disubstituted
triazole
1,5-disubstituted
triazole
Scheme 1: Huisgen azide-alkyne cycloaddition
A good number of works have been done using copper (I) source in
regioselective azide-alkyne cycloaddition. The copper (I) species
required in the catalyzed version of the Huisgen cycloaddition are
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reactions.[25] Here, we developed a magnetic catalyst with Cu in
order to use in azide-alkyne cycloaddition.
Figure 1: TEM images of (a) & (b) CS-Fe3O4 and SAED pattern (inset),
(c) & (d) CS-Fe3O4-Cu and SAED pattern (inset).
To continue our interest on click chemistry,[26] here we applied
magnetically recoverable and reusable chitosan stabilised copper
iron oxide nanocomposite material as heterogeneous catalyst for
regioselective synthesis of 1,2,3-triazoles. In the catalyst, Cu0
nanoparticles were attached on chitosan coated Fe3O4 (CS-Fe3O4-
Cu0).
The XRD pattern of CS-Fe3O4 [Figure 2 (a)] contains a sharp peak at
2 θ = 21.2 which is characteristic for chitosan. The diffraction peaks
appeared at 2 θ = 18.6, 30.9, 35.7, 38.5, 43.7, 52.6, 57.5, and 63.1
were assigned to (111), (220), (311), (222), (400), (422), (511) and
(440) reflections respectively, which are indexed to the Fe3O4
(JCPDS Card No. 19-0629). For CS-Fe3O4-Cu nanocomposite
material, the characteristic peaks due to chitosan and Fe3O4 was
retained with a little shift in their peak position which is depicted in
Figure 2 (b). The characteristic peak due to metallic Cu was
observed at 2 θ = 43.7, 50.3 and 74.1 which is assigned to (111),
(200) and (220) indexed to the face centered cubic (fcc) lattice of
metallic Cu (JCPDS Card No. 4-0836). But peak due to (111)
reflection of metallic Cu merged with the (400) reflection of Fe3O4.
2. Results and Discussion:
The synthesis of CS-Fe3O4-Cu (Represented as Cu@Fe3O4) was
depicted in Scheme 2 which consists of three steps. Firstly, we have
synthesized CS-Fe3O4 by co-precipitation of Fe2+ and Fe3+ at pH 12.
Secondly the Cu2+ ions were adsorbed by the amino and hydroxyl
group of chitosan coated on Fe3O4. Finally the adsorbed Cu2+ ions
were reduced to Cu0 by NaBH4 and the Chitosan stabilized the Cu0
nanoparticles.
The FT-IR spectra (Figure 3a) of CS-Fe3O4 exhibited characteristic
peaks for chitosan and Fe3O4.[16] The peak at 3385 cm-1 was assigned
as the asymmetric stretching vibration of N-H and O-H. The C-H
stretching vibration appears at 2930 and 2864 cm-1. The other
characteristic peaks at 1640, 1383, 1119, 613 cm-1 correspond to
NH (bending), C-N (stretching), bridging C-O-C (asymmetric), Fe-O-
Fe (stretching). In case of CS-Fe3O4-Cu all characteristic peaks due to
chitosan and Fe3O4 are retained with little shift of their position
[Figure 3 (a) & (b)].
(b)
(a)
1200
)
1400
1300
1200
0
2
Scheme 2. Synthesis of Cu0 nanoparticles on chitosan coated Fe3O4
2
(
)
)
1
1
1
1
1100
1000
900
5
1
(
(
Chitosan
)
0
0
Chitosan
2
(
The TEM images of the CS-Fe3O4 showed that the diameters of the
Fe3O4 nanoparticles are 10-15 nm and mostly spherical shape
[Figure 1(a) & (b)]. The SAED pattern depicted in Figure 1 (b) inset
confirmed the single crystallinity of the Fe3O4 nanoparticles. In case
of CS-Fe3O4-Cu, the Cu0 nanoparticles can easily be recognized as it
appears brighter than Fe3O4 nanoparticles in the TEM [Figure 1 (c) &
(d)]. The Cu0 nanoparticles are spherical in shape and average
diameters are 10 nm. The single crystalline nature of the Cu and
Fe3O4 nanoparticles are seen from their SAED pattern [Figure 1(c)
inset].
F
e
O
3
4
Cu
10
20
30
40
50
60
70
80
10
20
30
40
50
60
70
80
2θ
(deg.)
Figure 2: PXRD patterns of (a) CS-Fe3O4 and (b) CS-Fe3θO4-Cu.
2
(deg.)
(b)
(a)
44
40
36
32
28
24
20
48
44
40
36
32
28
24
20
ν
(C-N)
(a)
(b)
ν
(N-H)
ν
(Fe-O-Fe)
ν
(N-H)
ν
(C-H)
ν
(C-N)
ν
(C-H)
ν
(C-O-C)
ν
(C-O-C)
(Fe-O-Fe)
ν
ν
(O-H)&ν (N-H)
ν
(O-H) &ν (N-H)
4000 3500 3000 2500 2000 1500 1000 500
4000 3500 3000 2500 2000 1500 1000 500
-1
Wavenumber
(
cm
)
-1
Wavenumber
(
cm
)
(c)
(d)
Figure 3: FT-IR spectra of (a) CS-Fe3O4 and (b) CS-Fe3O4-Cu.
Cu0
Cu0
We applied this magnetically recoverable and reusable catalyst for
carrying out CuAAC reactions leading to regioselective formation of
Fe3O4
2 | J. Name., 2012, 00, 1-3
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1,2,3-triazoles. The experiments began with the intention of condition, various alkynes-both aromatic and aliphatic react with
optimizing the reaction conditions for dipolar cycloaddition of azides to afford 1,2,3-triazoles in good to excellent yields (Table 2,
benzylazide and phenylacetylene. To find out the most effective Entries 1-11). Moreover, the catalyst was found to be affective for
solvent for the CuAAC reaction using our catalyst, the reaction of non terminal alkynes also (Table 2, Entry 12).
benzyl azide and phenyl acetylene was carried out in different
Table 2. Study of azide–alkyne cycloaddition of a variety of azides
and alkynesa
solvent systems (Table 1, Entries 1-8). Dichloromethane was found
to be the best solvent system for the azide-alkyne cycloaddition
reaction with our catalyst (Table 1, Entry 6). At room temperature
with 20 mg (1.54 mol%) of the catalyst the reaction seemed to
proceed very well to give the desired triazole product in excellent
yield in 12 h.
N
Cu@Fe3O4
N
N
R-N3
R'
R'
DCM, r.t., 12 h
R
Table 1. Solvent optimization studya
TOF (per
hour)
Entry
Azides
Alkynes
Product
% Yieldsb
N
N
N
Cu@Fe3O4
N3
+
DCM, r.t., 12 h
N3
1
2
a
b
c
4.98
4.17
5.19
4.22
5.14
4.65
4.27
4.76
5.03
4.87
4.82
5.19
92
77
96
78
95
86
79
88
93
Entry
Solvent
% Yieldsb
N3
N3
3
1
2
3
4
5
6
7
8
H2O/t-BuOH (1:1)
THF
30
30
N3
4
d
e
f
N3
7
5
( )
THF/H2O (1:1)
Acetonitrile
H2O
60
6
Cl
N3
<10
60
7
g
h
Br
N3
8
Br
N3
OH
DCM
92
N3
9
i
OH
DMF
<10
<10
10
11
12
j
Cl
N3
N3
90
89
OH
DMSO
k
OH
N3
a Reagents and reaction conditions: benzyl azide (1 mmol), phenyl
acetylene (1.1 mmol), catalyst {20 mg (1.54 mol%) , 4.89 wt%} in the
given solvent was stirred at room temperature for 12 h; b Isolated
yields
O
OCH3
O
l
96
H3CO
a
All reactions were carried out using azide (1 mmol), alkynes (1.1
mmol), Catalyst (20 mg, 1.54 mol%, 4.89 wt%), in DCM (3 mL) at room
temp, 12 h.
Therefore,
further
reactions
were
performed
using
dichloromethane as the solvent. Reactions using CS-Fe3O4 (without
the Cu nanoparticles) and the CS-Fe3O4-Cu(CH3COO)2 (before the
reduction) were also performed to be sure that the observed
catalytic activity is only a result of the supported Cu nanoparticles.
The use of CS-Fe3O4 shows no conversion and use of CS-Fe3O4-
Cu(CH3COO)2 gives lower yields under our reaction conditions.
Therefore it is found that only CS-Fe3O4-Cu0 has good catalytic
activity for the azide –alkyne cycloaddition.
b Isolated yields.
For the useful applications of such heterogeneous systems, the
lifetime of the catalyst and its level of reusability are very significant
factors. In order to find out whether our catalyst fulfils its
applicability or not, a set of experiments were performed for the
cycloaddition of phenyl azide and phenylacetylene using the
recycled CS-Fe3O4-Cu catalyst. After the completion of the first
reaction, the product was extracted and the catalyst was recovered
easily which, due to its magnetic nature, got stuck with magnetic
After finding the best reaction condition, CuAACreactions were
carried out with various azides and alkynes. Under this reaction
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bead used in the reaction. A fresh reaction was then performed The TEM image of recovered catalyst after 4th cycle was depicted in
with new reactants, under the same conditions. The results Figure 4. The sizes and shape Fe3O4 and Cu nanoparticles seemed
obtained in our experiment confirmed that it was possible to to be retained from the TEM spectra
recycle and reuse the catalytic system for at least up to four times
.
without losing any catalytic activity (Table 3, Entries 1-4).
Experimental section
Table 3. Recyclability of the catalytic systema
Reagents and solvents were obtained from commercial suppliers
and used without further purification. All reactions were carried out
in oven dried glassware under atmospheric conditions otherwise
noted. All reported yields are isolated yields.
N
N
N
N3
Cu@Fe3O4
+
DCM, r.t.
Synthesis of chitosan coated Fe3O4 (CS-Fe3O4):
Entry
Run
1st
% Yieldb
96
TON
62.3
62.3
61.0
59.1
The chitosan coated Fe3O4 nanoparticles were synthesized by a little
modification of the reported procedure.[16] In a typical experimental
procedure, 2 g of chitosan was dissolved in 5 % acetic acid solution.
Then anhydrous FeCl3 (4.8660 g) and FeCl2.4H2O (2.9820 g) were
added to the chitosan solution and sonicated for 30 minutes
(Scheme 2). Then the mixture was magnetically stirred at 1400 rpm
for 3 h. After 3 h of stirring, a solution of 4M NaOH solution was
added drop wise to the stirring solution until the pH became 12.
The products from this step were washed by centrifugation with
double distilled water until the neutral pH was obtained. The brown
solid product was then dried in a desiccator. The as-synthesized
material was designated as CS-Fe3O4.
1
2
3
4
2nd
3rd
4th
96
94
91
a)
Reagents and reaction conditions: phenyl azide (1 mmol),
phenyl acetylene (1.1 mmol), catalyst (20 mg) in DCM was
stirred at room temperature for 12 h.
b) Isolated yields
Synthesis of Cu0 nanoparticles on chitosan coated Fe3O4 (CS-Fe3O4-
Cu):
In order to establish the heterogeneity of the catalyst, the following
technique was followed which confirmed that during the progress
of the reaction, metal loss from the solid surface did not occur. To
perform this test, an experiment was carried out for the
cycloaddition of benzyl azide (1 mmol) and phenyl acetylene (1.1
mmol) in presence of the catalyst using dichoromethane as solvent.
The reaction was allowed to run for 6 h. Then the progress of the
reaction was noticed and catalyst was removed from the reaction
mixture.
0.5 g of CS-Fe3O4 was taken into a 100 ml round bottom flask and
dispersed in 25 ml ethanol then 25 ml (0.25 mmol) ethanolic
solution of Cu(CH3COO)2 was added slowly under vigorous stirring
condition. The stirring was continued for another 4 h. After 4 h of
stirring, Cu2+ ions were completely adsorbed by chitosan and CS-
Fe3O4– Cu(CH3COO)2 composite was separated by an external
magnet and dried in a desiccator. The dry CS-Fe3O4–Cu(CH3COO)2
composite was again dispersed in 50 ml of methanol and 15 ml
solution of NaBH4 (5 mmol) in methanol was then added slowly in a
nitrogen environment under constant stirring conditions. The
reaction started immediately and the colour changed from brown
to black, due to conversion of adsorbed Cu (II) into Cu (0)-
nanoparticles. The black solid material was recovered using an
external magnet and washed with distilled methanol for several
times and then dried in a desiccator. The as-synthesized material
was designated as CS-Fe3O4-Cu. The material was characterized by
PXRD, FT-IR, TEM etc.
After that the reaction mixture was again allowed to run for
another 6 h. It was found that there was no progress of the reaction
after the removal of the catalyst. It clarifies that our catalyst does
not undergo any loss of metal from the solid support during
reaction which proves its useful applicability to a wide extent.
FE-SEM: The FESEM images [Figure 5 (a) & (b)] showed an
aggregate morphological structure of CS-Fe3O4 due to magnetic
attraction among chitosan coated Fe3O4. The EDX pattern
determined the elemental compositions and spatial distributions of
different
Figure 4: TEM images of recovered CS-Fe3O4-Cu catalyst (after
th cycle)
4
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dispersion of all elements across the CS-Fe3O4. In case of CS-Fe3O4-
Cu, no change in morphological structure was observed [Figure 6 (a)
& (b)].The corresponding EDX pattern determined the Cu along with
C, N, O and Fe elements of CS-Fe3O4 [Figure 6 (c)].The amount of Cu
obtained from EDX analysis is 4.66 (wt%). Further confirmation on
uniform dispersion of elements obtained from EDS mapping
analysis [Figure 6 (d)].
(a)
(b)
The FESEM-EDS analysis was performed in Carl Zeiss Ultra 55 FE-
SEM.
(c)
(d)
AAS analysis:
The amount of Cu was derived from AAS analysis of CS-Fe3O4-Cu
sample which is 4.89 (wt%). This amount of Cu is quite resemble
with EDX data which confirmed the uniform dispersion of Cu and its
presence mostly in the surface of CS-Fe3O4-Cu as SEM scans only
surface topography of a sample.
C Ka
N Ka
Fe Ka
O Ka
The Atomic absorption spectroscopy (AAS) measurement was
carried out using PerkinElmer (Model-AAnalyst-700) spectrometer.
Prior to analysis the sample was digested in aqua regia.
Figure 5: FESEM images (a) & (b) of CS-Fe3O4, (c) EDX pattern of CS-
Fe3O4 (d) EDS mapping analysis from the selected rectangle in
Figure (c).
Powder XRD patterns were recorded on a Rigaku, Ultima IV X-ray
diffractometer in the 2θ range of 10-90◦ using Cu Kα source (λ =
1.54 Å). FTIR spectra (4000-400 cm-1) were recorded as KBr pellets
in a Shimadzu IR affinity-1 spectrophotometer. The Transmission
electron microscopy (TEM) images were taken using JEOL (Model
JEM-2011).
(a)
(b)
Thin layer chromatography (TLC) was carried out using aluminium
sheets pre-coated with silica gel 60F254 (Merck) and was visualized
under 254 nm UV light. 1H NMR (300 MHz), 13C NMR (75 MHz)
were measured on a Brucker Avance 300 MHz spectrometer.
Chemical shifts are reported in parts per million (ppm, ) downfield
from residual solvents peaks and coupling constants are reported as
Hertz (Hz). Splitting patterns are designated as singlet (s), doublet
(d), triplet (t), quartet (q), broad (br) etc. Splitting patterns that
could not be interpreted or easily visualized are designated as
multiplet (m). ESI-MS spectra were recorded on an Agilent 6510 ESI-
QTOF LC/MS mass spectrometer. Melting points were measured
with a Büchi B-540 melting point apparatus.
(d)
(c)
C Ka
N Ka
O Ka
Fe Ka
Cu Ka
Azides. All azides were synthesized according to the reported
procedure.[27]
A typical CuAAC procedure for the preparation of 1,2,3-
triazole: To a mixture of catalyst (20 mg, 1.54 mol%) and
azide ( 1 mmol) in dichloromethane (3 ml), alkyne (1.1 mmol)
was added at room temperature. The resultant mixture was
stirred until the reaction was complete. Then the reaction
mixture was washed with H2O and brine, and dried over
anhydrous Na2SO4. Removal of the solvent yielded a residue,
which was purified by column chromatography over silica gel.
Figure 6: FESEM images (a) & (b) of CS-Fe3O4-Cu, (c) EDX pattern of
CS-Fe3O4-Cu (d) EDS mapping analysis from the selected rectangle in
Figure (c).
elements in the of CS-Fe3O4 sample [Figure 5 (c)]. The characteristic
peaks of C, N, O and Fe confirmed that the CS-Fe3O4 sample is
composed of C, N, O and Fe elements. Furthermore, the EDS
mapping analysis [Figure
5 (d)] demonstrates the uniform
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1
1-Benzyl-4-phenyl-1H-1,2,3-triazole (a). White solid, mp 128- Yellowish solid, mp 146-148 °C, 90% yield, H NMR (300 MHz,
1
130 °C, 92% yield. H NMR (300 MHz, CDCl3): δ 7.81 (d, J= 7.2 CDCl3): δ 8.01 (s, 1H), 7.68 (d, J= 8.5 Hz, 2H), 7.50 (d, J= 8.5 Hz,
Hz, 2H), 7.66 (s, 1H), 7.43-7.30 (m, 5H), 5.59 (s, 2H) ; 13C NMR 2H) 4.88(s, 2H); 13C NMR (75 MHz, CDCl3): 135.5, 134.6, 129.9,
(75 MHz, CDCl3):
δ 148.2, 134.6, 130.4, 129.1, 128.8, 121.7, 56.2.
128.2,128.0, 125.7, 119.5, 54.2.
(1-Benzyl-1H-1,2,3-triazol-4-yl) methanol (k). White solid, mp
1
75-78 °C, 89% yield. H NMR (300 MHz, DMSO-d6): δ 8.02 (s,
1-Benzyl-4-butyl-1H-1,2,3-triazole (b). White solid, mp 64-66
1
°C, 77% yield. H NMR (300 MHz, CDCl3): δ 7.41-7.26(m, 6H),
1H), 7.40-7.31 (m, 5H), 5.50 (s, 2H), 4.52 (s, 2H), 2.50(s, 1H).
13C NMR (75 MHz, DMSO-d6): δ 148.7, 136.6, 129.1, 128.5,
128.3, 123.2, 55.5, 53.1.
5.50(s, 2H), 2.73(t, J=7.5 Hz, 2H), 1.68-1.58(m, 2H), 1.42-
1.30(m, 2H), 0.93(t, J= 7.5 Hz, 3H). 13C NMR (75 MHz, CDCl3): δ
148.8, 134.8, 128.9, 128.7, 128.4, 127.8, 120.3, 53.8, 31.3,
25.2, 22.2, 13.7.
1-Phenyl-1H-[1,2,3]triazole-4,5-dicarboxylic acid dimethyl
1
ester (l). White solid, mp 106-1080C, 95% yield, H NMR (300
1-(4-Diphenyl)-1H-1,2,3-triazole (c).
Pale yellow solid, mp 183-184 °C, 96% yield. 1H NMR (300
MHz, CDCl3): δ 8.52(s, 1H), 8.22 (d, J=5.4 Hz, 2H), 7.93 (d, J=6.9
Hz, 2H), 7.81-7.28 (m, 6H); 13C NMR (75 MHz, CDCl3): δ 148.3,
136.9, 130.1, 129.6, 128.8, 128.6, 128.3, 125.7, 120.4, 117.5.
MHz, CDCl3): δ 7.77-7.23 (m, 5H), 4.15-3.66 (m, 6H); 13C NMR
(75 MHz, CDCl3): 160.0, 159.3, 138.6, 135.4, 129.8, 129.7,
129.6, 129.5, 52.6, 52.2.
4-Butyl-1-phenyl-1H-1,2,3-triazole (d). Colorless liquid, 78%
yield. 1H NMR (300 MHz, CDCl3): δ 7.73 (d, J = 8.1Hz, 2 H),
7.53–7.39 (m, 3 H), 7.48 (s, 1 H), 2.83–2.78 (t, 2 H), 1.77–1.67
(m, 2 H), 1.49–1.37 (m, 2 H), 0.98 (t, J = 7.2 Hz, 3 H); 13C NMR
(75 MHz, CDCl3): δ 149.0, 137.1, 129.4, 128.3, 120.4, 118.7,
31.4, 25.2, 22.2, 13.7.
Conclusions
In conclusion, we have developed
a simple and efficient
heterogeneous catalytic system for the [3+2] cycloaddition of azides
and alkynes. This heterogeneous method offers a wide scope giving
excellent results with various azides and alkynes (including internal
alkynes) and provides a very high regioselectivity, with only the 1,4-
disubstituted 1,2,3-triazole regioisomer being formed. Moreover,
this heterogeneous CS-Fe3O4-Cu catalyst can be recovered
magnetically and reused at least up to 4 times without losing
catalytic activity. The easy recoverability of the catalyst and milder
reaction condition for regioselective synthesis of 1,2,3-triazoles lead
to its applicability towards various scientific prospects.
1-Octyl-4-phenyl-1H-1,2,3-triazole (e). White solid, mp 74-76
1
°C, 95 % yield. H NMR (300 MHz, CDCl3): δ 7.84(d, J=7.3 Hz,
2H), 7.74(s, 1H), 7.44-7.29(m, 3H), 4.40(t, J= 7.2 Hz, 2H), 1.96(t,
J=7.0 Hz, 2H), 1.34-1.26(m, 10H), 0.89(t, J= 6.9Hz, 3H). 13C NMR
(75 MHz, CDCl3): δ 147.5, 130.6, 129.0, 128.7, 127.9, 125.5,
119.3, 50.3, 31.5, 30.2, 28.9, 28.8, 26.3, 22.4, 13.9.
1-(4-Chlorophenyl)-4-phenyl-1H-1,2,3-triazole (f).
Yellow
1
solid, mp 225-227°C, 86% yield. H NMR (300 MHz, CDCl3): δ
8.17 (s, 1H), 7.92 (d, J =7.5 Hz, 2H), 7.77 (d, J = 8.6 Hz, 2H),
7.54–7.36 (m, 5H). 13C NMR (75 MHz, CDCl3): δ 134.4, 129.8,
128.8, 128.4, 125.7, 121.5, 117.2.
Acknowledgements
DS is thankful to CSIR, New Delhi for a research grant [No.
02(0154)/13/EMR-II]. The authors also acknowledge the
Department of Science and Technology for financial assistance
under DST-FIST programme and UGC, New Delhi for Special
Assistance Programme (UGC-SAP) to the Department of Chemistry,
Dibrugarh University.
1-(4-Bromophenyl)-4-phenyl-1H-1,2,3-triazole (g) .
White solid, mp 231-233 ºC, 79 % yield. 1H NMR (300 MHz,
CDCl3): δ 8.17 (s,1H), 7.91-7.35(m,9H). 13C NMR (75 MHz,
CDCl3): δ 135.9, 132.8, 130.8, 129.8, 128.8, 128.7, 128.5, 125.7,
122.3, 121.7, 117.2.
[1-(4-Bromo-phenyl)-1H-[1,2,3]triazol-4-yl]-methanol (h).
Notes and references
1
Yellowish solid, mp 135-1370C, 88% yield. H NMR (300 MHz,
1
2
3
4
R. Huisgen, in 1,3-Dipolar Cycloaddition Chemistry, (Eds.: A.
Padwa), Wiley, New York, 1984, pp. 1–176.
CDCl3): δ 8.00 (s, 1H), 7.72-7.59(m, 4H), 4.89 (s, 2H), 2.14(brs,
1H). 13C NMR (75 MHz, CDCl3): 135.9, 132.8, 122.4, 121.8, 56.3.
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(1-Phenyl-1H-[1,2,3]triazol-4-yl)-methanol (i). White solid, mp
115-118 °C, 93% yield. 1H NMR (300 MHz, DMSO-d6): δ 8.68 (s,
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2H), 2.50(brs,1H). 13C NMR (75 MHz, DMSO-d6): δ 149.6,
137.2, 130.3, 128.9, 121.4, 120.4, 55.4.
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6 | J. Name., 2012, 00, 1-3
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