CuSO4 nanoparticles loaded on carboxymethylcelulose/polyaniline composites: A highly efficient catalyst with enhanced catalytic activity in the synthesis of propargylamines, benzofurans, and 1,2,3-triazoles

Article abstract of DOI:10.1002/aoc.6349

A novel and efficient heterogeneous CuSO₄ nanoparticles (CuSO₄ NPs) immobilized on carboxymethylcellulose/polyaniline (CuSO₄NPs@CMC/PANI) composites were prepared via one-pot and one-step interfacial oxidative polymerizati

Full text of DOI:10.1002/aoc.6349

Received: 30 April 2021
DOI: 10.1002/aoc.6349
Revised: 15 June 2021
Accepted: 16 June 2021
R E S E A R C H A R T I C L E
CuSO4 nanoparticles loaded on carboxymethylcelulose/
polyaniline composites: A highly efficient catalyst with
enhanced catalytic activity in the synthesis of
propargylamines, benzofurans, and 1,2,3-triazoles
Zhian Xu
| Jinxi Xu
| Yiqun Li
Department of Chemistry, College of
Chemistry and Materials Science, Panyu
Campus, Jinan University, Guangzhou,
China
Abstract
A novel and efficient heterogeneous CuSO4 nanoparticles (CuSO4 NPs)
immobilized on carboxymethylcellulose/polyaniline (CuSO4NPs@CMC/PANI)
composites were prepared via one-pot and one-step interfacial oxidative poly-
merization of aniline with sodium carboxymethylcellulose (CMC) as soft tem-
plate and CuSO4 as catalyst. The in situ formed CuSO4 NPs were dispersed
uniformly and firmly on the resultant composites and stabilized by complexa-
tion with hydroxyl groups (─OH), carboxylate groups (─COOÀ), nitrogen
atoms, and delocalized π-π conjugate benzenoid and quinoid moieties of
CMC/PANI composites. The morphology, composition, and structure of the
as-fabricated composites were systematically characterized by X-ray photoelec-
tron spectroscopy (XPS), transmission electron microscopy (TEM), scanning
electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fou-
rier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), ther-
mogravimetric analysis (TGA), and derivative thermogravimetry (DTG)
techniques. The CuSO4NPs@CMC/PANI composites were successfully applied
as catalysts in aldehyde-alkyne-amine (A3) coupling reactions, A3-
cycloisomerization tandem reactions, and Cu-catalyzed azide-alkyne cycload-
dition (CuAAC) reactions. All reactions proceeded smoothly and afforded the
desired products in excellent yields. Moreover, no significant decrease in cata-
lytic ability was observed in A3 model reaction after 15 recycles, indicating
CuSO4NPs@CMC/PANI composites exhibited easy separability and high reus-
ability. Tolerance of wide scope of substrate, excellent catalytic activity, easy
operation, recycling of catalyst, and environmental benign are the salient fea-
tures of these catalytic process.
Correspondence
Yiqun Li, Department of Chemistry,
College of Chemistry and Materials
Science, Panyu Campus, Jinan University.
Guangzhou 511443, China.
Email: tlyq@jnu.edu.cn
Funding information
the Natural Science Foundation of
Guangdong Province, Grant/Award
Number: 2020A1515010399
K E Y W O R D S
A3 reactions, carboxymethylcellulose, CuAAC reactions, CuSO4 nanoparticles, polyaniline
Appl Organomet Chem. 2021;e6349.
wileyonlinelibrary.com/journal/aoc
© 2021 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.6349

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1 | INTRODUCTION
mechanical strength, multistep synthetic approaches, and
tedious operation in some cases are the main disadvan-
tage that needs to be optimized. To mitigate these disad-
vantages, it is reasonable to develop one composite
material merging the preponderances of both CMC─Na
and PANI may be of potential interest for immobilization
of metal nanoparticle to enhance the catalytic efficiency.
Recently, great efforts have been made to the Cu-
catalyzed one-pot multicomponent reaction of A3
reactions,[23,24] CuAAC reactions,[25,26] and many other
reactions[27,28] because they have become one of the most
powerful tools in diverse fields such as drug discovery,
polymer chemistry, and material science. Therefore, the
development of a novel Cu-composite catalyst with supe-
rior catalytic activity for these reactions is of great impor-
tance and highly desirable.
With the development of modern nanoscience, nanoscale
transition metal catalysts have attracted great attention
in scientific research and extensively used in organic
catalysis.[1–3] However, bare metal nanoparticles are eas-
ily aggregated during the catalysis process, thereby lower-
ing their catalytic performance and practical
application.[4,5] Thus, heterogenization of metal
nanoparticles on a desired supportive material has been
regarded as an efficient approach to increase the stability
of metal nanoparticles, which is conducive to the advan-
tageous of maintenance of catalytic activity, simple oper-
ation, convenient recovery and recycling of catalyst, easy
separation of product, and cost reduction.[6–10] However,
the performance of heterogenized catalysts greatly
depends on the physical and chemical properties of the
supportive materials. Among the reported supportive
materials, the composite materials, composed of two or
more inorganic and/or organic constituents, have
received great concerns owing to their intriguing proper-
ties superior to the individual component in regard of
high loading capacity, excellent catalytic activity, good
stability, and recycling performance.[11] Therefore, it is
worthwhile to further develop novel and efficient com-
posite catalysts, and some pioneering works on the
design and fabrication of various composite catalysts
have been reported in the past decade.[12,13] Among the
documented works, the template-guided method is one
of the commonly and efficient method to synthesis of
composite materials.[14] However, most of the synthetic
templates containing specific structure and functional
groups are usually requirement of tedious multistep syn-
thesis and thus made them inconveniently available and
costly. Alternatively, inexpensive and naturally available
multifunctional templates such as cellulose, starch,
chitosan, alginate, and carboxymethylcellulose are now
being captured considerable attention.
Sodium carboxymethylcellulose (CMC─Na), a water-
soluble anionic polymer derived from naturally abundant
cellulose bearing a great number of free hydroxyl (─OH)
and negatively charged carboxymethyl (─CH2COOÀNa+)
groups along its repeat glucose-unit chain, which make it
capable of coordination with various multivalent metal
cations.[15] Polyaniline (PANI), composed of benzoid and
quinoid moieties, is a useful supportive material due to
the unique coordination with metal ions via lone-pair
electrons present in the nitrogen atoms and delocalized
π-π conjugate system of PANI.[16] Based on these unique
properties, a number of CMC-based[17–20] and PANI-
based[16,21,22] composite catalysts recently have been
reported. Although these reported catalysts have excel-
lent catalytic activity, the shortcomings such as poor
In light of the above facts, for the first time, we have
attempted to synthesize CuSO4NPs@CMC/PANI com-
posites by a one-pot and single-step method via in situ
interfacial oxidative polymerization of aniline using CMC
as soft template and CuSO4 as catalyst and further
explored it as
a
catalyst for A3 reactions, A3-
cycloisomerization tandem reactions, and CuAAC reac-
tions (Scheme 1).
2 | EXPERIMENTAL
2.1 | Materials and instrumentations
Sodium carboxymethylcellulose (CMC─Na) and all other
chemicals were obtained from commercial sources and
used as received without further purification.
Gas chromatography (GC) was performed on a
Shimadzu GCMS-QP2020. The elemental copper content
of the catalyst was determined by inductively coupled
plasma atomic emission spectrometry (ICP-AES) using X
Series 2 instrument. X-ray photoelectron spectroscopy
(XPS) was carried out on a Thermo Fisher Scientific
K-Alpha instrument. Transmission electron microscopy
(TEM) was obtained with a Philips Tecnai instrument.
Scanning electron microscopy (SEM) and energy-
dispersive spectroscopy (EDS) were conducted with a
Zeiss Sigma 500 instrument. Flourier transform infrared
spectra (FTIR) were collected on a Nicolet 6,700 spectro-
photometer in KBr pellet within the spectral range of
4,000–400 cmÀ1at 2 cmÀ1 resolution and 32 scans. X-ray
powder diffraction (XRD) data were collected on an
MSALXRD2 diffractometer using Cu Kα radiation in a
range of Bragg's angles (5–80ꢀ). Thermogravimetric anal-
ysis (TGA) and derivative thermogravimetric analysis
(DTG) were performed on a Netzsch STA449 under a
nitrogen atmosphere from 30ꢀC to 800ꢀC in
a

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SCHEME 1 CuSO4NPs@CMC/PANI-mediation of A3, A3-cycloisomerization tandem reactions, and CuAAC reactions
50 mlÁminÀ1 N2 flow and a ramp rate of 10ꢀCÁminÀ1. H
NMR (300 MHz) and 13C NMR (75 MHz) spectra were
obtained with a Bruker Avance instrument with CDCl3
as solvent and TMS as internal standard. HRMS was
determined by using Agilent 6545 Q-TOF MS.
at 60ꢀC for 12 h. The CuSO4NPs@CMC/PANI composites
was obtained as dark green powders.
1
2.3 | General procedure for
CuSO4NPs@CMC/PANI-catalyzed A3 three-
component coupling reactions
2.2 | Preparation of CuSO4NPs@CMC/
PANI composites
A mixture of aldehyde/ketone (1.0 mmol), amine
(1.2 mmol), terminal alkyne (1.5 mmol), and catalytic
amount of CuSO4NPs@CMC/PANI (30 mg, 6.0 mol% of
Cu) was stirred in neat at 120ꢀC in a sealed vessel for the
specific time indicated by TLC. After the completion of
reaction, ethyl acetate was added to the vessel to extract
the product, and the left catalyst was separated by filtra-
tion. The catalyst was washed with ethyl acetate ade-
quately and dried at 60ꢀC for the next run. The crude
product was obtained after removal of the organic solvent
using a rotary evaporator under reduced pressure. The
crude products were further purified by silica gel column
chromatography to afford pure compounds. All the prod-
CMC─Na (7.26 g, 30 mmol) was dissolved in 400 ml
deionized water at ambient temperature with continuous
stirring for overnight. Then aniline monomer (2.79 g,
30 mmol) was dissolved in 250 ml methanol and then
mixed with as-prepared CMC─Na solution with stirring
until the mixture was homogeneous. The mixture was
then sonicated for 30 min to facilitate self-assemble of
aniline on CMC─Na molecular chain. After that, pre-
prepared CuSO4Á5H2O solution (7.50 g, 30 mmol, in
100 ml deionized water) was added dropwise into the
mixture at room temperature with constant stirring.
The green precipitation appeared and further allowed to
oxidative polymerize at room temperature for 8 h. The
precipitates were separated from the solution by suction
filtration and washed five to six times successively with
deionized water and methanol and then dried in vacuum
1
ucts except 1h and 1i are known, and their H NMR and
13C NMR data were found to be identical to those
reported in the literature. The new compounds 1h and 1i
1
were fully characterized by H NMR, 13C NMR, FTIR,
and HRMS.

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2.4 | General procedure for
Briefly, aqueous CuSO4 were added into the mixture of
CMC─Na and aniline monomer solution, which was self-
organized together by H-bond interactions, to initiate the
oxidative polymerization of aniline monomers on
the molecular chain of CMC─Na. Simultaneously, CuSO4
NPs grew in situ on the resultant CMC/PANI composites
and stabilized by complexation with hydroxyl groups
(─OH), carboxylate groups (─COOÀ), nitrogen atoms
(─NH─ and ─N═) of CMC/PANI composites. The Cu
content in fresh CuSO4NPs@CMC/PANI composites was
determined by ICP-AES to be 2.006 mmol/g. The syn-
thetic route to prepare CuSO4NPs@CMC/PANI compos-
ite catalyst was outlined in Scheme 2.
CuSO4NPs@CMC/PANI-catalyzed A3-
cycloisomerization tandem processes for
synthesis of benzofurans
A mixture of aldehyde (1.0 mmol), amine (1.2 mmol), ter-
minal alkyne (1.5 mmol), DMAP (0.5 mmol), toluene
(1.0 ml), and CuSO4NPs@CMC/PANI (30 mg, 6.0 mol%
of Cu) was stirred at 120ꢀC in a sealed vessel. The pro-
gress of the reaction was tracked by TLC. Upon the com-
pletion of reaction, ethyl acetate was added to the vessel
to extract the product, and the catalyst was recovered by
suction filtration. The crude product was obtained after
removal of the combined organic solvent and further
purified with column chromatography to afford pure
compound. All the products are known, and their 1H
NMR and 13C NMR data were found to be in accordance
with those reported in the literature.
Then, various analytical techniques including XPS,
TEM, SEM, EDS, FTIR, XRD, TGA, and DGT were per-
formed to identify the components and structures of
CuSO4NPs@CMC/PANI composites.
The XPS is used to confirm the oxidation state of ele-
ments present in the CuSO4NPs@CMC/PANI compos-
ites. Figure 1 showed the survey scan XPS spectra of the
typical elements in the binding energy rang of 0–1,400 eV
and high-resolution spectra of Cu2p, S2p, C1s, N1s, and O1s
of fresh catalyst. It was found that Cu, S, C, N, and O ele-
ments were the predominate species in Figure 1a. As
shown in Figure 1b, the binding energies of Cu2p3/2 and
Cu2p1/2 are found at 933.71 and 953.24 eV correspond-
ingly, which confirmed that the oxidation state of Cu in
fresh catalyst is divalent.[30,31] Besides, the shake-up sat-
ellites (940.23, 943.18, and 962.18 eV) in Cu2p spectra are
also the indication of the presence of Cu (II) species.[30]
In Figure 1c, the S2p peak at 168.5 eV matched the
reported values of the binding energy of S from
CuSO4.[32,33] The C1s XPS spectra in Figure 1d exhibited
the peak with binding energies of 284.7 eV, which were
attributed to the presence of carbon-containing groups.
Figure 1e depicted two distinct peaks centered at 401.3
and 399.2 eV corresponding N1s, which can be ascribed
to benzenoid amine and protonated amine in the PANI
components,[34] respectively. In Figure 1f, the binding
2.5 | General procedure for
CuSO4NPs@CMC/PANI-catalyzed CuAAC
reaction
Benzyl halides (1.0 mmol), NaN3 (1.2 mmol), terminal
alkyne (1.0 mmol), and catalytic amount of
CuSO4NPs@CMC/PANI (20 mg, 4.0 mol% of Cu) were
added in 3.0 ml solvent (H2O/MeOH = 1:1, v/v), and the
mixture was rigorously stirred at 70ꢀC for the specific
time indicated by TLC. After the completion of reaction,
ethyl acetate was added to the vessel to extract the prod-
uct and separate the catalyst. The filtrate was washed
with saturated brine and dried over anhydrous Na2SO4.
The desired pure products were obtained by column
chromatography after removal of organic solvent using a
rotary evaporator. All the products except 3r and 3s are
known, and their 1H NMR and 13C NMR data were
found to be consistent with those reported in the litera-
ture. The new compounds were fully characterized by 1H
NMR, 13C NMR, FTIR, and HRMS.
energies of O1s at 531.8 eV was satisfactorily correspond
2À
to the presence of the oxygen in CMC and SO4
respectively.
,
3 | RESULTS AND DISCUSSION
In order to have an insight into the morphology of
the composites, the SEM and TEM images of freshly
CuSO4NPs@CMC/PANI composites were examined and
depicted in Figure 2. As can be seen from SEM images,
the composites were composed of micron-scale grains
with very rough surface (Figure 2a). For easy clarity and
comparison, the images with more high magnification
showed these grains were built by the accretion of
smaller flakes composed of nanoscale spherical particles
(Figure 2b). It also can be clearly observed in TEM
images that quasi-spherical nanoparticles deposited well
3.1 | Synthesis and characterization of
catalyst
The CuSO4-catalyzed polymerization of aniline onto a
CMC molecular chain led to the formation of
CuSO4NPs@CMC/PANI nanocomposites. Notably, in
this process, Cu(I) ions resulted from Cu (II)-initiated the
oxidative polymerization of aniline could be re-oxidized
by oxygen in the air to form Cu (II) ions in solution.[29]

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SCHEME 2 Schematic illustration of the preparation process of CuSO4NPs@CMC/PANI composites
onto the CMC/PANI nanofibers with dendritic structure
(Figure 2c–e). The histogram of nanoparticle sizes
showed that the average diameter of nanoparticles was
5.78 nm (Figure 2f).
the moiety of N═Q═N (where Q represents a quinoid
ring), while the peak at 1,482 and 802 cmÀ1 are corre-
lated to the structure of N─B─N (where B represents a
benzenoid
ring).[31]
From
the
spectrum
of
The EDS analysis shown in Figure 3 revealed local
elemental information for the CuSO4NPs@CMC/PANI
composites. The non-metallic elements C, N, O, and S as
well as metallic element Cu are clearly visible, which
indicated that the Cu, S, and O elements were success-
fully incorporated into the prepared composites, while
the CMC─Na and aniline components were free any Cu
and S elements. These findings imply the successful
introduction of CuSO4 in the composites.
The distribution of Cu has impact on the catalytic
activity. To adequately analyze the elemental distribution
of CuSO4NPs@CMC/PANI composites, SEM element
mapping images are presented in Figure 4. The elemental
mappings conclusively evidence the C, N, O, S, and Cu
elements are homogeneously dispersed throughout the
composites.
The FTIR of CMC─Na (curve a), PANI (curve b), and
CuSO4NPs@CMC/PANI composites (curve c) in the
range of 4,000–500 cmÀ1 are presented in Figure 5.
According to the spectrum of CMC─Na (curve a), the
characteristic absorption peaks at 1,607 and 1,424 cmÀ1
are, respectively, assigned to the asymmetric and sym-
metric stretching vibration of carboxylate (─COOÀ)
groups.[17–20] In the spectrum of PANI (curve b), the
peaks at 1,558 and 1,126 cmÀ1 are attributed to
CuSO4NPs@CMC/PANI composites (curve c), a new
absorption band at around 1,159 cmÀ1 is indicative for
the SO42À presence,[35] which may be due to the presence
of CuSO4. Meanwhile, the peaks at 1,624 (group
─COOÀ), 1,495 (group N─B─N), 1,421 (group ─COOÀ),
and 1,111 cmÀ1 (group N═Q═N) in the curve c confirm
that CMC and PANI were successfully merged into the
composites. Moreover, the shift of the peaks (group
─COOÀ: 1,607 shift to 1,624 cmÀ1; group N─B─N: 1,482
shift to 1,495 cmÀ1; group N═Q═N: 1,126 shift to
1,111 cmÀ1) indicate that both CMC and PANI are coor-
dinated with Cu (II) ions.
The X-ray diffraction (XRD) patterns of the CMC─Na
(curve a), PANI (curve b), and CuSO4NPs@CMC/PANI
composites (curve c) were shown in Figure 6. The amor-
phous aboard diffraction peaks at 2θ = 20.7ꢀ in curve
(a) and 2θ = 25.4ꢀ in curve (b) were assigned to native
Na─CMC[20] and PANI,[31] showing a very low degree of
crystallinity in the pure form. These peaks of CMC─Na
and PANI can be also observed in curve (c) of
CuSO4NPs@CMC/PANI, which proved the successful
combination of CMC and PANI. But no CuSO4 crystal-
line related peaks was detected in curve c; it is probably
attributed that CuSO4 NPs was dispersed in the
CMC/PANI matrix as an amorphous form.

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FIGURE 1 The XPS and spectra scan of element survey (a), Cu2p (b), S2p (c), C1s (d), N1s (e), and O1s (f)
In order to explain thermal behaviors of catalyst,
TGA and corresponding DTG analyses of CMC─Na,
PANI, and CuSO4NPs@CMC/PANI composites were per-
formed and depicted in Figure 7. All the samples revealed
the first stage mass loss below 160ꢀC, originated from the
removal of physical adsorptive moisture. The sample of
CMC─Na (curve a) exhibited sharp loss in mass between
255ꢀC and 312ꢀC, related to the polymeric chain decom-
position, including the disintegration of side groups and
glycoside bonds. PANI (curve b) showed the second

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FIGURE 2 SEM images of fresh CuSO4NPs@CMC/PANI composites (a in 10 μm, b in 300 nm), TEM images of fresh
CuSO4NPs@CMC/PANI composites (c in 100 nm, d in 50 nm, and e in 20 nm) and nanoparticles diameter histogram of fresh catalyst (f)
step extending from 220ꢀC to 800ꢀC was mainly
caused by the chemical decomposition of PANI. The
CuSO4NPs@CMC/PANI composites (curve c) showed
the second one at the temperature range of 195–255ꢀC
may account for the PANI decomposition, and the last
one ranged from 255ꢀC to 420ꢀC was assigned the
degradation of CMC─Na. In addition, the curve
(c) produced higher ash content, which is associated with
copper. In the DTG analysis, as can be seen from curve d,
the maximal mass loss rate of CMC─Na was obtained for
the temperature at 291ꢀC. The plot of PANI (curve e)
seemed to consist of three broad peaks around 88ꢀC,

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FIGURE 3 The EDS element analysis of CuSO4NPs@CMC/PANI composites
267ꢀC, and 518ꢀC. The obvious uneven loss of
CuSO4NPs@CMC/PANI (curve f) from 188ꢀC to 438ꢀC
was attributed to the decomposition of the catalyst; two
stages of mass losses like as shoulders are observed at the
temperature ranges of 188–233ꢀC. The first and second
shoulders are related to the degradation of CMC─Na and
PANI, respectively. The DTG intension peak in
CuSO4NPs@CMC/PANI was shifted to lower tempera-
tures, illustrating the interaction between PANI and
disappearance of satellites. Similarly, the appearance of
peaks at 932.82 (Cu 2p3/2 BE), 952.61 (Cu 2p1/2 BE)
(Figure 8d), and 569.62 eV (Cu LMM BE) (Figure 8e)
indicated
the
generation
of
Cu(I)
in
A3-
cycloisomerization tandem processes. In conclusion, the
Cu (II) species in fresh catalyst were converted into
Cu(I) species in all of A3 couplings, A3-
cycloisomerization tandem reactions, and CuAAC reac-
tions. Notably, after CuAAC reaction, the SEM images
showed the grains turned to rigid with rough surface
(Figure 8f), and the TEM images showed the resultant
Cu(I) nanoparticles have a slight agglomeration with the
average diameter of 12.83 nm by comparison with fresh
catalyst (Figure 8g).
CMC─Na.
These
results
indicated
that
CuSO4NPs@CMC/PANI composite has a good thermal
stability from room temperature to 188ꢀC and suitable
for the following reactions.
Furthermore, XPS, TEM, and SEM of recovered cata-
lyst were also performed to explore the change in valence
of copper and morphology of catalyst. As shown in
Figure 8a, the peaks at 932.30(Cu 2p3/2 BE) and
952.05 eV (Cu 2p1/2 BE) prove that parts of Cu (II) in the
recovered catalyst from CuAAC reaction were converted
into Cu(I)[30] and the shoulder peaks (934.33 and
954.28 eV) and satellites peaks (943.13 and 961.91 eV)
illustrate the remain of Cu (II). It also can be observed
that after A3 coupling reaction, nearly all the Cu (II) was
turned into Cu(I) by evidence of the presence of peaks at
932.97 (Cu 2p3/2 BE), 952.77 (Cu 2p1/2 BE) (Figure 8b),
and 569.88 eV (Cu LMM BE) (Figure 8c)[36] as well as the
3.2 | Application of CuSO4NPs@CMC/
PANI composites in A3 three-component
coupling reactions
To search the optimal reaction conditions for A3 reac-
tions, p-chlorobenzaldehyde (1.0 mmol), morpholine
(1.2 mmol), and phenylacetylene (1.5 mmol) were
selected as model substrates, and different conditions
were systematically explored (Table S1). The optimized
reaction condition for the A3 model reaction was set

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FIGURE 4 SEM corresponding elemental mapping images of CuSO4NPs@CMC/PANI composites
FIGURE 6 The XRD patterns of the CMC─Na (a), PANI (b),
and CuSO4NPs@CMC/PANI composites (c)
FIGURE 5 The FTIR spectra of the CMC─Na (a), PANI (b),
and CuSO4NPs@CMC/PANI composites (c)

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FIGURE 7 The TGA and DTG curves of the CMC─Na (a, d), PANI (b, e), and CuSO4NPs@CMC/PANI (c, f)
at the usage of p-chlorobenzaldehyde (1.0 mmol),
morpholine (1.2 mmol), phenylacetylene (1.5 mmol), and
30 mg CuSO4NPs@CMC/PANI (6 mol % of Cu) under
neat conditions at 120ꢀC.
N,N-dimethylaminopyridine (DMAP) as Brønsted base
which facilitated the deprotonation of the ─OH group
and in favor of the 5-exo-dig-cyclization process.[37]
The model reaction of salicylaldehyde (1.0 mmol),
morpholine (1.2 mmol), and phenylacetylene (1.5 mmol)
was selected to optimize reaction condition; several
important parameters including solvent, the loading of
catalyst, base, and temperature were systematically
investigated (Table S2). It could be concluded that the
optimal condition for A3-cycloisomerization tandem reac-
tions involves the usage of salicylaldehyde (1.0 mmol),
morpholine (1.2 mmol), phenylacetylene (1.5 mmol),
DMAP (0.5 equiv.), and 30 mg CuSO4NPs@CMC/PANI
(6.0 mol% of Cu) in toluene at 120ꢀC.
Having the optimal condition, diverse aldehydes,
amines, and alkynes were chosen to investigate the scope
and limitation of this methodology. The results were
summarized in Table 2. When phenylacetylene reacted
with morpholine and piperidine, the phenylacetylene
bearing with the electron-withdrawing group afforded
lower product yields comparing to electron-donating
groups due to the electron-withdrawing group decreases
the nucleophilic activity. Besides, 1-octyne afforded only
31% product yield due to its low reactivity. It is noticeable
that diethylamine and aniline gave no products because
they are hard to underwent A3 couplings.
On obtaining the optimal reaction conditions, we fur-
ther examined the generality and limitation of this meth-
odology; various aldehydes, amines, and alkynes were
investigated under optimized condition. The results
were summarized in Table 1. It can be seen that aryl
aldehydes with either electron-donating or electron-
withdrawing group afforded satisfactory yields.
Phenylacetylenes with electron-donating groups on its
aromatic ring afforded higher yields compared to
electron-withdrawing groups due to the electron-
withdrawing group reduces the nucleophilic activity.
Notably, trace amount of product was found when
aliphatic alkyne was applied owing to the activity of
aliphatic alkyne is too low to form a Cu-alkyne
intermediate. Among the different amines studied,
morpholine and piperidine proceeded smoothly to
furnish the superior yields compared with dialkylamine
and arylamine. Unfortunately, aliphatic primary amines
afforded no desired products.
3.3 | Application of CuSO4NPs@CMC/
PANI composites in A3-cycloisomerization
tandem processes for synthesis of
benzofurans
3.4 | Application of CuSO4NPs@CMC/
PANI composites in one-pot catalytic
CuAAC reactions
In keeping with our former research, the
CuSO4NPs@CMC/PANI composite catalyst was furtherly
extended to the synthesis of benzofuran via A3-
cycloisomerization tandem processes in the presence of
In order to furtherly explore the application universality
of CuSO4NPs@CMC/PANI composites, CuAAC reactions

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FIGURE 8 XPS of recovered catalyst from CuAAC reaction (a), recovered catalyst from A3 reaction (b, c), recovered catalyst from A3-
cycloisomerization tandem reaction (d, e), SEM images of recovered catalyst from CuAAC reaction (f), TEM images of recovered catalyst
from CuAAC reaction (g) and nanoparticles diameter histogram of recovered catalyst from CuAAC reaction (h)

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TABLE 1 CuSO4NPs@CMC/PANI-catalyzed A3 couplings to synthesis of propargylamines[a]
aReaction conditions: aldehyde/ketone (1.0 mmol), alkyne (1.5 mmol), amine (1.2 mmol), CuSO4NPs@CMC/PANI (6.0 mol% of Cu), 120ꢀC, solvent-free
condition. All yields are isolated.
b1 ml of toluene as solvent was added in this reaction.
cDetected by TLC.
dImine intermediate was determined by GC-MS.
eNo desired product and imine intermediate were determined by GC–MS.

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TABLE 2 CuSO4NPs@CMC/PANI-catalyzed A3-cycloisomerization tandem reactions to synthesis of benzofurans[a]
aReaction conditions: aldehyde (1.0 mmol), alkyne (1.5 mmol), amine (1.2 mmol), CuSO4NPs@CMC/PANI (6.0 mol% of Cu), DMAP (0.5 mmol), toluene
(1.0 ml), 120ꢀC. All yields are isolated.
bDetected by TLC.
cImine intermediate was determined by GC-MS.
dNo desired product was determined by GC–MS.
had
been
performed
in
the
presence
of
(1.0 equiv.), and 20 mg CuSO4NPs@CMC/PANI (4 mol %
of Cu) in 3 ml aqueous methanol (H2O/MeOH = 1:1,
v/v) at 70ꢀC.
Having optimized reaction conditions, we explored
the generality of the CuSO4NPs@CMC/PANI composite
catalyst for the CuAAC reaction of structurally diverse
benzyl (alkyl) halides and alkynes, and the results are
summarized in Table 3. All the substrates bearing with
CuSO4NPs@CMC/PANI catalytic system to prepare
corresponding 1,2,3-triazoles. The model reaction of ben-
zyl bromide (1.0 mmol), NaN3 (1.2 mmol), and
phenylacetylene (1.0 mmol) was exerted to search of the
optimal reaction conditions (Table S3). The optimal con-
dition for model reaction involved the usage of benzyl
bromide (1.0 equiv.), NaN3 (1.2 equiv.), phenylacetylene

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TABLE 3 CuSO4NPs@CMC/PANI-catalyzed CuAAC reactions to synthesis a variety of 1,2,3-triazoles[a]
aReaction conditions: halide (1.0 mmol), alkyne (1.0 mmol), NaN3 (1.2 mmol), CuSO4NPs@CMC/PANI (4.0 mol% of Cu), H2O/MeOH (v:v = 1:1, 3 mL), 70 ꢀC.
All yields are isolated.
electron-donating and electron-withdrawing groups pro-
duced the expected cycloaddition product in good to
excellent yields with high selectivity. By comparison with
benzyl bromide, a longer reaction time was required for
benzyl chloride due to its lower reactivity. Furthermore,
it was observed that the yield of phenylacetylene con-
taining electron-donating substituents were higher than
those with electron-withdrawing groups, which probably
attributed to the higher reactivity promoted by electron-
donating substituents which increase the electron cloud
density of the terminal alkynyl. Additionally, it was worth
noting that 1-octyne and 2-bromo-1-phenylethanone
also achieved good yields, which meant this composite
catalyst was compatible of wide scope of substrates.

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FIGURE 9 Recycling of CuSO4NPs@CMC/PANI composites in A3 coupling reaction
TABLE 4 Comparison of the A3 coupling reaction using CuSO4NPs@CMC/PANI catalyst and other reported Cu-catalysts
Temp
(ꢀC)
Time
(h)
Yield
(%)
Entry Catalyst (mol%)
Solvent
Ref
1
CuSO4@CMC/PANI (6)
Solvent
free
120
1
95
This work
2
Fe3O4@SiO2-Se-T/CuI (20 mg)
Solvent
free
100
2.3
93
Rangraz et al.[38]
3
4
Cu0NPs@CMC (7.5)
CuI/HTNT-5 (20 mg)
Neat
120
70
2
80
96
Liu et al.[39]
Reddy et al.[40]
Solvent
free
1.5
5
6
CMC-Cu (II) (5)
Solvent
free
100
15
2
88
85
Liu et al.[41]
Cu-MCM-41 (40 mg)
CuI/II@Cys-MGO (0.01 g)
Solvent
free
90–100
Abdollahi-Alibeik and
Moaddeli[42]
Rafiee and Khavari[43]
Jiang et al.[44]
Dulle et al.[45]
Islam et al.[46]
7
Toluene
110
1
85
95
94
85
98
8
CuII@PAA/PVC mesoporous fibers (3) Toluene
120
36
22
6
9
Cu/Al oxide mesoporous sponges (12)
Cu-PS-ala (0.01 g)
Toluene
H2O
100
10
11
Reflux
100–110
Cu nanoparticles (15)
CH3CN
5.5
Kidwai et al.[47]

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XU ET AL.
3.5 | Recyclability and heterogeneity test
of CuSO4NPs@CMC/PANI composites in
A3 three-component coupling reactions
using CuSO4 as initiator and CMC─Na as template in
which quasi-spherical CuSO4 nanoparticles with 5.78 nm
average diameter are successfully loaded on the
CMC/PANI matrix. This as-prepared composites were
well characterized by ICP, XPS, TEM, SEM, EDS, FTIR,
and TGA analyses. It was proven that CuSO4NPs@CMC/
PANI composite was a highly efficient catalyst for A3
coupling reactions, A3-cycloisomerization tandem reac-
tions, and CuAAC reactions in terms of low catalyst load-
ing, remarkable catalytic performance, tolerance of wide
scope of substrates, recyclability, robustness, and benign
to environment. These salient features of this catalytic pro-
cess make it more competitive for practical applications.
For practical application, the recyclability of the
CuSO4NPs@CMC/PANI composites was evaluated using
the A3 model reaction under the afore-mentioned opti-
mal condition. The results shown in Figure 9 demon-
strated that the composite catalyst could be effectively
reused for more than 15 consecutive runs with marginal
dropping its catalytic activity. The Cu content of the
recovered catalyst after 15 cycles was determined using
ICP-AES analysis to be 1.374 mmol/g, which is slightly
lower than 2.006 mmol/g of Cu content in fresh catalyst.
The average loss of Cu in each run was calculated to be
2%, which make us to further investigate the homogene-
ity/heterogeneity of CuSO4NPs@CMC/PANI catalysts.
Then, hot filtration test was performed using the A3
model reaction. The reaction was quenched in 10 min
(18% conversion) by adding excessively ethyl acetate to
separate the solid catalyst. After entire removal of ethyl
acetate, the residues were then continued to react for 1 h
at 120ꢀC, and only a slight improvement in conversation
(18% to 22%) was observed, suggesting that the catalysis
was characteristically heterogeneous in nature.
ACKNOWLEDGMENTS
We are grateful to the Natural Science Foundation of
Guangdong Province (No. 2020A1515010399) for finan-
cial support.
AUTHOR CONTRIBUTIONS
Zhian Xu: Conceptualization; investigation; methodol-
ogy. Jinxi Xu : Investigation; methodology. Yiqun Li:
Conceptualization; funding acquisition; project adminis-
tration; resources; supervision.
CONFLICT OF INTEREST
The authors declare no competing interest.
3.6 | Comparison of catalytic activity in
A3 coupling reaction between
CuSO4NPs@CMC/PANI composite and
other reported catalysts
DATA AVAILABILITY STATEMENT
The data that support the finding of this study are avail-
able in the supporting information in this article.
To illustrate the merits and applicability of
CuSO4NPs@CMC/PANI catalyst, it has been compared
with other previously reported copper catalysts using the
A3 model reaction as a reference. The comparative results
presented in Table 4 clearly demonstrate that the present
composite catalyst indeed has some significant benefits
over other solid copper catalysts in terms of superior cata-
lytic activity, low catalyst loading, short reaction time,
excellent yield, easy separation, and recycling of catalyst.
The superior catalytic performance of CuSO4NPs@CMC/
PANI composites can be presumably attributed to the
coordination and stabilizing effect of CMC and PANI
which make the high dispersity of CuSO4 NPs on
CMC/PANI framework and thus prevent aggregation.
ORCID
Zhian Xu https://orcid.org/0000-0002-2748-0046
Jinxi Xu https://orcid.org/0000-0002-5369-6131
Yiqun Li https://orcid.org/0000-0002-3303-1730
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How to cite this article: Z. Xu, J. Xu, Y. Li, Appl
Organomet Chem 2021, e6349. https://doi.org/10.
1002/aoc.6349