Star-shaped Keggin-type heteropolytungstate nanostructure as a new catalyst for the preparation of quinoxaline derivatives

Article abstract of DOI:10.1016/j.crci.2014.01.021

In this work, we report the novel successful preparation of the Keggin-type Cs(CTA)₂PW₁₂O₄₀ (CTA = cetyltrimethylammonium cation) nanostructure by a microemulsion method. The microemulsion system included the cationic surfactant CTAB, 1-butanol as co-surfactant, isooctane as oil phase, and an aqueous solution containing CsNO₃. The Cs(CTA)₂PW₁₂O₄₀ nanostructure was formed by the addition of an aqueous solution of phosphotungstic acid to the microemulsion solution. Characterization of the resultant nanostructure was done using FT-IR spectroscopy, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, and CHN elemental analysis. The product was found to be a star-shaped nanostructure composed of some nanorods whose diameter and length are about 100 nm and 500 nm, respectively. The prepared nanostructure was used as a recoverable catalyst for the synthesis of quinoxaline derivatives by the condensation of 1,2-diamines with 1,2-dicarbonyl compounds, which afforded the products in good to high yields in short reaction times.

Full text of DOI:10.1016/j.crci.2014.01.021

C. R. Chimie 17 (2014) 1136–1143
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´
Full paper/Memoire
Star-shaped Keggin-type heteropolytungstate nanostructure
as a new catalyst for the preparation of quinoxaline
derivatives
a
b
b
Majid Masteri-Farahani a, , Melika Ghorbani , Ali Ezabadi , Niki Farrokhinia ,
*
Atekeh-Sadat Ghaemmaghami b
a Faculty of Chemistry, Kharazmi University, Tehran, Iran
b Department of Chemistry, Central Tehran Branch, Islamic Azad University, Tehran, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
In this work, we report the novel successful preparation of the Keggin-type
Cs(CTA)2PW12O40 (CTA = cetyltrimethylammonium cation) nanostructure by a micro-
emulsion method. The microemulsion system included the cationic surfactant CTAB,
1-butanol as co-surfactant, isooctane as oil phase, and an aqueous solution containing
CsNO3. The Cs(CTA)2PW12O40 nanostructure was formed by the addition of an aqueous
solution of phosphotungstic acid to the microemulsion solution. Characterization of the
resultant nanostructure was done using FT–IR spectroscopy, X-ray diffraction, scanning
electron microscopy, energy-dispersive X-ray analysis, and CHN elemental analysis. The
product was found to be a star-shaped nanostructure composed of some nanorods whose
diameter and length are about 100 nm and 500 nm, respectively. The prepared
nanostructure was used as a recoverable catalyst for the synthesis of quinoxaline
derivatives by the condensation of 1,2-diamines with 1,2-dicarbonyl compounds, which
afforded the products in good to high yields in short reaction times.
Received 18 October 2013
Accepted after revision 28 January 2014
Available online 16 September 2014
Keywords:
Heteropolytungstate
Keggin
Nanostructure
Microemulsion
Quinoxaline
Catalyst
´
ß 2014 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
1. Introduction
acids, such as montmorillonite K-10 [10], mesoporous
silica SBA-15 covalently anchored with copper (II) Schiff
The synthesis of quinoxaline and of its derivatives
played an important role in organic synthesis because of
their wide range of biological activities, such as anti-
bacterial [1], antidepressant [2], anti-inflammatory [3],
and antitumor [4] ones. Due to their great importance,
many synthetic strategies have been developed for the
synthesis of quinoxalines [5–9]. However, most of these
methodologies involve pollution, long reaction time and
difficult work-up and recovery of the catalysts, leaving
considerable scope for the development of further clean,
facile and efficient catalytic processes for these important
molecules. Condensation of a 1,2-diamine with a 1,2-
dicarbonyl compound in the presence of Brønsted or Lewis
base complex [11], alumina [12], and silica-supported
perchloric acid [13], Wells–Dawson heteropoly acid
(H6P2W18O62Á24H2O) [14], iron exchanged molybdopho-
sphoric acid [15], and Keggin-type H4SiW12O40 heteropoly
acid [16], is one of the important methods for the
preparation of quinoxalines. However, to the best of our
knowledge, there is no any example of the use of
nanostructured Keggin-type heteropolyanions as catalysts
for the synthesis of quinoxaline derivatives.
Heteropoly acids are discrete metal–oxygen clusters
built from the connection of MOx polyhedra in which M is a
d-block element in a high oxidation state [17–20]. They
possess both acidic and redox properties and thus are of
great importance for practical applications, especially in
catalysis [21–28]. Pure heteropoly acids have high
solubility in polar reaction systems, which hinders their
applications as heterogeneous catalysts and so results in
*
Corresponding author.
E-mail address: mfarahany@yahoo.com (M. Masteri-Farahani).
1631-0748/$ – see front matter ß 2014 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.crci.2014.01.021

M. Masteri-Farahani et al. / C. R. Chimie 17 (2014) 1136–1143
1137
separation problems during the isolation of the product
after completion of the reaction. It has been found that
water-insoluble salts of heteropoly acids with large
cations, such as Cs+, K+, NH4+, and organic cations can be
used as efficient heterogeneous catalysts [28–30]. These
compounds are prepared by partial or complete cation
exchange with protons in heteropoly acids. For example, a
caesium salt of H3PW12O40, Cs2.5H0.5PW12O40 has lately
gained attention because of strong acidity and insolubility
in water and organic solvents, and so can be considered as
a solid acid catalyst. This salt was reported to exhibit
significantly higher activity than the parent acid in gas-
phase acid-catalyzed reactions [28–31].
DR UV–Vis spectra were collected using a PG Instrument
Ltd T90+ UV–Vis Spectrometer with BaSO4 as a standard.
Elemental analyses were performed using a scanning
electron microscope equipped with EDX detector INCA
Penta FETx3. 1. The carbon and nitrogen contents of the
samples were analyzed using a Thermo Finnigan (Flash
1112 Series EA) CHN Analyzer. 1H NMR spectra were
recorded on a Bruker AQS AVANCE-300 MHz spectrometer
using TMS as an internal standard. All products were well
characterized by comparison with authentic samples by
TLC, spectral and physical data recording.
2.2. Preparation of the Cs(CTA)2PW12O40 nanostructure
Polyoxometalate nanostructures have attracted con-
siderable interest owing to their interesting properties
and wide range of applications [32–36]. Some methods
have been developed for the preparation of polyoxome-
talate nanostructures, such as homogeneous precipita-
tion using decomposition of urea [35], solid-state
chemical reaction [36], and microemulsion methods
[37,38].
Recently, we have reported the first successful one-pot
preparation and characterization of heteropolymolybdate
nanoparticles with a microemulsion method [38]. Micro-
emulsions are systems composed of a mixture of an
aqueous phase, an oil phase, a surfactant, and a co-
surfactant [39–41]. They are transparent solutions that are
thermodynamically stable and optically isotropic. The
nanosized water droplets in microemulsions act as
nanoreactors for producing the desired nanostructures.
The advantage of this method is the good control on the
size and morphology of the prepared nanostructure.
Here, we further explore the potential of microemulsion
method for the preparation of a novel Cs(CTA)2PW12O40
The quaternary microemulsion system consisted of
H2O/CTAB/isooctane/n-butanol and had been prepared as
follows: CTAB (2 g) in water (2 mL) was added to a stirred
solution of n-butanol (2 g) and isooctane (4 g). Then, 1 mL
CsNO3 (0.5 M) in water was added to the above mixture
and stirred for 10 min to give a transparent solution.
Under stirring, 1 mL of H3PW12O40 (0.5 M) was added and
the reaction continued for another 2 h. The resultant
white product was collected by centrifugation and
washed several times with water and ethanol to remove
the remaining organic residue and dried at 110 8C for
12 h.
2.3. General method for the preparation of quinoxaline
derivatives
A mixture of 1,2-dicarbonyl (1 mmol) and 1,2-diamine
(1 mmol) derivatives in the presence of an appropriate
amount of the Cs(CTA)2PW12O40 catalyst was stirred at a
given temperature. The progress of the reaction was
monitored by thin layer chromatography (TLC). After
completion of the reaction, 5 mL of hot ethanol was added
to the reaction mixture and the solid catalyst was filtered.
The pure products were obtained after crystallization
and analyzed without any further purification. All of
the obtained quinoxalines are known compounds and
identified by 1H NMR and melting points compared with
the literature values. The melting points, spectral (1H NMR)
and elemental analysis data for the products are given
below.
nanostructure. The prepared nanostructure acts as
a
recoverable heterogeneous catalyst for green and efficient
synthesis of quinoxaline derivatives in high yields and
short reaction times. In comparison with previous
catalytic systems for the synthesis of quinoxaline deriva-
tives [10–16], it has the following advantages: easy
recoverability, comparable yields with short reaction times,
and especially solvent-free conditions that make it an
environmentally friendly and cost-effective process.
2. Experimental
2.4. 2,3-Diphenyl-quinoxaline
2.1. Materials and instrumentations
Mp. 120–122 8C; 1H NMR (500 MHz, CDCl3):
d (ppm):
All chemicals were purchased from Merck Chemicals
and used without further purification. Phosphotungstic
acid was prepared by a method taken from the literature
[28].
8.20 (d.d, 3.35, 3.35 Hz, 2H), 7.79 (dd, 3.3, 3.35 Hz, 2H), 7.54
(d, J = 6.65 Hz, 4H), 7.38 (m, 6H); FT–IR (KBr): 3059, 1436,
1395, 1341, 707, 695 cmÀ1. Anal. calcd. for C20H14N2: C,
85.08; H, 5.00; N, 9.92. Found: C, 85.25; H, 5.12; N, 9.98.
FT–IR spectra were recorded with
a PerkinElmer
Spectrum RXI FT–IR spectrometer using pellets of the
materials diluted with KBr. X-ray powder diffraction
measurements (XRD) were performed on a SIEFERT XRD
2.5. 2,3-Bis (4-methoxyphenyl) quinoxaline
Mp. 140–141 8C; 1H NMR (500 MHz, CDCl3):
d (ppm):
3003 PTS diffractometer using Cu K
a
radiation (wave-
8.14 (m, 2H), 7.73 (m, 2H), 7.51 (d, J = 8.25 Hz, 4H), 6.89 (d,
J = 8.25 Hz, 4H), 3.85 (s, 6H); FT–IR (KBr): 2936, 2836, 1603,
length = 0.154 nm). The patterns were recorded from 58
l
to 808 with steps of 0.028 every second. Scanning electron
microscopy images were taken with a ZEISS-DSM 960A
microscope with an attached camera operating at 30 kV.
1509, 1340, 1293, 1245, 832 cmÀ1
.
Anal. calcd. for
22H18N2O2: C, 77.17; H, 5.30; N, 8.18. Found: C, 76.97;
H, 5.21; N, 8.01.
C

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M. Masteri-Farahani et al. / C. R. Chimie 17 (2014) 1136–1143
2.6. 2,3-Di-p-tolyl quinoxaline
2.13. 5,6-Diphenyl-2,3-dihydro pyrazine
Mp. 160–161 8C; 1H NMR (500 MHz, CDCl3):
d (ppm):
Mp. 147–148 8C; 1H NMR (500 MHz, CDCl3):
d
(ppm):
8.17 (m, 2H), 7.75 (m, 2H), 7.44 (d, J = 7.75 Hz, 4H), 7.16
(d, J = 7.65 Hz, 4H), 2.38 (s, 6H); FT–IR (KBr): 2911, 1610,
7.41 (d, J = 7.4 Hz, 6H), 7.33 (d, J = 6.6 Hz, 4H), 3.73 (s, 4H);
FT–IR (KBr): 3040, 2946, 1549, 1437, 984, 694 cmÀ1. Anal.
calcd. for C16H14N2: C, 82.02; H, 6.02; N, 11.96. Found: C,
82.12; H, 6.10; N, 12.01.
1462, 1396, 1337, 1210,758 cmÀ1
.
Anal. calcd. for
C
22H18N2: C, 85.13; H, 5.84; N, 9.03. Found: C, 84.91;
H, 5.71; N, 8.89.
2.14. 5,6-Di-p-tolyl-2,3-dihydro pyrazine
2.7. 2,3-Di (furan-2-yl) quinoxaline
Mp. 164–166 8C; 1H NMR (500 MHz, CDCl3):
d (ppm):
Mp. 128–130 8C; 1H NMR (500 MHz, CDCl3):
d
(ppm):
7.31 (d, J = 8.15 Hz, 4H), 7.06 (d, J = 7.85, 4H), 3.67 (s, 4H),
2.32 (s, 6H); FT–IR (KBr): 3029, 2959, 1611, 1552, 982,
822 cmÀ1. Anal. calcd. for C18H18N2: C, 82.41; H, 6.92; N,
10.68. Found: C, 82.49; H, 7.02; N, 10.77.
8.18 (dd, J = 3.4 Hz, 2H), 7.78 (dd, J = 3.25 Hz, 2H), 7.65
(s, 2H), 6.71 (s, 2H), 6.59 (s, 2H); FT–IR (KBr): 3107, 1566,
1485, 1397, 1328, 755 cmÀ1. Anal. calcd. for C16H10N2O2:
C, 73.27; H, 3.84; N, 10.68. Found: C, 73.48; H, 3.96; N,
10.77.
3. Results and discussion
2.8. 6-Methyl-2,3-diphenyl quinoxaline
3.1. Preparation of Cs(CTA)2PW12O40 nanostructure
Mp. 109–110 8C; 1H NMR (500 MHz, CDCl3):
d (ppm):
The Cs(CTA)2PW12O40 nanostructure was prepared by
partial exchange of the protons of phosphotungstic acid by
caesium ions in the nanoreactors of the water droplets in
the microemulsion system. The sequence of events was
shown in Fig. 1. Stoichiometric addition of phosphotungs-
tic acid solution to the caesium-containing microemulsion
system results in the formation of a Cs(CTA)2PW12O40
nanostructure, which is insoluble in water and organic
solvents and precipitates immediately. On the other hand,
the CTAB species act as protecting groups against the
assembly and growth of the as-prepared nanostructure.
8.08 (d, J = 8.45 Hz, 1H), 7.97 (s, 1H), 7.63 (d, J = 8.3 Hz, 1H),
7.52 (d, J = 6.3 Hz, 4H), 7.35 (d, J = 6.9 Hz, 6H), 2.62 (s, 3H);
FT–IR (KBr): 3050, 1615, 1482, 1441, 1340, 697 cmÀ1. Anal.
calcd. for C21H16N2: C, 85.11; H, 5.44; N, 9.45. Found: C,
85.24; H, 5.56; N, 9.52.
2.9. 2,3-Bis (4-methoxyphenyl)-6-methylquinoxaline
Mp. 120–121 8c, 1H NMR (500 mhz, cdcl3):
d (ppm):
8.03 (d, J = 8.45 Hz, 1H), 7.92 (s, 1H), 7.57 (d, J = 8.25 Hz,
1H), 7.49 (d, J = 6.5 Hz, 4H), 6.88 (d, J = 8.25 Hz, 4H), 3.84 (s,
6H), 2.61 (s, 3H); FT–IR (KBr): 2925, 1599, 1259,
833 cmÀ1. Anal. calcd. for C23H20N2O2: C, 77.51; H, 5.66;
N, 7.86. Found: C, 77.63; H, 5.75; N, 7.96.
3.2. Spectroscopic characterization of the Cs(CTA)2PW12O40
nanostructure
FT–IR spectroscopy was used to check whether the
Keggin structure is preserved in the prepared nanostruc-
ture. In the FT–IR spectrum of the Cs(CTA)2PW12O40
nanostructure (Fig. 2), the four main features of the
2.10. 6-Methyl-2,3-di-p-tolyl quinoxaline
Mp. 135–136 8C; 1H NMR (500 MHz, CDCl3):
d (ppm):
8.05 (d, J = 8.4 Hz, 1H), 7.94 (s, 1H), 7.59 (d, J = 8.2 Hz, 1H),
7.43 (d, J = 6.8 Hz, 4H), 7.15 (d, J = 7.4 Hz, 4H), 2.61 (s, 3H),
2.38 (s, 6H); FT–IR (KBr): 3036, 2917, 1613, 1445, 1340,
824 cmÀ1. Anal. calcd. for C23H20N2: C, 85.15; H, 6.21; N,
8.63. Found: C, 85.05; H, 6.12; N, 8.51.
2.11. 2,3-Di (furan-2-yl)-6-methyl quinoxaline
Mp. 113–114 8C; 1H NMR (500 MHz, CDCl3):
d (ppm):
8.13 (d, J = 8.3 Hz, 1H), 8.057 (s, 1H), 7.64 (m, 3H), 6.77 (d,
J = 18.75 Hz, 2H), 6.60 (s, 2H), 2.62 (s, 3H); FT–IR (KBr):
3110, 2917, 1615, 1563, 1491, 1329, 752 cmÀ1. Anal. calcd.
for C17H12N2O2: C, 73.90; H, 4.38; N, 10.14. Found: C,
74.01; H, 4.45; N, 10.21.
2.12. 2,3-Dimethyl quinoxaline
Mp. 104–106 8C; 1H NMR (500 MHz, CDCl3):
7.97 (m, 2H), 7.65 (m, 2H), 2.72 (s, 6H) ppm; FT–IR (KBr):
3020, 2930, 1648, 1485, 760 cmÀ1
Anal. calcd. for
10H10N2: C, 75.92; H, 6.37; N, 17.71. Found: C, 75.85;
H, 6.26; N, 17.62.
d (ppm):
.
C
Fig. 1. Schematic illustration for the preparation of the Cs(CTA)2PW12O40
nanostructure.

M. Masteri-Farahani et al. / C. R. Chimie 17 (2014) 1136–1143
1139
Fig. 2. FT–IR spectra of (a) H3 PW12O40, and (b) Cs(CTA)2PW12O40 nanostructures.
Keggin-type phosphotungstate anions [42] for the pre-
the represented spectrum, the strong peak at 265 nm is
assigned to an oxygen-to-tungsten charge transfer in edge-
shared WO6 octahedra and the shoulder at 330 nm is
attributed to an oxygen-to-tungsten charge transfer in
corner-shared WO6 octahedra, which further confirms the
presence of a Keggin-type Cs(CTA)2PW12O40 nanostructure.
pared nanostructure are observed at 1078 cmÀ1
(
nas
,
P–O),
977 cmÀ1
808 cmÀ1
(
nas
,
WO), 895 (
n
,
W–O–W) and
W–O–W). Compared with bulk
as,corner sharing
(n
as,edge sharing
H3PW12O40, the observed blue shift of nas,corner sharing W–O–
and nas,edge peaks in Cs(CTA)2PW12O40
W
sharing W–O–W
nanostructures results from the substitution of the H+ by
Cs+ and CTA+ cations with stronger interactions, since it has
been shown that the protons in the heteropoly acids are
linked to the bridging oxygens rather than to terminal
oxygens. On the other hand, the bands at 2851 and
2924 cmÀ1 are attributed to the symmetric and asym-
metric C–H stretching vibrations of the CH2 groups of CTAB
species associated with the Cs(CTA)2PW12O40 nanostruc-
ture. Also, the bands at 1400–1500 cmÀ1 were assigned to
the symmetric and asymmetric C–H deformations. A
noteworthy feature in this spectrum is the significant
absence of O–H stretching vibrations near 3400–
3700 cmÀ1, which indicates the hydrophobic and water
tolerant nature of the prepared nanostructure. Thus, the
FT–IR spectrum of the product showed the existence of the
Keggin-type nanostructure associated with CTAB species.
The UV–Vis spectrum of the Cs(CTA)2PW12O40 nanos-
tructure is presented in Fig. 3. In the UV–Vis spectra of
Keggin heteropolyanions, there are two main absorptions
corresponding to the ligand-to-metal charge transfer (from
mainlyoxygen2porbitalstomainlymetaldorbitals)[43]. In
3.3. X-ray analyses of the Cs(CTA)2PW12O40 nanostructure
The X-ray diffraction pattern of Cs(CTA)2PW12O40
nanostructure is shown in Fig. 4a. As can be seen in the
Fig. 3. (Color online.) UV–Vis spectrum of the Cs(CTA)2PW12O40
nanostructure.

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M. Masteri-Farahani et al. / C. R. Chimie 17 (2014) 1136–1143
Fig. 4. (a) X-ray diffraction pattern and (b) energy-dispersive X-ray analysis of the Cs(CTA)2PW12O40 nanostructure.
XRD pattern of the Cs(CTA)PW12O40 nanostructure, only
one intense peak at about 2 = 88 is observable, which is a
scanning electron microscopy. A typical SEM image of the
obtained nanoparticles after 5 min is shown in Fig. 5a. As
can be seen in this figure, the product is composed of
nearly spherical particles. With stoichiometric addition of
phosphotungstic acid solution to the caesium-containing
microemulsion system, the nucleation of the nanostruc-
ture occurs immediately in the nanoreactors of the water
droplets, and nanoparticles with surfactant coatings are
formed in a very short time. But with collision of the
reverse micelles, the coalescence of the nearly spherical
nanoparticles shows the morphological evolution of a new
nanostructure as a function of the processing time. When
processed for 2 h, the aggregation between the spherical
nanoparticles was induced by the coalescence process,
resulting in the agglomeration and growth of star-shaped
nanostructures. Fig. 5b shows that each nanostructure is
composed of some nanorods whose diameter and length
are about 100 nm and 500 nm, respectively, and extending
radially from the centre.
u
typical feature of the Keggin structure [28]; the other peaks
are very weak and broad. These observations indicate that,
unlike the parent phosphotungstic acid, the prepared
nanostructure has no good crystalline nature and is mainly
amorphous. The long-chain hexadecyl groups in the
prepared nanostructure inhibit the good ordering of the
individual Keggin units to form any crystalline phase.
Moreover, this can be also a result of the small size of the
prepared nanostructure and of the absence of any crystal
plane.
Stoichiometry and chemical composition of the pre-
pared nanomaterial was examined by energy-dispersive
X-ray analysis (EDX) and CHN analysis. EDX analysis of
the nanocrystals in Fig. 4b showed the molar ratio Cs:P:W
of 1.1:1:11.7. On the other hand, CHN analysis showed
12.89% of carbon and 0.82% of nitrogen, which showed the
presence of 2 equiv of CTA+ cations in the product. These
values are close to the stoichiometric composition and
further confirm the formation of the Cs(CTA)2PW12O40
nanostructure.
3.5. Investigation of the catalytic activity of the
Cs(CTA)2PW12O40 nanostructure in the preparation of
quinoxaline derivatives
3.4. Scanning electron microscopy analysis and formation
mechanism of the prepared nanostructure
The catalytic properties of the Cs(CTA)2PW12O40
nanostructure were examined in the preparation of
quinoxaline derivatives. The prepared nanostructure can
activate the carbonyl compounds and facilitate the attack
The morphology and microstructure of the
Cs(CTA)2PW12O40 nanostructure were investigated with

M. Masteri-Farahani et al. / C. R. Chimie 17 (2014) 1136–1143
1141
Table 1
Effect of various solvents on the synthesis of quinoxaline.
Entry
Solvent
Time (h)
Yield (%)
1
3
4
5
6
Ethanol
4:00
77
40
90
91
72
Water
6:00
Dichloromethane
Acetonitrile
Ethyl acetate
11:00
15:00
13:00
Reaction conditions: benzil (1.0 mmol), o-phenylenediamine (1.0 mmol),
catalyst (25 mg), solvent (5 mL), reflux conditions.
temperature on the reaction times and yields have been
shown in Table 2. It can be seen that the increase of
reaction temperature led to the enhancement of the yield
of quinoxaline. On the other hand, in the absence of the
catalyst the reaction did not complete even after 24 h.
Since the recyclability of the catalyst is crucial to its
application, we conducted an experiment to evaluate the
recyclability of the Cs(CTA)2PW12O40 nanostructure in the
catalytic preparation of quinoxaline derivatives. After
filtration, the catalyst was washed several times with
ethanol and dried in a vacuum oven. Then, it was used in
the reaction with a fresh reaction mixture and the result is
given in Table 2. As can be seen, the product yield showed
no significant decrease, implying that the nanostructure
was stable and retained its activity during the catalytic
cycle. On the other hand, the FT–IR spectrum of the
recycled catalyst (not shown here) showed the character-
istic bands of the original catalyst, indicating the stability
of the catalyst during the course of the catalytic reaction.
In order to show the generality of this method, we used
some substituted 1,2-phenylenediamines and diketones
under optimized conditions in solvent-free conditions, and
the results are summarized in Table 3. All the reactions
proceeded very cleanly and no side product was observed.
The results show the excellent catalytic activity of the
Cs(CTA)2PW12O40 nanostructure in the preparation of
quinoxaline derivatives. The prepared catalyst has the
advantages of easy recoverability in comparison with
Wells–Dawson heteropoly acid (H6P2W18O62Á24H2O) [14]
and Keggin-type H4SiW12O40 heteropoly acid [16] catalytic
systems and shorter reaction times in comparison with
iron exchanged molybdophosphoric acid [15]. On the other
hand, solvent-free conditions make it an environmentally
friendly and cost-effective process for the preparation of
quinoxaline derivatives.
Fig. 5. Scanning electron microscopy images of (a) the obtained
nanoparticles after 5-min stirring of the reaction mixture, and (b) the
final Cs(CTA)2PW12O40 nanostructure.
Table 2
Effect of temperature on the reaction times and yields in solvent-free
conditions.
of the amino groups to carbonyl compounds. The reaction
Entry
Temperature
Time (h:min)
Yield (%)
proceeded in
products.
a one-pot procedure and free of side
1
20
40
60
80
80
80
5:00
4:00
2:30
1:15
24:00
1:15
81
80
99
99
1 >
97
2
In order to find the optimum conditions for the synthesis
of quinoxalines derivatives, we investigated the effect of
solvent, temperature and catalyst amounts on the model
reaction between benzil and o-phenylenediamine.
3
4
5a
6b
Table 1 presents the results of condensation reactions in
various solvents, including CH2Cl2, CH3CN, H2O, C2H5OH,
and CH3COOC2H5. The results of performing the reaction in
solvent-free conditions as well as the effect of the
Reaction conditions: benzil (1.0 mmol), o-phenylenediamine (1.0 mmol),
catalyst (25 mg).
a
The reaction was carried out in the absence of the catalyst.
b
The reaction was carried out with recycled catalyst.

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M. Masteri-Farahani et al. / C. R. Chimie 17 (2014) 1136–1143
Table 3
Synthesis of quinoxaline derivatives in solvent-free conditions.
Entry
1
1,2-Diamine
1,2-Dicarbonyl
Product
Time (h:min)
1:15
Yield (%)
99
NH2
N
N
O
O
NH2
2
2:15
99
NH2
NH2
OCH3
OCH3
OCH3
N
O
O
N
OCH3
CH3
3
00:10
95
NH2
CH3
O
O
N
NH2
N
CH3
CH3
4
00:15
99
O
NH2
NH2
O
N
N
O
O
O
O
5
00:30
90
H3C
NH2
NH2
H3C
N
N
O
O
6
1:30
99
OCH3
H3C
NH2
NH2
OCH3
OCH3
H3C
N
N
O
O
OCH3
CH3
7
8
9
0:10
0:10
0:10
99
83
98
CH3
H3C
NH2
NH2
H3C
N
N
O
O
CH3
CH3
O
H3C
NH2
NH2
O
H3C
N
N
O
O
O
O
N
N
CH3
CH3
NH2
NH2
O
O
CH3
CH3

M. Masteri-Farahani et al. / C. R. Chimie 17 (2014) 1136–1143
1143
Table 3 (Continued )
Entry
10
1,2-Diamine
1,2-Dicarbonyl
Product
Time (h:min)
0:30
Yield (%)
98
NH2
NH2
N
N
O
O
11
1:30
62
CH3
CH3
CH3
CH3
NH2
NH2
N
N
O
O
Reaction conditions: 1,2-diamine (1.0 mmol), 1,2-dicarbonyl (1.0 mmol), catalyst (25 mg), 80 8C.
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In this paper, we reported the preparation and char-
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using
a microemulsion system. The physicochemical
characterizations showed the uniform star-shaped mor-
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proposed method is widely applicable for the preparation
ofpolyoxometalatenanostructures withnew morphologies.
On the other hand, we developed a simple, eco-friendly,
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