Sulfanilic acid-functionalized silica-coated magnetite nanoparticles as an efficient, reusable and magnetically separable catalyst for the solvent-free synthesis of 1-amido- and 1-aminoalkyl-2-naphthols

Article abstract of DOI:10.1039/c4ra03676j

Sulfanilic acid-functionalized silica-coated nano-Fe₃O ₄ particles (MNPs-PhSO₃H) have been prepared as a reusable heterogeneous acid catalyst using a facile process. The catalytic performance of this novel material has been studied in the synthesis of 1-amido- and 1-aminoalkyl-2-naphthol derivatives via a one-pot three-component condensation reaction of aldehydes, 2-naphthol, and amides/urea/amines in good to excellent yields, under solvent-free classical heating conditions. The catalyst was easily separated from the reaction mixture with the assistance of an external magnetic field and reused for several consecutive runs without significant loss of its catalytic efficiency. Results obtained from transmission electron microscopy (TEM), scanning electron microscope (SEM), powder X-ray diffraction (XRD) and sample magnetometery (VSM) show that the synthesized magnetic nanocomposites are superparamagnetic with a size range of 15-30 nm.

Full text of DOI:10.1039/c4ra03676j

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Sulfanilic acid-functionalized silica-coated
magnetite nanoparticles as an efficient, reusable
Cite this: RSC Adv., 2014, 4, 28176
and magnetically separable catalyst for the solvent-
free synthesis of 1-amido- and 1-aminoalkyl-2-
naphthols
a
H. Moghanian, A. Mobinikhaledi,b A. G. Blackmanc and E. Sarough-Farahanib
*
Sulfanilic acid-functionalized silica-coated nano-Fe3O4 particles (MNPs–PhSO3H) have been prepared as
a reusable heterogeneous acid catalyst using a facile process. The catalytic performance of this novel
material has been studied in the synthesis of 1-amido- and 1-aminoalkyl-2-naphthol derivatives via a
one-pot three-component condensation reaction of aldehydes, 2-naphthol, and amides/urea/amines in
good to excellent yields, under solvent-free classical heating conditions. The catalyst was easily
separated from the reaction mixture with the assistance of an external magnetic field and reused for
several consecutive runs without significant loss of its catalytic efficiency. Results obtained from
transmission electron microscopy (TEM), scanning electron microscope (SEM), powder X-ray diffraction
(XRD) and sample magnetometery (VSM) show that the synthesized magnetic nanocomposites are
superparamagnetic with a size range of 15–30 nm.
Received 22nd April 2014
Accepted 17th June 2014
DOI: 10.1039/c4ra03676j
www.rsc.org/advances
Thus, due to their biological, medicinal and pharmacological
importance, many procedures have been developed for the
1. Introduction
preparation of 1-amidoalkyl-2-naphthols from aldehydes,
2-naphthols, and amides or urea under thermal heating and
sonication conditions using catalysts such as pTSA,16 mont-
morillonite K10,17 iodine,18 Fe(HSO4)3,19 N,N,N0,N0-tetra-
bromobenzene-1,3-disulphonamide [TBBDA],20 SnCl4$5H2O,21
H4SiW12O40,22 dodecylphosphonic acid,23 cyanuric chloride,24
Bi(NO3)3$5H2O,25 ZrO(OTf)2,26 P2O5,27 thiamine hydrochloride,28
HClO4–SiO2,29 cation-exchange resins,30 silica sulfuric acid,31
zwitter ionic salts32 and Brønsted acidic ionic liquids.33
However, some of these methods are not environmentally
friendly and suffer from one or more limitations, such as
prolonged reaction times, high reaction temperature, low yields
of the desired product, tedious work-up, toxicity, and poor
recovery and reusability of the catalyst. Therefore, a great
demand still exists for versatile, simple, and environmentally
friendly processes for the synthesis of 1-amido- or 1-aminoalkyl-
2-naphthols under simple and practical conditions.
Organic–inorganic hybrid materials as heterogeneous cata-
lyst have received much recent attention as they permit mutual
advantages of both homogeneous as well as heterogeneous
catalysts in organic synthesis.34–37 In this context, the use of
nanoparticles as heterogeneous catalyst supports have received
increasing attention because their small diameters provide
large external surface areas for catalysis, which allows a high
dispersion of the active species and provides a large amount of
the active and accessible centers.38–40 However, tedious recovery
Multicomponent reactions (MCRs) are of increasing impor-
tance in organic synthesis for building diverse and complex
organic molecules through tandem carbon–carbon and carbon–
heteroatom bond formation.1–5 Advantages of these reactions
include the use of simple procedures, time and energy effi-
ciency, high bond formation yields and low cost.6 The devel-
opment of one-pot MCRs and the improvement of known MCRs
are areas of research which have attracted considerable atten-
tion in recent years.7,8 One of these MCRs is the preparation of
amidoalkyl naphthols. Amidoalkyl naphthols having 1,3-amino-
oxygenated functional groups exist in a variety of biologically
signicant natural products as well as in drugs including a
number of nucleosides, antibiotics and HIV protease inhibitors,
such as lipinavir and ritonavir.9–11 It is worth to noting that
1-amidoalkyl-2-naphthols can be easily converted to 1-amino-
alkyl-2-naphthol derivatives, which shows important biological
activities like depressor and bradycardiac effect12,13 by amide
hydrolysis reactions. These 1-aminoalkyl alcohol-type ligands
have been used for both asymmetric synthesis and catalysis.14,15
aDepartment of Chemistry, Dezful Branch, Islamic Azad University, Dezful, Iran.
E-mail: moghanian@gmail.com
bDepartment of Chemistry, Faculty of Science, Arak University, Arak 38156-8-8349,
Iran
cSchool of Applied Sciences, Auckland University of Technology, Private Bag 92006,
Auckland 1142, New Zealand
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procedures via ltration or centrifugation and the inevitable bind covalently to the free-OH groups at the surface of the
loss of solid catalysts in the separation process have limited particles. Finally, reaction of the 3-chloropropyl-functionalized
their application.
magnetic silica nanoparticles (Fe3O4@SiO2–Cl) with sulfanilic
In recent years, magnetic nanoparticles (MNPs) (e.g. Fe3O4) acid gives the sulfanilic acid-functionalized silica-coated
have been extensively investigated as inorganic catalyst magnetite nanoparticles (MNPs–PhSO3H).
supports in the synthesis of organic–inorganic hybrid catalysts,
The as-prepared catalyst was also characterized by Fourier
because of their good stability, easy synthesis and functionali- transform infrared spectroscopy (FTIR), X-ray diffraction (XRD),
zation and high surface area, as well as low toxicity and eld emission scanning electron microscopy (FE-SEM), trans-
price.41,42 An important feature of these nano-catalysts is their mission electron microscopy (TEM), the energy dispersive X-ray
separation from the reaction mixture using an external magnet, (EDX),vibrating sample magnetometry (VSM), and thermogra-
thereby obviating the need for ltration. However, magnetic vimetric analysis (TGA). Fig. 1 shows the FT-IR spectrum of
nanoparticles can easily aggregate into larger clusters, due to Fe3O4, Fe3O4@SiO2, Fe3O4@SiO2–Cl, and MNPs–PhSO3H
anisotropic dipolar attraction, and thereby lose their dis- nanoparticles in the wavenumber range 4000–400 cmꢀ1. The
persibility and catalytic activity.43 In addition, Fe3O4 nano- FT-IR spectrum of the MNPs was similar to those of Fe3O4
particles undergo reactions in an acid environment which lead materials described in the literature. FT-IR spectra of the bare
to loss of their magnetic properties, and thus oen require magnetic Fe3O4 nanoparticles displayed the characteristic Fe–O
coating with a protective shell of silica to form a core-shell absorption around 575 cmꢀ1 (Fig. 1a).
(Fe3O4@SiO2) structure. The silica shell can prevent the aggre-
gation of the Fe3O4 particles and provide numerous surface Si– about 1090, 950, 800 and 465 cmꢀ1 which are attributed to the
OH groups for further modication.44,45
asymmetric stretching, symmetric stretching, in plane bending
Fe3O4@SiO2 shows characteristic IR absorption bands at
With the aim of developing a more efficient synthetic and rocking mode of the Si–O–Si group, respectively. These
process, herein, we report the synthesis of a new silica-coated results conrm the presence of SiO2. The broad peaks in the
Fe3O4 nanoparticle-supported sulfanilic acid (MNPs–PhSO3H) range 3200–3500 cmꢀ1 and the weak peak at 1620 cmꢀ1 are due to
and its application as an inexpensive, highly efficient and the O–H stretching vibration mode (Si–OH) and twisting vibra-
magnetically recoverable catalyst for the synthesis of 1-amido- tionmodeofH–O–Hadsorbedinthesilicashell, respectively.The
or aminoalkyl naphthol via the one-pot three-component reac- presence of the anchored alkyl groups is conrmed by the weak
tion of b-naphthol, aldehydes, and amides/urea/amines under aliphatic C–H symmetric andasymmetric stretchingvibrationsat
solvent-free classical heating conditions.
2926 and 2963 cmꢀ1 in Fig. 1c and d. Thus the above results
indicate that the functional groups weresuccessfully graed onto
the surface of the magnetic Fe3O4@SiO2 nanoparticles.
2. Results and discussion
2.1. Preparation and characterization of the catalyst
The nanoparticle size and morphology of MNPs–PhSO3H
catalyst were investigated by eld emission scanning electron
microscopy (FE-SEM) (Fig. 2). As can be seen from Fig. 2, MNPs–
PhSO3H particles have a mean diameter of about 15–35 nm and
a nearly spherical shape. The energy dispersive X-ray spectros-
copy (EDS) results, obtained from SEM analysis of MNPs–
PhSO3H, are shown in Fig. 3, and clearly show the presence of S
in the MNPs–PhSO3H catalyst. Moreover, the presence of Si, O,
and Fe signals indicates that the iron oxide particles are loaded
The magnetic nanoparticle supported sulfanilic acid catalyst
(MNPs–PhSO3H) was prepared following the procedure shown
in Scheme 1. Magnetite (Fe3O4) nanoparticles were easily
prepared via the chemical co-precipitation of Fe2+ and Fe3+ ions
in basic solution. These were subsequently coated with silica
(Fe3O4@SiO2) through the well-known Stober method.46 The
Fe3O4@SiO2 core–shell structures were then sequentially
treated with 3-chloropropyltriethoxysilane (CPTS), which can
Scheme 1 Preparation of sulfanilic acid-functionalized silica-coated Fig. 1 The comparative FT-IR spectra for (a) Fe3O4, (b) Fe3O4@SiO2,
nano-Fe3O4 particles.
(c) Fe3O4@SiO2–Cl and (d) MNPs–PhSO3H.
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Fig. 2 FE-SEM images of MNPs–PhSO3H nanoparticles.
Fig. 3 EDS spectra of MNPs–PhSO3H nanoparticles.
into silica, and the higher intensity of the Si peak compared with
the Fe peaks indicates that the Fe3O4 nanoparticles were trapped
by SiO2. According to the above analysis, it can be concluded that
the MNPs–PhSO3H have been successfully synthesized. In
addition, TEM analysis shows a dark nano-Fe3O4 core sur-
rounded by a grey silica shell about 5–10 nm thick and the
average size of the obtained particles is 15–30 nm (Fig. 4).
The presence as well as the degree of crystallinity of magnetic
Fe3O4 and the MNPs–PhSO3H catalyst was obtained from XRD
measurements (Fig. 5). The same peaks were observed in the
both of the MNPs and MNPs–PhSO3H XRD patterns, indicating
retention of the crystalline spinel ferrite core structure during
the silica-coating process. The XRD data of the synthesized
magnetic nanoparticles show diffraction peaks at 2q ¼ 30.4ꢁ,
35.7ꢁ, 43.3ꢁ, 53.9ꢁ, 57.3ꢁ, 63.0ꢁ, and 74.5ꢁ which can be assigned
to the (220), (311), (400), (422), (511), (440) and (533) planes of
Fe3O4, respectively, indicating that the Fe3O4 particles in the
nanoparticles were pure Fe3O4 with a cubic spinel structure;
these match well with the standard Fe3O4 sample (JCPDS card
no. 85-1436). The broad peak from 2q ¼ 20ꢁ to 27ꢁ (Fig. 2b) is
consistent with an amorphous silica phase in the shell of the
silica-coated Fe3O4 nanoparticles (Fe3O4@SiO2).47
Fig. 4 TEM image of MNPs–PhSO3H nanoparticles.
(311) powder peak, and q corresponds to the Bragg angle of the
(311) peak in degrees.48 From the width of the peak at 2q ¼ 35.7ꢁ
(311), the crystallite size of the magnetic nanoparticle is calcu-
lated to be 14.7 nm using Scherrer's equation, which is smaller
than the size determined by FE-SEM and TEM analysis (Fig. 2
and 4). The observed difference can be attributed to the fact that
XRD measurements consider crystallite sizes as sizes of
“coherently diffracting domains” of crystals while grains may
contain several of these domains.
The (311) XRD peak was used to estimate the average crys-
tallite size of the magnetic nanoparticles by Scherrer's formula
(D ¼ 0.9l/b cos q), where D is the average crystalline size, l is the
X-ray wave-length (0.154 nm), b denotes the full width in
radians subtended by the half maximum intensity width of the
The stability of the MNPs–PhSO3H catalyst was determined
by thermogravimetric analysis (TGA) and derivative thermo-
gravimetry (DTG) (Fig. 6). The magnetic catalyst shows two
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Fig. 7 The magnetic hysteresis loops of Fe3O4 MNPs (a), and MNPs–
PhSO3H (b). Left inset: the magnified field from ꢀ15 to 15 Oe. Right
inset: the picture displays the catalyst was dispersed in liquid and
captured by the outer magnet.
Fig. 5 XRD diffraction pattern of Fe3O4 MNPs (a), and Fe3O4@SiO2–
PhSO3H MNPs (b).
shows the plots of room temperature magnetization (M) versus
magnetic eld (H) (M–H curves or hysteresis loops) of Fe3O4 and
MNPs–PhSO3H nanoparticles. The hysteresis curve allows
determination of the saturation magnetization (Ms), remanent
magnetization (Mr) and coercivity (Hc). The magnetization of
samples could be completely saturated at high elds of up to
ꢂ8000.0 Oe and the Ms of samples changed from 57.6 to 38.5
emu gꢀ1, due to the formation of a silica shell around the Fe3O4
core. The hysteresis loops show the super-paramagnetic
behavior of the Fe3O4 and MNPs–PhSO3H particles in which the
Mr and the Hc are close to zero (Mr ¼ 0.85 and 0.45 emu per g,
and Hc ¼ 4.90 and 4.0 Oe, respectively).49 The strong magneti-
zation of the nanoparticles was also revealed by simple attrac-
tion with an external magnet (Fig. 7).
Fig. 6 TG-DTG analyses for MNPs–PhSO3H nanoparticles.
weight loss steps over the temperature range of TG analysis
(Fig. 6). The rst stage, including a low amount of weight loss at
T < 250 ꢁC, is due to the removal of physically adsorbed solvent
and surface hydroxyl groups, and the second step at about 300
2.2. Synthesis of 1-amido or aminoalkyl-2-naphthols using
MNPs–PhSO3H
ꢁC to nearly 550 ꢁC is attributed to the decomposition of the Aer the characterization of the MNPs–PhSO3H catalyst, its role
coating organic layer in the nanocomposite. Therefore, the as a catalyst was evaluated for the synthesis of 1-amido- or
weight loss between 300–550 ꢁC gives the organic graing ratios aminoalkyl-2-naphthols (Scheme 2).
of the magnetic catalyst. The graed sulfanilic acid on the
An important feature of these nano-catalysts is simple
magnetic Fe3O4@SiO2 nanoparticles was approximately separation of them using an external magnet, thereby removing
15.5 wt%. In accordance with this mass loss, it was calculated the necessity for ltration or centrifugation. In order to opti-
that 0.72 mmol of sulfanilic acid was loaded on 1 g of MNPs– mize the reaction conditions and obtain the best catalytic
PhSO3H catalyst. The weight loss over the range 300–370 ꢁC activity, the reaction of benzaldehyde (1 mmol), b-naphthol
could be mainly attributed to the evaporation and subsequent (1 mmol), and acetamide (1.2 mmol) was used as a model, and
decomposition of SO3H groups. Furthermore, the DTG curve was conducted under different reaction parameters such as
shows that the decomposition of the organic structure mainly solvent and amount of catalyst. Initially, the model reaction was
occurred at 460 ꢁC. Therefore, the MNPs–PhSO3H is stable carried out in several solvents as well as under solvent-free
around or below 300 ꢁC. The agreement between the acid conditions, to investigate the efficiency of the catalyst (Table 1).
amount of MNPs–PhSO3H (0.65 mmol gꢀ1) measured by back As shown in Table 1, it was found that conventional heating at
titration using HCl and the organic group loading determined 120 ꢁC under solvent-free conditions is more efficient than
by TGA (0.72 mmol gꢀ1), is clear evidence that the sulfonic acid using organic solvents, with respect to reaction time and yield of
groups are principally located on the surfaces of Fe3O4@SiO2 the desired amidoalkyl naphthol (Table 1, entry 7). Indeed in
nanoparticles, where they are accessible for adsorption and many cases, solid organic reactions occurred efficiently and
catalytic reaction processes.
more selectively than those of their solution counterparts. To
The magnetic properties of the nanoparticles were charac- investigate the effect of catalyst loading, the model reaction was
terized using a vibrating sample magnetometer (VSM). Fig. 7 carried out in the presence of different amounts of catalyst. The
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Scheme 2 Synthesis of 1-amido- and 1-aminoalkyl naphthols.
short reaction times, without formation of any side products
such as di-benzoxanthenes, which are normally observed in the
presence of strong acids. As can be seen in Table 2, the proce-
dure was highly effective and the nature of substituents on the
aromatic ring of aldehydes did not show obvious effects in
terms of yields and times under the reaction conditions.
Furthermore, when compared to the amides, N-methylurea
afforded the corresponding amidoalkyl naphthol using shorter
reaction times (Table 2, entries 10–13). The acid sensitive
substrate thiophene-2-carbaldehyde gave the expected 1-ami-
doalky-2-naphthol 5e in very good yield (Table 2, entry 5).
However, when some aliphatic aldehydes, such as propio-
naldehyde and isobutyraldehyde, were used in this protocol
under the above optimized conditions, only trace amounts of
product were detected.
In order to show the efficiency of this catalytic system
further, the synthesis of 1-aminoalky-2-naphthols was investi-
gated in the presence of MNPs–PhSO3H. As shown in Table 2,
treatment of a variety of aldehydes and 2-naphthol with
heterocyclic amines such as 2-aminopyridine and 2-amino-4-
chloro-6-methylpyrimidine in the presence of catalytic amounts
of MNPs–PhSO3H under the optimized reaction conditions
afforded the corresponding 1-aminoalky-2-naphthol derivatives
in 81–92% yields (Table 2, entries 18–23). However, all our
attempts with the usual aromatic amines such as aniline and p-
toluidine failed to yield the corresponding aminoalkyl naph-
thols. Instead, the Schiff base was prepared from the reaction of
these amines and aldehydes under the reaction conditions.
A plausible mechanism for the formation of 1-amido- or
1-aminoalky-2-naphthols catalyzed by MNPs–PhSO3H, which is
supported by the literature,50,51 is shown in Scheme 3. The
MNPs–PhSO3H catalyst participates in the reaction which acti-
vates the carbonyl group of the aldehyde (intermediate I)
followed by the nucleophilic addition of b-naphthol to obtain
complex II. The removal of water from complex II produces
intermediate III as an ortho-quinone methide (o-QM). MNPs–
PhSO3H again activates intermediate III to give IV as a Michael
acceptor. The activated o-QM then reacts with amides, amines
or urea via a Michael addition to afford the expected amidoalkyl
naphthols. The reaction results from amines, which have been
presented in Table 2 (entries 18–23), conrm the mechanism.
The reaction of usual aromatic amines such as aniline and
p-toluidine produced the stable Schiff base and o-QMs were not
formed under the reaction conditions. Conversely, the Schiff
bases obtained from amides or heterocyclic amines are
Table
1 Optimization of the conditions for synthesis of N-((2-
hydroxynaphthalen-1-yl)(phenyl)methyl)acetamide (Table 2, entry 1)a
Entry Catalyst (mg)
Solvent
Condition Time
Yieldb (%)
1
2
3
4
5
6
7
8
MNPs–PhSO3H (20) THF
MNPs–PhSO3H (20) THF
MNPs–PhSO3H (20) EtOH
MNPs–PhSO3H (20) CH3CN
R.T.
24 h
12 h
12 h
12 h
12 h
4 h
40 min 94
40 min 79
40 min 94
4 h
3 h
3 h
3 h
20
32
15
22
<10
75
Reux
Reux
Reux
MNPs–PhSO3H (20) n-Hexane Reux
MNPs–PhSO3H (20)
MNPs–PhSO3H (20)
MNPs–PhSO3H (10)
MNPs–PhSO3H (40)
—
Fe3O4 (20)
Fe3O4@SiO2 (20)
MNPs–Cl (20)
—
—
—
—
—
—
—
—
80 ꢁ
C
120 ꢁ
120 ꢁ
120 ꢁ
120 ꢁ
120 ꢁ
120 ꢁ
120 ꢁ
C
C
C
C
C
C
C
9
10
11
12
13
<10
54
45
40
a
Benzaldehyde (1 mmol), 2-naphthol (1 mmol), acetamide (1.2 mmol).
Isolated yields.
b
best result was obtained in the presence of just 20 mg of MNPs–
PhSO3H (Table 1, entries 7–9). Moreover, the catalyst is essential
and in the absence of the catalyst, only 10% of the corre-
sponding amidoalkyl naphthol was produced even aer pro-
longed reaction times (Table 1, entry 10). The efficiencies of
Fe3O4, Fe3O4@SiO2 and MNPs–Cl as the catalyst towards the
model reaction were compared and the results are depicted in
Table 1. It was observed that the MNPs–PhSO3H was more
efficient than the Fe3O4, Fe3O4@SiO2 and MNPs–Cl catalysts
(entries 11–13).
In order to determine the generality and efficacy of the
catalyst, different kinds of aldehyde carrying either electron-
donating or electron-withdrawing groups were reacted with
2-naphthol, and a number of structurally and electronically
diverse amides or urea, under the optimized reaction condi-
tions; the respective results are summarized in Table 2. All
reactions proceeded efficiently in the presence of catalytic
amounts of MNPs–PhSO3H at 120 ꢁC and the desired products
were obtained in good to excellent yields (87–96%) in relatively
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Table 2 Synthesis of amido or aminoalkyl naphthols in the presence of MNPs–PhSO3H under solvent-free conditions
M.P. (ꢁC)
Entry
Ar
R or Ar0
Product
Time (min)
Yielda (%)
Found
Reported Lit.
1
2
3
4
5
6
7
8
C6H5
CH3
CH3
CH3
CH3
CH3
NH2
NH2
NH2
NH2
CH3NH
CH3NH
CH3NH
CH3NH
Ph
Ph
Ph
Ph
2-Pyridyl
2-Pyridyl
4-Cl-6-Me-2-pyrimidinyl
4-Cl-6-Me-2-pyrimidinyl
4-Cl-6-Me-2-pyrimidinyl
4-Cl-6-Me-2-pyrimidinyl
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
5o
5p
5q
6r
40
30
30
40
30
25
45
25
35
12
10
12
15
25
30
40
35
10
15
15
20
25
20
94
96
93
89
90
91
87
89
88
92
94
93
91
90
91
86
91
92
85
86
88
81
83
241–242
221–223
226–227
212–213
220–222
178–179
238–240
185–186
152–153
192–193
195–197
175–176
174–175
234–235
176–177
183–184
232–234
174–176
181–182
160–162
185–186
170–172
182–184
238–24052
220–22252
228–23019
214–21633
224–22553
177–17925
241–24354
183–18552
150–15255
190–19156
191–19230
174–17656
176–17730
23650
4-ClC6H4
4-BrC6H4
4-MeC6H4
2-Thiophine
C6H5
3-MeOC6H4
3-NO2C6H4
2-ClC6H4
C6H5
3-NO2C6H4
4-MeC6H4
4-FC6H4
C6H5
4-ClC6H4
4-BrC6H4
3-NO2C6H4
C6H5
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
178–18052
182–18433
230–23351
—
4-ClC6H4
C6H5
4-ClC6H4
2-Cl-6-F- C6H3
2-ClC6H4
6s
6t
6u
6v
6w
—
—
—
—
—
a
Isolated yields.
Scheme 3 Possible mechanism for the synthesis of amido or aminoalkyl naphthols using MNPs–PhSO3H.
unstable and can be easily converted to starting material by a choices as an environmentally benign and user-friendly catalyst.
hydrolysis reaction. Thus, this reaction can proceed via the Also, it can be seen that, in addition to having the general
o-QMs intermediate.
advantages attributed to the inherent magnetic properties of
To compare the applicability and the efficiency of our catalyst nano-catalysts, MNPs–PhSO3H is an equal or more efficient
with the reported inorganic or organic catalysts for the synthesis catalyst for this three-component reaction.
of 1-amidoalkyl-2-naphthols, we have tabulated the results of
these catalysts in the condensation reaction of benzaldehyde,
b-naphthol and acetamide under optimized conditions in 2.3. Catalyst recovery and reuse
Table 3. This shows that the MNPs–PhSO3H is a moderately good
catalyst for this reaction in terms of short reaction times and
simple conditions and it could be considered as one of the best
process considerations. Thus, the recovery and reusability of
The recovery and reusability of the catalyst are very important
for commercial and industrial applications as well as green
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Table 3 Comparison of MNPs–PhSO3H with other catalysts reported in the literature for the synthesis of N-[phenyl-(2-hydroxynapthalen-1-yl)-
methyl] acetamidea
Entry
Catalyst (amount)
Condition
Time
Yieldb (%)
Ref.
1
2
3
4
5
6
7
8
pTSA (10 mol%)
ClCH2CH2Cl (r.t.)
Solvent-free (125 ꢁC)
Solvent-free (110 ꢁC)
Solvent-free (120 ꢁC)
EtOH (80 ꢁC)
15 h
1.5 h
20 min
10 min
4 h
15
2 h
65 min
4.5 h
3.5
89
89
92
87
88
88
85
83
87
94
90
88
94
16
17
22
33
28
57
58
19
18
59
60
23
Montmorillonite K-10 (0.1 g)
H4SiW12O40 (5 mol%)
[TEBSA][HSO4] (5 mol%)
Thiamin HCl (10 mol%)
Sulfamic acid (50 mol%)
Silica sulfuric acid (0.02 g)
Fe(HSO4)3 (5 mol%)
Solvent-free (30 ꢁC)
Solvent-free (r.t.)
Solvent-free (85 ꢁC)
Solvent-free (125 ꢁC)
Ethylacetate (65 ꢁC)
Solvent-free (125 ꢁC)
Solvent-free (90 ꢁC)
Solvent-free (120 ꢁC)
9
I2 (5 mol%)
Molybdophosphoric acid (0.12 g)
10
11
12
13
K5CoW12
O
40$3H2O (1 mol%)
2 h
20 min
40
DPA (10 mol%)
MNPs–PhSO3H (0.02 g)
This work
a
Reaction conditions: b-naphthol (1 mmol), benzaldehyde (1 mmol), and acetamide (1.2 mmol). b Isolated yields.
MNPs–PhSO3H (20 mg) was investigated in the sequential subsequent reaction. Nearly quantitative recovery of catalyst (up
reaction of 3-nitrobenzaldehdye (1 mmol) with 2-naphthol (1 to 98%) could be obtained from each run. As seen in Fig. 8, the
mmol) and N-methylurea (1.2 mmol) under solvent-free condi- recycled catalyst could be reused six times without any addi-
tions for 10 min at 120 ꢁC. Aer completion of the reaction, the tional treatment or appreciable reduction in catalytic activity.
resulting solidied mixture was diluted with hot THF (10 mL). The recovered catalyst aer six runs had no obvious change in
Then, the catalyst was easily separated using an external structure, as shown by comparison of the FT-IR spectra to that
magnet, washed with THF, dried under vacuum and reused in a of fresh catalyst (Fig. 9). The consistent structure and activity of
recovered and reused MNPs–PhSO3H catalyst indicates that the
reused MNPs–PhSO3H also shows excellent performance for the
synthesis of 1-amidoalkyl-2-napthols.
3. Experimental
All chemicals were purchased from Merck or Fluka chemical
companies and used without further purication. Melting
points were measured by using capillary tubes on an electro
thermal digital apparatus and are uncorrected. Known products
were identied by comparison of their melting points and
spectral data with those reported in the literature. Thin layer
chromatography (TLC) was performed on UV active aluminum-
backed plates of silica gel (TLC Silica gel 60 F254). FTIR spectra
Fig. 8 Recyclability of MNPs–PhSO3H in the reaction of 3-nitro-
benzaldehdye (1 mmol), 2-naphthol (1 mmol), N-methylurea (1.2
were recorded on a Unicom Galaxy Series FT-IR 5000 spectro-
photometer in the region 4000–400 cmꢀ1 using pressed KBr
discs. The 1H and 13C-NMR spectra were recorded on a Brucker
mmol) and catalyst (0.02 g) under solvent-free conditions.
1
Avance spectrometer operating at 300 and 75 MHz for H and
13C-NMR, respectively in DMSO-d6 with TMS as an internal
standard. X-ray diffraction (XRD) was performed on Philips X-
Pert (Cu-Ka radiation, l ¼ 0.15405 nm) over the range 2q ¼ 20–
80ꢁ using 0.04ꢁ as the step length. Thermal gravimetric analysis
(TGA) and differential thermal gravimetric (DTG) data for
MNPs-PhSO3H were recorded on a Mettler TꢁA4000 System
under an N2 atmosphere at a heating rate of 10 C minꢀ1. The
magnetization and hysteresis loop were measured at room
temperature using a Vibrating Sample Magnetometer (Model
7300 VSM system, Lake Shore Cryotronic, Inc., Westerville, OH,
USA). The scanning electron microscope measurement was
carried out on a Hitachi S-4700 eld emission-scanning electron
Fig. 9 FT-IR spectra of the fresh catalyst and the six-times reused
catalyst.
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microscope (FE-SEM). Transmission electron microscopy (TEM) dichloromethane and nally with acidied ethanol followed by
ꢁ
measurements were carried out on a Philips CM10 analyzer drying at 80 C for 6 h under vacuum.
operating at 150 kV.
3.5. Acidity of MNPs–PhSO3H
The concentration of sulfonic acid groups was quantitatively
estimated by back titration using HCl (0.01 N). 2 mL of KOH
(0.01 N) was added to 0.02 g of the magnetic nanoparticles and
the mixture was stirred for 30 min. The catalysts were magnet-
ically separated and washed with deionized water. The excess
amount of KOH was titrated with HCl (0.01 N) in the presence of
phenolphthalein as indicator. Averages of 3 separate titrations
were performed to obtain an average value for the acid amount
of MNPs–PhSO3H. The results revealed that the samples of
MNPs–PhSO3H possessed 0.65 mmol gꢀ1 acid amount.
3.1. Preparation of the magnetic Fe3O4 nanoparticles
(MNPs)
Fe3O4–MNPs were prepared using simple chemical co-precipi-
tation described in the literature.61 Briey, FeCl2$4H2O (0.9941
g, 5 mmol) and FeCl3$6H2O (2.7029 g, 10 mmol) were dissolved
in 100 mL of deionized water in a three-necked round bottomed
ask (250 mL). The mixture was heated under N2 at 80 ꢁC for 1
h, and then 10 mL of concentrated ammonia (25%) were added
quickly. The solution was stirred under N2 for another 1 h and
then cooled to room temperature. The black precipitate formed
was isolated by magnetic decantation, exhaustively washed with
double-distilled water until neutrality, and further washed twice
3.6. General procedure for the synthesis of 1-amido or
aminoalkyl-2-naphthols
ꢁ
with ethanol and dried at 60 C under vacuum.
MNPs–PhSO3H (0.02 g) were added as a catalyst to a mixture of
b-naphthol (1 mmol), an aldehyde (1 mmol), and an amide or an
amine (1.2 mmol). The mixture was magnetically stirred under
thermal solvent-free condition on a preheated oil bath at 120 ꢁC
for the appropriate time. Aer completion of the reaction, as
indicated by TLC, the resulting solidied mixture was diluted
with hot THF (10 mL) and the catalyst easily separated by an
external magnet. The solvent was then evaporated; the
remaining solid product was recrystallized from aqueous
ethanol.
3.2. Synthesis of silica-coated MNPs (Fe3O4@SiO2 MNPs)
The Fe3O4@SiO2 core–shell nanoparticles were prepared
46
¨
according to the Stober method. The details are as follows:
Magnetic nanoparticles MNPs (1.0 g) were homogeneously
dispersed by ultrasonic vibration in a mixture of 40 mL of
ethanol, 6 mL of deionised water, and 1.5 mL of 25 wt%
concentrated aqueous ammonia solution, followed by the
addition of 1.4 mL of tetraethylorthosilicate (TEOS). Aer stir-
ring for 12 h at room temperature under an N2 atmosphere, the
black precipitate (Fe3O4@SiO2) was collected from the solution
using a magnet, and then washed several times with water and
3.7. Characterization data for new compounds
3.7.1. 1-(Phenyl(pyridin-2-ylamino)methyl)naphthalen-2-ol
ꢁ
ethanol and dried at 25 C under vacuum.
(6r). IR (KBr): nmax ¼ 3370, 3061, 1607, 1570, 1512, 1449, 1331,
1
1275, 1235, 1163, 1063, 999, 812, 747, 696, 637 cmꢀ1; H-NMR
3.3. Synthesis of 3-chloropropyl-functionalized magnetic
silica nanoparticles (Fe3O4@SiO2–Cl MNPs)
(300 MHz, DMSO-d6): d ¼ 10.00 (s, 1H), 8.45 (d, J ¼ 8.4, 1H),
7.82–7.75 (m, 3H), 7.36 (t, J ¼ 7.4, 1H), 7.28–7.21 (m, 6H), 7.17–
7.13 (m, 6H); 13C-NMR (75 MHz, DMSO-d6): d ¼ 169.2, 153.1,
153.9, 142.6, 132.3, 129.2, 128.5, 128.4, 127.9, 126.3, 126.0,
125.9, 123.3, 123.2, 122.3, 118.8, 118.7, 118.4, 118.3, 47.7; anal.
calcd for C22H18N2O: C, 80.96; H, 5.56; N, 8.58. Found: C, 80.89;
H, 5.61; N, 8.51%.
3.7.2. 1-((4-Chlorophenyl)(pyridin-2-ylamino)methyl)naph-
thalen-2-ol (6s). IR (KBr): nmax ¼ 3410, 3063, 1615, 1568, 1516,
1437, 1329, 1273, 1155, 1089, 1013, 955, 885, 820, 768 cmꢀ1; 1H-
NMR (300 MHz, DMSO-d6): d ¼ 10.23 (s, 1H), 7.97–7.93 (m, 2H),
7.81–7.76 (m, 2H), 7.41–7.36 (m, 2H), 7.30–7.21 (m, 8H), 6.82 (d,
J ¼ 8.4 Hz, 1H), 6.52 (t, J ¼ 6.1 Hz, 1H); 13C-NMR (75 MHz,
DMSO-d6): d ¼ 158.3, 153.0, 147.2, 143.0, 136.8, 132.2, 130.2,
129.2, 128.5, 128.0, 127.7, 126.3, 123.6, 122.4, 119.7, 118.6,
118.4, 112.3, 109, 49.1; anal. calcd for C22H17ClN2O: C, 73.23; H,
Chloropropyl-modied silica-coated magnetic nanoparticles
was prepared according to the reported procedure.62 In a typical
procedure, 1.0 g of Fe3O4@SiO2 MNPs were dispersed in 50 mL
of dry toluene using an ultrasonic bath to produce a uniform
suspension, to which 2.0 g of 3-chloropropyl-trimethoxysilane
(CPTS) was added usiꢁng a syringe. The resulting mixture was
stirred for 48 h at 60 C under an N2 atmosphere. Finally, the
chloropropyl-functionalized solid Fe3O4@SiO2–Cl MNPs were
washed with toluene, separated using a magnet, and dried
under vacuum.
3.4. Sulfanilic acid-functionalized silica-coated magnetic
nanoparticles (MNPs–PhSO3H)
The MNPs–PhSO3H magnetic nanoparticles were prepared 4.75; N, 7.76. Found: C, 73.26; H, 4.81; N, 7.73%.
according to the method of Adama et al.63 1 g of Fe3O4@SiO2–Cl
3.7.3. 1-(((4-Chloro-6-methylpyrimidin-2-yl)amino)(phenyl)-
nanoparticles were dispersed in 50 mL dry toluene by sonica- methyl)naphthalen-2-ol (6t). IR (KBr): nmax ¼ 3381, 3063, 2998,
tion over 1 h. To this suspension, 2 g (11.5 mmol) of sulfanilic 1628, 1572, 1514, 1437, 1360, 1290, 1211, 1132, 895, 814, 742,
acid was added, followed by 1.6 mL (11.5 mmol) of triethyl- 698 cmꢀ1; 1H-NMR (300 MHz, DMSO-d6): d ¼ 10.26 (s, 1H), 8.09
amine acting as a proton scavenger. Then, the reaction mixture (d, J ¼ 7.8, 1H), 7.83–7.76 (m, 3H), 7.45–7.18 (m, 9H), 6.65 (s,
was reuxed for 2 days under nitrogen. The solid material was 1H), 2.25 (s, 3H); 13C-NMR (75 MHz, DMSO-d6): d ¼ 170.5, 162.1,
obtained by magnetic separation and washed with toluene, 160.6, 153.6, 142.9, 132.7, 129.8, 129.1, 128.8, 128.6, 128.5,
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127.2, 126.8, 126.5, 123.1, 119.5, 119.1, 109.5, 50.8, 24.1; anal.
calcd for C22H18ClN3O: C, 70.30; H, 4.83; N, 11.18. Found: C,
70.37; H, 4.93; N, 11.14%.
Acknowledgements
We gratefully acknowledge nancial support from the Research
3.7.4. 1-(((4-Chloro-6-methylpyrimidin-2-yl)amino)(4-chlor-
ophenyl)methyl)naphthalen-2-ol (6u). IR (KBr): nmax ¼ 3379,
3059, 2992, 1628, 1572, 1516, 1437, 1358, 1289, 1269, 1211,
1092, 1014, 899, 814, 742 cmꢀ1; 1H-NMR (300 MHz, DMSO-d6): d
¼ 10.28 (s, 1H), 8.05 (d, J ¼ 7.4, 1H), 7.82–7.75 (m, 3H), 7.46–
7.27 (m, 8H), 6.66 (s, 1H), 2.25 (s, 3H); 13C-NMR (75 MHz,
DMSO-d6): d ¼ 171.0, 161.9, 157.5, 154.5, 153.9, 141.9, 140.2,
132.5, 131.9, 130.8, 130.0, 129.3, 128.6, 128.4, 128.1, 123.3,
118.4, 116.9, 99.4, 50.4, 18.8; anal. calcd for C22H17Cl2N3O: C,
64.40; H, 4.18; N, 10.24. Found: C, 64.44; H, 4.23; N, 10.28%.
3.7.5. 1-((2-Chloro-6-uorophenyl) ((4-chloro-6-methylpyr-
imidin-2-yl)amino)methyl) naphthalen-2-ol (6v). IR (KBr): nmax
¼ 3420, 3065, 2996, 1630, 1572, 1518, 1437, 1373, 1290, 1269,
Council of Arak University.
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