Preparation and characterization of Fe3O4@SiO 2@PMA:AS an efficient and recyclable nanocatalyst for the synthesis of 1-amidoalkyl-2-naphthols

Article abstract of DOI:10.1016/j.materresbull.2014.04.019

In this paper, we report a method for preparation of functionalized superparamagnetic Fe₃O₄@SiO₂ that is synthesized based on several stages. First of all, the Fe₃O ₄@SiO₂ nanosphere core-s

Full text of DOI:10.1016/j.materresbull.2014.04.019

Accepted Manuscript
Title: Preparation and characterization of
Fe3O4@SiO2@PMA: AS an efficient and recyclable
nanocatalyst for the synthesis of 1-amidoalkyl-2-naphthols
Author: Esmaeilpour Mohsen Javidi Jaber Zandi Maryam
PII:
S0025-5408(14)00201-3
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.materresbull.2014.04.019
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25-12-2013
7-4-2014
8-4-2014
Please cite this article as: Esmaeilpour Mohsen, Javidi Jaber, Zandi Maryam,
Preparation and characterization of Fe3O4@SiO2@PMA: AS an efficient and
recyclable nanocatalyst for the synthesis of 1-amidoalkyl-2-naphthols, Materials
Research Bulletin http://dx.doi.org/10.1016/j.materresbull.2014.04.019
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Preparation and characterization of Fe3O4@SiO2@PMA: AS an
efficient and recyclable nanocatalyst for the synthesis of 1-
amidoalkyl-2-naphthols
Esmaeilpour Mohsen(1), Javidi Jaber(2)* Zandi Maryam(1)
(1) Chemistry Department, College of Science, Shiraz University, Shiraz, Iran
(2) Department of Pharmaceutics, School of Pharmacy, Shahid Beheshti University of
Medical Sciences, Tehran, Iran
*Corresponding author. Tel.: +98 7116137738, fax: +98 7112286008.
E-mail address: Jaber Javidi @ sbmu.ac.ir
Research Highlight
• Preparation of the magnetic nanocatalyst.
• Immobilization of PMA nanoparticles on imidazole functionalized
Fe3O4@SiO2.
• Identification of catalyst by XRD, TEM, DLS, FE-SEM, FT-IR, BET and
VSM.
• Catalyst recycling by external magnetic field.
• The preparation of 1-amidoalkyl-2-naphthols as biologically compounds.
Graphical abstract
Abstract
In this paper, we report a method for preparation of functionalized superparamagnetic
Fe3O4@SiO2 that is synthesized based on several stages. First of all, the Fe3O4@SiO2
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nanosphere core-shell is synthesized. Then, H3PMo12O40 nanoparticles were synthesized by
the treatment of H3PMo12O40 with n-Octane as solvent by a solvothermal method and this
nano hetero polyacid immobilized onto imidazole functionalized Fe3O4@SiO2 nanoparticles.
The structure of the samples was characterized by XRD, TEM, DLS, FE-SEM, FT-IR, N2
adsorption–desorption isotherm analysis and VSM. Moreover, an efficient and direct protocol
is described for the preparation of amidoalkyl naphthols employing a multi-component, one-
pot condensation reaction of β-naphthol, aldehydes and acetamide, benzamide and urea in the
presence of Fe3O4@SiO2-Imid-PMAn under solvent-free and microwave conditions. Also,
nanocatalyst can be easily recovered by a magnetic field and reused for the next reactions for
at least 5 times without distinct deterioration in catalytic activity.
KEYWORDS: A. Nanostructures; A. organic compounds; B. magnetic structure; B.
chemical synthesis; D. catalytic properties
1. Introduction
Nanomaterials have been interested extensively because of their unique properties [1]
and used extensively in biology [2], physics [3] and chemistry [4]. Also, nanoparticles
have gained an interest because of their potential applications in areas such as
ceramics [5], optics [6], electronics [7], magnetic data storage [8], catalysis [9-11] and
nanocomposites. When size of the particle is decreased to nanometer scale, the surface
area of them significantly increased and those activities could be improved [12].
In the past decade, the synthesis of superparamagnetic nanoparticles had been
intensively developed due to their different applications such as magnetic inks for jet
printing [13], targeted drug delivery [14,15], contrast agents in magnetic resonance
imaging (MRI) [16], catalysts for carbon nanotube formation[17], sorbents for
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environmental remediation [18,19] and hyperthermia treatment of cancer cells [20].
These applications attributed to those unique properties, such as size,
superparamagnetism, the crystallinity, size distribution and monodispersity. Currently,
much attention has been focused on the synthesis of magnetic metal oxide structures
that coating with a silica shell [21]. In contrast to most of solid catalysts that recovery
and reusability of them are very difficult, recovery and reusability of core-shell
nanostructure magnetic catalysts could be easily carried out under magnetic field.
Therefore, the magnetic core–shell structures are a good supports for the catalysts
[22].
In recent years, brønsted acids such as Keggin-type heteropolyacids have been used as
efficient catalysts for a variety of organic reactions because of their superacidic and
redox properties, low toxicity, ease of handling, low cost, high thermal stability, high
proton mobility, water tolerance, recoverability and reusability [23]. Although HPAs
are versatile compounds in their acidic form, their main disadvantages are high
solubility in polar solvents and low surface area (<10 m2/g). Therefore, in a
homogeneous reaction the isolation of the products and the reuse of the catalyst after
reaction become difficult [23]. Therefore, in order to overcome this problem, these
materials disperse on supports (such as silica, acidic ion-exchange resins, active
carbon and etc.) which possess large surface area. The use of support allows the
heteropolyacids to be dispersed over a large surface area and increases theirs catalytic
activity [24].
Recently, a number of functionalized Fe3O4 nanoparticles have been employed in a
range of organic transformations, and the studies on immobilization of organo
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catalysts on silica coated ironoxide nanoparticles have been reported [25]. Therefore
in this work, we report the immobilization of H3PMo12O40 nanoparticles (PMAn) on
imidazole functionalized Fe3O4@SiO2 as a convenient building block for the grafting
of catalysts and reagents (scheme1).
Multicomponent reactions (MCRs) have attracted considerable attention in organic
synthesis as they can produce the target products in a single operation without
isolating the intermediates, thus reducing reaction times and energy consumption.
MCRs have merits over conventional linear type syntheses in several aspects
including simple procedures, possible structural variations, and rapid access to
complex molecules [26]. Multi-component reactions (MCRs) play an important role in
combinatorial chemistry because of their ability to synthesize small drug-like
molecules with several degrees of structural diversity [27]. Therefore, discovery and
development of new MCRs is highly desirable.
1-Amidoalkyl-2-naphthol derivatives are of prominence as they can be easily
hydrolyzed to 1-aminoalkyl-2-naphthol. 1-Aminoalkyl-2-naphthols have been
commonly applied as hypotensive and bradycardiac agents [28-29]. 1-Amidoalkyl-2-
naphthols can also be converted to 1,3-oxazine derivatives [30] with different
biological activities, such as antitumor [31], antibiotic [32], antipsychotic [33],
anticonvulsant [34], antimalarial [35], analgesic [36], antihypertensive [37],
antirheumatic [38], and antianginal [39] properties.
Therefore paying attention to the importance of amidoalkyl naphthols, various
procedures have been reported. Many of these reported methods employ different
homogeneous or heterogeneous catalysts such as p-toluenesulfonic acid [40],
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dodecylphosphonic acid (DPA) [41], H2NSO3H [42], oxalic acid [43], Fe(HSO4)3
[44], Sr(OTf)2 [45], I2 [46], K5CoW12O40.3H2O [47], HPMo [48], Yb(OTf)3 in ionic
liquid [49], montmorillonite K10 [50], TMSCl/NaI [51], Al2O3–HClO4 [52], InCl3
[53], 2,4,6-trichloro-1,3,5-triazine [54], CuPW and CuPMo [55], H3MoO40P [56],
H4SiW12O40 [57], and P2O5 [58]. However, most of the synthetic protocols for 1-
amidoalkyl-2-naphthol reported so far suffer from drawbacks such as requiring
reagents, which are not readily available, highly toxic and hazardous catalyst,
unsatisfactory yields, long reaction times, use of harmful organic solvents and the
production of environmental pollutants. Therefore, a great demand still exists for
versatile, simple, and environmentally friendly processes whereby 1-amidoalkyl-2-
naphthols may be formed under simple and practical conditions.
Therefore, we utilized H3PMo12O40 nanoparticles (PMAn) on Fe3O4@SiO2-Imidazol
nanoparticle in the production of 1-amidoalkyl 2-naphthols.
2. Experimental
2.1. Chemicals and Instrumentation
All the chemical reagents used in our experiments were purchased from the Merck
Chemical Company in high purity. All the solvents were distilled, dried and purified
by standard procedures. Melting points were determined on a Mel-Temp apparatus.
The NMR spectra were recorded on a Bruker avance DPX 250MHz spectrometer in
chloroform (CDCl3) using tetramethylsilane (TMS) as an internal reference. Fourier
transform infrared (FT-IR) spectra were obtained using a Shimadzu FT-IR 8300
spectrophotometer. XRD patterns were recorded by a Bruker AXS D8-advance X-ray
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diffractometer with Cu Kα radiation (λ=1.5418). The BET surface area and porosity
of catalysts were determined from nitrogen physisorption measured on a
Micromeritics ASAP 2000 instrument at 196 oC. Transmission electron microscopy
(TEM) images were obtained on a Philips EM208 transmission electron microscope
with an accelerating voltage of 100 kV. Dynamic light scattering (DLS) were recorded
on a HORIBA-LB550. Magnetic properties were obtained on a BHV-55 vibrating
sample magnetometer (VSM). Microwave oven (LG Smart Chef MS-255R operating
at 2450 MHz having maximum out put power of 960 W) was used for microwave
irradiation. Elemental analysis was done on a 2400 series Perkin-Elmer analyzer.
Melting points were determined on a Mel-Temp apparatus and were Uncorrected.
Therefore, all of the products were characterized by FT-IR, 1H NMR and 13C NMR,
and also by comparison with authentic samples. The progress of the reaction was
monitored by TLC and purification was achieved by silica gel column
chromatography.
2.2. Catalyst preparation
2.2.1. Preparation of Fe3O4@SiO2 Core-Shell
The core–shell Fe3O4@SiO2 nanospheres were prepared by a modified Stober method
in our previous work [25]. In a typical procedure, the mixture of FeCl3.6H2O (1.3g,
4.8mmol) in water (15ml) was added to the solution of polyvinyl alcohol (PVA
15000), as a surfactant, and FeCl2.4H2O (0.9g, 4.5mmol) in water (15 ml), which was
prepared by completely dissolving PVA in water followed by addition of FeCl2.4H2O.
The resultant solution was left to be stirred for 30 min in 80oC. Then,
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hexamethylentetraamine (HMTA) (1.0mol/l) was added drop by drop with vigorous
stirring to produce a black solid product when the reaction media reaches pH 10. The
resultant mixture was heated on water bath for 2h at 60oC and the black magnetite
solid product was filtered and washed with ethanol three times and was then dried at
80oC for 10h.Then Fe3O4 nanoparticle (0.50g, 2.1mmol) was dispersed in the mixture
of ethanol (50mL), deionized water (5mL) and tetraethoxysilane (TEOS) (0.20mL),
followed by the addition of 5.0mL of NaOH (10wt%). This solution was stirred
mechanically for 30 min at room temperature. Then the product, Fe3O4@SiO2, was
separated by an external magnet, and was washed with deionized water and ethanol
three times and dried at 80oC for 10 h.
2.2.2. Preparation of Fe3O4@SiO2-Imid
Fe3O4@SiO2 (1g) was added to the solution of 3-chlorotriethoxypropylsilane (1
mmol, 0.241 g) and imidazole (1 mmol, 0.0680 g) in p-xylene (20 mL) and the
resultant mixture was under reflux for 24h under nitrogen atmosphere. After refluxing
for about 24 h, the mixture was cooled to room temperature, filtered by an external
magnet and the product was washed with xylene to remove any reacted species and
dried at 70 oC for 6 h.
2.2.3. Preparation of H3PW12O40 nanoparticles (PMAn)
PMAn nanoparticles were prepared in our previous work [59], which is a simple and
single step method. In a typical procedure, 5 mmol of bulk H3PMo12O40 (PMAb) was
dispersed in 50 mL n-Octane and the resulting dispersion was stirred vigorously for 30
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min at room temperature to form a homogeneous dispersion. This dispersion was
transferred into a Teflon-lined stainless autoclave filling 80% of the total volume. The
autoclave was sealed and maintained at 150oC for 12 h. The autoclave was then
cooled to room temperature. Finally, the resulted powder was filtered and washed for
several times by Octane, and dried in a vacuum at 80oC for 12 h.
2.2.4. Preparation of Fe3O4@SiO2-Imid-PMAn
Scheme1 represents the anchoring of PMAn onto Fe3O4@SiO2-Imid. Fe3O4@SiO2-
Imid (1.0g) was added to an acetonitrile solution of PMAn (1.0mmol) in 20mL was
taken in a round-bottom flask. The mixture was refluxed for 24h under nitrogen
atmosphere. After 24h, the mixture was filtered by an external magnet, washed with
acetonitrile and dichloromethane, and dried at 70oC for 6h. FT-IR spectrum of the
catalyst showed the expected bands, including distinctive bands due to anchoring of
PMAn onto Fe3O4@SiO2-Imid. Also, the same method was used for the synthesis of
Fe3O4@SiO2-Imid-PMAb (PMAn = nano H3PMo12O40, PMAb= H3PMo12O40).
2.3. General synthesis for the preparation of amidoalkyl naphthols catalyzed by
Fe3O4@SiO2-Imid-PMAn
A mixture of aldehyde (1 mmol), 2-naphthol (1 mmol), amide or urea (1.1 mmol) and
Fe3O4@SiO2-Imid-PMAn (0.03g) were taken in round bottom flask and stirred for the
desired time (as indicated by TLC) at 100 ◦C in a preheated oil bath or under
microwave-irradiation. After completion of the reaction, and separation of
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Fe3O4@SiO2-Imid-PMAn with using magnetic field, the mixture was diluted with 10
cm3 ethyl acetate, washed with 10 cm3 water, and the aqueous layer was then
extracted with 2×10 cm3 ethyl acetate. The organic layer was dried over Na2SO4,
filtered, and concentrated to afford the crude product. If further purification was
needed it was passed through a short column of silica gel.
3. Results and discussion
FT-IR spectra of Fe3O4@SiO2, Fe3O4@SiO2-Imid, PMAn, PMAb and Fe3O4@SiO2-
Imid-PMAn are shown in Fig 1a, b, c, d and e. Some of the important bands which are
observed in the spectra are given in Table 1. From the IR spectra presented in Fig1a,
the absorption peak at 554cm−1 belonged to the stretching vibration mode of Fe-O
bonds in Fe3O4@SiO2, the absorption peak presented at 1000-1150 cm−1 most due to
stretching vibration of framework and Si–O-Si groups. Also, the peaks at around 3400
cm-1 and 1622 cm-1 in Fig1a are due to the adsorbed water in the sample.
In Fig1b, the presence of vibration bands in 556, 1000-1150 and 3400 cm-1, which is
due to the Fe-O, Si-O-Si, and –OH respectively, demonstrates the existence of
Fe3O4@ SiO2-Imid. IR spectral analysis of Fe3O4@SiO2-Imid in the range of 1360–
1490 cm–1 indicated three band at 1369, 1443, and 1484 cm–1, can be attributed,
respectively, to the vibrations ω(СН2), ν (C=N) and δ(СН2) of the CH2 groups linked
to imidazol ring. Also, the presence of several bands with medium intensity in 2808–
2993cm-1 region is allocated to C-H stretching of methylene groups (Fig1b).
FT-IR spectroscopy, as a means of providing the structure of the HPAs, is convenient
and widely used for the characterization of heteropolyacid [60].
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The FT-IR spectrum for PMAn shows four bands in the range 500–1250 cm−1 are
assigned at 786, 856, 954 and 1057 cm−1, which correspond to νas(Mo–Oe–Mo),
νas(Mo–Oc–Mo), νas(Mo–Ot) and νas(P–O*), respectively [61] (Fig1c). According to
FT-IR spectroscopy data that was shown in Table1, the characteristic bands of Keggin
structure for PMAn compared to PMAb (Fig1d), are shifted to higher wave numbers
(blue shift).
The presence of vibration bands in 556, 794, 864, 956, 1055, 1095, 1454 and 2792-
2985 which is due to the Fe-O, Mo-Oe-MO, Mo-Oc-MO, Mo-Ot, P-O, Si-O-Si, C=N
and CH respectively, demonstrates the existence of Fe3O4@SiO2-Imid-PMAn in the
spectrum (Fig 1e). The band at 1443 cm-1 for Fe3O4@SiO2-Imid is assigned to the
C=N of the imidazole group, which is shifted toward 1454 cm-1 in Fe3O4@SiO2-Imid-
PMAn which could be due to the change in environment of the double-bonded
nitrogen in imidazole. Also, a small band between 1400-1420 cm-1 in Fe3O4@SiO2-
Imid and Fe3O4 @SiO2-Imid-PMAn is the characteristic band of the C-N bond which
can be attributed to anchoring of imidazole to the propyl group [23].
Fig. 2 shows the XRD patterns for Fe3O4, Fe3O4@SiO2, PMAn and Fe3O4@SiO2-Imid-
PMAn nanoparticles.
The characteristic peaks at 2θ: 30.1◦, 35.4◦, 43.1◦, 53.4◦, 57◦ and 62.6◦ for Fe3O4
nanoparticles, which were marked respectively by their indices (220), (311), (400),
(422), (511) and (440), were also observed for Fe3O4@SiO2 nanoparticles (reference
JCPDS card no.19-629) (Fig2a,b). This revealed that the surface modification of the
Fe3O4 nanoparticles does not lead to their phase changes. The XRD pattern of
Fe3O4@SiO2 shows an obvious diffusion peak at 2Ө = 15–25◦ that appeared because
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of the existence of amorphous silica (Fig2b).The strong characteristic peaks at
2θ=9.05◦, 23.7◦, 26.35◦, 28.25◦ and 32.4 in Fig2c, are assigned to Keggin structure of
PMAn [JCPDS File 1-32] [59]. For Fe3O4@SiO2-Imid-PMAn nanoparticles, the broad
peak was transferred to lower angles due to the synergetic effect of amorphous silica
and Imid-PMAn (Fig2d). Also, the presence of the silica and Imid-PMAn layers on the
Fe3O4 nanoparticles, leads to amorphous structure and the disappearance of peaks
corresponding to Fe3O4 and PMAn (Fig2d). The average sizes of Fe3O4, Fe3O4@SiO2
and PMAn are determined according to calculation with the Scherrer formula method
(D= 0.9λ/βcosθ), where D is the average diameter in A˚, β is the broadening of the
diffraction line measured at half of its maximum intensity in radians, λ is the
wavelength of the X-rays and θ is the Bragg diffraction angle. The mean crystallite
sizes of Fe3O4, Fe3O4@SiO2 and PMAn nanoparticles were found to be around 12, 20
and 12 nm, respectively.
The morphology of the synthesized (a) Fe3O4, (b) Fe3O4@SiO2, (c) PMAn and
Fe3O4@SiO2-Imid-PMAn particles were determined by TEM (Fig3).
TEM image of Fe3O4 clearly shows that Fe3O4 nanoparticles are almost spheroidal in
shape with diameters in the 8–16nm range, which is almost the same with average
particle size obtained from XRD (Fig3a).
Fig.3b display the TEM image of Fe3O4 nanoparticles coated with silica layers. The
size of nanoparticles obtained from the TEM images, turned out to be approximately
20 and 15nm for Fe3O4@SiO2, PMAn respectively, and their shapes are nearly
spherical (Fig3b,c). Fig.3d displays the high resolution TEM images of Fe3O4
nanoparticles coated with silica layers and PMAn nanoparticles. Fig3e shows FE-SEM
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image of Fe3O4@SiO2-Imid-PMAn. As it is shown, these nanoparticles have spherical
shapes with approximately 50 nm diameters.
To investigate the size distribution of these nanoparticles, particle size histograms
were prepared for Fe3O4, Fe3O4@SiO2, PMAn and Fe3O4@SiO2-Imid-PMAn (Fig 4a to
d respectively) by DLS analysis. This size distribution is centered at a value of 12, 20,
12 and 55 nm for Fe3O4, Fe3O4@SiO2, PMAn and Fe3O4@SiO2-Imid-PMAn,
respectively.
The surface areas of PMAb, PMAn, Fe3O4@SiO2-Imid-PMAb, Fe3O4@SiO2-Imid-
PMAn and Fe3O4@SiO2 were measured by N2 adsorption. While the BET (Calculated
by the BJH method) surface area was 10.0 and 250.0 m2/g for PMAb and
Fe3O4@SiO2-Imid-PMAb respectively (Table2, entries 1,3), nano HPAs have the
much higher surface area (Table2, entries 2,4). Reducing the particle size from bulk
powder to nanometer scale, caused the surface area was increased from 10 to 270 m2/g
for PMA and from 250 to 422 m2/g for Fe3O4@SiO2-Imid- PMA (Table2, entries 1-4).
The magnetic properties of Fe3O4, Fe3O4@SiO2, Fe3O4@SiO2-Imid- PMAn
nanoparticles were measured by VSM at room temperature. As it is shown in the
Fig5A, all the samples show a typical superparamagnetic behavior. Hysteresis
phenomenon was not found and the magnetization and demagnetization curves were
coincident. The saturation magnetization of samples (a–c) is 63.4, 39.7, 33.2 emu/g,
respectively (Fig 5Aa, b, c). These results indicated that the magnetization of Fe3O4
decreased considerably with the increase of SiO2 and functionalization of Fe3O4.
Nevertheless, in all cases, the separation of the catalyst was achieved by applying an
external permanent magnet, making the recovery of the catalyst very straightforward.
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The magnetic Fe3O4@SiO2-Imid-PMAn stably dispersed in acetonitrile can be readily
separated from the dispersion when an external magnetic field is applied (Fig5B).
After the external magnet is removed, the accumulation can be redispersed into
acetonitrile by mild shaking.
The acidity of HPAs compounds has been investigated with different methods of
analysis: (i) Hammett indicators + visual inspection [62], (ii) ammonia + temperature
programmed desorption (TPD) [63,64], FT-IR spectroscopy [65], calorimetry [66,67],
(iii) pyridine + TPD, FT-IR spectroscopy [68, 69], (iv) H1 NMR [70] and O17 NMR
[71].
The interaction of pyridine with HPAs was confirmed by FT-IR spectroscopy.
Pyridinium ions can be identified by the band at 1540 cm−1 [72]. The characteristic
chemisorbed pyridium ion was detected after the removal of physisorbed pyridine
from HPAs by evacuation. The absorption band corresponding to the Mo=O stretch
might be expected to track the extent of proton transfer upon interaction with basic
molecules such as pyridine. As shown in Fig6 1d, the P–O, Mo=O (terminal oxygen),
and Mo–O–Mo (corner sharing and edge-sharing) bands of fresh H3PMo12O40
appeared at 1051, 950, 853 and 781 cm−1, respectively. The P–O, Mo=O (terminal
oxygen), and Mo–O–Mo (corner sharing and edge-sharing) bands of pyridine-exposed
Fe3O4@SiO2-Imid-PMAb appeared at 1032, 927, 838 and 769 cm−1, respectively
(Fig6e). Shifting of IR bands of pyridine-exposed HPAs were attributed to the
interaction of the cationic species, pyridinium ions, with the heteropolyanions. In the
FT-IR analyses of pyridine-exposed HPAs shown in Fig.6, the quantification of
bridging oxygen bands was not simple. Thus the absorption band corresponds to the
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Mo=O stretch might be expected to track the extent of proton transfer upon interaction
with basic molecules such as pyridine. We measured the IR intensity of pyridium ion
at 1540 cm−1 of the pyridine-exposed PMA and calculated the intensity ratio of I
(1540 cm−1)/I (Mo=O) bands in an attempt to track the acidic properties of PMA.
I value for Fe3O4@SiO2-Imid-PMAb and Fe3O4@SiO2-Imid-PMAn were 1.1 and 2.8
respectively, these indicated that Fe3O4@SiO2-Imid-PMAn have more acidic site then
Fe3O4@SiO2-Imid-PMAb (Fig6 c,e).
Herein we report a new, convenient, mild and efficient procedure for one-pot three-
component synthesis of amidoalkyl naphthol derivatives from various aldehydes, 2-
naphthol and different amides in the presence of Fe3O4@SiO2-Imid-PMAn
nanocatalyst as an effective and recoverable catalyst under solvent-free and
microwave conditions (Scheme 2).
Initially, to find the best optimum conditions, a model reaction of benzaldehyde (1
mmol), 2-naphthol (1 mmol) and acetamide (1.1 mmol) in the presence of
Fe3O4@SiO2-Imid-PMAn (0.03 g) was performed in different solvents such as 1,2-
dichloroethane, ethylacetate, DMF, ethanol, acetonitrile, dichloromethane, toluene,
cyclohexane, 1,4- dioxane under reflux conditions (Table3, Entries 1-9). Among these
solvents, 1,2-dichloroethane and ethylacetate provided the highest yields at refluxed
temperature after 4 h (Table3, Entries 1,2). However, a higher yield of product could
be obtained under solvent-free condition in the presence of (0.03g) catalyst at 100°C
only after 25 min in 95% yield (Table3, Entry 10). Decrease of the yield was observed
when the reaction was repeated in the presence of lower amount of the catalyst so that
in the absence of any catalyst no product was observed, even after a prolonged
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reaction time (Table3, Entries 11-14). Enhancement of the catalyst loading did not
show any effect on the yield or the reaction time (Table 3, Entries 15-16). In addition,
the effect of temperature was studied and the results indicated that at lower
temperatures, the reaction did not proceed properly and most of the initial substances
remained unreacted. (Table3, Entry 17). In order to find the best conditions, the model
reaction was performed in the presence of Fe3O4@SiO2-Imid-PMAn (0.03g) under
solvent free condition in microwave (Table3, Entry 18). The result showed that under
this condition, the corresponding product was obtained in 96% yield after very short
time (6 min).
This three-component condensation of various aldehydes and amides with 2-naphthol
catalyzed by Fe3O4@SiO2-Imid-PMAn was then explored under the optimized
reaction conditions described above. The results are summarized in Table 4.
Aldehydes bearing electron-donating and withdrawing substituents in the reaction
with acetamide as an aliphatic amide and 2-naphthol led to good yields of the desired
1- amidoalkyl-2-naphthols (Table 4, Entries 1-13). Using benzamide as an aromatic
amide, instead of acetamide, resulted in the corresponding 1-amidoalkyl-2- naphthols
in good yields when it was treated with 2-naphthol and aldehydes in the presence of
Fe3O4@SiO2-Imid-PMAn under solvent free and in microwave conditions (Table 4,
Entries 14-26). In addition, the reaction of aldehydes and 2-naphthol with urea
afforded the corresponding products in high yields (Table 4, Entries 27-30).
To test the worth of the present work in comparison with results in the literature, we
compared results of Fe3O4@SiO2-Imid-PMAn and Fe3O4@SiO2-Imid-PMAb with
other applied Lewis and Bronsted acids in synthesis of 1-amidoalkyl-2-naphthols.
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These data, which are shown in Table 5, revealed that Fe3O4@SiO2-Imid-PMAn is a
better catalyst than most of the conventional catalysts mentioned with respect to
reaction times and yields of the obtained products.
The recyclability of the Fe3O4@SiO2-Imid-PMAn was also investigated using the
above model reaction. In order to confirm the reusability and stability of magnetic
nanocatalyst it was separated from the reaction mixture after it was first used in the
preparation of amidoalkyl naphthol. The recovered catalyst was found to be reusable
for five cycles with a slight loss in activity (Fig7A,B).
4. Conclusions
In conclusion, superparamagnetic Fe3O4@SiO2-Imidazol- PMAn nanospheres have
been prepared by immobilizing H3PMo12O40 nanoparticles on the surface of
Fe3O4@SiO2-Imidazol. H3PMo12O40 nanoparticles (PMAn) were synthesized by the
reaction of H3PMo12O40 with n-Octane as solvent by a solvothemal method. The
nanocatalyst was successfully synthesized and structural, surface, morphological, and
magnetic properties of these nanoparticles were evaluated. The nanospheres possessed
a spherical shape and a porous structure and the crystalline structure of Fe3O4 was
unchanged during the synthesis process of magnetic nanocatalyst. FT-IR
spectroscopy, as a means of providing the structure of the heteropolyacids, is
convenient and widely used for catalyst characterization. TEM microscopy revealed
the formation of very fine layer of SiO2 on the Fe3O4. The crystallite size obtained
from X-ray line profile fitting is comparable with the particle size obtained from
TEM. Magnetization curves demonstrated a high degree of superparamagnetism and
16
Page 16 of 37

magnetic nanocatalyst with saturation magnetization value of about 33.2 emu/g can be
easily recover under an external magnetic field.
Therefore, considering the importance of this catalyst, we have elaborated an efficient
and expeditious synthesis of 1-amidoalkyl-2-naphthol derivatives accomplished via
three-component reactions of aldehydes, 2-naphthol and benzamide, acetamide or urea
in the presence of Fe3O4@SiO2-Imid-PMAn by two methods. These two methods offer
several significant advantages such as: high conversions, easy handling, short reaction
times, easy and green work up, recovery and reusability of catalyst, cost efficient and
versatility. These advantages, in general, highlight this protocol as a useful and
attractive methodology, among the methods reported in the literature, for the rapid
synthesis of 1-amidoalkyl-2-naphthols as precursors of biological active 1-
aminoalkyl-2-naphthols.
Acknowledgements
Authors are grateful to the council of Iran National Science Foundation and
University of Shiraz for their unending effort to provide financial support to undertake
this work.
Spectral data
N-((2-hydroxynapthalen-1-yl)(4-methyl-phenyl) methyl] acetamide (Table 4, Entry9)
1HNMR (250 MHz, DMSO-d6): δ=1.96 (s, 3H), 2.21 (s, 3H), 7.03—7.08 (m, 5H), 7.19 (d, J=
4.4 Hz, 1H), 7.24 (t, J= 3.6 Hz, 1H), 7.33-7.35 (m, 1H), 7.74 (d, J= 4.4 Hz, 1H), 7.78 (d,
J=3.8 Hz, 1H), 7.82 (br, 1H), 8.36 (d, J= 4.1 Hz, 1H), 9.91 (s, 1H); 13C NMR (125 MHz,
17
Page 17 of 37

DMSO-d6): 20.4, 22.6, 47.6, 118.4, 118.9, 122.2, 123.1, 125.9, 126.1, 128.3, 128.4, 128.9,
132.2, 134.9, 139.4, 143.2, 152.9, 168.9; Anal. Calcd: C, 78.66; H, 6.27; N, 4.59; Found: C,
78.58; H, 6.18; N, 4.61%.
N-((2-hydroxynaphthalen-1-yl)(4-nitrophenyl) methyl) benzamide (Table 4, Entry17)
1HNMR (250 MHz, DMSO-d6): δ= 7.24 (d, 1H), 7.45 (d, 1H), 7.39-7.54 (m, 7H), 7.79-7.90
(m, 4H), 8.11 (m, 3H), 9.04 (d, 1H), 10.49 (s. 1H). 13CNMR (62 MHz, DMSO-d6): δ= 49.75,
115.46, 118.63, 121.66, 122.58, 123.24, 126.43, 128.34, 128.86, 128.94, 129.26, 132.34,
134.31, 145.96, 148.98, 153.54, 167.71; Anal. Calcd: C, 72.35; H, 4.55; N, 7.03; Found: C,
72.29; H, 4.66; N, 7.08%.
1
N-(1-(2-hydroxynaphthalen-1-yl) propyl) acetamide (Table 4, Entry13) H NMR (250
MHz, DMSO-d6): 0.77 (t, J= 3.7 Hz, 3H), 1.81 (s, 3H), 1.89–1.84 (m, 2H), 5.63 (q, J= 3.8
Hz, 1H), 7.13 (d, J= 4.6 Hz, 1H), 7.21 (t, J= 3.7 Hz, 1H), 7.39 (t, J= 3.7 Hz, 1H), 7.64 (d, J=
4.4 Hz, 1H), 7.72 (d, J= 4.0Hz, 1H), 8.03 (s, 1H), 8.08 (d, J= 4.3 Hz, 1H), 9.94 (s, 1H). 13C
NMR (62 MHz, DMSO-d6): δ= 11.9, 23.2, 27.2, 48.0, 119.1, 120.0, 122.7, 123.1, 126.6,
128.7, 128.9, 129.0, 132.9, 153.5, 169.1; Anal. Calcd: C, 74.05; H, 7.04; N, 5.75. Found: C,
74.11; H, 6.96; N, 5.71%.
N-(1-(2-hydroxynaphthalen-1-yl) propyl) benzamide (Table 4, Entry24) 1H NMR (250
MHz, DMSO-d6): δ= 0.90 (t, J= 3.6 Hz, 3H,), 1.89 (m, 2H), 5.85 (t, J= 3.7 Hz, 1H), 7.09 (d,
J= 4.4 Hz, 1H), 7.29 (dd, J= 3.6 Hz, 1H), 7.43–7.53 (m, 4H), 7.66 (d, J= 4.4 Hz 1H), 7.75 (t,
J= 3.6 Hz, 3H), 8.18 (d, J= 4.4 Hz, 1H), 8.61 (d, J= 4.0 Hz, 1H), δ=10.08 (s, 1H). 13C NMR
(62 MHz, DMSO-d6): δ= 11.35, 26.91, 48.49, 118.57, 119.53, 122.34, 126.22, 126.87,
128.19, 131.06, 132.23, 134.71, 152.85, 165.37; Anal. Calcd: C, 78.66; H, 6.27; N, 4.59.
Found: C, 78.57; H, 6.21; N, 4.54.
18
Page 18 of 37

1
N-(1-(2-Hydroxynaphthalen-1-yl)-3-phenylpropyl) benzamide (Table 4, Entry25) H
NMR (250 MHz, DMSO-d6): δ= 2.04 (m, 2H), 2.74 (t, 2H), 5.98 (d, 1H), 7.13–7.24 (m, 6H),
7.40–7.47 (m, 4H), 7.66– 7.82 (m, 4H), 8.02 (d,1H), 8.66 (d, 1H), 10.16 (s, 1H). 13C NMR
(62 MHz, DMSO-d6): δ= 32.46, 35.60, 46.70, 118.59, 119.62, 122.38, 125.66, 126.22,
126.96, 127.33, 128.18, 128.26, 128.35, 128.45, 128.52, 131.13, 132.02, 134.63, 141.68,
152.90, 165.55; Anal. Calcd: C, 81.86; H, 6.08; N, 3.67. Found: C, 81.80; H, 6.01; N, 3.55.
(E)-N-(1-(2-Hydroxynaphthalen-1-yl)-3-phenylallyl benzamide (Table 4, Entry26) 1H
NMR (250 MHz, DMSO-d6): δ= 7.08 (d, 1H), 7.17 (d, 1H), 7.21 (m, 4H), 7.41 (m, 3H), 7.75
(m, 3H), 8.07 (d, 1H), 9.01 (d, 1H), 10.43 (s, 1H). 13C NMR (62 MHz, DMSO-d6): δ= 48.15,
123.51, 127.61, 128.30, 131.27, 132.47, 133.60, 135.81, 137.28, 141.84, 158.24, 165.54;
Anal. Calcd: C, 82.30; H, 5.58; N, 3.69. Found: C, 82.24; H, 5.53; N, 3.65.
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Figure captions:
Scheme1: Process for preparation of immobilization of H3PMo12O40 nanoparticles (PMAn)
on imidazole functionalized Fe3O4@SiO2 nanoparticle.
Scheme.2: Synthesis of amidoalkyl naphthol using Fe3O4@SiO2-Imid-PMAn.
Fig.1: FT-IR spectra a) Fe3O4@SiO2 [25], b) Fe3O4@SiO2-Imid, c) PMAn [59], d) PMAb[59]
and e) Fe3O4@SiO2-Imid-PMAn.
Fig. 2: XRD patterns of a) Fe3O4 [25] b) Fe3O4@SiO2 [25] c) PMAn [59] d) Fe3O4@SiO2-
Imid- PMAn.
Fig.3: TEM images of Fe3O4 (a) [25] Fe3O4@SiO2 (b) [25] PMAn (c) [59] and HRTEM and
FE-SEM images Fe3O4@SiO2-Imid- PMAn (d), (e) respectively.
Fig.4: DLS size distributions of Fe3O4 (a) [25] Fe3O4@SiO2 (b) [25] PMAn (c) [59] and
Fe3O4@SiO2-Imid- PMAn (d).
Fig.5: A) Magnetization curves at 300oK for a) Fe3O4 b) Fe3O4@SiO2 c) Fe3O4@SiO2-Imid-
PMAn nanoparticles. B) The dispersion (a) and separation (b) process of magnetic
Fe3O4@SiO2-Imid- PMAn nanocatalyst.
Fig.6: FT-IR spectra a) Pyridine b) Fe3O4@SiO2-Imid-PMAn c) Fe3O4@SiO2-Imid-PMAn-
Pyridine d) Fe3O4@SiO2-Imid-PMAb e) Fe3O4@SiO2-Imid-PMAb - Pyridine.
Fig.7: Recyclability of Fe3O4@SiO2-Imid-PMAn in the synthesis of amidoalkyl-2-naphthols.
24
Page 24 of 37

Table.1: Infrared spectroscopic data for Fe3O4@SiO2, Fe3O4@SiO2-Imid, PMAb, PMAn and
Fe3O4@SiO2-Imid-PMAn before the catalytic reaction.
vibration
mode
Fe3O4@SiO
2 cm-1
Fe3O4@SiO2-
PMA PMA Fe3O4@SiO2-Imid-
b
n
Imid
cm-1
556
-
PMAn
assignment
Fe-O
cm-1
-
cm-1
-
cm-1
556
554
-
Mo-Oe-MO
Mo-Oc-MO
Mo-Ot
781
853
950
786
856
954
794
864
-
-
956
P-O
-
-
1051 1057
1055
1095
1454
2792-2985
Si-O-Si
C=N
1000-1150
1000-1150
1443
-
-
-
-
-
-
-
-
C-H
2808-2993
25
Page 25 of 37

Table2. BET result of PMAb, PMAn, Fe3O4@SiO2-Imid-PMAb, Fe3O4@SiO2-Imid- PMAn
and Fe3O4@SiO2.a
Entry
Sample
PMAb
BET(m2/g) Pore volume (cm3/g)
1
2
3
4
5
10
-
PMAn
270
250
422
430
0.465
0.333
0.535
0.755
Fe3O4@SiO2-Imid-PMAb
Fe3O4@SiO2-Imid-PMAn
Fe3O4@SiO2
a Calculated by the BJH method.
26
Page 26 of 37

Table3. Optimization of different proportions of Fe3O4@SiO2-Imid-PMAn catalyst and also
effect of solvents and temperature on the model reaction of benzaldehyde, β-naphthol, and
acetamide.
Entry
Solvent
Amount of Catalyst
Temperature
(oC)
Time
Yield
(%)a
81
83
69
41
67
63
35
72
48
95
0
(g)
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
-
(h)
1
2
ClCH2CH2Cl
CH3COOC2H5
DMF
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
100
4
4
3
4
4
EtOH
4
5
CH3CN
4
6
CH2Cl2
4
7
Toluene
4
8
Cyclohexane
1,4-Dioxane
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
4
4
9
10
11
12
13
14
15
16
17
18
25 min
16
100
0.01
0.02
0.025
0.035
0.04
0.03
0.03
100
4
53
79
87
94
95
18
96
100
2
100
45 min
30 min
30 min
4
100
100
r.t
MW/450w
6 min
aIsolated yield.
27
Page 27 of 37

Table4. One-pot preparation of 1-amidoalkyl-2-naphthols with different aldehydes and
amides catalyzed by Fe3O4@SiO2-Imid-PMAn.
Mp (lit. mp)ref
Method Bb
Time(min)/Yield
(%)c
Method Aa
Time (min)/Yield
(%)
R2
R1
243-244 (241–243)
6/96
25/95
CH3
CH3
CH3
CH3
CH3
CH3
C6H5
1
2
3
4
5
6
[73]
217-219 ( 218–
219)[58]
10/91
5/95
30/88
25/92
20/96
35/86
25/90
2- NO2C6H4
3- NO2C6H4
4-NO2C6H4
2-ClC6H4
255-257 (256–
258)[58]
235-237 (237–
238)[58]
5/96
208-2010 (206-
207)[58]
12/89
8/91
227-229 (224–
227)[73]
4-ClC6H4
(224—226)[74]
10/92
12/87
35/91
35/88
CH3
CH3
2,4-Cl2C6H4
4-BrC6H4
7
8
229-231 (228–
230)[75]
222-224(224–
225)[58]
12/85
12/87
10/87
15/89
35/83
40/84
30/86
40/87
CH3
CH3
CH3
CH3
4-CH3C6H4
4-CH3OC6H4
3-CH3OC6H4
9
183-185 (184–
186)[73]
10
11
12
201-203 (203–
205)[75]
123-125 (123)[76]
4-
(CH3)2NC6H4
28
Page 28 of 37

178-180
12/92
8/93
30/91
35/92
CH3
CH3CH2
C6H5
13
14
239-241 (238–
240)[58]
C6H5
264-266 (266–
267)[58]
12/88
12/90
8/93
45/87
35/89
25/94
55/85
35/93
40/90
55/85
55/79
70/81
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
2-NO2C6H4
3-NO2C6H4
4-NO2C6H4
2-ClC6H4
15
16
17
18
19
20
21
22
23
241-243 (242–
243)[58]
229-231 (231–
232)[75]
285-287 (284–
285)[58]
16/84
10/94
12/89
15/86
18/84
18/86
169-171(168–
170)[58]
4-ClC6H4
262-264 (262–
263)[58]
2,4-ClC6H4
4-CH3C6H4
4-CH3OC6H4
215- 216 (214–
215)[58]
204-206 (206–
208)[58]
218-220 (220-
221)[58]
4-
(CH3)2NC6H4
CH3CH2
244-246
156-158
232-233
10/90
15/85
15/81
8/95
30/91
50/86
50/80
25/92
C6H5
24
25
26
27
C6H5 C6H5CH2CH2
C6H5 C6H5CH = CH
174-176 (175–
177)[75]
NH2
C6H5
170-172 (170–
171)[75]
8/93
25/91
NH2
4-ClC6H4
28
29
Page 29 of 37