Synthesis and characterization of polyvinylpyrrolidone immobilized on magnetic nanoparticles modified by ionic liquid as a novel and recyclable catalyst for the three-component synthesis of amidoalkyl naphthols

Article abstract of DOI:10.1002/aoc.5090

In this study, an efficient and green procedure is explained for the preparation of 1-amidoalkyl-2-naphthols applying one-pot condensation reaction of 2-naphthol, amide and aromatic nanoparticles (Fe₃O₄@SiO₂@IL-PVP) as a n

Full text of DOI:10.1002/aoc.5090

Received: 28 February 2019
DOI: 10.1002/aoc.5090
Revised: 16 May 2019
Accepted: 2 June 2019
F U L L P A P E R
Synthesis and characterization of polyvinylpyrrolidone
immobilized on magnetic nanoparticles modified by ionic
liquid as a novel and recyclable catalyst for the three‐
component synthesis of amidoalkyl naphthols
Shahla Vaysipour | Masoud Nasr‐Esfahani
| Zahra Rafiee
Department of Chemistry, Faculty of
In this study, an efficient and green procedure is explained for the preparation
of 1‐amidoalkyl‐2‐naphthols applying one‐pot condensation reaction of 2‐
naphthol, amide and aromatic nanoparticles (Fe3O4@SiO2@IL‐PVP) as a novel
solid acid catalyst under solvent‐free conditions. The remarkable features of
this method are short reaction time, high conversions, and high yield of prod-
uct, easy workup procedures and solvent‐free conditions. The
Fe3O4@SiO2@IL‐PVP catalyst was characterized via Fourier transform infrared
spectroscopy (FT‐IR), X‐ray diffraction patterns (XRD), scanning electron
microscopy (SEM), Transmission electron microscopy (TEM), thermal gravi-
metric analysis (TGA), vibrating sample magnetometer (VSM), and energy‐
dispersive X‐ray spectroscopy (EDS). Also, nanocatalysts could be easily recov-
ered by a simple magnet and reused for the next reactions without significant
loss of its catalytic activity.
Science, Yasouj University, Yasouj 75918‐
74831, Iran
Correspondence
Masoud Nasr‐Esfahani, Department of
Chemistry, Faculty of Science, Yasouj
University, Yasouj, 75918‐74831. Iran.
Email: manas@yu.ac.ir
Funding information
Yasouj University, Iran
KEYWORDS
Amidoalkyl naphthols, ionic liquid, magnetic nanoparticles, Polyvinylpyrrolidone, solvent‐free
1 | INTRODUCTION
than 100 nanometers in a proper range.[4] Also, the use
of magnetic nanoparticles in many scientific fields has
The tendency towards magnetic field by magnetic nano-
particles in organic synthesis and industrial production
of materials is important because of their high surface
area and unique magnetic properties. Furthermore,
recent studies show that magnetic nanoparticles (MNPs)
are excellent supports for ILs because of their good ther-
mal stability, easy synthesis and functionalization, high
surface area, low toxicity and price,[1,2] due to the facility
of separation from the reaction mixture using an external
magnet, also to the fact that such types of systems
possess high potential active sites for loading of other
functional groups, it would be suitable to use magnetic
attracted the attention of many scientists, such as mag-
netic fluids, catalysis, biology and medical applications,
magnetic resonance imaging (MRI), data storage and
environmental remediation.[5–13]
Beyond their simple use as substitute reaction, ionic
liquids have received considerable attachment as eco‐
friendly solvents, catalysts, and reagents in organic syn-
thesis. Ionic liquids (ILs) or room‐temperature molten
salts, which are called green solvents because of their
unique properties, such as low volatility, high electrical
conductivity, non‐flammability, thermal stability, con-
trolled miscibility, partial steam pressure, excellent salva-
tion properties, and structure‐tunability, it replaces the
compounds with organic solvents that do not have such
nanoparticles.[3]
superparamagnetic characteristics when their size is less
Fe3O4
nanoparticles
display
Appl Organometal Chem. 2019;e5090.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5090

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VAYSIPOUR ET AL.
properties.[14–16] Although ionic liquids (ILs) have
promising benefits, their extensive practical application
was hampered by several disadvantages such as high vis-
cosity, which resulted in only a small section of ILs taking
in the catalyzed reaction for chemical production, homo-
geneous reaction, which was difficult for dissociation and
reuse methods, As a result high cost for the use of rela-
tively large amounts of ILs as opposed to economic
criteria.[17,18]
Polyvinylpyrrolidone (PVP) is of excellent industrial
importance.[19] PVP is usually prepared by solution
polymerization of N‐vinylpyrrolidone (NVP) that is a
synthetic polymer and amphiphilic that can well be dis-
solved in a wide range of organic solvents and water.[20]
From a chemical outlook, it is a polymer lactam with
an internal amide bond and ranks amongst poly‐N‐
vinylamides. According to the monomer unit structure,
PVP shows an amphoteric characteristic, due to it con-
taining a high polar amide group and non‐polar methy-
lene groups in its main chain and ring, which exhibits
its hydrophilic and polar properties and hydrophobic
properties, respectively. PVP is used in the manufactur-
ing of textiles, paper, adhesives, membranes, plastics,
cosmetics, pharmaceutical products, and food indus-
tries.[21–24]
Herein, to further develop magnetic nanoparticles sup-
ported ionic liquids in polymer immobilization; we pre-
pared magnetic nanoparticles supported ionic liquids
with a modified way and developed their application in
PVP immobilization. ILs were loaded on the surface of
magnetic silica nanoparticles (MNPs) through chemical
bonds formed by the reaction between methoxy groups
on ILs and silanol groups on MNPs surface.[25] PVP was
immobilized onto the magnetic supports via physical
adsorption. The development and improvement of eco‐
friendly reactions is the most important task in the con-
temporary chemistry and chemical industry. The use of
heterogeneous catalysts and solvent‐free reactions have
many advantages such as their non‐toxicity, low costs, sim-
plicity in the process, ease handling of catalyst, cleaner
reactions, easier work up, decreasing corrosive problems,
reduced reaction times, reusability and environmentally
benign nature evoked extensive research interest.[26,27]
Multicomponent reactions (MCRs) have attracted consid-
erable attention since they are performed without isolating
the intermediates during their processes; this reduces the
time and saves both energy and raw materials.[28] They
have competences over two‐component reactions in sev-
eral respects including the facility of a one‐pot procedure,
possible structural changes, and construction of complex
molecules by the formation of several bonds in a one‐pot
process without the addition of more reagents.[29] The syn-
thesis of amidoalkyl naphthol derivatives is the attractive
sample of these MCRs. These 1‐amidoalkyl‐2‐naphthols
are of a certain value because of their promising biological
and pharmacological activities.[30,31] The synthesis of 1‐
amidoalkyl‐2‐naphthols can be accomplished using con-
densation of aldehydes, amides, and β‐naphthol in the
presence of various catalysts such as AIL@MNP,[30]
montmorillonite K‐10 clay,[32] Fe3O4@SiO2@PMA,[33]
K5CoW12O40.3H2O,[34] Ce (SO4)2,[35] silica sulfuric acid,[36]
sulfamic acid,[37] SiO2‐HClO4,[38] NiFe2O4@SiO2–PPA,[39]
MCM‐41‐SO3H,[40] Fe3O4‐CNTs,[41] POCl3/Na2B4O7,[42]
polyphosphate ester,[43] MNPs‐PhSO3H,[44] p‐TSA,[45]
polymer‐supported
sulphonic
acid,[46]
ionic
liquids,[29,33,47–49] heteropoly acid,[50] PPA‐SiO2,[51]
NaHSO4.SiO2,[52] ZrO (OTf)2,[53] NiO‐SnO2 composite
nano‐powder,[54] SnCl4.5H2O,[55] nano‐sulfated zirco-
nia,[56] dodecylphosphonic acid,[57] ferric hydrogen sul-
fate[58] and Bi (NO3)3.5H2O.[59]
However, these methods each have some defects, such
as low product yield, high reaction temperature,
prolonged reaction times, the use of toxic solvents, and
harsh reaction conditions. Therefore, the purpose of this
protocol is to introduce a new catalyst for the synthesis
of 1‐amidoalkyl‐2‐naphthols that can be easily separated
and reused and does not become infected through the
products (Scheme 1).
2 | EXPERIMENTAL
2.1 | Methods and materials
Chemical reagents in high purity were purchased from
Merck and Aldrich chemical companies. All materials
were of commercial reagent grade the produced products
were identified by comparing their spectral data and
melting points to their reported data in the literature.
Purity determinations of the products were accomplished
by TLC on silica‐gel Polygram SILG/UV 254 plates. Melt-
ing points were determined using an Electrothermal
SCHEME 1 One‐pot synthesis of
amidoalkyl naphthol in the presence
Fe3O4@SiO2@IL‐PVP

VAYSIPOUR ET AL.
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KSB1N apparatus and are correct. 1H NMR was measured
on a Bruker Advance UltraShield 400 MHz instrument
spectrometer and 13C NMR spectra were measured at
100 MHz. IR spectra were obtained using a Fourier trans-
form JASCO FT‐IR/680 spectrometer instrument using
KBr discs. Nanostructure catalysts were characterized
using an X‐ray powder diffraction (XRD) patterns were
recorded using a Bruker AXS (D8 Advance) X‐ray diffrac-
tometer with Cu Ka radiation (λ = 0.15406 nm). Energy
dispersive spectroscopy (EDS) was obtained using the
EDS Sirius SD model instrument. The magnetic measure-
ment was carried out in a vibrating sample magnetometer
(VSM LBKFB Model‐Maghnatis Daghigh Kavir Com-
pany) at room temperature. The shape and surface mor-
phology of the samples were examined on a scanning
electron microscope (SEM) images were recorded using
an EM3200 operated at a 14.1 KV acceleration voltage.
Transmission electron microscopy (TEM) analysis was
performed using a Zeiss‐EM10C microscope at 100 KV.
The thermal stability was determined by thermogravimet-
ric analysis (STA 6000 Perkin Elmer). The TGA thermo-
grams were recorded for 5 mg of a powder sample at a
heating rate of 20 °C/min in the temperature range 30–
800 °C, under a nitrogen atmosphere.
The solid was washed with ethanol and deionized water
three times and dried at 80 °C for 10 hr.[61]
2.4 | Synthesis of 1‐methyl‐3‐(3‐
trimethoxysilylpropyl)‐1H‐imidazole‐3‐ium
chloride (IL)
A mixture of 1‐methylimidazole (1.26 ml, 15.86 mmol)
and (3‐chloropropyl) trimethoxysilane (3.82 ml,
15.86 mmol) was refluxed at 80 °C for three days in the
solvent‐free condition and absence of any catalyst under
Ar atmosphere. The resulting viscous yellowish liquid
was washed with diethyl ether (3 × 5 ml) to remove any
unreacted material. The reaction product was dried under
high vacuum.[62]
2.5 | General procedure for the
preparation of 1‐methyl‐3‐(3‐
trimethoxysilylpropyl)‐1H‐imidazole‐3‐ium
chloride functionalized magnetic
nanoparticles (Fe3O4@SiO2@IL)
2.2 | Synthesis of magnetic Fe3O4
nanoparticles (MNPs)
In a typical procedure, Fe3O4@SiO2 nanoparticles (0.1 g)
were dispersed in toluene (20 ml) by ultrasonication for
10 min afterward, 1 g of the as‐prepared ionic liquid
was to the solution and the mixture was stirred under
reflux condition at 85 °C for 24 hr under argon atmo-
sphere. Finally, the obtained product (Fe3O4@SiO2@IL)
was separated by a magnet, washed three times with
acetonitrile and ethanol, and then dried at 60 °C in the
vacuum oven.[63]
A solution of FeCl3.6H2O (2.7 g, 10 mmol) and
FeCl2.4H2O (1 g, 5 mmol) in 50 ml double distilled water
in a three‐necked bottom (250 mL) was mechanically
stirred under an argon atmosphere at 80 °C for 30 min.
Subsequently, the ammonium hydroxide solution
(10 ml, 25%) was added dropwise with vigorous stirring
to make a black solid product. After continuous stirring
at 80 °C for 1 hr under an argon atmosphere, the black
precipitate of Fe3O4 magnetic nanoparticles was decanted
using an external magnetic field and washed three times
with deionized water and ethanol to remove the remain-
ing impurities and dried at 60 °C for 10 hr.[60]
2.6 | Procedure for the synthesis
polyvinylpyrrolidone (PVP) immobilized
magnetic nanoparticles (Fe3O4@SiO2@IL‐
PVP)
2.3 | Procedure for the synthesis of
Fe3O4@SiO2 nanoparticles
The preparation of Fe3O4@SiO2@IL‐PVP was carried out
as mentioned following. 0.25 g of polyvinylpyrrolidone
and 20 ml ethanol were mixed together in a beaker was
dispersed into the mixture by ultra‐sonication for
30 min. Then, 0.1 g of (Fe3O4@SiO2@IL) nanoparticles
was added to the mixture. The resulting mixture was son-
icated for 4 hr and then the solid product was magnetic
separated and washed with ethanol. Lastly, the resulting
PVP impregnated Fe3O4@SiO2@IL was dried under
vacuum at 60 °C and use for further studies.
Fe3O4 magnetic nanoparticles (0.50 g) was dispersed in
the mixture of deionized water (20 ml) and ethanol
(80 ml) for 15 min, then 3.0 ml of 28 wt% concentrated
ammonia aqueous solution, followed by the dropwise
addition of 0.5 ml of tetraethylorthosilicate (TEOS).
This solution was stirred mechanically for 24 hr under
reflux condition, and finally the Fe3O4‐silica coated
(Fe3O4@SiO2) was separated by an external magnet.

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VAYSIPOUR ET AL.
1627, 1604, 1562, 1535, 1469,1442, 1346, 1272, 1238,
1176, 821, 752; H NMR (400 MHz, DMSO‐d6) δ (ppm):
2.7 | General procedure for the synthesis
of amidoalkyl naphthol derivatives
1
6.81 (d, 1H, J = 3.6 Hz, CH),7.32 (d, 3H, J = 15.0 Hz,
Ar‐H), 7.54 (d, 6H, J = 12.6 Hz, Ar‐H), 7.76–7.89 (m,
4H, Ar‐H), 8.28 (d,1H, J = 3.6 Hz, Ar‐H), 8.95 (s, 1H,
NH), 10.01 (brs, 1H, OH), 10.24 (brs, 1H, OH); 13C
NMR (100 MHz, DMSO‐d6) δ (ppm): 54.93, 110.25,
117.78, 118.67, 119.30, 123.05, 123.55, 126.79, 127.75,
128.75, 128.85, 128.92, 129.60, 130.94, 131.01, 131.76,
132.03, 133.03, 134.85, 153.78, 154.68, 165.74.
In a round‐bottom flask, a mixture of aldehydes (1 mmol),
β‐naphthol (1 mmol) and amides (1.2 mmol),
Fe3O4@SiO2@IL‐PVP (0.015 g) was added. The reaction
mixture was magnetically stirred on a preheated oil bath
at 80 °C under the solvent‐free condition for an appropri-
ate time. The reaction was monitored by thin‐layer chro-
matography (n‐hexane: EtOAc, 3:1). After completion of
the reaction, the mixture was cooled to room tempera-
ture, and then the solid residue was dissolved in hot
ethanol (5 ml). The mixture stirred for 5 min and the
catalyst was separated by an external magnet. The
catalyst was washed four times with ethyl acetate
(4 × 5 ml), and then recovered catalyst was dried in an
oven and reused for subsequent runs. The solvent was
then evaporated and the crude products were recrystal-
lized in ethanol to give pure products. The following is
the physical and spectral data of the new compound.
3 | RESULTS AND DISCUSSION
3.1 | Characterization of the prepared
Fe3O4@SiO2@IL‐PVP
Scheme 2 comprehensively shows a procedure for the
preparation of Fe3O4@SiO2@IL‐PVP. The bare Fe3O4
nanoparticles were easily prepared via the chemical co‐
precipitation method of two different salts of iron (Fe2+
and Fe3+ ions) in basic solution. The concentration ratio
of Fe2+/Fe3+ was 1:2, and the experiment was carried
N‐[5‐Bromo‐2‐hydroxyphenyl)
(2‐
hydroxynaphthalene‐1‐yl) methyl] benzamide (4 m).
Mp: 225–228 °C; R f = 0.42 (n‐hexane: ethyl acetate,
3:1); FT‐IR (KBr) Vmax cm−1: 3378, 3232, 3066, 2981,
out under argon gas to prevent Fe2+ oxidation to Fe3+
.
SCHEME 2 Synthesis of magnetic silica nanoparticles modified by ionic liquids and immobilizationof polyvinylpyrrolidone (PVP)

VAYSIPOUR ET AL.
5 of 11
The magnetic nanoparticles produced by this method had
considerable numbers of hydroxyl groups on the surface.
The MNPs are easily coated with amorphous silica using
the conventional sol–gel method. The sol–gel process is
based on the hydrolysis of TEOS, and subsequent conden-
sation of hydrolyzed TEOS on surface iron hydroxyls and
this prevented the agglomeration of the Fe3O4 nanoparti-
cles. 1‐Methyl‐3‐(3‐trimethoxysilylpropyl) imidazolium
chloride (IL), was prepared from the reaction of N‐methyl
imidazole with (3‐chloropropyl) trimethoxysilane at
80 °C. Then, the ionic liquid was immobilized on the sur-
face of Fe3O4@SiO2 nanoparticles through the covalent
bond between the hydroxyl groups on the surface of
Fe3O4@SiO2 and organosilane group of the ionic
liquid.[62] finally; the external surface of Fe3O4@SiO2@IL
was coated with polyvinylpyrrolidone to obtain
MNPs@SiO2@IL‐PVP. Chemical analysis of prepared
Fe3O4@SiO2@IL‐PVP was performed by using FT‐IR,
EDX, XRD, SEM, TEM and TGA. The magnetic measure-
ments were performed by using VSM.
FT‐IR spectra proved that ionic liquid is immobilized on
the surface of Fe3O4@SiO2 nanoparticles through cova-
lent bond between the hydroxyl groups on the surface
of Fe3O4@SiO2 and organosilane group of ionic liquid. In
Figure 1d, the absorbent peak at 1662 cm−1 belongs to
C=O group of N‐vinylpyrrolidone stretching and bending
vibrations of the CH2 group of N‐vinylpyrrolidone are
appeared at 2958 and 1434 cm−1, respectively. The absor-
bent peak centered at 1288 cm−1 is due to C‐N stretching
vibration of N‐vinylpyrrolidone. Overall, these FT‐IR
spectra indicated that polyvinylpyrrolidone polymer
chains were successfully attached to the surface of
Fe3O4@SiO2@IL nanoparticles.
The crystalline phase analysis of the as‐synthesized
powder was performed by XRD, and the diffraction pat-
tern is presented in Figure 2. The XRD patterns of the
particles show six characteristic peaks reveal a cubic iron
oxide phrase in the 2θ range of 5–90° are diagnosed at
30.2°, 35.5°, 43.2°, 53.6°, 57°, and 62.4°. These are related
to their corresponding indices (220), (311), (400), (422),
(511), and (440) respectively. The mentioned indexes
reveal that the catalyst has a similar structure to Fe3O4
nanoparticles. The appearance of an obvious broad peak
at 2θ = 10–16° in XRD pattern of the catalyst can be
attributed to the presence of amorphous silica around
the magnetic Fe3O4 nanoparticles. Hence, this shows that
no phase change was observed after surface modification
of the magnetite nanoparticles and they retained their
crystalline structure.
Figure
1 shows the FT‐IR spectra of Fe3O4,
Fe3O4@SiO2, Fe3O4@SiO2@IL, Fe3O4@SiO2@IL‐PVP
and PVP. The presence of characteristic peaks corre-
sponding to Fe‐O stretching vibration near 580 cm−1 in
all compared spectra is a confirmation of how nanostruc-
ture of Fe3O4 is preserved throughout the process. Bonds
at 3419 and 1646 cm−1 represent the stretching and bend-
ing vibrations of OH on the surface of Fe3O4, respectively
(Figure 1a). Three additional bands were present around
806, 1099 and 3417 cm−1 for the Fe3O4@SiO2 nanoparti-
cles (Figure 1b). These bands result from symmetric and
asymmetric stretching vibrations Si‐O‐Si and O‐H
stretching vibration respectively, which indicated
that SiO2 had been successfully loaded on the surface
of Fe3O4. In the FT‐IR spectrum of ionic liquid‐
functionalized silica‐coated Fe3O4 NPs (Figure 1c), the
relatively weak peaks at 2944, 2843 and 1637 cm−1 repre-
sent the stretching vibrations of CH3, CH2 groups, and
C=N stretching respectively, present in the ionic liquid,
Energy‐dispersive X‐ray spectroscopy (EDS) is often
used to provide useful information on the elements that
make up of the Fe3O4@SiO2@IL‐PVP nanoparticles.
EDX spectra of the Fe3O4@SiO2@IL‐PVP shown in
Figure 3 clearly indicate the presence of Iron, Oxygen,
Silicon, Nitrogen, Carbon, and Chloride. The structural
and morphological characterization of Fe3O4@SiO2@IL‐
PVP nanostructure was performed by scanning electron
microscope (SEM) (Figure 4). From the SEM picture, it
FIGURE 1 The FT‐IR spectra of (a) Fe3O4, (b) Fe3O4@SiO2, (c)
Fe3O4@SiO2@IL, and (d) Fe3O4@SiO2@IL‐PVP
FIGURE 2 XRD patterns of Fe3O4@SiO2@IL‐PVP

6 of 11
VAYSIPOUR ET AL.
nano‐Fe3O4 core surrounded by a gray silica shell
thickness.
The vibrating‐sample magnetometer (VSM) technique
was applied for studying the magnetic property of the cat-
alyst as shown in Figure 6. The room temperature magne-
tization curves proved that the Fe3O4@SiO2@IL‐PVP is
super‐paramagnetic. As it is expected, immobilizing the
sequential layers on the Fe3O4 nanoparticles reduced
the magnetic saturation values from 58.9 emu g−1 in
FIGURE 3 Energy‐dispersive X‐ray spectroscopy (EDS) spectra
of Fe3O4@SiO2@IL‐PVP
FIGURE
6
Room‐temperature magnetization curve of
Fe3O4@SiO2@IL‐PVP
FIGURE 4 The SEM image of Fe3O4@SiO2@IL‐PVP
was found that particles are roughly spherical in nature.
The transmission electron microscopy (TEM) image of
Fe3O4@SiO2@IL‐PVP is presented in Figure 5. From
TEM analysis, it was found that the size of particles is
ranging from 50–70 nm. Also, TEM analysis shows a dark
FIGURE 5 The transmission electron microscopy (TEM) image
of Fe3O4@SiO2@IL‐PVP
FIGURE 7 TGA thermograms of (a) Fe3O4@SiO2@IL, and
Fe3O4@SiO2@IL‐PVP

VAYSIPOUR ET AL.
7 of 11
Fe3O4 nanoparticles to 9.57 emu g−1. Therefore, the
Fe3O4@SiO2@IL‐PVP MNPs prepared here could be
rapidly separated from the solution with a permanent
magnet even with this reduction in the saturation Magne-
tization. This difference suggests that Fe3O4@SiO2@IL
stabilized on polyvinylpyrrolidone.
groups. In the second stage of thermal decomposition,
the catalyst loses about 20% from 250 to 370 °C its weight
assigned to the decomposition of PVP. While the other
stage beginning at about 480 to 600 °C was due to the
decomposition of catalyst structure may be attributed to
the removal of the organic group. Thus, the catalyst was
stable up to 250 °C, confirming that it could be safely
used in organic reactions at temperatures in the range
of 200 °C.
Thermogravimetric analysis (TGA) revealed the
weight loss process of the organic materials as they
decompose upon heating and thermal stability, which
indicated the difference between the Fe3O4@SiO2@IL
and Fe3O4@SiO2@IL‐PVP. In this paper, TGA was con-
ducted in a nitrogen atmosphere, and the heating rate
employed was 20 °C min−1 all cases from 30 to 800 °C.
The TGA curve of the Fe3O4@SiO2@IL showed two
decreasing peaks. The first peak appears at the tempera-
ture below 140 °C due to desorption of water molecules
from the catalyst surface. This is followed by a second
peak at 380–620 °C, corresponding to the decomposition
of organic materials. This observation shows that the
ILs had been located on the surface of Fe3O4@SiO2
(Figure 7a). As shown in Figure 7b, for the
Fe3O4@SiO2@IL‐PVP first weight loss stage (below
100 °C) can be ascribed to the evaporation of water mol-
ecules in the polymer matrix and surface hydroxyl
3.2 | Evaluation of the catalytic activity of
Fe3O4@SiO2@IL‐PVP through the synthesis
of amidoalkyl naphthols
After identifying the solid acid catalyst, we have tested its
catalytic activity in the preparation of amidoalkyl naph-
thol derivatives. The effects of reaction parameters such
as the role of the reaction temperature, solvent, and
amount of catalyst were investigated to optimize the reac-
tion conditions (Table 1). The solvents played a great role
in amidoalkyl naphthols synthesis. To optimize the reac-
tion conditions, the reaction was accomplished using dif-
ferent solvents (Table 1, entries 6–10) or solvent‐free
TABLE 1 Optimization of the amount of catalyst, solvent and the reaction temperature for the synthesis of N‐[(2‐hydroxynaphthalen‐1‐yl)
(phenyl) methyl] benzamide
Entry
Catalyst (g)
Solvent
Temperature (°C)
Time
Yielda (%)
1
‐
‐
80
8 hr
23
70
83
95
91
38
20
13
<10
15
28
50
69
83
88
2
0.005
0.01
‐
80
55 min
25 min
15 min
13 min
6 hr
3
‐
80
4
0.015
0.02
‐
80
5
‐
80
6
0.015
0.015
0.015
0.015
0.015
0.015
0.015
0.015
0.015
0.015
H2O
Reflux
Reflux
Reflux
Reflux
Reflux
25
7
EtOH
6 hr
8
CH3CN
6 hr
9
CH2Cl2
6 hr
10
11
12
13
14
15
EtOAC
6 hr
‐
‐
‐
‐
‐
150 min
93 min
61 min
40 min
15 min
40
60
70
100
aIsolated yield.

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VAYSIPOUR ET AL.
condition (Table 1, entries 1–5 and 11–15) using the
model reaction of β‐naphthol, benzamide, and benzalde-
hyde. Based on the results, it was found that solvent‐free
is the best conditions of the reaction in terms of reaction
times and yields (Table 1, entry 4). Thereafter, the effect
of catalyst amount on the reaction was investigated. For
TABLE 2 Synthesis of amidoalkyl naphthols in the presence of Fe3O4@SiO2@IL‐PVP under thermal solvent‐free conditionsa
Entry
Ar
Product
R
Time (min)
Yieldsb(%)
Mpc(°C)
1
C6H5
4a
4b
4c
Ph
15
18
45
60
20
55
35
40
45
35
25
45
30
40
17
30
35
25
95
91
88
84
82
81
92
85
86
89
92
85
82
85
94
90
89
91
233–235
186–188
227–230
257–260
175–177
207–209
261–263
183–185
206–208
228–230
264–266
223–225
225–228
220–222
248–250
231–233
246–249
221–224
2
4‐Cl C6H4
Ph
3
2‐OH C6H4
3‐OH C6H4
4‐CN C6H4
4‐OMe C6H4
2,4‐Cl C6H4
4‐Br C6H4
Ph
4
4d
4e
Ph
5
Ph
6
4f
Ph
7
4 g
4 h
4i
Ph
8
Ph
9
4‐Me C6H4
4‐NO2 C6H4
2‐NO2 C6H4
3‐OEt‐4‐OH C6H4
5‐Br‐2‐OH C6H4
3‐OMe‐4‐OH C6H4
C6H5
Ph
10
11
12
13
14
15
16
17
18
4j
Ph
4 k
4 l
4 m
4n
4o
4p
4q
4r
Ph
Ph
Ph
Ph
CH3
CH3
CH3
CH3
2,4‐Cl C6H4
4‐NO2 C6H4
5‐Br‐2‐OH C6H
aReaction conditions:aldehyde = 1 mmol; 2‐naphthol = 1 mmol; amide = 1.2 mmol; Fe3O4@SiO2@IL‐PVP=0.015g
bIsolated yield.
cMelting points are uncorrected.
SCHEME 3 Suggested mechanism for
the synthesis of amidoalkyl naphthol
derivatives via Fe3O4@SiO2@IL‐PVP

VAYSIPOUR ET AL.
9 of 11
this purpose, a typical reaction without any catalyst was
carried out. It was found that only an insignificant
amount of product was obtained in the absence of
the catalyst even after prolonged reaction time (8 hr).
reactive molecules was investigated for the amidoalkyl
naphthol formation. The highest yield of 95% is obtained
with low reaction time at a molar ratio of 1:1:1.2 of benz-
aldehyde, β‐naphthol, and benzamide, respectively. After
studying the effect of different reaction parameters, we
continued the reaction for the synthesis of a wide variety
of substituted 1‐amidoalkyl‐2‐naphthols. The results are
shown in Table 2.
In all cases, the corresponding 1‐amidoalkyl‐2‐
naphthols were gained in good to excellent yields
without the formation of any side products such as
dibenzoxanthenes, which are normally observed under
the influence of strong acids.[42] Another possibility is
the quantitative formation of dibenzoxanthenes when β‐
naphthol is used with an aldehyde in 2:1 molar ratio.
However, the use of 1:1 mol ratio of β‐naphthol and alde-
hyde with amides in the presence of nanocatalyst
Fe3O4@SiO2@IL‐PVP solely resulted in amidoalkyl
naphthols.[45] Aromatic aldehydes in the reaction with
benzamide as an aromatic amide and β‐naphthol led to
good yields of the desired 1‐amidoalkyl‐2‐naphthols
(Table 2, Entries 1–14). Using acetamide as an aliphatic
amide, instead of benzamide, resulted in the correspond-
ing 1‐amidoalkyl‐2‐naphthols in good yields when it was
treated with β ‐naphthol and aldehydes in the presence of
Fe3O4@SiO2@IL‐PVP.
A
quantitatively increase in catalyst amount of
Fe3O4@SiO2@IL‐PVP from 0.005 to 0.015 g increased
the reaction yield from 70 to 95% (Table 2, entries 2–4).
The results showed that 0.015 g of catalyst led to the best
yield in the shortest time. A further increase in the cata-
lyst (0.02 g) causes the reaction performed at short times
(13 min) but reduces the yield of the product (Table 1,
entry 2). After optimization of catalyst amount and
solvent, the effect of temperature was investigated. The
reaction has been studied at various temperatures from
25 to 100 °C. The yield of the product increases with
increase in temperature up to 80 °C. Further increase in
temperature resulted in a slight decrease in the yield of
product, which may due to the unwanted side reactions
at the higher temperature (Table 1, entry 15). In continu-
ation of this study, the effect of the molar ratio of the
Aromatic aldehydes containing either electron‐
donating or withdrawing groups reacted successfully
and gave the desired products in good to excellent yields
without the formation of any side products such as
dibenzoxanthenes. However, as it is reported,[34–36] using
aromatic aldehydes with electron‐withdrawing groups as
reactive for the synthesis of amidoalkyl naphthols the
reaction time was shorter than those with electron‐
donating groups. The reactions of aliphatic aldehydes
FIGURE 8 Catalys Recovery and reusability in the reaction
between benzaldehyde, 2‐napththol and benzamide
TABLE 3 Comparison of Fe3O4@SiO2@IL‐PVP with other catalysts reported in the literature for the synthesis of amidoalkyl naphthols
Entry
Catalyst
Conditions
Time
Yield (%)
References
1
Montmorillonite K10 Clay
p‐TSA
Solvent free/125 °C
Solvent‐free/125 °C
Solvent‐free ultrasonic/28 °C
Solvent‐free/120 °C
Solvent‐free/125 °C
CH3CN reflux/125 °C
Solvent‐free/110 °C
Solvent‐free/r.t
1.5 hr
5 hr
89
88
89
81
90
72
89
85
89
91
90
91
[32]
[45]
2
[37]
[44]
[34]
[35]
[38]
[36]
3
Sulfamic acid
15 min
40 min
2 hr
4
MNPs‐PhSO3H
K5CoW12O40.3H2O
Ce (SO4)2
5
6
36 hr
7
SiO2‐HClO4
40 min
2 hr
8
silica sulfuric acid
Fe3O4@SiO2@PMA
polyphosphate ester
POCl3/Na2B4O7
Fe3O4@SiO2@IL‐PVP
9
Solvent‐free/100 °C
Solvent‐free/80 °C
Solvent‐free/120 °C
Solvent‐free/80 °C
40 min
15 min
30 min
15 min
[33]
10
11
12
[43]
[42]
Present study

10 of 11
VAYSIPOUR ET AL.
instead of aromatic aldehydes were also examined, but
they would fail to give the desired products even after
24 hrs, probably because of less stability of an o‐QM inter-
mediate from aliphatic aldehydes. In Scheme 3, we pro-
of this method are operational simplicity, short reaction
time, excellent yields, simple work‐up procedure, ease of
separation, and recyclability of the magnetic catalyst by
an external magnet.
pose
a possible mechanism for the formation of
amidoalkyl naphthol derivatives in the presence of
Fe3O4@SiO2@IL‐PVP as the catalyst. In the first stage,
the proton catalyst communicates with the oxygen atom
of the carbonyl group of the aldehydes probably through
the hydrogen bond formation, as a result increasing the
electrophilic character of the carbonyl group of the alde-
hyde.[63] Then, reaction with 2‐naphthol to give ortho‐
quinone methides (o‐QMs). The same in situ generated
o‐QMs have been reacted with amide to form amidoalkyl
naphthol derivatives. A reasonable explanation for this
result can be given by considering the addition to o‐
QMs intermediate favorable via conjugate addition on
the β‐unsaturated carbonyl group and finally this inter-
mediate will aromatize to produce the final aromatic
compound. The electron‐withdrawing groups substituted
on benzaldehyde in o‐QM intermediate increase the rate
of 1,4‐addition reaction because of alkene LUMO (a car-
bonyl group as in o‐QM intermediate), which is at the
lower energy in the neighboring withdrawing groups
compared to that of alkene containing electron‐donating
groups.[55,64–67]
ACKNOWLEDGEMENTS
We gratefully acknowledge the partial support of this
work by Yasouj University, Iran.
ORCID
Masoud Nasr‐Esfahani
https://orcid.org/0000-0001-5823-
4254
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