ZnO-loaded mesoporous silica (KIT-6) as an efficient solid catalyst for production of various substituted quinoxalines

Article abstract of DOI:10.1016/j.catcom.2016.10.026

Conventional homogeneous and microporous heterogeneous catalysts for quinoxalines production from diamines and diketones usually suffer from difficult separation or harsh reaction conditions. Here, we demonstrate the production of various substituted quin

Full text of DOI:10.1016/j.catcom.2016.10.026

ZnO-loaded mesoporous silica (KIT-6) as an efficient solid catalyst for
production of various substituted quinoxalines
Oveisi Hamid, M. Adharvana Chari, Chi Van Nguyen, Jeffrey E. Chen,
Yusuke Yamauchi¡ce:sup¿d¡/ce:sup¿, Kevin C.-W. Wu
PII:
DOI:
Reference:
S1566-7367(16)30392-2
doi:10.1016/j.catcom.2016.10.026
CATCOM 4831
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Catalysis Communications
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Revised date:
Accepted date:
28 July 2016
30 September 2016
24 October 2016
Please cite this article as: Oveisi Hamid, M. Adharvana Chari, Chi Van Nguyen, Jeffrey
E. Chen, Yusuke Yamauchi¡ce:sup¿d¡/ce:sup¿, Kevin C.-W. Wu, ZnO-loaded mesoporous
silica (KIT-6) as an efficient solid catalyst for production of various substituted quinox-
alines, Catalysis Communications (2016), doi:10.1016/j.catcom.2016.10.026
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ACCEPTED MANUSCRIPT
ZnO-Loaded Mesoporous Silica (KIT-6) as an Efficient Solid
Catalyst for Production of Various Substituted Quinoxalines
Oveisi Hamid,a M. Adharvana Chari,b* Chi Van Nguyen,c Jeffrey E. Chen,c Yusuke
Yamauchid* and Kevin C.-W. Wuc*
a Department of Materials and Polymer Engineering, Hakim Sabzevari University,
Sabzevar 9617976487, Khorasan Razavi, Iran.
b Dr.MACS Bio-Pharma Pvt. Ltd., R&D centre, Plot:79/B&C, EPIP, Pashamylaram,
Patancheru, Hyderabad
c Department of Chemical Engineering, National Taiwan University, No. 1, Sec. 4,
Roosevelt Road, Taipei 10617, Taiwan.
d World Premier International (WPI) Research Center for Materials
Nanoarchitectonics, National Institute for Materials Science (NIMS), 1-1 amiki,
Tsukuba, Ibaraki 305-0044, Japan
*Corresponding Author’s E-mail:
drmac_s@yahoo.com (M. A. Chari)
kevinwu@ntu.edu.tw (K.C.W. Wu)
Yamauchi.Yusuke@nims.go.jp (Y. Yamauchi)
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Abstract
Conventional homogeneous and microporous heterogeneous catalysts for
quinoxalines production from diamines and diketones usually suffer from difficult
separation or harsh reaction conditions. Here, we demonstrate the production of
various substituted quinoxalines using ZnO nanoparticle-loaded, highly ordered,
mesoporous silica KIT-6 materials as solid catalysts in room temperature. The results
show that the KIT-6-130-10Zn sample (aged at 130 °C and containing 10 wt% ZnO)
effectively produces quinoxalines up to the maximum of 99%. We propose that the
enhanced performance of the ZnO-loaded KIT-6 materials resulted from the
homogeneous distribution of ZnO nanoparticles, along with the KIT-6’s high specific
surface area and large pore sizes.
Keywords: mesoporous materials, ZnO, o-phenylene-diamines, 1,2-diketones,
quinoxalines
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1. Introduction
Quinoxaline derivatives, a type of nitrogen containing heterocyclic
compounds, are particularly attractive due to their vast exhibited biological activities
that includes antibacterial, antidiabetic, antiviral, and other pharmacological activities
[1-4]. Synthetic quinoxaline ring moiety can be classified as a type of antibiotics that
also includes echinomycin, leromycin, and actinomycin, which have been found to be
active against various transplantable tumors and inhibit Gram-positive bacterial
growth [5]. As a nitrogen-containing heterocyclic compound, Quinoxalinone and its
derivatives have been widely used in dyes [6], efficient electroluminescent materials
[7], organic semiconductors [8], building blocks for the synthesis of anion receptors
[9], cavitands [10], dehydroannulenes [11], and DNA cleaving agents [12].
Of the numerous substituted quinoxalines synthesis reported, the condensation
of an aryl 1,2-diamine with 1,2-dicarbonyl compounds in refluxing solvents, such as
ethanol or acetic acid, is one of the most common [13]. Catalytic systems involving
various metal precursors, acids, and zeolites have been reported as improved methods
[14]. In addition, other well-known methods also include microwave-assisted [15] and
solid phase synthesis [16], with chemicals such as molecular iodine [17], KOH [18],
Ga(OTf)3 [19], ionic liquid [20], ZrCl4 [21], and K10 clayzic [22]. Although increased
reaction efficiencies were reported in these pioneering studies, homogeneous catalysts
were mainly the catalyst employed. Additionally, several of the reported methods
endure disadvantages that commonly includes high required amounts of reagent
precursors, dependence on strong oxidizing reagents, expensive and rare catalysts,
long reaction durations, occasion of side reactions, severe reaction environments, and
difficult product separation from reaction mixture. For this reason, the breakthrough
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of mild and facile synthesis with stable, recyclable, and ecofriendly heterogeneous
catalysts for quinoxalines synthesis is important and very much in demand.
Recently, heterogeneous catalysts applied for organic synthesis [23-30] have
been acknowledged as considerably important due to their ease of processing,
superior reaction rates, higher selectivity, and easy work-up. Of the available solid
catalysts, ZnO is well known to be highly active, recyclable, non-toxic, and abundant
for several organic transformations [31-33]. In continuation of our interest in various
heterogeneous nanoporous catalysts application, herein we want to explore the use of
ZnO nanoparticles loaded mesoporous silica (namely ZnO-KIT-6) for the production
of quinoxalines with methanol as the solvent, and o-phenylenediamines and diverse
ketones as the reactants. Excellent product yields with high selectivity could be
achieved with short reaction times (10-60 min) while being conducted under mild and
convenient conditions.
2. Materials and Methods
2.1 Chemicals
Triblock copolymer Pluronic™ P123 (EO20PO70EO20, M = 5800), n-butanol,
and tetraethyl orthosilicate (TEOS) were obtained from Aldrich to be used as the
template, co-solvent, and silica source, respectively. Zinc nitrate hydrate
(Zn(NO3)2·6H2O) was purchased from Wako and used as the zinc source. All
chemicals and solvents used for this study were acquired from either Aldrich or
AVRA and used without further purification. Column chromatographic separations
were carried out on silica gel with a 60-120 mesh size.
2.2 Synthesis of KIT-6 with varying pore diameters
Pluronic P123 (4 g) was dissolved and stirred at 35°C for 3h in HCl solution
(0.532M, 151 mL) for a typical synthesis of highly ordered 3D mesoporous KIT-6
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silica. Then, n-butanol (4.0 g) was added immediately with continuous stirring, and
stirred for another hour. Subsequently, TEOS (8.6 g) was added, and continuously
stirred for 24 h at 35 °C. Following the hydrothermal treatment, the solution was
poured into a polypropylene bottle and left stationary in an oven for 24h at 100 °C .
Without washing, the white coloured product was filtered and dried inside an oven set
for various temperatures to control KIT-6’s pore diameter. By varying the aging
temperature (100, 130, and 150 °C), various KIT-6 samples were prepared and
denoted as KIT-6-T, where the synthesis temperature is represented by T. The final
as-synthesized products were calcined in air at 540 °C.
2.3 Synthesis of KIT-6 supported zinc oxide
Zinc oxide nanoparticles were immobilized in the KIT-6 mesopores by a wet
impregnation method. The desired amount of zinc source and the synthesized KIT-6
(1 g) were added to ethanol (25 mL) in a typical preparation. The mixture was then
stirred at 50 °C for 24 h and dried overnight at 100 °C to remove any remaining
ethanol. Finally, the sample was heated at 300 °C for 5 h in air. Samples of KIT-6
with varying pore diameters and amounts of zinc oxide were hereby prepared, and
denoted as KIT-6-T-X, where X represents the zinc oxide weight percentage.
2.4 Characterization
Rigaku diffractometer with Cu Kα (λ = 0.154 nm) radiation was used to
collect powder X-ray diffraction patterns (XRD) of KIT-6 with varying pore
diameters and amounts of immobilized zinc oxide. Low-angle diffractograms were
collected for the 2θ range of 0.7–10o and high-angle ones in the range of 10–80o. A
Bellsorp-mini II analyser was used to collected nitrogen adsorption and desorption
isotherms at -196 °C. All samples were degassed at 100 °C for 24 h prior to nitrogen
adsorption measurements. The Brunauer-Emmett-Teller (BET) method and the
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Barrett-Joyner-Halenda (BJH) method were used to calculate the specific surface
areas and pore size distributions (obtained from the nitrogen isotherms adsorption
branch), respectively. Sample morphology was observed by using a Hitachi S-4800
high-resolution field emission SEM (HR-FESEM) with a 15 kV acceleration voltage,
whereas a 20 kV acceleration voltage was used for elemental mapping and energy
dispersive spectroscopy (EDS) analysis. A JEOL JEM-2100F TEM with a 200 kV
accelerating voltage was used to obtain High-resolution TEM (HRTEM) images.
HRTEM sample preparation involved 2–5 min of sonication in ethanol and copper
grid deposition.
2.5 Typical procedure for catalytic reaction
The ZnO-KIT-6 catalyst (10 mg) was added to a methanol solution (4 mL) of
diamine (1 mmol) and 1,2-diketone (1 mmol), and stirred for various durations at
room temperature. After the reaction has been completed, as indicated by thin-layer
chromatography (TLC, using ethyl acetate/n-hexane 1/9), all products were
characterized by spectral (infrared (IR), nuclear magnetic resonance (NMR)) data and
also by melting point. The spectral data for two typical quinoxalines are given below.
Compound 3a: 2,3-Diphenylquinoxaline: Off white solid; Mp: 126-127oC; yield
1
98%; IR (KBr): νmax 3055, 1965, 1540, 1440, 1350, 1060, 980, 775 cm-1; H NMR
(400 MHz, CDCl3) δ : 8.18 (dd, J=6.10, 3.42 Hz, 2 H), 7.78 (dd, J=6.34, 3.41 Hz, 2
H), 7.51 - 7.53 (m, 4 H), 7.32 - 7.35 (m, 6 H) ppm. Compound 3e: 2,3,2',3'-
Tetraphenyl-[6,6']biquinoxalinyl: yellow solid; Mp: 309-311oC (lit.,22 >295oC);
yield 95%; Rf; 0.53, IR (KBr): νmax 3055, 1615, 1480, 1345, 1060, 770, 695 cm-1; 1H
NMR (400 MHz, CDCl3) δ : 8.17 (d, J=1.71 Hz, 2 H), 8.10 (d, J=9.02 Hz, 2 H), 7.71
(dd, J=8.78, 1.71 Hz, 2 H), 7.51 (d, J=6.83 Hz, 8 H), 7.29 - 7.41 (m, 12 H) ppm.
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3. Results and discussion
3.1 Catalyst characterization
KIT-6 type mesoporous silica was successfully synthesized with Pluronic™
P123 as the structure-directing agent. The KIT-6 pore size could be controlled from
7.7 to 11.3 nm by aging the as-synthesized samples at different temperatures (from
100 to 150 °C, respectively), as summarized in Table 1. As the pore size increased,
however, the corresponding specific surface area decreased. These samples of KIT-6-
T (where T represents aging at 100, 130, or 150 °C) were then used as the host
materials for further encapsulation of ZnO nanoparticles because of their suitable pore
size (7.7 to 11.3 nm), pore volume (1.05 to 1.35 cm3g-1), and specific surface area
(717 to 542 m2g-1).
Various amounts of ZnO nanoparticles from 5 to 30 wt% could be
successfully encapsulated in the synthesized KIT-6-T samples (with the ZnO loaded
samples denoted as KIT-6-T-X, where X represents the Zn weight percent). The
synthesized ZnO-loaded KIT-6 samples were further characterized by nitrogen
adsorption-desorption isotherms, scanning electron microscopy (SEM) with elemental
mapping, and transmission electron microscopy (TEM). As shown in Fig. 1(a), the
KIT-6-130 samples with different ZnO loading all exhibit similar isotherms, i.e. type
IV with a hysteresis, for the typical KIT-6 mesoporous architecture. The nitrogen
adsorption/desorption isotherms of all samples are shown in Fig. S1. As shown in
Table 1, both the specific surface area and the pore volume of all three KIT-6-T hosts
decreased but their pore sizes retained similar values as the loading amount of ZnO
was increased.
The corresponding small-angle X-ray diffraction (XRD) patterns showed well
defined peaks assignable to a typical Ia-3d mesostructure, which indicated the
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maintenance of the ordered mesostructure even after the encapsulation of the ZnO
nanoparticles, as shown in Fig. S2. The SEM element mapping for KIT-6-130-10Zn
in Fig. 1(b) clearly shows the homogeneous distribution of Zn element over the entire
area. The bright-field TEM image and the high-angle annular dark field – scanning
TEM (HAADF-STEM) image of the same sample confirmed the ordered
mesostructure (Fig. 1(c)) and the formation of uniform ZnO particles (Fig. 1(d)).
Other TEM images are also shown in the Fig. S3. These results indicate that ZnO
nanoparticles with an average particle size of around 9 nm were indeed formed inside
the KIT-6-T mesopores with the wet impregnation method described in the
experimental section.
3.2 Catalytic reaction
To optimize the reaction conditions for producing quinoxalines, o-
phenylenediamine 1 (OPDA, 1 mmol) and 1,2-diketone 2 (1 mmol) were employed as
the reactants, and methanol as the solvent in room temperature (Scheme 1). We then
screened all the samples and found that KIT-6-130-10Zn (10 mg) exhibited the best
catalytic performance. Therefore, we used KIT-6-130-10Zn as the catalyst (hereafter
denoted as ZnO-KIT-6). The reaction was also carried out in the absence of ZnO-
KIT-6 solid catalyst, and no product formed under the same reaction conditions. In
addition, bare KIT-6-130 sample (no ZnO) was also tested, but the quinoxaline yield
was also low (less than 10%).
To extend the possibility of producing various kinds of quinoxalines, different
substituted OPDA 1 and 1,2-diketones 2 were also used with the ZnO-KIT-6 catalyst
for 10 to 60 min at room temperature to achieve the maximum corresponding
quinoxalines yield. As shown in Table 2, several types of substituted OPDA, such as
chloro, nitro, dichloro, cyclohexyl, and bis-OPDA, were used as reactants to obtain
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the corresponding quinoxalines 3. Substituted diamines 1 and various aromatic
diketones 2 such as benzyl and furyl were used to produce various kinds of
quinoxalines (Table 2, entry 3a-l). In addition, the ZnO-KIT-6 catalyst also provided
a good yield when 3,3ʹ-diamino benzidine was used (Table 2, entry 3e & j). Finally,
aliphatic diamines such as cyclohexyldiamine (Table 2, entry 3k & l) also worked
well in the presence of this catalyst with good yields.
We propose that the ZnO-KIT-6 catalyst can act as a Lewis acid catalyst, and
the possible formation mechanism of quinoxalines 3 is proposed in Scheme 2. During
the reaction, the di-ketone is activated, and the intermediate A is formed with the
ZnO-KIT-6. Finally, the intermediate A is further reacted with the diketone, which is
thus condensed to become the final product 3. These results reveal that the ZnO-KIT-
6 catalyst is a very efficient catalyst for producing various kinds of quinoxalines with
excellent yields.
4. Conclusion
We have synthesized ZnO-loaded KIT-6 mesoporous silica as an efficient
catalyst for producing various kinds of quinoxalines using various aromatic diamines
and 1,2-diketones as reactants. The catalyst is proved to be very active and affords a
high yield of quinoxalines with short reaction durations. We propose that the ZnO-
KIT-6 catalyst can also be used in various acid-catalyzed multi-component reactions
(MCRs) and can create a platform for the development of various pharmaceutical
products.
Acknowledgments
The authors are grateful to the Director of Dr.MACS Bio-Pharma Pvt. Ltd., for
providing facilities. K.W. would like to thank the Ministry of Science and Technology
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(MOST), Taiwan (104-2628-E-002-008-MY3) and the National Taiwan University
(105R7706) for the funding support.
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Figures and Table Caption.
Figure 1. (a) Nitrogen adsorption-desorption isotherms of KIT-6-130 with different
ZnO loadings. (b) SEM elemental mapping and (c) a bright field TEM image for the
KIT-6-130-10Zn sample.
Scheme 1. Chemical equation representing the production of quinoxalines 3 from the
raw materials, diamines 1 and 1,2-diketones 2, using the synthesized ZnO-KIT-6
catalyst.
Scheme 2 Proposed mechanism for the production of quinoxalines using ZnO-KIT-6
as the catalyst.
Table 1 Summary of porous properties of all samples. Samples are denoted as KIT-6-
T-X, where T refers to the aging temperature and X refers to the weight percent of Zn.
Table 2. Production of various kinds of quinoxalines 3 with the maximum yields
obtained using ZnO-KIT-6 as the catalyst and the diamines 1 and 1,2-diketones 2 raw
materials as reactants.
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Figure 1
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Table 1
Surface
Pore volume
(cm3 g-1)
Pore size
(nm)
Sample names
area
(m2 g-1)
KIT-6-100
717
547
490
398
275
614
531
485
400
275
542
453
410
368
334
1.05
0.86
0.81
0.71
0.54
1.21
1.22
1.14
0.97
0.67
1.35
1.39
1.26
1.15
1.05
7.7
7.1
KIT-6-100-5Zn
KIT-6-100-10Zn
KIT-6-100-20Zn
KIT-6-100-30Zn
KIT-6-130
7.1
7.1
7.1
9.1
KIT-6-130-5Zn
KIT-6-130-10Zn
KIT-6-130-20Zn
KIT-6-130-30Zn
KIT-6-150
9.3
9.3
9.3
9.3
11.3
10.6
10.6
10.6
10.6
KIT-6-150-5Zn
KIT-6-150-10Zn
KIT-6-150-20Zn
KIT-6-150-30Zn
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Table 2
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Scheme 1
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Scheme 2
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Highlights
Highly ordered mesoporous KIT-6 materials are synthesized.
ZnO nanoparticles are uniformly formed in the KIT-6.
An efficient production of various substituted quinoxalines is demonstrated.
KIT-6-130-10Zn sample exhibits the most efficient catalytic ability.
Various quinoxalines with yields of 82 to 99% are produced.
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