A magnetic nanoparticle-supported sulfuric acid as a highly efficient and reusable catalyst for rapid synthesis of amidoalkyl naphthols

Article abstract of DOI:10.1016/j.molcata.2013.08.028

Sulfuric acid functionalized magnetic Fe₃O₄ nanoparticles (MNPs-SO₃H) efficiently catalyze one-pot multicomponent condensation of β-naphthol with aromatic and aliphatic aldehydes and amide derivatives under solvent-free co

Full text of DOI:10.1016/j.molcata.2013.08.028

Accepted Manuscript
Title: A Magnetic nanoarticle-supported sulfuric acid as a
highly efficient and reusable catalyst for rapid synthesis of
amidoalkyl naphthols
Author: Javad Safari Zohre Zarnegar
PII:
S1381-1169(13)00320-8
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2013.08.028
MOLCAA 8849
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
18-7-2013
27-8-2013
29-8-2013
Please cite this article as: J. Safari, Z. Zarnegar, A Magnetic nanoarticle-supported
sulfuric acid as a highly efficient and reusable catalyst for rapid synthesis
of amidoalkyl naphthols, Journal of Molecular Catalysis A: Chemical (2013),
http://dx.doi.org/10.1016/j.molcata.2013.08.028
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A Magnetic nanoarticle-supported sulfuric acid as a highly efficient and
reusable catalyst for rapid synthesis of amidoalkyl naphthols
Javad Safari٭, Zohre Zarnegar
Laboratory of Organic Compound Research, Department of Organic Chemistry, College of Chemistry,
University of Kashan, P.O. Box: 87317-51167, Kashan, I.R., Iran.
Abstract
Sulfuric acid functionalized magnetic Fe3O4 nanoparticles (MNPs-SO3H) efficiently catalyze
one-pot multicomponent condensation of β-naphthol with aromatic and aliphatic aldehydes and
amide derivatives under solvent-free conditions to afford the corresponding amidoalkyl
naphthols in excellent yields and in very short reaction times. High catalytic activity and ease of
recovery using an external magnetic field are additional eco-friendly attributes of this catalytic
system.
Keywords: Sulfuric acid functionalized Fe3O4 nanoparticles, Amidoalkyl naphthol, β-Naphthol,
Multi-component reaction, Solvent-free.
1. Introduction
Sulfuric acid is an essential and efficient catalyst for the production of industrial important
chemicals. Over 15 million tons of sulfuric acid are annually consumed as “an unrecyclable
catalyst” which requires costly and inefficient separation of the catalyst from homogeneous
reaction mixtures [1]. The use of recyclable strong solid acids in organic reactions are often
considered to follow the principles of green chemistry, that is these catalyzed processes consume
a minimum of energy and reagents or auxiliaries and minimize waste [2].
٭Corresponding author. E-mail addresses: Safari@kashanu.ac.ir, Tel: +98 3615912320; Fax: +98 361
5912397.
1
Page 1 of 22

Magnetic nanoparticles (MNPs) have recently appeared as an excellent type of catalyst support
because of their good stability, easy synthesis and functionalization, high surface area and facile
separation by magnetic forces, as well as low toxicity and price [3]. Also, surface
functionalization of magnetic particles is an elegant way to bridge the gap between
heterogeneous and homogeneous catalysis. These attractive features have made MNPs a
promising alternative to porous/mesoporous catalyst supports. Thus, the development of silica-
coated magnetite nanoparticles as attractive candidates in the search for supporting of catalysts is
currently a subject of increasing interest in chemical process [4,5]. Sulfuric acid functionalized
silica-coated magnetite nanoparticles as recyclable strong solid acid catalyst open up new avenue
to introduce an amazing and efficient system for facilitating catalyst recovery in different organic
reactions. This catalyst allows the combination of well known procedures for catalyst
heterogenization with techniques for magnetic separation [6, 7].
The developing of one-pot multicomponent reactions (MCRs) and improving the known
MCRs have attracted considerable attention in recent years [8, 9]. One of these MCRs is the
preparation of amidoalkyl naphthol derivatives. 1-Amidoalkyl-2-naphthol derivatives are
important class of compounds as they can be easily converted to biologically active compounds,
1-aminoalkyl-2-naphthols, by amide hydrolysis reaction [10, 11]. The synthesis of 1-amidoalkyl-
2-naphthols can be carried out by multicomponent condensation of aldehydes, 2-naphthol and
amide in the presence of various catalysts such as SnCl4. 5H2O [12], Nano-sulfated zirconia [13],
Zirconium(IV) oxide chloride [14], dodecylphosphonic acid [15], ZrO(OTf)2 [16], and Bi(NO3)3.
5H2O [17]. However, some of these methods are not environmentally friendly and suffer from
one or more disadvantages, such as prolonged reaction times, low yields, toxicity and recovery
and reusability of the catalyst. Therefore, the development of clean processes and utilizing eco-
2
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friendly and green catalysts which can be simply recycled at the end of reactions have been
under permanent attention. The demand for environmentally benign procedure with
heterogeneous and reusable catalyst, promoted us to develop a safe alternate method for the
preparation of amidoalkyl naphthols [18].
The aim of this protocol is to highlight the synergistic effects of the combined use of
multicomponent reactions under solvent-free conditions and application of recyclable strong
solid acid catalyst with inherent magnetic property for the development of new eco-compatible
strategy for amidoalkyl naphthols synthesis. Therefore, we now wish to explore a straight
forward convergent synthesis of 1-amidoalkyl-2-naphthols via the one-pot three-component
reaction of β-naphthol, aldehydes derivatives, amides or urea under solvent free conditions using
MNPs-SO3H as an proficient, mild, harmless to the environment, non-toxic and magnetic
powerful solid acid catalyst with good stability (Scheme 1). To the best of our knowledge, the
use of magnetically solid acid catalyst for the synthesis of amidoalkyl naphthols previously has
not been reported.
R1
CHO
O
OH
O
3
MNPs-SO3H
N
R2
+
+
H2N
R2
H
Solvent free,
100°C
R1
OH
1
2
4a-x
Scheme 1. Synthesis of amidoalkyl naphthols.
2. Experimental
Chemical reagents in high purity were purchased from the Merck and Sigma Chemical
Company. All materials were of commercial reagent grade. 1H NMR and 13C NMR spectra were
recorded with a Bruker DRX-400 spectrometer at 400 and 100 MHz respectively. FT-IR spectra
were obtained with potassium bromide pellets in the range 400-4000 cm–1 with a Perkin–Elmer
3
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550 spectrometer. The element analyses (C, H, N) were obtained from a Carlo ERBA Model EA
1108 analyzer carried out on Perkin–Elmer 240c analyzer. The thermogravimetric analysis
(TGA) curves are recorded using a PL-STA 1500 device manufactured by Thermal Sciences.
Nanostructures were characterized using a Holland Philips Xpert X-ray powder diffraction
(XRD) diffractometer (CuK, radiation, λ= 0.154056 nm), at a scanning speed of 2°/min from 10°
to 100° (2θ). Scanning electron microscope (SEM) was performed on a FEI Quanta 200 SEM
operated at a 20 kV accelerating voltage. The samples for SEM were prepared by spreading a
small drop containing nanoparticles onto a silicon wafer and being dried almost completely in air
at room temperature for 2 h, and then were transferred onto SEM conductive tapes. The
transferred sample was coated with a thin layer of gold before measurement.
2.1. Preparation of the magnetic Fe3O4 nanoparticles (MNPs)
Fe3O4-MNPs were prepared using simple chemical coprecipitation described in the literature
[19]. Typically, 20 mmol of FeCl3.6H2O and 10 mmol of FeCl2.4H2O were dissolved in 75 ml of
distilled water in a three-necked bottom (250 mL) under Ar atmosphere for 1 h. Thereafter,
under rapid mechanical stirring, 10 ml of NaOH (10 M) was added into the solution within 30
min with vigorous mechanical stirring and ultrasound treatment under continuous Ar atmosphere
°
bubbling. After being rapidly stirred for 1 h, the resultant black dispersion was heated to 85 C
for 1 h. The black precipitate formed was isolated by magnetic decantation, exhaustively washed
with double-distilled water until neutrality, and further washed twice with ethanol and dried at 60
°C in vacuum. To obtain the well-dispersed Fe3O4 nanoparticles, the prepared magnetic
nanoparticles were added to 100 mL citric acid solution (0.3 M) and heated at 80 °C for 1 h. The
obtained citric acid modified magnetic nanoparticles (CMP) were precipitated with acetone to
4
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remove the excessive citrate groups adsorbed on the nanoparticles, collected with a magnet, and
vacuum-dried at 30 °C.
2.2. Silica coated magnetic nanoparticles (Fe3O4@SiO2 MNPs)
The Fe3O4@SiO2 core–shell nanoparticles were prepared according to the modified by the
Stöber method [20]. The details were as follows: 0.50 g of the obtained CMP above were
homogeneously dispersed in a mixture of 50 ml of ethanol, 9 ml of deioned water, and 1.0 ml of
28 wt% concentrated ammonia aqueous solution (NH3·3H2O), followed by the addition of 0.50
mL of tetraethyl orthosilicate (TEOS). After vigorous stirring at room temperature for 16 h, the
core–shell magnetic nanoparticles (Fe3O4@SiO2 MNPs) were isolated by magnetic decantation
to remove the unbounded silica particles and dried at room temperature at vacuum after being
washed with de-ionized water, ethanol and acetone.
2.3. General procedure for the synthesis of sulfuric acid functionalized Fe3O4 nanoparticles
(MNPs-SO3H)
A 500 ml suction flask was equipped with a pressure equalizing dropping funnel containing
chlorosulfunic acid and gas inlet tube for conducting HCl gas over adsorbing the solution water.
A flask was charged with Fe3O4@SiO2 MNPs (500 mg) and dispersed in dry CH2Cl2 by
ultrasonic bath for 10 min. Subsequently, chlorosulfunic acid (0.4 mL in dry CH2Cl2) was added
drop-wise manner to a cooled (ice-bath) solution of Fe3O4@SiO2 over a 30 min period, which
HCl gas evolved from the reaction vessel immediately. After the addition was completed, the
mixture was shaken for 30 min and brown solid (MNPs-SO3H) collected using an external
magnet and washed with methanol before being dried in an oven at 60 °C.
2.4. General synthesis for the preparation of amidoalkyl naphthols
5
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A mixture of β-naphthol (2 mmol), aldehyde (2 mmol), amide/urea (2.4 mmol) and MNPs-
SO3H (0.02 g) were taken in round bottom flask and stirred and heated at 100 °C. After the TLC
indicates the disappearance of starting materials, the reaction was cooled to room temperature.
The resultant solid was then washed with hot water to remove excess amide and the catalyst was
separated by an external magnet and reused as such for the next experiment. Then acetone was
added to it stirred well and filtered off. The filtrate was evaporated to remove solvent and the
crystalline material left was taken up in ethanol for recrystallization. The synthesized amidoalkyl
naphthols were characterized by IR, 1H NMR, 13C NMR and elemental analysis and comparison
of their physical data with the literatures.
2.5. Spectral data for new compounds
2.5.1. N-[(3-hydroxy-4-methoxyphenyl)-(2-hydroxynapthalen-1-yl)-methyl]acetamide (4l). IR
(KBr) (υmax/cm–1): 3400 (NH stretch), 3300-3050 (OH stretch), 1643 (C=O stretch), 1605, 1450
(C=C stretch), 1547 (NH bend), 753 (CH bend); 1H NMR (400 MHz, DMSO-d6): δH 9.90 (s, H,
OH), 8.75 (s, H, OH), 8.35 (d, J=8 Hz, 1H), 7.73 (d, J=7.8 Hz, 1H), 7.02-7.72 (m, 4H, Ar–H),
13
6.950-6-973 (m, 5H, Ar–H), 3.63 (s, 3H, OCH3), 1.90 (s, 3H, CH3) ppm; C NMR (100 MHz,
DMSO-d6): δC 169.4, 160.4, 146.7, 145.5, 140.4, 138.8, 134.1, 130.4, 127.4, 126.7, 125.5, 124.2,
119.3, 115.2, 55.6, 49.2, 23.1 ppm; Anal. Calcd. for C20H19NO4: C, 71.20; H, 5.68; N, 4.15; O,
18.97%. Found: C, 71.18; H, 5.66; N, 4.13; O, 18.94%.
2.5.2. N-[(2,3-dimethoxyphenyl)-(2-hydroxynapthalen-1-yl)-methyl]acetamide (4m). IR (KBr)
(υmax/cm–1): 3398 (NH stretch), 3300-3000 (OH stretch), 1645 (C=O stretch), 1600, 1455 (C=C
1
stretch), 1547 (NH bend), 750 (CH bend); H NMR (400 MHz, DMSO-d6): δH 10.49 (s, 1H,
OH), 8.84 (d, J=8 Hz, 1H), 8.02 (d, J=7.8 Hz, 1H), 7.96-8.54 (m, 4H, Ar–H), 6.54-7.69 (m, 5H,
13
Ar–H), 4.27 (s, 3H, OCH3), 3.30 (s, 3H, OCH3), 1.47 (s, 3H, CH3) ppm; C NMR (100 MHz,
6
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DMSO-d6): δC 169.3, 160.7, 155.2, 148.7, 136.3, 134.7, 130.2, 128.4, 127.5, 126.8, 124.2, 123.1,
119.5, 116.5, 113.3, 62.8, 57.5, 45.2, 23.2 ppm; Anal. Calcd. for C21H21NO4: C, 71.78; H, 6.02;
N, 3.99; O, 18.21%. Found: C, 71.74; H, 5.97; N, 3.95; O, 18.19%.
2.5.3. N-[(2-fluorophenyl)-(2-hydroxynapthalen-1-yl)-methyl]acetamide (4n). IR (KBr)
(υmax/cm–1): 3392 (NH stretch), 3300-2900 (OH stretch), 1639 (C=O stretch), 1600, 1452 (C=C
stretch), 1538 (NH bend), 752 (CH bend); 1H NMR (400 MHz, DMSO-d6): δH 9.91 (s, 1H, OH),
8.69 (d, J=8.2 Hz, 1H), 8.02 (d, J=7.8 Hz, 1H), 7.57-7.83 (m, 4H, Ar–H), 7.71-6.97 (m, 6H, Ar–
H), 2.14 (s, 3H, CH3) ppm; 13C NMR (100 MHz, DMSO-d6): δC 170.2, 167.6, 160.8, 137.1,
134.5, 133.8, 131.4, 127.3, 126.5, 125.2, 124.5, 119.7, 116.6, 48.7, 24.1 ppm; Anal. Calcd. for
C19H16FNO2: C, 73.77; H, 5.21; F, 6.14; N, 4.53; O, 10.34%. Found: C, 73.72; H, 5.17; F, 6.09;
N, 4.48; O, 10.30%.
2.5.4. N-((2-Hydroxynaphthalen-1-yl)-(naphthalen-1-yl)methyl)acetamide (4o). IR (KBr)
(υmax/cm–1): 3415 (NH stretch), 3300-2310 (OH stretch), 1638 (C=O stretch), 1605, 1437 (C=C
stretch), 1523 (NH bend), 748 (CH bend); 1H NMR (400 MHz, DMSO-d6): δH 9.41 (s, 1H, OH),
8.52 (d, J=8.5 Hz, 1H), 8.12 (d, J=8.1 Hz, 1H), 7.81-7.85 (m, 7H, Ar–H), 7.28-7.34 (m, 6H, Ar–
H), 2.88 (s, 3H, CH3) ppm; 13C NMR (100 MHz, DMSO-d6): δC 169.3, 161.4, 139.6, 137.5, 137,
134.1, 130.8, 126.8, 125.6, 124.7, 124.1, 119.4, 48.1, 23.5 ppm; Anal. Calcd. for C23H19NO2: C,
80.92; H, 5.61; N, 4.10; O, 9.37%. Found: C, 80.85; H, 5.57; N, 4.02; O, 9.33%.
3. Results and discussion
The magnetite nanoparticles were prepared by coprecipitation of iron(II) and iron(III) ions in
basic solution. To improve the chemical stability of Fe3O4 nanoparticles, their surface
engineering was successfully performed by the suitable deposition of silica onto nanoparticles
surface by the ammonia-catalyzed hydrolysis of tetraethylorthosilicate (TEOS). Then, the
7
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Fe3O4@SiO2 served as support for the immobilization of SO3H groups by simple mixing of
core–shell nanocomposite and chlorosulfonic acid in CH2Cl2 (MNPs-SO3H) (Scheme 2). The
number of H+ sites of MNPs-SO3H was determined by pH-ISE conductivity titration (Denver
Instrument Model 270) and found to be 1.85 H+ sites per 1 g of solid acid at 25 °C.
Scheme 2. Preparation steps for fabricating sulfuric acid-functionalized magnetic Fe3O4 nanoparticles.
Fig. 1 shows the FTIR spectra of both the unfunctionalized and functionalized magnetic
nanoparticles. The Fe–O stretching vibration near 580 cm–1, O–H stretching vibration near 3432
cm–1, O-H deformed vibration near 1625 cm-1 were observed for both in Fig. 1(a) and 1(b). The
significant features observed for Fig. 1(b) are the appearance of the peaks at 476, 808, and 1090
cm-1 are ascribed to the asymmetric stretching vibration, symmetric stretching vibration and bending
vibration Si–O–Si groups respectively. The wider and stronger peak at about 3448 cm–1
demonstrates that there are some free Si-OH in the samples [21]. The presence of sulfonyl group
is confirmed by 1217 and 1124 cm–1 bands that were covered by a stronger absorption of Si-O
8
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bond at 1090 cm-1. In addition, the Si-OH group peak at 900 cm-1 was disappeared for
Fe3O4@Silica sulfuric acid [22]. The increase in the intensities of the band at 2800–3700 cm−1
suggests that there are more OH groups under the magnetic nanoparticle surface after the
sulfonation. On the other hand, the band in this region became much broader [1]. All these
observations confirm that the sulfonic groups have functionalized the surface of the magnetic
nanoparticles (MPs).
(a)
(b)
(c)
Fig. 1. The comparative FT-IR spectra for (a) Fe3O4, (b) Fe3O4@SiO2 and (c) MNPs-SO3H.
Fig. 2 presents the XRD-diffraction patterns of the prepared MNPs and MNPs-SO3H. The
same peaks were observed in the both of the MNPs and MNPs-SO3H XRD patterns, indicating
retention of the crystalline spinel ferrite core structure during the silica-coating process. The
XRD patterns of the particles (JCPDS card No. 85-1436) show six characteristic peaks reveal a
cubic iron oxide phrase (2θ = 30.35, 35.95, 43.45, 53.70, 57.25, 62.88, 71.37, 74.46). These are
related to their corresponding indices (2 2 0), (3 1 1), (4 0 0), (3 3 1), (4 2 2), (3 3 3), (4 4 0) and
(5 3 1) respectively [29]. The broad peaks at 2θ from 23◦ to 27◦ shown in Fig. 2(b) are ascribed to
amorphous silica [23].
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3 1 1
(b)
3 3 3
2 2 0
MNPs-SO3H
4 2 2
3 3 1
4 0 0
5 3 1
4 4 0
(a) MNPs
Fig. 2. XRD patterns of (a) Fe3O4 and (b) MNPs-SO3H.
The components of the Fe3O4, Fe3O4@SiO2 and MNPs-SO3H nanoparticles were analysis by
using energy dispersive spectrometer (EDS) in Fig 3(a), (b) and (c), respectively. The presence
of Si, O, and Fe signals in Fig. 3(b) indicates that the iron oxide particles were loaded into silica,
and the higher intensity of Si peak compared with Fe peaks indicates Fe3O4 nanoparticles were
trapped by SiO2. The characteristic peak of S in Fig. 3(c) indicates that the iron oxide
nanoparticles have been coated by SO3H. According to the above analysis, it could be concluded
MNPs-SO3H have been successfully synthesized.
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11000
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
FeK
(a)
OK
FeL
(b)
20000
15000
10000
5000
0
OK
FeL
SiK
MNPs
Fe3O4@SiO2
FeK
FeK
FeK
keV
keV
0
5
10
0
5
10
(c)
MNPs-SO3H
Fig. 3. The EDS spectra of (a) Fe3O4, Fe3O4@SiO2 and (c) MNPs-SO3H nanoparticles.
The thermogravimetric analysis (TGA) curves of the Fe3O4 MNPs, and MNPs-SO3H show the
mass loss of the organic materials as they decompose upon heating (Fig. 4). The initial weight
loss from the Fe3O4 MNPs up to 126 ◦C is due to the removal of physically adsorbed solvent and
surface hydroxyl groups. The TGA curve of the MNPs-SO3H was divided into several regions
corresponding to different mass lose ranges. The first region, which occurred below 160 °C,
displayed a mass loss that was attributable to the loss of adsorbed solvent or trapped water from
the catalyst. The weight loss at higher temperature (250-350°C) could be mainly attributed to the
evaporation and subsequent decomposition of SO3H groups. Thus, the catalyst was stable up to
200 °C, confirming that it could be safely used in organic reactions at temperatures in the range
of 100 °C [7, 1].
11
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Description: C:\Documents and Settings\Zarnegar\Desktop\ﻣﻘﺎﻟﮫ\overlay[1].jpg
Fig. 4. TGA curve of (a) Fe3O4 MNPs, and (b) MNPs-SO3H nanoparticles.
Fig. 5 shows SEM images of the relative nanoparticles. It can be seen from Fig. 5(a) that
magnetite (Fe3O4) particles have a mean diameter of about 28-35 nm and a nearly spherical
shape. The SEM image shown in Fig. 5(b) demonstrates that most of Fe3O4@SiO2 nanoparticles
are spherical with particle size in the about 120 nm. Fig. 5(c) shows that Fe3O4@SiO2-SO3H
nanoparticles are nearly spherical with nano dimension ranging from 120 to 150 nm in size and
smoother surface.
(a)
(b)
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(c)
Fig. 5. The SEM image of (a) Fe3O4 (b) Fe3O4@SiO2 and (c) MNPs-SO3H nanoparticles.
The magnetic property of the catalyst was studied by vibrating-sample magnetometer (VSM)
in Fig. 6. The magnetization curve for Fe3O4 nanoparticles, Fe3O4@SiO2 and MNPs-SO3H are
shown in Fig. 6. The saturation magnetization of Fe3O4@SiO2 and MNPs-SO3H were found to
be 22.67 and 45.87 emu/g, respectively, which are much lower than bare Fe3O4 MNPs (67.22
emu/g) [19].
80
60
Fe3O4 MNPs
40
Fe3O4@SiO2
20
MNPs-SO3H
0
-20
-40
-60
-80
-10000 -8000 -6000 -4000 -2000
0
2000 4000 6000 8000 10000
Applied Field(Oe)
Fig. 6. Magnetization curves for the prepared Fe3O4 MNPs, Fe3O4@SiO2 and MNPs-SO3H at room
temperature.
13
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After characterization of the solid acid catalyst, we have tested its catalytic activity in the
preparation of amidoalkyl naphthol derivatives. In a typical experimental procedure, a mixture of
aldehyde (2 mmol), β-naphthol (2 mmol), amide (2.4 mmol) and MNPs-SO3H (0.02 g) as a
model study were taken in round bottom flask and stirred for a certain period of time as required
°
to complete the reaction (as indicated by TLC) at 100 C in a preheated oil bath. As shown in
Table 1, the best result was obtained by carrying out the reaction using 0.02 g of MNPs-SO3H at
°
100 C under solvent-free conditions (Table 1, Entry 8). Furthermore, no reaction was observed
when the mixture was heated to 100 ◦C for 6 h in the absence of catalyst (Table 1, Entry 10).
Table 1
Optimization of the amount of catalyst and the reaction temperature for the preparation of amidoalkyl
naphthols. a
Entry
Catalyst (g)
0. 008
0.010
0.015
0.020
0.025
0.020
0.020
0.020
0.020
-
Temperature (◦C)
Time (min)
Yieldb (%)
1
2
3
4
5
6
7
8
9
90
90
90
90
90
70
80
100
110
100
60
45
35
15
15
60
30
10
10
55
67
78
90
90
70
83
95
95
0
10
12 (h)
a Reaction conditions: benzaldehyde (2 mmol), β-naphthol (2 mmol), and acetamide (2.4 mmol) under solvent-free
conditions.
b Isolated yields.
Using these optimized reaction conditions, we extended the reaction to substituted aromatic
and aliphatic aldehydes, which reacted with amides/urea and β-naphthol in Table 2. As evident
from the results, this procedure is uniformly effective for both aliphatic and aromatic aldehydes.
The aliphatic aldehydes such as n-butyraldehyde and propionaldehyde were subjected under the
reaction conditions and corresponding desired products were isolated in excellent yields.
Aromatic aldehydes with both activating and deactivating groups such as Me, OMe, Cl, N(Me)2,
F and NO2 reacted to afford the corresponding products in high yields. It was shown that
14
Page 14 of 22

aromatic aldehydes with electron-withdrawing groups reacted faster than those with electron-
releasing groups as expected and sterically hindered aromatic aldehydes required longer reaction
times. The rate of reaction of these aldehydes decreased compared to aldehydes with electron-
donating groups, but the yield of the corresponding products was higher than benzaldehydes with
electron-donating groups. In addition, urea, acetamide and benzamide underwent smooth
transformation under the reaction conditions, whereas the reaction was unsuccessful with
thiourea.
Table 2
Synthesis of amidoalkyl naphthols in the presence of MNPs-SO3H without solvent.a
Entry R1
R2
Product Time (min) Yieldb (%) Mp (lit. mp)[ref]
1
C6H5
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
10
30
35
20
7
93
85
80
83
97
93
93
90
87
85
87
90
93
80
95
85
90
82
92
80
80
83
88
77
242-244 [245–246]24
223-224 [222–223]24
120-122 [123–125]24
184-186 [183–185]24
253-254 [256–258]25
228-230 [230–232]24
202-203 [201–203]24
253-254 [251–253]24
236-237 [235–237]24
214-216 [213–215]24
217-219 [218–219]25
236-238
4a
4b
4c
4d
4e
4f
2
3
4
5
4-CH3C6H4
4-N(CH3)2C6H4
4-CH3OC6H4
3-NO2C6H4
4-FC6H4
6
10
7
7
8
9
2,4-Cl2C6H3
2,5-(CH3O)2C6H3
3,4-(CH3O)2C6H3
2-ClC6H4
2-NO2C6H4
3-OH,4-CH3OC6H3 CH3
2,3-(CH3O)2C6H3
2-FC6H4
C10H7
CH3CH2
CH3CH2CH2
C6H5
3-NO2C6H4
4-CH3OC6H4
2-ClC6H4
C6H5
3-NO2C6H4
4-CH3C6H4
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
4q
4r
4s
10
10
20
25
10
10
20
10
10
10
10
7
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
CH3
CH3
CH3
CH3
CH3
C6H5
C6H5
C6H5
C6H5
NH2
NH2
NH2
231-233
244-245
229-230
179-181 [179–180]26
222-223 [224–226]26
238-240 [237–238]26
230-233 [232–234]26
209-211 [208–210]26
285-287 [284–285]25
177-178 [177–179]26
190-192 [193]27
20
20
10
7
4t
4u
4v
4w
4x
20
113-115 [115–117]28
a Reaction conditions: β-naphthol 2 mmol, aldehyde 2 mmol, amide 2.4 mmol, MNPs-SO3H 0.02 g, at 100 ◦C.
b Isolated yields.
15
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In a plausible mechanism (Scheme 3) which is supported by the literature [24, 27]; at first,
aromatic aldehyde is activated by acidic group of MNPs to produce I. Then, β-naphthol attacks
to the carbonyl group of the activated aldehyde, and affords intermediate II. Next, by removing
H2O from II, ortho-quinone methides (o-QMs, III) is prepared. MNPs-SO3H again activates
intermediate
to give
as a Michael acceptor. Afterward, Michael addition of amide or urea
IV
III
to intermediate IV affords the expected 1-amidoalkyl-2-naphthol. The aromatic aldehydes with
electron-withdrawing groups reacted faster as compared with those having electron-releasing
groups. As per earlier report [24], the lower energy of LUMO of the alkene containing electron-
withdrawing groups (a carbonyl group as in o-QM intermediate) as compared to that of alkene
containing electron-donating groups may be responsible for making the present reaction faster.
SO3H
O
O
OH
R1
H
SO3H
OH
..
H
H
O
-H2O
R1
R1
II
I
O
R1
R2
OH
N
O
H
R1
SO3H
R1
O
..
H2N
R2
O
HSO3
(o-QMs)
III
1-Amidoalkyl-2-naphtol
IV
Scheme 3. Possible mechanism for the synthesis of amidoalkyl naphthol using MNPs-SO3H.
A comparison of the efficacy of MNPs-SO3H catalyst with some of those reported in the
literature is presented in Table 3 for the preparation of N-[Phenyl-(2-hydroxynapthalen-1-yl)-
methyl]acetamide (4a). The results showed that MNPs-SO3H is a better catalyst with respect to
reaction times and yields of the products. Also, it is seen in addition to having the general
16
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advantages attributed to the inherent magnetic property of nanocatalysts, MNPs-SO3H is an equally
or more efficient catalyst for this three component reaction.
Table 3
Comparison of MNPs-SO3H with other catalysts reported in the literature for the synthesis of N-[phenyl-
(2-hydroxynapthalen-1-yl)-methyl]acetamide.a
Entry Catalyst
Amount; condition
Time
5 h
Yieldb (%) Ref.
p-TSA
10 mol%; solvent-free, 125 ◦C
50 mol%; solvent-free, 30 ◦C
0.02 g; solvent-free, r.t
85
88
85
90
90
93
30
1
Sulphamic acid
Silica sulfuric acid
15 min
2 h
18
22
2
3
4
5
6
Montmorillonite K10 0.1 g; solvent-free, 125 ◦C
1.5 h
40 min
10 min
31
SiO2–HClO4
MNPs-SO3H
0.6 mol%; solvent-free, 125 ◦C
0.02 gr, solvent-free, 100 ◦C
21
This work
a Reaction conditions: β-naphthol (2 mmol), benzaldehyde (2 mmol), and acetamide (2.4 mmol).
b Isolated yields.
The reusability is one of the important properties of this catalyst. The recyclability of MNPs-
SO3H was investigated for the reaction of 3-nitrobenzaldehdye, acetamide and β-naphthol. After
completion of reaction the separated catalyst can be reused after washing with acetone and
◦
drying at 80 C. It was shown that the catalyst could be reused for the next cycle without any
appreciable loss of its activity (Fig 7). The effect of catalyst was unchanged which was
determined by measuring the acidic site loading of the reused MNPs-SO3H and hence
conforming the purity of MNPs-SO3H.
17
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Fig. 7. Recyclability of MNPs-SO3H in the reaction of β-naphthol (2 mmol), 3-nitrobenzaldehdye (2
mmol), acetamide (2.4 mmol), catalyst (0.02 g) at 100 ◦C.
4. Conclusion
Sulfuric acid functionalized Fe3O4 nanoparticles is successfully achieved by a multiple
synthetic procedure which is confirmed with XRD, FT-IR, TGA, VSM, and SEM. The most
interesting features of the present work include durability as well as efficient catalytic activity for
one-pot synthesis of amidoalkyl naphthols by one-pot three-component coupling of β-naphthol,
◦
aromatic and aliphatic aldehydes and urea or amides under solvent free at 100 C, MNPs-SO3H
as an inexpensive and non-hazardous solid acid catalyst which can be handled easily and
removed from the reaction mixtures by applying an external magnetic field. This method offers
several advantages including short reaction time, excellent yields, simple work-up, ease of
separation, and recyclability of the magnetic catalyst, as well as the ability to tolerate a wide
variety of substitutions in the reagents.
Acknowledgments
18
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We gratefully acknowledge the financial support from the Research Council of the University
of Kashan for supporting this work by Grant NO. (256722/IV).
References
[1] N. Koukabi, E. Kolvari, M.A. Zolfigol, A. Khazaei, B.S. Shaghasemi, B. Fasahatib, Adv.
Synth. Catal. 354 (2012) 2001-2008.
[2] S. Rostamnia, A. Nuri, H. Xin, A. Pourjavadi, S. H. Hosseini, Tetrahedron Lett. 54 (2013)
3344-3347.
[3] X. Zheng, S. Luo, L. Zhang, J.P. Cheng, Green Chem. 11 (2009) 455–458.
[4] Y. Lin, H. Chen, K. Lin, B. Chen, C. Chiou, J. Environ. Sci. 23(1) (2011) 44–50.
[5] N.M. Mahmoodi, S. Khorramfar, F. Najafi, Desalination 279 (2011) 61-68.
[6] F. Nemati, R. Saeedirad, Chinese Chem Lett. 24 (2013) 370-372.
[7] F. Nemati, M. M. Heravi, R. Saeedirad, Chinese J Catal. 33 (2012) 1825-1831.
[8] M. Kidwai, R. Chauhan. J. Mol. Catal. A: Chem. 377 (2013) 1–6.
[9] A. Hasaninejad, S. Firoozi, F. Mandegani. Tetrahedron Lett. 54 (2013) 2791-2794.
[10] T. Dingermann, D. Steinhilber, G. Folkers, In Molecular Biology in Medicinal Chemistry,
Wiley-VCH, 2004.
[11] A.Y. Shen, C.T. Tsai, C.L. Chen, Eur. J. Med. Chem. 34 (1999) 877-882.
[12] M. Wang, Y. Liang, T.T. Zhang, J. J. Gao, Chem. Nat. Compd. 48 (2012) 185-188.
[13] A. Zali, A. Shokrolahi, Chinese Chem. Lett. 23 ( 2012) 269-272.
[14] M.A. Zolfigol, A. Khazaei, A.R. Moosavi-Zare, A. Zareb, V. Khakyzadeha, Clin. Biochem.
44 (2011)163-S164.
19
Page 19 of 22

[15] M. Zandi, A.R. Sardarian, C.R. Chimi. 15 (2012) 365-369.
[16] H. Hashemi, A.R. Sardarian, J Iran Chem Soc. 10 (2013) 745–750.
[17] M. Wang, Y. Liang, T.T. Zhang, J.J. Gao, Chinese Chem. Lett. 23 (2012) 65–68.
[18] R.R. Nagawade, D.B. Shinde, Chin. J. Chem. 25 (2007) 1710-1714.
[19] J. Safari, Z. Zarnegar, M. Heydarian, Bull. Chem. Soc. Jpn. 85 (2012) 1332-1338.
[20] W. Stöber, A. Fink, E. Bohn, J. Colloid Interface Sci. 26 (1968) 62-69.
[21]. G. Feng, D. Hu, L. Yangc, Y. Cuic, X. Cui, H. Li, Sep. Purif. Technol. 74 (2010) 253–260.
[22] M.Z. Kassaee, H. Masrouri, F. Movahedi, Appl. Catal. A: Gen. 395 (2011) 28–33
[23]. G. Feng, D. Hu, L. Yangc, Y. Cuic, X. Cui, H. Li, Sep. Purif. Technol. 74 (2010) 253–260.
[24] H.R. Shaterian, H. Yarahmadi, Tetrahedron Lett. 49 (2008) 1297–1300.
[25] G.Ch. Nandi, S. Samai, R. Kumar, M.S. Singh, Tetrahedron Lett. 50 (2009) 7220–7222.
[26] M. Wang, Y. Liang, T.T. Zhang, J.J. Gao, Chinese Chem. Lett. 23 (2012) 65–68.
[27] D.A. Kotadia, S.S. Soni, J Mol. Catal. A: Chem. 353– 354 (2012) 44–49.
[28] A. Zali, A. Shokrolahi, Chinese Chem. Lett. 23 (2012) 269–272.
[29] J. Safari, Z. Zarnegar, Monatsh Chem. 144 (2013) 1389–1396.
[30] H.R. Shaterian, H. Yarahmadi, M. Ghashang, Tetrahedron. 64 (2008) 1263-1269.
[31] B. Das, K. Laxminarayana, B. Ravikanth, B.R. Rao, J. Mol. Catal. A: Chem. 261 (2007)
180-183.
20
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Graphical Abstract
A Magnetic nanoarticle-supported sulfuric acid as a highly efficient and reusable
catalyst for rapid synthesis of amidoalkyl naphthols
Javad Safari*, Zohre Zarnegar
R1
CHO
O
OH
O
3
MNPs-SO3H
N
R 2
+
+
H2N
R2
H
Solvent free,
100°C
R1
OH
1
2
4a-x
21
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highlights
 MNP-SO3H was prepared and amidoalkyl naphthol was synthesized using this catalyst.
 Sulfuric acid functionalized Fe3O4 nanoparticles were caracterized by XRD, FT-IR,
TGA, VSM, and SEM.
 The catalyst was separated by an external magnet and reused as such for the next
experiment.
22
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