A highly active and recyclable catalyst for the synthesis of indole and phenyl ether

Article abstract of DOI:10.1039/c5ra16134g

A new simple catalytic system consisting of copper-aluminium and hydrotalcite (CuAl-HT) has been developed using a facile one-pot method without harm to the environment. The catalyst was characterized using TEM, XRD and XPS. It could be used as an efficient catalyst for the synthesis of both indole and phenyl ether. As expected, the catalyst afforded high catalytic activity for the selective synthesis of indole via intramolecular dehydrogenative N-heterocyclization of 2-(2-aminophenyl)ethanol. Meanwhile, it also exhibited superior catalytic properties for an Ullmann-type coupling reaction to synthesise phenyl ether from iodobenzene and phenol. The CuAl-HT catalyst showed higher activity than conventional catalysts based on copper and could be recycled several times with stable catalytic activity. This procedure has real economic advantages since no expensive materials were used.

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A highly active and recyclable catalyst for the synthesis of indole and
phenyl ether
Bo Qiaoa, Le Zhanga,b, Rong Lia*
Received (in XXX, XXX) XthXXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
A new simple catalytic system consisting of copperꢀaluminium and hydrotalcite(CuAlꢀHT)had been
developed by a facile oneꢀpot method without harm to the environment. The catalyst was characterized by
TEM, XRD and XPS. It could be used as an efficient catalyst for the synthesis of both indole and phenyl
ether. As expected, the catalyst afforded high catalytic activity for the selective synthesis of indole via
10 intramolecular dehydrogenative Nꢀheterocyclization of 2ꢀ(2ꢀaminophenyl)ethanol. Meanwhile, it also
exhibited superior catalytic property for Ullmannꢀtype coupling reaction to synthesis phenyl ether with
iodobenzene and phenol. The CuAlꢀHT catalyst showed higher activity than conventional catalysts based
on copper group and could be recycled several times with a stable catalytic activity. This procedure had
real economic advantages since one of expensive materials were used.
15
coupling reaction of phenols with aryl halides in the presence of a
catalyst containing a transition metal. It has been reported that
Pdꢀcatalyzed methods can function in this role, organicꢀinorganic
hybrid materials13 also has been used to catalysis Ullmann–type
50 coupling reaction for synthesis phenyl ether, but their high costs
and elaborate ligands are drawbacks when compared with copperꢀ
mediated reactions.14
Introduction
Benzoꢀfused Nꢀheterocyclic compounds, particularly indoles, are
important precursors for the synthesis of fine chemicals,
pharmaceuticals, dyes and agrochemicals.1 A number of methods
20 for synthesis of indoles have been developed and reviewed.2
Previously, considerable efforts have focused on the synthesis of
indoles by transitionꢀmetalꢀcatalyzed Nꢀheterocyclization of nonꢀ
amino alcohols.3 However, the synthesis of such substituted Nꢀ
heterocycles with many traditional approaches suffers from
25 requiring harsh conditions and delivering poor selectivity.
Recently, an attractive route for the synthesis of Nꢀheterocycles is
to utilize alcohols as substrates as these are readily available and
easy to handle.4 A variety of transition metals catalysts such as
ruthenium,5 iridium6 and palladium,7 nickel and copper8, have
30 been reported for the intramolecular dehydrogenative Nꢀ
heterocyclization of 2ꢀ(2ꢀaminophenyl)ethanol and derivatives.
Although the majority of reported catalytic systems are active for
this reaction, they are significantly more expensive, nonꢀ
recoverable, even long reaction time. From ecological and
35 practical points of view, the development of a reusable and less
expensive baseꢀmetal catalyst is highly desirable. Given that
oxidation of an alcohol to an aldehyde is the key step in this
route, the Cu catalyst is an attractive alternative.9
Herein, we designed and prepared CuAlꢀHT catalysts with three
different contents of copper and aluminum, and their applications
55 for the synthesis of indole and phenyl ether. The catalyst can
successfully promote the oxidantꢀfree dehydrogenation of various
alcohols under liquidꢀphase conditions. This feature would
increase the scope of this oxidative intramolecular oxidative
cyclization and allow us to prepare Nꢀheterocycles using
60 substrate containing alcohol functionality. Meanwhile, the
catalysts afforded excellent yields of diaryl ethers in the
Ullmannꢀtype coupling reaction to synthesis phenyl ether with
iodobenzene and phenol. It is important to note that the CuAlꢀHT
catalyst could be recycled by a simple filtration of the reaction
65 solution and used for 6 consecutive trials without significant loss
of its reactivity. What more, this material is easy to achieved, and
is no harmless to the environment.
Experimental
Materials
On the other hand, aryl carbonꢀoxygen forming reactions are
40 important transformations in synthetic chemistry.10The formation
of diaryl ethers via a CꢀO crossꢀcoupling reaction represents a
powerful and straightforward method in organic synthsis.11 Diaryl
ethers are not only important structures in biological systems , but
also common moieties in pharmaceutical research and materials
45 interest.12Common synthesis of diaryl ethers usually requires the
70 Copper(ii) nitrate hydrate, aluminum nitrate nonahydrate, sodium
hydroxide,
potassiumcarbonate, calciumchloride, toluene, dimethylsulfoxide,
dioxane, dimethyl formamide, oꢀxylene, acetonitrile,
potassiumhydroxide,
sodiumcarbonate,
tetrahydrofuran, sodiumbicarbonate, copperacetate and copper
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powder were purchased from Sinopharm Chemical Reagent Co.,
Ltd. Various reaction reagents, such as 2ꢀ(2ꢀaminophenyl)ethanol,
sodium isopropyl alcohol, phenol, iodobenzene, pꢀ
iodonitrobenzene, pꢀcresol, pꢀiodoanisole, pꢀmethoxyphenol, pꢀ
chlorophenol and were purchased from Alfa Aesar. All chemicals
were of analytical grade and used as received without further
purification. Deionized water was used throughout the
experiments.
analysis. For recycling, the recovered catalyst was washed with
methanol several times, and then dried under vacuum at 60 °C.
Results and discussion
5
60 Characterization of catalysts
The phase composition and structure of the catalysts were
determined by XRD. Fig. 1 showed the XRD pattern between 10°
and 85° of the catalysts. Bragg’s reflections at 2θ value of 43.5°,
50.6°, 74.4° represented (111), (200), (220) planes of fcc crystal
65 structure of metal copper. The sharp and strong peaks revealed
that Cu nanoꢀcrystals were highly oriented.
Preparation of CuAl-HT catalysts
10 CuAlꢀHT3 (Cu: Al=3:1) is prepared as follows: About 100 mL of
deionized water was taken into a 250 mL three neck round
bottom flask and stirred at 25 °C with a overhead mechanical
stirrer. A mixture of solution of Cu(NO3)2·3H2O (16.46g, 0.0702
moles) and Al(NO3)3·9H2O (8.44g, 0.0225 moles) in deionised
15 water were added simultaneously dropꢀwise from the respective
burettes into the round bottomed flask. The pH of the reaction
mixture was maintained constantly (8ꢀ9) by the continuous
addition of the base solution (NaOH/Na2CO3). The resulting
slurry was washed with distilled water thoroughly to give a pH of
20 7 and separated by filtration. The collected sample(Cu2+AlꢀHT3
(Cu: Al=3:1)) was dried at 70°C for 12 h, and then treated in a
20% H2/N2 flow (100 cmꢀ3 gꢀ1 minꢀ1) at 300°C(ramping rate, 5°C
minꢀ1) for 2 h and passivation (0.1% O2/N2, 40 cmꢀ3 gꢀ1 minꢀ1) at A
Headings are the primary heading type ambient temperature for 4
25 h. CuAlꢀHT2 (Cu: Al=2:1) and CuAlꢀHT3 (Cu: Al=1:1) were
prepared using the same procedure.
Characterization of catalysts
Fig. 1 XRD pattern of the catalysts: (a) CuAlꢀHT1; (b) CuAlꢀHT2; (c)
All of the reagents and solvents were commercially available and
used without further purification. XRD measurements were
30 performed on a Rigaku D/maxꢀ2400 diffractometer using CuꢀKα
radiation as the Xꢀray source in the 2θ range of 10ꢀ85°. The
conversion was estimated by GC (P.E. AutoSystem XL) or GCꢀ
MS (Agilent 6,890N/5,973N). CuꢀAl content of the catalyst was
measured by inductively coupled plasma (ICP) on IRIS
35 Advantage analyzer. The morphology of the catalyst was
observed by a Tecnai G2 F30 transmission electron microscopy
and samples were obtained by placing a drop of a colloidal
solution onto a copper grid and evaporating the solvent in air at
room temperature. Inductively coupled plasma (ICP)
40 measurement indicated that it contented 66.58% Cu and 9.84%
Al2O3 in CuAlꢀHT3, as it contented 59.44% Cu and 12.80%
Al2O3 in CuAlꢀHT2, 45.20% Cu and 19.86% Al2O3 in CuAlꢀHT1.
CuAlꢀHT3.
70 To further probe the morphology of the catalyst, we used TEM
measurement to analysis the catalysts. Fig. 2 showed the TEM
images of the catalysts, in which wellꢀdispersed copper
nanoparticles could be observed clearly. The differences in
synthesis conditions and the contents of Cu(NO3)2·3H2O and
75 Al(NO3)3·9H2O affected the particle size of copper nanoparticles.
The TEM images in Fig. 2 showed the copper particle size in the
range of 10ꢀ30 nm for all of the asꢀprepared catalysts. This
indicated that copper nanoparticles were uniformly distributed in
the hydrotalcite, which was advantageous for the catalytic
80 activity.
Catalytic tests
Dehydrogenative reaction
45 Under nitrogen atmosphere, 10 mL roundꢀbottomed flask was
charged with 2ꢀ(2ꢀaminophenyl)ethanol (0.5 mmol), KOꢀtꢀBu
(0.5mmol), CaCl2 (0.25 mmol), oꢀxylene (4.0 mL) and catalyst
(0.1 g). The reaction was performed at 140°C for 12 h and was
monitored by GC analysis. For recycling, the recovered catalyst
50 was washed with methanol several times, and then dried under
vacuum at 60 °C.
Fig. 2TEM micrograph of the catalysts:(A)CuAlꢀHT1, (B)CuAlꢀHT2;
(C)CuAlꢀHT3.
Fig. 3 presented XPS elemental survey scans of the surface of the
85 CuAlꢀHT3 catalyst (CuAlꢀHT1 and CuAlꢀHT2 are similar to
CuAlꢀHT3). Peaks corresponding to copper, aluminum oxide
could be clearly observed. To ascertain the oxidation state of Cu,
Al2O3, Xꢀray photoelectron spectroscopy (XPS) studies were
carried out. The XPS analysis of the spent Cu(0) and Al2O3 were
90 shown in the Fig. 3b, c. And, as expected, the spectrum of the Cu
Ullmann-type coupling reaction
Under nitrogenatmosphere, 10 mL roundꢀbottomed flask was
charged with phenol (1.0mmol), iodobenzene (1.0mmol), KF (2.0
55 mmol), DMSO (4.0 mL) and catalyst (0.2mmol). The reaction
was performed at 135°C for 16 h and was monitored by GC
2
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region confirmed the presence of Cu(0) with a peak binding
energy of 952.5 eV and 932.7 eV, while Al2O3 with a peak
binding energy of 74.4 eV.
Table 1 Effect of solvent, temperature and time reactiona.
Entry
solvent
MeCN
Toluene
DMSO
Dioxane
DMF
T [°C]/t(h)
60/24
Yield [%]b
1
2
3
4
5
6
7
8
39
1
100/20
140/12
140/12
140/12
70/12
84
32
4
THF
trace
100
12
oꢀxylene
oꢀxylene
140/12
100/12
a Reaction conditions: 2ꢀ(2ꢀaminophenyl)ethanol (0.5mmol), KOꢀtꢀBu
(0.5mmol), CaCl2 (0.25 mmol), CuAlꢀHT2 (0.1 g), under 1 atm of N2.
20 b Determined by GC.
The reaction was carried out using 0.5 molar amounts of 2ꢀ(2ꢀ
aminophenyl)ethanol in oꢀxylene (4 mL) in the presence of CuAlꢀ
HT2 as catalyst under different bases. The results were
summarized in Table 2. The results of these reactions showed that
25 KOꢀtꢀBu was much more effective and lead to better yields
(Table 2, entry 8). Other bases, such as Na2CO3 and NaHCO3,
were also effective (Table 2, entries 4, 6), while KOH, NaOH and
K2CO3 were not (Table 2, entries 2, 3, 5). In contrast, the yield of
indole was increased by the addition of Lewis acidic additive
30 (CaCl2) (Table 2, entries 1, 8). The result indicated that CaCl2
played a great role on the Nꢀheterocyclization reaction.
Table 2 Effect of base and additive reaction a.
Entry
base
KOꢀtꢀBu
KOH
Additive
None
Yield [%]b
1
2
3
4
5
6
7
8
61
63
15
99
25
96
96
100
CaCl2
CaCl2
CaCl2
CaCl2
CaCl2
CaCl2
CaCl2
NaOH
5
Fig. 3 XPS of the catalysts (a)CuAlꢀHT3; (b) CuAlꢀHT3 showing Cu
2p1/2and Cu 2p3/2 binding energies, and CuAlꢀHT3 showing Al 2p binding
energies
Na2CO3
K2CO3
NaHCO3
none
Catalysts used for indole synthesis
Table
1 presented the influence of solvent on the Nꢀ
10 heterocyclization reaction for the synthesis of indole over CuAlꢀ
HT2 at different temperature and time. It was observed that the
reaction provided a good yield with the use of DMSO and oꢀ
xylene as a solvent, employing best results with oꢀxylene (100 %
yield) (Table 1, entries 1ꢀ7), which was then employed for further
15 study. According to the experimental data, the yield of indole at
140°C was obviously higher than 100°C (Table 1, entries 7ꢀ8).
KOꢀtꢀBu
a Reaction conditions: 2ꢀ(2ꢀaminophenyl)ethanol (0.5 mmol), KOꢀtꢀBu
(0.5 mmol), CaCl2 (0.25 mmol), oꢀxylene (4.0 mL) and CuAlꢀHT2 (0.1
35 g), 140 °C, 12h, under 1atm of N2.
b Determined by GC.
Finally, the catalytic activity for the Nꢀheterocyclization reaction
was compared among various catalysts (Table 3). CuAlꢀHT2
showed the highest catalytic activity and gave the corresponding
40 product in 100% yield under the present conditions (Table 3,
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entry10). The reaction was not easily proceeded in the absence of
the catalyst, or in the presence of Cu(AcO)2, CuCl2, CuCl, Cu
powder, Ni45Cu10, Cu/Al2O3 and Cu2+AlꢀHT2 (Table 3, entries 1ꢀ
8). A series of CuꢀAl catalysts with different Cu/Al mass ratio
(Table 3, entries 9, 10, 13) were tested their activity for the
reaction. Out of the CuAlꢀHT catalysts with CuAlꢀHT1, CuAlꢀ
HT2 and CuAlꢀHT3, CuAlꢀHT2 catalyst was found to be the
most effective catalyst for the Nꢀheterocyclization reaction.
Meanwhile, the catalyst revealed a remarkable activity and was
10 reused up to four consecutive cycles without an appreciable loss
of its high catalytic performance (Table 3, entry11). This result
might be due to the Cu nanoparticles on surface of catalyst were
partially oxidized. Furthermore, the reaction was catalyzed by
CuAlꢀHT2 proceeded even in air to give indole in a yield of 83%
15 (Table 3, entry12).
5
30 Table 4 The substrate extension
Entry
substrates
Yield [%]
1
2
3
4
5
6
5ꢀH
5ꢀMe
100
99
94
99
95
94
5ꢀCO2Me
5ꢀMeO
5,6ꢀ(MeO)
6ꢀMeO
Table 3 Nꢀheterocyclization of 2ꢀ(2ꢀaminophenyl)ethanol using various
catalystsa
Entry
1
Catalyst
none
Yield [%]b
63
a Reaction conditions: alcohols (0.5 mmol), KOꢀtꢀBu (0.5 mmol), CaCl2
(0.25 mmol), oꢀxylene (4.0 mL) and CuAlꢀHT2 (0.1 g), 140 °C, 12h,
under 1atm of N2.
2
Cu(AcO)2
CuCl2
26
b Determined by GC.
3
14
35
4
CuCl
16
The separation and recovery of the catalyst from the reaction
system is one of the most important issues, the reusability of
CuAlꢀHT2 was further investigated. To make the synthetic
protocol more economical, recyclability study of the catalyst was
40 examined for the synthesis of indole via dehydrogenative Nꢀ
heterocyclization (Fig. 4). We observed that the catalyst was
highly active under the present reaction conditions and could be
effectively reused for six consecutive recycles.
5
Cu powder
69
16
6
Ni45Cu10
66
7
Cu/ Al2O3
Cu2+AlꢀHT2
CuAlꢀHT1
CuAlꢀHT2
CuAlꢀHT2
CuAlꢀHT2
CuAlꢀHT3
67
8
58
9
98
10
11
12
13
100
91 c
83 d
97
a Reaction conditions: 2ꢀ(2ꢀaminophenyl)ethanol (0.5 mmol), KOꢀtꢀBu
(0.5 mmol), CaCl2 (0.25 mmol), oꢀxylene (4.0 mL) and catalyst (0.1 g),
20 140 °C,12h, under 1 atm of N2.
b Determined by GC.
c Yield after fifth cycle.
d Reaction in air.
We had investigated the reactions using a variety of alcohols as
25 the substrates under the reaction conditions and the results were
summarized in Table 4. It could be concluded that all of the
electronꢀneutral, electronꢀrich and electronꢀpoor alcohols could
be reaction very well to generate indoles production excellent
yields under the standard reaction conditions.
45
Fig.4 Catalyst recyclability study.
From these essential observations and discussions on CuꢀAl
based catalyst, we proposed a catalytic cycle in Scheme 1 for the
selective direct synthesis of indole via intramolecular
dehydrogenative
Nꢀheterocyclization
of
2ꢀ(2ꢀ
50 aminophenyl)ethanol using CuAlꢀHT2 catalyst, and named it as
15
“borrowing hydrogen” mechanism.5,
The first step of the
reaction would involve the oxidation of an alcohol to the
corresponding carbonyl compound and a hydrido CuꢀAl species.
The catalyst with KOꢀtꢀBu slightly increased the initial step of the
4
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reaction. Then the carbonyl intermediate would readily cyclize to
afford indole via intramolecular nucleophilic attract of amino
group to carbonyl carbon followed by dehydration. A Lewis acid
(CaCl2) may promote the formation of indole.39 Considering the
result in Table 2, that CaCl2 with higher Lewis acidity played a
great role on the Nꢀheterocyclization reaction. From the angle of
reaction equilibrium, the removal of water (by anhydrous CaCl2)
clearly helped to drive the reaction towards indole production.
Release of hydrogen in the reaction of the hydrido CuꢀAl could
indicated that KF played a great role on the Ullmannꢀtype
coupling reaction.
5
35 Table 6 Effect of base
Entry
1
base
KF
Yield [%]b
95
2
3
4
5
6
7
8
KOH
NaOH
Na2CO3
K2CO3
NaHCO3
none
46
43
51
83
47
36
53
10 regenerate the catalytic active CuꢀAl species.
OH
H2
M
NH2
KO-t-Bu
O
H
H
M
H-M-H
NH2
Cs2CO3
O
CaCl2
aReaction conditions: Phenol (1.00 mmol),iodobenzene (1.00 mmol),
CuAlꢀHT2 (0.02g, contains 0.2 mmol of Cu), DMSO (4 mL) at 135oC
stirring for 16 h.
N
NH2
H
M=Cu-Al
bDetermined by GC.
Scheme. 1 A possible “borrowing hydrogen” mechanism.
Catalysts used for phenyl ether synthesis
40 Whereafter, the catalytic activity for the Ullmannꢀtype coupling
reaction was compared among various catalysts (Table 7). CuAlꢀ
HT3 showed the highest catalytic activity and gave the
corresponding product in 94% yield under the present conditions
(Table 7, entry11). The reaction was not easily proceeded in the
45 absence of the catalyst, or in the presence of Cu(AcO)2, CuCl2,
CuCl, Cu powder, Ni45Cu10, Cu/Al2O3 and Cu2+AlꢀHT3 (Table 7,
entries 1ꢀ8). A series of CuꢀAl catalysts with different Cu/Al
mass ratio (Table 7, entries 9, 10) were tested their activity for the
reaction. Out of the CuAlꢀHT catalysts with CuAlꢀHT1, CuAlꢀ
50 HT2 and CuAlꢀHT3, CuAlꢀHT3 catalyst was found to be the
most effective catalyst for the Ullmannꢀtype coupling reaction.
Table 5 presented the influence of solvent on the Ullmannꢀtype
15 coupling reaction for synthesis phenyl ether over CuAlꢀHT3 at
different temperature and time. It was observed that the reaction
provided a good yield with DMSO as solvent, employing best
results with DMSO (95 % yield) (Table 5, entries 5ꢀ3), which
was then employed for further study. According to the
20 experimental data, the yield of phenyl ether at 135°C is obviously
higher.
Table 5 Effect of solvent, temperature and time reactiona.
Entry
solvent
MeCN
Toluene
DMSO
Dioxane
DMF
T [°C]/t(h)
70/24
Yield [%]b
trace
trace
95
Table 7 Ullmannꢀtype coupling reaction using various catalysts a
1
2
3
4
5
6
7
Entry
Catalyst
none
Yield [%]b
100/20
135/16
90/16
1
2
10
38
16
13
60
58
72
58
90
91
94
Cu(AcO)2
CuCl2
3
10
4
CuCl
130/16
60/16
55
5
Cu powder
Ni45Cu10
Cu/ Al2O3
Cu2+AlꢀHT3
CuAlꢀHT1
CuAlꢀHT2
CuAlꢀHT3
THF
trace
trace
6
oꢀxylene
140/16
7
a Reaction conditions: Phenol (1.00 mmol),iodobenzene (1.00 mmol),
CuAlꢀHT2 (0.02g contains 0.2 mmol of Cu), KF (2.00 mmol) in DMSO
25 (4 mL) at 135oC stirring for 16 h.
8
9
10
11
b Determined by GC.
The reaction was carried out using 1 mole of phenol DMSO (4
mL) in the presence of CuAlꢀHT3 as catalyst under different
bases. The results were summarized in Table 6. The results of
30 these reactions showed that KF was much more effective and lead
to better yield (Table 6, entry 1). Other bases, such as Na2CO3
and Cs2CO3, were also effective (Table 6, entries 4, 8). The result
a Reaction conditions: Phenol (1.00 mmol), iodobenzene (1.00 mmol), KF
(2.00 mmol) in DMSO (4 mL) at 130oC stirring for 16 h.
55 b Determined by GC.
We had investigated the reactions using a variety of aryl iodides
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and phenols as the substrates under the reaction conditions and
the results were summarized in Table 8. It could be concluded
highly efficient, recyclable heterogeneous catalyst for the
dehydrogenative Nꢀheterocyclization of 2ꢀ(2ꢀ
that all of the electronꢀneutral, electronꢀrich and electronꢀpoor 25 aminophenyl)ethanol in the presence of base and a catalytic
aryl iodides could be reaction with phenol very well to generate
the corresponding crossꢀcoupling production excellent yields
under the standard reaction conditions.
amount of Lewis acidic. The present catalytic system would
provide a new and useful method for the synthesis of various Nꢀ
Heterocyclic compounds. And also we found an efficient and
economic catalyst system for the Ullmann phenyl ether by using
30 the CuAlꢀHT3 as the catalyst in DMSO. The crossꢀcoupling
reactions of phenols with iodobenzene generated the
corresponding coupling products with excellent yields at the
present reaction conditions. Furthermore, the CuAlꢀHT can be
recovered and recycled by a simple filtration of the reaction
35 solution and used for 6 consecutive trials without decreases in
activity.
5
Table 8 The substrate extension
Entry
Phenol
Aryl iodide
pꢀCH3OC6H4I
C6H5I
Yield [%]b
1
2
3
4
5
6
7
8
9
C6H5OH
88
94
98
91
90
98
92
88
98
C6H5OH
C6H5OH
pꢀNO2C6H4I
pꢀCH3OC6H4I
C6H5I
pꢀCH3C6H4OH
pꢀCH3C6H4OH
pꢀCH3C6H4OH
pꢀClC6H4OH
pꢀClC6H4OH
pꢀClC6H4OH
Acknowledgements
The authors are grateful to Projects in Gansu Province Science and
Technology Pillar Program (1204GKCA047), and the Key Laboratory of
40 Catalytic engineering of Gansu Province, China Gansu Province for
financial support.
pꢀNO2C6H4I
pꢀCH3OC6H4I
C6H5I
Notes and references
a College of Chemistry and Chemical Engineering Lanzhou University,
The Key Laboratory of Catalytic engineering of Gansu Province,
45 Lanzhou 730000, China, Fax: +86 0931 891 2582, Tel.: +86 0931 891
2311,Eꢀmail: liyirong@lzu.edu.cn (R. Li).
pꢀNO2C6H4I
a Reaction conditions: Phenol (1.00 mmol), aryl iodide (1.00 mmol),
CuAlꢀHT2 (0.02g, contains 0.2 mmol of Cu), KF (2.00 mmol) in DMSO
b Department of Chemical Engineering, College of Jiu quan Vocational
Technology, Jiu quan ,735000, China
10 (4 mL) at 135oC stirring for 16 h.
b Determined by GC.
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The separation and recovery of the catalyst from the reaction
system was one of the most important issues, the reusability of
CuAlꢀHT3 was further investigated. To make the synthetic
15 protocol more economical, recyclability study of the catalyst was
examined for the synthesis phenyl ether via Ullmannꢀtype
coupling reaction (Fig. 5). We observed that the catalyst was
highly active under the present reaction conditions and could be
effectively reused for six consecutive recycles.
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