Fe3O4@SiO2–ZrCl2-MNPs: A novel magnetic catalyst for the clean and efficient cascade synthesis of 1-(benzothiazolylamino)methyl-2-naphthol derivatives in the absence of solvent

Article abstract of DOI:10.1002/aoc.3972

A green, simple and eco-friendly three-component condensation for the synthesis of 1-(benzothiazolylamino)methyl-2-naphthols using new magnetic nanoparticles formulated as Fe₃O₄@SiO₂–ZrCl₂-MNPs is described. Con

Full text of DOI:10.1002/aoc.3972

Received: 6 March 2017
DOI: 10.1002/aoc.3972
Revised: 16 May 2017
Accepted: 17 June 2017
F U L L P A P E R
Fe3O4@SiO2–ZrCl2‐MNPs: A novel magnetic catalyst for the
clean and efficient cascade synthesis of
1‐(benzothiazolylamino)methyl‐2‐naphthol derivatives in
the absence of solvent
Fatemeh Kamali | Farhad Shirini
Department of Chemistry, College of
A green, simple and eco‐friendly three‐component condensation for the synthe-
Science, University of Guilan, Rasht zip
code 41335, I.R. Iran
sis of 1‐(benzothiazolylamino)methyl‐2‐naphthols using new magnetic nano-
particles formulated as Fe3O4@SiO2–ZrCl2‐MNPs is described. Considering
Correspondence
the economic and environmental aspects, the method provides some advan-
tages such as clean procedure, solvent‐free conditions, simple operation and
work‐up, relatively short reaction times and high yields of the products.
Moreover the introduced catalyst can be readily recovered up to 4 consecutive
runs with consistent activity using an external magnet.
Farhad Shirini, Department of Chemistry,
College of Science, University of Guilan,
Rasht, zip code 41335, I.R. Iran.
Email: shirini@guilan.ac.ir
KEYWORDS
2‐Aminobenzothiazole, mild reaction conditions, nano catalyst, one‐pot three‐component
condensation, solvent‐free conditions
1 | INTRODUCTION
to
possess
anti‐inflammatory,[5]
anti‐tumor,[6]
anti‐convulsant,[7] anti‐bacterial,[8] anti‐fungal,[9] and
topoisomerase II inhibitory activities.[10] Among them,
1‐(benzothiazolylamino)phenyl‐ methyl‐2‐naphthols have
two biologically active parts, 2‐aminobenzothiazole and
Betti0s base. Betti0s base derivatives [1‐(a‐aminoalkyl)‐2‐
naphthols] have provided comfortable access to many
effective synthetic building blocks via the amino and
phenolic hydroxy functional groups.[11] Because of this,
the synthesis of 1‐(benzothiazolylamino)methyl‐2‐
naphthols is a significant and beneficial duty in organic
chemistry processes.
The development of eco‐friendly, effectual, and economi-
cal methodologies for the synthesis of biologically impor-
tant compounds is still a great challenge in organic
chemistry. Multi‐component reactions have newly
attracted much attention as a diversity oriented synthetic
methodologies due to their high efficiency, the creation of
several new bonds in a one‐pot reaction, time and energy
saving and environmental friendliness.[1] Accordingly,
academic and industrial research groups have increas-
ingly emphasized on the use of MCRs to synthesize a
broad range of structural variations.[2]
In recent years, accomplishment of MCRs in the
absence of solvent have attracted great interest. These
methods have many benefits such as high efficiency and
selectivity, operational easiness, mild reaction conditions,
and waste reduction.[3]
The majority of the novel heterogenized catalysts are
based on magnetic nanoparticles (MNPs) Fe3O4 supports,
primarily because Fe3O4 displays some advantageous
properties, such as readily availability, relatively large
surface area to volume ratio, heterogeneous characteris-
tics and recoverability using an external permanent
magnet. In characteristic, Fe3O4 nanoparticles coated
with a layer of silica have advantageous properties, such
as constant catalytic activity and stability.[12–15]
Benzothiazole and its derivatives are of interesting
compounds because they found in many natural products
and pharmaceuticals.[4] These compounds were reported
Appl Organometal Chem. 2017;e3972.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.3972

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KAMALI AND SHIRINI
The susceptibility of transition elements to mediate
0.85 ml of HCl was added dropwise to a solution of 15 g
of sodium hydroxide (NaOH) in 25 ml of deionized water
with vigorous stirring to make a black solid product. Then
the resultant mixture was heated in a water bath for 4 h at
80 °C. The black solid MNPs were isolated using an exter-
nal magnet and washed with deionized water and ethanol
three times and then dried at 80 °C for 10 h.[21]
organic synthesis constitutes one of the most efficient strat-
egies to attain both selectivity and efficiency in synthetic
chemistry.[16] Zirconium pertain to group IV transition
elements that can be considered as efficient catalysts due
to easy availability, low cost and low toxicity. Despite these
advantages, this metal is also unstable to moisture, corro-
sive and difficult to handle. Considering these limitations
and in continuation of our previous reports on the applica-
tion of zirconium based and supported reagents in organic
transformations,[17–20] we were interested to investigate
the stabilization of ZrCl4 on magnetic supports. In this
regard, Fe3O4@SiO2ZrCl2‐MNPs is successfully prepared,
characterized and used as an efficient catalyst in the
promotion of one‐pot three‐component condensation of
aryl aldehydes, β‐naphthol and 2‐aminobenzothiazole to
obtain 1‐(benzothiazolylamino)methyl‐2‐naphthols in the
absence of solvent.
2.2.2 | Preparation of Fe3O4@SiO2 mag-
netic nanoparticles
300 mg Fe3O4‐MNPs were dispersed in a mixture of 40 ml
of EtOH and 4 ml of deionized water by ultrasonication
for 15 min, followed by the addition of 5 ml of NH3.H2O
(28 wt.%) and 2 ml of tetraethylorthosilicate (TEOS). The
mixture was stirred at 400 rpm for 12 h at room tempera-
ture. The products were collected by magnetic separation,
washed with diluted hydrochloric acid and deionized
water, and dried under vaccum.[22]
2 | EXPERIMENTAL
2.1 | Chemicals
2.2.3 | Preparation of Fe3O4@SiO2–ZrCl2
magnetic nanoparticles
Chemicals were purchased from Fluka, Merck and
Aldrich Chemical Companies. The purity determination
of the substrate and reaction monitoring were accompa-
nied by thin‐layer chromatography (TLC) on a silica
gel Polygram SILG/UV 254 plate. The products were
separated and purified by different chromatographic
techniques and were identified by the comparison of their
IR, NMR and refractive index with those reported for the
authentic samples. All yields refer to the isolated
products. The IR spectra were run on a Perkin–Elmer
Fe3O4@SiO2 (0.5 g) was dispersed in dry chloroform
(15 ml) and sonicated for 30 min. Then, ZrCl4 (0.5 g)
was added to the dispersed solution of Fe3O4@SiO2 at
room temperature and stirred for 60 min. The suspended
substance was separated using an external magnet and
washed with chloroform (60 ml) and dried at room
temperature.
Because that Fe3O4@SiO2–ZrCl2‐MNPs procreates
HCl in water, we have specified the concentration of the
acquired acidic aqueous solution by titration. For this pur-
pose 0.1 g Fe3O4@SiO2–ZrCl2‐MNPs placed in conical
flask. Then 10 ml of water and 3 drops of phenolphthalein
was added and titrated with NaOH (0.1 M). The obtained
results clarified that 0.1 g of catalyst manufactured a
0.5 mmol of H+.
1
bio‐spectrometer. The H NMR and 13C NMR (300 MHz)
were run on a Bruker Avance DPX‐300 FTNMR
spectrometer (d in ppm). Melting points were recorded
on a Bu¨ chi B‐545 apparatus in open capillary tubes. A
Philips PW1840 diffractometer with Cu Kα radiation was
used to record the X‐ray patterns of the synthesized
nanoparticles. Scanning electron microscope images were
obtained with LEO 1430 VP. The chemical composition
was obtained using energy dispersive Xray spectroscopy
(EDX) (ESEM, Philips, XL30). The magnetic properties
were determined using vibrating sample magnetometry
(VSM; Lake Shore 7200 at 300 kVsm Rasht, Iran).
2.3 | Catalytic activity
2.3.1 | General procedure for the prepara-
tion of 1‐(benzothiazolylamino)methyl‐2‐
naphthol derivatives
A mixture of 2‐aminobenzothiazole (1 mmol), β–naphtol
(1 mmol), aldehyde (1 mmol) and Fe3O4@SiO2–ZrCl2‐
MNPs (0.030 g) was heated in an oil bath at 100 °C for
an appropriate time [TLC: n‐hexane: ethyl acetate
(10:5)]. After completion of the reaction, the mixture
was cooled to room temperature, acetone (10 ml) was
added and the catalyst was removed using an
external magnet. Evaporation of the solvent from mixture
2.2 | Catalyst preparation
2.2.1 | Preparation of Fe3O4 magnetic
nanoparticles
Firstly, a mixture of 2 g of FeCl2.4H2O, 5.2 g of
FeCl3.6H2O in 25 ml of deionized water containing

KAMALI AND SHIRINI
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gave the solid residue which recrystallized from EtOH
to afford the pure product. Finally Fe3O4@SiO2–ZrCl2‐
MNPs washed with chloroform and be used for the
next run.
OH); 13C NMR (DMSO‐d6, 125 MHz): d = 53.08, 118.54,
118.71, 118.83, 121.41, 121.60, 122.02, 123.02, 123.90,
125.68, 125.93, 127.00, 129.03, 129.12, 129.55, 130.36,
130.82, 131.30, 132.46, 146.10, 152.44, 153.67, 166.59.
2.4.6 | 1‐((benzo[d]thiazol‐2‐ylamino)(4‐
bromophenyl) methyl)naphthalen‐2‐ol (f)
2.4 | Spectroscopic data
2.4.1 | 1‐(benzo[d]thiazol‐2‐ylamino)(phe-
nyl)methyl)naphthalene‐2‐ol (a)
1H NMR (DMSO‐d6, 400 MHz): d = 7.04–7.85 (15H, m,
14H arom and 1H–CH), 8.84 (1H, s, NH), 10.21 (1H, s,
OH); 13C NMR (DMSO‐d6, 100 MHz): d = 53.1, 118.6,
118.7, 118.8, 119.6, 121.4, 121.6, 123.0, 124.1, 125.9,
126.9, 128.8, 129.1, 130.3, 131.3, 131.4, 132.5, 142.7,
152.5, 153.7, 166.6.
1H NMR (DMSO‐d6, 400 MHz): d = 6.96–7.93 (16H, m,
15H arom and 1H–CH), 8.67 (1H, s, NH), 10.11 (1H, s,
OH); 13C NMR (DMSO‐d6, 100 MHz): d = 53. 36, 118.02,
118.57, 118.81, 120.49, 120.84, 122.27, 123.58, 125.23,
126.04, 127.83, 128.34, 128.56, 129.28, 130.59, 132.12,
142.25, 151.96, 153.19, 166.33.
2.4.7 | 1‐((benzo[d]thiazol‐2‐ylamino)(4‐
fluoro‐phenyl)methyl)naphthalen‐2‐ol (g)
2.4.2 | 1‐(benzo[d]thiazol‐2‐ylamino)(2‐
chloro phenyl)naphthalene‐2‐ol (b)
1H NMR (DMSO‐d6, 500 MHz): d = 6.99–7.85 (15H, m,
14H arom and 1H–CH), 8.80 (1H, s, NH), 10.17 (1H, s,
OH); 13C NMR (DMSO‐d6, 125 MHz): d = 53.13, 115.21,
115.38, 118.55, 118.80, 118.84, 121.40, 121.57, 122.93,
124.11, 125.94, 126.80, 128.37, 128.43, 129.07, 130.18,
131.14, 132.50, 138.98, 152.28, 153.65, 160.25, 162.17,
166.71.
1H NMR (DMSO‐d6, 500 MHz): d = 6.97–8.01 (15H, m,
14H arom and 1H–CH), 8.89 (1H, s, NH), 9.91 (1H, s,
OH); 13C NMR (DMSO‐d6, 125 MHz,): d = 52.59, 118.62,
119.47, 121.45, 121.68, 122.45, 122.68, 123.19, 123.69,
126.32, 126.60, 126.99, 129.13, 129.16, 129.49, 129.81,
131.16, 142.52, 153.20, 154.29, 167.17.
2.4.8 | 1‐(benzo[d]thiazol‐2‐ylamino)(3‐
nitro phenyl)naphthalene‐2‐ol (h)
2.4.3 | 1‐((benzo[d]thiazol‐2‐ylamino)(3‐
chlorophenyl)methyl)naphthalen‐2‐ol (c)
1H NMR (DMSO‐d6, 400 MHz): d = 7.05–7.88 (15H, m,
14H arom and 1H–CH), 8.90 (1H, s, NH), 10.12 (1H, s,
OH); 13C NMR (DMSO‐d6, 100 MHz): d = 54.38, 116.12,
118.72, 119.41, 119.62, 119.82, 121.84, 121.91, 123.28,
126.43, 126.99, 129.41, 129.55, 130.27, 131.23, 133.12,
146.14, 152.48, 154.06, 167.22.
1H NMR (DMSO‐d6, 400 MHz): d = 7.04–8.06 (15H, m,
14H arom and 1H–CH), 8.49 (1H, s, NH), 10.25 (1H, s,
OH); 13C NMR (DMSO‐d6, 100 MHz): d = 53.13, 118.53,
118.70, 118.82, 121.42, 121.61, 123.01, 123.87, 125.30,
125.94, 126.16, 126.66, 126.99, 129.01, 129.11, 130.35,
130.52, 131.29, 132.46, 133.32, 145.86, 152.40, 153.68,
166.62.
2.4.9 | 1‐(benzo[d]thiazol‐2‐ylamino)(4‐
nitro phenyl)methyl)naphthalene‐2‐ol (i)
2.4.4 | 1‐(benzo[d]thiazol‐2‐ylamino)(4‐
chloro phenyl)naphthalene‐2‐ol (d)
1H NMR (DMSO‐d6, 400 MHz): d = 6.73–7.30 (15H, m,
14H arom and 1H–CH), 8.65 (1H, s, NH), 10.00 (1H, s,
OH); 13C NMR (DMSO‐d6, 100 MHz): d = 53.43, 117.81,
118.31, 118.58, 119.59, 120.41, 122.54, 123.24, 125.20,
125.33, 126.65, 127.32, 128.57, 128.98, 129.89, 145.99,
150.68, 153.38, 166.69.
1H NMR (DMSO‐d6, 400 MHz): d = 6.67–7.78 (15H, m,
14H arom and 1H–CH), 8.57 (1H, s, NH); 10.27 (1H, s,
OH); 13C NMR (DMSO‐d6, 100 MHz): 53.48, 117.71,
118.13, 118.96, 120.95, 121.12, 122.43, 122.47, 125.81,
126.82, 127.30, 127.78, 128.22, 129.54, 130.32, 134.52,
138.16, 151.61, 153.28, 166.89.
2.4.10 | 1‐((benzo[d]thiazol‐2‐ylamino)(3‐
methoxy‐phenyl)methyl)naphthalen‐2‐ol
(j)
1H NMR (DMSO‐d6, 400 MHz): d = 3.65 (3H, s, OCH3),
6.76–7.88 (15H, m, 14H arom and 1H–CH), 8.79 (1H, s,
NH), 10.17 (1H, s, OH); 13C NMR (DMSO‐d6, 100 MHz):
2.4.5 | 1‐((benzo[d]thiazol‐2‐ylamino)(3‐
bromo‐phenyl)methyl)naphthalen‐2‐ol (e)
1H NMR (DMSO‐d6, 500 MHz): d = 7.01–7.89 (15H, m,
14H arom and 1H–CH), 8.83 (1H, s, NH), 10.21 (1H, s,

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KAMALI AND SHIRINI
d = 53.43, 55.33, 111.11, 113.08, 118.56, 118.83, 118.94,
119.09, 121.35, 121.45, 122.88, 125.90, 126.68, 128.99,
129.07, 129.68, 130.01, 131.22, 132.58, 144.67, 152.54,
153.60, 159.60, 166.72.
121.14, 121.23, 122.60, 123.97, 125.79, 125.96, 126.33,
128.40, 128.71, 128.81, 129.45, 130.09, 131.06, 133.09,
152.79, 153.84, 157.20, 166.16.
3 | RESULTS AND DISCUSSION
2.4.11 | 1‐(benzo[d]thiazol‐2‐ylamino)(4‐
methoxy phenyl)methyl)naphthalene‐2‐ol
(k)
1H NMR (DMSO‐d6, 400 MHz): d = 3.69 (3H, s, OCH3),
6.69–7.97 (15H, m, 14H arom and 1H–CH), 8.51 (1H, s,
NH), 10.53 (1H, s, OH); 13C NMR (DMSO‐d6, 100 MHz):
d = 54.81, 67.47, 118.11, 119.03, 119.12, 120.58, 122.53,
125.52, 126.22, 127.42, 128.47, 128.79, 129.38, 130.22,
132.16, 133.56, 132.12, 142.25, 151.69, 153.35, 166.84.
As we have mentioned previously, the focus of this article
is on the preparation of Fe3O4@SiO2–ZrCl2 as a new and
stable nano‐magnetic derivative of zirconium (Scheme 1)
and its applicability in the acceleration of the synthesis
of 1‐(benzothiazolylamino)methyl‐2‐naphthols as a model
organic reaction.
3.1 | Characterization of Fe3O4@SiO2–
ZrCl2‐MNPs
2.4.12 | 1‐(benzo[d]thiazol‐2‐ylamino)(p‐
tolyl)methyl)methyl)naphthalene‐2‐ol (l)
The synthesized catalyst was characterized by FT‐IR,
1H NMR (DMSO‐d6, 400 MHz): d = 2.23 (3H, s, CH3),
6.95–7.39 (15H, m, 14H arom and 1H–CH), 8.66 (1H, s,
NH), 10.14 (1H, s, OH); 13C NMR (DMSO‐d6, 100 MHz):
d = 20.60, 53.33, 118.00, 118.66, 118.92, 120.51, 120.85,
122.27, 125.26, 126.03, 128.34, 128.50, 128.60, 129.22,
130.55, 132.13, 135.17, 139.13, 151.97, 153.20, 166.39.
XRD, SEM, EDX and VSM techniques.
3.1.1 | FT‐IR study
Successful coating of ZrCl4 on the surface of Fe3O4@SiO2
core could be proven by FT‐IR spectroscopy. Figure 1
shows the FT‐IR spectra of ZrCl4, Fe3O4‐MNPs,
Fe3O4@SiO2‐MNPs and Fe3O4@SiO2–ZrCl2‐MNPs. In
all of the spectra, the broad absorption around the
3350 cm−1 due to O‐H stretching vibrations are observed
with a strong intermolecular hydrogen bonding. FT‐IR
spectrum of Fe3O4‐MNPs (Figure 1a) showed characteris-
tic absorption at 590 and 443 cm−1 due to the Fe–O–Fe
vibration related to the magnetite phase. After coating
with a layer of SiO2, FT‐IR spectrum of Fe3O4@SiO2‐
MNPs (Figure 1b) exhibits new peaks at 1090 and
960 cm−1 which are assigned to Si–O–Si and Si–OH
stretching vibrations, respectively. Weak band at
475 cm−1 is attributable to the Si–O–Fe stretching vibra-
tions of Fe3O4@SiO2‐MNPs. The ZrCl4 is adsorbed on the
Fe3O4@SiO2 surface by Si–O–Zr bonds. This adsorption
band cannot be seen in the FT‐IR spectrum because it
appears at around 982 cm−1 and therefore overlaps with
the Si–OH vibration of Fe3O4@SiO2 nanoparticles
(Figure 1c).
2.4.13 | 1‐((benzo[d]thiazol‐2‐ylamino)
(otolyl) methyl)naphthalen‐2‐ol (m)
1H NMR (DMSO‐d6, 400 MHz): d = 2.10 (3H, s), 6.97–7.96
(15H, m, 14H arom and 1H–CH), 8.81 (1H, s, NH), 10.08
(1H, s,OH); 13C NMR (DMSO‐d6, 100 MHz): d = 19.5,
53.1, 117.4, 118.5, 118.6, 121.3, 121.5, 123.0, 123.9, 125.9,
126.1, 126.7, 127.4, 127.5, 129.0, 129.1, 130.1, 130.7,
131.1, 133.0, 136.6, 139.8, 152.5, 153.7, 166.0.
2.4.14 | 1‐((benzo[d]thiazol‐2‐ylamino)(2‐
methoxyphenyl)methyl)naphthalen‐2‐ol
(n)
1H NMR (DMSO‐d6, 400 MHz): d = 3.79 (3H, s, OCH3),
6.83–7.73 (15H, m, 14H arom and 1H–CH), 8.16 (1H, s,
NH), 10.47 (1H, s, OH); 13C NMR (DMSO‐d6, 100 MHz):
d = 50.63, 55.82, 111.38, 118.40, 118.68, 119.03, 120.15,
SCHEME 1 Preparation of
Fe3O4@SiO2–ZrCl2‐MNPs

KAMALI AND SHIRINI
5 of 12
3.1.3 | SEM study
The morphologies and structures of the synthesized
Fe3O4@SiO2‐MNPs and Fe3O4@SiO2–ZrCl2‐MNPs were
investigated by the scanning electron microscopy (SEM).
The SEM images indicate that Fe3O4@SiO2‐MNPs are
spherical and their average size is about 70
18 nm
(Figure 3a). Atfer interaction with ZrCl4, the typical
core–shell structure of Fe3O4@SiO2‐MNPs can be
observed and the average size increases to about
100 20 nm (Figure 3b).
3.1.4 | XRD study
Figure 4 shows the X‐ray diffraction pattern for pure
Fe3O4‐MNPs (Figure 4a), Fe3O4@SiO2‐MNPs (Figure 4b)
and Fe3O4@SiO2–ZrCl2‐MNPs (Figure 4c). In XRD
patterns of Fe3O4‐MNPs diffraction peaks with 2θ at
30.0°, 35.6°, 43.2°, 57.2°, and 62.5° are observed which
confirm the structure of the magnetite material (JCPDS
FIGURE
1
FT‐IR spectra of (a) Fe3O4‐MNPs and (b)
Fe3O4@SiO2‐MNPs (c) Fe3O4@SiO2–ZrCl2‐MNPs (d) ZrCl4
3.1.2 | EDX study
The energy‐dispersive Xray analysis (EDX) spectrum of
Fe3O4@SiO2–ZrCl2‐MNPs also indicates the presence of
all expected elements (Fe, Si, Zr, Cl and O) and confirm
the supporting of ZrCl4 on Fe3O4@SiO2‐MNPs
(Figure 2). The elemental compositions of Fe3O4@SiO2–
ZrCl2 were found to be 43.49, 13.15, 13.92, 17.79 and
11.56% for Fe, O, Si, Zr and Cl respectively. Pursuant to
EDX data, the molar ratio of Zr:Cl, was 1:2 and for this
reason the possible structure of Fe3O4@SiO2–ZrCl2‐MNPs
was suggested as shown in Scheme 1.
FIGURE
3
SEM images of (a) Fe3O4@SiO2‐MNPs (b)
FIGURE 2 EDX data for Fe3O4@SiO2–ZrCl2‐MNPs
Fe3O4@SiO2–ZrCl2‐MNPs

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KAMALI AND SHIRINI
FIGURE 4 XRD pattern of Fe3O4‐
MNPs (a), Fe3O4@SiO2‐MNPs (b) and
Fe3O4@SiO2–ZrCl2‐MNPs (c)
card no. 79–0418). The characteristic peaks for pure
Fe3O4‐MNPs also observed for Fe3O4@SiO2‐MNPs. This
revealed that the surface modification of Fe3O4 nano-
particles with SiO2 did not lead to their phase change.
In Figure 4c, the XRD pattern of Fe3O4@SiO2–ZrCl2‐
MNPs showed a much broader diffraction pattern and
increased the noise to that of Figure 4b, which can be
attributed to linking ZrCl2 on the surface of
Fe3O4@SiO2.
shown in Figure 5. The saturation magnetization (Ms) of
Fe3O4@SiO2 nanoparticles (curve a) was about
39.37 emu/g, which decreased to 15.82 emu/g after
supporting Fe3O4@SiO2 with ZrCl2 (curve b). The
obtained Ms value is lower than that of Fe3O4@SiO2 nano-
particles, which confirms the presence of a diamagnetic
outer shell (ZrCl2). Such magnetizations are sufficient
for performing magnetic separation.
3.2 | Application of Fe3O4@SiO2–ZrCl2‐
MNPs
3.1.5 | VSM study
The magnetization hysteresis for the synthesized
Fe3O4@SiO2 and Fe3O4@SiO2‐ZrCl2 nanoparticles are
The catalytic activity of Fe3O4@SiO2–ZrCl2‐MNPs was
explored in the synthesis of 1‐(benzothiazolylamino)

KAMALI AND SHIRINI
7 of 12
tion at 60, 80, 100, and 110 °C. When the model reac-
tion was carried out in 100 °C, the good yield was
obtained in a short time. Moreover, the effect of the cat-
alyst amounts on the reaction output was explored. The
results showed that 0.030 g Fe3O4@SiO2–ZrCl2‐MNPs
was enough to promote the reaction (Table 1,
Scheme 2).
Using these optimized reaction conditions, a series
of 1‐(benzothiazolylamino)methyl‐2‐naphthols were
synthesized in high yields by utilization of one‐pot
condensation of aromatic aldehydes, β‐naphtol and 2‐
aminobenzothiazole in the presence of Fe3O4@SiO2–
ZrCl2‐MNPs and the results are tabulated in Table 2.
The obtained results showed that the reaction work
well with aromatic aldehydes containing electron‐
donating and electron‐withdrawing substituents on the
aromatic ring. Because of the formation of a mixture
of unidentified products the method is not recom-
mended for aliphatic aldehydes.
The plausible mechanism of the reaction in the
presence of Fe3O4@SiO2–ZrCl2‐MNPs is shown in
Scheme 3. On the basis of this mechanism
Fe3O4@SiO2–ZrCl2‐MNPs plays an important role in
activating of aromatic aldehyde. Then activated
aldehyde in reaction with β–naphtol produces the
FIGURE
Fe3O4@SiO2–ZrCl2‐MNPs (b)
5
VSM pattern of Fe3O4@SiO2‐MNPs (a) and
methyl‐2‐naphthols. In our primary study, the best reac-
tion conditions were surveyed by using the reaction
between 2‐aminobenzothiazole (1 mmol), β–naphtol
(1 mmol) and 4‐chlorobenzaldehyde (1 mmol) as a
model reaction. The best results were obtained under
solvent‐free conditions. In the next step, the effect of
temperature on completion of the reaction in the
absence of solvent was studied by performing the reac-
TABLE 1 Optimization of three‐component reaction of β–naphthol, 4‐chlorobenzaldehyde, and 2‐aminobenzothiazole under various
conditionsa
Entry
Catalyst (g)
Conditions
Time (min)
Yield (%)b
1
None
Solvent free, 70 °C
100
Trace
2
Fe3O4@SiO2‐MNPs (0.035)
Solvent‐free, 100 °C
Solvent‐free, 60 °C
Solvent‐free, 80 °C
Solvent‐free, 100 °C
Solvent‐free, 110 °C
H2O (3 ml), 70 °C
CH3CN, 60 °C
70
50
25
7
60
75
3
Fe3O4@SiO2–ZrCl2‐MNPs (0.035)
Fe3O4@SiO2–ZrCl2‐MNPs (0.030)
Fe3O4@SiO2–ZrCl2‐MNPs (0.030)
Fe3O4@SiO2–ZrCl2‐MNPs (0.030)
Fe3O4@SiO2–ZrCl2‐MNPs (0.025)
Fe3O4@SiO2–ZrCl2‐MNPs (0.025)
Fe3O4@SiO2–ZrCl2‐MNPs (0.025)
Fe3O4@SiO2–ZrCl2‐MPs (0.025)
4
86
5
95
6
7
95
7
75
70
60
120
65
8
50
9
EtOH, 70 °C
58
10
n‐hexane, 60 °C
Trace
aReaction conditions: β–naphthol (1 mmol), 2‐aminobenzothiazole (1 mmol), 4‐chlorobenzaldehyde (1 mmol) and Fe3O4@SiO2–ZrCl2‐MNPs under different
condition.
bThe yield refers to pure isolated product.
SCHEME 2 One‐pot three‐component
reaction of 2‐aminobenzothiazole, β–
naphtol and different aromatic aldehydes
catalyzed by Fe3O4@SiO2–ZrCl2‐MNPs in
the absence of solvent

8 of 12
KAMALI AND SHIRINI
TABLE 2 Scope of catalytic activity of Fe3O4@SiO2–ZrCl2‐MNPs in the synthesis of 1‐(benzothiazolylamino)methyl‐2‐naphthol derivativesa
Mp (°C)
Time
(min)
Yield
(%)
90
b,c
Entry
ArCHO
Product
Found reported [ref.]
1
15
204–205
202–203[23]
(a)
2
3
12
92
90
188–190
189–190[23]
(b)
10
193–194
193–195[26]
(c)
(d)
4
5
7
95
90
210–211
203–204
209–210[23]
10
200–202[24]
(e)
(f)
6
7
9
93
90
198–199
186–187
200–202[26]
188–189[23]
(Continues)
10
(g)

KAMALI AND SHIRINI
9 of 12
TABLE 2 (Continued)
Mp (°C)
Time
(min)
Yield
(%)
90
b,c
Entry
ArCHO
Product
Found reported [ref.]
8
15
197–199
198–199[25]
(h)
9
14
20
90
90
190–192
184–186
188–190[24]
(i)
10
185–187[24]
(j)
11
12
20
23
89
90
174–175
181–183
175–176[25]
(k)
182–183[25]
(l)
13
14
20
25
88
90
191–193
164–166
191–193[26]
(m)
168–170[26]
(n)
aReaction conditions: aldehyde (1 mmol), 2‐aminobenzothiazole (1 mmol), β‐naphtol (1 mmol) and Fe3O4@SiO2–ZrCl2‐MNPs (0.030 g); reactions conducted
under solvent‐free conditions at 100 °C.
bIsolated yields.
cAll the products are known compounds and are identified by the comparison of their spectroscopic data with the authentic samples.

10 of 12
KAMALI AND SHIRINI
SCHEME 3 Plausible mechanism for
the formation of 1‐(benzothiazolylamino)
methyl‐2‐naphthol derivatives in the
presence of Fe3O4@SiO2–ZrCl2‐MNPs
FIGURE 6 Magnetic separation and
reuse
intermediate
(Ι)
that
subsequently
undergoes
elimination reaction to afford intermediate (ІІ). This
compound undergoes further addition with the 2‐
aminobenzothiazole to produce 1‐(benzothiazolylamino)
methyl‐2‐naphthol derivatived.
The reusability of the catalyst in the model
reaction of the preparation of 1‐(benzothiazolylamino)
methyl‐2‐naphthol derivatives under the optimized
reaction conditions was also investigated for at least
four runs. For this purpose and because of the solubil-
ity of the products in acetone, after completion of the
reaction, acetone (10 ml) was added, the mixture was
stirred for 5 minute and then the catalyst was removed
using an external magnet (Figure 6). In continue evap-
oration of the acetone from mixture gave the solid res-
idue which recrystallized from EtOH to afford the pure
product. Finally Fe3O4@SiO2–ZrCl2‐MNPs was washed
with chloroform which can be used for four successive
runs without a considerable loss of its catalytic activity
(Figure 7). The same FT‐IR of the recovered catalyst
with the freshly prepared one confirms the stability
of the catalyst in reaction media.
FIGURE 7 Recycling of the catalyst in the synthesis of 1‐
(benzothiazolylamino)methyl‐2‐naphthol derivatives
prepared catalyst with some of those reported in the
literature, for the reaction of β–naphtol, 2‐
aminobenzothiazole and 4‐Chlorobenzaldehyde. As
shown in Table 3, Fe3O4@SiO2–ZrCl2‐MNPs can act as a
useful catalyst and lead to an improved protocol in terms
of compatibility with environment, yields of the products
and reaction times compared to the other reported
systems.
In order to show the merit of the above mentioned
method we further compared the efficiency of the

KAMALI AND SHIRINI
11 of 12
TABLE 3 Comparison of the results obtained in the presence of Fe3O4@SiO2–ZrCl2‐MNPs under solvent‐free conditions with other cata-
lysts reported in the literature in the synthesis 1‐(benzo[d]thiazol‐2‐ylamino)(4‐chloro phenyl)naphthalene‐2‐ol
Entry
Catalyst
Conditions
Time (min)
Yield (%)
[ref.]
[27]
1
HPA (0.12 g)
Ultrasound, H2O (3 ml), 45 °C
110
90
[26]
[30]
[28]
[29]
[26]
[30]
[30]
[26]
[26]
[25]
2
NaHSO4.H2O (10 mol %)
SDS (20 mol %)
Solvent‐free, 100 °C
H2O (3 ml), 100 °C
Neat, 60 °C
6
60
8
83
88
95
95
39
40
55
62
71
92
95
3
4
NBS (0.1 mmol)
5
Triton X‐100 (10 mol %)
ZnCl2 (10 mol %)
H2O (10 ml) 60 °C
Solvent‐free, 70 °C
H2O (3 ml), 100 °C
H2O (3 ml), 100 °C
Solvent‐free, 70 °C
Solvent‐free, 70 °C
H2O (3 ml), 90 °C
Solvent free, 100 °C
72
120
6 h
60
53
19
6 h
7
6
7
YbCl3 (20 mol %)
8
Sc(OTf)3 (20 mol %)
Al(H2PO4)3 (10 mol %)
MgCl2 (10 mol %)
9
10
11
12
LiCl (0.5 g, 71 mmol)
Fe3O4@SiO2–ZrCl2‐MNPs (0.030 g)
This work
[3] H. Bienaym0e, C. Hulme, G. Oddon, P. Schmitt, Chemistry 2000,
6, 3321.
4 | CONCLUSION
[4] C. J. Paget, K. Kisner, R. L. Stone, D. C. DeLong, J. Med. Chem.
1969, 12, 1016.
In conclusion, in this study a simple method for the syn-
thesis of the Fe3O4@SiO2–ZrCl2‐MNPs as a magnetically
heterogeneous nano catalyst was demonstrated. This
catalyst can effectively promote the synthesis of
2′‐aminobenzothiazolo‐arylmethyl‐2‐naphthols through
three‐component condensation of various aromatic alde-
hydes, β‐naphtol and 2‐aminobenzothiazole under sol-
vent‐free conditions. The protocol is simple, efficient and
eco‐friendly because it has some advantages such as sim-
ple catalyst preparation, short reaction times, high yields,
mild reaction conditions and use of a reusable catalyst.
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Choo, Bioorg. Med. Chem. 2006, 14, 1229.
[11] C. Cardellicchio, M. A. M. Capozzi, F. Naso, Tetrahedron:
Asymmetry 2010, 21, 507.
We are thankful to the University of Guilan Research
Council for the partial support of this work.
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2013, 42, 3371.
ORCID
[13] S. Roy, M. A. Pericas, Org. Biomol. Chem. 2009, 7, 2669.
Farhad Shirini http://orcid.org/0000-0002-0768-3241
[14] S. Shojaei, Z. Ghasemi, A. Shahrisa, Appl. Organomet. Chem.
2017, e3788.
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How to cite this article: Kamali F, Shirini F.
Fe3O4@SiO2–ZrCl2‐MNPs: A novel magnetic
catalyst for the clean and efficient cascade synthesis
of 1‐(benzothiazolylamino)methyl‐2‐naphthol
derivatives in the absence of solvent. Appl
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