Natural phosphate-supported Cu(ii), an efficient and recyclable catalyst for the synthesis of xanthene and 1,4-disubstituted-1,2,3-triazole derivatives

Article abstract of DOI:10.1039/C8RA08260J

Cu(NO₃)₂ supported on natural phosphate, Cu(ii)/NP, was prepared by co-precipitation and applied as a heterogeneous catalyst for synthesizing xanthenes (2-3 h, 85-97%) through Knoevenagel-Michael cascade reaction of aromatic aldehydes with 1,3-cyclic diketones in ethanol under refluxing conditions. It was further used for regioselective synthesis of 1,4-disubstituted-1,2,3-triazoles (1-25 min, 95-99%) via a three-component reaction between organic halides, aromatic alkynes and sodium azide in methanol at room temperature. The proposed catalyst, Cu(ii)/NP, was characterized using X-ray fluorescence, X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller, Barrett-Joyner-Halenda and inductively coupled plasma analyses. Compared to other reports in literature, the reactions took place through a simple co-precipitation, having short reaction time (<3 hours), high reaction yield (>85%), and high recyclability of catalyst (>5 times) without significant decrease in the inherent property and selectivity of catalyst. The proposed protocols provided significant economic and environmental advantages.

Full text of DOI:10.1039/C8RA08260J

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PAPER
Natural phosphate-supported Cu(II), an efficient
and recyclable catalyst for the synthesis of
xanthene and 1,4-disubstituted-1,2,3-triazole
derivatives†
Cite this: RSC Adv., 2018, 8, 41536
Abbas Amini, *ab Azadeh Fallah, *cd Chun Cheng and Mahmood Tajbakhsh
e
f
3 2
Cu(NO ) supported on natural phosphate, Cu(II)/NP, was prepared by co-precipitation and applied as
a heterogeneous catalyst for synthesizing xanthenes (2–3 h, 85–97%) through Knoevenagel–Michael
cascade reaction of aromatic aldehydes with 1,3-cyclic diketones in ethanol under refluxing conditions.
It was further used for regioselective synthesis of 1,4-disubstituted-1,2,3-triazoles (1–25 min, 95–99%)
via a three-component reaction between organic halides, aromatic alkynes and sodium azide in
methanol at room temperature. The proposed catalyst, Cu(II)/NP, was characterized using X-ray
fluorescence, X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy,
Brunauer–Emmett–Teller, Barrett–Joyner–Halenda and inductively coupled plasma analyses. Compared
to other reports in literature, the reactions took place through a simple co-precipitation, having short
reaction time (<3 hours), high reaction yield (>85%), and high recyclability of catalyst (>5 times) without
significant decrease in the inherent property and selectivity of catalyst. The proposed protocols provided
significant economic and environmental advantages.
Received 6th October 2018
Accepted 28th November 2018
DOI: 10.1039/c8ra08260j
rsc.li/rsc-advances
7–9
metal oxides, silica, clay, alumina, carbon) catalysts. These
exhibit high catalytic activities in a wide range of chemical reac-
Introduction
In recent years, methodological developments have signi- tions, for instance, in synthesizing aromatic nitriles from aromatic
1
0
11
12
cantly enhanced syntheses of heterocyclic compounds via aldehydes, CO oxidation, carbon dioxide reduction, asym-
1,2
separation/purication processes.
Recycling catalysts can metric addition of aryl boronic acids to a,b-unsaturated carbonyl
minimize the consumption of auxiliary substances, concluding compounds, and hydrogenation of CO
Natural phosphate (NP) is a widely available resource in
To signicantly enhance the catalytic activity, a support is many countries. As it is cheap, nontoxic and non-polluting,
added to the reaction system; that is, the intimate contact between major efforts have focused on evaluating its applications in
the supported ions and the support surface can favorably affect the the synthesis of essential compounds. Ma et al. reported the
reaction process. Over the past decade, considerable attention has adsorption capacity of natural phosphate in immobilizing
been given to recycling catalysts and heterogeneous metal-based heavy metals from aqueous solutions.
systems, including homogenous metal complexes or noble natural phosphate for the removal of heavy metals from
1
3
1
4
.
2
3,4
in economic and environmental benets.
15
16
5
17,18
Aklil et al. examined
6
18
metals (e.g., Pt, Pd, Au, Ag, Ru, Cu) on inorganic substances (e.g., aqueous solution. Natural phosphate was examined to treat
soil, waste and wastewater resources contaminated with heavy
1
9
20
a
metals, for the sorption affinity of Pb, Cu and Zn. In these
Centre for Infrastructure Engineering, Western Sydney University, Kingswood
Campus, Bld Z, Locked Bag 1797, Penrith 2751, NSW, Australia. E-mail: a.amini@
applications, natural phosphate was considered as a support for
westernsydney.edu.au; a.amini@ack.edu.kw; Fax: +61-2-9685-9298; Tel: +61-2-404- homogeneous catalysts, due to its chemical and thermal
0
60-787
stability, high surface area, and potential sorbents for
numerous heavy metals.
Xanthene (1,8-dioxo-octahydroxanthene) is a phenyl with
pyran ring fused on either sides along with two other cyclo-
hexanone rings. This compound has biological capability for
b
Department of Mechanical Engineering, Australian College of Kuwait, Mishref, Kuwait
21
c
Department of Chemistry, Payame Noor University, Tehran, Iran
d
Pharmaceutical Sciences Research Center, Department of Medicinal Chemistry,
Mazandaran University of Medical Sciences, Sari, Iran. E-mail: azadehfallah84@
gmail.com
2
2,23
e
anti-inammatory, antibacterial and antiviral activities,
dye
Department of Materials Science and Engineering, South University of Science and
24
25
Technology, Shenzhen, China
applications, corrosion inhibitory, pH-sensitive uores-
cence and laser technologies. For the synthesis of xanthenes,
Knoevenagel condensation has been employed followed by the
f
26
27
Department of Organic Chemistry, University of Mazandaran, Babolsar, Iran
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c8ra08260j
1
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Michael addition of carbonyl compounds to 1,3-dicarbonyl is needed for the preparation of 1,4-disubstituted-1,2,3-
compounds along with using a wide range of solid catalysts and triazoles. The proposed protocols for the synthesis of
inorganic salts. Various catalysts have been reported to promote xanthene and 1,4-disubstituted-1,2,3-triazole present an effi-
the synthesis of xanthene, including ICl /SiO and In(CF - cient and robust chemical processes with high yield products at
3
2
3
2
8
29
30
SO
3
)
0
3
,
lactic acid, 2,6-pyridinedicarboxylic acid, poly(- considerable short reaction times. The utilized catalyst in this
31
N,N -dibromo-N-ethylnaphtyl-2,7-sulfonamide) (PDNES), W- study (Cu(II)/NP) is recyclable by a simple ltration process,
doped ZnO, silica-supported Preyssler nanoparticles, ceric readily available, and easy to prepare with high stability.
ammonium nitrate-supported HY-zeolite, and Fe
imid-H PMo12O40 nanoparticles. However, these catalysts
possess several disadvantages, such as less availability, difficult
preparation process, containing toxic organic solvents and
32
33
34
3
O
4
@SiO
2
-
35
3
Experimental
Reagents and materials
harsh reaction conditions (microwave irradiation and high All chemicals were purchased from Merck, Germany, and Sigma
temperature). New catalysts are required to synthesize Aldrich, USA. The structural data of all synthesized products
xanthenes via simple, efficient and environmentally friendly were compared with the authentic data from literature.
processes.
1,2,3-Triazoles belong to an important class of nitrogen-
Instrumentation
containing heterocyclic compounds with enormous applica-
The chemical compositions of NP and Cu(II)/NP were deter-
mined using a PANalytical's XRF spectrometer Venus 200. X-ray
powder diffraction analyses were performed at room tempera-
ture on a vertical Philips PW1050/25 goniometer mounted with
Bragg–Brentano conguration (q, 2q) using Ni-ltered Cu-Ka
36,37
tions in biology, pharmaceutics,
and medicinal chem-
38–41
42
istry.
They are used as corrosion inhibitors,
43
44
agrochemicals, optical brighteners and dyes. The Huisgen (3
45
+
2) cycloaddition reaction of azide and alkyne (AAC) was
facilitated by Cu(I) catalysts (CuAAC) to afford 1,4-disubstituted-
˚
radiation (l ¼ 1.54 A) and facilitated with the PANalytical X'Pert
4
6,47
1
,2,3-triazoles as a regioselective product.
CuAAC-reaction
High Score Plus soware. The surface imaging was performed
using a scanning electron microscope (SEM) EM-3200. Surface
areas were characterized at 77 K using a Coulter SA 31000
instrument through an automated gas volumetric method with
nitrogen as the adsorbate. Fourier Transform Infrared (FT-IR)
spectra were recorded on a Bruker Tensor 27 spectrometer,
48
was catalyzed by various copper sources, such as Cu(I) salts,
in situ reduction of Cu(II), oxidation of Cu(0) metal, and
Cu(II)/Cu(0) comproportionation. To establish reusable cata-
lysts, Cu(I) AAC catalysts were immobilized onto polymers,
49
50
51
52
53
54
zeolite, montmorillonite, silica-supported N-heterocyclic
55
56
57
58
carbine, activated charcoal, alumina, titanium dioxide
1
13
using KBr pellets for solids. H and C Nuclear Magnetic
Resonance (NMR) spectra were recorded using a Bruker
59,60
and CuO nanoparticles.
Nevertheless, heterogeneous cata-
lysts, immobilized with Cu(I) species, suffer from inherent
thermodynamic instability of Cu(I) species, which results in an
easy oxidation to Cu(II) and/or disproportionation to Cu(0) and
Advance DRX spectrometer at 400 MHz in DMSO-d and CDCl3
6
with tetra-methyl-silane as the internal reference.
6
1
62
Cu(II) as well as copper nanoparticles. For the AAC reaction,
in which Cu(II) species are directly employed, a protocol without
Preparation of catalyst
63
deliberate addition of a reducing agent is necessitated.
The present study introduces a new surface modied natural Ni(NO
Different metal salts, including NaNO
3 3 2
, NaCl, KF, Cu(NO ) ,
3
)
2
, CuCl , CoCl , were doped on NP. They were prepared
2
2
phosphate, Cu(II) supported-natural phosphate, for the by adding 5 g NP to the aqueous metal salts solution (50 mL, 0.4
synthesis of xanthenes via Knoevenagel–Michael cascade reac- M). The mixture stirred at room temperature for 1 hour, then,
tion of aromatic aldehydes with 1,3-cyclic diketones under the water content was evaporated at vacuum pressure. The
reuxing in ethanol (Scheme 1a). This catalyst is further used suspended solid was calcined in air at three different temper-
ꢀ
ꢀ
ꢀ
3 3 2
for the region-selective generation of 1,4-disubstituted-1,2,3- atures of 160 C for NaCl, 150 C for KF, NaNO , Cu(NO ) ,
64
triazoles in
a
three-component reaction from terminal Ni(NO ) , CuCl , CoCl and 105 C for Cu(NO ) .
3 2 2 2 3 2
alkynes, benzyl halides, and NaN3 in methanol at room
temperature (Scheme 1b). With this method, no additional base
Scheme 1 Preparation of (a) xanthene 3a–3r, and (b) 1,4-disubsti-
tuted-1,2,3-triazole 8a–8o by Cu(II)/NP, as the heterogeneous
catalyst.
Fig. 1 FT-IR spectrum (a) NP, (b) Cu(II)/NP.
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1
3
and C NMR spectra. Selected spectral data of some obtained
xanthenes are as follow:
9-(4-Bromo-phenyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahy-
dro-2H-xanthene-1,8-dione (3b). White solid; mp ¼ 240–
ꢀ
65
ꢁ1
2
1
6
2
6
1
2
42 C, IR (KBr, cm ): y ¼ 2952.5, 2875.3, 1658.5, 1361.5,
1
197.6, 1004.7. H NMR (400 MHz, CDCl
.4 Hz, H–Ar), 7.20 (d, 2H, J ¼ 8.8 Hz, H–Ar), 4.71 (s, 1H, H
.47 (t, 4H, 2CH ), 2.21 (q, 4H, 2CH ), 1.11 (s, 6H, 2Me), 1.00 (s,
H, 2Me). C NMR (400 MHz, DMSO-d
3
): d ¼ 7.35 (d, 2H, J ¼
9
),
2
2
1
3
6
): d (ppm) ¼ 196.3,
62.4, 143.2, 131.1, 130.2, 120.2, 115.2, 50.7, 40.8, 32.2, 31.6,
9.3, 27.3. Calcd for C H BrO : C, 64.34; H, 5.87; Br, 18.16.
2
3
25
3
Found: C, 64.32, H, 5.85; Br, 18.59.
-(3,3,6,6-Tetramethyl-1,8-dioxo-2,3,4,5,6,7,8,9-octahydro-
4
1
2
1
H-xanthen-9-yl) benzonitrile (3c). White solid; mp ¼ 222–
ꢀ
66
ꢁ1
24 C, IR (KBr, cm ): y ¼ 2952.5, 2875.3, 2260.5, 1660.4,
1
Fig. 2 X-ray diffraction of Cu(II)/NP.
471.4, 1361.5, 1197.6, 1151.3, 1004.7, 844.7. H NMR (400
MHz, CDCl
8.0 Hz, H–Ar), 4.78 (s, 1H, H-9), 2.50 (brs, 4H, 2CH
J ¼ 16 Hz, CH ), d (ppm) ¼ 2.15 (d, 2H, J ¼ 16 Hz, CH ), 1.13 (s,
3
): 7.53 (d, 2H, J ¼ 8.0 Hz, H–Ar), 7.43 (d, 2H, J ¼
Preparation and characterization of Cu(II)/NP catalyst
2
), 2.25 (d, 2H,
2
2
NP was collected from ore resources in Yazd (Iran). NP was
1
3
6
H, 2Me), 1.00 (s, 6H, 2Me). C NMR (400 MHz, CDCl ): d (ppm)
3
reuxed in water for 4 hours, then, ltered and washed with
ꢀ
ꢀ
¼ 196.4, 162.4, 142.7, 132.0, 129.8, 128.2, 115.2, 50.7, 40.8, 32.2,
1.5, 29.33, 27.3. Anal. calcd for C24 : C, 76.77; H, 6.71; N,
3.73. Found: C, 76.71, H, 6.69; N, 3.71.
water, dried at 80 C overnight and calcined at 900 C for
another 2.5 hours. The obtained solid was washed again and
3
H25NO
3
ꢀ
recalcined at 900 C for 30 minutes. To obtain Cu(II)/NP, NP (5 g)
3 2 2
was added to an aqueous Cu(NO ) $3H O solution (50 mL, 0.4
M). The mixture was stirred at room temperature for 30
minutes, then, evaporated in vacuum. The nal solid was
calcined under air at 105 C for 2 hours.
Synthesis of 1,4-disubstituted-1,2,3-triazoles
ꢀ
Cu(II)/NP catalyst (0.06 g) was added to a stirred suspension of
NaN (78 mg, 1.2 mmol), alkyl halide (1.0 mmol) and methanol
3
Synthesis of xanthenes
(2 mL). The procedure was followed by slow drop-wise addition
To a solution of aromatic aldehyde (1 mmol) and diketone (2 of a solution of terminal alkyne (1.0 mmol) and methanol (2
mmol) in ethanol (3 mL), Cu(II)/NP catalyst (0.2 g) was added mL). The mixture was stirred at room temperature, aer the
and reuxed 2–3 hours to result xanthene 3, while the reaction completion of reaction, it was characterized by TLC (silica gel,
progress was characterized by TLC (silica gel, hexane : EtOAc, hexane : EtOAc, 7 : 3). The mixture was ltered and washed with
7
: 3). Aer the completion of reaction, the mixture was ltered methanol. All the products were carefully isolated from meth-
and washed with hot ethanol (boiling). Evaporation of the anol or a mixture of ethanol/water (1 : 3, v/v) through recrys-
1
13
ethanoic ltrate provided xanthene 3 (Scheme 1(a)), the melting tallization. The spectral data ( H, C NMR) of the obtained
1
point of the nal product was characterized through FT-IR, H products were evaluated with the spectra of authentic samples
Fig. 3 X-ray diffraction of (a) NP, (b) Cu(II)/NP, (c) fluorapatite, (d) copper nitrate hydrate, (e) copper hydroxide nitrate.
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Fig. 4
2
N adsorption–desorption isotherm (BET) of (a) NP, and (b) Cu(II)/NP.
reported in literature. Selected spectral data of some obtained
Table 1 Surface properties of NP and Cu(II)/NP
1
,4-disubstituted-1,2,3-triazoles are presented below:
-Benzyl-4-phenyl-1H-1,2,3-triazole (8a). Mp ¼ 133–134 C,
H NMR (400 MHz, CDCl ): d (ppm) ¼ 7.82 (d, J ¼ 7.2 Hz, 2H),
ꢀ
67
1
Specic
Specic
1
surface area
pore volume
Pore
diameter [nm]
3
2
ꢁ1
3
ꢁ1
1
3
[m g
]
[cm g
]
7
.70 (s, 1H), 7.44–7.32 (m, 8H), 5.60 (s, 2H). C NMR (100 MHz,
CDCl
): d (ppm) ¼ 148.15, 134.67, 130.52, 129.08, 128.74,
28.70, 128.09, 127.99, 125.65, 119.48, 54.15.
-(4-Bromobenzyl)-4-phenyl-1H-1,2,3-triazole (8b). Mp
3
Sample
S
BET
S
BJH
V
tot BET
V
BJH
D
average
D
BJH
1
1
¼
NP
Cu(II)/NP
2.081
1.849
1.948
2.513
0.00662
0.00912
0.00722
0.00972
12.73
19.70
3.675
3.089
ꢀ
67
1
1
7
7
56–158 C, H NMR (400 MHz, CDCl
3
): d (ppm) ¼ 7.83 (d, J ¼
.2 Hz, 2H), 7.73 (s, 1H), 7.53 (d, J ¼ 8.4 Hz, 2H), 7.43 (t, J ¼
.4 Hz, 2H), 7.34 (t, J ¼ 7.4 Hz, 1H), 7.20 (d, J ¼ 8.4 Hz, 2H), 5.54
1
3
The X-ray diffraction (XRD) patterns of Cu(II)/NP in Fig. 2
show sharp and distinct peaks which conrm a high degree of
(
1
1
s, 2H). C NMR (100 MHz, CDCl ): d (ppm) ¼ 53.59, 118.75,
3
22.97, 125.69, 128.29, 128.86, 129.67, 130.43, 147.04, 133.71,
32.34.
69
crystallinity. The structure of NP is shown to be modied by
the solid phase reaction with copper nitrate (Cu(NO ). The
XRD peaks t with standard patterns of uorapatite JCPDS 15-
76 (Fig. 3c), and some other new crystalline phases, including
copper nitrate hydrate, Cu(NO ) (H O)2.5, JCPDS 75-1493
3 2
)
Results and discussion
Characterization of Cu(II)/NP catalyst
8
3
2
2
The FT-IR spectrum of NPs shows strong peaks at: 1092, 1044, (Fig. 3d), and copper hydroxide nitrate, Cu
(OH)
(NO ), JCPDS
3 3
2
ꢁ
1
6
00, 576 and 473 cm which can be referred to the vibrational 75-1779 (Fig. 3e). Compared to NPs, the intensity of typical
3ꢁ
modes of P–O, P–O–P bands in PO
groups of the apatite diffraction peaks of Cu(II)/NP signicantly differs, which indi-
4
68
structure (Fig. 1a). In the spectrum of Cu(II)/NPs, these bands cates disordering the crystalline structure of Cu(II)/NP. No
are weakened or disappeared (Fig. 1b). The FT-IR characteriza- detection of Cu(NO phase on the doped materials implies
3 2
)
70
tion of Cu(II)/NP shows strong bands with the maximums at that Cu(NO
3
)
2
is highly dispersed in NP. CaO phase (2q ¼ 32.2,
ꢁ
1
ꢀ
ꢂ1633 and 1423 cm , which are associated to N]O, O–NO–O 37.5 and 54.0 ) has no peaks, which veries no solid phase
bands and nitrate groups of Cu(NO
3
)
2
$3H
absorption peak at 3480 cm attributes to H
O absorbed either phosphate of NP during the copper nitrate decomposition
in the samples or in the KBr pellet. These spectra show that the process.
decomposition of nitrate does not happen at the temperature of concluded that copper phosphate or any other types of mixed
2
O. The strong reaction between the supported copper nitrate and the calcium
ꢁ1
2
12,70
From the XRD curves of Cu(II)/NP (Fig. 2), it is
ꢀ
15
calcination (105 C).
calcium copper phosphate does not combine with the NP
Fig. 5 Pore size distribution curve (BJH) of: (a) NP, and (b) Cu(II)/NP.
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Table 3 Effect of copper nitrate concentration, supported on NP, and
a
the catalyst loading for the synthesis of xanthene 3a
Catalyst
Entry
Catalyst
loading (g)
Time (h)
Yield 3a (%)
1
2
3
4
5
6
7
8
Cu(NO
Cu(NO
Cu(NO
Cu(NO
Cu(NO
Cu(NO
Cu(NO
Cu(NO
3
3
3
3
3
3
3
3
)
)
)
)
)
)
)
)
2
(0.2 M)/NP
2
(0.2 M)/NP
2
(0.3 M)/NP
2
(0.3 M)/NP
2
(0.4 M)/NP
2
(0.4 M)/NP
2
(0.4 M)/NP
2
0.2
0.5
0.1
0.2
0.1
0.15
0.2
7
7
4
3
4
3
2
4
70
90
90
89
92
95
98
50
0.064
a
Reaction conditions: dimedone (2 mmol), 4-chlorobenzaldehyde (1
mmol), catalyst in reuxing EtOH (3–5 mL).
the special surface area (S), the total pore volume (Vtot BET),
micro pore volume (VBJH), and the average pore diameter
Fig. 6 SEM images of: (a) NP, and (b) Cu(II)/NP.
(Daverage) are calculated using the adsorption data. The special
crystalline framework. The remarkable fact is that the main surface area (SBET) of NP and Cu(II)/NP is calculated through
modications in the pattern are produced in the range of 2q ¼ BET method and the surface area of meso-pore SBJH, and the
ꢀ
ꢀ
ꢀ
1
2–15 , with new lines at 12.92 and 15.13 together with an meso-pore volume VBJH of NP and Cu(II)/NP are calculated using
increase in the intensity of other lines (Fig. 2). The intense lines BJH method (Table 1). According to the classication standard
related to NP are weakened against uorapatite (see Fig. 3a–c); of International Union of Pure and Applied Chemistry (IUPAC),
the lack of intense bands may account for the formation of very the characteristics of NP and Cu(II)/NP as mesoporous solids
71,72
small crystals, partially amorphous materials or mixed phos- display a type IV isotherm with H3 hysteresis loop.
phates with different stoichiometry.
Accord-
ing to BET and BJH results, the shape of Cu(II)/NP was similar to
16
The porosity of Cu(II)/NP is investigated via Brunauer– NPs, and the porosity of Cu(II)/NP did not change during the
Emmett–Teller (BET) (Fig. 4) and Barrett–Joyner–Halenda (BJH) stabilization of Cu(II) on the surface of NP. These results
2
(Fig. 5) methods using N adsorption–desorption isotherms. introduced permanent porosity of the Cu(II)/NP surface. From
The type IV isotherm of Cu(II)/NP possesses a hysteresis loop Table 1, according to the BET calculation, the specic surface
2
ꢁ1
2
ꢁ1
and typical property of mesoporous materials (2–50 nm), such area decreased from 2.081 m g for NP to 1.849 m g for
2
ꢁ1
as high surface areas (>1000 m
g ), large internal pore Cu(II)/NP. These observations veried no clogging of pores with
volumes and unique ordered porous structures, similar to NP, copper species. The specic pore volume increased aer
73
but at a higher relative pressure of N gas. The surface area of supporting NP with copper nitrate. Aer loading Cu(II), larger
2
Cu(II)/NP is higher compared to other mesoporous NPs with no pores generated; as a result, the average pore diameter
74
Cu particles (Fig. 4). The N
NP and Cu(II)/NP are measured by BET and BJH methods, where adsorption displayed a decline in pore diameter from 3.67 to
.08 nm, which was originated from introducing copper species
2
adsorption–desorption isotherms of increased from 12.73 to 19.70 nm. The BJH curves of nitrogen
3
a
Table 2 Synthesizing xanthene 3a using various solid catalysts
Calcination
temperature ( C)
Time
(h)
Isolated
Table 4 Effect of various solvents on the reaction time and yield of
o
Entry
1
Catalyst
yield 3a (%) 1,4-disubstituted-1,2,3-triazole 8a upon using Cu(II)/NP
78
NP
900
6.5
90
Present study
2
3
4
5
NaNO
NaCl/NP
KF/NP
Cu(NO
NP
Cu(NO
NP
Cu(NO
NP
Ni(NO
3
/NP
150
160
150
500
6.5
5
5
15
70
10
15
3
3
3
)
)
)
2
2
2
/
/
/
48
Isolated yield
8a (%)
6
7
150
105
6
2
50
98
Entry
Solvent
Time (min)
1
2
3
4
5
6
7
8
H
2
O
60
60
15
10
90
95
25
20
5
EtOH
MeOH
8
9
1
3
)
2
/NP
150
150
150
5
3.5
6.5
25
98
20
CH
CH
CH
2
3
3
Cl
CN
OAc
2
120
CuCl
CoCl
2
/NP
/NP
90
120
90
0
2
a
Reaction conditions: 4-chlorobenzaldehyde (1 mmol), dimedone (2
THF
1,4-Dioxane
80
5
mmol), catalyst (0.2 g) in reuxing EtOH (3–5 mL).
120
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Table 5 Effect of Cu(II)/NP loading on the synthesis of 1,4-disubsti- concluded in the formation of copper hydroxide nitrate, Cu
(-
2
a
tuted-1,2,3-triazole 8a
77
OH) (NO ) and copper nitrate hydrate, Cu(NO ) (H O)2.5)
3
3
3 2
2
which in our study were conrmed by XRD analysis (Fig. 2). At
ꢀ
the lower calcination temperature, e.g., 105 C, a high yield
(
7
98%) of 3a was created in a short reaction time (Table 2, entry
). In fact, the initial state of Cu on the support was Cu(NO
3H O and the nal state of Cu on the support was copper
nitrate hydrate, Cu(NO (H O)2.5, copper hydroxide nitrate and
Cu (OH) (NO ), supported on the surface of NP. The decom-
3 2
) -
$
2
3
)
2
2
Cu(II)/NP
(g)
Isolated yield
8a (%)
Entry
Time (min)
120
90
60
45
15
1
2
3
3
position of nitrate groups proceeded at the same temperature
range as dehydration did.
1
2
3
4
5
6
0.01
0.02
0.03
0.04
0.05a
0.06
10
62
73
87
95
99
ꢀ
The treatment at 500 C resulted in a very low yield 15% of 3a
aer a long period of reaction time 48 hours (Table 2, entry 5).
The decomposition of Cu(II) species to copper oxide was
conrmed by the decreased weight of catalyst, its black color
77
a
and reported results from other researchers. The non-catalytic
Cu content is 0.026 g: 6.7% mol.
ꢀ
activity of Cu(NO
3
)
2
/NP [calcinated at 500 C] might be due to
the formation of copper oxide on NP and its non-porous surface
8
0
78
7
5
morphology of copper oxide. As previously reported, this
reaction under the same condition is carried out by using NP as
catalyst, which provides 90% high yield of 3a in a little long
reaction time 6.5 hours (Table 2, entry 1). When NP is modied
complex to the interior side of some pores in NP. High surface
area and large pore size of Cu(II)/NP favoured a high dispersion
of active elements, and made the large amounts of the reactive
76
molecules to be easily accessible.
3 2
by Cu(NO ) , the reaction time decreases to 2 hours and the
yield of the products increases to 98% (Table 2, entry 5). In
short, compared to NP, Cu(NO
produces xanthenes with much higher yields at shorter reaction
times.
In order to determine the best ratio of Cu(NO ) /NP, sup-
ported copper catalyst was prepared by impregnating NP with
different concentrations of Cu(NO
0.1, 0.2, 0.3, and 0.4 M). These supported copper catalysts
were prepared according to the procedures introduced in
Surface structure of Cu(II)/NP was investigated by SEM
method in order to visualise the textural modications aer
adding copper nitrate to natural phosphate (Fig. 6). Compared
to NP (Fig. 6a), Cu(II)/NP (Fig. 6b) had a rougher surface with
more distorted areas, along with uniform spherical particles. In
fact, the addition of copper nitrate increased the size of catalyst
ꢀ
3
)
2
/NP calcined at 105
C
3 2
15,72,77
particles in Cu(II)/NP.
3 2 2
) $3H O aqueous solution
(
Coupling reaction-based synthesis of xanthenes
Authors have introduced NP as a catalyst for synthesizing Sections 2.3 and 2.4. Their catalytic effect on the yield and time
xanthene derivatives through the reaction of 4-chlor- of the reaction of 4-chlorobenzaldehyde with dimedone for the
obenzaldehyde (1 mmol) with dimedone (2 mmol) in reuxing synthesis of xanthene 3a as model reaction were investigated
78
ethanol. To afford xanthene 3 with a high yield, relatively high (Table 3). As shown in Table 3, the best result was obtained by
weight of NP catalyst (1.5 g) and long reaction time are required Cu(NO
Table 1, no. 1). Here, to increase the NP activity, it is doped with Cu(NO
3
3
)
)
2
2
/NP, prepared with 0.4 molar concentration of
$3H O aqueous solution; we name it Cu(II)/NP (Table
(
2
different metal salts (i.e., sodium nitrate, NaNO ; sodium 3, entry 7). To determine the effect of support in the reaction,
3
chloride, NaCl; potassium uoride, KF; nickel nitrate, Ni(NO
3
)
2
;
3 2
the catalytic effect of sole Cu(NO ) was investigated in the
copper nitrate, Cu(NO
chloride, CuCl
3
)
2
; cobalt chloride, CoCl
2
; and copper model reaction. The unsupported copper catalyst was
ꢀ
) (Table 2). The results show that copper salts are prepared via calcination of Cu(NO
)
$3H
O at 105 C for 2
2
3
2
2
the best candidates to synthesize xanthene 3a (Table 2, entries 7 hours. In order to determine the role of NP in the catalytic
and 9). Table 2 (entries 5–7) represents the results of calcination activity of Cu(II)/NP, the amount of copper nitrate existed in
temperatures for preparing Cu(NO
3
)
2
/NP. The treatment of 0.2 g Cu(II)/NP was calculated as 0.064 g. So, 0.064 g of
was used as catalyst in the model reaction; it affor-
ꢀ
Cu(NO ) /NP at 150 and 500 C led to catalysts with poor or no Cu(NO
3
)
2
3
2
catalytic activities (Table 2, entries 5 and 6). This is due to ded 3a only with 50% of yield aer 4 hours (Table 3, entry 8).
thermal decomposition of nitrate groups of Cu(NO
3
)
2
/NP at The result show that, in contrast with NP, the sole modied
cannot positively affect the reaction time and yield
ꢀ
temperatures over 200 C as well as the formation of the copper Cu(NO
3
)
2
77
oxide (CuO). The decomposition of d-metal nitrates hydrates of 3a.
proceeded with slow pace that rarely led to anhydrous salts.
Usually the dehydration process is not complete and the
Click-reaction-base synthesis of 1,4-disubstituted-1,2,3-
triazoles
beginning of nitrate (V) groups decomposition occurs simulta-
79
neously with the evolution of water hydration. The following
+
+
+
+
molecular and fragmentation ions of H O , NO , N O , NO
2
The catalytic activity of Cu(II)/NP was studied in the 1,3-dipolar
2
2
can be formed during the decomposition of nitrates. These cycloaddition reactions using benzyl bromide (4a), sodium
ionic products from the decomposition of copper nitrate azide (5, 1.1 mmol) and phenyl acetylene (7a) as model
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Table 6 Synthesis of 1,4-disubstituted-1,2,3-triazole derivatives by using Cu(II)/NP as catalyst
2
6
2
Entry
X
R
Ar
Product 8
Time (min)
Isolated yield 8 (%)
1
2
3
4
5
6
7
8
9
Br
Br
Br
Cl
Cl
Br
Cl
Br
Br
Cl
Cl
Br
Br
Br
Br
C
H
5
CH
2
C
C
C
C
C
C
C
C
C
C
C
6
H
H
H
H
H
H
H
H
H
H
H
5
5
5
5
5
5
5
5
5
5
5
8a
8b
8c
8d
8e
8f
8g
8h
8i
8j
8k
8l
8m
8n
8o
1
5
99
99
97
98
98
96
96
95
95
96
96
97
95
96
94
4-BrC
4-NO
3,5-Cl
6
H
4
CH
CH
CH
2
6
6
6
6
6
6
6
6
6
6
2
C
6
H
4
2
10
10
15
20
20
20
25
25
20
15
20
10
15
C
2 6
H
3
2
C
6
H
5
CH
2-ClC
CH
4-BrC
2
6
H
4
CH
2
O
O
O
O
O
O
C
6
H
5
2
6
H
4
CH
CH
CH
2
4-NO
3,5-Cl
2-ClC
2
C
6
H
4
2
10
11
12
13
14
15
C
2 6
H
3
2
6
H
4
CH
2
C
C
6
H
H
5
CH
CH
2
6 4
4-Br-C H O
3,5-Cl
4-Br-C
6
5
2
2
-C
6
H
3
3
O
O
4-NO
4-NO
2
C
C
6
H
H
4
CH
CH
2
6
H
4
O
H
2
6
4
2
2 6
3,5-Cl -C
substrates under various conditions. This three-component from extensive mechanical degradation aer running the tests.
reaction proceeded via in situ formation of benzyl azide from Here, the separated Cu(II)/NP from the reaction was dried at
ꢀ
benzyl bromide and sodium azide. Benzyl azide underwent the room temperature and calcined at 105 C for half an hour for its
1,3-dipolar cycloaddition reaction with phenyl acetylene (7a) to recovery and reuse. The catalyst leaching in the reaction media
afford 1-benzyl-4-phenyl-1H-1,2,3-triazole (8a). This model was evaluated by measuring the copper content in recycled
reaction was carried out in different solvents with Cu(II)/NP Cu(II)/NP, by means of Inductively Coupled Plasma (ICP) anal-
(
0.05 g) at room temperature (Table 4). Among the used ysis. From the ICP analysis, the copper contents of fresh catalyst
th
solvents, the best result was earned from using methanol with and 5 run reused catalyst were 20.3 and 16.4 w/w%, respec-
5% yield of the desired product 8a aer 15 minutes (Table 4, tively. The difference of copper contents between fresh and
9
th
20,82
entry 3). The model reaction with EtOH synthesized the product reused catalyst (5 run) was only 4 w/w%.
Aer the calcu-
a with an excellent yield (90%) aer a longer reaction time (60 lation, 0.056 g of Cu(II) existed in 5 recycled Cu(II)/NP rather
minutes) (Table 4, entry 2). than 0.064 g of Cu(II) in fresh Cu(II)/NP, so 0.008 g of Cu(II) was
th
8
The catalyst loading of the model reaction was investigated removed (Table 3, entry 8). This indicated very low leaching
in the synthesis of 1,4-disubstituted-1,2,3-triazole 8a (Table 5). amount of copper catalyst into the reaction mixture. So, Cu(II)/
0.06 g of Cu(II)/NP (with 6.7 mol% Cu content) afforded the best NP can be reused up to 5 runs without any signicant decline
yields with ꢂ100% isolated yield of 1,4-disubstituted-1,2,3- in the yield during the synthesis of xanthene 3a (Fig. 7), and 6
triazole 8a aer 1 minute (Table 5, entry 6), whereas runs during the synthesis of 1,4-disubstituted-1,2,3-triazole 8a
Cu(NO
hours.
3
)
2
$3H
2
O (0.026 g, 6.7 mol%) afforded 70% yield aer 2 (Fig. 8).
The surface of Cu(II)/NP possesses multiple catalytic active
83
By implementing the optimized conditions (Cu(II)/NP 0.06 g, sites.
The excellent catalytic efficiency was mainly
methanol (3 mL), room temperature), various aryl halides and corresponded to the surface cooperation between the Lewis
sodium azide were reacted with various terminal acetylenes for basic sites of NP (oxygen in phosphate PO and calcium oxide
4
the synthesis of 1,4-disubstituted-1,2,3-triazole 8 (Table 6). The
desired 1,4-disubstituted-1,2,3-triazole derivatives were synthe-
sized and characterized by checking reported melting points of
related products in the literatures and spectroscopic methods.
As shown in Table 6, corresponding products were obtained
with excellent yields in short reaction times at room
temperature.
A proper supported catalyst should not leach to the reaction
mixture. The recyclability of the supported catalyst is another
important characteristic which should not suffer from Fig. 7 Recyclability of Cu(II)/NP in coupling reaction for the synthesis
81
of xanthene 3a. Reaction conditions: 4-chlorobenzaldehyde (1 mmol),
dimedone (2 mmol), Cu(II)/NP (0.2 g) in refluxing EtOH (3–5 mL).
mechanical degradation. As such, Cu(II)/NP did not suffer
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Fig. 8 Recyclability of Cu(II)/NP in click reaction for the synthesis of
1
,4-disubstituted-1,2,3-triazole 8a. Reaction conditions: benzyl
bromide (1 mmol), NaN (1.1 mmol), phenyl acetylene (1 mmol) and
Cu(II)/NP (0.06 g) in MeOH (3 mL) at room temperature.
3
8
4
+
++
CaO) and the Lewis acidic site of adjacent Cu /Cu species
2
+
(
copper ion Cu coordinated with the basic sites of NP
84,85
surface).
The basic sites on NP held the key role in the
abstraction of protons from the methylene in 1,3-diketones.
Further, the carbonyl group of aldehyde interacted with the
acidic sites (Cu ) of Cu(II)/NP, thereby, activated the carbonyl Cu(II)/NP catalyst.
carbon for the nucleophilic attack. So, the Knoevenagel–
Michael cascade reactions accelerated the Knoevenagel–
84
Scheme 2 Plausible mechanism for synthesis of xanthene while using
2
+
86
Michael cascade reactions for the synthesis of xanthenes
Scheme 2). According to previous reports, a stepwise mecha-
83
(
nism can be proposed for synthesizing 1,4-disubstituted-1,2,3-
triazoles (Scheme 3). In stage 1, benzyl azide was formed in
situ beside the terminal hydrogen of alkyne. It deprotonated in
the basic medium of NP, while Cu(I) acetylide formed through
the p-alkyne copper complex intermediate I. This p-coordina-
tion of alkyne with copper was activated to form s-acetylide
(stage 2). Then, the azide was activated by the coordination with
copper to form intermediate II (stage 3). The coordination
phenomena were synergistic for both reactive partners in
intermediates I and II. Coordination of azide revealed the b-
nucleophilic which resulted in vinylidene-like properties of
acetylide. So, the azide's terminus became even more electro-
philic and a strained copper triazolide B was formed (stage 4).
Protonation of B, followed by the dissociation of product 8,
completed the reaction, transferred the dehydrogenation of Scheme
3
Plausible mechanism for one-pot CuAAC protocol
synthesis of 1,4-disubstituted-1,2,3-triazole while using Cu(II)/NP
catalyst.
basic sites on NP (stage 5), and regenerated the catalyst Cu(II)/
NP.
To illustrate the efficiency of present protocols for the
synthesis of xanthene, our results are compared with the
existing results in literature (Table 7). As shown in Table 7, the
synthesis of xanthene with Fe -montmorillonite, alumina-
sulfuric acid and SBSSA, the preparation of catalyst needs
more time (at least 48 hours). It also includes several steps and
working with hazardous and expensive materials (Table 7,
conditions (Table 7, entry 10). The reaction by NP needs a high
amount of NP at a long reaction time (Table 7, entry 11).
To illustrate the efficiency of present protocols for the
synthesis of 1,4-disubstituted-1,2,3-triazole derivatives, the
results are compared with the existing results in literature
+
3
(Table 8). Different catalysts are used for the synthesis of 1,4-
entries 1, 2 and 5). By using other catalysts, e.g., SBSAN, ICl
3
/
disubstituted-1,2,3-triazole derivatives which suffer from
SiO , In(CF SO ) , PANI-PTSA and Nano ZnAl O , the reactions
2
3
3 3
2 4
several disadvantages. For example, by using Cu/Al O and Cu/
2
3
are completed in a little shorter period of time than our process,
however, they suffer from their difficult, multi-step and costly
routs as well as extra material preparation (Table 7, entries 3–8).
Using LUS-Pr-SO H is accomplished under harsh reaction
3
conditions, in a longer period, and multi-step preparation
process which requires more devices (Table 7, entry 9). The
SiO2 as catalysts, the reactions are performed under harsh
conditions, such as ball-milling and MW irradiation (Table 8,
entries 2 and 4). The preparation process of some other cata-
lysts, i.e., Cu(II)-PBS–HPMO and SiO
a long period of time under 100 C and 80 C, respectively (Table
2
–NHC–Cu(I), is multistep at
ꢀ
ꢀ
8
, entries 5 and 9). CuNP/C as the catalyst can result in a desired
4
reaction by [cmmim][BF ] as the catalyst takes place under
microwave condition and suffers from the harsh reaction
ꢀ
product with 99% yield but it needs 70 C temperature and
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a
Table 7 Comparison of the reaction conditions and results for the synthesis of xanthene 3a
Entry
Catalyst
Condition
Time
Yield 3a (%)
Ref.
+
3
ꢀ
1
2
3
4
5
6
7
8
9
Fe -montmorillonite (15 wt%)
Alumina-sulfuric acid (200 mg)
100 C/EtOH
6 h
4 h
2 h
6 h
10 h
15 min
1 h
1 h
15 min
2 h
97
83
95
75
98
88–98
90
95
90
87
88
89
90
91
92
28
28
Reux/EtOH
50 C/solvent-free
Reux/H
Reux/EtOH
Reux/EtOH
b
ꢀ
SBSAN (0.5 g)
PANI-PTSA (25 wt%)
SBSSA (0.1 g)
Nano ZnAl
c
2
O
d
2
O
4
(90 mg)
(5 mol%)
(2 mol%)
ꢀ
ICl
3
/SiO
2
75 C/solvent free
ꢀ
ꢀ
In(CF
LUS-Pr-SO
[cmmim][BF
NP (1.5 g)
Cu(II)/NP (0.2 g)
3
SO
3
)
3
100 C/solvent free
e
3
H (0.02 g)
140 C/solvent free
93
94
78
ꢀ
10
11
12
4
] (0.2 g)
80 C/solvent free, MW
Reux/EtOH
Reux/EtOH
94
90
98
6.5 h
2 h
This study
a
b
c
Reaction conditions: dimedone (2 mmol), 4-chlorobenzaldehyde (1 mmol), catalyst. Silica boron-sulfuric acid nano particles (SBSAN). Nano
d
e
ferrite-glutathione-copper (PANI-PTSA). Silica bonded S-sulfonic acid (SBSSA). Propyl sulfonic acid functionalized LUS-1 (Laval University
silica) (LUS-Pr-SO H).
3
a
Table 8 Comparison of the reaction conditions for the synthesis of 1,4-disubstituted-1,2,3-triazole 8a
Entry
1
Catalyst
Condition
Rt/H
Time
13 h
Yield 8a (%)
Ref.
63
2-Pyrrole carbaldiminato–Cu(II) complex
2
O
97
(
0.005 mmol)
Cu/Al (10 mol%)
Cu(I)-zeolite (10 mol%)
Cu/SiO (20 mol%)
2
3
4
5
6
7
8
9
2
O
3
Ball-milling, rt/neat
1 h
92
80
92
96
99
93
99
98
99
98
95
96
90
99
95
96
97
98
ꢀ
20 C/MeOH
15 h
10 min
3.5 h
6 h
8 h
20 min
6 h
15 h
1 h
2.5 h
2 h
1 h
1 min
ꢀ
2
MW, 70 C/H
2
O
b
ꢀ
Cu(II)-PBS –HPMO (10 mg)
100 C/H
2
O
c
ꢀ
CuNP/C (0.5 mol%)
70 C/H
2
O
99
d
CuNP (0.025 mmol)
rt/MeOH
100
101
102
61
103
104
74
e
Cu(II)-TD@nSiO
2
(0.3 mol%)
rt/sodium ascorbate, H
2
O/EtOH (2 : 1)
h
f
ꢀ
SiO
2
–NHC -Cu(I) (1 mol%)
80 C/H
2
O
g
10
11
12
13
14
15
PS-C22-CuI (0.6 mol%)
Rt/H
2
O
ꢀ
CuNPs/Mag silica (4.3 mol%)
70 C/H
2
2
2
2
O
O
h
ꢀ
MNP@PILCu (4 mg)
50 C/H
i
ꢀ
MNP@PDMA-Cu (0.3 mol%)
50 C/H
O, sodium ascorbate
O
j
ꢀ
Cu@bCD-PEG-mesoGO (5 mol%)
Cu(II)/NP (0.06 g)
25 C/H
105
This study
rt/MeOH
a
c
b
Reaction condition: three-component reaction of the benzyl bromide, phenyl acetylene and NaN
3
.
Porphyrin-bridged silsesquioxane (PBS).
f
d
e
Copper nanoparticles on activated carbon (CuNP/C). Nano-copper (CuNP). Copper Immobilized on Nano silica Triazine Dendrimer. N-
g
h
heterocyclic carbene. Polystyrene resin-supported copper(I) iodide-cryptand-22 complex. Magnetic nanoparticles into the cross-linked
poly(imidazole/imidazolium) immobilized Cu(II). Copper sulphate onto multi-layered poly (2-dimethylaminoethyl acrylamide)-coated Fe
nanoparticles. Copper supported b-cyclodextrin functionalized PEGylated mesoporous silica nanoparticle-graphene oxide hybrid.
i
3
O
4
j
more time (Table 8, entry 6). Although, the reactions by using
Conclusions
Cu(II)-TD@nSiO and PS-C22-Cu(I) complexes as catalysts are
2
completed at room temperature but they suffer from hard and In summary, we established copper nitrate, supported on meso-
lengthy preparation process (Table 8, entries 8 and 10). pores of natural phosphate (Cu(II)/NP), as new, inexpensive, eco-
Although the syntheses in the presence of some catalysts, like 2- friendly and recyclable heterogeneous catalyst for the synthesis
pyrrole carbaldiminato-Cu(II) complex, Cu(I)-zeolite, Cu NP and of heteroatom-containing chemicals including xanthene and
PS-C22-CuI, were carried out at room temperature, they took 1,4-disubstituted-1,2,3-triazole in good to excellent yields.
much longer reaction times (Table 8, entries 1,3,7 and 10). The Cu(II)/NP efficiently catalyzed the synthesis of xanthenes by the
preparations of CuNPs/Mag Silica, MNP@PILCu, MNP@PDMA- condensation of aromatic aldehydes with 1,3-cyclic diketones in
Cu and Cu@bCD-PEG-mesoGO are also difficult or costly (Table ethanol under the reux condition. Cu(II)/NP also showed as an
8, entries 11–14). The advantages of Cu(II)/NP as catalyst for the efficient catalyzer in the regioselective synthesis of 1,4-
synthesis of 1,4-disubstituted-1,2,3-triazole 8a are listed in disubstituted-1,2,3-triazoles via azide/alkyne ‘‘click’’-reaction or
Table 8, entry 15.
CuAAC reaction at room temperature. The reaction for the
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stable Cu(II) instead of unstable Cu(I) species in the absence of
any ligand or base. By using the heterogeneous catalyst Cu(II)/
NP, the processes afforded the products with high yields in
short reaction times, while the preparation process of the
catalyst was easy, using inexpensive materials, recyclable,
environmentally benign, stable, and almost leaching-free. The
use of natural phosphate (NP) as a support for Cu(II) provides
the advantages due to its excellent stability (both chemical and
thermal), high surface area, low cost, and availability.
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Conflicts of interest
There are no conicts of interest to declare.
7
7.
0 X. Cao, L. Q. Ma, D. R. Rhue and C. S. Appel, Environ. Pollut.,
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2
2
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2
Acknowledgements
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1 M. Sljivic, I. Smiciklas, I. Plecas and M. Mitric, Chem. Eng. J.,
´ ˇ
ˇ
´
ˇ
´
We are grateful of Payame Noor University (PNU) for their
partial support, Mazandaran University of Medical Sciences for
providing laboratory facilities to carry out this research and
Australian College of Kuwait for the funding of IRC-2017-18-
SOE-ME-PR01 and PR02 is also acknowledged.
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