TiO2-nanoparticles as efficient catalysts for the synthesis of pyridine dicarbonitriles

Article abstract of DOI:10.1002/jccs.201900041

The catalytic effects of two forms of nano-TiO₂, which are prepared via an ordinary or a magnetized process, are investigated in the synthesis of pyridine dicarbonitriles by one-pot multicomponent reaction of 4-methyl thiophenol, malononitrile, and aryl aldehydes. The results have shown that both prepared nano-TiO₂ exhibited high catalytic activities toward the synthesis of pyridine dicarbonitrile derivatives but the nano-TiO₂, which is prepared via a magnetized process, has shown better catalytic activity. Furthermore, this new catalytic method for the synthesis of pyridine dicarbonitriles provides rapid access to the desired compounds in high yields and so a simple work-up procedure in the presence of water at room temperature. Therefore, this method represents a significant improvement incompatible of the other methods that are available for the synthesis of pyridine dicarbonitriles.

Full text of DOI:10.1002/jccs.201900041

Received: 1 February 2019
Accepted: 21 March 2019
DOI: 10.1002/jccs.201900041
A R T I C L E
TiO -nanoparticles as efficient catalysts for the synthesis of
2
pyridine dicarbonitriles
1
1
2
Sayyed Jalal Shams-Najafi
| Mostafa Gholizadeh
| Ali Ahmadpour
1
Department of Chemistry, Faculty of
The catalytic effects of two forms of nano-TiO , which are prepared via an ordi-
Science, Ferdowsi University of Mashhad,
Mashhad, Iran
2
nary or a magnetized process, are investigated in the synthesis of pyridine
dicarbonitriles by one-pot multicomponent reaction of 4-methyl thiophenol,
malononitrile, and aryl aldehydes. The results have shown that both prepared nano-
TiO2 exhibited high catalytic activities toward the synthesis of pyridine
2
Department of Chemical Engineering,
Faculty of Engineering, Ferdowsi University
of Mashhad, Mashhad, Iran
Correspondence
dicarbonitrile derivatives but the nano-TiO , which is prepared via a magnetized
2
Mostafa Gholizadeh, Department of
Chemistry, Faculty of Science, Ferdowsi
University of Mashhad, Mashhad, Iran.
Email: m_gholizadeh@um.ac.ir
process, has shown better catalytic activity. Furthermore, this new catalytic method
for the synthesis of pyridine dicarbonitriles provides rapid access to the desired
compounds in high yields and so a simple work-up procedure in the presence of
water at room temperature. Therefore, this method represents a significant improve-
ment incompatible of the other methods that are available for the synthesis of pyri-
dine dicarbonitriles.
Funding information
Ferdowsi University of Mashhad Research
Council, Grant/Award Number: 3/41305
K E Y W O R D S
2
fast synthesis, multicomponent reaction, nano-TiO , pyridine dicarbonitriles
[
3]
1
| INTRODUCTION
diseases. They are also inhibitors of cholinesterases and
may be used for treating neurodegenerative diseases. These
compounds have also been studied as potential anti-HBV,
antibacterial, antibiofilm, and anti-infective agents and as
potassium channel openers with applications in treating uri-
nary incontinence. Moreover, some of these derivatives also
inhibit prion replication and may be used for treating
Among the nitrogen-containing heterocycles, densely
substituted pyridine derivatives are one of the most impor-
tant classes of compounds as they widely occur as key struc-
tural subunits in numerous natural products that exhibit
[1]
many interesting biological activities. In addition, these
heterocyclic compounds have found a variety of applications
[
4]
Creutzfeldt–Jacob disease. Many synthetic protocols were
developed to accelerate the rate of pyridine dicarbonitrile
reaction and to improve the yield. These compounds have
been synthesized in the presence of various catalyst such as
[2]
in medicinal and pharmaceutical sciences. Among these
pyridine derivatives, 2-amino-6-(arylthio)pyridine-3,-
-dicarbonitrile is a privileged scaffold for developing phar-
5
[
5]
[6]
[7]
[8]
[9]
[10]
maceutical agents because various compounds with this
structural motif display significant and diverse biological
activities. For example, adenosine receptors are associated
with Parkinson's disease, hypoxia, asthma, epilepsy, cancer,
Et N, IBX, DABCO, K CO , KOH, MS 4A,
3
2
3
[
11]
[12]
Nano-CuI,
Nano-MgO,
and have been utilized in the
construction of the pyridine dicarbonitriles. Major draw-
backs of these procedures include expensive reagents, use of
large amounts of organic solvents, and prolonged heating
and side reactions. In recent years, economic and environ-
mental concerns encourage the application of heterogeneous
[3]
and cardiovascular diseases. These pyridine compounds
have been shown to be active inhibitors of the adenosine
receptors and, therefore, can be used for treating these
©
2019 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
J Chin Chem Soc. 2019;1–6.
http://www.jccs.wiley-vch.de
1

2
SHAMS-NAJAFI ET AL.
Me
Ar
N
CN
CN
nano-TiO2
NC
CN
S
Me
+
+
ArCHO
H2N
SH
1
2
3
4
SCHEME 1 Synthesis of pyridine dicarbonitriles catalyzed by
nano-TiO
2
[13]
catalysts to carry out various organic transformations.
These catalysts have very high catalytic activities due to their
large specific surface area and make the processes clean, safe,
[14]
high-yielding, and inexpensive.
Nowadays, application of
magnetic nanocomposites as heterogeneous catalysts is an
interesting research area. The surface functionalization of
these materials is an elegant way to bridge the gap between
2
FIGURE 1 SEM image of prepared nano-TiO via ordinary
process
[15]
heterogeneous and homogeneous catalyses.
As a part of our research in developing efficient methods
of organic synthesis that involve reusable catalysts, we stud-
for 1h and then utilized for the preparation of NaOH. Subse-
quently, the obtained sodium hydroxide was applied for the
ied application of nano-TiO prepared via an ordinary or a
2
synthesis of nano-TiO via a hydrothermal method. The
2
magnetized process as an efficient acid catalyst in the syn-
thesis of pyridine dicarbonitrile derivatives by the reaction
of thiophenol 1, malononitrile 2, and aryl aldehydes 3.
Nano-TiO2 could be removed from the reaction mixture
through filtration and reused several times. However, there
were no reports on application of FGOSA as an acidic het-
erogeneous catalyst in the synthesis of pyridine
dicarbonitriles (Scheme 1).
hydrothermal process is discussed in the experimental. Inter-
estingly, when water is magnetized, the morphology of final
prepared samples is totally different. Therefore, it is clear
that the property of water changed by applying the perma-
nent magnetic field (0.6Tesla or 6,000 Guass) and the prop-
erties are reserved at least for 48 hr even at high temperature
and pressure.
2
.1 | Catalytic activity of TiO nanostructures
2
2
| RESULTS AND DISCUSSION
prepared via magnetized process in the
synthesis of pyridine dicarbonitrile derivatives
In this study, nano-TiO structures were prepared via ordi-
2
The catalytic activity of this material was evaluated in the
synthesis of pyridine dicarbonitrile derivatives. Synthesis of
compound 4b was selected as a model reaction for optimiz-
ing the reaction conditions. The reaction was carried out
with 4-methyl thiophenol 1, malononitrile 2, and
nary or magnetized processes. In both pathways,
TiO nanostructures were synthesized using a hydrothermal
2
process. In the magnetized process, NaOH was obtained
from magnetized water. The model of water magnetization
is discussed in the experimental section. The SEM image of
4
-chlorobenzaldehyde 3b in the presence of different
the prepared nano-TiO via an ordinary process is shown in
2
amounts of catalysts and in various solvents and also under
solvent-free conditions (Table 1). Long reaction times and
poor yields of the product 4b were obtained in the absence
of the catalyst in all cases (entries 1–5). Also, low yields of
the desired product were obtained under solvent-free condi-
tions in the presence or absence of the catalyst (entries 4–6).
The presence of temperature was necessary for all situations.
Therefore, the best results were reached under catalytic con-
ditions upon refluxing solvents, preferably ethanol (entries
Figure 1. The average size of TiO nanoparticles is about
2
38 nm and they are exactly distinguishable from each other.
Figure 2 shows SEM images of the prepared TiO via a
2
magnetized process. In this pathway, water was magnetized
Nano-TiO2
Nano-TiO2
CN
R1S
R
NH
CN
R1S
NC
NH
R
N
O
CN
CN
CN
CN
R1SH
CN
+
CN
R
H
R
H
H
Nano-TiO2
1
2–16). According to the final outcomes, the reaction was
H
H
R1S
NC
N
NH
CN
R1S
NC
N
NH2
CN
R1S
NC
N
NH2
CN
more facile and proceeded to give the highest yield (97%),
and a short reaction time (14 min), using 0.06 g of the cata-
lyst in ethanol (5 mL) at reflux temperature (entry 12). An
increase of the catalyst amount up to 0.08 g did not improve
the product yield or shorten the reaction time (entry 12).
-H2
H
R
R
R
SCHEME 2 Mechanism for the synthesis of pyridine
dicarbonitriles

SHAMS-NAJAFI ET AL.
3
TABLE 1 Optimization of reaction conditions for the synthesis of
a
compound 4b catalyzed by nano-TiO
2
prepared via magnetized process
Catalyst
Entry (g)
Isolated
Time/min yield/%
ꢀ
Solvent T/ C
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
—
H
2
O
Reflux
Reflux
r.t.
135
135
180
150
150
100
60
32
44
34
16
19
31
76
88
89
78
96
97
83
63
51
41
—
EtOH
EtOH
—
—
—
100
—
—
120
0.06
0.02
0.04
0.06
0.06
0.08
0.06
0.06
0.06
0.06
0.06
—
120
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
Reflux
Reflux
80
40
45
0
1
2
3
4
5
6
r.t.
30
Reflux
20
Reflux 14
H
2
O
Reflux
Reflux
25
40
50
60
MeOH
CH
3
CN Reflux
Cl Reflux
CH
2
2
a
Reaction conditions: 4-methyl thiophenol 1, malononitrile 2, and
-chlorobenzaldehyde 3b (1.5 mmol).
4
Catalytic effects of the both prepared TiO were evalu-
2
ated in the synthesis of pyridine dicarbonitrile derivatives
under optimized conditions. According to the optimization
experiments, both nanocatalysts involved demonstrated good
catalytic effects in the model reaction but the nano-TiO cat-
2
alyst prepared via magnetized process promoted the reaction
more efficiently than the other, leading to higher yields of
products 4 in a shorter reaction time (Table 2).
TABLE 2 Synthesis of pyridine dicarbonitriles with different
a
aldehydes
Time (min)
Yield (%)
b
c
b
c
Entry Ar
Product TiO
2
TiO
20
14
21
23
19
24
26
27
2
TiO
87
91
89
88
85
89
90
87
2
TiO
93
97
95
90
89
93
94
94
2
1
2
3
4
5
6
7
8
C
6
H
5
4a
4b
4c
4d
4e
4f
28
21
32
33
27
37
31
36
4-Cl-C
3-Cl-C
6
H
H
4
4
6
4-Br-C
3-Br-C
6
H
H
4
4
6
3-NO
4-NO
2
-C
6
H
4
2
-C
6
H
4
4g
4h
4-CH
3
O-C
6
H
4
a
Reaction conditions: 4-methyl thiophenol, malononitrile, and aryl aldehydes,
and TiO (0.06 g) in refluxing water.
2
2
FIGURE 2 The SEM images of prepared nano-TiO via
magnetized process
b
TiO
2
prepared via ordinary process.
c
TiO
2
prepared via magnetized process.

4
SHAMS-NAJAFI ET AL.
Probably, the catalyst could act as a Lewis acid and,
therefore, promote the reactions. The catalyst would play a
significant role in increasing the electrophilic character of
the electrophiles in the reaction (Scheme 2).
3
| CONCLUSIONS
In this article, we synthesized pyridine dicarbonitrile deriva-
tives in the presence of nano-TiO via an ordinary or a mag-
2
netized process as highly effective heterogeneous catalysts.
This method provided these products in high yields over a
short reaction time in both the forms of nano-TiO , but the
2
FIGURE 3 The model of solvent-magnetizing apparatus (SMA)
nano-TiO prepared via magnetized process showed better
2
yields in the shorter reaction times. Also, the catalyst was
inexpensive and easily obtainable, stable, and storable.
autoclave and the reaction takes place at constant tempera-
ture in a given time. In this part of the process (transmission
and heat), there are some parameters that affect Nanotube
properties including the particle size and primary powder
shape, molarity of potassium hydroxide solution (in the
4
| EXPERIMENTAL
1
All products were characterized by m.p., IR, H NMR, and
GC/MS. Melting points were measured by using the capil-
lary tube method with an electro thermal 9,200 apparatus.
range 5–15 mol), the ratio of TiO in gram to potassium
2
1
13
H and CNMR spectra were recorded on a Bruker DRX
solution in milliliter (in the range 0.25–20 g in 300 mL),
ꢀ
Avance spectrometer at 300 and 75 MHz, respectively, with
CDCl3 as solvent. IR spectra were recorded from KBr disk
on the FT-IR Bruker Tensor 27. GC/MS spectra were
recorded on an Agilent Technologies 6,890 network GC sys-
tem and an Agilent 5,973 network Mass selective detector.
Thin layer chromatography (TLC) on commercial
aluminum-backed plates of silica gel, 60 F254 was used to
monitor the progress of reactions. All products were charac-
terized by spectra and physical data.
reaction temperature (in the range 110–160 C), duration of
reaction time (20–110 hr). The effect of these parameters
[
18,19]
has been studied in various resources.
After the com-
pletion of reaction, the solution should be allowed to cool
slowly to room temperature. Then, the white precipitate is
removed from the solution and washed with distilled water
so that the solution reaches pH = 7. After this phase, it is
washed with sulfuric acid (0.05 M) and distilled water,
respectively. The resulting wet powder is dried under vac-
ꢀ
uum (50–80 C), though in some articles drying is performed
[
20]
under atmospheric pressure.
In this regard, the effect of
4
.1 | Solvent-magnetizing apparatus
atmospheric drying on nanotube properties has not been
studied yet.
The permanent magnet in a compact form, a unit called
AQUA CORRECT,” was used. This equipment is a coaxial
static magnetic system with field strength of 0.6 Tor
,000 G (H.P.S Co., Germany). The equipment was con-
“
6
4
.3 | Typical procedure for the preparation of
nected from one end to the liquid pump and the other end to
the pipelines of the solvent reservoir. Solutions flow through
a coaxial static magnetic field and came back to the solvent
pyridine dicarbonitriles
To a magnetically stirred solution of aldehyde (1 mmol),
4-methyl thiophenol (1 mmol), malononitrile (2 mmol), and
nano-TiO2 (5 mol%) in ethanol (5 mL) were added and stir-
ring was continued for appropriate time. The reaction was
monitored by TLC. Upon completion of the transformation,
the catalyst was filtered under hot conditions. The catalyst
was washed with a small portion of hot ethanol. After
cooling, the combined filtrate was allowed to stand at room
temperature. The precipitated solid was collected by filtra-
tion, and recrystallized from ethanol to give a desired com-
pound in high yields.
[
16,17]
reservoir.
Therefore, solution could pass through the
field many times, in a closed cycle (Figure 3).
4
.2 | Synthesis of nano-TiO via magnetized
2
process
Hydrothermal method is a very simple and common method.
In this method, TiO powder is first released in sodium
hydroxide that was prepared by magnetized water and then
it is mixed. The prepared solution is placed inside the
2

SHAMS-NAJAFI ET AL.
5
0
0
0
4
.3.1 | 3-amino-5-(p-tolylthio)-[1,1 -biphenyl]-
,6-dicarbonitrile (4a)
4.3.5 | 3-amino-3 -bromo-5-(p-tolylthio)-[1,1 -
biphenyl]-2,6-dicarbonitrile (4e)
2
−
1
−1
IR (KBr) (νmax/cm ): 3,432, 3,374, 3,073, 2,922, 2,231,
IR (KBr) (νmax/cm ): 3,441, 3,326, 3,025, 2,998, 2,231,
1
1
1
3
2
,621, 1,585, 1,456, 1,073, and 723; H NMR (DMSO,
00 MHz) (δ, ppm): 2.38 (s, 3H, CH ), 7.32 (d, J = 7.1 Hz,
H, aromatic H), 7.33–7.55 (m, 5H, aromatic H), 7.57 (d,
J = 7.3 Hz, 2H, aromatic H), 7.60 (s, 1H, aromatic H), and
.76 (br., s, 2H, NH2); C NMR (DMSO, 75 MHz) (δ,
ppm): 167.51, 161.12, 159.31, 141.23, 135.54, 134.63,
35.21, 133.89, 130.11,129.54, 128.89, 124.37, 116.58,
15.87, 95.21, 86.25, and 22.48; GC/MS: 341 (M ).
1,678, 1,589, 1,521, 1,229, 998, and 796; H NMR (DMSO,
300 MHz) (δ, ppm): 2.37 (s, 3H, CH ), 7.31 (d, J = 6.9 Hz,
3
3
2H, aromatic H), 7.35–7.75 (m, 7H, aromatic H), and 7.81
13
(br, s, 2H, NH2); C NMR (DMSO, 75 MHz) (δ, ppm):
167.56, 162.25, 158.58, 142.20, 140.99, 138.55, 135.89,
134.11, 133.22,131.78, 130.41, 125.25, 124.31, 116.28,
1
3
7
+
1
1
115.66, 94.52, 87.66, and 20.73; GC/MS: 420 (M ).
+
0
0
4
.3.6 | 3-amino-3 -nitro-5-(p-tolylthio)-[1,1 -
biphenyl]-2,6-dicarbonitrile (4f)
0
0
4
.3.2 | 3-amino-4 -chloro-5-(p-tolylthio)-[1,1 -
−
1
biphenyl]-2,6-dicarbonitrile (4b)
IR (KBr) (νmax/cm ): 3,413, 3,258, 3,023, 2,969, 2,245,
1
1
3
2
,639, 1,528, 1,468, 1,247, 985, and 729; H NMR (DMSO,
00 MHz) (δ, ppm): 2.79 (s, 3H, CH ), 7.33 (d, J = 7.3 Hz,
H, aromatic H), 7.47 (d, J = 7.3 Hz, 2H, aromatic H), 7.61
s, 1H, aromatic H), 7.66 (m, 1H, aromatic H), 7.68 (d,
J = 7.1 Hz, 1H, aromatic H), 7.69–7.78 (m, 2H, aromatic
H), and 8.13 (br., s, 2H, NH2); C NMR (DMSO, 75 MHz)
δ, ppm): 166.33, 159.52, 158.12, 141.23, 137.48, 136.20,
35.41, 133.77, 132.71, 131.01, 129.66, 128.21, 126.27,
−
1
IR (KBr) (νmax/cm ): 3,421, 3,374, 3,101, 2,965, 2,219,
,647, 1,585, 1,421, 1,225, and 852; H NMR (CDCl3,
00 MHz) (δ, ppm): 2.39 (s, 3H, CH ), 7.28 (d, J = 6.9 Hz,
H, aromatic H), 7.30–7.40(m, 2H, aromatic H), 7.43-7.60
m, 4H, aromatic H), and 7.79 (br., s, 2H, NH2); C NMR
CDCl , 75 MHz) (δ, ppm): 170.21, 160.23, 159.21, 142.32,
37.23, 136.54, 132.65, 130.30, 130.01,129.11, 122.99,
16.32, 115.54, 97.01, 87.63, and 23.29; GC/MS: 375 (M ).
1
3
1
3
2
(
(
3
(
1
3
13
3
(
1
1
1
1
+
+
16.89, 114.22, 95.21, 88.01, and 23.11; GC/MS: 386 (M ).
0
0
0
0
4
.3.3 | 3-amino-3 -chloro-5-(p-tolylthio)-[1,1 -
4.3.7 | 3-amino-4 -nitro-5-(p-tolylthio)-[1,1 -
biphenyl]-2,6-dicarbonitrile (4g)
biphenyl]-2,6-dicarbonitrile (4c)
−
1
−1
IR (KBr) (νmax/cm ): 3456, 3,372, 3,099, 2,903, 2,221,
IR (KBr) (νmax/cm ): 3,503, 3,458, 3,058, 2,968, 2,214,
1
1
1
3
2
7
,671, 1,559, 1,486, 1,001, and 803; H NMR (CDCl3,
00 MHz) (δ, ppm): 2.47 (s, 3H, CH ), 7.32 (t, J = 7.1 Hz,
H, aromatic H), 7.38 (d, J = 7.3 Hz, 2H, aromatic H),
.40–7.55 (m, 4H, aromatic H), 7.57 (s, 1H, aromatic H),
1,652, 1,565, 1,497, 1,341, 1,254, 1,037, and 789; H NMR
(DMSO,300 MHz) (δ, ppm): 2.26 (s, 3H, CH ), 7.36 (d,
J = 7.1 Hz, 2H, aromatic H), 7.39 (d, J = 7.1 Hz, 2H, aro-
matic H), 7.40–7.75 (m, 5H, aromatic H), and 8.31 (br, s,
3
3
1
3
13
and 7.80 (br., s, 2H, NH2); C NMR (CDCl , 75 MHz) (δ,
2H); C NMR (DMSO, 75 MHz) (δ, ppm):165.73, 160.71,
3
ppm): 169.89, 159.21, 157.92, 143.13, 142.03, 139.28,
158.21, 137.72, 136.01, 134.92, 132.21, 130.42,129.33,
1
1
36.67, 135.09, 132.54,130.98, 130.85, 128.62, 125.81,
16.52, 115.11, 96.11, 88.23, and 22.13; GC/MS: 375 (M ).
128.52, 126.21, 116.31, 114.71, 91.95, 88.27, and 24.10;
GC/MS: 386 (M ).
+
+
0
4
.3.8 | 3-amino-4 -methoxy-5-(p-tolylthio)-
0
0
4
.3.4 | 3-amino-4 -bromo-5-(p-tolylthio)-[1,1 -
0
[
1,1 -biphenyl]-2,6-dicarbonitrile (4h)
biphenyl]-2,6-dicarbonitrile (4d)
−
1
IR (KBr) (νmax/cm ): 3,468, 3,329, 3,029, 2,909, 2,215,
,667, 1,559, 1,545, 1,459, 1,371, 1,073, and 868; H NMR
CDCl , 300 MHz) (δ, ppm): 2.37 (s, 3H, CH ), 3.91 (s, 3H,
OCH ), 7.10–7.20 (m, 4H, aromatic H), 7.34 (d, J = 7.2 Hz,
H, aromatic H), 7.56 (s, 1H, aromatic H), 7.66 (d,
J = 7.2 Hz, 2H, aromatic H), and 7.72 (br., s, 2H, NH2);
NMR (CDCl3, 75 MHz) (δ, ppm): 167.51, 161.42,
59.72,142.21, 136.61, 133.20, 132.06, 131.13, 127.33,
−
1
IR (KBr) (νmax/cm ): 3,441, 3,336, 3,122, 3,962, 2,231,
,628, 1,571, 1,560, 1,006, and 811; H NMR (DMSO,
00 MHz) (δ, ppm): 2.35 (s, 3H, CH ), 7.30-7.70 (m, 6H,
aromatic H), 7.75 (s, 1H, aromatic H), 7.79 (d, J = 7.1 Hz,
H, aromatic H), and 7.83 (br., s, 2H, NH2); C NMR
DMSO, 75 MHz) (δ, ppm): 167.65, 161.58, 158.41,
41.52, 135.82, 134.14, 133.03, 132.69, 131.26,125.45,
24.65, 117.01, 115.21, 93.96, 88.11, and 22.07;
1
1
(
1
1
3
3
3
3
3
2
1
3
2
(
1
1
13
C
1
1
25.03, 122.62, 115.33, 113.42, 93.66, 88.63, and 22.33;
+
GC/MS: 420 (M ).
+
GC/MS: 371 (M ).

6
SHAMS-NAJAFI ET AL.
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[
The authors gratefully acknowledge the partial support of
this study by Ferdowsi University of Mashhad Research
Council (Grant Number 3/41305).
2
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3
ORCID
2
Sayyed Jalal Shams-Najafi https://orcid.org/0000-0001-
[
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6
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Mostafa Gholizadeh https://orcid.org/0000-0002-9947-
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