Yb modified NaY zeolite: A recyclable and efficient catalyst for quinoxaline synthesis

Article abstract of DOI:10.1016/j.cclet.2014.03.003

In this study, Yb immobilized NaY zeolite catalyst (Yb/NaY) was obtained by a hydrothermal method and characterized by XRD, BET, FT-IR, ICP-AES, and NH₃-TPD. The catalyst displayed good catalytic activity when applied to the synthesis of quinoxalines via condensation of α-hydroxyketones with 1,2-diamines, and could be reused several times without any loss of catalytic activity.

Full text of DOI:10.1016/j.cclet.2014.03.003

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Chinese Chemical Letters xxx (2014) xxx–xxx
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Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
Original article
Yb modified NaY zeolite: A recyclable and efficient catalyst for
quinoxaline synthesis
*
Li-Yan Fan , Lin Wei, Wen-Jun Hua, Xiang-Xiong Li
Department of Chemistry, Tongji University, Shanghai 200092, China
A R T I C L E I N F O
A B S T R A C T
Article history:
In this study, Yb immobilized NaY zeolite catalyst (Yb/NaY) was obtained by a hydrothermal method and
characterized by XRD, BET, FT-IR, ICP-AES, and NH3-TPD. The catalyst displayed good catalytic activity
Received 23 December 2013
Received in revised form 20 February 2014
Accepted 21 February 2014
Available online xxx
when applied to the synthesis of quinoxalines via condensation of a-hydroxyketones with 1,2-diamines,
and could be reused several times without any loss of catalytic activity.
ß 2014 Li-Yan Fan. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords:
Yb/NaY
Recyclable
Quinoxaline
a-Hydroxyketone
1. Introduction
fabrication of Yb immobilized NaY zeolite catalyst (Yb/NaY) by a
hydrothermal method [18] and an application of this catalyst for
Quinoxaline and its derivatives are an important class of
heterocycles which have a variety of applications in many fields,
such as antibacterials [1–3], electroluminescent materials [4],
organic semiconductors [5] and useful intermediates in organic
synthesis [6–8]. In light of this significance, a number of synthetic
strategies have been developed for the preparation of substituted
the synthesis of quinoxaline. The catalyst gave the desired
products in good to excellent yields (up to 94%) and could be
reused several times without any loss of its catalytic activity. This
finding provides an example of NaY-based zeolite as an efficient
catalyst for widespread applications of quinoxaline synthesis.
quinoxalines from
a-hydroxyketones and diamines, in which
2. Experimental
diverse catalysts such as CuCl2 [9], Pd(OAc)2, RuCl2(PPh3)2 [10],
and FeCl3 [11] have been reported. Even though these existing
catalysts have advantages, they face the difficulty of recycling.
Recently, Lingaiah et al. [12] reported a heterogeneous process
utilizing the iron exchanged molybdophosphoric acid (FePMA) as a
catalyst. The catalyst is efficient and recoverable, but the reaction
requires an oxygen atmosphere, and the catalytic efficiency
decreases significantly upon reuse. Therefore, it has become a
very important task to obtain a stable and recyclable catalyst for
the highly efficient synthesis of quinoxaline.
Rare earth catalysts showed several advantages in some
important organic reactions [13–15], such as heterocyclic synthe-
sis, in our previous study [16]. Y zeolite has large specific area, good
thermal stability, and solid acidity, which make it widely used as a
substrate [17]. In this study, we report the ion-exchange
General procedure for catalyst preparation: Powdered NaY
(8.3 g) was dispersed in distilled water (160 mL) and then mixed
with desiccative YbCl3 (8.2 g) under stirring for 0.5 h. After stirring
for 0.5 h, the mixture was transferred into a 200 mL PTFE
autoclave, sealed, and heated in a hot air oven at 180 8C for 1 h.
The solid product was recovered by filtration and washed with an
excess of distilled water, then dried at 100 8C in an oven. The dried
sample was calcined from room temperature to 550 8C at a heating
rate of 10 8C/min and held at 550 8C for 5 h. Finally, the sample was
cooled to ambient temperature.
Typical procedure for the condensation synthesis of compound
3a: Benzoin 1a (1.0 equiv.), 1,2-diamine 2a (2.0 equiv.), oxidant
(0.35 mol%), and Yb/NaY catalyst (Yb3+ 0.05 equiv.) were reacted in
solvent (5 mL) in a 25 mL round bottom flask. The mixture was
stirred for 4 h at 80 8C. After completion of the reaction, the
mixture was centrifuged and washed with ethyl acetate (3
times  10 mL). The solid catalyst was recovered and dried at
80 8C for 2 h. The combined organic solution was evaporated under
*
Corresponding author.
E-mail address: fanly@tongji.edu.cn (L.-Y. Fan).
http://dx.doi.org/10.1016/j.cclet.2014.03.003
1001-8417/ß 2014 Li-Yan Fan. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Please cite this article in press as: L.-Y. Fan, et al., Yb modified NaY zeolite: A recyclable and efficient catalyst for quinoxaline synthesis,
Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.03.003

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L.-Y. Fan et al. / Chinese Chemical Letters xxx (2014) xxx–xxx
1034
Yb/NaY
NaY
1641
Yb/NaY
NaY
5
10
15
20
25
30
35
40
500
1000
1500
2000
2500
3000
3500
4000
2 Theta / Degree
Wavenumbers (cm-1)
Fig. 2. XRD patterns of parent NaY and Yb/NaY.
Fig. 1. IR spectra of parent NaY and Yb/NaY.
reduced pressure and purified by column chromatography on silica
gel, eluting with petroleum ether/ethyl acetate (20:1, v/v), to get
2,3-diphenyl-quinoxaline 3a. Other products were synthesized
through typical procedures. All 1H NMR results are summarized in
Supporting information. The configuration of compounds 3a–3n
was assigned by comparing 1H NMR data with known compounds
[19–23].
Yb/NaY zeolite effectively doped high concentrations of rare earth
metal.
According to the BET results, the specific surface areas of parent
NaY and Yb/NaY are 404 m2/g and 487 m2/g, respectively, which
means modification increased the specific surface area of NaY.
Based on previous reports [25,26], Yb3+ could migrate to the
sodalite cage of NaY zeolite through hydrothermal method, and
this would improve its surface area, as well as generate charge
effect and change the microenvironment of reaction sites. These
features of Yb/NaY may affect its catalytic performance.
The NH3-TPD results are listed in Table 1. Compared with
parent NaY zeolite, the acid amount of modified NaY zeolite was
significantly higher, especially in the middle-strong acid amount,
which means the introduction of Yb3+ has a significant effect on the
surface acid of Y zeolite. The change in acidity indicates that the
synthesized catalyst may have better catalytic activity in addition
to being recyclable.
To test its catalytic efficiency, the Yb/NaY was further applied to
condensation reactions for the synthesis of quinoxalines. The
results are summarized in Table 2. Synthesis of 2,3-diphenylqui-
noxaline 3a was chosen as a model reaction to optimize the
reaction conditions. It turned out that in the absence of the
catalyst, the product was obtained in only 65% yield (Table 2, entry
1). With the addition of Ln(OTf)3, the yields improved to 79%
(Table 2, entries 2–4). While with the catalysis of Yb/NaY, the yield
was up to 85% (Table 2, entry 5). To further improve the yield,
various oxidants were added into the model reaction (Table 2,
entries 6–8). The results revealed that morpholine is the most
efficient oxidant, and with it the highest yield (93%) was obtained.
Encouraged by the results, the synthetic protocol and scope
were further explored by employing a variety of 1,2-aryldiamines
3. Results and discussion
The FTIR spectra of NaY and Yb/NaY are presented in Fig. 1.
Characteristic peaks of Yb/NaY are basically the same with parent
NaY, except a slight shift due to the introduction of Yb3+. The peaks
around 1034 cmÀ1 and 1641 cmÀ1 are assigned to Si–O–Si
asymmetric stretching vibration and H–O–H symmetric stretching
vibration, respectively. Peaks between 600 cmÀ1 and 800 cmÀ1
correspond to the internal and external symmetric stretching
vibration of TO4 tetrahedron (T = Si or Al) [24]. This result shows
that the zeolite skeleton and crystal structure of NaY remain intact,
as supported by the XRD patterns of the same samples (Fig. 2).
From XRD analysis, all the peaks of the Yb/NaY can be indexed
to the diffraction peak of NaY at a slightly higher 2u region, and
these narrow peaks suggest that the Yb/NaY particles are highly
crystalline according to the Scherrer equation. Besides, no
significantly different peak is observed between the two diffraction
patterns, which indicate that the Yb3+ was finely dispersed
throughout the NaY zeolite.
Fig. 3 shows the SEM images of the parent NaY and ytterbium
modified NaY. These images show similar morphology and well-
ordered porous structure, as well as favorable dispersity, suggest-
ing that the loading of ytterbium has a negligible effect on the main
structure of the NaY zeolite. Hence, even when the Yb doped
concentration is up to 10.6 wt%, detected by ICP-AES, the
supported zeolite still has a structure similar to NaY. This implies
(1 equiv.) and
a-hydroxyketones (2 equiv.) (Table 3). In all cases,
the reaction gave the corresponding products in good yields.
Importantly, the solid catalyst in several reactions can be recycled
Fig. 3. SEM images of parent NaY (a) and Yb/NaY (b).
Please cite this article in press as: L.-Y. Fan, et al., Yb modified NaY zeolite: A recyclable and efficient catalyst for quinoxaline synthesis,
Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.03.003

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3
Table 1
Table 4
NH3-TPD results of NaY and Yb/NaY.
Reuse of the catalyst for synthesis of 3a.a
Zeolite
Acid amount (
m
m mol/g)
Total acid amount
m mol/g)
Entry
Benzoin (mmol)
Catalyst (mg)
Yieldb (%)
(
m
Fresh
2.0
1.7
1.5
1.3
170
144
127
110
91
93
92
93
Weak acid
Middle-strong acid
1st turn
2nd turn
3rd turn
(100–300 8C)
(300–450 8C)
NaY
485
493
310
587
795
1080
a
Mole ratio = 1:2 (benzoin/1,2-diamine), Yb/NaY (Yb3+ 0.05 equiv.), morpholine
Yb/NaY
(0.35 equiv.), 80 8C in HOAc, 4 h.
b
Isolated yield.
that the Yb/NaY catalyst has a good comparability with traditional
catalysts in terms of yields and reusability.
Table 2
Optimization of model reaction and comparison of catalysts.a
NH2
N
N
O
Catalyst, Oxidant
HOAc, 80 oC
4. Conclusion
+
.
NH2
OH
In this study, the Yb/NaY catalyst for the condensation synthesis
of quinoxaline was obtained by a simple hydrothermal method.
Both structural and chemical features made it efficient and
recyclable. The catalyzed reactions gave the desired products in
good to excellent yields, and the catalyst could be reused several
times without any loss of its high catalytic activity. This finding
highlights the potential of the Yb/NaY zeolite as an efficient
catalyst for widespread applications.
2 a
1 a
3 a
Entry
Catalyst (5 mol%)
Oxidant (35 mol%)
Yieldb (%)
1
2
3
4
5
6
7
8
None
None
65
77
77
79
85
84
83
93
La(OTf)3
Y(OTf)3
Yb(OTf)3
Yb/NaY
Yb/NaY
Yb/NaY
Yb/NaY
None
None
None
None
AATEMPOÁBF4À
PhI(OAc)2
Morpholine
Acknowledgment
We gratefully acknowledge the National Natural Science
Foundation of China (No. 20802052) for financial support.
a
a
-Hydroxyketone (1a, 1.0 equiv.), 1,2-aryldiamine (2a, 2.0 equiv.), catalyst
(0.05 equiv.), oxidant (0.35 equiv.), 80 8C in HOAc, 4 h.
b
Isolated yield.
Appendix A. Supplementary data
by simple centrifugation with a recovery rate of more than 95%.
When applying the recycled Yb/NaY in the same reactions (Table 3,
entries 1–3), the yields of the corresponding products remain
unchanged or even improved. It is inferred that the catalysts was
activated in the first run.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.cclet.2014.03.003.
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Reusability of the catalyst was studied through the model
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smoothly with a yield of 93%–91% (Table 4). This result indicates
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2 a-c
3 a-n
1 a-f
Entry
Ar
Ph
R
Product
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1
2
H
3a
3b
3c
3d
3e
3f
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94(92)c
89(93)c
89
4-Me-C6H4
4-F-C6H4
4-Cl-C6H4
4-MeO-C6H4
Ph
H
3
H
4
H
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H
84
6
OMe
OMe
NO2
NO2
NO2
NO2
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H
87
7
4-Me-C6H4
Ph
3g
3h
3i
87
8
84
9
4-MeO-C6H4
4-Me-C6H4
4-F-C6H4
4-Cl-C6H4
2-Furyl
81
10
11
12
13
14
3j
80
3k
3l
81
82
3m
3n
76
2-Furyl
OMe
76
a
a
-Hydroxyketone (1.0 equiv.), 1,2-aryldiamine (2.0 equiv.), Yb/NaY (Yb3+
0.05 equiv.), morpholine (0.35 equiv.), 80 8C in HOAc, 4 h.
b
Isolated yield.
c
Catalyzed by recovered Yb/NaY under same conditions.
Please cite this article in press as: L.-Y. Fan, et al., Yb modified NaY zeolite: A recyclable and efficient catalyst for quinoxaline synthesis,
Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.03.003

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Please cite this article in press as: L.-Y. Fan, et al., Yb modified NaY zeolite: A recyclable and efficient catalyst for quinoxaline synthesis,
Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.03.003