Magnetic ZnO?CuO?Iron ore nanocomposites as a green and highly efficient heterogeneous nanocatalyst for solventless synthesis of α-aminophosphonates

Article abstract of DOI:10.1177/1747519819883883

A green novel synthesis of ZnO?CuO?Iron ore nanocomposites as a novel and magnetic heterogeneous nanocatalyst is used for the one-pot synthesis of α-aminophosphonates under solventless conditions. This study benefits from the magnetic iron ore acting as a multi-mineral Lewis acid system, the green properties and the large surface area due to its nanostructure. Moreover, scanning electron microscope analysis confirmed that the nanocatalyst gave an excellent yield and good recyclability; which, even after the 10th cycle of the model reaction retained its potential with no significant loss of catalytic activity.

Full text of DOI:10.1177/1747519819883883

883883CHL0010.1177/1747519819883883Journal of Chemical ResearchSajadi
research-article2019
Research Paper
Journal of Chemical Research
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Magnetic ZnO@CuO@Iron ore nanocomposites
as a green and highly efficient heterogeneous
nanocatalyst for solventless synthesis of
α-aminophosphonates
https://doi.org/10.1177/1747519819883883
DOI: 10.1177/1747519819883883
journals.sagepub.com/home/chl
S Mohammad Sajadi1,2,3
Abstract
A green novel synthesis of ZnO@CuO@Iron ore nanocomposites as a novel and magnetic heterogeneous nanocatalyst
is used for the one-pot synthesis of α-aminophosphonates under solventless conditions. This study benefits from the
magnetic iron ore acting as a multi-mineral Lewis acid system, the green properties and the large surface area due to its
nanostructure. Moreover, scanning electron microscope analysis confirmed that the nanocatalyst gave an excellent yield
and good recyclability; which, even after the 10th cycle of the model reaction retained its potential with no significant
loss of catalytic activity.
Keywords
α-aminophosphonates, green synthesis, solventless, trialkyl phosphite, ZnO@CuO@Iron ore NCs
Date received: 14 May 2019; accepted: 1 October 2019
used as potential nanocatalysts in various applications. In
Introduction
recent years, natural supporting materials have attracted
Nature as a source of biological system has great potential
the attention of researchers as they prevent agglomeration,
to produce nanomaterials using biomimetic approaches.
over-stoichiometric use of metal reagents, and also increase
The approaches are safe and biocompatible due to the coat-
the stability of the produced nanostructures by altering
ing of biological molecules on the surface of nanoparticles
their sensitivity to oxygen, water, and other chemical
(NPs). Nowadays, nanomaterials, especially those consist-
entities.7–10
ing of metal, metal oxide, and mixed alloy nanoparticles
have been used to make significant progress in science and
technology; mainly, for providing a very large surface area
1Department of Nutrition, Cihan University-Erbil, Erbil, Iraq
as a principal site of thermodynamical reactions.1–4
2Scientific Research Center, Soran University, Soran, Iraq
In fact, the large surface area of nanosized systems
(nanocatalysts) covers a huge number of active sites per
unit area of the catalyst which leads to a considerable
improvement of their catalytic ability.5,6
Currently, the attention of scientists is focused on pre-
venting or decreasing agglomeration and aggregation side
processes and increasing the stability of NPs when they are
3Department of Petroleum Geoscience, Faculty of Science, Soran
University, Soran, Iraq
Corresponding author:
S Mohammad Sajadi, Department of Petroleum Geoscience, Faculty
of Science, Soran University, PO Box 624, Soran, Kurdistan Regional
Government, Iraq.
Email: smohammad.sajadi@gmail.com

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Journal of Chemical Research 00(0)
Nowadays, solvent-free reactions benefit remarkably
from shorter reaction times, higher yields, easier workups,
and follow green approaches. Besides the selection of eco-
friendly types of reactions, the employment of safe and
green heterogeneous catalysts in chemical transformations
leads to the better efficiency with evident economic and
ecological advantages especially for industrial processes.25
Until now, there have been no reported applications of
green ZnO@CuO@Iron ore nanocomposites (NCs) as a
multi-mineral acidic nanocatalysts for the synthesis of α-
aminophosphonates under solventless conditions. This
study benefits from advantages such as a greener synthesis
without organic solvents, the application of a green nano-
catalyst possessing a huge surface area to increase the reac-
tion yield, the presence of plant phytochemicals on the
surface of the nanocatalyst which has increased the syner-
gistic properties of the catalyst, and also excellent reusabil-
ity of the catalyst in subsequent reactions (Scheme 1).
α-Aminophosphonates are used widely and their synthe-
sis, in a more efficient and safe way, has become a focus of
synthetic organic chemistry and medicinal chemistry.11–13 The
addition reaction of nucleophilic phosphorous compounds to
imines catalyzed by Lewis acids is a useful synthetic method
for their preparation. However, the mentioned process does
not progress in one pot from a carbonyl compound, an amine
and a phosphite as the produced water during the process
degrades or deactivates the Lewis acids.14,15 This drawback
has been overcome by some recent methods using lanthanide
triflates/magnesium sulfate,16 InCl3,17 TaCl5–SiO2,18 ZrCl4,19
Sc(DS)3,20 H3PW12O40,21 BiNO3·5H2O,22 Mg(ClO4)2,23 and
β-cyclodextrine.24 As these methods require long reaction
times and demonstrate low efficiencies, more efficient, eco-
nomic catalytic processes for the synthesis of α-
aminophosphonates are highly desirable.
Results and discussion
The catalytic reaction of aniline and 4-methylbenzaldehyde
was studied as a model reaction in various solvents media and
also solvent-free conditions. Different amounts of the green
catalyst were detected at various temperatures, and also under
solventless conditions. According to Table 1, the solventless
system (entries 10, 11, 12, 14, and 15) gave higher yields and
shorter reaction times compared to the solvent-containing sys-
tems. Furthermore, among the solventless conditions, the best
Scheme 1. Solventless synthesis of α-aminophosphonates using
green ZnO@CuO@Iron ore NCs.
Table 1. Optimization of the conditions for the synthesis of α-aminophosphonatesa.
Entry
Catalyst
Solvent
Time
Yield (%)b
TON
1
2
3
4
5
6
7
8
Zinc oxide NPs (20mol%)
Magnesium oxide (20mol%)
Potassium aluminum sulfate (20mol%)
Potassium aluminum sulfate (20mol%)
Natrolite zeolite (0.05g)
Natrolite zeolite (0.05g)
Natrolite zeolite (0.05g)
Natrolite zeolite (0.05g)
ZnO@CuO@Iron ore NCs (5mg)
ZnO@CuO@Iron ore NCs (5mg)
ZnO@CuO@Iron ore NCs (10mg)
ZnO@CuO@Iron ore NCs (10mg)
ZnO@CuO@Iron ore NCs (15mg)
ZnO@CuO@Iron ore NCs (15 mg)
ZnO@CuO@Iron ore NCs (15mg)
Solventless (100°C)
Solventless (100°C)
THF (rt)
PhMe (rt)
EtOH (65°C)
20h
30h
20h
20h
40h
40h
8h
4h
8h
13h
3h
5h
53
0
37
40
0
265
0
185
200
0
THF (65°C)
0
0
Solventless (rt)
Solventless (100°C)
Solventless (100°C)
Solventless (rt)
Solventless (100°C)
Solventless (rt)
THF (65°C)
72
89
55
72
81
53
61
77
98
477
593
1375
1800
2025
1325
1525
1925
2450
9
10
11
12
13
14
15
9h
3h
80min
Solventless (rt)
Solventless (100°C)
THF: tetrahydrofuran;TON: turnover number; rt: room temperature.
aReaction conditions: 4-methylbenzaldehyde (1mmol), aniline (1mmol), triethyl phosphite (1mmol), ZnO@CuO@Iron ore NCs (15mg), at 100°C.
bIsolated yield.

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3
Table 2. Synthesis of α-aminophosphonates using ZnO@CuO@Iron ore NCs (15mg) under solventless conditions at 100°C.
Entry
Carbonyl compound
Amine
p-Nucleophile
Time (h)
Yield (%)a
1
2
3
4
5
6
7
8
Benzaldehyde
Benzaldehyde
Aniline
Aniline
Aniline
Aniline
Aniline
Aniline
Aniline
p-Methyl aniline
p-Methoxy aniline
p-Methoxy aniline
m-Bromo aniline
Benzylamine
Aniline
Aniline
Aniline
m-Nitro aniline
Triethyl phosphite
Trimethyl phosphite
Triethyl phosphite
Triethyl phosphite
Triethyl phosphite
Triethyl phosphite
Triethyl phosphite
Triethyl phosphite
Triethyl phosphite
Triethyl phosphite
Triethyl phosphite
Triethyl phosphite
Triethyl phosphite
Triethyl phosphite
Triethyl phosphite
Triethyl phosphite
2
2
8
1
1.20
1
1
1.35
1.5
1.5
2
96
94
93
91
98
91
87
87
91
88
90
94
67
87
84
89
p-Nitro benzaldehyde
p-Chloro benzaldehyde
p-Methyl benzaldehyde
p-Cyano benzaldehyde
Furan-2-carbaldehyde
Benzaldehyde
9
Benzaldehyde
10
11
12
13
14
15
16
p-Methoxy benzaldehyde
p-Methoxy benzaldehyde
Benzaldehyde
3
Cyclohexanon
2.10
2.15
4
Methyl phenyl ketone
Methyl p-methoxy phenyl ketone
p-Methoxy benzaldehyde
3.5
aYield of pure isolated product.
Table 3. Effect of various catalysts on the synthesis of diethyl (4-methoxybenzaldehyde) (phenylamino)methylphosphonate by the
reaction of 4-methoxybenzaldehyde, aniline, and alkyl phosphite.
Compound
Catalyst
Solvent
Time (h)
Yield (%)
Ref.
p-Methoxy benzaldehyde
p-Methoxy benzaldehyde
p-Methoxy benzaldehyde
p-Methoxy benzaldehyde
p-Methoxy benzaldehyde
p-Methoxy benzaldehyde
p-Methoxy benzaldehyde
p-Methoxy benzaldehyde
p-Methoxy benzaldehyde
p-Methoxy benzaldehyde
p-Methoxy benzaldehyde
TaCl5–SiO2
InCl3
[Cu(3,4-tmtppa)](MeSO4)4
ZrCl4
CH2Cl2
THF
H2O
CH3CN
CH3CN
CH3CN
–
19
11
3
8.5
8.5
3.5
3
4
3
3
1.20
88
92
90
85
80
92
90
78
90
93
98
Rao et al.25
Bloemink et al.26
Sobhani et al.27
Bloemink et al.26
Bloemink et al.26
Rao et al.25
AlCl3
SbCl3/Al2O3 and molecular sieves 5Å
Al(OTf)3
Ce(OTf)4
AlKIT-5
Natrolite zeolite
ZnO@CuO@Iron ore NCs
SchÖllkopf et al.28
SchÖllkopf et al.28
Vinu et al.29
Bahari and Sajadi30
–
–
CH3CN
–
–
THF: tetrahydrofuran; NCs: nanocomposites.
result was obtained using 15mg of the nanocatalyst at 100°C, was calculated as 2450, which clearly indicates that the
thus these reaction conditions were selected for the synthesis method is useful for the synthesis of α-aminophosphonates.
of the α-aminophosphonates. The optimum amount of ZnO@
To study the scope of the optimized reaction process, the
CuO@Iron ore NCs was found to be 15mg in the presence of solventless reactions of several aldehydes, amines (primary
4-methylbenzaldehyde (1mmol), aniline (1mmol), and trie- and secondary), and trimethyl or triethyl phosphites were
thyl phosphite (1mmol). Besides the large surface area of the assessed in the presence of 15mg of ZnO@CuO@Iron ore
nanocatalyst which provides a suitable substrate for the reac- NCs at 100°C. Benzaldehyde and electron-deficient aro-
tion fractions in a high concentration, the multi-mineral sys- matic aldehydes reacted with aromatic and aliphatic amines
tem of iron ore substrate composed of a homogeneous to give the corresponding α-aminophosphonates in excel-
crystalline structure involving magnetite, hematite, quartz, and lent yields. No promoter was required for this method
chromite constituents as active acid sites caused a considera- (Table 2). In the case of benzaldehyde, aniline and trime-
ble increase in the yield and rate of the reaction. The ZnO@ thyl phosphite, the reaction did not occur in the absence of
CuO@Iron ore NCs exhibited good catalytic activity in which the green catalyst. Besides the selected aldehydes, several
the turnover number (TON) was calculated for the model reac- ketones were also screened in this three-component cou-
tion according to the following equation
pling under solvent-free conditions.
Table 3 compares the potential of our green catalyst–
based method with other reports on the same reaction cata-
lyzed by different catalysts. From the results, the ZnO@
CuO@Iron ore NCs demonstrate a better performance in
terms of the reaction rate and obtained higher yields of the
products.
% conversion ×mmol of substrate
TON =
mmol of catalyst
Based on the above equation, the TON obtained from the
optimum conditions of the model reaction (Table 1, entry 15)

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Journal of Chemical Research 00(0)
Figure 1. The ZnO@CuO@Iron ore nanocatalyst consisting
of the natural iron ore substrate, CuO NPs, ZnO NPs, and a
covering of plant phytochemicals on its surface.
In contrast to heterogeneous catalysts, the homogene-
ous ones show problems on large-scale operation such as
recycling and economic aspects. ZnO@CuO@Iron ore
nanocatalyst shows a high potential for commercialization
because of its ability to solve recycle problems and to give
excellent product yields, even when it used in a very low
amount.
Figure 2. The SEM micrograph of the recycled nanocatalyst
after the 10th cycle.
In fact, besides the multi-mineral system of the iron ore
substrate acting as a Lewis acid and the nonostructural
properties of the ZnO@CuO@Iron ore nanocatalyst, coat-
ing the plant phytochemicals on the surface of the catalyst
as capping agents resulted in a high concentration of rea-
gents on the large surface of the nanocatalyst and also acti-
vated the carbonyl compounds considerably to enhance the
reaction rate and yield (Figure 1). Finally, after removal of
the solvent and purification, the products were character-
ized by infrared (IR), H NMR, 13C NMR, and from their
melting points.
1
Figure 3. A field image of iron ore deposit, north west of
Choman, Iraqi Kurdistan.
At the end of the reaction, the green nanocatalyst was
efficiently isolated from the reaction medium with a simple
magnet then washed with ethanol and dried; this process
can be continued for several consequent times without any
loss of the catalyst activity, for example, the reaction of
benzaldehyde (Table 2, entry 1) with aniline and triethyl
phosphite has been repeated ten times using the same cata-
lyst with consistently high yields of 93%–96%. The scan-
ning electron microscope (SEM) micrograph of the recycled
nanocatalyst after 10th cycle reveals its excellent stability,
where its size, shape, and morphology were almost
unchanged (Figure 2). Besides the structure of the catalyst
and its natural origin, the phytochemicals coated on the sur-
face of the nanocatalyst preserve it from the instability pro-
cesses such as decomposition and deformation.
ore nanocatalyst which can be used for the synthesis of α-
aminophosphonates by treatment of aldehydes or ketones
with amines and trialkyl phosphites. The catalyst benefits
from a large surface area, a phytochemical coating on its
surface acting as a capping agent, and a multi-mineral sys-
tem acting as a Lewis acid. Therefore, in view of its easy
recovery, eco-friendliness, good reaction rates, high yields,
and better performance compared to previously reported
catalytic procedures for the synthesis of α-
aminophosphonates, this method has significant advan-
tages. In addition, the syntheses are solvent-free and involve
short reaction times and a simple work-up procedure.
Conclusion
Experiment
Due to the significance of α-aminophosphonates in medici-
nal and pharmaceutical applications, the development of
novel, fast, and safe synthetic methodologies, especially
using heterogeneous catalysts with important economic
properties, is of great importance. This study has intro-
duced a potent and green synthesized ZnO@CuO@Iron
All reagents were purchased from Merck and Sigma–
Aldrich Ltd and were used without further purification.
Products were characterized by spectroscopic data (IR, 1H
NMR, and 13C NMR) and from melting points. The NMR
spectra were recorded in CDCl3. H NMR spectra were
recorded on a Bruker Avance DRX 500-MHz instrument.
1

Sajadi
5
Figure 4. The XRD diffractogram of the ZnO@CuO@Iron ore NCs.
The chemical shifts (δ) are reported in parts per million
(ppm) relative to the tetramethylsilane (TMS) as internal
standard. J values are given in Hertz (Hz). 13C NMR spec-
tra were recorded at 125MHz. IR (KBr) spectra were
recorded on a Shimadzu 470 spectrophotometer. Melting
points were recorded in open capillary tubes with a
BUCHI 510 melting point apparatus and are uncorrected.
X-ray diffraction (XRD) measurements were carried out
using a Philips powder diffractometer type PW 1373 goni-
ometer with a scanning rate of 2°min−1 in the 2θ range
from 0° to 90°. The sizes, shape, and chemical composi-
tion of the nanocatalyst were investigated by SEM (SEM-
Quanta 450) equipped with energy dispersive X-ray
spectroscopy (EDS).
Magnetic iron ore collection
The iron ore deposit was collected in the north west of
Choman, Iraqi Kurdistan (Figure 3). The sample was
Figure 5. SEM micrograph of the green synthesized ZnO@
CuO@Iron ore NCs.
washed with hot water to remove possible impurities, then
dried, and powdered to use as a natural magnetic substrate
during this study.
and the same volumes of 0.8% CuCl2·2H2O and 0.3%
Zn(NO3)2 solutions in an alkaline medium adjusted using
0.1M Na2CO3 while stirring at 80°C. After the color of the
reaction mixture had changed from light yellow to black, it
Preparation of the Bryonia dioica
root extract
An amount of 20.0g of dried root powder of the plant (col- was filtered and the obtained precipitate was dried and
lected in Summer 2018 in the Haji Umran alpine region) identified for use as a green nanocatalyst.
was boiled in 150mL of double distilled water for 30min at
80°C. The obtained extract was filtered and used for the
green synthesis of the nanocatalyst.
Catalyst characterization
The XRD pattern of the NCs (Figure 4) revealed the
phase purity and crystal planes of numerous minerals in
the texture of the iron ore substrate including ZnO and
CuO NPs. This mineral matrix of the NCs indicates a
Green synthesis of ZnO@CuO@
Iron ore NCs
The ZnO@CuO@Iron ore NCs was synthesized according valuable Lewis acid surface present in the catalyst sys-
to our previous report with some modifications.8 Briefly, tem, which makes it an excellent catalyst for organic
2g iron ore powder was mixed with 100mL of plant extract transformations.

6
Journal of Chemical Research 00(0)
Figure 6. Point analysis of the ZnO@CuO@Iron ore NCs.
Furthermore, the SEM micrograph shown in Figure 5 Declaration of conflicting interests
demonstrates a nanosized system (mostly in the range of
The author(s) declared no potential conflicts of interest with
50–70nm) for the ZnO@CuO@Iron ore NCs, including a
semi-spherical shape and homogeneous morphology with
some agglomeration on the surface of the nanostructure.
Also, the point analysis of a determined section of the
nanocatalyst shows peaks related to the Fe, O, Zn, Si, and
Cu, thereby confirming the successful anchoring of the
CuO and ZnO NPs on the iron ore substrate and fabrication
of the ZnO@CuO@Iron ore NCs (Figure 6).
respect to the research, authorship, and/or publication of this
article.
Funding
The author received no financial support for the research, author-
ship, and/or publication of this article.
ORCID iD
S Mohammad Sajadi
https://orcid.org/0000-0001-8284-5178
Preparation of α-
aminophosphonates
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