Magnetite (Fe3O4) nanoparticles-supported dodecylbenzenesulfonic acid as a highly efficient and green heterogeneous catalyst for the synthesis of substituted quinolines and 1-amidoalkyl-2-naphthol derivatives

Article abstract of DOI:10.1007/s13738-020-02069-9

Abstract: Magnetically retrievable, magnetite (Fe₃O₄) nanoparticles-supported dodecylbenzenesulfonic acid (DDBSA@MNP) was synthesized and characterized through different analytical techniques such as TEM, XRD, FTIR, TGA, SEM, EDX and

Full text of DOI:10.1007/s13738-020-02069-9

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-020-02069-9
ORIGINAL PAPER
Magnetite (Fe O ) nanoparticles‑supported dodecylbenzenesulfonic
3
4
acid as a highly eꢀcient and green heterogeneous
catalyst for the synthesis of substituted quinolines
and 1‑amidoalkyl‑2‑naphthol derivatives
1
1
2
1
Deepak Katheriya · Nipun Patel · Harsh Dadhania · Abhishek Dadhania
Received: 14 June 2020 / Accepted: 18 September 2020
©
Iranian Chemical Society 2020
Abstract
Magnetically retrievable, magnetite (Fe O ) nanoparticles-supported dodecylbenzenesulfonic acid (DDBSA@MNP) was
3
4
synthesized and characterized through diꢀerent analytical techniques such as TEM, XRD, FTIR, TGA, SEM, EDX and
VSM. The catalytic eꢁciency of synthesized DDBSA@MNP was evaluated for the synthesis of substituted quinolines and
1
-amidoalkyl-2-naphthols through one-pot condensation. The methodology provides a facile approach for the synthesis of
targeted compounds with excellent isolated yields. Additionally, the catalyst can be recovered through external magnet and
reused up to ꢂve reaction cycles with prominent reactivity. The present approach oꢀers many advantages such as green and
mild reaction condition, facile catalyst recovery and excellent isolated yield of ꢂnal products.
Graphic abstract
Keywords Magnetic nanoparticles · Heterogeneous catalyst · One-pot condensation · Friedlander reaction
Introduction
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s13738-020-02069-9) contains
supplementary material, which is available to authorized users.
Homogeneous catalysts have been known for several years
due to their distinct features such as high activity and selec-
tivity [1–3]. Homogeneous nature of the catalyst renders all
catalytic sites available for the reactants and also provides
the stereo- and regioselectivity to the reaction [4]. How-
ever, homogeneous catalysts contribute not more than 15%
of the industrial processes as compared to its counterpart
heterogeneous catalysts [5]. The reason behind this trend is
diꢁculties associated with their separation and reusability.
*
Abhishek Dadhania
abhishekdadhania.bt@charusat.ac.in
1
Department of Chemical Sciences, P. D. Patel Institute
of Applied Sciences, Charotar University of Science
and Technology (CHARUSAT), Changa, Gujarat 388421,
India
2
Department of Chemistry, Sardar Patel University,
Vallabh Vidyanagar 388120, Gujarat, India
Vol.:(0
1
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Journal of the Iranian Chemical Society
Separation of trace amount of catalysts from ꢂnal product is
very much important, especially in highly regulated pharma-
ceutical sector [6]. Likewise, reusability is directly related
to sustainability of the process and has a huge impact on
product cost and pollution. Even after utilization of diꢀerent
experimental techniques such as extraction, distillation and
chromatography, the catalyst separation remains a huge chal-
lenge [7]. An ideal solution for this problem is heterogeni-
zation of homogeneous catalyst through its immobilization
on solid supports such as polymer, silica, carbon and some
metal oxides [8–12]. However, heterogenization usually
lowers its catalytic eꢁciency as it limits the access of cata-
lytic sites for reactants. In order to overcome this drawback,
porous material such as zeolite has been utilized as a solid
support [13, 14]. Another way to tackle this issue is to use
nano-size solid support for the immobilization of catalyst.
The higher surface area of nanomaterial will enhance the
accessibility of catalytic sites for reactants [15]. However,
due to nanometer size the separation of catalyst through ꢂl-
tration is cumbersome. The feasible solution for this issue is
to utilize magnetic nanoparticles (MNPs) as a solid support
for immobilization of homogeneous catalyst. MNPs emerged
as an ideal support due to their distinct features such as easy
synthesis, lower toxicity and cost, higher stability and most
importantly its paramagnetic nature, which provides an easy
separation through external magnet [16–19].
in compounds with comprehensive biological activities
including anti-tumor [24, 25], anticancer [26, 27], anti-
plasmodial [23], analgesic [28], anti-bacterial [29, 30],
fungicidal [31], anti-allergic [32], antimalarial [33], anti-
microbial [34], anti-inꢃammatory [35] and anti-tubercular
[36]. Many reports were published on the Friedlander reac-
tion using diꢀerent homogeneous as well as heterogene-
ous catalysts [37–42]. Likewise, 1-amidoalkyl-2-naphthols
have emerged as privileged medicinal scaꢀolds due to
their hydrolyzed product 1-aminoalkyl-2-naphthols, which
possess attractive biological activities such as bradycardic
and hypotensive eꢀects [43]. Moreover, these 1,3-amino-
oxygenated derivatives are ubiquitous and found in many
natural products and drug molecules such as ritonavir and
lopinavir [44–46]. Owing to important medicinal prop-
erties, many synthetic methods are reported for the syn-
thesis of 1-amidoalkyl-2-naphthols via a one-pot multi-
component reaction between 2-naphthol, aldehydes and
amides using diꢀerent catalysts [47–52]. However, the use
of excessive catalyst, strong acidic condition, use of toxic
and expensive metal catalyst, longer reaction time, lower
to moderate yields and poor recovery and reusability of
catalyst limits the scope for some of these methodologies
for the synthesis of quinolines and 1-amidoalkyl-2-naph-
thol derivatives. Hence, a facile and eꢁcient strategy using
sustainable catalyst is required for the synthesis of these
derivatives.
The Friedlander reaction is the condensation of 2-ami-
noaryl ketones and β-ketoester followed by a cyclode-
hydration reaction [20]. Quinoline is the product of this
condensation, which has great impact on pharmaceutical
and agrochemical industries due to its attractive biologi-
cal activities [21]. Furthermore, quinoline is an impor-
tant moiety widely present in many natural products [22,
In this contribution, we report the utilization of magnet-
ite nanoparticles-supported dodecylbenzenesulfonic acid
(DDBSA@MNP) as a catalyst for the synthesis of substi-
tuted quinolines (Scheme 1) and 1-amidoalkyl-2-naphthol
derivatives (Scheme 2). The catalyst was found highly eꢁ-
cient, eco-friendly, magnetically separable and reusable to
obtained corresponding products in excellent yields.
2
3]. The structural nuclei based on quinoline can serve
Scheme 1 DDBSA@MNP-cat-
alyzed synthesis of substituted
quinolines
Scheme 2 DDBSA@
MNP-catalyzed synthesis of
1
-amidoalkyl-2-naphthols
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Journal of the Iranian Chemical Society
Experimental
General procedure for the synthesis of substituted
quinoline derivatives
Materials and instruments
A mixture of the 2-aminoaryl ketone (1 mmol), β-ketoester/
ketone (1.5 mmol) and DDBSA@MNP (0.15 g) in EtOH
(5 mL) was stirred under reꢃux condition for appropriate
time as indicated by TLC. After completion of the reaction,
the catalyst was separated through magnetic decantation,
thoroughly washed with ethanol and dried under vacuum
for its further use in next reaction cycle. The crude product
was puriꢂed over silica gel to obtain pure quinoline deriva-
tives. Aꢀorded products were characterized by their melting
All the chemicals and reagents were purchased from the
commercial sources and used without further puriꢂcation.
Melting points were determined through VMP-D melting
point apparatus and were uncorrected. A Thermo Nicolet
6
700 spectrophotometer was used to record FTIR spectra
using KBr pellets. TG analysis was performed on a Met-
tler Toledo thermal analyzer under nitrogen atmosphere.
A Bruker D2 phaser bench-top diꢀractometer was used to
record X-ray diꢀraction pattern. TEM images were recorded
on a JEOL JEM 2100 instrument. FESEM micrographs were
recorded using a JEOL JSM-7100F instrument. VSM-7400,
Lake Shore, USA, was used to record magnetization curves.
1
13
points, H and C NMR data and found in agreement with
the literature. The spectral data of representative quinoline
derivatives are given in the following.
1
13
1
H and C NMR spectra were recorded on a 400 MHz
Ethyl 2‑methyl‑4‑phenylquinoline‑3‑carboxylate (3a) H
Bruker Avance spectrometer. EDX spectrum was recorded
on a JEOL JSM-5610 scanning electron microscope.
NMR (400 MHz, CDCl ) δ (ppm): 0.98 (t, 3H), 2.80 (s, 3H),
3
4.07(q, 2H), 7.37–7.39 (m, 2H), 7.42–7.49 (m, 4H), 7.59
1
3
(
d, 1H), 7.73 (t, 1H), 8.09 (d, 1H); C NMR δ: 8.88, 19.05,
5
6.57, 120.43, 121.66, 121.75, 122.68, 123.47, 123.69,
Synthesis of silica‑coated Fe O nanoparticles
123.85, 124.12, 124.65, 125.49, 131.02, 141.52, 142.98,
149.88, 163.70.
3
4
(
SiO @Fe O )
2 3 4
1
Magnetite (Fe O ) nanoparticles were synthesized through
Methyl 2‑methyl‑4‑phenylquinoline‑3‑carboxylate (3b) H
3
4
co-precipitation method [53]. Initially, FeCl ·6H O (5.4 g)
NMR (400 MHz, CDCl ) δ (ppm): 2.79 (s, 3H), 3.59 (s, 3H),
3
2
3
and NH CONH (3.6 g) were dissolved in water (200 mL)
7.29 (s, 2H), 7.37–7.51 (m, 4H), 7.60 (d, 1H), 7.74 (t, 1H),
8.10 (d, 1H); 13C NMR δ: 23.81, 52.14, 125.09, 126.46,
126.53, 127.28, 128.27, 128.49, 128.89, 129.25, 129.40,
130.31, 135.69, 146.40, 147.78, 154.55, 169.00.
2
2
and kept at 90 °C for 2 h to turn the solution brown. After
that, FeSO ·7H O (2.8 g) was added to the mixture at
4
2
room temperature and 0.1 M NaOH solution was added
drop wise to adjust the pH of resultant solution at 10.
The precipitates were sonicated for 30 min and kept aside
for 5 h at room temperature. The obtained black powder
was washed with water and dried under vacuum. The
obtained Fe O nanoparticles were dispersed in the mix-
1
1‑(2‑Methyl‑4‑phenylquinolin‑3‑yl)ethanone (3c) H NMR
(400 MHz, CDCl ) δ (ppm): 2.02 (s, 3H), 2.72 (s, 3H), 7.37
3
(s, 2H), 7.38 (d, 1H), 7.46–7.54 (m, 3H), 7.64 (d, 1H), 7.76
1
3
(t, 1H), 8.10 (d, 1H); C NMR δ: 24.10, 31.84, 121.70,
124.08, 126.17, 126.53, 128.72, 128.89, 128.91, 130.06,
130.11, 135.23, 145.33, 155.96, 195.42.
3
4
ture of ethanol and water (80:20) through sonication for
h. After that, concentrated NH ·H O (5 mL) and TEOS
1
3
2
(
5 mL) were added to the dispersion and stirred vigorously
1
for 24 h to obtain silica-coated Fe O nanoparticles and
9‑Phenyl‑1,2,3,4‑tetrahydroacridine (3e) H NMR
3
4
washed with ethanol and dried under vacuum.
(400 MHz, CDCl ) δ (ppm): 1.78–1.86 (m, 2H), 1.92–2.02
3
(
m, 2H), 2.62 (t, 2H), 3.22 (t, 2H), 7.26 (t, 2H), 7.32 (d,
1
3
2
H), 7.46–7.64 (m, 4H), 8.04 (d, 1H); C NMR δ: 22.02,
Synthesis of DDBSA@MNP catalyst
23.21, 28.57, 34.81, 120.81, 122.89, 125.36, 125.79, 126.68,
1
27.72, 128.34, 128.40, 128.61, 129.12, 137.23, 144.99,
Silica-coated Fe O nanoparticles were decorated with
146.70, 159.20.
3
4
dodecylbenzenesulfonic acid to attain the DDBSA@MNP.
1
Initially, SiO @Fe O nanoparticles (1 g) were added in
3,3,9‑Trimethyl‑3,4‑dihydroacridin‑1(2H)‑one (3k) H NMR
2
3
4
MeOH (25 mL) and sonicated for 60 min to get proper dis-
persion. DDBSA (1.04 mL) was added to the dispersion,
and the solution was reꢃuxed for 4 h. Solvent was removed
through reduced pressure, and resulting powder was dried
at 110 °C for 2 h to get DDBSA@MNP.
(400 MHz, CDCl ) δ (ppm): 1.14 (s, 6H), 2.67 (s, 2H), 3.07
3
(s, 3H), 3.18 (s, 2H), 7.57 (t, 1H), 7.77 (t, 1H), 8.00 (d, 1H),
1
3
8.22 (d, 1H); C NMR δ: 15.98, 28.31, 32.12, 48.59, 54.86,
124.17, 125.54, 126.37, 127.64, 129.21, 131.45, 148.29,
149.69, 161.09, 200.69.
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Journal of the Iranian Chemical Society
General procedure for the synthesis
N‑((2‑Hydroxynaphthalen‑1‑yl)(2‑nitrophenyl)methyl)‑ben‑
zamide (7l) H NMR (400 MHz, DMSO) δ (ppm): 7.13
1
of 1‑amidoalkyl‑2‑naphthol derivatives
(
d,1H), 7.29 (t, 1H), 7.42–7.52 (m, 6H), 7.62 (t, 1H), 7.74–
1
3
In a typical procedure, a round-bottom ꢃask was charged
with 2-naphthol (1 mmol), aldehyde (1 mmol), amide
7.90 (m, 6H), 7.99 (d, 1H), 9.09 (d, 1H), 9.90 (s, 1H);
C
NMR δ: 47.20, 116.20, 119.10, 122.95, 124.63, 127.08,
128.11, 128.40, 128.71, 128.99, 129.81, 130.34, 131.82,
132.70, 133.56, 136.32, 149.53, 154.45, 166.43.
(
1.2 mmol) and DDBSA@MNP (0.15 g). The reaction
mixture was stirred at 80 °C till the completion of reac-
tion as monitored by TLC. After the completion of reac-
tion, hot water was added to the reaction mixture to remove
unreacted water-soluble starting materials. After that, solid
residue was dissolved in EtOH and catalyst was easily sepa-
rated through external magnet, washed with ethanol and
dried under vacuum to reuse in the next cycle. The solution
was concentrated to get crude residue and was puriꢂed by
recrystallization to aꢀord ꢂnal product. All the synthesized
compounds were characterized through their melting points,
N‑((2‑Hydroxynaphthalen‑1‑yl)(3‑nitrophenyl)methyl)‑ben‑
1
zamide (7m) H NMR (400 MHz, DMSO) δ (ppm): 7.27 (d,
2H), 7.33 (t, 1H), 7.41 (d, 3H), 7.49 (t, 2H), 7.73 (d, 1H),
7.84–7.92 (m, 4H), 8.11 (t, 3H) 9.16 (d, 1H), 10.40 (s, 1H);
1
3
C NMR δ: 49.43, 117.78, 119.10, 121.44, 122.11, 123.01,
127.51, 128.87, 129.22, 130.23, 130.47, 132.04, 132.69,
133.78, 134.50, 145.03, 148.28, 153.93, 166.72.
1
13
H and C NMR data and matched well with the reported
data. The spectral data for some selected compounds are
given in the following.
Results and discussion
Synthesis and characterization of DDBSA@MNP
N‑((2‑Hydroxynaphthalen‑1‑yl)(phenyl)methyl)acetamide
1
(
7a) H NMR (400 MHz, DMSO) δ (ppm): 1.98 (s, 3H),
Magnetite (Fe O ) nanoparticles-supported catalyst was
3
4
7
.12–7.36 (m, 9H), 7.76–7.82 (m, 3H), 8.45 (d, 1H), 10.00
prepared in a three-step procedure as shown in Scheme 3.
1
3
(
s, 1H); C NMR δ: 23.13, 48.28, 118.94, 119.32, 122.84,
Initially, Fe O nanoparticles were synthesized by a co-
3
4
1
1
23.77, 126.32, 126.75, 128.43, 128.92, 129.00, 129.68,
32.79, 143.09, 153.61, 169.67.
precipitation method, and then, it underwent surface coat-
ing with tetraethyl orthosilicate (TEOS) under alkaline
condition to acquire silica-coated magnetite nanoparticles
(SiO @Fe O ) in an almost quantitative yield. Synthesized
N‑((2‑Hydroxynaphthalen‑1‑yl)(phenyl)methyl)‑benzamide
2
3
4
1
(
7j) H NMR (400 MHz, DMSO) δ (ppm): 7.20–7.30 (m,
SiO @Fe O nanoparticles were used as solid support for
2 3 4
8
9
1
1
1
H), 7.49–7.55 (m, 4H), 7.79–7.88 (m, 4H), 8.10 (d, 1H),
the grafting of dodecylbenzenesulfonic acid (DDBSA). The
successful grafting was conꢂrmed through the appearance of
1
3
.02 (s, 1H), 10.34 (s, 1H); C NMR δ: 49.71, 109.11,
18.83, 119.17, 123.15, 126.56, 126.92, 127.01, 127.23,
27.61, 127.92, 128.66, 128.86, 128.98, 129.09, 129.75,
29.84, 131.90, 132.79, 134.82, 142.49, 153.66, 166.22.
−
1
the characteristic band around 1450 cm for S=O stretch-
−
1
ing and strong band around 2925 cm for C–H stretching
in FTIR spectrum and also supported by the presence of S
in EDX spectrum. The loading of DDBSA was determined
−
1
N‑((4‑Chlorophenyl)(2‑hydroxynaphthalen‑1‑yl)methyl)
through TG analysis and was found to be 0.56 mmol g .
The crystalline nature of the Fe O nanoparticles was
1
benzamide (7k) H NMR (400 MHz, DMSO) δ (ppm):
3
4
7
8
1
1
1
.25–7.36 (m, 7H), 7.46–7.57 (m, 4H), 7.80–7.89 (m, 4H),
identiꢂed with XRD (Fig. 1). The peak positions and rela-
tive intensities match well with XRD pattern of magnetite
nanoparticles in the literature (JCPDS card no. 01-1111)
[54]. The same characteristic peaks were observed in
the XRD pattern of SiO @Fe O and DDBSA@MNP,
13
.08 (d, 1H), 9.04 (d, 1H), 10.38 (s, 1H); C NMR δ: 49.25,
18.38, 119.15, 123.19, 127.32, 127.50, 128.01, 128.59,
28.82, 129.13, 130.15, 131.94, 132.72, 134.68, 141.58,
53.78, 166.37.
2
3
4
Scheme 3 Synthesis of DDBSA@MNP
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Journal of the Iranian Chemical Society
Transmission electron microscopy (TEM) was used to
check morphology of the catalyst. TEM images show the
core–shell structure of the catalyst with an average particle
size of ~16 nm (Fig. 2). The selected-area electron diꢀrac-
tion (SAED) pattern conꢂrms the polycrystalline nature of
the nanoparticles. The core–shell morphology of the dode-
cylbenzenesulfonic acid-coated magnetite nanoparticles was
corroborated by TEM images of DDBSA@MNP.
FTIR spectroscopy was used to conꢂrm the silica coating
and grafting of DDBSA on magnetite nanoparticles. FTIR
spectra of SiO @Fe O and DDBSA@MNP are shown in
2
3
4
Fig. 3. Both the spectra show broad bands around 3410 and
−
1
1
630 cm due to hydroxyl group of adsorbed water [55].
−1
Characteristic band of Fe–O bond observed around 580 cm
in both spectra conꢂrms the presence of magnetite core [56].
Silica coating on magnetite core shows a characteristic band
due to stretching and bending vibrations of Si–O–Si around
Fig. 1 XRD patterns of Fe O , SiO @Fe O and DDBSA@MNP
3
4
2
3
4
−
1
−1
1
100 cm , along with shoulder around 1200 and 460 cm
showing the crystallinity of both materials after function-
alization (Fig. 1). The particle size of the DDBSA@MNP
calculated using the Scherrer equation is 15.37 nm, which
is in accordance with the particle size obtained from the
TEM analysis.
[57]. The grafting of DDBSA was conꢂrmed through char-
−1
acteristic band for S=O around 1172 cm and band for C–H
−
1
stretching vibrations around 2855 and 2925 cm [58].
Surface morphology of the DDBSA@MNP was charac-
terized by the ꢂeld emission scanning electron microscopy
Fig. 2 a–c TEM images of as synthesized DDBSA@MNP, d, e TEM images of recycled catalyst and f SAED pattern of Fe O
3
4
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Journal of the Iranian Chemical Society
Fig. 3 FTIR spectra of SiO @
2
Fe O and DDBSA@MNP
3
4
(
FESEM) technique. FESEM images of DDBSA@MNP
of catalyst using ethanol as a solvent under reꢃux condi-
tion. The reaction was run for 6 h and ended with poor
yield of the corresponding ethyl 2-methyl-4-phenylquino-
line-3-carboxylate (Table 1, entry 1). Among the diꢀerent
amount of DDBSA@MNP screened, 0.15 g of catalyst
shows the best results under reꢃux condition with ethanol
(Table 1, entries 2–5). The eꢀect of solvent on reaction
was evaluated through utilizing diꢀerent organic solvents
and solvent-free reaction at 80 °C using optimum amount
of DDBSA@MNP (Table 1, entries 6–9). The obtained
results were suggested that the eꢁciency and the yield of
reaction in ethanol were much higher than other organic
solvents and solvent-free condition. The capability of
DDBSA@MNP catalyst is compared with reported cat-
alysts for the synthesis of 3a (Table 1, entries 10–14).
The present catalyst is found superior than some of the
reported catalysts in terms of facile catalyst recovery and
reusability, easy handling, mild reaction condition and
excellent isolated yields.
are depicted in Fig. 4. The images show rough surface due
to functionalization around core magnetite nanoparticles.
Additional information regarding chemical composition of
DDBSA@MNP was checked with energy-dispersive x-ray
(
EDX) spectroscopy. The EDX spectrum of the catalyst
shows the presence of C, O, Fe, Si and S (Fig. 4), which con-
ꢂrms the grafting of DDBSA on SiO @Fe O nanoparticles.
2
3
4
The thermal stability of the catalyst was investigated by
thermogravimetric (TG) analysis (Fig. 5). The curve indi-
cates an initial weight loss of 6.72% up to 100 °C, which
corresponds to the silanol groups and adsorbed water on
the support. Thermal degradation of the catalyst was
mainly occurred between 280 and 500 °C, due to degra-
dation of organic moiety. TG analysis revealed the excel-
lent stability of the catalyst and also suggests the loading of
−
1
0
.56 mmol g DDBSA on SiO @Fe O .
2 3 4
The magnetic property of the catalyst was checked
through vibrating sample magnetometry (VSM) analysis at
room temperature (Fig. 6). The magnetization of the catalyst
was found less compared to necked Fe O nanoparticles due
Generality and scope of the reaction were investigated
through utilization of substituted 2-aminoaryl ketones
and β-ketoester/ketone in the reaction under optimum
condition, and the results are depicted in Table 2. All the
reactions were monitored through TLC and yielded the
corresponding products with short reaction time. Plausi-
ble mechanism of DDBSA@MNP-catalyzed Friedlander
reaction is proposed (Scheme 4). It is anticipated that
catalyst activates the carbonyl carbon of 2-aminoaryl
ketone for the nucleophilic attack by active methylene of
β-ketoester/ketone to form a product of cross-aldol reac-
tion. The resultant β-hydroxy ketone loses water molecule
to generate α,β-unsaturated ketone, which upon cyclization
generates targeted quinoline derivative.
3
4
to silica coating and grafting of DDBSA. Nevertheless, it
was suꢁcient for magnetic decantation of the catalyst from
reaction mixture.
Catalytic eꢀciency of the DDBSA@MNP
for the synthesis of quinolines via Friedlander
reaction
The Friedlander reaction was performed to exploit the
catalytic performance of DDBSA@MNP. Reaction opti-
mization was commenced with the model reaction of
2
-aminobenzophenone and ethyl acetoacetate (Table 1).
Initially, the model reaction was performed in the absence
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Journal of the Iranian Chemical Society
Fig. 4 a, b FESEM images of DDBSA@MNP, c EDX spectrum of DDBSA@MNP
Fig. 5 TG analysis of DDBSA@MNP
Fig. 6 Magnetization curves of Fe O and DDBSA@MNP
3 4
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Journal of the Iranian Chemical Society
Table 1 Optimization of
the reaction condition for
the synthesis of quinoline
derivatives
Yield (%)a
–b
60
80
95
92
74
68
56
38
92 [59]
84 [60]
91 [61]
90 [62]
92 [63]
Entry
Catalyst (g)
Solvent
Temperature (°C)
Time (h)
1
2
3
4
5
6
7
8
9
0
1
2
3
4
No catalyst
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Water
Reꢃux
Reꢃux
Reꢃux
Reꢃux
Reꢃux
Reꢃux
Reꢃux
Reꢃux
80
Reꢃux
RT
100
55
50
6
6
5
3
3
6
6
6
DDBSA@MNP (0.05)
DDBSA@MNP (0.10)
DDBSA@MNP (0.15)
DDBSA@MNP (0.20)
DDBSA@MNP (0.15)
DDBSA@MNP (0.15)
DDBSA@MNP (0.15)
DDBSA@MNP (0.15)
APTPOL60
CH Cl
2
2
CHCl3
Solvent-free
Ethanol
6
1
1
1
1
1
24
19
0.75
24
2
HCl
Water
[Msim][OOCCCl3]
α-Chymotrypsin
DBSA
No solvent
[EMIM][BF4]
Water
Reaction condition: 2-aminobenzophenone (1 mmol) and ethyl acetoacetate (1.5 mmol)
a
Isolated yield
Poor yield
b
Table 2 Preparation of
substituted quinoline derivatives
using DDBSA@MNP as a
catalyst
Time (h) Yield (%)a Melting point (°C)
Found Reported
100–102 99–102 [64]
Product R1
R2
R3
3
3
3
3
3
3
3
3
3
3
3
a
b
c
d
e
f
g
h
i
C H CH3
CO C H
CO CH
COCH3
3
4
4
6
5
4
3
5
4
4
3
95
94
92
90
91
93
90
86
90
90
89
6
5
2
2
5
C H CH3
98–100 99–100 [65]
6
5
2
3
C H CH3
110–112 111–112 [64]
148–150 148–149 [66]
130–132 131–132 [66]
190–192 189–192 [67]
6
5
C H –(CH ) –
6
5
2 3
C H –(CH ) –
6
5
2 4
C H –(CH C(CH ) CH CO–
6
5
2
3 2
2
CH3 CH3
CH3 CH3
CH3 C H
CH3 –(CH2)4–
CH3 –(CH C(CH ) CH CO–
CO C H
COCH3
H
Oil
Oil
Oil
80–82
Oil [68]
Oil [68]
Oil [68]
78 [68]
2
2
5
6
5
j
k
106–108 104–106 [64]
2
3 2
2
aIsolated yield
Catalytic eꢀciency of the DDBSA@MNP
for the synthesis of 1‑amidoalkyl‑2‑naphthols
4). After that, the inꢃuence of temperature was taken into
consideration for the model reaction with 0.15 g catalyst
(
Table 3, entries 6–7). From the optimization, it was found
The catalytic eꢀectiveness of DDBSA@MNP was investi-
gated for the synthesis of 1-amidoalkyl-2-naphthol deriva-
tives. The condensation between 2-naphthol, benzaldehyde
and acetamide was chosen as the model reaction under sol-
vent-free condition (Table 3). In the beginning, the model
reaction was performed without catalyst at 80 °C, and even
after 60 min, no progress was observed in the reaction
that the model reaction at 80 °C aꢀorded a satisfactory yield
with shorter reaction time. The catalytic eꢁciency of the
present catalyst is compared with some recent reports for
the synthesis of 7a (Table 3, entries 8–12). The DDBSA@
MNP was found better as compared to some reported cata-
lysts concerning easy recovery of catalyst through magnetic
decantation, eꢁcient reusability of the catalyst, hassle-free
workup, shorter reaction time and higher yield.
(
Table 3, entry 1). The eꢀect of the catalyst loading was
tested through utilizing diꢀerent amounts of DDBSA@MNP
in the model reaction (Table 3, entries 2–5). Interestingly, it
was found that the catalyst accelerates the reaction and the
best result was obtained with 0.15 g catalyst (Table 3, entry
With this optimum condition in hand, general adapt-
ability of the catalyst was tested through its utilization for
the synthesis of diꢀerent 1-amidoalkyl-2-naphthol deriva-
tives. As shown in Table 4, the condensation between
1
3

Journal of the Iranian Chemical Society
Scheme 4 Plausible mechanism for the DDBSA@MNP-catalyzed synthesis of substituted quinolines
Table 3 Optimization of the reaction condition for the synthesis of
-amidoalkyl-2-naphthol derivatives
MNP-catalyzed synthesis of 1-amidoalkyl-2-naphthol deriv-
1
atives is shown in Scheme 5. Initially, the nucleophilic attack
of 2-naphthol on activated aldehyde to get an intermediate,
which upon removal of water molecule produce an ortho-
quinone methide intermediate. This on reaction with amide
via a Michael addition acquires the expected 1-amidoalkyl-
Tempera- Time (min) Yield (%)a
Entry Catalyst (g)
ture (°C)
1
2
3
4
5
6
7
8
9
1
1
1
No catalyst
80
60
30
18
12
12
15
12
25
180
15
35
45
NRb
64
82
91
90
86
91
75 [69]
80 [70]
83 [52]
90 [71]
87 [72]
DDBSA@MNP (0.05) 80
DDBSA@MNP (0.10) 80
DDBSA@MNP (0.15) 80
DDBSA@MNP (0.20) 80
DDBSA@MNP (0.15) 60
DDBSA@MNP (0.15) 100
2
-naphthol derivative.
Catalyst recovery and reusability
In order to design economic and ecological favorable meth-
odology, sustainability of the catalyst is an important factor.
Therefore, the recyclability of the catalyst was investigated
in both transformations through its utilization for the syn-
thesis of ethyl 2-methyl-4-phenylquinoline-3-carboxylate
and N-((2-hydroxynaphthalen-1-yl)(2-nitrophenyl)methyl)
acetamide. In both reactions, the catalyst could be eas-
ily separated from the reaction mixture through external
magnet after completion of reaction. The recovered cata-
lyst was washed three times with ethanol and dried under
vacuum to reuse in the subsequent reactions. As shown in
Fig. 7, the catalyst was found almost equally eꢁcient up
to ꢂve reaction cycles in both tested cases. The morphol-
ogy of the recovered catalyst was checked by TEM analysis
(Fig. 2). TEM images of the recovered catalyst conꢂrm that
2
−
[C (MPy) ] [CoCl ]
120
120
RT
6
2
4
PhB(OH)2
Tetrachlorosilane
RGO/CoFe O @Cu(II) 120
0
1
2
2
4
Ba (PO )
100
3
4 2
Reaction condition: 2-naphthol (1 mmol), benzaldehyde (1 mmol),
acetamide (1.2 mmol), solvent-free
a
Isolated yield
No reaction
b
substituted aldehydes, amides and 2-naphthol, proceeded
eꢁciently to achieve the corresponding products in excel-
lent isolated yield. The proposed mechanism for DDBSA@
1
3

Journal of the Iranian Chemical Society
Table 4 Preparation of
Yield (%)a
Product
R4
R5
Time (min)
Melting point (°C)
1
-amidoalkyl-2-naphthol
derivatives using DDBSA@
MNP as a catalyst
Found
Reported
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
C H –
CH3–
CH3–
CH3–
CH3–
CH3–
CH3–
NH2–
NH2–
NH2–
C H –
12
10
10
10
14
15
10
12
10
14
14
12
12
10
12
91
90
92
92
91
89
92
88
91
90
89
91
90
89
88
241–243
237–238
256–258
237–238
231–232
225–228
172–174
168–169
186–188
238–240
187–188
266–267
242–243
228–229
262–263
239–240 [73]
218–220 [74]
256–258 [74]
248–250 [73]
229–230 [75]
226–228 [76]
172–174 [50]
170–172 [77]
184–186 [50]
234–236 [75]
180–182 [75]
266–267 [74]
240–242 [78]
228–229 [74]
262–263 [74]
6
5
2-NO –C H –
3-NO –C H –
4-NO –C H –
4-Cl–C H –
2
6
4
2
6
4
2
6
4
6
4
2,4-Cl –C H –
2
6
3
C H –
6 5
4-Cl–C H –
3-NO –C H –
6
4
2
6
4
C H –
6
5
6
5
4-Cl–C H –
2-NO –C H –
3-NO –C H –
4-NO –C H –
C H –
6
4
6 5
C H –
6 5
2
6
4
C H –
2
6
4
6 5
C H –
6 5
2
6
4
2,4-Cl –C H –
C H –
2
6
3
6 5
aIsolated yield
Scheme 5 Plausible mecha-
nism for the DDBSA@
MNP-catalyzed synthesis of
1
-amidoalkyl-2-naphthols
DDBSA@MNP maintained its crystallinity and size after
ꢂve repeated catalytic cycles. To assess the leaching of the
dodecylbenzenesulfonic acid from the DDBSA@MNP dur-
ing the reaction, the solid catalyst was separated through
magnetic decantation from the reaction mixture at halfway
of the reaction. The reaction was continued in the absence of
the catalyst for appropriate time and monitored by TLC. No
further rise in the conversion was detected, which indicates
the no leaching of the grafted dodecylbenzenesulfonic acid
from the magnetite nanoparticles during reaction.
Conclusions
In conclusion, we have successfully synthesized dode-
cylbenzenesulfonic acid-grafted magnetite nanoparticles
(DDBSA@MNP) and exploited its catalytic eꢁciency
for the synthesis of substituted quinoline and 1-ami-
doalkyl-2-naphthol derivatives via one-pot condensation.
Importantly, the catalyst could be easily separated from
the reaction mixture through magnetic decantation and
1
3

Journal of the Iranian Chemical Society
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