Nano-construction of CuO nanorods decorated with g-C3N4 nanosheets (CuO/g-C3N4-NS) as a superb colloidal nanocatalyst for liquid phase C[sbnd]H conversion of aldehydes to amides

Article abstract of DOI:10.1016/j.molliq.2021.116063

Herein, we describe an intelligent strategy to fabricate nanosheets of graphitic carbon nitride (g-C₃N₄) decorated with nanorods copper oxide (CuO NRs). Then, the catalytic activity of CuO_NRs/g-C₃N₄-NS was developed for the synthesis of primary amides in water. The morphology of CuO and its synergetics effect with nanosheets g-C₃N₄ a major role in the yield of products. Furthermore, hydroxylamine hydrochloride (NH₂OH·HCl) due to availability and affordability was used as a suitable substitute for ammonia source. The findings demonstrate that this layer nanostructure is a superb catalyst for converting various derivatives of aldehyde to their corresponding amides. The current protocol can be useful criterion in the synthesis and stabilization of metal oxides and provides new insight in organic transformation.

Full text of DOI:10.1016/j.molliq.2021.116063

Journal of Molecular Liquids 334 (2021) 116063
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Nano-construction of CuO nanorods decorated with g-C N nanosheets
3
4
(
CuO/g-C N -NS) as a superb colloidal nanocatalyst for liquid phase CAH
3
4
conversion of aldehydes to amides
Robabeh Mohammadi , Behnam Gholipour , Hassan Alamgholiloo b,1, Sadegh Rostamnia a,b,
⇑
,
b
c,1
b
c
d
e,
⇑
Hamed Mohtasham , Afsaneh Zonouzi , Seeram Ramakrishna , Mohammadreza Shokouhimehr
a
Organic and Nano Group (ONG), Department of Chemistry, Iran University of Science and Technology (IUST), PO Box 16846-13114, Tehran, Iran
Organic and Nano Group (ONG), Department of Chemistry, Faculty of Science, University of Maragheh, PO Box 55181-83111, Maragheh, Iran
School of Chemistry, College of Science, University of Tehran, PO Box 14155-6455, Tehran, Iran
Department of Mechanical Engineering, Center for Nanofibers and Nanotechnology, National University of Singapore,119260, Singapore
b
c
d
e
Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
3 4
Herein, we describe an intelligent strategy to fabricate nanosheets of graphitic carbon nitride (g-C N )
Received 18 February 2021
Revised 28 March 2021
Accepted 3 April 2021
Available online 8 April 2021
decorated with nanorods copper oxide (CuO NRs). Then, the catalytic activity of CuONRs/g-C
developed for the synthesis of primary amides in water. The morphology of CuO and its synergetics effect
with nanosheets g-C a major role in the yield of products. Furthermore, hydroxylamine hydrochloride
NH
The findings demonstrate that this layer nanostructure is a superb catalyst for converting various deriva-
tives of aldehyde to their corresponding amides. The current protocol can be useful criterion in the syn-
thesis and stabilization of metal oxides and provides new insight in organic transformation.
Ó 2021 Elsevier B.V. All rights reserved.
3 4
N -NS was
3 4
N
(
2
OHÁHCl) due to availability and affordability was used as a suitable substitute for ammonia source.
Keywords:
CuO/g-C N -NS
3 4
Layer nanostructure
Primary amides
CuO nanorods
Green synthesis
1
. Introduction
Primary amides with two hydrogen donors and two hydrogen
sion of heterogeneous catalysts because of low toxicity and eco-
friendly path present a green and reliable protocol.
3 4
Recently, graphitic carbon nitride (g-C N ) as a fascinating con-
receptors are exceptional supramolecular synthons that can be uti-
lized for the construction of pharmaceuticals, polymers, and natu-
ral products [1]. For this reason up to now, various catalytic green
procedures have been developed by using nitrile [2], primary ami-
nes [3], decarboxylative ammoxidation of phenylacetic acids [4],
ammoxidation primary alcohols [5], and Baylis–Hillman [6] for
the synthesis of primary amides (Scheme 1). However, most of
these reported methods use homogeneous and non-recoverable
catalytic systems or harsh reaction conditions that lead to the for-
mation of by-products. The present research team has recent suc-
cess is applying the catalytic application nanomaterials including
jugated polymer has possessed a lot of attention in the arena of the
catalytic process [11,12]. Due to its unique properties such as high
thermal and chemical stability, as well as the existence of abun-
3 4
dant nitrogen sites on the surface, g-C N acts as a strong Lewis
base site [13]. Also, this layered structure makes the appropriate
substrate for the anchor eligible metal and allows its direct utiliza-
tion as a heterogeneous catalyst [14]. In recent years, the develop-
3 4
ment of copper-based g-C N catalysts in organic transformations
have been a growing trend [15–18]. For instance, it can be referred
to hydroxylation of aryl iodides [19], hydrochlorination [20], aero-
bic oxidations of alkyl aromatics [21], and synthesis triazoles [22].
Therefore, the development of green and efficient protocols for
organic transformations is an attractive and challenging path.
Transition-metal oxides are the most promising candidates for
catalytic process because of their low preparation cost, high stabil-
ity, and high compatibility with microelectronic processing [23–
SBA-15/PrEn-NHSO
3
H [7], SEP123-GO/PdNPs [8], SBA-15/En–Cu [9],
and ZIF-8/TFE [10] for amide bond construction. Thus, the expan-
⇑
Corresponding authors.
E-mail addresses: rostamnia@iust.ac.ir (S. Rostamnia),
2
7]. Among transition-metal oxides, CuO as an important p-type
mrsh2@snu.ac.kr
semiconductor has attracted increasing interest because of its high
stability, and nontoxicity. Recently, CuO structure with different
(
M. Shokouhimehr).
These authors contributed equally.
1
https://doi.org/10.1016/j.molliq.2021.116063
167-7322/Ó 2021 Elsevier B.V. All rights reserved.
0

R. Mohammadi, B. Gholipour, H. Alamgholiloo et al.
Journal of Molecular Liquids 334 (2021) 116063
Scheme 1. Routes for the synthesis of primary amides.
3 4
Fig. 1. Synthetic pathway of CuONRs/g-C N -NS.
morphologies such as nanoparticles [28], nanorods/wires [29,30],
nanoribbons [31], micro-dandelions [32], nanoflowers [33], hollow
spheres [34], nanoplates [35], and spindle-like [36] has been
reported for improving catalytic/photocatalytic process. Tailored
preparation of the nanorod CuO system is therefore a strategic sub-
ject of ongoing investigations.
Based on the above finding, we envisioned an economical
method for the fabrication of layer nanostructure using a fusion
3 4
of nanosheets g-C N with CuO nanorods. We also indicate the
2. Experimental
2.1. Materials and methods
Melamine (99%), Cu(NO ) Á3H O, NH OHÁHCl (98%), K CO
3
2
2
2
2
3
(98%), and benzaldehyde (99.5%) were purchased from Sigma
Aldrich and Merck. Sodium hydroxide (NaOH), ethanol (EtOH),
Dimethyl sulfoxide (DMSO), and Dimethylformamide (DMF) were
obtained from commercial sources.
ability of this layer nanostructure in the synthesis of primary
amides from relevant aldehydes. To the best of our knowledge, this
is the first example of the layer nanostructure that exhibits
enhanced catalytic activity toward synthesis of primary amides
The materials and solvents used in the current work were pur-
chased from Sigma-Aldrich, Merck Fluka, and were used without
further purification. The Fourier-transform infrared (FT-IR) spectra
were performed using a Shimadzu IR-460 spectrometer with an
ATR probe. The morphologies of the samples were taken on
2
in the presence of H O.
2

R. Mohammadi, B. Gholipour, H. Alamgholiloo et al.
Journal of Molecular Liquids 334 (2021) 116063
2
.3. Preparation of activated g-C
3 4
N -NS
Initially, 0.2 g of light yellow powder g-C
3
N4-NS was dissolved
in 25 mL of NaOH (0.10 M) solutions under sonication at 30 min.
Then, the resulting solution was transferred to autoclave (50 mL
capacity) and exposed to hydrothermal treatment at 100 °C for
2
4. After cooling the autoclave to ambient temperature, the
2
afforded light-yellow powder washed with DI-H O several times
and dried at 60 °C for 12 h.
3 4
2.4. Synthesis of CuONRs/g-C N -NS
0
.5 g of activated g-C
pure water under ultrasonic irradiation for 30 min. Then, 0.3 g
Cu(NO O were dissolved in 20 mL H O, and dropwise added
Á3H
into the solution above under sonication. After 30 min sonicating,
2 mL NaOH solution (1 M) was added dropwise with magnetic
3 4
N -NS was immersed into 100 mL ultra-
3
)
2
2
2
1
stirring. After stirring for 2 h at room temperature, the mixture
was washed with deionized water and EtOH and dried at 60 °C
overnight. Finally, the green powder was calcined in a muffle fur-
nace at 200 °C for 2 h, to obtain the CuONRs/g-C
3
N
4
-NS.
2.5. General procedure for the synthesis of amide bond
The mixture of benzaldehyde (1 mmol), NH
CO (1.1 mmol), DI-H O (2 mL) were added to 10 mol % of
-NS catalyst in a Schlenk tube. Then, the reaction
2
OHÁHCl (1.2 mmol),
K
2
3
2
3 4
CuONRs/g-C N
mixture was stirred at 80 °C for 20 h. After completing the reaction,
the catalyst was separated by centrifugation and organic phase
purified by column chromatography on silica to obtain the amide
1
product 3. Finally, all primary amides were identified by H and
1
3
C NMR spectroscopy.
3
. Results and discussion
In continuation of our recent report in the introduction of new
nanostructures [37–40], herein, the synthesis and characterization
of CuONRs/g-C -NS layer nanostructure was reported (Fig. 1). The
g-C -NS was synthesized during melamine thermal polymeriza-
tion and then exfoliation through the sonication process. The pres-
ence of g-C nanosheets inside of CuO metal oxide plays a vital
role in the excellent control of the size and homogeneous disper-
sion of nanorods, which boosts the catalytic activity for the synthe-
sis of primary amides under sustainable reaction conditions.
3
N
4
3
N
4
3
N
4
3 4
Fig. 2. XRD patterns (a), FT-IR spectra (b), and EDX of CuONRs/g-C N -NS (c).
3 4
The crystalline structure of CuONRs/g-C N -NS was analyzed
using the XRD pattern. As depicted in Fig. 2a, the characteristic
diffraction peaks at 12.9° and 27.6° for the planes (100) and
Scanning Electron Microscopy (SEM), Zeiss-DSM 960A microscope.
Transition Electron Microscopy (TEM) images were recorded on
Zeiss-EM 900. The crystalline structure of the nanorods of CuO,
(
002) can be indexed using the interlayer stacking of aromatic g-
segments (JCPDS 87-1526) [41,42]. In addition, the peak
appeared at 32.6°, 35.3°, 38.5°, and 48.9° reflections to (110),
002), (111), and (202) CuO monoclinic symmetry planes (JCPDS:
as well as layer nanostructures, were examined by X-Ray Diffrac-
3 4
C N
1
tion (XRD) instrument (Philips-PW1800 diffractometer). The
H
1
3
and C NMR spectra were recorded on a Bruker AVANCE NMR
spectrometer at 300 and 100 MHz, respectively.
(
8
9-2529), respectively [43]. Besides, The FT-IR spectra of CuONRs/g-
C
3
N
4
-NS was studied to further investigate the composition of the
À1
2.2. Synthesis of g-C
N
3 4
nanosheets
materials Fig. 2b. The strong adsorption at 807 cm corresponds
to the vibration of triazine units [44]. Also, the peaks observed at
1228, 1317, 1458 cm are ascribed to CAN aromatic, and peaks
À1
À1
The nanosheets g-C
report [12]. First, the g-C
3
N
4
was prepared according to our previous
was prepared by calcination of mela-
3
N
4
at 1551 and 1632 cm are ascribed to C@N heterocycle stretching
mine powder, in a covered alumina crucible ceramic at 520 °C in a
muffle furnace for 4 h by heating rate of 5 °C min . Then, the yel-
mod [45,46]. The characteristic adsorption at in 601, 588, and
466 cm are attributed to the tensile vibration CuAO bond [47],
À1
À1
low powder was collected after decreasing the furnace tempera-
3 4
which suggests the successful preparation of CuONRs/g-C N -NS.
ture to ambient temperature. After that, to achieve g-C
nanosheets, 40 mg of yellow g-C powder was dispersed in
0 mL of water and the mixture was exposed to the ultrasonic fol-
lowing for 12 h. Finally, the obtained upper part of the homoge-
neous mixture was isolated by centrifugation (5000 rpm).
3
N
4
The energy-dispersive X-ray spectroscopy (EDS) analysis confirms
the presence of all anticipated elements (i.e., N, C, O, and Cu) in
3
N
4
5
the CuONRs/g-C
successful deposition of CuO onto the g-C
more, the wt% of CuO in the CuONRs/g-C N
4
3
N
4
-NS structures exhibit purity while achieving a
nanosheets. Further-
-NS was calculated via
3 4
N
3
3

R. Mohammadi, B. Gholipour, H. Alamgholiloo et al.
Journal of Molecular Liquids 334 (2021) 116063
3 4
Fig. 3. XPS patterns of CuONRs/g-C N -NS. (a) survey, (b) C1s, (c) N1s, (d) O1s, (e), and Cu2p.
atomic absorption spectroscopy (AAS) and the resultant yield was
6.65%.
The chemical states of the layer nanostructure was determined
The structural morphology of the layer nanostructures were
studied by SEM technique, and corresponding images before and
after treated with NaOH as well as growth of CuONRs are depicted
7
using X-ray photoelectron spectroscopy (XPS) measurements, and
the corresponding results are depicted in Fig. 3. The survey spec-
3 4
in Fig. 4. As shown in Fig. 4 a, g-C N shows a two-dimensional
structure with wrinkle-like morphology and irregular shape. After
hydrothermal treatment with alkaline solution, bulky sheets g-
trum of CuONRs/g-C
sponding to carbon, nitrogen, oxygen, and copper in the catalysts
Fig. 3a). The C 1s XPS spectra indicate two peaks at 285.6 and
83.5 eV, which correspond to CAN@C in the heterocycle rings,
3 4
N -NS contains characteristic peaks corre-
3
C N
4
have been broken down into small fragments that led to
the formation of the nanosheets g-C Fig. 4 b. Besides, Fig. 4c
indicates that the interaction of Cu(NO O with triazine units
Á3H
led to the formation of the CuO nanorods on the surface of g-C
(
2
3 4
N
3
)
2
2
CAOH, and CAC [48,49]. Furthermore, peak N 1s around 400 eV
3 4
N .
is related to pyrrolic N, pyridine N, and graphitic N [50]. On the
A close inspection of TEM images indicates formation CuO nanor-
ods with an approximate diameter of 6–12 nm and a length of
about 10–60 nm. The interplanar spacing distance from the high-
resolution TEM (HRTEM) image indicates 0.27 nm, which corre-
sponding to the (110) plane of CuO (Fig. 3e). Also, the correspond-
ing selected area electron diffraction pattern (SAED) revealed the
other than, the specific O 1s peak that appears around the 530 V
À
region can be related to O
2
in the CuONRs, surface-absorbing hydro-
xyl or C@O, and CAO [51]. Finally, the Cu 2p spectrum shows that
Cu 2p3/2 and Cu 2p1/2 are located at 932.8 eV and 953.6 eV, respec-
tively, which is attributed to the (II) oxidation state of copper pre-
sent in the catalyst [52]. Besides, the peaks corresponding to 941.5
and 960.6 eV demonstrate existence of copper atom in (II) oxida-
tion state as CuO [53,54].
formation of highly crystalline CuO on the surface of g-C
(Fig. 4f).
3 4
N
4

R. Mohammadi, B. Gholipour, H. Alamgholiloo et al.
Journal of Molecular Liquids 334 (2021) 116063
Fig. 4. SEM micrograph of g-C
pattern of CuONRs/g-C -NS.
3 4 3 4 3 4 3 4
N (a), nanosheets g-C N after treated with NaOH (b), CuONRs/g-C N -NS (c), TEM and HRTEM images of CuONRs/g-C N -NS (d, e), and SAED
3
N
4
3 4
Fig. 5. STEM images of CuONRs/g-C N -NS (a) and STEM mapping (b).
In addition to TEM, scanning transmission electron microscopy
STEM) can provide even more detail about the morphology of the
(
3 4
CuONRs/g-C N -NS nanosheets. The dark-field STEM images show
that CuO nanorods were heterogeneously deposited onto the sur-
face of the nanosheets (Fig. 5a). Besides, the STEM-mapping images
in Fig. 5b confirm the presence of elements such as carbon, nitro-
3 4
gen, oxygen, and copper in the CuONRs/g-C N -NS layer
nanostructure.
The importance of the C-H amidations in natural products,
pharmaceutical drugs, and polymeric materials has led to broad
interdisciplinary attention research [55,56]. After full identification
Scheme 2. Synthesis of benzamide catalyzed by CuONRs/g-C
3
N
4
-NS.
3 4
of CuONRs/g-C N -NS, we turned our attention to employing this
5

R. Mohammadi, B. Gholipour, H. Alamgholiloo et al.
Journal of Molecular Liquids 334 (2021) 116063
Table 1
a
Screening of optimization of reaction conditions for primary amide formation.
o
Yield (%)b
Entry
Cat.
Solvent
Base
T( C)
Time (h)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
–
H
H
H
H
H
H
H
2
2
2
2
2
2
2
O
O
O
O
O
O
O
K
K
2
CO
CO
3
3
80
70
80
80
80
80
80
80
80
80
80
80
80
80
80
80
25
24
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
10>
72
95
32
39
69
56
41
34
26
16
55
66
74
10>
61
19
3 4
CuONRs/g-C N -NS
CuONRs/g-C
2
3
N
4
-NS
-NS
-NS
-NS
-NS
-NS
-NS
-NS
-NS
-NS
-NS
-NS
2 3
K CO
CuONRs/g-C
CuONRs/g-C
CuONRs/g-C
CuONRs/g-C
CuONRs/g-C
CuONRs/g-C
CuONRs/g-C
CuONRs/g-C
CuONRs/g-C
CuONRs/g-C
CuONRs/g-C
3
3
3
3
3
3
3
3
3
3
3
N
N
N
N
N
N
N
N
N
N
N
4
Et
NaHCO
CaCO
NaOH
3
N
4
4
4
4
4
4
4
4
4
4
3
3
PhMe
K
K
K
K
K
K
K
K
K
K
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
3
3
3
3
3
3
3
3
3
3
n-hexane
dioxane
DMSO
DMF
EtOH
3
CH CN
0
1
2
3
4
5
6
7
g-C
CuO
CuONRs/g-C
N
3 4
H
H
H
2
2
2
O
O
O
3
N
4
-NS
a
Reaction conditions: benzaldehyde (1 mmol), NH
Isolated yield of amide.
2
OHÁHCl (1.2 mmol), K
2
CO
3
(1.1 mmol), H
2
O (5 mL) in 10 mol% of catalyst.
b
Table 2
a
Substrates scope for the synthesis of primary amides from aldehydes.
a
Reaction condition: 1 (1 mmol), 2 (1.2 mmol), and catalyst (10 mol%) at 80 °C. The yields were isolated
after column chromatography.
nanomaterial as a heterogeneous catalyst for the synthesis of
essential for the conversion of aldehydes to primary amides. There-
fore, by increasing the amount of catalyst to 10 mol%, the yield pro-
duction increased up to 72% (Table 1, entry 2) also, yield being
benzamide using benzaldehyde and NH
tion. The reaction in the presence 1 mol% of the catalyst leads to
the formation of benzamide with 95% yield (Scheme 2).
2
OHÁHCl as a model reac-
improved to 95% when K
entry 3). However, screening a range of bases indicated that K
performed best among other bases such as Et N, NaHCO , CaCO
and NaOH, (Table 1, entries 4–7). After screening different solvents
in optimized conditions H O turned out to give the best yields.
Solvents nonpolar such as PhMe, n-Hexane, and dioxane were
2
CO
3
was used as a base at 80 °C (Table 1,
The experiments demonstrate that in the absence CuONRs/g-
2
CO
3
3
C N
4
-NS yield fewer than 10% (Table 1, entry 1). Also, in presence
3
3
3
,
of the acid-base catalyst instead metal-catalyst lead to the forma-
tion of secondary amides via Beckman rearrangement [57,58]. The
addition of the CuONRs/g-C N -NS as a heterogeneous catalyst is
3 4
2
6

R. Mohammadi, B. Gholipour, H. Alamgholiloo et al.
Journal of Molecular Liquids 334 (2021) 116063
Table 3
Comparison of catalytic performance of different systems for synthesis of primary amide.
Catalyst
Solvent
Time (h)
T (o C)
Yield (%)
Ref
CuO/HMS (3 wt%)
H
H
2
O
O
10
48
15
2
100
110
100
110
160
80
110
110
78
84
99
98
95
99
97
95
88
89
95
91
95
[59]
[60]
[61]
[60]
[62]
[63]
[64]
[65]
[66]
[67]
[68]
This work
Cu(OAc)
Pd(OAc)
CuSO
Á5H
Rh(OH)x/Al
FSC-Cu (1 mol%)
RuCl(CO)(PPh )(TAC)] (1 mol%)
TerpyRu(PPh )Cl (1 mol%)
Ru(L)(CO)Cl(AsPh
2
(2 mol%)
2
2
(5 mol%)
DMSO–H
Solvent free
2
O
4
2
O (5 mol%)
(4 mol% Rh)
2
O
3
H
H
2
O
O
7
2
24
12
17
18
20
48
20
[
3
toluene
toluene
MeCN
3
2
[
)
3 2
]
FeCl
3
(5 mol%)
H
2
O
100
125
80
Metal-free
CuONRs/g-C
DMSO/H
2
O
3 4
N -NS (10 mol%)
H
2
O
3 4
Scheme 3. Proposed reaction mechanism for the conversion of aldehydes to amides through CuONRs/g-C N -NS.
3 4
Scheme 4. Chemoselectivity of CuONRs/g-C N -NS in amidation reaction.
scrutinized and showed inferior results (Table 1, entries 8–10). In
addition to H O, the effect of various polar solvents such as DMSO,
DMF, EtOH, and CH CN turned out to give the moderate yields
Table 1, entries 11 and 14). As a proof of the synergetic effect of
CuO nanorods and g-C sheets in convert aldehydes to amides,
a series of controlled experiments were carried out. Bare g-C
Table 1, entry 15) and CuO (Table 1, entry 16) result in a low con-
version under optimized conditions. When CuO nanorods decorate
on the surface g-C indicate that they deliver product with more
After determining the optimum reaction conditions, the scope
and efficacy of this method were investigated through the one-
pot conversion for a wide range of aldehyde derivatives (Table 2).
Excellent yields were obtained for all the desired primary amides.
For electron-donating or electron-withdrawing on aldehydes,
excellent yields were obtained, which indicate reaction is not sen-
sitive to the electronic effects. However, the electron-donating
groups on the aromatic ring indicate yields about 85–95% (Table 2,
3a-3j), and also, for the electron-withdrawing groups on the ring
yielded 80–90% (Table 2, 3k-3m). Similar results were obtained
for thiophene-2-carbaldehyde (Table 2, 3m). Only for 2-hydroxy
benzaldehyde, a low yield (43%) was observed, which may be
2
3
(
3
N
4
3 4
N
(
3
N
4
than 95% yield. Finally, by decreasing the temperature reaction
from 80 °C to ambient condition, we observed a decrease in the
yield of reaction (Table 1, entry 17).
7

R. Mohammadi, B. Gholipour, H. Alamgholiloo et al.
Journal of Molecular Liquids 334 (2021) 116063
analysis of the mixture after 24 h demonstrated that the yield of
benzamide is 87% (3a), whereas production of 3a’ was around 6%.
A controlled leaching experiment is performed to reach a dee-
per understanding of the heterogeneous nature of the proposed
catalyst. The inductively coupled plasma optical emission spec-
trometry (ICP-OES) results imply that after each cycle, the leaching
of Cu is below 1.0 ppm. Furthermore, hot filtration test (Fig. 6) of
3 4
the reaction suspension to remove the insoluble CuONRs/g-C N -
NS also led to the inhibition of homogeneous reaction. However,
analysis of the mixture reaction demonstrates that, after the
removal of catalyst, the yield of primary amide increases from 53
to 55%, indicating negligible copper leaching in the catalytic reac-
tion. ICP-OES analysis and hot filtration test confirmed that the
CuONRs/g-C
The study of recovery and reusability of the heterogeneous
CuONRs/g-C -NS catalyst was investigated according to the opti-
3 4
N -NS is truly heterogeneous in nature.
3 4
N
mized conditions in 8 cycles (Fig. 7a). For this purpose, the catalyst
was separated by centrifugation after each use and prepared for
the subsequent cycle. After 8 cycles, yields of 75% were observed
3 4
indicating that CuONRs /g-C N -NS was stable under reaction con-
Fig. 6. Hot filtration test was carried out by separating the catalyst from reaction
mixture after 7 h of reaction time.
ditions. Stable layer nanostructure and CuO nanorods aggregation
after the reuse was confirmed by SEM (Fig. 7b). The results indicate
3 4
that CuONRs/g-C N -NS has recyclable, heterogeneous, and excel-
lent physicochemical stability during the conversion of aldehydes
to amides.
due to the formation of a complex between copper and 2-
hydroxybenzaldehyde (Table 2, 3m).
3 4
The catalytic activity of CuONRs/g-C N -NS layer nanostructure
was also compared with previously reported catalytic protocols
and results are shown in Table 3. The proposed layer nanostructure
exhibits a better catalytic activity in comparison to the best cata-
lyst systems, with remarkable differences in terms of stability
and reusability.
4. Conclusions
In conclusion, activated g-C N nanosheets manufactured by
exfoliation of bulk powder g-C N have been developed as an
3
4
3
4
Based on the mentioned characterization and analysis, two
acceptable mechanism for the one-pot synthesis of a primary
active matrix for the embedded of CuO nanorods. We also devel-
oped a general and highly efficient protocol toward green synthesis
of primary amides from aldehydes. Our findings showed that the
base and solvent roles are important in the synthesis of the desired
aromatic amides. We envisage that the modifying of g-C N sheets
with various metals and metal oxides can be provide new inside
for the synthesis of inexpensive, reusable, and environmentally
friendly catalysts in the catalytic arena.
amide using CuONRs/g-C
CuONRs/g-C -NS/K CO
3
N
4
-NS is presented in Scheme 3. In the
3
N
4
2
3
system in H O, CuONRs weakly coordinate
2
with oxime to the formation of intermediate RAC„NACuO. The
first mechanism proceeds through route A, which involves the for-
mation of a five-membered ring intermediate containing the CuO
via the oxime coordination to the corresponding intermediate
RAC„NACuO, which eventually results in the formation of the
amide. The other mechanism proceeds through the dehydration/
hydration route (route B) followed by subsequent rearrangement
to the corresponding amide product. Based on the results and pre-
viously reported activities for copper in the synthesis of primary
amide [27], we believe that the B (dehydration/hydration) route
is the most plausible mechanism.
3
4
CRediT authorship contribution statement
Robabeh
Mohammadi:
Data
curation,
Investigation.
Behnam Gholipour: Validation, Formal analysis, Writing
-
original draft. Hassan Alamgholiloo: Validation, Writing - review.
Sadegh Rostamnia: Supervision. Hamed Mohtasham: Methodol-
ogy. Afsaneh Zonouzi: Supervision. Seeram Ramakrishnad:
review & editing. Mohammadreza Shokouhimehre: Supervision.
In order to examine selectivity, deploying an equimolar mixture
of benzaldehyde and salicylaldehyde with NH
mized conditions is used for the selectivity study (Scheme 4). An
2
OHÁHCl under opti-
Fig. 7. The reusability performance for the synthesis of primary amides (a) and SEM image of the (a) after 8th run.
8

R. Mohammadi, B. Gholipour, H. Alamgholiloo et al.
Declaration of Competing Interest
Journal of Molecular Liquids 334 (2021) 116063
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Supplementary data to this article can be found online at
https://doi.org/10.1016/j.molliq.2021.116063.
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