Synthesis of chloroesters by the reaction of ethers with acyl chlorides catalyzed by ZnO

Article abstract of DOI:10.1007/s11696-020-01267-2

An efficient method for the synthesis of chloroesters by the reaction of ethers with acyl chlorides catalyzed by nano-ZnO under solvent-free condition at room temperature was described. The method is compatible with a range of ethers including tricyclic ethers, tetracyclic ethers, pentacyclic ethers and hexacyclic ethers and have afforded the products with moderate to good yields. The ZnO could be reused up to three times and the product yield after three cycles is 87%.

Full text of DOI:10.1007/s11696-020-01267-2

Chemical Papers
https://doi.org/10.1007/s11696-020-01267-2
ORIGINAL PAPER
Synthesis of chloroesters by the reaction of ethers with acyl chlorides
catalyzed by ZnO
Yuqi Tang1 · Chengliang Feng2 · Wanfeng Yang1 · Min Ji3 · Wei Wang1 · Junqing Chen1
Received: 16 February 2020 / Accepted: 23 June 2020
© Institute of Chemistry, Slovak Academy of Sciences 2020
Abstract
An efcient method for the synthesis of chloroesters by the reaction of ethers with acyl chlorides catalyzed by nano-ZnO
under solvent-free condition at room temperature was described. The method is compatible with a range of ethers including
tricyclic ethers, tetracyclic ethers, pentacyclic ethers and hexacyclic ethers and have aforded the products with moderate to
good yields. The ZnO could be reused up to three times and the product yield after three cycles is 87%.
Keywords Chloroesters · Cyclic and acyclic ethers · Zinc oxide · Solvent-free
Introduction
(Kwon and Kim 2002), Bi(NO3)3·5H2O (Suresh et al. 2007),
InBr (Yadav et al. 2007), La(NO3)3·6H2O (Suresh et al.
2008), FeCl2 (Enthaler and Weidauer 2012a) etc. However,
these methods displayed some disadvantages, such as using
toxic, expensive and non-recyclable catalysts, long reaction
time and low product yields. Thus, it is necessary to develop
a novel method to synthesize chloroesters.
The synthesis of chloroesters is a versatile organic transfor-
mation by the reaction of ethers with acyl chlorides. Ether
cleavage synthesis of chloroesters was frequently utilized to
simplify the synthesis of complex bio-active molecules by
producing various key intermediates (Burwell 1954; Schel-
haas and Waldmann 1996). Catalysts for cracking cyclic
ethers to form chloroesters using Lewis acids had been
reported, such as ZnCl2 (Cloke and Pilgrim 1939), Mo(CO)6
(Alper and Huang 1973), FeCl3 (Ganem and Small 1974),
TiCl4 (Delaney et al. 1986), NaI (Oku et al. 1982) (Mimero
et al. 1994), PdCl2(PPh3)2 (Pri-Bar and Stille 1982), CoCl2
(Iqbal and Srivastava 1991), WCl6 (Guo et al. 2001), MoCl5
(Guo et al. 2002), BCl3 (Malladi and Kabalka 2002), SmI2
ZnO as a non-toxic, inexpensive, non-hygroscopic Lewis
acid catalyst has been widely used in many organic trans-
formations. For example, Zhang et al. (2013) described
solvent-free synthesis of 2-acylpyrroles and its derivatives;
Javadi and Tayebee (2016) and Tayebee et al. (2012, 2013a)
proposed synthesis of 2-aminothiophenes via the Gewald
reaction; Tayebee et al. (2010, 2013b) reported the one-pot
synthesis of 2,4,6-trisubstituted-1,3,5-trioxanes and as an
efcient and environmentally benign catalyst for homoge-
neous benzoylation of hydroxyl functional groups. Bah-
rami et al. (2009) reported the highly efcient solvent-free
synthesis of dihydropyrimidinones; Hosseini-Sarvari and
Sharghi (2007) reported a novel method for the synthesis of
N-sulfonylaldimines; Sarvari and Sharghi (2004) proposed
an efcient Friedel–Crafts acylation reaction. At present,
there is no report about the synthesis of chloroesters by the
cleavage of cyclic and acyclic ethers catalyzed by ZnO.
In our study (Scheme 1), nano-ZnO powder was utilized
as the catalyst to decompose cyclic ether and acyclic ether
with acyl chlorides to form chloroesters under solvent-free
condition. The method has the advantages of high yields,
environmental friendliness, simple operation and mild reac-
tion condition.
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s11696-020-01267-2) contains
supplementary material, which is available to authorized users.
* Junqing Chen
jqchen@seu.edu.cn
1
School of Chemistry and Chemical Engineering,
Southeast University, Nanjing 211189, Jiangsu,
People’s Republic of China
2
Institute of Pharmaceutical Engineering, Jiangsu College
of Engineering and Technology, Nantong 226000, Jiangsu,
People’s Republic of China
3
School of Biological Sciences and Medical Engineering,
Southeast University, Nanjing 211189, Jiangsu,
People’s Republic of China
Vol.:(0123456789)
1 3

Chemical Papers
(DMSO-d6, 75 MHz) δ: 165.6, 134.3, 133.3, 129.1, 128.7,
Experimental
61.7, 41.9, 31.1 (Guo et al. 2002).
1
4-Chlorobutyl benzoate (Table 2, entry 3): H NMR
Materials and instruments
(DMSO-d6, 500 MHz) δ: 8.00 (d, J=10 Hz, 2H), 7.70–7.67
(m, 1H), 7.56 (t, J=7.5 Hz, 2H), 4.34 (t, J=5 Hz, 2H), 3.74
(t, J=7.5 Hz, 2H), 1.92–1.86 (m, 4H). 13C NMR (DMSO-d6,
126 MHz) δ: 166.1, 133.7, 130.3, 129.5, 129.2, 64.4, 45.5,
29.3, 26.2 (Bodduri et al. 2015).
The reagents utilized in the experiment were purchased
from commercial channels and could be used directly
without further purifcation. ZnO nanoparticles with the
average particle size of about 30 nm. All reactions were
monitored by thin-layer chromatography (TLC) on GF-254
silica gel plates and viewed under UV light at 254 nm. The
1H NMR and 13C NMR spectra were recorded on Bruker
Avance DPX-300 MHz/500 MHz instrument in CDCl3
or DMSO-d6 with TMS as the internal standard and the
chemical shifts (δ) were given in parts per million (ppm).
1
4-Chloropentyl benzoate (Table 2, entry 4): H NMR
(DMSO-d6, 500 MHz) δ 7.93 (d, J=10 Hz, 2H), 7.65–7.60
(m, 1H), 7.49 (t, J = 12.5 Hz, 2H), 4.28–4.24 (m, 2H),
4.22–4.16 (m, 1H), 1.90–1.72 (m, 4H), 1.45 (d, J=10 Hz,
3H). 13C NMR (DMSO-d6, 126 MHz) δ: 165.7, 133.2, 129.8,
129.0, 128.7, 64.1, 59.1, 36.2, 25.5, 25.1 (Guo et al. 2002).
1
5-Chloropentyl benzoate (Table 2, entry 5): H NMR
(DMSO-d6, 500 MHz) δ: 8.00 (d, J=5 Hz, 2H), 7.70–7.67
(m, 1H), 7.56 (t, J=7.5 Hz, 2H), 4.31 (t, J=5 Hz, 2H), 3.68
Typical experimental procedure for the synthesis
of chloroesters by the cleavage of cyclic and acyclic
ethers
(t, J=5 Hz, 2H), 1.84–1.74 (m, 4H), 1.58–1.52 (m, 2H). 13
C
NMR (DMSO-d6, 126 MHz) δ 166.2, 133.7, 130.3, 129.5,
129.2, 64.9, 45.6, 32.1, 27.9, 23.4 (Bodduri et al. 2015).
1
4-Chlorobutyl acetate (Table 3, entry 2): H NMR
In the mixture of cyclic/acyclic ether (11 mmol) and acid
chloride (10 mmol), nano-ZnO (5 mol%) was added at
0–5 °C and stirred at room temperature for an appropriate
time. After the TLC monitoring reaction, the ZnO was
removed by fltration and washed repeatedly with dichlo-
romethane and water. It was then dried at 60 °C for 3 h
and used for the next catalytic cycle. The solution was
extracted three times with dichloromethane and water, and
dried on anhydrous Na2SO4. The product was purifed on
a silica gel column chromatography using a mixture of
petroleum ether/ethyl acetate (150:1, v/v). The product is
obtained by vacuum distillation to remove the solvent. The
compounds were characterized by 1H NMR and 13C NMR.
(DMSO-d6, 500 MHz) δ 4.06 (t, J = 7.5 Hz, 2H), 3.69 (t,
J=5 Hz, 2H), 2.03 (s, 3H), 1.83–1.78 (m, 2H), 1.75–1.69
(m, 2H). 13C NMR (DMSO-d6, 126 MHz) δ 170.8, 63.6,
45.4, 29.2, 26.1, 21.1 (Bodduri et al. 2015).
4-Chlorobutyl 2-chlorobenzoate (Table 3, entry 3):
1H NMR (DMSO-d6, 500 MHz) δ 7.83 (d, J = 5 Hz, 1H),
7.62–7.58 (m, 2H), 7.52–7.47 (m, 1H), 4.35 (t, J= 5 Hz,
2H), 3.73 (t, J=7.5 Hz, 2H), 1.93–1.84 (m, 4H). 13C NMR
(DMSO-d6, 126 MHz) δ 165.6, 133.5, 132.1, 131.4, 131.2,
130.8, 127.8, 65.1, 45.41, 29.3, 26.1 (Yadav et al. 2007).
1
4-Chlorobutyl 3-chlorobenzoate (Table 3, entry 4): H
NMR (DMSO-d6, 300 MHz) δ 7.89–7.87 (m, 2H), 7.71–7.68
(m, 1H), 7.56–7.50 (m, 1H), 4.28 (t, J=6 Hz, 2H), 3.67 (t,
J = 6 Hz, 2H), 1.88–1.77 (m, 4H). 13C NMR (DMSO-d6,
75 MHz) δ 185.5, 164.5, 133.0, 131.8, 130.7, 128.6, 127.7,
64.5, 44.9, 28.8, 25.6 (Chen et al. 2014).
Characterization of compound
1
4-Chlorobutyl 4-chlorobenzoate (Table 3, entry 5): H
1,3-Dichloropropan-2-yl benzoate (Table 2, entry 1):
1H NMR (DMSO-d6, 300 MHz) δ: 7.99–7.95 (m, 2H),
7.69–7.64 (m, 1H), 7.55–7.49 (m, 2H), 5.43–5.38 (m,
1H), 4.06–3.89 (m, 4H). 13C NMR (DMSO-d6, 75 MHz)
δ: 164.7, 133.8, 133.6, 129.3, 128.8, 72.3, 43.5 (Bodduri
et al. 2015).
NMR (DMSO-d6, 300 MHz) δ 7.92 (d, J = 8.5 Hz, 2H),
7.56 (d, J = 8.5 Hz, 2H), 4.27 (t, J = 5.8 Hz, 2H), 3.67 (t,
J=6.0 Hz, 2H), 1.89–1.74 (m, 4H). 13C NMR (DMSO-d6,
75 MHz) δ 164.8, 138.2, 130.9, 128.9, 128.6, 64.2, 44.9,
28.8, 25.6 (Enthaler and Weidauer 2012b).
1
1
4-Chlorobutyl 4-methylbenzoate (Table 3, entry 6): H
2,3-Dichloropropyl benzoate: H NMR (DMSO-d6,
NMR (CDCl3, 300 MHz) δ 7.92 (d, J=8.1 Hz, 2H), 7.23 (d,
J=8.0 Hz, 2H), 4.34 (t, J=5.8 Hz, 2H), 3.61 (t, J=6.0 Hz,
2H), 2.40 (s, 3H), 1.95 (m, 4H). 13C NMR (CDCl3, 75 MHz)
δ 166.1, 143.1, 129.1, 128.6, 127.0, 63.4, 44.0, 28.8, 25.7,
21.1 (Bodduri et al. 2015).
300 MHz) δ: 7.98–7.29 (m, 2H), 7.66–7.59 (m, 1H),
7.54–7.48 (m, 2H), 3.94–3.80 (m, 3H), 3.76–3.69 (m, 2H).
13C NMR (DMSO-d6, 75 MHz) δ: 165.4, 133.6, 133.4,
129.2, 128.7, 75.9, 64.1, 44.1 (Bodduri et al. 2015).
1
3-Chloropropyl benzoate (Table 2, entry 2): H NMR
1
4-Chlorobutyl 4-fuorobenzoate (Table 3, entry 7): H
(DMSO-d6, 300 MHz) δ: 7.95 (d, J=6 Hz, 2H), 7.65–7.60
(m, 1H), 7.49 (t, J = 7.5 Hz, 2H), 4.35 (t, J = 6 Hz, 2H),
3.76 (t, J = 6 Hz, 2H), 2.18–2.10 (m, 2H). 13C NMR
NMR (CDCl3, 300 MHz) δ 8.07–8.02 (m, 2H), 7.13–7.08
(m, 2H), 4.34 (d, J=5.0 Hz, 2H), 3.62–3.59 (m, J=5.4 Hz,
2H), 1.99–1.89 (m, 4H). 13C NMR (CDCl3, 75 MHz) δ
1 3

Chemical Papers
Table 1 Optimization of the
reaction conditions
Entry
ZnO (mol%)
T (oC)
RT
Time
8h
Yield a(%)
N.R.
1
2
-
1
RT
25min
49
3
4
2
5
RT
RT
RT
RT
RT
-10
0
25min
25min
25min
25min
25min
8h
67
95
5
7
95
6
10
12
5
89
7
85
8
N.R.
38
9
5
25min
25min
25min
10
11
5
10
79
5
50
94
Reaction condition: THF (11 mmol) and benzoyl chloride (10 mmol) were used
N.R. no reaction
aIsolated yield
167.0, 165.1 (d, J =109.5 Hz), 131.6 (d, J=9.3 Hz), 126.0
(d, J = 3 Hz), 115.2 (d, J = 22.5 Hz), 63.7, 43.9, 28.8, 25.7
(Bodduri et al. 2015).
7.34–7.28 (m, 2H), 4.27–4.16 (m, 3H), 1.89–1.72 (m, 4H),
1.45 (d, J=6.5 Hz, 3H). 13C NMR (DMSO-d6, 75 MHz) δ:
166.7, 164.7 (d, J = 99.8 Hz), 132.0 (d, J = 9.8 Hz), 126.4
(d, J=3 Hz), 116.0 (d, J=22.5 Hz), 64.3, 59.1, 36.2, 25.5,
25.1 (Bodduri et al. 2015).
4-Chlorobutyl 4-methoxybenzoate (Table 3, entry 8):
1H NMR (CDCl3, 300 MHz) δ 7.88 (d, J = 8.9 Hz, 2H),
7.01 (d, J = 8.9 Hz, 2H), 4.23 (t, J = 5.9 Hz, 2H), 3.80 (s,
3H), 3.67 (t, J=6.1 Hz, 2H), 1.87–1.75 (m, 4H). 13C NMR
(CDCl3, 75 MHz) δ 165.3, 163.1, 131.1, 122.1, 114.0,
63.6, 55.5, 44.9, 28.9, 25.8 (Bodduri et al. 2015).
4-Chlorobutyl 2-chloronicotinate (Table 3, entry 9): 1H
NMR (CDCl3, 300 MHz) δ 7.84–7.76 (m, 1H), 7.55 (d,
J = 4.9 Hz, 1H), 7.15–7.07 (m, 1H), 4.33 (t, J = 5.8 Hz,
2H), 3.63–3.57 (m, 2H), 1.94–1.86 (m, 4H). 13C NMR
(CDCl3, 75 MHz) δ 185.5, 161.7, 133.3, 132.9, 131.9,
127.3, 63.8, 43.9, 28.7, 25.7 (Suresh et al. 2007).
4-Chloropentyl 4-chlorobenzoate (Table 4, entry 2): 1H
NMR (DMSO-d6, 300 MHz) δ 7.92 (d, J = 8.6 Hz, 2H),
7.56 (d, J = 8.6 Hz, 2H), 4.28–4.16 (m, 3H), 1.90–1.71
(m, 4H), 1.45 (d, J = 6.5 Hz, 3H). 13C NMR (DMSO-d6,
75 MHz) δ 164.8, 138.2, 130.9, 128.9, 128.6, 64.4, 59.1,
36.2, 25.4, 25.1 (Bodduri et al. 2015).
4-Chloropentyl 4-methoxybenzoate (Table 4, entry
4): 1H NMR (DMSO-d6, 300 MHz) δ 7.89–7.85 (m, 2H),
7.02–6.99 (m, 2H), 4.27–4.18 (m, 3H), 3.79 (s, 3H),
1.88–1.71 (m, 4H), 1.45 (d, J = 6.5 Hz, 3H). 13C NMR
(DMSO-d6, 75 MHz) δ 165.3, 163.1, 131.1, 122.0, 114.0,
63.7, 59.1, 55.5, 36.2, 25.6, 25.1 (Bodduri et al. 2015).
5-Chloropentyl 2-chlorobenzoate (Table 4, entry 6):
1H NMR (CDCl3, 300 MHz) δ 7.80 (dd, J = 7.6, 1.1 Hz,
1H), 7.45–7.36 (m, 2H), 7.32–7.26 (m, 1H), 4.34 (t,
J = 6.4 Hz, 2H), 3.54 (t, J = 6.6 Hz, 2H), 1.88–1.75 (m,
4H), 1.65–1.55 (m, 2H). 13C NMR (CDCl3, 75 MHz) δ
165.6, 133.5, 132.1, 131.3, 131.2, 130.9, 127.8, 65.5, 45.6,
32.0, 27.8, 23.3 (Suresh et al. 2007).
Benzyl benzoate (Table 4, entry 7): 1H NMR (DMSO-
d6, 300 MHz) δ 7.97 (d, J=7.2 Hz, 2H), 7.63 (t, J=7.4 Hz,
1H), 7.52–7.31 (m, 7H), 5.32 (s, 2H). 13C NMR (DMSO-
d6, 75 MHz) δ 165.5, 136.1, 133.3, 129.6, 129.1, 128.7,
128.5, 128.0, 127.9, 127.4, 66.1 (Shen et al. 2020).
4-Chloropentyl 4-fuorobenzoate (Table 4, entry 3):
1H NMR (DMSO-d6, 300 MHz) δ 8.01–7.96 (m, 2H),
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Chemical Papers
Table 2 Cleavage of diferent
cyclic ethers using catalyst
nano-ZnO
Entry
1
Ether
Product
Time (h)
Yielda (%)
1
79
18
2
3
0.5
0.5
93
95
4
3
4
94
81
5
aIsolated yield
Prop-2-yn-1-yl benzoate (Table 4, entry 8): 1H
NMR (DMSO-d6, 300 MHz) δ 7.95–7.92 (m, 2H),
7.65 (t, J = 7.4 Hz, 1H), 7.51 (t, J = 7.6 Hz, 2H), 4.92
(d, J = 2.4 Hz, 2H), 3.56 (t, J = 2.4 Hz, 1H). 13C NMR
(DMSO-d6, 75 MHz) δ 164.9, 133.6, 129.2, 129.0, 128.8,
78.3,77.9, 52.4 (Yadav et al. 2007).
when the catalyst was increased to 5 mol%. Thereafter,
the amount of catalyst continued to increase, and the ef-
ciency of the catalytic system gradually decreased. This
phenomenon can be explained by the fact that with the
increase of the amount of catalyst, the number of active
sites increases, leading to a decrease in the concentration
of reactants at the active sites and diminishing yield. To
investigate the optimum temperature for the reaction, no
products were formed at − 10 °C for 12 h (Table 1, entry
8). The yield of the reaction at 0 °C for 25 min was 38%,
and the yield did not increase when the reaction time was
prolonged. The yield was 79% at 10 °C for 25 min and 94%
at 50 °C for 25 min (Table 1, entry 9–11). Therefore, room
temperature is the optimal reaction temperature.
Results and discussion
In our initial study, the reaction of benzoyl chloride
(10 mmol) with tetrahydrofuran (11 mmol) was chosen
as a model to optimize the reaction conditions (Table 1).
As shown in Table 1, the reaction of benzoyl chloride
and tetrahydrofuran without the addition of zinc oxide cat-
alyst at room temperature for 8 h and product had not been
found, which was consistent with our expectation (Table 1,
entry 1). The reaction was conducted in the presence of
1%, 2%, 5%, 7%, 10% and 12% of ZnO and the product
4-chlorobutyl benzoate was isolated in 49%, 67%, 95%,
95%, 89% and 85% yield, respectively (Table 1, entry 2–7).
The results showed that the yield reached the maximum
To study the range and limitation of cracking ring ethers
in this catalytic system, ring opening experiments were
carried out on benzoyl chloride and a series of ring ethers,
and the corresponding benzoates were obtained (Table 2).
Epichlorohydrin reacted violently with benzoyl chloride
and the ratio of symmetric to asymmetric dichlorobenzo-
ates was 8:2, and the yield was 79% and 18%, respec-
tively (Table 2, entry 1). It was found that cyclic ethers
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Chemical Papers
Table 3 Cleavage of THF by a
series of acyl chlorides
Entry
1
R
Product
Time
Yielda (%)
C6H5-
25min
95
2
3
H-
15min
30min
73
93
2-(Cl)C6H4-
4
3-(Cl)C6H4-
30min
85
5
6
4-(Cl)C6H4-
4-(CH3)C6H4-
4-(F)C6H4-
30min
40min
35min
40min
30min
8h
82
76
7
90
8
4-(CH3O)C6H4-
2-chloropyridine-
Thiophene-
69
9
92
-
-
10
11
N.R.
N.R.
C2H5OOC-
8h
N.R. no reaction
aIsolated yield
with substituents, such as 2-methyltetrahydrofuran could
form C–O bonds with excellent selectivity, and the yield
of 4-chloropentyl benzoate was 94% at room temperature
(Table 2, entry 4). The cracking rate of tetrahydropyran
ring was much slower than that of tetrahydrofuran. The
reaction of tetrahydropyran was completed in 4 h and the
yield was 81% (Table 2, entry 5). This can be explained
as the ring tension of tetrahydrofuran is larger than that of
tetrahydropyran, and the ring stability is lower; therefore,
C–O bond is more prone to fracture. The low regioselec-
tivity of products formed from epichlorohydrin may be
due to the steric efect of chlorine atoms. The ring sta-
bility of tricyclic ether, tetracyclic ether and pentacyclic
ether is lower than that of hexacyclic ether, the chemical
reaction is more vigorous, the reaction time with benzoyl
chloride is relatively short, and the yield is high. The
results showed that benzoyl chloride can react with a series
1 3

Chemical Papers
Table 4 Nano-ZnO catalyzed
cleavage of other cyclic ethers
and acyclic ethers by acyl
chloride
Entry
Ether
Acyl chloride
Product
Time (h) Yielda
(%)
1
2
2
94
2
89
3
4
5
2
2.5
4
92
95
81
6
0.5
91
7
8
2.5
3
98
65
-
-
9
24
24
N.R.
N.R.
10
N.R. no reaction
aIsolated yield
Table 5 Synthesis of chloroesters using ZnO as an efcient and reus-
with diferent aryl chlorides was studied. We frst investi-
gated the solvent-free reaction of tetrahydrofuran with acetyl
chloride at room temperature and obtained the correspond-
ing 73% yield (Table 3, entry 2). The yield of the same sub-
stituted aromatic chloride with electron-withdrawing group
is signifcantly higher than that of the electron-donating
group (Table 3, entry 5–8). The position of electron-with-
drawing also has great infuence on the yield (Table 3, entry
3–5). The higher the electron-withdrawing capacity of the
substituent, the higher the yield (Table 3, entry 5, 7). The
reaction of 4-methylbenzoyl chloride and 4-methoxybenzoyl
chloride with THF demonstrates that the higher the electron
supply, the lower the yield (Table 3, entry 6, 8).
able catalyst
Entry
Cycle
Time (min)
Yield (%)a
1
2
3
Cycle 1
Cycle 2
Cycle 3
25
25
25
95
92
87
aIsolated yield
of cyclic ethers and the product yields were medium to
good (Table 2).
To study the efect of substituents on the reactivity and
product distribution of acid chloride, the reaction of THF
1 3

Chemical Papers
Scheme 1 The mechanism of
ZnO catalyst for synthesis of
chloroesters by the cleavage of
cyclic and acyclic ethers
n
Z
R2 R1
O
O
O
R2
O
R
R
O
O
l
C
O
O
R
ma or
j
R1
R2
O
..
R
l
C
l
C
..
R1 R2
R1
l
C
m nor
i
R= H, aryl; R1= H, alkyl or aryl; R2= alkyl, aryl
To investigate the selectivity of the reaction, acylation
and cleavage reactions of 2-methyltetrahydrofuran and tet-
rahydropyran and other cyclic ethers, as well as a range of
symmetric acyclic ethers including benzyl ether, diethyl
ether, dibutyl ether and asymmetric cyclic ethers such as
tetrahydro-2-(2-propynyloxy)-2H-pyran were studied
(Table 4). With the observation of the regioselectivities
of 2-methyltetrahydrofuran products, we can also see that
the yield of aryl chloride with electron-donating groups is
slightly higher than that of aryl chloride with electron-with-
drawing groups (Table 4, entry 2–4). Other acyclic ethers,
such as benzyl ether, can be smoothly cleaved and the yield
of benzyl benzoate can reach 98% (Table 4, entry 7). For the
reaction of the unsymmetric ethers, such as tetrahydro-2-(2-
propynyloxy)-2H-pyran, it is interesting to note that the C-O
bond of the ethers was selectively cleaved (Table 4, entry
8). Ethyl ether and dibutyl ether react with benzoyl chloride
(Table 4, entry 9, 10), but no product was produced even at
room temperature for 24 h. We hypothesized that this may be
due to the absence of orbital approach onto the sp2-hybrid-
ized aromatic carbons and the lower boiling point of ethers.
On the whole, the yield of aryl chloride is better; while, aryl
chloride has more stable benzoyl radicals or acylium ions.
The reusability of ZnO was studied under optimized
reaction conditions. After the reaction, ZnO was removed
by fltration. After repeated washing with distilled water
and dichloromethane, ZnO was dried at 60 °C for 3 h for
the next catalytic cycle, and more than 80% of ZnO can
be recovered from the reaction mixture. The ideal prod-
uct was obtained by concentrating the organic layer under
reduced pressure, and the desired product was obtained
in 95% (Table 5, entry 1), 92% (Table 5, entry 2), and
87% (Table 5, entry 3) yields after one to three runs,
respectively.
Conclusion
The acylation cleavage of cyclic and acyclic ethers cata-
lyzed by nano-ZnO powder under solvent-free conditions
was developed. The method has the following advantages:
reusable catalysts, high yields, environmental friendliness
and simple operation, and essential process for the syn-
thesis of chloroesters. Hence, it is an essential comple-
ment to existing methodologies. We anticipate that our
cost-efective nano-zinc oxide catalyzed for acylative ether
cleavage will fnd broad utility.
Acknowledgements This work was partially supported by the
Fundamental Research Funds for the Central Universities (No.
2242014R30019).
Compliance with ethical standards
Conflict of interest The authors declare no competing fnancial inter-
est.
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