(α-Fe2O3)-MCM-41-SO3H as a novel magnetic nanocatalyst for the synthesis of N-aryl-2-amino-1,6-naphthyridine derivatives

Article abstract of DOI:10.1016/j.catcom.2012.04.013

The new (α-Fe₂O₃)-MCM-41-SO₃H catalyst was prepared directly through the reaction of chlorosulfonic acid with silica-coated nanoparticles (α-Fe₂O₃)-MCM-41 and used as a magnetically recyclable catalyst for an efficient one-pot synthesis of N-aryl-2-amino-1,6-naphthyridine derivatives. The catalyst with 10 wt% of loaded iron oxide nanoparticles could be recovered from the reaction mixture by an external magnet and reused without significant decrease in activity even after 5 runs. This new prepared catalyst exhibited better activities to other commercially available sulfonic acid catalysts.

Full text of DOI:10.1016/j.catcom.2012.04.013

Catalysis Communications 25 (2012) 83–91
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Catalysis Communications
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Short Communication
(α-Fe2O3)-MCM-41-SO3H as a novel magnetic nanocatalyst for the synthesis of
N-aryl-2-amino-1,6-naphthyridine derivatives
a
a
b
Shahnaz Rostamizadeh a, , Mohammad Azad , Nasrin Shadjou , Mohammad Hasanzadeh
⁎
a
Department of Chemistry, K. N. Toosi University of Technology, P.O. Box 15875‐4416, Tehran, Iran
Drug Applied Research Center, Tabriz University of Medical Science, Tabriz, Iran
b
a r t i c l e i n f o
a b s t r a c t
Article history:
The new (α-Fe2O3)-MCM-41-SO3H catalyst was prepared directly through the reaction of chlorosulfonic acid
with silica-coated nanoparticles (α-Fe2O3)-MCM-41 and used as a magnetically recyclable catalyst for an
efficient one-pot synthesis of N-aryl-2-amino-1,6-naphthyridine derivatives. The catalyst with 10 wt% of
loaded iron oxide nanoparticles could be recovered from the reaction mixture by an external magnet and
reused without significant decrease in activity even after 5 runs. This new prepared catalyst exhibited better
activities to other commercially available sulfonic acid catalysts.
Received 15 February 2012
Received in revised form 10 April 2012
Accepted 12 April 2012
Available online 21 April 2012
Keywords:
© 2012 Elsevier B.V. All rights reserved.
Magnetic nanocatalyst
Heterogeneous catalyst
Sulfonic acid
N-aryl-2-amino-1,6-naphthyridines
1. Introduction
that covalent anchoring of various molecules on silica surfaces is
based on the presence of silanol groups [10].
Acidic catalysts are widely used in a variety of organic transforma-
tions, such as aldol condensations, hydrolysis, acylations, and nucleophilic
additions. However, use of soluble or liquid acids (homogeneous
catalysts) has been inhibited in manufacturing synthesis because of dif-
ficulty in their waste neutralization, separations, reactor corrosion, and
reusability [1].
The recovery and reusability of the catalyst are the two most impor-
tant features for many catalytic processes. Hence, one efficient way to
overcome the problem of homogeneous catalysts is the heterogenization
of active catalytic molecules, creating a heterogeneous catalytic system.
In contrast, the recovery of the most heterogeneous catalysts from the
final reaction systems requires a filtration or centrifugation step and/
or a tedious workup. For this purpose, by applying magnetic supports
and an external magnet the catalysts can be easily recovered and subse-
quently reused in another cycle without significant decrease in their
activity.
MCM-41 is an ordered mesoporous material which has only mildly
acidic sites [2,3]. In order to promote their acidic character, sulfonic
acid groups have been covalently bonded to these supports by various
methods such as, oxidation of attached thiols [4], hydrolysis of sulfonic
acid chlorides [5], sulfonation of supported phenyl groups [6], ring
opening of perfluorosulfonic acid sultones [7,8], and immobilization
of perfluorosulfonic acid triethoxysilanes [9]. It should be mentioned
Hence, for the first time the present work illustrates the immobili-
zation of sulfonic acid groups on silica coated magnetic nanoparticles
for its use as recyclable, solid acid catalyst for the synthesis of N-aryl-
2-amino-1,6-naphthyridine derivatives.
Over the past few years, naphthyridine derivatives have received
considerable attention because of their wide range of biological and
pharmaceutical activities, such as antitumor, anti-inflammatory, and
antifungal properties [11–13]. These compounds are very useful in
the treatment of hypertension, myocardial infarction, hyperlipidemia,
cardiac arrhythmia, and rheumatoid arthritis [14–16].
In view of these useful properties, and since we were interested in the
synthesis of N-aryl-2-amino-1,6-naphthyridine derivatives, a literature
survey revealed that there are only a few reports for the synthesis of
these compounds. El-Subbagh et al. have reported the synthesis of 1,6-
naphthyridine derivatives through the two component reaction of α,β-
unsaturated ketones and cyanoacetamide in butanol [12]. Recently,
Shu-Jiang Tu et al. [17] reported the synthesis of N-aryl-2-amino-1,6-
naphthyridine derivatives through three component reaction between
α,β-unsaturated ketones, aniline, and malononitrile using microwave ir-
radiation in the presence of acetic acid as catalyst.
However, these methods are time-consuming and use a lot of toxic
solvents and reagents. Thus, the development of a green, simple, efficient,
and general method for the synthesis of these widely used organic com-
pounds, from readily available reagents, remains one of the major chal-
lenges in organic synthesis.
⁎
Corresponding author. Fax: +98 21 22853650.
Therefore in this work, magnetic nanoparticles which have been em-
bedded in MCM-41 and subsequently functionalized with chlorosulfonic
E-mail addresses: rostamizadeh@kntu.ac.ir, shrostamizadeh@yahoo.com
(S. Rostamizadeh).
1566-7367/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2012.04.013

84
S. Rostamizadeh et al. / Catalysis Communications 25 (2012) 83–91
Scheme 1. (α-Fe2O3)-MCM-41-SO3H as a magnetic catalyst for the synthesis of N-aryl-2-amino-1,6-naphthyridine derivatives.
acid [(α-Fe2O3)-MCM-41-SO3H] have been used as new acidic catalyst
for the one-pot synthesis of N-aryl-2-amino-1,6-naphthyridine deriva-
tives under solvent free conditions (Scheme 1).
ammonium nitrate. The surfactant template was then removed from
the synthesized material by calcination at 450 °C for 4 h to give the
[(α-Fe2O3)-MCM-41].
2. Experimental
2.2. Preparation of (α-Fe2O3)-MCM-41-SO3H
Melting points were recorded on a Buchi B-540 apparatus. IR
spectra were recorded on an ABB Bomem Model FTLA200-100 instru-
ment. 1H and 13 C NMR spectra were measured on a Bruker DRX-300
spectrometer, at 300 and 75 MHz, using TMS as an internal standard.
Chemical shifts (δ) were reported relative to TMS, and coupling con-
stants (J) were reported in hertz (Hz). Mass spectra were recorded on
a Shimadzu QP 1100 EX mass spectrometer with 70-eV ionization poten-
tial. X-ray powder diffraction (XRD) was carried out on a Philips X'Pert
diffractometer with CuKα radiation. The pore structure of the prepared
catalyst was verified by the nitrogen sorption isotherm ([5.0.0.3] Belsorp,
BEL Japan, Inc.). Transmission electron microscope (TEM) was recorded
on a Philips CM-10 instrument on an accelerating voltage of 100 kV.
To (α-Fe2O3)-MCM-41 (1 g), chlorosulfonic acid (1 g, 9 mmol) in
5 mL dichloromethane was added dropwise at room temperature dur-
ing 30 min. After completion of the addition, the mixture was mechan-
ically stirred for other 30 min until HCl was removed from reaction
vessel. The mixture was then filtered and washed with CH2Cl2 to give
(α-Fe2O3)-MCM-41-SO3H as brown powder. The amount of sulfonic
acid groups of (α-Fe2O3)-MCM-41-SO3H which were determined by
acid–base titration was found to be (0.56 SO3H per g).
2.3. General procedure for the synthesis of 3,5-dibenzylidenepiperidin-4-one
[12]
In a 50-mL reaction vial, a mixture of the 4-piperidone (10 mmol),
the appropriate aldehyde (20 mmol), 10% NaOH (1 mL) and 95%
EtOH (30 mL) was stirred at room temperature for 0.5–2 h. The
separated solid was collected by filtration and for further purification
was recrystallized from ethanol.
2.1. Catalyst preparation
A solution with molar composition of 3.2 FeCl3:1.6 FeCl2:1 CTABr:39
NH4OH:2300 H2O was used for preparation of naked Fe3O4
nanoparticles at room temperature. Typically, 2 g of iron (III) chloride
(FeCl3⋅6H2O) and 0.8 g of iron (II) chloride (FeCl2⋅4H2O) were dis-
solved in 10 mL of distilled water under N2 atmosphere. The resulting
solution was added dropwise to a 100 mL solution of 1.0 M NH4OH so-
lution containing 0.4 g of cetyltrimethylammonium bromide (CTABr) to
construct a colloidal suspension of iron oxide magnetic nanoparticles.
The magnetic MCM-41 was prepared by adding 20 mL of the magnetic
colloid to a 1 L solution with the molar composition of 292 NH4OH:1
CTABr:2773 H2O under vigorous mixing and sonication. Then sodium
silicate (16 mL) was added, and the mixture was allowed to react at
room temperature for 24 h under well-mixed conditions. The magnetic
MCM-41 [(Fe3O4)-MCM-41] was filtered and washed with alcoholic
2.4. General procedure for the synthesis of N-aryl-2-amino-1,6-naph-
thyridine derivatives
To the mixture of 3,5-dibenzylidenepiperidin‐4-one (0.33 mmol), an-
iline (0.33 mmol), and malononitrile (0.33 mmol) was added (α-Fe2O3)-
MCM-41-SO3H (40 mg); it was then stirred at 120 °C for an appropriate
period of time (Table 4). After completion of the reaction (monitored
by thin-layer chromatography, TLC; petroleum ether and EtOAc, 1:1),
the ethanol was added to the reaction mixture and the catalyst was col-
lected with an external magnet. Then, the mixture was filtered and the
Scheme 2. Preparation of (α-Fe2O3)-MCM-41-SO3H.

S. Rostamizadeh et al. / Catalysis Communications 25 (2012) 83–91
85
product was further purified by recrystallization from EtOH/H2O (1:1) to
give the pure product.
3. Results and discussion
At first the (α-Fe2O3)-MCM-41 with 10 wt% of loaded iron oxide
nanoparticles was prepared according to the reported method in
the literature with some modifications [18] (Scheme 2).
In order to prepare [(Fe3O4)-MCM-41-SO3H], 1 g of uncalcined cata-
lyst [(Fe3O4)-MCM-41] was reacted with 1 g chlorosulfonic acid in 5 mL
dichloromethan. However because of the low stability of Fe3O4
nanoparticles in the presence of chlorosulfonic acid, the desired
catalyst [(Fe3O4)-MCM-41-SO3H] was not formed and nonmagnetic cat-
alyst (MCM-41-SO3H) was obtained (Scheme 3). Therefore, ((Fe3O4)-
MCM-41) was calcined at 450 °C and converted to its stable form [(α-
Fe2O3)-MCM-41] [19,20]. It was then modified with chlorosulfonic
acid to give the desired catalyst (Scheme 2).
Scheme 3. Reaction of (Fe3O4)-MCM-41-SO3H with chlorosulfonic acid.
a
95
90
85
80
75
70
65
60
3800 3600 3400 3200 3000 2800 2600 2400 2200 2000 1800 1600 1400 1200 1000 800 600
Wavenumbers (cm-1)
75.0
70.0
65.0
60.0
55.0
50.0
45.0
40.0
35.0
b
3800 3600 3400 3200 3000 2800 2600 2400 2200 2000 1800 1600 1400 1200 1000 800 600
Wavenumbers (cm-1)
Fig. 1. The IR spectra of (a) (α-Fe2O3)-MCM-41; (b) (α-Fe2O3)-MCM-41-SO3H.

86
S. Rostamizadeh et al. / Catalysis Communications 25 (2012) 83–91
The prepared catalyst [(α-Fe2O3)-MCM-41-SO3H] was characterized
two small peaks identical to those of MCM-41 materials (Fig. 2a). In ad-
dition, XRD pattern in the region of 10.0° (2θ) to 80.0° (2θ) confirmed
that change of sample's color from black to brick-red after calcination
of the catalyst is due to the oxidation of embedded Fe3O4 to α-Fe2O3
nanoparticles (Fig. 2b).
Also the SEM (Fig. 3a and b) and the TEM (Fig. 3c and d) showed
that the embedded nanoparticles were present as uniform particles
with spherical morphology.
The N2 adsorption isotherms after grafting of SO3H group were
recorded and shown in Fig. 4. The specific surface area and total pore
volume obtained by the N2 adsorption isotherms and calculated by
the Brunauer–Emmett–Teller (BET) method [21] were 1024 m2 g−1
and 1.25 cm3 g−1, respectively. The pore diameter of the (α-Fe2O3)-
with IR, XRD, SEM, TEM, nitrogen physisorption measurements, and
acid–base titration. In FT-IR spectra the band in the region of
400–650 cm−1 is attributed to the stretching vibrations of the (Fe―O)
bond in α-Fe2O3, and the band at about 1100 cm−1 belongs to (Si―O)
stretching vibrations (Fig. 1a and b). The peaks placed in 1047 and
1220 cm−1 are related to the stretching of the S O bonds. A peak
appeared at about 3400 cm−1 due to the stretching of OH groups in
the SO3H (Fig. 1b).
The XRD patterns of the synthesized catalyst are presented in Fig. 2.
The XRD analysis was performed from 1.0° (2θ) to 10.0° (2θ), and 10.0°
(2θ) to 80.0° (2θ). The sample of (α-Fe2O3)-MCM-41-SO3H showed
relatively well-defined XRD patterns, with one major peak along with
a
16000
14000
12000
10000
8000
6000
4000
2000
0
Magnetic MCM-41S03H
Magnetic MCM-41
0
2
4
6
8
10
12
2 Theta (o)
b
400
100
0
20
30
40
50
60
70
Position [o2Theta]
Fig. 2. (a) The XRD patterns of the (α-Fe2O3)-MCM-41 and (α-Fe2O3)-MCM-41-SO3H in the region of 1.0° (2θ) to 10.0° (2θ). (b) The XRD patterns of (α-Fe2O3)-MCM-41-SO3H in
the region of 10.0° (2θ) to 80.0° (2θ).

S. Rostamizadeh et al. / Catalysis Communications 25 (2012) 83–91
87
a
b
Fe2O3
100nm
100nm
Fe2O3
c
d
Fig. 3. The TEM (a, b) and SEM (c, d) images of (α-Fe2O3)-MCM-41-SO3H.
MCM-41-SO3H was 4.89 nm derived from the adsorption and desorp-
tion branches by the Broekhoff and deBoer model [22]. Also, detailed
textural properties of (α-Fe2O3)-MCM-41 and (α-Fe2O3)-MCM-41-
SO3H are summarized in Table 1, in which the surface area and pore vol-
ume of functionalized magnetic MCM-41 were lower than those of
corresponding mesoporous silica due to the grafting of ‐SO3H groups.
The FT-IR analysis of the recovered catalyst after the reaction was
recorded in which no sign of degradation of the anchored sulfonic acid
groups as well as leaching of embedded nanoparticles was observed
(Fig. 5).
For optimization of the reaction conditions, 3,5-bis(4-
chlorobenzylidene)-1-methylpiperidin-4-one (0.33 mmol), aniline
(0.33 mmol), and malononitrile (0.33 mmol) were used as model re-
actants under solvent-free conditions (Scheme 4). At first, in order to
show the unique catalytic behavior of (α-Fe2O3)-MCM-41-SO3H and to
compare its activity with other catalysts, this reaction was performed in
Fig. 4. (a) Nitrogen adsorption/desorption isotherm and (b) BJH of (α-Fe2O3)-MCM-41-SO3H.

88
S. Rostamizadeh et al. / Catalysis Communications 25 (2012) 83–91
Table 1
Table 2
Surface area, average pore size, and pore volume of (α-Fe2O3)-MCM-41 and (α-Fe2O3)-
Comparing the efficiency of different catalysts in the synthesis of 6d.
MCM-41-SO3H.
Entry
Catalysta
Time (min)
Yield (%)
Adsorbent
Surface area
Average pore
size (nm)a
Pore volume
1
2
3
4
5
6
7
8
No catalyst
H3PW12O40
HClO4/SiO2
NaHSO4/SiO2
NaHSO4
Nano CuO
Fe3O4 NPs
Acetic acid, MW, 110 °C, 200 W
MCM-41
180
180
180
180
240
300
360
5
trace
45
50
47
35
Trace
Trace
96 [17]
Trace
Trace
95
b
(m2 g−1
)
(cm3 g−1
)
(α-Fe2O3)-MCM-41
(α-Fe2O3)-MCM-41-SO3H
1213
1024
5.26
4.89
1.59
1.25
a
Pore size is calculated by method described by Brunauer–Emmett–Teller.
Pore volume determined from nitrogen physisorption isotherm.
b
9
10
11
180
180
130
(α-Fe2O3)-MCM-41
(α-Fe2O3)-MCM-41-SO3H
the presence of catalytic amount of H3PW12O40, HClO4/SiO2, NaHSO4/
SiO2, NaHSO4, MCM-41, (α-Fe2O3)-MCM-41 and nanocrystalline
metal oxides such as CuO and Fe3O4 nanoparticles (Table 2). It was ob-
served that only acidic catalysts were able to catalyze this reaction
(Table 2, entry 2–5, 11). Also, at the first glance, according to reported
method by Shu-Jiang Tu et al. [17], running the reaction in acetic acid at
110 °C, under microwave condition at 200 W, seemed appealing
(Table 2, entry 8). Yet, such a procedure suffers from using an extra re-
agent (ammonium acetate) along with a toxic solvent (DMF) as well as
employment of possibly harmful and rather expensive electromagnetic
waves. [23]. Hence, it seems that the (α-Fe2O3)-MCM-41-SO3H is the
most effective catalyst for this purpose, leading to the synthesis of
N-aryl-2-amino-1,6-naphthyridine derivatives in higher yields and
shorter reaction times. The efficiency of this catalyst is due to the syner-
getic effect of Brönsted acidity of -SO3H and Lewis acidity of the Fe3+
groups.
a
Catalytic amount of all compared catalysts is 40 mg per 0.33 mmol of reactants.
Table 3
Solvent screening for the synthesis of 6d.
Entry
Solvent
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
DMF
Ethylenglycol
Dioxane
CH3CN
CH3OH
C2H5OH
H2O
Solvent-free condition
135
145
160
180
180
180
180
130
70
75
68
20
30
30
No reaction
95
98
96
94
92
90
88
86
84
82
80
78
76
74
72
70
68
3800 3600 3400 3200 3000 2800 2600 2400 2200 2000 1800 1600 1400 1200 1000 800 600
Wavenumbers (cm-1)
Fig. 5. The IR spectra of the recycled (α-Fe2O3)-MCM-41-SO3H.
Scheme 4. Model reaction for the optimization.

S. Rostamizadeh et al. / Catalysis Communications 25 (2012) 83–91
89
Table 4
The reaction time (min) and the yield (%) of N-aryl‐2-amino-1,6-naphthyridine product.
Entry
Product
Time
(min)
Yield (%)
98
M.P (°C)
Found
M.P (°C)
Reported
1
6a
6b
6c
160
155
120
221–223
239–240
244–245
–
HN
CN
Cl
N
Cl
Cl
Cl
N
2
3
96
93
–
HN
CN
Cl
N
Cl
N
Cl
Cl
244–246 [17]
HN
CN
N
F
N
F
4
6 d
130
95
254–255
253–255 [17]
HN
CN
N
Cl
N
Cl
5
6
6e
6f
185
150
84
86
233–235
229–231
233–235 [17]
229–231 [17]
HN
CN
N
H3C
N
CH3
HN
CN
N
N
7
8
6g
6h
120
110
95
92
243–245
243–245
243–245 [17]
244–247 [17]
HN
CN
N
O2N
N
NO2
HN
CN
N
O2N
NO2
N
9
6i
165
92
268–269
268–270 [17]
HN
CN
N
Br
N
Br

90
S. Rostamizadeh et al. / Catalysis Communications 25 (2012) 83–91
Scheme 5. The structure of 3,5-dibenzylidenepiperidin-4-one derivatives.
Fig. 6. Catalyst recovery at the end of the reaction.
A comparison of the performance of the (α-Fe2O3)-MCM-41-SO3H
The plausible mechanism is shown in Scheme 6. Because of two-
dimensional pores of MCM-41, the reactants easily transfer toward
the nanocatalyst channels, and they are accompanied by the inherent
Brönsted acidity of -SO3H and Lewis acidity of the Fe3+, both of
which are capable of bonding with the carbonyl oxygen of the 3,5-
dibenzylidenepiperidin-4-one moiety. Afterwards, the Michael addi-
tion between activated 3,5-dibenzylidenepiperidin-4-one (1) and
malononitrile (2) occurs, and then nucleophilic addition of aniline
(3) to one of the cyano groups in the intermediate (4) results in the
formation of the intermediate (5). Subsequently, through cyclization
and aromatization, the product (6) is formed. In other words, ionic
intermediates (4, 5) are generated inside the nanocatalyst because of
the strong polarity of the ‐SO3H and Fe3+ groups. Finally, by using this
magnetic nanocatalyst, the reaction rates and yields under the reaction
condition are enhanced (Scheme 6).
in various solvents is shown in Table 3. Among the solvents tested
(DMF, ethylenglycol, dioxane, acetonitrile, methanol, ethanol, water)
and solvent-free conditions the latter gave the highest yields with
shorter reaction times. This means that the higher concentration of re-
actants in the absence of solvents usually leads to more favorable
kinetics than in solution [24]. Hence the solvent free condition has been
selected as optimized condition.
After optimization of the reaction condition, a variety of aromatic al-
dehydes, possessing both electron-donating and electron-withdrawing
groups, was employed for N-aryl-2‐amino-1,6-naphthyridine formation,
and the results indicated that for 3,5-dibenzylidenepiperidin-4-one
bearing different functional groups, the reaction proceeded smoothly in
all cases. It is worth mentioning that 3,5-dibenzylidenepiperidin-4-one
with electron-withdrawing groups reacted rapidly whereas with those
having electron-rich groups, longer reaction times were required.
Electron-withdrawing groups on the phenyl rings (Table 4, entries 1–4,
and 7–9) induce greater electronic positive charge on the corresponding
β-atoms than electron donating moieties (Scheme 5).
It is important to note that the magnetic property of this catalyst
facilitates its efficient recovery from the reaction mixture during work-
up procedure. In the presence of an external magnet, recoverable (α-
Fe2O3)-MCM-41-SO3H moved onto the magnet steadily and the reaction
Scheme 6. A plausible mechanism for the synthesis of N-aryl-2-amino-1,6-naphthyridine in the presence of (α-Fe2O3)-MCM-41-SO3H.

S. Rostamizadeh et al. / Catalysis Communications 25 (2012) 83–91
91
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coated nanoparticles (α-Fe2O3)-MCM-41 and used as a magnetically
recyclable catalyst for an efficient one-pot synthesis of N-aryl-2-
amino-1,6-naphthyridine derivatives. The catalyst with 10 wt% of load-
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was used in subsequent runs without observation of significant de-
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Acknowledgements
We gratefully acknowledge the support of this work to K. N. Toosi
University of Technology.
Appendix A. Supplementary data
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