ClO 4 - /Al-MCM-41 nanoparticles as a solid acid catalyst for the synthesis of 2-amino-3-cyanopyridines

Article abstract of DOI:10.1007/s11164-015-2183-2

A one-pot four-component reaction of various types of aldehydes, acetophenone, malononitrile, and ammonium acetate was studied in the presence of perchlorated Al-MCM-41 (ClO ₄ ^- /Al-MCM-41) nanoparticles for the synthesis of 2-amino-

Full text of DOI:10.1007/s11164-015-2183-2

Res Chem Intermed
DOI 10.1007/s11164-015-2183-2
ClO24 /Al-MCM-41 nanoparticles as a solid acid catalyst
for the synthesis of 2-amino-3-cyanopyridines
Mohammad Abdollahi-Alibeik1 Neda Sadeghi-Vasafi1
•
•
Ali Moaddeli1 Ali Rezaeipoor-Anari1
•
Received: 20 March 2015 / Accepted: 17 July 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract A one-pot four-component reaction of various types of aldehydes,
acetophenone, malononitrile, and ammonium acetate was studied in the presence of
perchlorated Al-MCM-41 (ClO-4 /Al-MCM-41) nanoparticles for the synthesis of
2-amino-3-cyanopyridines. Mesoporous Al-MCM-41 molecular sieves with the Si/
Al molar ratios of 30, 40, and 50 were synthesized by the sol–gel method and ClO-4 /
Al-MCM-41 with different calcination temperatures were prepared and character-
ized by SEM, TEM, XRD, FT-IR, potentiometric titration and, N2 adsorption-
desorption techniques. The characterization results show that ClO-4 /Al-MCM-41
with calcination temperature of 300 °C has the best catalytic activity for the syn-
thesis of 2-amino-3-cyanopyridines. The catalyst is reusable many times with
moderate loss in its activity.
Keywords Nanoparticle Á ClO-4 /Al-MCM-41 Á 2-Amino-3-cyanopyridine Á
Mesoporous silica Á Solid acid catalyst Á Multi-component
Introduction
Compounds with pyridine scaffold are known to possess a broad spectrum of
biological activities such as anti HIV [1], anticonvulsant [2], anti-inflammatory [3],
and antitumor [4] activity. Since the first report for the synthesis of substituted
pyridine using multi-component reaction by Hantzsch [5], many synthetic methods
and catalysts have been developed to improve structural features of these
&
Mohammad Abdollahi-Alibeik
abdollahi@yazd.ac.ir; moabdollahi@gmail.com
1
Department of Chemistry, Yazd University, Yazd 89158-13149, Iran
123

M. Abdollahi-Alibeik et al.
compounds. The most popular method for the synthesis of polysubstituted pyridines
using multi-component reaction includes three- or four-component reaction of
aldehydes, active methylene compounds, and ammonium acetate [6, 7]. Among
them, 2-amino-3-cyanopyridins have been synthesized by four-component reaction
of aldehydes, acetophenone, malononitrile, and ammonium acetate [8] in the
presence of various catalysts such as diphenyl ammonium triflate [9], montmoril-
lonite K-10 [10], and ytterbium perfluorooctanoate [Yb(PFO)3] [11].
However, due to importance of these compounds, improvement of new catalytic
systems for this type of reaction is desirable. Recently, there has been increasing
interest in the use of heterogeneous catalysts in organic reactions due to their
remarkable advantages such as reusability, ease of recovery, ease of handling, and
environmental considerations.
MCM-41 belongs to a family of mesoporous silica and has been used as both a
catalyst and as catalyst support due to high surface area of its ordered mesoporous
channels [12]. Incorporation of foreign ions into the MCM-41 framework or surface
modification of mesoporous channels enhances acidity and thus catalytic activity of
this type of materials. Many framework modifiers such as; Al [13], Zr [14], Cu [15],
and also surface modifiers such as BF3 [16] and H3PW12O40 [12] have been used for
preparation of MCM-41-based catalysts.
In this paper, we aim to report the preparation, characterization, and the use of
perchlorated Al-MCM-41 (PAM) nanoparticles as a novel solid acid catalyst for the
synthesis of 2-amino-3-cyanopyridines by one-pot, four-component reaction of aryl
aldehyde, malononitrile, ammonium acetate and acetophenone (Scheme 1).
Experimental
Materials and methods
All chemicals were commercial products. All reactions were monitored by TLC and
product purification was performed by recrystallization in ethanol and all yields
refer to isolated products. 1H and 13C NMR spectra were recorded in DMSO-d6 on a
Bruker DRX-400 AVANCE (400 MHz for 1H and 100 MHz for 13C) spectrometer.
Infrared spectra of the catalysts and reaction products were recorded on a Bruker
FT-IR Equinax-55 spectrophotometer in KBr tablet. XRD patterns were recorded on
Scheme 1 Four-component synthesis of 2-amino-3-cyanopyridines catalyzed by perchlorated Al-MCM-41
123

ClO-4 /Al-MCM-41 nanoparticles as a solid acid catalyst…
a Bruker D8 ADVANCE X-ray diffractometer using nickel-filtered Cu-Ka radiation
˚
(k = 1.5406 A). The morphology was studied using a KYKY-EM3200 scanning
electron microscopy. Melting points were obtained by Buchi B-540 apparatus and
are uncorrected. The BET surface area was measured using a PHS-1020
(PHSCHINA) from the nitrogen adsorption–desorption isotherms at 77 K. All
samples were degassed at 120 °C under flowing nitrogen for 2 h. The specific
surface area (SBET) was calculated from the adsorption data using the BET equation.
Transmittance electron microscopy was performed with Zeiss-EM10C at 80 kV.
ICP analysis was performed by VARIAN model Vista-pro instrument.
Preparation of Al-MCM-41
The synthesis of nanosized Al-MCM-41 with various Si/Al molar ratios carried
out using tetraethylorthosilicate (TEOS) as the Si source, aluminium sulfate as
the aluminium source, cetyltrimethylammonium bromide (CTAB) as the
template and ammonia as the pH control agent with the gel composition of
SiO2:Al2(SO4)3:CTAB:NH4OH:H2O = 22.5:X:2.86:53.5:11555 (X varies with the
Si/Al ratio).
In a typical procedure, to a solution of CTAB (1.04 g, 2.86 mmol) in deionized
water (200 ml), TEOS (5 ml) was added dropwise at 70 °C for about 30 min. The
mixture was allowed to cool to room temperature and a solution of aluminium
sulfate (0.109 g, 0.32 mmol) in deionized water (5 ml) was added dropwise. Then
aqueous ammonia (25 wt%) was added until the pH of the solution was adjusted to
10.5 and was stirred for 12 h. The gel was separated by centrifuge and washed with
distilled water (20 ml) and EtOH (2 9 10 ml), respectively. The solid was dried in
an oven at 120 °C for 2 h and then calcined at 550 °C for 4 h. The obtained solid
was denoted as AM-550.
Preparation of ClO24 /Al-MCM-41
ClO-4 /Al-MCM-41 catalyst was prepared by mixing of AM-550 (Al-MCM-41 that
template was removed at 550 °C) (100 mg) and perchloric acid (0.1 M, 2 ml). The
resulting suspension was stirred at ambient temperature for 4 h. The mixture was
separated by centrifuge and washed with deionized water (2 9 3 ml). The obtained
solid was dried in an oven at 120 °C for 2 h to obtain perchlorated Al-MCM-41,
denoted as PAM-120, and then calcined at 250, 300, 350, and 400 °C for 4 h. The
obtained samples were denoted as PAM-250, PAM-300, PAM-350, and PAM-400,
respectively.
General procedure for the synthesis of 2-amino-3-cyanopyridine derivatives
in the presence of ClO24 /Al-MCM-41
A mixture of acetophenone (1 mmol), aldehyde (1 mmol), malononitrile (1 mmol),
ammonium acetate (1.5 mmol) and catalytic amount of ClO-4 /Al-MCM-41 (20 mg)
was stirred under solvent-free condition at 100 °C. After completion of the reaction
(monitored by TLC, eluent; n-hexane:EtOAc, 80:20), the catalyst was separated by
123

M. Abdollahi-Alibeik et al.
centrifuge and washed with EtOH (2 9 3 ml). The crude products were crystallized
from EtOH and purified by column chromatography to give pure 2-amino-3-
cyanopyridines.
Physical and spectroscopic data of compounds (4a-i)
2-Amino-3-cyano-4,6-diphenylpyridine (4a): Yellow solid, mp 186 °C (Lit. [4]
186 °C). IR (KBr) tmax (cm-1): 3463 (NH2), 3302 (NH2), 2205 (C:N), 1637
(C=N), 1573 (C=C).1H NMR (400 MHz, DMSO-d6): d (ppm) = 7.0 (s, 2H, NH2),
7.3 (s, 1H), 7.5 (m, 3H), 7.6 (m, 3H), 7.7 (m, 2H), 8.1 (m, 2H).13C NMR (100 MHz,
DMSO-d6): d (ppm) = 109.2, 117, 127.2, 128.3, 128.6, 128.7, 129.6, 130.1, 136.6,
137.5, 154.8, 158.6, 160.7, 160.8.
2-Amino-3-cyano-4-(4-methoxyphenyl)-6-phenylpyridine (4b): Yellow solid,
mp 180–182 °C (Lit. [8] 180–182 °C). IR (KBr) tmax (cm-1): 3466 (NH2), 3308
(NH2), 2206 (C:N), 1639 (C=N), 1575 (C=C).1H NMR (400 MHz, DMSO-d6): d
(ppm) = 3.8 (s, 3H, OCH3), 6.9 (s, 2H, NH2), 7.1 (d, 2H, J = 8.8 Hz), 7.3 (s, 1H),
7.5 (m, 3H), 7.7 (d, 2H, J = 8.8 Hz), 8.1 (m, 2H).13C NMR (100 MHz, DMSO-d6):
d (ppm) = 55.3, 109.0, 114.1, 117.3, 127.2, 128.6, 129.0, 129.8, 137.6, 154.4,
158.4, 160.4, 160.88, 160.9.
2-Amino-3-cyano-4-(4-chlorophenyl)-6-phenylpyridine (4c): Pale yellow solid,
mp 187–188 °C (Lit. [4] 188–190 °C). IR (KBr) tmax (cm-1): 3486 (NH2), 3363
(NH2), 2216 (C:N), 1632 (C=N), 1574 (C=C).1H NMR (400 MHz, DMSO-d6): d
(ppm) = 7.1 (s, 2H, NH2), 7.3 (s, 1H), 7.5 (m, 3H), 7.6 (d, 2H, J = 8.4 Hz), 7.7 (d,
2H, J = 12.6 Hz), 8.14 (m, 2H).13C NMR (100 MHz, DMSO-d6):
d
(ppm) = 109.1, 116.8, 127.2, 128.6, 130.3, 134.5, 135.7, 137.4, 153.0, 158.7,
160.7, 158.6, 160.8.
2-Amino-3-cyano-4-(4-methylphenyl)-6-phenylpyridine (4d): With solid, mp
173–174 °C (Lit. [17] 175–176 °C). IR (KBr) tmax (cm-1): 3466 (NH2), 3296
(NH2), 2205 (C:N), 1632 (C=N), 1578 (C=C).
2-Amino-3-cyano-6-(3,4-dimethoxyphenyl)-4-phenyl pyridine (4e): Yellow
solid, mp 218–220 °C (Lit. [18] 212–214 °C). IR (KBr) tmax (cm-1): 3512
(NH2), 3405 (NH2), 2199 (C:N), 1603 (C=N), 1580 (C=C).
2-Amino-3-cyano-6-(3,4-dimethoxyphenyl)-4-(4-methoxyphenyl)pyridine (4f):
Yellow solid, mp 174–176 °C (Lit. [18] 165–167 °C). IR (KBr) tmax (cm-1):
3482 (NH2), 3325 (NH2), 2205 (C:N), 1632 (C=N), 1574 (C=C).
2-Amino-3-cyano-6-(3,4-dimethoxyphenyl)-4-(4-chlorophenyl)pyridine
(4g):
Pale yellow solid, mp 202–204 °C (Lit. [18] 203–207 °C). IR (KBr) tmax (cm-1):
3480 (NH2), 3315 (NH2), 2208 (C:N), 1637 (C=N), 1574 (C=C).
2-Amino-3-cyano-6-(3,4-dimethoxyphenyl)-4-(4-hydroxyphenyl)pyridine (4h):
Yellow solid, mp 207–209 °C (Lit. [18] 205–207 °C). IR (KBr) tmax (cm-1):
3489 (NH2), 3391 (NH2), 2212 (C:N), 1635 (C=N), 1575 (C=C).
2-Amino-3-cyano-6-(4-chlorophenyl)-4-(4-methoxyphenyl)pyridine (4i): Yellow
solid, mp 200–201 °C (Lit. [19] 177 °C). 3460 (NH2), 3367 (NH2), 2207 (C:N),
1608 (C=N), 1584 (C=C) (Fig. 1).
123

ClO-4 /Al-MCM-41 nanoparticles as a solid acid catalyst…
Fig. 1 SEM images of (a) AM-
550 and (b) PAM-300
Results and discussion
Catalyst characterization
The MCM-41, AM, and PAM samples were characterized by FT-IR, SEM, and
XRD techniques. The SEM images of AM-550 and PAM-300 show spherical
nanoparticles with sizes of\100 nm (Fig. 1). TEM images of MCM-41, Al-MCM-
41, and PAM-300 were observed in Fig. 2. As shown in Fig. 2a, the ordered
mesostructure of MCM-41 as well as mesopore channels is completely obvious.
Incorporation of the Al in MCM-41 lattice had not dramatic effect on the
mesostructure of Al-MCM-41 (with Si/Al molar ratio of 40) (Fig. 2b). Mesostruc-
ture of the PAM-300 sample was further studied by TEM (Fig. 2c). Porosity of the
catalyst is clear and pores size is observed in range of the mesoporous material
(2–3 nm). Partial disarray in mesoporous structure of PAM-300 is related to the
incorporation of Al into the MCM-41 framework and also acid treatment.
123

M. Abdollahi-Alibeik et al.
Fig. 2 TEM images of
(a) MCM-41, (b) Al-MCM-41
(Si/Al mol ratio of 40), and
(c) PAM-300
The FT-IR spectra of PAM-300, PAM-120, HClO4, AM-550, MCM-41, and
Al2O3 are shown in Fig. 3. MCM-41 shows characteristic peaks at 460 cm-1 related
to the bending vibration of Si–O–Si, 810 cm-1 relating to symmetric stretching of
Si–O–Si, 960 cm-1 due to Si–OH and the peak at 1083 cm-1 relating to
asymmetric stretching of Si–O–Si (Fig. 3c). The spectrum of Al2O3 shows
corresponding peaks at 594, 1037, 1120, 1378, 1633, and 2921 cm-1. The AM-
550 (Al-MCM-41 calcined at 550 °C) sample exhibits characteristic peaks of
MCM-41. The PAM-120 sample (Fig. 3e) shows peaks of perchlorate around
630 cm-1. Perchlorate peaks in the range of 933 and 1103 cm-1 overlap with the
strong peak of MCM-41 around 960 and 1080 cm-1, resulting in increase of
intensity and broadening of this peak. In the spectrum of PAM-300 (Fig. 3f), the
characteristic bands of perchlorate at 630 cm-1 disappeared, indicating the absence
of free perchloric acid after calcination process. However, slight broadening of the
123

ClO-4 /Al-MCM-41 nanoparticles as a solid acid catalyst…
Fig. 3 FT-IR spectra of
(a) Al2O3, (b) MCM-41,
(c) AM-550, (d) HClO4,
(e) PAM-120, (f) PAM-300
peaks in the region of 1100–1200 cm-1 confirms the presence of perchlorate in the
sample. Increase in the intensity of the peak of PAM-300 at 960 cm-1 compared
with AM-550, may be due to increase of the number of silanol groups (Si–OH) on
the surface because of the interaction of perchlorate with surface. Displacement of
large aluminum atoms with small silica atoms change lattice vibration bands to
lower wavenumber at 1168 and 1180 cm-1. The peak at 1635 cm-1 in all of
samples is assigned to bending vibration of HOH due to the presence of water on the
pellet samples.
The low-angle XRD patterns of MCM-41, Al-MCM-41, and ClO-4 /Al-MCM-41
are shown in Fig. 4. The MCM-41 pattern shows characteristic peaks at 2h = 2.42°,
4.24°, 4.74°, and 6.18°. The XRD patterns of Al-MCM-41 and also PAM-300
(Fig. 4b, d) show that incorporation of Al into the network and also anchoring of the
123

M. Abdollahi-Alibeik et al.
Fig. 4 Low-angle XRD
patterns of (a) MCM-41,
(b) AM-550, (c) PAM-300
Fig. 5 Potentiometric titration
of MCM-41, PAM-250, PAM-
300, PAM-350, and PAM-400
200
150
100
50
'MCM-41'
'PAM-250'
'PAM-300'
'PAM-350'
'PAM-400'
0
-50
0
2
4
6
8
10x10-3
meq/g
123

ClO-4 /Al-MCM-41 nanoparticles as a solid acid catalyst…
Fig. 6 FT-IR spectra of pyridine adsorption (a) PAM-300 no pyridine adsorbed, (b) pyridine adsorbed
PAM-300 at ambient temperature, (c) pyridine adsorbed PAM-300 at 300 °C
perchlorate on the surface of the Al-MCM-41, affected on the intensity and width of
the main peak. This is due to decrease in long-range order of hexagonal
mesostructure of MCM-41.
The number of acid sites can be compared using potentiometric curves.
According to this method, the initial potential electrode (Ei) shows the strength of
surface acid sites and the meq of used base shows number of acid sites. The
potentiometric curve of MCM-41 and PAM-300 is shown in Fig. 5. MCM-41 with
the lowest potential is weak acid and PAM-300 with the greatest potential, is
stronger than all. Due to highest meq of the used n-butyl amine per gram of the
catalyst, PAM-300 has more acidic sites.
To investigate the distribution of Brønsted and Lewis acid sites on the catalyst
surface, the pyridine adsorption techniques were used. Figure 6 shows the FT-IR
spectra of the pyridine adsorbed PAM-300 at ambient temperature and 300 °C. The
spectrum of pyridine adsorbed PAM-300 at ambient temperature (Fig. 6b) shows
123

M. Abdollahi-Alibeik et al.
1000
800
600
400
200
(Ads)
(des)
0.0
0.2
0.4
0.6
0.8
Relative Pressure (P/P°)
Fig. 7 N2 adsorption–desorption isotherms of PAM-300
Table 1 Surface area of MCM-
Entry
Catalyst
SBET (m2 g-1
)
41, AM-550 and PAM-300
1
2
3
MCM-41
1505
1150
847
Al-MCM-41
PAM-300
that the peak at 1446 and 1598 cm-1 corresponded Lewis acid sites. Weak peaks at
1543 and 1491 cm-1 show the Brønsted acid sites. The very weak peak at
1483 cm-1 is the combination band of pyridine bonded to both Brønsted and Lewis
acid sites. Peaks of Lewis acid sites (1446 and 1598 cm-1) are stronger than the
Brønsted acid sites, which represent a higher number of Lewis acid sites. Lewis acid
sites are more powerful because at high temperature, the peak of pyridine is visible
(Fig. 7).
Textural properties of the catalysts were studied by surface measurement using
BET method. As shown in Table 1, surface area of MCM-41 was decreased by
incorporation of Al into the framework of MCM-41. Results show that impregnation
of perchlorate onto the mesoporous channels of Al-MCM-41 reduces the surface
area.
Figure 7 shows N2 adsorption–desorption isotherms of PAM-300. In this
isotherm, a mesoporous inflection, type IV according to IUPAC classification of
adsorption isotherms [20], was observed at the relative pressure of p/po = 0.2–0.4
because of capillary condensation. A sharp hysteresis was observed at higher p/po
(p/po [ 0.7) due to the condensation of N2 within voids formed by nanoparticles.
The presence of the Al content in the samples and also Si/Al molar ratios of the
Al-MCM-41 and perchlorated Al-MCM-41 was investigated by means of an ICP
method. The Si/Al molar ratio of AM-550 and PAM-350 was measured equal to
123

ClO-4 /Al-MCM-41 nanoparticles as a solid acid catalyst…
Table 2 Optimization of the reaction conditions for the synthesis of 2-amino-3-cyanopyridine in the
presence of catalytic amount of ClO-4 /Al-MCM-41
Entry
Catalyst
Solvent
Temperature (°C)
Si/Ala
Catalyst
amount (mg)
Time
(min)
Yieldb
(%)
1
2c
PAM-300
PAM-300
PAM-300
PAM-120
PAM-250
PAM-350
AM-550
–
100
100
100
100
100
100
100
100
100
90
30
40
50
40
40
40
40
40
40
40
40
40
40
20
20
20
20
20
20
20
15
25
20
20
20
20
20
20
50
–
73
3
–
25
44
4
–
20
44
5
–
25
49
6
–
15
48
7
–
80
29
8
PAM-300
PAM-300
PAM-300
PAM-300
PAM-300
PAM-300
–
20
50
9
–
30
68
10
11
12
13
a
–
60
70–80
60–70
50–60
–
–
110
120
Reflux
150
90
–
EtOH
720
The Si/Al molar ratio refer to the initial gel composition, mol% of the Al content for the optimized
condition (for 20 mg of the PAM-300) was measured equal to 0.35 mol% relative to reactants by an ICP
method
b
Isolated yield
c
Optimized conditions
61.96 and 73.45, respectively. Acid treatment of the Al-MCM-41 provokes the
partial leaching of the Al from the mesoporous structure. Despite this fact,
mesoporous structure of the catalyst was proved by TEM image and XRD data.
To investigate the loading amounts of perchlorate on the different PAM samples,
the Cl content was determined using potentiometric titration. The wt% of ClO4-
were obtained 11.2, 8, and 3.2 % for PAM-120, PAM-300, and PAM-350,
respectively. Reduction from 11.2 in PAM-120 to 8 in PAM-300 may be due to
decomposition of free HClO4 on the surface. Reduction of the perchlorate content in
the PAM-350 confirms rapid decomposition of perchlorate at the temperature of
more than 300 °C according to literature report [21].
Catalytic activity of ClO24 /MCM-41
The catalysis performance of ClO-4 /MCM-41 was investigated in the synthesis of
2-amino-3-cyanopyridine by the reaction of benzaldehyde (1 mmol), acetophenone
(1 mmol), ammonium acetate (1.5 mmol), and malononitrile (1 mmol) under
solvent-free conditions as the model reaction and results are summarized in Table 2.
In order to optimize the amount of the ClO-4 /Al-MCM-41, the model reaction
was performed with various amounts of the catalyst and in terms of reaction time
and yield of the product, 20 mg of the catalyst in the model reaction was selected as
the best amount (Table 2, entries 2, 8–9).
123

M. Abdollahi-Alibeik et al.
Table 3 Four-component reaction of aldehydes, acetophenone, ammonium acetate and malononitrile in
the presence of catalytic amount of ClO-4 /Al-MCM-41 for the synthesis of 2-amino-3-cyanopyridineunder
solvent-free condition
M.P.
Aldehyde Acetophenone 2-amino-3-cyanopyridine Time Yield
Entry
(1)
(2)
(4)
(min)
(%)
(Found) (Reported)
a
20
73
186
186 [4]
180–182
[8]
b
25
79
180–182
188–190
[4]
c
15
82
187–188
175–176
[17]
d
20
75
173–174
212–214
[18]
e
30
82
218–220
123

ClO-4 /Al-MCM-41 nanoparticles as a solid acid catalyst…
Table 3 continued
M.P.
Aldehyde Acetophenone 2-amino-3-cyanopyridine Time Yield
Entry
(1)
(2)
(4)
(min)
(%)
(Found) (Reported)
165–168
174–176
f
25
80
[18]
203–207
202–204
g
h
i
25
78
[18]
205–207
207–209
25
72
[18]
30
79
200–201 177 [19]
To investigate the effect of the ratio of Si/Al on the catalytic activity of ClO-4 /Al-
MCM-41, the model reaction was performed in the presence of 20 mg of the
catalyst with various Si/Al molar ratios (Table 2, entries 1–3). The results show that
the molar ratio of Si/Al = 40 has the best catalytic activity.
123

M. Abdollahi-Alibeik et al.
Yield (%)
Table 4 Reusability of ClO-4 /
Al-MCM-41 in the reaction of
benzaldehyde, acetophenone,
ammonium acetate, and
malononitril
Run
Time (min)
1
2
3
4
20
30
45
40
73
70
65
68a
a
After calcination at 300 °C for
4 h
The effect of the calcination temperature on the catalytic activity was
investigated in the model reaction in the presence of 20 mg of PAM-120, PAM-
250, PAM-300, PAM-350, and PAM-400 catalysts. As shown in Table 2 (entries 1,
4–6), the results show that PAM-300 has the best catalytic activity. This result is in
agreement with results of potentiometric titration of PAM samples (Fig. 5) and also
decrease in the activity of PAM-350 relative to PAM-300 is in agreement with
perchlorate content of PAM-300 (8 % in PAM-300 was reduced to 3.2 % in PAM-
350).
To investigate the effect of temperature in the reaction, the model reaction in the
presence of 20 mg PAM-300 was performed under solvent-free conditions (Table 2,
entries 2, 10–12). The best temperature is 100 °C with the best yield and time for
the reaction.
In order to evaluate efficiency of the ClO-4 /Al-MCM-41 catalyst in the synthesis
of various derivatives of 2-amino-3-cyanopyridine, the model reaction was extended
to various aldehydes. Therefore, four-component reaction of aldehydes (1 mmol),
acetophenone (1 mmol), ammonium acetate (1.5 mmol), and malononitrile
(1 mmol) were investigated in the presence of 20 mg PAM-300 (Si/Al = 40) at
100 °C under solvent-free conditions and the corresponding 2-amino-3-cyanopy-
ridine were obtained in 72–82 % yields (Table 3). The workup and the catalyst
recovery are very easy. After completion of the reaction (monitored by TLC, eluent;
n-hexane:EtOAc, 80:20), the reaction mixture was centrifuged and the catalyst was
washed with EtOH (3 9 2 ml). Organic phase was collected and crystallized in
ethanol to obtain pure product.
To study of the reusability of the PAM-300, the recovered catalyst from the
model reaction was washed with EtOH, dried in an oven at 120 °C for 2 h, and
reused in the same reaction three times. The obtained results show the moderate
decrease in the catalytic activity. This may be due to blockage of active sites of the
catalysts. The recycled catalyst after third run was calcined at 300 °C for 4 h. Then
again, the catalyst was used in the model reaction. Decrease in the reaction time and
increase in the yield, demonstrate blocking of holes in previous reaction (Table 4).
The FT-IR vibrational peaks of various functional groups of organic material in the
spectrum of reused catalyst confirm blocking of surface on the catalyst. However,
ICP analysis of Al content and also analysis of perchlorate confirms that there is not
any leaching in the reaction media.
123

ClO-4 /Al-MCM-41 nanoparticles as a solid acid catalyst…
Conclusions
In this work, we prepared Al-MCM-41 with various Si/Al molar ratio. To promotion
of the catalytic activity, Al-MCM-41 was treated with perchloric acid. It was
concluded that acid treatment of the Al-MCM-41 by perchloric acid promotes its
catalytic activity. We also investigated parameters such as Si/Al mol ratio and
temperature of calcination that have notable effects on the activity of the catalyst. In
order to characterize the catalyst, various techniques such as SEM, TEM, FT-IR,
potentiometric titration, pyridine adsorption, and nitrogen adsorption–desorption
have been applied to investigate the structure and catalytic activity of the catalyst.
To testify the activity of the prepared catalyst, synthesis of 2-amino-3-cyanopy-
ridines was performed in the presence of a catalytic amount of perchlorated Al-
MCM-41 as an efficient and reusable catalyst. High yields, simple operation, non-
toxic catalyst and solvents, short reaction time, and minimum pollution of the
environment are some other advantages of this method.
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