Epoxy ether cleaving reactions catalyzed by supporting Lewis acidic ionic liquid

Article abstract of DOI:10.1016/j.cclet.2012.09.015

Lewis acidic ionic liquids were used to catalyze the reaction of epoxypropane with POCl₃. Considering the lower cost and catalytic activities, we concluded that [Et₃NH]Cl/AlCl₃ was the most attractive ionic liquid from an economical point of view. But it would be easily inactivated because of sensitive to water and air. Moreover, it could not be reused easily because of difficulty recovery in the reaction. However, supporting [Et₃NH]Cl/AlCl₃ catalyst could resolve above problems. Supporting [Et₃NH]Cl/AlCl₃ catalyst could be separated by filter easily and reused 5 times in 98% yield. Furthermore, the catalyst was applicable to other epoxy ether cleaving reactions.

Full text of DOI:10.1016/j.cclet.2012.09.015

Available online at www.sciencedirect.com
Chinese Chemical Letters 23 (2012) 1217–1220
www.elsevier.com/locate/cclet
Epoxy ether cleaving reactions catalyzed by supporting
Lewis acidic ionic liquid
*
Hui Zhen Zhi, Hong Li Shi, Yun Hu, Ke Dan Xia, Peng Zhang, Jin Fei Yang
School of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210046, China
Received 26 June 2012
Available online 23 October 2012
Abstract
Lewis acidic ionic liquids were used to catalyze the reaction of epoxypropane with POCl3. Considering the lower cost and
catalytic activities, we concluded that [Et3NH]Cl/AlCl3 was the most attractive ionic liquid from an economical point of view. But it
would be easily inactivated because of sensitive to water and air. Moreover, it could not be reused easily because of difficulty
recovery in the reaction. However, supporting [Et3NH]Cl/AlCl3 catalyst could resolve above problems. Supporting [Et3NH]Cl/
AlCl3 catalyst could be separated by filter easily and reused 5 times in 98% yield. Furthermore, the catalyst was applicable to other
epoxy ether cleaving reactions.
# 2012 Jin Fei Yang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Lewis acidic ionic liquid; Supporting catalyst; Epoxy ether cleaving; [Et3NH]Cl/AlCl3
Since the discovery of room temperature chloroaluminate ionic liquids in the 1980s, their Lewis and Brønsted
acidic properties were exploited for various reactions [1–5]. In recent years, Lewis acidic ILs, as one kind of
environmental friendly catalysts, are being gotten more and more attention of researchers [6–10], and many Lewis
acidic ionic liquids, such as [BMIM]Cl–nAlCl3 (combing 1-butyl-3-methylimidazolium chloride with AlCl3) [11–14],
[Et3NH]Cl/AlCl3 (combing triethylamine hydrochloride with AlCl3) [15,16] and other ionic liquids based on metal
chloride [17–21] have been synthesized and reported to catalyze organic reactions with excellent selectivity and yield
[22–27]. The outstanding advantage of ILs [28,29] is that their acidity can be adjusted in a wide range depending on the
proportion of organic base to Lewis acid [30–34]. The mechanism of effectiveness of additives was referred to the
formation of super acids or complexes which act as super acids [35–39].
Moreover, chloroaluminate ionic liquids can cleave aromatic methyl ethers under surprisingly mild conditions [40].
However, using Lewis acidic IL as the catalyst for epoxy ether cleaving reactions was seldom studied. It was found that
[Et3NH]Cl/AlCl3 could catalyze epoxy ether cleaving reactions in high yield with little catalyst. Unfortunately, Lewis
acidic IL was easily inactivated because of sensitive to water and air. And [Et3NH]Cl/AlCl3 could not be reused easily
in the reaction because it could dissolve most in product and was difficult to recovery. In order to resolve these
problems, the supporting ionic liquid triethylamine hydrochloride aluminum chloride ([Et3NH]Cl/AlCl3) was
* Corresponding author.
E-mail address: yangjinefei@njnu.edu.cn (J.F. Yang).
1001-8417/$ – see front matter # 2012 Jin Fei Yang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2012.09.015

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H.Z. Zhi et al. / Chinese Chemical Letters 23 (2012) 1217–1220
prepared and used to catalyze the epoxy ether cleaving reactions. And the supporting catalyst could be filtered and
reused 5 times in 98% yield.
1. Experimental
3-Butyl-1-methylimidazolium chloride aluminum chloride ([BMIM]Cl/AlCl3), triethylamine hydrochloride
aluminum chloride ([Et3NH]Cl/AlCl3) were performed as described in Refs. [41,42]. [HMIM][HSO4],
[IMIMPS][HSO4], triethylamine, 1,3-propane sultone and H2SO4 ([TEAPS][HS04]) were performed in Ref. [43].
Supporting [Et3NH]Cl/AlCl3 catalyst: 5 g [Et3NH]Cl/AlCl3 was dissolved in 20 mL CH2Cl2 with 5A molecular sieves
for 6 h at room temperature, then filtered and ovened dry in muffle furnace for 36 h.
The catalyst and POCl3 (0.1 mol) was added into the autoclave. Then epoxypropane (0.33 mol) was dropped in a way
that the temperature did not increase more than 10 8C. Then the resulting mixture was stirred for 2 h at reflux temperature.
After the stirring had been stopped, the reaction mixture was evaporated under reduced pressure to remove excessive
epoxypropane. Thecatalystwasfilteredandtheproductwasillustrated by1HNMRandIR. TheIR spectrawasrecordedon
a Nicolete spectrometer and expressed in cmÀ1 (KBr). 1H NMR spectra was recorded with a Varian XL-400 spectrometer.
2. Results and discussion
First, the reaction of epoxypropane with POCl3 was performed. The reactions catalyzed by different catalysts were
listed in Table 1.
The experimental results from Table 1 showed that [BMIM]Cl/AlCl3 IL exhibited the best catalytic activity with a
yield of 98.5% for TCPP (entry 2). On the other hand, [Et3NH]Cl/AlCl3 had the higher catalytic activity in the reaction
in 98.1% yield (entry 3). The catalytic activity order of the Lewis acidic ILs was consistent with that of their Lewis
acidic strengths [44,45].
With respect to reaction rates, ionic liquids [Et3NH]Cl/AlCl3 and [BMIM]Cl/AlCl3 showed nearly identical
performances. From an economical point of view, however, imidazolium-based ionic liquids were too expensive to be
used for most applications on large scale. Considering the much-lower cost of [Et3NH]Cl/AlCl3 in comparison to
Table 1
The catalytic activities of the Lewis acidic ILs on the product.
Entry
IL
Yield/%
1
2
[BMIM]/BF4
[BMIM]Cl/AlCl3
[Et3NH]Cl/AlCl3
[BMIM]Cl/FeCl3
[Et3NH]Cl/FeCl3
AlCl3
86.7
98.5
98.1
89.7
90.3
74.1
60.4
88.2
98.3
65.1
76.2
75.4
3
4
5
6
7
Nb2O5
8
TiSiWl2O40/TiO
2
9
Supporting [Et3NH]Cl/AlCl3
[HMIM][HSO4]
10
11
12
[IMIMPS][HS04]
[TEAPS][HS04]
Table 2
Effect of the dropped velocity of epoxypropane on reaction.
Entry
Dropped time/h
Yield/%
1
2
3
4
5
6
1
Polymerization
1.5
2
54.3
83.2
98.3
97.2
96.5
2.5
3
3.5

H.Z. Zhi et al. / Chinese Chemical Letters 23 (2012) 1217–1220
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Table 3
Effect of the reused supporting [Et3NH]Cl/AlCl3 on yield.
Entry
Cycle
Yield/%
1
2
3
4
5
6
7
8
0
1
2
3
4
5
6
7
98.3
98.3
98.3
98.2
98.1
98.2
97.1
95.5
[BMIM]Cl/AlCl3, we concluded that [Et3NH]Cl/AlCl3 was the preferred ionic liquid for the reaction. Unfortunately,
[Et3NH]Cl/AlCl3 was dissolved most in the product and was not easy to recovery. So, in order to obtain pure product
and reused catalyst, supporting [Et3NH]Cl/AlCl3 was used to catalyze the reaction and the catalyst was filtered in
98.3% yield (entry 9).
Table 2 showed that dropped velocity of epoxypropane was crucial to avoid high reaction temperature because of
easy ring-opening reaction of epoxides in the reaction. When the dropped velocity of epoxypropane was quick
(dropped time was less than 1 h, entry 1), the temperature would increase immediately following with side reactions.
But high yield could be obtained at appropriate temperature according to different dropped velocity.
The reusability of supporting [Et3NH]Cl/AlCl3 catalyst was investigated, and the results were given in Table 3. The
yield was almost unchanged when supporting [Et3NH]Cl/AlCl3 was used repeatedly 5 times. This showed that the
supporting Lewis acidic IL had excellent reusability. This good reusability may be which gave an easier separation of
IL from the reaction mixture, and the IL was not easily lost in the separation process. Therefore, its activity was stable.
To demonstrate the feasibility of the methodology, other epoxy oxides were used to react with POCl3, such as
ethylene oxide, epoxypropane, epoxy chloropropane, 1,2-epoxybutane, oxetane, 2-methyl oxetane and tetrahy-
drofuran. It could be seen from Table 4 that good yields (86.1–99.2%) could be obtained with 7 epoxy oxides. The
yield of 1,2-epoxybutane was lower than epoxypropane because of steric hindrance. It was demonstrated that
supporting [Et3NH]Cl/AlCl3 was excellent catalyst for epoxy ether cleaving reactions.
Table 4
Epoxy ether cleaving reactions catalyzed by supporting [Et3NH]Cl/AlCl3.
Entry
1
Material
Product
Yield/%
99.2
O
Product
O
ClH2CH2CO
P
OCH2CH2Cl
OCH2CH2Cl
O
O
P
Cl
(OCH2CHCH3)3
2
98.3
CH3
O
O
P
Cl Cl
(OCH2CHCH2)3
3
4
86.1
96.4
CH2Cl
O
O
P
Cl
(OCH2CHCH2CH3)3
CH2CH3
O
P
O
5
6
7
91.4
93.4
90.6
(OCH2CH2CH2Cl)3
O
P
Cl
O
O
CH3
(OCH2CH2CHCH3)3
O
P
ClH2CH2CH2CH2CO
OCH2CH2CH2CH2Cl
OCH2CH2CH2CH2Cl

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3. Conclusions
The results described in this paper showed how the application of supporting [Et3NH]Cl/AlCl3 could be used for
epoxy ether cleaving reactions. Supporting [Et3NH]Cl/AlCl3 catalyst could be filtered and reused 5 times in 98%
yield.
Acknowledgment
A Project Funded by Jiangsu Natural Science Foundation of China (No. BK2011369).
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