Cu(II)-supported graphene quantum dots modified NiFe2O4: A green and efficient catalyst for the synthesis of 4H-pyrimido[2,1-b]benzothiazoles in water

Article abstract of DOI:10.1002/jccs.202000213

NiFe₂O₄ nanoparticles are modified by graphene quantum dots (GQDs) and utilized to stabilize the Cu(II) nanoparticles as a novel magnetically retrievable catalytic system (Cu(II)/GQDs/NiFe₂O₄) for green formatio

Full text of DOI:10.1002/jccs.202000213

Received: 13 June 2020
Accepted: 24 August 2020
DOI: 10.1002/jccs.202000213
A R T I C L E
Cu(II)-supported graphene quantum dots modified NiFe O :
2
4
A green and efficient catalyst for the synthesis of
H-pyrimido[2,1-b]benzothiazoles in water
4
Khatereh Khazenipour | Farid Moeinpour
| Fatemeh S. Mohseni-Shahri
Department of Chemistry, Bandar Abbas
Abstract
Branch, Islamic Azad University, Bandar
Abbas, Iran
NiFe O nanoparticles are modified by graphene quantum dots (GQDs)
2 4
and utilized to stabilize the Cu(II) nanoparticles as a novel magnetically
retrievable catalytic system (Cu(II)/GQDs/NiFe O ) for green formation of
Correspondence
Farid Moeinpour, Department of
Chemistry, Bandar Abbas Branch, Islamic
Azad University, Bandar Abbas
2
4
4H-pyrimido[2,1-b]benzothiazoles. The prepared catalyst can be isolated
assisted by an outer magnet and recovered for five courses without signifi-
cant reduction in its efficiency. The as-prepared magnetic heterogeneous
nanocomposite was characterized by UV–Vis, FT-IR, XRD, EDS, VSM,
TEM, and ICP. Performing the reactions in environmentally friendly and
affordable conditions (water), the low catalyst percentage, high yield of
products, short reaction times, and easy workup are the merits of this
protocol.
7915893144, Iran.
Email: fmoeinpour@iauba.ac.ir
Funding information
Islamic Azad University
K E Y W O R D S
4
2 4
H-pyrimido[2,1-b]benzothiazoles, graphene quantum dots, nanocatalyst, NiFe O
1
| INTRODUCTION
focus of attention to researchers for consecutive
[
4]
years.
indicated that the importance of magnetic catalysts.
Among them, NiFe O has been getting more consider-
Many works have been published and also
[
5]
Graphene quantum dots (GQDs) are the zero-
dimension nanographenes with special characteristics
like small size, chemical inertness, photoluminescence,
ease to be functionalized with biomolecules and bio-
compatibility have received a lot of attention in the
nanotechnology research studies. Nevertheless, the
diverse uses of GQD, little consideration has been
given for applying GQD as a solid support or catalyst in
2
4
ation, owing to its strong coercive power, appropriate
[
6]
magnetic induction, and high permanence. Several
research studies verify the outlooks of using NiFe O
2
4
[
1]
[7]
as an effective nanocatalyst. The immobilization of
nano-NiFe O on GQDs will lead to a multi-purpose
2
4
[
8]
nanoscaffold for efficient catalytic activity.
Ben-
[
2]
the reactions.
Preparation of high-performing
zothiazoles and their condensed system make a wider
category of nitrogen and sulfur-comprising compounds
nanocatalysts for organic reactions remains a major
challenging task. To achieve greater specific area and
more effective sites, nanocatalysts should be
functionalized by activated moieties. It is proved that
the modification of the nanocatalyst with GQDs avoids
the aggregation of fine particles and therefore
enhances the active specific area for an effective cata-
[
9]
with an extensive biological activity. Among fused
benzothiazoles, pyrimido[2,1-b]benzothiazoles have
fascinated significant attention due to their effective
pharmaceutical actions. An overview of the literature
indicated that pyrimido[2,1-b]benzothiazoles show sev-
eral biological operations such as anti-tumoral
[
3]
[10]
[11]
[12]
lytic reaction. Magnetic nanoparticles have been the
agents,
anti-allergic,
antimicrobial,
and
J Chin Chem Soc. 2020;1–10.
http://www.jccs.wiley-vch.de
© 2020 The Chemical Society Located in Taipei & Wiley-VCH GmbH
1

2
KHAZENIPOUR ET AL.
[
13]
anticonvulsant.
[
Given the significance of pyrimido
2 | RESULTS AND DISCUSSION
2,1-b]benzothiazoles, the advancement of efficient pol-
icies for the synthesis of these condensed heterocycles
will be noteworthy in both medicinal and organic chem-
istry. Three component linkage of 2-amino ben-
zothiazole, b-ketoesters, and aldehydes is a conventional
synthetic way to pyrimido[2,1-b]benzothiazole deriva-
The catalyst (Cu(II)/GQDs/NiFe O ) was synthesized as
2 4
specified by the procedure outlined in Scheme 1, by
means of GQDs and NiFe2O4 nanoparticles produced in
[
2c,6,8,18]
accord with literature.
To verify synthesis of the
nanocatalyst, it was completely identified using diverse
methods comprising UV–vis and fluorescence spectros-
copy, FT-IR spectroscopy, XRD, EDS, TEM, VSM, and
ICP spectroscopy.
[14]
tives.
acetic acid,
Formerly, this procedure has been catalyzed by
[10b]
[15]
Chitosan,
aluminum chloride,
tetrabutylammonium hydro-
[14c]
[16]
gen sulfate,
acid-modified poly(styrene-maleic anhydride).
and N-sulfonic
[17]
Never-
The light-conducting characteristics of the prepared
graphene quantum dots were examined by UV–Visible
and fluorescence spectroscopy. The absorbing spectrum
of graphene quantum dots give not any peak as illus-
trated in Figure 1a. The fluorescence spectra of graphene
quantum dots could be observed in Figure 1b. The
graphene quantum dots were excited at wavelengths of
360, 380, and 400 nm and the proper fluorescence emis-
sion peaks were found at 454, 463, and 469 nm, respec-
tively. The emission peaks indicate a gentle red shift with
a raising in the excitation wavelengths (360–400 nm). It
has been observed that the color of the GQDs aqueous
theless, some of these procedures have impediments that
must be considered. Therefore, the application of newer
and greener approaches is remaining necessary. Herein,
the preparation of Cu(II)/GQDs/NiFe O by the way of
2
4
an easy co-sedimentation of NiFe O nanoparticles on
2
4
GQDs is described and its identification by diverse
methods was investigated. The catalyst synthesis process
is illustrated in Scheme 1. Upon full identification, the
catalyst performance was investigated in preparation of
pyrimido[2,1-b]benzothiazole derivatives. The overall
reaction is shown in Scheme 2.
2 4
SCHEME 1 Method for synthesis of Cu(II)/GQDs/NiFe O

KHAZENIPOUR ET AL.
3
2 4
SCHEME 2 Synthesis of 4H-pyrimido[2,1-b]benzothiazoles using Cu(II)/GQDs/NiFe O
2 4
FIGURE 2 Fluorescence spectra of Cu(II)/GQDs/NiFe O
FIGURE 1 (a) UV–Vis absorbance spectrum of GQDs.
b) Fluorescence spectra of GQDs. Inset indicates images of GQDs
FT-IR spectroscopy was accomplished to validate the
exterior framework of the nanocatalyst. The FT-IR spec-
trum has been displayed in Figure 3 for Cu(II)/GQDs/
(
solution taken under visible light (weak yellow) and 365 nm
excitation (blue)
−1
NiFe O . The wide peak at 3,362.97 cm is assigned to
2
4
the hydroxyl (O H) bond, showing the absorption of
water by the Cu(II)/GQDs/NiFe O . The bands located at
2
4
1
−1
solution is weak yellow under visible light, but when
excited by UV light at 365 nm, it seems blue, as indicated
in inside of Figure 1b. Changes in fluorescence intensity
after the synthesis of GQDs/NiFe O were also examined.
2,981 cm− and 1,450 cm are related to the C H bond
vibrational stretching from remaining citric acid, imply-
ing the partial citric acid carbonization.
[
19]
The peak
located at 1,001.35 cm− is related to the vibrational
stretching of the C O C bond. The peaks located at
1,415.34 and 1,594.81 cm− would be the result of skeletal
vibrations of aromatic rings in graphene quantum
1
2
4
The fluorescence spectra of GQDs/NiFe O , excited at
2
4
1
3
60, 380, and 400 nm are indicated in Figure 2. The fluo-
rescence emission peaks were found at 486, 483, and
80 nm respectively. It has been found that with increas-
[
20]
4
dots.
The presence of NiFe O is validated by absorp-
2 4
tion bands located at 550.64 and 685.24 cm , which are
correlated to Ni O and Fe O bonds vibrations, respec-
The outcomes of this analysis confirm success-
ful synthesis of magnetic nanocatalyst.
−
1
ing excitation wavelengths, a slight blue shift is observed
in emission peaks. This differentiation in the fluores-
cence properties in comparison to the graphene quantum
dots demonstrate the change in the chemical surface of
[
21]
tively.
the GQDs/NiFe O4 implying a probable linkage of
X-ray diffraction technique was employed to acquire
information about the crystallinity of the nanocatalyst.
XRD pattern of GQDs/NiFe O is displayed in Figure 4.
2
graphene quantum dots on the nickel ferrite
nanoparticles, leading to a change in the surface charac-
teristics of graphene quantum dots.
2
4
The GQDs/NiFe O diffraction pattern agrees well with
2
4

4
KHAZENIPOUR ET AL.
FIGURE 3 FT-IR spectrum of
Cu(II)/GQDs/NiFe O
2 4
FIGURE 4 XRD pattern of
Cu(II)/GQDs/NiFe
2 4
O
the standard NiFe O (JCPDS 10-0325) and exhibits the
micrograph of the nanocatalyst indicates that the mean
sizes of Cu(II)/GQDs/NiFe O nanoparticles are approxi-
mately not more than 40 nm.
2
4
ꢀ
ꢀ
ꢀ
important diffraction lines at 2θ = 17.15 , 30.59 , 35.76 ,
2
4
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
3
7.30 , 43.43 , 53.84 , 57.34 , and 63.01 , which may be
attributed to the (220), (311), (222), (400), (422), (511),
and (440) planes of NiFe2O4, respectively. The diffraction
peak of graphene quantum dots (004) (JCPDS 26-1080) is
not recognizable, may have been due to their high dis-
persals, and low crystallization degree of graphene quan-
The magnetic characteristic of Cu(II)/GQDs/NiFe O
2 4
was studied by VSM. As evidenced in Figure 7, the value
of the saturation magnetization of Cu(II)/GQDs/NiFe O
2
4
−
1
(60.82 emu.g ), almost equal to Fe O nanoparticles
3
4
−1
(61.60 emu.g ) which indicates that the nanocatalyst
has magnetic properties and their magnetic characteris-
tics are so high that they could be isolated by a typical
magnet.
[6,22]
tum dots in GQDs/NiFe O .
2
4
The EDS was employed as an influential method to
identify the chemical constitution of the produced
nanocatalyst. The EDS analysis verifies the existence of
envisaged elements comprising nickel, iron, oxygen, car-
bon, and copper in the catalyst structure (Figure 5).
The morphology and structural characteristics of the
synthesized nanocatalyst was observed under TEM tech-
nique (Figure 6). It is revealed that the darker region in
Cu(II)/GQDs/NiFe O image, is related to agglomeration
The quantity of Cu loading onto the nanocatalyst was
determined by the ICP technique, which was obtained to
−
1
be 0.94 mmol g .
After validating the successful synthesis of
nanocatalyst by various techniques, its catalytic capability
was examined in the synthesis of 4H-pyrimido[2,1-b]ben-
zothiazoles. To achieve this goal, 4-nitrobenzaldehyde,
ethyl acetoacetate, and 2-aminobenzothizole were used
2
4
of NiFe O4 nanoparticles on GQDs. Also, the TEM
2

KHAZENIPOUR ET AL.
5
2 4
FIGURE 5 EDS pattern of Cu(II)/GQDs/NiFe O
2 4
FIGURE 7 Magnetization curve of Cu(II)/GQDs/NiFe O
2 4
FIGURE 6 TEM image of Cu(II)/GQDs/NiFe O
in the reaction under optimal conditions. The outcomes
are displayed in Table 1 (Entries 18–20). As illustrated,
no progress was detected in the model reaction when
applying the other components of nanocatalyst in the
absence of Copper, verifying that the existence of copper
is vital for catalyzing the reaction.
as model substrates for optimizing the reaction elements
including solvent, nanocatalyst amount, and tempera-
ture. At the beginning, the above reaction was also con-
ducted without and in the presence of various quantities
of the nanocatalyst (Table 1). The outcomes revealed that
the reaction did not progress in the lack of nanocatalyst
in some polar and non-polar solvents and solvent-free
state, even after 24 hr (Entries 1–7). In the presence of
nanocatalyst, the best results were achieved in EtOH and
water (Entries 8–15). Enhancing the nanocatalyst dosage
to 10 mg raised the reaction efficiency (Entries 15–16).
Increasing the amount of catalyst more than this did not
increase the efficiency of the reaction (Entry 17). Lastly,
the greatest efficiency was achieved when the model
After creating optimal reaction conditions, Cu(II)/
GQDs/NiFe O the range of the reaction was expanded
2
4
to diverse 4H-pyrimido[2,1-b]benzothiazoles. In accord
with the outcomes presented in Table 2, the electronic
influence did not have extraordinary affection on out-
come of the reaction, thus all 4H-pyrimido[2,1-b]ben-
zothiazoles with electron-withdrawing or electron-
releasing groups and heterocyclic moiety provided similar
yields (30–90 min).
[
17,25]
In accord with literature,
a plausible catalytic
reaction was performed in H O in the presence of 10 mg
mechanism for the preparation of 4H-pyrimido[2,1-b]
benzothiazoles by Cu(II)/GQDs/NiFe O is suggested in
2
of nanocatalyst at room temperature (Entry 16). To illus-
trate the role of copper in the reaction progress, the func-
tion of other components of the nanocatalyst like
NiFe O , GQDs, and GQDs/NiFe O was also examined
2
4
Scheme 3 in which Cu(II)/GQDs/NiFe O could perform
2
4
as a Lewis acid to actuate the carbonyl groups. It looks
benzaldehyde as an electrophile and β-ketoester as active
2
4
2 4

6
KHAZENIPOUR ET AL.
TABLE 1 Optimization of solvent, temperature, and nanocatalyst dosage
ꢀ
a
Entry
Condition
Catalyst (mg)
Temp. ( C)
Time (hr)
Yield (%)
1
2
3
4
5
6
7
8
9
Toluene
—
—
—
—
—
—
—
5
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
70
rt
rt
rt
rt
rt
rt
rt
rt
24
24
24
24
24
24
24
5
Trace
Trace
Trace
Trace
Trace
Trace
Trace
Trace
Trace
15
CH
EtOH
n-Hexane
CH CN
Solvent-free
2 2
Cl
3
2
H O
Toluene (Cu/GQDs/NiFe
n-Hexane (Cu/GQDs/NiFe
CH CN (Cu/GQDs/NiFe
2 4
O )
2
O
4
)
5
5
10
11
12
13
14
15
16
17
18
19
20
3
2
O
4
)
5
5
Solvent-free (Cu/GQDs/NiFe
Solvent-free (Cu/GQDs/NiFe
2
2
O
4
4
)
)
5
5
Trace
20
O
5
5
CH
2
Cl
2
(Cu/GQDs/NiFe
2
O
4
)
5
5
Trace
30
EtOH (Cu/GQDs/NiFe
2
O
4
)
5
5
H
H
H
H
H
H
2
2
2
2
2
2
O (Cu/GQDs/NiFe
O (Cu/GQDs/NiFe
O (Cu/GQDs/NiFe
2
2
2
O
O
O
4
4
4
)
5
5
60
)
)
10
0.15
10
10
10
0.5
0.5
1.0
1.0
1.0
98
98
O (NiFe
O (GQDs)
O (GQDs/NiFe
2
O
4
)
None
None
None
2 4
O )
a
On the basis of isolated yield.
a
TABLE 2 Synthesis of 4H-pyrimido[2,1-b]benzothiazoles 4a-n using Cu(II)/GQDs/NiFe
2
O
4
as catalyst
ꢀ
Melting point ( C)
b
c
Entry
Ar
Product
4a
Time (min)
Yield (%)
Found
177–180
171
Reported
[
[
[
11]
1
2
3
4
5
6
7
8
9
Ph
40
30
30
30
35
45
40
45
40
30
30
60
60
90
98
98
92
95
98
95
91
93
89
88
90
96
92
97
177–179
170–172
110–114
16]
4-NO
2
Ph
4b
14b]
4-Br Ph
4-Cl Ph
4c
112
[
17]
4d
86
86–88
[
15]
16]
17]
23]
23]
14c]
14c]
23]
23]
24]
4-OCH
4-OH Ph
3-NO Ph
3-OH Ph
2-NO Ph
3
Ph
4e
130–132
212
130–132
210–212
222–224
260–263
122–125
125–127
133–135
164–166
225–227
180–182
[
[
[
[
[
[
[
[
[
4f
2
4g
222–224
260–262
122–125
125–127
133–134
165
4h
4i
2
1
1
1
1
1
0
1
2
3
4
2-Cl Ph
2,4-(Cl)
4j
2
Ph
4k
4l
2,4-(OCH
3,4-(OH)
Tiophenyl
3
)
2
Ph
2
Ph
4m
4n
224–226
180–182
a
2 4
Reaction conditions: aldehydes (1.0 mmol), 2-aminobenzothiazole (1.0 mmol), ethyl acetoacetate (1.0 mmol) and Cu(II)/GQDs/NiFe O
(
0.01 g) at room temperature in H
Known products identified by comparison of their melting points; some selected compounds identified by H- NMR.
2
O.
b
1
c
Isolated yields.

KHAZENIPOUR ET AL.
7
2 4
SCHEME 3 Proposed mechanism for the synthesis of 4H-pyrimido[2,1-b]benzothiazoles in the presence of Cu(II)/GQDs/NiFe O
methylene compounds participate within an on-site
Knoevenagel reaction and an alkene is initially produced.
Subsequently, during the Michael addition reaction,
2
-aminbenzothiazole, as a donor, attacks alkene during
nucleophilic reaction, therefore, an iminium ion is pro-
duced. Afterward, with a proton exchange and an intra-
molecular cyclization, 4H-pyrimido[2,1-b]benzothiazoles
are produced.
The reusability of the catalyst (Cu(II)/GQDs/NiFe O )
2
4
was examined in the sample reaction. For this goal, upon
termination of the reaction, the nanocatalyst was separated
with the aid of a magnet and washed with acetone and
water to eliminate remaining product, dried, and reapplied
in subsequent reactions. The outcomes revealed that the
nanocatalyst could be successively retrieved without any
considerable reduction in its performance (Figure 8).
2 4
FIGURE 8 Reusability of Cu(II)/GQDs/NiFe O in the model
reaction
To explore the leaking of copper, ICP study of the
retrieved catalyst was additionally performed. In accord
with the acquired outcomes, no considerable reduction
was monitored in the Cu quantity. The Cu amount in the
new nanocatalyst and the recovered one was 0.94 and
the aid of a magnet and allowed the reaction to progress
for further time (30 min). The product generation was
not detected as monitored by TLC, which proves the
nanocatalyst is heterogeneous in character.
To validate the advantage of the present research,
application of Cu(II)/GQDs/NiFe O in producing of 4H-
−
1
0
.91 mmol g , respectively, which revealed the amount
2
4
of leached Cu for this nanocatalyst is very slight. To
investigate the heterogeneous character of the catalytic
process, the hot filtration examination for the model
reaction in attending Cu(II)/GQDs/NiFe O was studied.
The model reaction was ceased after half the required
reaction time and the nanocatalyst was fully isolated with
pyrimido[2,1-b]benzothiazole derivatives in comparison
with other formerly reported heterogeneous catalysts is
presented in Table 3. In accordance with the results, the
introduced catalyst indicates more adequate catalytic per-
formance quickly under environmentally friendly and
affordable conditions (water).
2
4

8
KHAZENIPOUR ET AL.
TABLE 3 Comparison of Cu(II)/GQDs/NiFe
benzothiazole 4a
2
O
4
nanocatalyst with other heterogeneous catalysts in synthesis of 4H-pyrimido[2,1-b]
ꢀ
a
Entry Catalyst
Solvent
Temp. ( C) Time (min.) Yield (%) Ref.
1
2
3
4
5
6
Chitosan/HOAc
N-sulfonic acid modified poly(styrene-maleic anhydride) Solvent-free 100
Nano-TiCl /cellulose PEG 400 70
AlCl
Fe
Cu(II)/GQDs/NiFe
H
2
O
60
100
180
90
92
72
80
79
83
98
[15]
[17]
2
[25]
3
Solvent-free 60
Solvent-free 80
72
[16]
3
O
4
@nano-cellulose/Cu(II)
45
[26]
2
O
4
H
2
O
rt
40
This study
a
Isolated yield.
3
3
| EXPERIMENTAL
consequent powder was grinded and then heated at
ꢀ
[6]
7
00 C for 3 hr.
.1 | General information
Citric acid, sodium hydroxide, nickel nitrate, Fe(III)
nitrate, and Cu(II) acetate were purchased from
Sigma. UV–vis absorption investigations were con-
ducted by Hach DR 6000 UV–visible spectrophotome-
ter. Fluorescence examinations were done on Jasco
FP-6200 spectrofluorophotometer (Hitachi Japan).
The phase crystallinity of the prepared nanocatalyst
was studied by a diffractometer at a wavelength of
3.3 | Synthesis of GQDs
GQDs were made from thermally decomposed citric
[
18]
acid.
Concisely, citric acid (0.2 g) was melted and
ꢀ
heated at 200 C for 5 min. Then, the subsequent yellow-
ish liquid was added progressively into 20 ml of 0.25 M
NaOH solution. Thereafter, the GQDs solution was dia-
lyzed in a 1 kDa dialysis bag for 24 hr (dialysate was
exchanged every 8 hr) to eliminate the unreacted
chemicals. The produced graphene quantum dots solu-
1
.540 Å (Philips Company). Transmission electron
microscopy (TEM) picture was captured by means of
Zeiss electron microscope, LEO 912AB (120 kV), Ger-
many. Fourier transform infrared (FT-IR) spectra
were recorded on a Bruker model 470 spectrophotome-
ter. Magnetic characteristics were registered on a
vibrating sample magnetometer apparatus (VSM,
LDJ9600) at environment temperature. EDS spectros-
copy study were conducted with 133 eV resolution
ꢀ
tion was maintained in 4 C.
3.4 | Synthesis of GQDs/NiFe O4
2
NiFe O nanoparticles, 1 g, were dispersed in water
2
4
(5 ml) for 15 min. Afterward, the GQDs suspension
(20 ml) was added to the flask comprising the NiFe O
(
model 7,353, Oxford Instruments, United Kingdom).
2
4
Copper determination was carried out by inductively
coupled plasma (ICP) technique on a Varian VISTA-
PRO. NMR spectra were registered in CDCl3 on a
Bruker Advance 300 MHz instrument. The melting
points were measured on an Electrothermal Type 9100
device
nanoparticles and the resulting mixture was shaken
for 48 hr at 60 C. The produced GQD-modified
ꢀ
NiFe O was isolated through the use of a magnet and
2
4
was washed with distilled water (3 × 20 ml) and etha-
nol (3 × 20 ml) and finally dried under low
[
8]
pressure.
3
.2 | Synthesis of NiFe O nanoparticles
3.5 | Synthesis of Cu(II)/GQDs/NiFe O
2 4
2
4
Egg white (60 ml) was added to distilled water (40 ml)
and was shaken hard to perfectly mix. Subsequently,
GQDs/NiFe O (0.5 g) was dispersed in acetone (25 ml)
2 4
at ordinary temperature for 30 min. Afterward, 0.1 mmol
copper(II) acetate (0.018 g) was added gently to the flask
comprising GQDs/NiFe O nanocomposite. The conse-
2
.9081 g of nickel nitrate hexahydrate and 8.0800 g of
Fe(III) nitrate nonahydrate were dissolved in the
above solution and was stirred hard at ordinary tem-
perature for 2 hr. Then, while the mixture was agi-
2
4
quent mixture was mechanically shaken for 48 hr at
ambient temperature. Then, the solid was isolated with
the aid of a magnet, washed with water (3 × 25 ml) and
ꢀ
tated, it was warmed to 80 C until dried. The

KHAZENIPOUR ET AL.
9
ꢀ
ethanol (3 × 25 ml), and finally dried at 60 C
particles as a very stable and recoverable nanocatalyst for
the green production of 4H-pyrimido[2,1-b]benzothiazoles
rapidly in aqueous media. The proposed reaction, in which
the designed Cu(II)/GQDs/NiFe O was a recoverable cata-
[2c]
overnight.
2
4
3
.6 | Synthetic typical manner for 4H-
lyst, consistent with the principles of green chemistry owing
to the following properties: no toxicity, great durability,
recovery capability, shorter times of reaction, aqueous
medium, and excellent products yields. Above all others,
the nanocatalyst could be recovered five runs without any
failure in its productivity. So, the nanomagnetic heteroge-
neous catalyst might be useful in related industries
pyrimido[2,1-b]benzothiazoles 4a-n
Cu(II)/GQDs/NiFe O catalyst (0.10 g) was added to a
2
4
solution comprising 2-aminobenzothiazole (1.0 mmol),
aldehyde (1.0 mmol), and ethyl acetoacetate in water
under continuous stirring for 30–90 min at room temper-
ature. The proceeding of the reaction was controlled
using TLC (thin layer chromatography), whenever the
reaction was completed, the reaction mixture was diluted
with ethyl acetate and the nanocatalyst was isolated with
the aid of a magnet, washed with acetone, and then dried
on a night to be ready to react again. The organic layer
was dried over anhydrate sodium sulfate and after that,
evaporated to separate the solvent. The remaining part
was recrystallized in ethanol to provide corresponding
ACKNOWLEDGMENTS
This work is financially assisted by the Islamic Azad
University—Bandar Abbas Branch. The authors are
grateful for that.
ORCID
Farid Moeinpour https://orcid.org/0000-0003-2380-
9
93X
Fatemeh S. Mohseni-Shahri https://orcid.org/0000-
002-3103-9421
4
H-pyrimido[2,1-b]benzothiazole derivatives. All the
products are known and were identified by comparison
of their melting points, and spectroscopic data ( HNMR)
0
1
with those of authentic samples. Selected spectral data of
some synthesized compounds are given below.
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| CONCLUSIONS
We have successfully synthesized a copper heterogeneous
catalyst on graphene quantum dots/NiFe O nanomagnetic
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SUPPORTING INFORMATION
Additional supporting information may be found online
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How to cite this article: Khazenipour K,
Moeinpour F, Mohseni-Shahri FS. Cu(II)-
supported graphene quantum dots modified
NiFe O : A green and efficient catalyst for the
[
[
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2
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synthesis of 4H-pyrimido[2,1-b]benzothiazoles in
water. J Chin Chem Soc. 2020;1–10. https://doi.org/
10.1002/jccs.202000213