Nanocrystalline 5 % Fe/ZnO as an efficient catalyst for quinoxaline synthesis

Article abstract of DOI:10.1007/s11164-012-0693-8

Various 2-aryl quanoxalines were synthesized with good yields from o-phenylene diamines and phenacyl bromides in one pot using novel nanocrystalline 5 % Fe/ZnO catalyst, at room temperature. The salient feature of this method includes mild reaction condit

Full text of DOI:10.1007/s11164-012-0693-8

Res Chem Intermed (2013) 39:1373–1383
DOI 10.1007/s11164-012-0693-8
Nanocrystalline 5 % Fe/ZnO as an efficient catalyst
for quinoxaline synthesis
•
Ashok V. Borhade Dipak R. Tope
Dattaprasad R. Patil
•
Received: 19 April 2012 / Accepted: 14 June 2012 / Published online: 11 July 2012
Ó Springer Science+Business Media B.V. 2012
Abstract Various 2-aryl quanoxalines were synthesized with good yields from
o-phenylene diamines and phenacyl bromides in one pot using novel nanocrystalline
5 % Fe/ZnO catalyst, at room temperature. The salient feature of this method
includes mild reaction conditions, short reaction time, good yield, high purity of
product, and recyclable catalyst without noticeable decrease in catalytic activity,
which can be used for large-scale synthesis. The synthesized 5 % Fe/ZnO nano-
particles were characterized by using XRD, SEM, and TEM techniques.
Keywords 5 % Fe/ZnO Á o-Phenylene diamines Á Phenacyl bromides Á
Quinoxaline Á Room temperature Á Recyclable catalyst
Introduction
Quinoxaline nucleus is an important pharmacophore in modern drug design and
discovery [1]. The substituted quinoxaline derivatives have been reported in a wide
range of applications in diverse therapeutic areas, including anti-inflammatory,
antiviral, antibacterial, antiprotozol, anticancer, antidepressant, antiHIV, and
antitumor [2–4]. Quinoxaline moieties are present in the various antibiotics such
as echinomycin, levomycin, and antinoleutin, which are known to inhibit the growth
of Gram-positive bacteria and are active against various transplantable tumors [5].
Quinoxalines are also used for technology up-gradation and also serve as useful
rigid subunits in macrocyclic receptors in molecular recognition [6–9]. The
widespread applications of quinoxaline containing structure have prompted studies
on their synthesis.
A. V. Borhade (&) Á D. R. Tope Á D. R. Patil
Research Centre, Department of Chemistry, HPT Arts and RYK Science College,
Nasik 422005, India
e-mail: ashokborhade2007@yahoo.co.in
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Numerous methods are available for the synthesis of quinoxaline and DHP’s
(dihydropyrazines) involving condensation of 1,2-diamines with 1,2 dicarbonyl
compound, aryl ketones using ZrOCl2, NbCl4, and HDNIB in PEG [10–12], bi-
catalyzed oxidative coupling of epoxides with 1,2-diamines [13], heteroannulation of
nitroketene N, S-aryliminoacetals with POCl3 [14], and iodine-catalyzed cyclocon-
densation of 1,2-dicarbonyl compounds with o-phenylene diamine in DMSO or
CH3CN [15]. The quinoxaline derivatives are also synthesized by reaction of a-
hydroxyl ketones with o-phenylene diamines in presence of HgI2 [16], followed by
oxidative cyclization of phenacyl bromides with 1,2-diamines using solid-phase
synthesis [17]. Recently, the synthesis of quinoxaline derivatives was reported by
reaction of 1,2 diamines with pencil bromides using catalysts like HClO4:SiO2 [18],
CuSO4Á5H2O [19], and DABCO [20]. However, many of these methods suffered from
some drawbacks such as low yield, long reaction time, drastic reaction condition, and
tedious work-up. Co-occurrence of several side reactions and in some cases more than
one step is involved in the synthesis of compound. As a part of our research, the use of
nanoparticles as a catalyst for organic synthesis, we have reported the use of Fe/ZnO
for the synthesis of quinoxalines.
Recently, metal oxide-based catalytic systems have been widely used in a variety
of organic reactions [21, 22]. These reactions have several disadvantages such as
long reaction time, low yield, and formation of bi-products [23]. These limitations
can be overcome by using metal-containing metal oxide: X-Meng et.al [24] have
reported catalytic oxidation by molecular oxygen catalyzed Ni–TiO2, a similar
catalyst to SO4/ZrO2 [25], Ru/SnO2 [26], Ag/SiO2[27], Au/SiO2 [28], etc., which
has been used for oxidation reaction.
With keeping all these things in our mind, we report the preparation of an efficient
and recyclable 5 % Fe/ZnO nanocrystalline catalyst by a hydrothermal method for
the synthesis of quinoxaline derivatives from phenacyl bromides and 1,2-diamines.
In this, Fe gives redox reaction between phenacyl bromide and 1,2-diamines by the
support of ZnO. The present study also includes the effect of metal-containing metal
oxide (Fe/Co/Cu containing ZnO) on the cyclization of quinoxaline in comparison
with ZnO nanocrystallite. The metal-containing ZnO and nanocrystalline ZnO
catalyst has gained more importance due to high thermal stability, large surface area,
easy recovery, good ability to perform organic reactions at lower temperatures, and
enviro-economic factors [29]. It has received more attention due to its non-toxic and
ecofriendly nature in performing organic reactions [30–32]. In addition, Nano ZnO is
an ecofriendly material which is non-toxic for human bodies and a widely used
antibacterial agent in biomedical applications [33, 34].
Experimental
All chemicals were purchased from Aldrich Chemical and were used without
purification. All yields refer to isolated products after purification using column
chromatography. Column chromatography was performed on silica gel
(120–240 mesh) supplied by Acme Chemical. 1H and 13C-NMR spectra were
recorded on Varian Mercury XL-300 and Bruker spectrometer instruments using
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Fe/ZnO as an efficient catalyst
1375
TMS as an internal standard and CDCl3, DMSO-d6 as a solvent. Infrared spectra
were taken on a Shimadzu FTIR-408 in KBr. The high resolution mass spectra were
recorded on a Bruker Daltonics mass spectrometer. The XRD patterns were
acquired on a multi-purpose X-ray diffractometer (Philips-1710 diffractometer
Cuka, k: 1.5406 A°) at a scan rate of 0.17° 2h s-1. The nanosize and morphology of
the Fe/ZnO nanoparticles were observed under Scanning Electron Micrography
(JEOL JEM-6360A model) equipped with JEOL JEC-560 auto carbon coater and
TEM with SAED (CM-200, Philips microscope).
Preparation of 5 % Fe/ZnO
The nanocrystalline ZnO was synthesized by the hydrothermal method using a
complexing agent like resorcinol (1.3 mol) and ZnCl2 (1 mol) in methanol (20 ml)
at 150 °C. The complex formed was filtered, dried, and calcined at 400 °C. The
product thus obtained was used for preparation of 5 % Fe/ZnO.
An appropriate amount of synthesized nanocrystalline ZnO was mixed with 5 %
FeCl3 solution along with buffer solution. A buffer solution (pH = 9.6) was
prepared by dissolving appropriate amounts of sodium hydroxide and sodium
bicarbonate in distilled water. The slurry obtained was stirred and transferred into a
steel-lined autoclave kept in an oven at 100 °C for 24 h. The precipitate obtained
was filtered, washed with deionized water, and dried at 100 °C for 12 h. The sample
was directly placed in the furnace for calcination at 600 °C for 3 h. The product was
characterized by XRD, SEM, EDAX, TEM, and SAED techniques.
Catalytic reaction
In a typical run, 1,2-diamines (1.1 mol), phenacyl bromides (1.3 mol), and Fe/ZnO
(0.3 mol) nanoparticles were allowed to react in methanol at room temperature for
25 min. The reaction was monitored by TLC using ethyl acetate–hexane (3:7 v/v) as the
solvent system. After the completion of the reaction, the reaction mixture was directly
filtered and washed with methanol. Filtrate was collected and evaporated under reduced
pressure to afford the crude product. The products obtained were purified by
recrystallization method using ethanol/water, followed by column chromatography on
silica gel with n-hexane:ethyl acetate (70:30) as an eluent to afford the pure product. All
1
products were characterized by IR, H, and 13C-NMR and mass spectrometry. The
recovered catalyst was dried and reused further in successive reactions.
Spectral data of selected and unknown compounds
2-(4-chlorophenyl)quinoxaline
1
IR (KBr) m: 3,039, 1,609, 829, 748 cm-1, H NMR (300 MHz, DMSO-d6): d 9.40
(s, 1H), 8.37 (d, J = 8.4 Hz, 2H), 8.3–8.11 (m, 2H), 7.90–7.85 (m, 2H), 7.65 (d,
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A. V. Borhade et al.
J = 8.7 Hz, 2H). 13C NMR (75 MHz, DMSO-d6): d 150.56, 142.86, 142.18,
141.63, 136.55, 135.15, 130.46, 129.76, 129.56, 129.38, 129.13, 128.75. EA
calculated: C, 69.86; H, 3.77; N, 11.64; Found C, 69.07; H, 4.21; N, 11.97.
2-(3-fluoro-4-methoxyphenyl)quinoxaline
1
IR (KBr) m: 3,090, 2,364, 1,620, 813, 763 cm-1, H NMR (400 MHz, CDCl3): d
9.26 (s, 1H), 8.12–8.08 (m, 2H), 7.78 (d, J = 8.2 Hz, 1H), 7.76 (d, J = 8.2 Hz, 1H),
7.14–7.10 (m, 2H), 3.98 (s, 3H). 13C NMR (75 MHz, CDCl3): [154.38, 151.11,
150.13, 149.61 (1c, d, J = 245 Hz)], 142.62, 142.12, 141.35, 130.35, 129.79,
129.40, 129.04, 123.55, 115.21, 114.95, 113.40, 56.28. EA Calculated: C, 70.54; H,
4.17; N, 11.22; Found: C, 70.97; H, 4.41; N, 11.03.
2-(3,5-bis(trifluoromethyl)phenyl)quinoxaline
IR (KBr) m: 3,093, 2,341.58, 1,624, 902, 763 cm-1, 1H NMR (400 MHz CDCl3): d
9.38 (s, 1H), 8.68 (s, 2H), 8.21–8.16 (m, 2H), 8.02 (s, 1H), 7.87–7.81 (m, 2H). 13C
NMR (75 MHz, CDCl3): [132.79, 132.46, 132.13, 131.79 (2c, q, J = 33 Hz)],
[126.90, 124.23, 121.52, 118.81 (2c, q, J = 271 Hz)], 148.07, 141.9, 141.77,
138.48, 130.67, 130.41, 129.48, 128.99. EA Calculated: C, 56.15; H, 2.36; N, 8.19;
Found C, 55.83; H, 2.74; N, 8.56.
2,3-dihydro-5-(4-nitrophenyl)pyrazine
1
IR (KBr) m: 3,058, 1,590, 1,364, H NMR (300 MHz, CDCl3): 8.67 (s, 1H), 7.89
(2H, d, J = 8.2 Hz), 7.58 (2H, d, J = 8.2 Hz), 3.62–3.48 (m, 2H), 3.22–2.90 (m,
2H). 13C NMR (75 MHz, CDCl3): 162.42, 157.59, 150.80, 147.65, 134.13, 128.90,
120.10, 54.34, 53.18. EA Calculated: C, 57.25; H, 3.14; N, 12.84; Found: C, 57.49;
H, 3.36; N, 12.52.
Results and discussion
In this study, we have prepared 5 % Fe/ZnO nanocatalyst by a hydrothermal method
using synthesized ZnO, FeCl3, deionized water, and NaOH. The XRD patterns of
5 % Fe/ZnO are shown in Fig. 1. The diffraction peaks at scattering angles (2h) of
29.0117, 31.8, 34.4, 36.2, 47.5, 56.6, 62.9, and 67.9° correspond to the reflection
from 002, 100, 102, 101, 102, 110, 103, and 112 crystal planes, respectively, which
matches with standard JCPDS data (Card No. 36-1451). The XRD pattern of 5 %
Fe/ZnO is identical to the hexagonal phase with wurtize structure having space
group (C6 V = P,3 mc). The XRD pattern of 5 % Fe/ZnO sample almost coincides
with that of pure ZnO showing no diffraction peaks due to Fe2O3, and also indicates
that Fe may be incorporated in ZnO. The value of 60–70 nm was calculated from
XRD data for the average diameter of this nanocrystalline 5 % Fe/ZnO using
Scherrer’s equation.
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Fe/ZnO as an efficient catalyst
1377
Fig. 1 XRD pattern of 5 % Fe/ZnO
The SEM images of 5 % Fe/ZnO powders are represented in Fig. 2a. The shapes
of the particles are quite similar to each other and are almost spherical. The SEM
images also reveal that the 5 % Fe/ZnO powder particles are agglomerates. The
agglomeration may result from the chemical treatment conditions. Figure 2b shows
EDAX analysis of 5 % Fe/ZnO, which indicates that 4.7 % of Fe is present in the
system. The loss in Fe content may be due to leaching out of unbound Fe by
washing.
The TEM image along with the selected area of the diffraction pattern (SAED)
(Fig. 3a, b) recorded for the sample corresponding to 5 % Fe/ZnO. TEM reveals
that the nanoparticles are hexagonal with several spherical-shaped crystallites. The
dark spot in the TEM micrograph can be alluded to synthesized 5 % Fe/ZnO
nanoparticles as the SAED pattern associated with such spots reveals the occurrence
of wurtize 5 % Fe/ZnO in total agreement with the XRD data. The average size of
the 5 % Fe/ZnO nanocrystallites was found to be 62.3 nm.
Catalytic results
In order to get effective results, the reaction conditions were optimized. For this
purpose, o-phenylene diamine and p-chloro phenacyl bromide was used as the
model substrate for the synthesis of quinoxaline (Scheme 1). The probable
mechanism for synthesis of quinoxaline is shown in Scheme 2. The process
conditions were optimized in terms of the following reaction variables.
Initially, a blank reaction was carried out using p-chloro phenacyl bromide and
o-phenylene diamine in methanol at room temperature which resulted in no
quinoxaline product even after 5 h at room temperature. The same reaction carried
out using a catalytic amount of 5 % Fe/ZnO afforded the desired quinoxaline with
94 % yield in 25 min.
To check the effectiveness of Fe/ZnO with different catalysts, we tried
synthesized ZnO, Fe/ZnO, Co/ZnO [35], and Cu/ZnO [36] for the cyclization
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A. V. Borhade et al.
Fig. 2 SEM and EDAX of 5 % Fe/ZnO
Fig. 3 TEM and SAED of 5 % Fe/ZnO
O
R
NH2
NH2
Br
N
N
Fe/ZnO
5%
R.T. MeOH
R
2
3
1
Scheme 1 Synthesis of quinoxaline
reaction of o-phenylene diamine and p-chloro phenacyl bromide. ZnO gave poor
yield while Cu and Co/ZnO gave good yield, but required more time as compared to
Fe/ZnO, also 5 % Fe/ZnO gave good yield with less time compared to 3 and 10 %
Fe/ZnO. The results are shown in Table 1.
With increasing Fe loading from 0 to 10 %, cyclization substantially increases
and reaches the maximum (94 %) at Fe content of 5 %. Further increasing Fe
content, however, lowers the cyclization rate. As evidenced by XRD, Fe species
loadings are lower than 10 %, whereas high Fe content results in microcrystalline
123

Fe/ZnO as an efficient catalyst
1379
O
Fe3+
Fe2+
Br
NH2
NH2
N
N
N
Fe/ZnO
5%
R
R
MeOH
N
H
R
2
1
3
3a
Scheme 2 Probable mechanism of quinoxaline
Table 1 Effect of different dopant on reaction time and yield
Entry
Catalyst
Time (min)
Yielda
1.
2.
3.
4.
5.
6.
a
ZnO
120
37
25
30
50
65
57
79
94
89
91
86
3 % Fe/ZnO
5 % Fe/ZnO
10 % Fe/ZnO
Cu/ZnO
Co/ZnO
Isolated yield
phase Fe located outside the internal channels, resulting in a remarkably poor
catalytic activity. Therefore, it is likely that a moderate incorporation of Fe results in
higher catalytic activity. Thus, it is obvious from our studies that 5 % Fe/ZnO was
superior in the cyclization reaction with good yield in a short time.
To optimize the amount of catalyst required for the cyclization, we tried various
mol equivalents of the catalyst compared to the quantity of the o-phenylene diamine
(Table 2). It was found that, when the reaction was carried out with 0.3 mol
equivalents, cyclization was 94 %.
The cyclization reaction was carried out in different solvents such as DMF,
MeOH, EtOH, CH3CN, and CH2Cl2, and the results clearly showed that methanol
was found to be the best choice, as shown in Table 3. Treatment of substituted
phenacyl bromides with o-phenylene diamine or ethylene diamine in methanol with
5 % Fe incorporating ZnO (0.3 mol) at room temperature afforded quinoxalines
with excellent yield, while the absence of the catalyst under similar conditions led
to the formation of DHQ (3a). The generality of the cyclization reaction of
o-phenylene diamine was checked by treating with a wide range of substituted
phenacyl bromides, and the results obtained are shown in Table 4.
However, with ethylene diamine, similar reactions furnished DHPs and in only
moderate yields. The method has also been applied for the preparation of
dihydropyrazine using phenacyl bromide and 1,2-diamine. It is worth mentioning
that the present method provides for the synthesis of some new furnished
quinoxalines (Table 4, entries 7, 8 and 11) which have not been previously
synthesized.
The effect of electron-donating and electron-withdrawing substituents on the
aromatic ring of phenacyl bromide on the rate of reaction was investigated.
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A. V. Borhade et al.
Table 2 Effect of mole percentage of 5 % Fe/ZnO
Entry
(mol) of Fe/ZnO
Time (min)
Yielda
1.
2.
3.
4.
a
0.1 mol
0.2 mol
0.3 mol
0.6 mol
120
45
77
89
94
87
25
25
Isolated yield
Table 3 Effect of solvent for quinoxaline formation using 5 % Fe/ZnO
Entry
Solvent
Time
Yielda
1.
2.
3.
4.
5.
a
MeOH
DMF
25
45
40
25
60
94
86
89
91
69
CH3CN
EtOH
CH2Cl2
Isolated yield
As Table 4 demonstrates, electron-donating groups and electron-withdrawing
substituents influence the reaction, with the electron-donating groups furnishing
the corresponding quinoxaline in high yield with less time (Table 4, entries 1–3, 5
and 7), whereas the electron-withdrawing substituents needed a longer reaction time
with low yield (Table 4, entries 4 and 11). Moreover, it has been observed that the
electronic properties of the aromatic ring of phenacyl bromide have some effect on
the yield and reaction times.
In order to study the possibility of reusability, the catalyst was filtered, washed
with methanol, and calcined at 200 °C in oven for 2 h. The reusability of the
catalyst was checked for several successive runs under identical reaction conditions.
The catalyst was found to be stable and reusable even after five cycles without
appreciable loss in activity, which is shown in Table 5.
In order to prove that the reaction is heterogeneous, a standard leaching
experiment was conducted. The catalyst was filtered at the reaction temperature and
the reaction was allowed to proceed without a catalyst. There was no change in yield
even after 12 h reflux, indicating that no homogeneous catalyst was involved.
Conclusion
In conclusion, the present paper describes a new, efficient, and eco-friendly catalyst
for the synthesis of quinoxalines. The 5 % Fe/ZnO catalyst exhibits excellent
catalytic activity for the condensation of various aromatic phenacyl bromides and
o-phenylene diamine. Most importantly, this catalyst facilitates the reaction at room
temperature providing solid supports in the reaction, enhances the reaction rate, and
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Fe/ZnO as an efficient catalyst
1381
Table 4 Synthesis of quinoxaline in the presence of 5 % Fe/ZnO nanoparticles
Entry Phenacyl bromide
1,2 diamine
Time
Product
Isolated Ref.
yielda,b
Cl
O
H2N
H2N
Br
N
N
1
2
25
94
18
Cl
Br
O
H2N
H2N
Br
N
N
20
35
91
18
Br
CH3
O
H2N
H2N
N
N
Br
3
4
93
86
18
20
18
H3C
NO2
OMe
F
O
H2N
H2N
N
N
Br
15
O2
N
O
H2N
H2N
N
N
Br
5
6
7
35
20`
15
94
92
96
MeO
O
H2N
H2N
Br
N
N
12
F
OMe
F
O
H2N
H2N
Br
Br
Br
N
N
--
--
MeO
F3C
F
CF3
O
H2N
H2N
N
8
15
91
CF3
CF3
N
F
F
O
H2N
H2N
N
N
9
25
60
30
87
87
83
16
18
--
F
F
Cl
O
H2N
H2N
Br
10
N
N
Cl
NO2
O
H2N
H2N
Br
N
11
O2
N
N
a
Isolated yield
All the products were characterized by 1H, 13C NMR and MS spectral data and were compared with the
b
reference compounds. The products were characterized by comparison of their spectroscopic and physical
data with reference samples
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A. V. Borhade et al.
Table 5 Results of the reaction run in the presence of recycled catalyst
Entry
Reaction run
Time
Yielda
1.
2.
3.
4.
5.
a
1
2
3
4
5
25
25
25
25
25
94
94
92
93
93
Isolated yield
thereby the excellent yields of the products. Therefore, we concluded that the 5 %
Fe/ZnO is the best catalyst for the synthesis of quinoxaline.
Acknowledgments Authors are grateful to UGC New Delhi for financial support, and also grateful to
University of Pune and IIT Mumbai for providing 1H and 13C NMR analysis.
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