Fe3O4@nano-cellulose/Cu(ii): a bio-based and magnetically recoverable nano-catalyst for the synthesis of 4H-pyrimido[2,1-b]benzothiazole derivatives

Article abstract of DOI:10.1039/c8ra09203f

Fe₃O₄@nano-cellulose/Cu(ii) as a green bio-based magnetic catalyst was prepared through in situ co-precipitation of Fe²⁺ and Fe³⁺ ions in an aqueous suspension of nano-cellulose. The mentioned magnetically heter

Full text of DOI:10.1039/c8ra09203f

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Fe3O4@nano-cellulose/Cu(II): a bio-based and
magnetically recoverable nano-catalyst for the
synthesis of 4H-pyrimido[2,1-b]benzothiazole
derivatives†
Cite this: RSC Adv., 2019, 9, 1278
a
b
Nasrin Safajoo,a Bi Bi Fatemah Mirjalili
and Abdolhamid Bamoniri
*
Fe3O4@nano-cellulose/Cu(II) as a green bio-based magnetic catalyst was prepared through in situ co-
precipitation of Fe2+ and Fe3+ ions in an aqueous suspension of nano-cellulose. The mentioned
magnetically heterogeneous catalyst was characterized by FT-IR, XRD, VSM, FESEM, TEM, XRF, EDS and
TGA. In this research, the synthesis of 4H-pyrimido[2,1-b]benzothiazole derivatives was developed via
a three component reaction of aromatic aldehyde, 2-aminobenzothiazole and ethyl acetoacetate using
Fe3O4@nano-cellulose/Cu(II) under solvent-free condition at 80 ꢀC. Some advantages of this protocol
are good yields, environmentally benign, easy work-up and moderate reusability of the catalyst. The
Received 7th November 2018
Accepted 13th December 2018
DOI: 10.1039/c8ra09203f
1
rsc.li/rsc-advances
product structures were confirmed by FT-IR, H NMR, and 13C NMR spectra.
alternatives for ordinary organic or inorganic supports for
catalytic applications.24 Cellulose is the most abundant natural
Introduction
material in the world and it can play an important role as
a biocompatible, renewable resource and biodegradable poly-
mer containing OH groups.25 Cotton is a natural, cheap, and
readily available source of cellulose. Fe3O4 nanoparticles are
coated with various materials such as surfactants,26 poly-
mers,27,28 silica,29 cellulose23 and carbon30 to form core–shell
structures. Magnetic nanoparticles as heterogeneous supports
have many advantages such as high dispersion in reaction
media and easy recovery by an external magnet.31–38 Cu(II) as
a safe and ecofriendly cation is a good Lewis acid and can
activate the carbonyl group for nucleophilic addition reactions.
Thus, the main purpose of the present work is the preparation
Fused heterocyclic compounds containing nitrogen and sulfur
are important compounds because of their pharmacological
properties.1 Among these compounds benzothiazoles and pyr-
imido[2,1-b]benzothiazoles have attracted considerable
interest. Some of these compounds have various biological
activities such as antiviral,2,3 antitumor,4–6 antiinammatory,7,8
antiallergic,9
proliferative13 and antifungal activities.14 Pyrimido[2,1-b]ben-
zothiazole derivatives were synthesized through
antimicrobial,10,11
anticonvulsant,12
anti-
multicomponent reaction between 2-amino benzothiazole,
aromatic aldehydes and b-ketoesters.15–18 Previously, this
protocol has been catalyzed by iron uoride,19 pyridine,11 acetic
acid,20
1,1,3,3-N,N,N0,N0-tetramethylguanidinium
tri-
of Fe3O4@nano-cellulose/Cu(II) as
a new and bio-based
uoroacetate (TMGT),16 tetrabutylammonium hydrogen sulfate
(TBAHS),17 N-sulfonic acid modied poly(styrene-maleic anhy-
dride) (SMI-SO3H),21 chitosan,18 aluminum trichloride22 and
Fe3O4@nano-cellulose/TiCl.23 Some of the reported protocols
have harsh conditions and long reaction times. Thus, in this
work, a new simple protocol for the synthesis of these
compounds is reported.
magnetic nanocatalyst for one-pot synthesis of pyrimido[2,1-b]
benzothiazoles via condensation of aromatic aldehydes, ethyl
acetoacetate and 2-aminobenzothiazole.
Results and discussion
Fe3O4@nano-cellulose/Cu(II) was prepared in
a two-step
Biopolymers, especially cellulose and its derivatives, have
some unparalleled properties, which make them attractive
process. First, Fe3O4@nano-cellulose was synthesized by co-
precipitation of Fe2+ and Fe3+ ions in the presence of nano-
cellulose and then it was used as a magnetic support for
loading CuCl2 onto the cellulose section of it (Scheme 1). The
magnetically heterogeneous catalyst named Fe3O4@nano-
cellulose/Cu(II), is characterized by Fourier transform infrared
(FT-IR) spectroscopy, X-ray diffraction (XRD), vibrating sample
magnetometer (VSM), eld emission scanning electron
microscopy (FESEM), transmission electron microscopy (TEM),
aDepartment of Chemistry, College of Science, Yazd University, Yazd, P. O. Box
89195-741, Islamic Republic of Iran. E-mail: fmirjalili@yazd.ac.ir; Fax: +98
3538210644; Tel: +98 3531232672
bDepartment of Organic Chemistry, Faculty of Chemistry, University of Kashan,
Kashan, Islamic Republic of Iran
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c8ra09203f
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Fig. 2 XRD pattern of Fe3O4@nano-cellulose/Cu(II).
The magnetic properties of Fe3O4 and Fe3O4@nano-cellu-
lose/Cu(II) were characterized at RT (300 K) by a vibrating
sample magnetometer (VSM) and their hysteresis curves are
presented in Fig. 3. The zero coercivity and remanence of the
hysteresis loops of these magnetic nanoparticles conrm
superparamagnetic property of them at room temperature. The
amount of specic saturation magnetization (Ms) for Fe3O4
nanoparticles was about 50 emu gꢁ1, which decreased to 25
emu gꢁ1 aer the bonding of Cu(II) on the surface of Fe3O4@-
nano-cellulose. Despite this signicant decrease, the saturated
magnetization of these magnetic nanoparticles is sufficient for
magnetic separation.
The particles size of Fe3O4@nano-cellulose/Cu(II) were
investigated by eld emission scanning electron microscopy
(FESEM) and transmission electron microscopy (TEM) in which
the dimensions of them were achieved below 70 nm (Fig. 4). The
chemical composition of catalyst has been measured using X-
Scheme 1 Synthesis protocol for Fe3O4@nano-cellulose/Cu(II).
X-ray uorescence (XRF), energy-dispersive X-ray spectroscopy
(EDS), and thermo-gravimetric analysis (TGA).
The FT-IR spectra of nano-cellulose, Fe3O4@nano-cellulose
and Fe3O4@nano-cellulose/Cu(II) are shown in Fig. 1.
The FT-IR spectrum of nano-cellulose has shown a broad
band at 3338 cmꢁ1 which corresponds to the stretching vibra-
tions of OH groups. The absorption bands at1058 and
1108 cmꢁ1 display the stretching vibrations of the C–O bonds.
For Fe3O4@nano-cellulose, in addition to the cellulose absorp-
tions bands, stretching vibrations of Fe/O groups at 586 and
634 cmꢁ1 are appeared which is indicated that the magnetic
Fe3O4 nano particles are coated by nano-cellulose. The FT-IR
spectrum of Fe3O4@nano-cellulose/Cu(II) has shown a charac-
teristic absorption band under 500 cmꢁ1 that may be attributed
to Cu–O band for Cu bonded to cellulose. X-ray diffraction
(XRD) pattern of Fe3O4@nano-cellulose/Cu(II) is shown in Fig. 2.
Fe3O4 has shown diffraction peaks at 2q ¼ 35.79ꢀ, 43.42ꢀ,
53.94ꢀ, 57.51ꢀ and 63.08ꢀ with FWHM equal to 0.39, 0.78, 0.94,
0.31 and 0.96 respectively, which are quite matched with the
cubic spinel structure of pure Fe3O4. A diffraction peaks at 2q ¼
16.45ꢀ and 22.18ꢀ with FWHM equal to 0.23 and 0.47, respec-
tively, has shown the existence of cellulose. Other signals in 2q
¼ 13.68, 29.10, 32.01, 34.25 and 45.71 probably reveal the
existence of cellulose and bonding of Cu(II) to cellulosic shell
(Table 1).
Table 1 Results of XRD analysis of Fe3O4@nano cellulose/Cu(II)
No.
1
2
3
4
5
6
Pos. [ꢀ2q]
13.6815 16.4566 22.1853 29.1068 32.0094 34.2572
FWHM [ꢀ2q] 0.6298 0.4723 0.2362 0.2362 0.3149 0.3149
No.
7
8
9
10
11
12
Pos. [ꢀ2q]
35.7935 43.4246 45.7114 53.9425 57.5101 63.0810
FWHM [ꢀ2q] 0.3936 0.7872 0.3149 0.9446 0.3149 0.9600
Fig. 1 FT-IR spectra of (a) nano-cellulose, (b) Fe3O4 @ nano-cellulose Fig. 3 Magnetization loop of (a) Fe3O4 and (b) Fe3O4@nano-cellulose/
and (c) Fe3O4@nano-cellulose/Cu(II).
Cu(II).
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ray uorescence (XRF) analysis (Table 2). In order to obtain the
The TGA curve illustrates four mass-loss steps. Firstly, a very
Cu : Cl ratio in Fe3O4@nano-cellulose/Cu(II) by XRF analysis, small weight loss (2.53%) from 50 to 100 ꢀC is corresponded to
Kilo Counts Per Seconds (KCPS) values of elements in catalyst remove of catalyst moisture. Subsequently, the main weight loss
were compared with KCPS values of the same elements in pure step in the temperature ranges 200–370 ꢀC (33%) is attributed to
samples, NaCl and CuSO4. By this comparison, the amount of the decomposition of cellulose units through the formation of
Cu and Cl were obtained 1.38 g (0.02 mol) and 0.12 g (0.003 levoglucosan and other volatile compounds. Finally, there are
mol), respectively. Thus, the ratio of Cu : Cl in catalyst is two weight loss steps in the temperature ranges 400–600 and
approximately 6 : 1.
And so, existence of Cu and Cl in catalyst was conrmed by diagram of Fe3O4@nano-cellulose/Cu(II), it was revealed that
650–690 ꢀC (5 and 16%, respectively). According to the TG–DTA
EDS analysis data (Fig. 5).
this catalyst is suitable for the promotion of organic reactions
The thermal stability of Fe3O4@nano-cellulose/Cu(II) was below 200 ꢀC.
investigated by thermo-gravimetric analysis (TGA) in the
ꢀ
temperature range of 30–800 C (Fig. 6).
Catalyst efficiency for synthesis of 4H-pyrimido[2,1-b]
benzothiazole derivatives
Aer characterization of Fe3O4@nano-cellulose/Cu(II), the
activity of catalyst was evaluated for the synthesis of 4H-pyr-
imido[2,1-b]benzothiazole derivatives.
For optimization of the reaction conditions, the reaction of 2-
aminobenzothiazole, 4-nitrobenzaldehyde and ethyl acetoacetate
as a model reaction was investigated (Table 3). As shown in Table
3, entry 14, it was found that 0.03 g of Fe3O4@nano-cellulose/Cu(II)
under solvent-free condition at 80 ꢀC is the best reaction condition.
In order to compare the efficiency of present nano-catalyst with
other catalysts, the model reaction was also performed using the
reported catalysts for the synthesis of 4H-pyrimido[2,1-b]benzo-
thiazole derivatives. As Table 4 indicates, in comparison with other
reported catalysts, we have found that Fe3O4@nano-cellulose/Cu(II)
Fig. 4 (a) FESEM image of Fe3O4@nano-cellulose/Cu(II) and (b) TEM of
Fe3O4@nano-cellulose/Cu(II).
Table 2 Results of XRF analysis of catalyst, pure NaCl and CuSO4
Fe3O4@nano-
cellulose/Cu(II)
CuSO4
NaCl
Elemental component KCPS wt%
KCPS wt%
KCPS wt%
CO2
Fe2O3
CuO
SiO2
Na2O
CaO
I
1.5 74.8
1118.9 21.7
0.2 13.3
0.6
0.0174
19.5
2.8
0.9
4.3
2.0
1.0
1.7
0.2
0.4
2.2
0.2
1.2
0.7
2.2
0.4
0.1
0.3
0.1
0.2
0.5
1.45
0.796
0.573
0.190
563.9 41.2
0.1
0.2
0.2
1.2
0.0403
0.218
0.00479
0.145
0.0799
0.0681
0.0606
0.0565
0.0523 184.8 43.7
0.0482
0.0432
0.0340
0.0333
0.0285
0.0100
0.00860
0.00860
0.00747
0.00734
0.00340
Cl
516.5 62
Fig. 5 EDS (EDX) spectra of Fe3O4@nano-cellulose/Cu(II).
Sb2O3
Al2O3
SO3
MnO
MgO
SnO2
Re
CoO
Cr2O3
Pd
TiO2
Rh
0.7
0.0746
2.2
0.7
0.5
1.02
0.0546
0.0585
K2O
SrO
Ho2O3
HfO2
P2O5
Rh
0.4
1.8
0.1
0.1
0.0446
0.0381
0.0346
0.0213
Fig. 6 Thermal gravimetric analysis pattern of Fe3O4@nano-cellulose/
Total
100
100
Cu(II).
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Table 3 The reaction of 2-aminobenzothiazole, 4-nitrobenzaldehyde, and ethyl acetoacetate in the presence of Fe3O4@nano-cellulose/Cu(II)
under various conditionsa
Entry
Solvent
Catalyst (g)
Condition
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
—
—
—
—
C2H5OH
C2H5OH
C2H5OH
H2O
CH3OH
—
—
—
—
—
—
—
—
—
—
CuCl2
Fe3O4
Fe3O4@nano-cellulose
—
80 ꢀ
80 ꢀ
70 ꢀ
80 ꢀ
R. T
R. T
Reux
Reux
Reux
R. T
C
C
C
C
7 h
3h
3h
30
69
37
41
—
35
57
42
51
43
85
93
97
97
84
93
88
83
4 h
7 h
3 h
3 h
3 h
3 h
3 h
1 h
0.5
0.5
0.5
0.5
0.5
0.5
0.5
Catalyst (0.04)c
Catalyst (0.04)c
Catalyst (0.04)c
Catalyst (0.04)c
Catalyst (0.04)c
Catalyst (0.04)c
Catalyst (0.05)c
Catalyst (0.04)c
Catalyst (0.03)c
Catalyst (0.02)c
Catalyst (0.03), 2thrunc
Catalyst (0.03), 3rdrunc
Catalyst (0.03), 4thrunc
9
10
11
12
13
14
15
16
17
18
70 ꢀ
80 ꢀ
80 ꢀ
80 ꢀ
80 ꢀ
80 ꢀ
80 ꢀ
80 ꢀ
C
C
C
C
C
C
C
C
a
b
The amount ratio of 2-aminobenzothiazole (mmol), 4-nitrobenzaldehyde (mmol) and ethyl acetoacetate (mmol) are equal to 1 : 1 : 1. Isolated
yield. c Fe3O4@ nano-cellulose/Cu(II).
promoted reaction has shorter reaction time, higher yields of
Substituents on the aldehyde showed a signicant effect in
products, green reaction conditions and simpler workup. Finally, terms of the yield and reaction time under the optimized
the above optimized reaction conditions were explored for the reaction conditions. The electron-withdrawing groups increase
synthesis of 4H-pyrimido[2,1-b]benzothiazole derivatives and the rate and yields of reaction compared to electron-donating
results are summarized in Table 5. The reusability of the catalyst groups. Suggested mechanism for the synthesis of 4H-pyr-
was also investigated on the model reaction. The magnetic nature imido[2,1-b]benzothiazole (IV) in presence of Fe3O4@ nano-
of the catalyst allowed its facile recovery by simple separation by an cellulose/Cu(II) was shown in Scheme 2. Cu(II) activate the
external magnet, washing with ethanol and drying at room carbonyl group of benzaldehyde (II) for Knoevenagel reaction
temperature to provide an opportunity for recycling experiments. with b-ketoesters (III) to production of intermediate (I). Mean-
The separated nano-catalyst was reused in the above-mentioned while, Cu(II) activate the carbonyl group in intermediate (I) for
reaction for the synthesis of IVb for four times without consider- Michael addition with 2-aminobenzothiazole and then inter-
able loss of its catalytic activity (Table 3). Partial loss of activity may amolecular cyclization to production of product (IV).
be due to blockage of catalyst active sites and/or partial leaching of
Cu from the catalyst.
The structures of the products IVa–m were studied by their
melting point, IR and H NMR spectra. In the FTIR spectra of
1
Table 4 Comparative study of the present method and some other reported methods for synthesis of 4H-pyrimido[2,1-b]benzothiazole
derivatives
Ent.
Solvent
Catal.
Tem. (ꢀC)
Time (h)
Yielda (%)
Ref.
1
2
3
4
5
6
7
CH3OH
EG
HOAc
—
—
—
Acetic acid (20 mol%)
TBAHS (30 mol%)b
65
120
70
100
65
18
2
1.6
5
1.2
0.6
0.5
62
72
93
53
97
96
97
20
17
18
16
22
23
Chitosan (0.080 g)
TMGT (0.080 g)c
AlCl3 (10 mol%)
Fe3O4@NCs/TiCl (0.03 g)
Fe3O4@ nano-cellulose/Cu(II) (0.03 g)
70
80
—
This work
a
Isolated yield. b Tetrabutylammonium hydrogen sulfate. c 1,1,3,3-N,N,N0,N0-Tetramethylguanidinium triuoroacetate.
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Table 5 Synthesis of 4H-pyrimido[2,1-b]benzothiazole derivatives (IVa–m) in the presence of Fe3O4@ nano-cellulose/Cu(II) under solvent-free
condition at 80 ꢀCa appear here with headings as appropriate
M. P.
Ent.
R
Prod.
Time (min)
Yieldb (%)
Found
Report
Ref.
1
2
3
4
5
6
7
8
H–
4-NO2–
4-Cl–
IVa
IVb
IVc
IVd
IVe
IVf
IVg
IVh
IVi
45
30
30
30
60
45
40
60
35
65
45
75
70
84
97
95
97
82
88
87
75
93
79
85
74
71
178–180
171–173
87–89
177–179
170–172
86–88
17
22
21
16
22
23
17
23
21
23
17
23
23
4-Br–
110–114
210–212
122–125
124–126
171–175
222–224
260–263
133–135
164–166
225–227
110–114
210–212
122–125
125–127
171–175
222–224
260–263
133–135
164–166
225–227
4-OH–
2-NO2–
2-Cl–
2-EtO–
3-NO2–
3-OH–
2,4-(Cl)2–
2,4-(MeO)2–
3,4-(OH)2–
9
10
11
12
13
IVj
IVk
IVl
IVm
a
b
I (mmol) : II (mmol) : III (mmol) : Fe3O4@ nano-cellulose/Cu(II) (g) is equal to 1 : 1 : 1 : 0.03. Isolated yield.
And so, magnetic separation and reusability of nanocatalyst is
other advantages of this protocol.
Experimental
General remarks
All compounds were purchased from Aldrich, Merck, and Fluka
chemical companies. Nano-cellulose and Fe3O4@nano-
cellulose were synthesized via our previously reported
methods.23 FT-IR spectra were run on a Bruker, Equinox 55
spectrometer. A Bruker (DRX-400 Avance) NMR was used to
record the 1H NMR and 13C NMR spectra. The X-ray diffraction
(XRD) pattern was obtained by a Philips Xpert MPD diffrac-
tometer equipped with a Cu Ka anode (k ¼ 1.54 Aꢀ) in the 2q
range from 10 to 80ꢀ. XRF analysis was done with Bruker, S4
Explorer instrument. VSM measurements were performed by
using a vibrating sample magnetometer (Meghnatis Daghigh
Kavir Co. Kashan, Iran). Melting points were determined by
a Buchi melting point B-540 B.V.CHI apparatus. Field emission
scanning electron microscopy (FESEM) image was obtained on
a Mira 3-XMU. Transmission electron microscopy (TEM) image
was obtained using a Philips CM120 with a LaB6 cathode and
accelerating voltage of 120 kV. energy-dispersive X-ray spec-
troscopy (EDS) of Fe3O4@nano-cellulose/Cu(II) was measured by
an EDS instrument and Phenom pro X. Thermal gravimetric
analysis (TGA) was conducted using “STA 504” instrument.
Scheme 2 Proposed mechanism for the synthesis of 4H-pyrimido
[2,1-b]benzothiazole derivatives IVa–m
.
products, the ester C]O stretching vibration band is appeared
at 1690 cmꢁ1 due to conjugation.
Conclusions
We have demonstrated the preparation and characterization of
Fe3O4@ nano-cellulose/Cu(II) as a novel magnetite recoverable,
eco-friendly, inexpensive and efficient nanocatalyst. The cata-
lytic activity of the prepared catalyst was investigated in the
synthesis of 4H-pyrimido[2,1-b] benzothiazole derivatives
through one-pot three-component reaction of aldehydes, ethyl
acetoacetate, and 2-aminobenzothiazole under solvent-free
condition at 80 ꢀC. This protocol includes some important
Preparation of Fe3O4@nano-cellulose/Cu(II)
advantages such as mild reaction conditions, short reaction In a ask containing 50 ml of 0.5 M NaOH, Fe3O4@nano-
time, excellent yields, easy work-up, high purity of products. cellulose (0.5 g) was added with stirring. Then, 75 ml of CuCl2
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General procedure for synthesis of 4H-pyrimido[2,1-b]
benzothiazole derivatives
A mixture of 2-aminobenzothiazole (1 mmol), aldehyde (1
mmol), ethyl acetoacetate (1 mmol) and Fe3O4@nano-cellulose/
Cu(II) (0.03 g) was heated at 80 ꢀC. Aer completion of the
reaction (monitored by TLC), the reaction mixture was dissolved
in hot ethanol (3 ml) and the catalyst was separated by using an
external magnet. Subsequently by adding water to the decanted
solution, the product was appeared as a pure solid in high
yields. The recovered catalyst was washed 3 times with ethanol,
dried and reused for subsequent runs under the same reaction
conditions.
Conflicts of interest
There are no conicts to declare.
Acknowledgements
25 A. Shaabani and A. Maleki, Appl. Catal., A, 2007, 331, 149–
151.
The Research Council of Yazd University is gratefully acknowl-
edged for the nancial support for this work.
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