Polyaniline/SiO2 nanocomposite catalyzed efficient synthesis of quinoxaline derivatives at room temperature

Article abstract of DOI:10.1002/jccs.201100482

Polyaniline/SiO₂ nanocomposite material has been synthesized by using chemical oxidative method. Prepared catalytic material was characterized by means of transmission electron microscopy (TEM), thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT-IR). Solvent stability for the catalyst has been screened using UV-Visible spectroscopy. Polyaniline/SiO₂ catalyzed route has found to be an efficient and rapid protocol for the synthesis of quinoxaline derivatives by cyclocondensation of 1,2-diketones and o-phenylenediamines at room temperature. This protocol has several advantages such as high yield, good thermal stability, simple work up procedure, non-toxic, clean, and easy recovery and reusability of the catalytic system.

Full text of DOI:10.1002/jccs.201100482

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
Polyaniline/SiO2 Nanocomposite Catalyzed Efficient Synthesis of Quinoxaline
Derivatives at Room Temperature
Ajeet A. Yelwande, Madhukar E. Navgire, Balasaheb R. Arbad and Machhindra K. Lande*
Department of Chemistry, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad (M.S.), 431004, India
(Received: Aug. 5, 2011; Accepted: Jan. 3, 2012; Published Online: ??; DOI: 10.1002/jccs.201100482)
Polyaniline/SiO2 nanocomposite material has been synthesized by using chemical oxidative method. Pre-
pared catalytic material was characterized by means of transmission electron microscopy (TEM), thermal
analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive
spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT-IR). Solvent stability for the cata-
lyst has been screened using UV-Visible spectroscopy. Polyaniline/SiO2 catalyzed route has found to be
an efficient and rapid protocol for the synthesis of quinoxaline derivatives by cyclocondensation of
1,2-diketones and o-phenylenediamines at room temperature. This protocol has several advantages such
as high yield, good thermal stability, simple work up procedure, non-toxic, clean, and easy recovery and
reusability of the catalytic system.
Keywords: Nanocomposite; Nanofibers; Oxidative method; Polyaniline/SiO2; Quinoxalines.
INTRODUCTION
In recent years, an extensive studies has been carried
acid.20-22 Recently, several methods have been reported
comprising the use of Lewis acids and many other catalysts
including I2,23,24 sulfamic acid,25 montmorillonite K-10,26
polyaniline-sulfate salt,27 H6P2W18O62×24H2O,28 InCl3,29
CuSO4×5H2O,30 Zn(L)proline31 and ceric ammonium ni-
trate32 However, some of these methods are plagued by one
or many drawbacks such as long reaction time, use of vola-
tile solvents, low yields and harsh reaction conditions.
Therefore, it is necessary to develop an improved protocol
for the synthesis of quinoxalines under mild reaction con-
ditions.
out on the use of conducting polyaniline materials as cata-
lysts because of their wide range of electrical, electrochem-
ical, and optical properties as well as their good stability.1-4
It is generally synthesized by oxidizing aniline monomers
using electrochemical or chemical methods.5-7 Polyaniline
supported catalysts bears good environmental, thermal and
chemical stability, electrical and optical properties, facile
redox and pH-switching behavior.8 Polyaniline and poly-
aniline supported metal oxides have been extensively used
as solid acid or redox catalysts for various organic transfor-
mations such as oxidation, dehydrogenation, condensation,
Michael, Suzuki–Miyaura cross-coupling and esterifica-
tion reactions.9-15
In continuation of our interest towards the develop-
ment and characterization of new heterogeneous catalyst
for the synthesis of bioactive heterocycles,33,34 here we re-
port, the synthesis, characterization and catalytic applica-
tion of polyaniline/SiO2 solid heterogeneous catalyst for
the synthesis of quinoxaline derivatives using cyclocon-
densation of 1,2-diketones with o-phenylenediamines at
room temperature. The noticeable advantage of the present
strategy is to introduce simple and eco-friendly procedure
for the preparation of quinoxalines.
Quinoxaline constitutes a very important class of ni-
trogen-containing heterocycles. Owing to their prominent
biological/physiological activities such as anticancer, anti-
microbial, antibacterial and antitumor activities16-18 quin-
oxaline derivatives are gaining an enormous importance in
pharmacetical/medicinal chemistry. In addition quinoxa-
lines play a significant role as a basic skeleton for design-
ing number of antibiotics like echinomycin, actinomycin
and leromycin.19 Considering their significance numerous
synthetic strategies have been developed for the synthesis
of substituted quinoxalines. By far, the most common
method is the condensation of aryl-1,2-diamine with 1,2-
dicarbonyl compounds refluxing in ethanol or acetic
EXPERIMENTAL
All Chemicals were purchased either from Merck or
Fluka and used without further purification. Melting points
were taken in an open capillary and are uncorrected. The
morphology of catalyst was characterized with CM-200
PHILIPS transmission electron microscopy (TEM) oper-
* Corresponding author. Tel: +91 0240 2403311; Fax: +91 0240 2403335; E-mail: mkl_chem@yahoo.com
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Yelwande et al.
ated at 200 kV, resolution at 0.23 nm. TG-DTA was per-
formed using PYRIS 1 thermogravimetric analysis. IR
spectra were recorded on JASCO-FT-IR/4100, Japan, in
KBr disc. Thin layer chromatography was performed on
Merck pre-coated silica gel 60-F254 plates. 1H NMR spec-
tra were recorded on an 300 MHz FT-NMR spectrometer in
CDCl3 as a solvent and chemical shifts values d (ppm) are
recorded relative to tetramethylsilane (Me4Si) as an inter-
nal standard. The X-ray diffraction (XRD) patterns were
recorded on Bruker 8D advance X-ray diffractometer using
monochromator Cu-Ka radiation of wavelength = 1.5405
Å. Scanning electron microscopy (SEM) images and en-
ergy dispersive spectroscopy (EDS) were obtained on
JEOL; JSM-6330 LA operated at 20.0 kV and 1.0000 nA.
Preparation of pure silica
specified time mentioned in Table 4. The progress of the re-
action was monitored by TLC (petroleum ether: ethyl ace-
tate = 7:3 as eluent). After completion of the reaction, reac-
tion mixture was heated to solubilise the product. The cata-
lyst is insoluble in ethanol; thus separation of catalyst was
easier by simple filtration. The filtrate was concentrated
under reduced pressure, and the crude product obtained
was recrystallized from ethanol to afford pure product
(3a-h).
Spectral data of representative compound
2,3-diphenylquinoxaline 3a
IR (KBr ) nmax: 3057, 1602, 1442, 1346, 1246, 852,
1
767, 698 cm-1. H NMR (300 MHz, CDCl3): d 8.18 (dd,
2H), 7.78 (dd, 2H), 7.52 (m, 4H), 7.34 (m, 6H). ES-MS:
m/z 283.50 (M+).
Silica samples were synthesized by using sol-gel pro-
cess. A quantity of 16 mL tetraethyl ortho-silicate (TEOS)
was mixed with 60 mL of aqueous ammonia. The resulting
reaction mixture was stirred continuously for 1 h at room
temperature to obtain uniform sized silica particles. The re-
sulting silica material was further retrieved by centrifuga-
tion and washed with distilled water and dried at 110 °C for
overnight. Finally, the dried material was calcined at 500
°C for 5 h under air atmosphere to produce solid porous
silica material.
TEM Analysis
Fig. 1(a,b) shows that the morphology of synthesized
catalytic materials. Fig. 1(a) polyaniline shows uniform
nanofiber morphology with a diameters 21-23 nm. The
length of fibers ranges from 100-500 nm.35 The TEM im-
ages shown in Fig. 1(b) indicate the obtained nanocompos-
ite material has particle size in the range 40-51 nm. It was
observed that nanofibered polyaniline clearly deposited on
spherical shaped SiO2.
TG-DTA analysis
Preparation of polyaniline/SiO2 catalyst
Fig. 2 illustrates the thermal analysis of polyaniline
and polyaniline/SiO2 nanocomposite. The initial weight
loss occurs at low temperature (140 ºC) due to the removal
of water molecules from polymer material. Second weight
loss was observed at (200 °C) which corresponds to the
degradation and decomposition of the polymer back bone.
However, complete decomposition occurs at (350 °C) for
polyaniline chain shown in Fig. 2(a). Fig. 2(b) shows the
thermal decomposition of polyaniline supported on SiO2.
From this, it can be seen that, the thermal stability of poly-
aniline/SiO2 material was noticeably improved, which may
be due to the strong interaction between polyaniline and
SiO2.
Series of polyaniline/SiO2 catalytic materials with
varying percentage of aniline (10, 20, 30 wt %) and SiO2
were prepared by chemical oxidative method. In a typical
procedure, 10 wt % polyaniline/SiO2 catalysts was synthe-
sized by slowly mixing a solution of aniline (0.3 mL) in dis-
tilled water (30.8 mL) with concentrated sulphuric acid
(0.61 mL) at 5-10 °C. The resultant mixture was succes-
sively treated with aqueous potassium persulphate (0.74 g
in 16 mL distilled water) (used as an oxidant) and solid po-
rous silica (2.68 g) was added to the reaction mixture. The
mixture was then kept at 5 °C and with continuous strring
for 5-6 h. The resultant product was isolated by filteration
and washed with distilled water and acetone. The product,
polyaniline/SiO2 salt, was then dried in an oven at 70 °C for
3 h. Similarly, 20 and 30 wt% polyaniline/SiO2 catalysts
were prepared.
General procedure for the synthesis of quinoxalines
(3a-h)
A mixture of 1,2-diketones (1 mmol), o-phenylene-
diamines (1 mmol) and catalytic amount of 10 wt % poly-
aniline/SiO2 (0.1 g) in ethanol (15 mL) was stirred for the
Fig. 1. TEM image of (a) Polyaniline (b) 10 wt % poly-
aniline/SiO2.
2
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Polyaniline/SiO2 Catalyzed Quinoxalines Reaction
XRD analysis
helps to generate the porous materials and the increased po-
rosity is responsible for the increase in catalytic activity of
the material.
Fig. 3(a-c) shows the XRD pattern of synthesized ma-
terials. Fig. 3(a) shows the broad peak at 2q (21.98°) corre-
sponding to the amorphous nature of silica.36 Fig. 3(b)
shows the broad peak at 2q (25.13°) which is a characteris-
tic of the polyaniline.37 Fig. 3(c) gives broad peak at 2q
(22.18°) for 10 wt % polyaniline/SiO2 which has just
slightly shifted due to the addition of polyaniline in porous
SiO2.
Elemental composition of 10 wt % polyaniline/SiO2
nanocomposite catalysts is represented in Fig. 5. The pres-
ence of constituent elements such as C, O, Si and S with its
SEM-EDS analysis
Fig. 4(a-c) shows the surface morphology of synthe-
sized materials. Fig. 4(a) shows good agglomeration of
particles of mesoporous silica with spherical in shape,
while a fibrous or globular morphology was observed in
Fig. 4(b) which is a characteristic of polyaniline.38 Fig. 4(c)
shows some porosity, it may be due to the insertion of 10 wt
% polyaniline on the surface of SiO2. Finally, from the
SEM micrograph, it can be concluded that, the polyaniline
addition clearly shows alteration in morphology, which
Fig. 3. XRD pattern of (a) SiO2 (b) polyaniline (c) 10
wt % polyaniline/SiO2.
Fig. 4. SEM image of (a) SiO2 (b) polyaniline (c) 10 wt
% polyaniline/SiO2.
Fig. 2. (a) TG-DTA patterns of Polyaniline. (b) TG-
DTA patterns of 10 wt % Polyaniline/SiO2.
Fig. 5. EDS image of 10 wt % polyaniline/SiO2.
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Article
Yelwande et al.
Table 1. Stability of catalyst in various solvent
atomic weight %, 47.35, 39.41, 12.51 and 0.74, respec-
tively.
Entry
Solvent
Optical density (O.D)
FT-IR analysis
1
2
3
4
Methanol
Acetone
0.309
0.264
0.231
0.179
Fig. 6(a-c) shows the FT-IR spectra of the synthe-
sized materials. Fig. 6a shows absorption band at 3477 cm-1
which is due to the Si-OH stretching vibration, 1627 cm-1
for the Si-OH bending mode, 1080 cm-1 for Si-O stretch-
ing vibration and 815 cm-1 due to the Si-O-Si bending vi-
brational mode. Fig. 6(b-c) shows the FT-IR spectra of the
pure polyaniline and 10 wt % polyaniline/SiO2 nanocom-
posite respectively. The characteristic bands of polyaniline
at 3389 and 3371 cm-1 is attributed to N-H stretching, 1572
and 1509 cm-1 is due to C=C stretching mode of the quinoid
ring, 1489 and 1454 cm-1 is due to C=C stretching vibration
of benzenoid ring, 1323 and 1309 cm-1 for C-N stretching
vibration, 1138 cm-1 is for N=Q=N, where Q represents the
quinoid ring, bands at 825 and 808 cm-1 are due to aromatic
C-H bending mode of 1,4-disubstituted benzene ring, Fig.
6(c) shows absorption band at 1084 cm-1 which is due to the
presence of silica.
Acetonitrile
Ethanol
ethanol with the lowest absorbance after 15 days. Hence, a
model study was conducted with benzil and o-phenylene-
diamine using ethanol as a solvent at room temperature to
examine catalytic efficiency for 10 wt % polyaniline/SiO2.
After optimization of solvent effect, we have also
studied the effect of amount of catalyst on the rate of reac-
tion. Initially, pure SiO2 was used for the model reaction
and the results so obtained were not satisfactory. When the
pure polyaniline was used for the same reaction, the results
with respect to yields are encouraging however the time re-
quired for completing the reaction has increased. When the
same reaction was carried out by using 10 wt % polyani-
line/SiO2 catalyst, the time required for the completion of
the reaction reduced dramatically with enhancement in the
yield of the product. Further increase in the amount of cata-
lyst did not show any significant change in time required
for the completion of reaction and yield of the product.
Hence 10 wt % polyaniline/SiO2 catalyst was considered as
optimum amount of catalyst for the running such trasfor-
mations Table 3. However, in the absence of this catalyst,
RESULTS AND DISCUSSION
In the present work, solvent effect on the catalytic ac-
tivity of catalyst have been screened by keeping 10 wt %
Polyaniline/SiO2 catalyst in appropriate volume of solvent
such as methanol, acetone, acetonitrile and ethanol for over
period of 15 days. The solvent effect on catalyst was moni-
trerd by measuring change in absorbance using UV-visible
spectrophotometer. The results are summarized in Table 1,
which indicates that the catalyst showed good stability in
Table 2. Effect of various amount of polyanilinea
Entry
Catalyst
Time (min) Yield (%)b
1a
1b
1c
1d
1e
SiO2
20
12
9
75
94
96
95
94
Polyaniline
10 wt % polyaniline/SiO2
15 wt % polyaniline/SiO2
20 wt % polyaniline/SiO2
10
12
a Reaction conditions: benzil (1 mmol), o-phenylenediamine
(1 mmol) catalyst (0.1 gm) and ethanol 15 ml; b Isolated yields.
Table 3. Effect of catalyst amount for the reaction of benzil and
o-phenylenediamine
Entry
Catalyst amount (g)
Time (min)
Yield (%)a
2a
2b
2c
2d
0
40
10
9
-
0.05
0.1
0.2
94
96
96
9
Fig. 6. FT-IR spectra of (a) SiO2 (b) polyaniline (c) 10
wt % polyaniline/SiO2.
a Isolated yields.
4
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Polyaniline/SiO2 Catalyzed Quinoxalines Reaction
formation of the desired product was not observed (Table 3,
entry 2a). As we increased the amount of catalyst the reac-
tion proceeds further by giving higher yields within shorter
times. From the results, 0.1 gm of catalyst was found to be
sufficient to complete the reaction efficiently.
diamines at room temperature. This method offers remark-
able advantages such as non-toxic, non-corrosive and an
inexpensive reaction conditions. Simple recovery and reus-
ability of the catalyst makes the reaction successful under
environmental benign conditions.
To explore the scope and applications of the present
method, variety of substituted O-phenylenediamines and
1,2-dicarbonyls compounds possessing electron rich and
electron deficient groups were tested and they all gave
good to excellent yields (90-97%) and reactions were com-
pleted within 9-27 min in ethanol at room temperature (Ta-
ble 4) (Scheme I).
ACKNOWLEDGEMENTS
Authors are thankful to the Head, Department of
Chemistry, Dr. Babasaheb Ambedkar Marathwada Univer-
sity, India, for providing the laboratory facilities.
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