Efficient and Reusable Sn(II)-containing Imidazolium-based Ionic Liquid as a Catalyst for the Oxidation of Benzyl Alcohol

Article abstract of DOI:10.1002/jccs.201600286

A simple and efficient catalytic system [BBIM]Br–SnCl₂ for the oxidation of benzyl alcohol using hydrogen peroxide as the oxidant has been developed. Reaction conditions such as the catalyst dose, the solvents, reaction temperature, reaction time, and the amount of hydrogen peroxide were investigated. The optimum reaction conditions identified were 0.11 g of catalyst, no solvent, 65°C, 15 min, and 2 mmol of hydrogen peroxide. Oxidation of various alcohols was also investigated under the optimized conditions. The catalyst [BBIM]Br–SnCl₂ can be easily recovered and reused for six reaction runs without significant loss of catalytic activity, because the Sn species of the catalyst can be coordinated with the imidazole ring of the ionic liquid. The reused catalyst was further characterized by Fourier transform infrared spectroscopy to evaluate its chemical properties. The results proved that the [BBIM]Br–SnCl₂ catalyst was stable and reusable for the oxidation reactions. A possible mechanism for the oxidation of benzyl alcohol to benzaldehyde is proposed.

Full text of DOI:10.1002/jccs.201600286

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
Efficient and Reusable Sn(II)-containing Imidazolium-based Ionic Liquid as a Catalyst
for the Oxidation of Benzyl Alcohol
a
a
a
a
Bingtong Wang,a,b Yulin Hu, Dong Fang, Lin Wu and Rong Xing
*
aCollege of Chemical and Environmental Engineering, Yancheng Teachers University, Jiangsu 224002, China
bCollege of Chemistry and Chemical Engineering, Nanjing Tech University, Jiangsu 210009, China
(Received: August 5, 2016; Accepted: September 29, 2016; DOI: 10.1002/jccs.201600286)
A simple and efficient catalytic system [BBIM]Br–SnCl2 for the oxidation of benzyl alcohol using
hydrogen peroxide as the oxidant has been developed. Reaction conditions such as the catalyst
dose, the solvents, reaction temperature, reaction time, and the amount of hydrogen peroxide were
investigated. The optimum reaction conditions identified were 0.11 g of catalyst, no solvent, 65ꢀC,
15 min, and 2 mmol of hydrogen peroxide. Oxidation of various alcohols was also investigated
under the optimized conditions. The catalyst [BBIM]Br–SnCl2 can be easily recovered and reused
for six reaction runs without significant loss of catalytic activity, because the Sn species of the cata-
lyst can be coordinated with the imidazole ring of the ionic liquid. The reused catalyst was further
characterized by Fourier transform infrared spectroscopy to evaluate its chemical properties. The
results proved that the [BBIM]Br–SnCl2 catalyst was stable and reusable for the oxidation reac-
tions. A possible mechanism for the oxidation of benzyl alcohol to benzaldehyde is proposed.
Keywords: Ionic liquid; Tin(II) chloride dihydrate; Benzyl alcohol; Solvent-free oxidation.
INTRODUCTION
The selective oxidation of alcohols into aldehydes
investigate and prepare cheap, abundant, and eco-
friendly heterogeneous or homogeneous catalysts with
promising catalytic performance.
or ketones is one of the fundamental transformations in
laboratory synthesis and industrial production,1–4
because aldehydes and ketones can serve as important
chemicals for the synthesis of perfumes, pharmaceuticals,
dyes, fragrances, and organic intermediates in fine chemi-
cals industries. Therefore, investigations on the liquid-
phase oxidation of benzyl alcohol to benzaldehyde, used
as a versatile intermediate in synthetic chemistry, have
been widely pursued.5 It is generally known that a suita-
ble catalyst plays an essential role in these oxidation
reactions. Various chemical reagents used as the catalysts
have been applied for this transformation efficiently and
selectively, including inorganic oxidants,1,6–8 supported
metals,9–15 copper(II) complexes,16–19 bipyridine–
heteropolyacid hybrid,20 Pd(OAc)2/ionic liquid,21 hetero-
poly acid/ionic copolymer,22 Au25(SPh-pNH2)17/SBA-
15,23 CoMgAl hydrotalcites,24 and a photocatalyst.25
From the viewpoint of green chemistry, a promising oxi-
dation process should take place at atmospheric pressure
under solvent-free and base-free conditions. On this
account, there exists still opportunity for researchers to
Ionic liquids (ILs) have attracted considerable
attention since the discovery of air- and water-stable
ILs by Wilkes and Zaworotko in 1992.26 They are
promising candidates for developing green chemical
processes for fine chemicals syntheses, and exhibit
favorable properties such as very low volatility, a wide
liquid temperature range, thermal stability, good electri-
cal conductivity, excellent electrochemical properties,
ease of recyclability, and catalytic ability.27–35 ILs pos-
sess the significant ability to solubilize organic and inor-
ganic reagents and form the homogeneous or biphasic
reaction systems.36 Based on this point, they usually
serve as reaction media in a wide range of organic reac-
tions. From the viewpoints of practical and fundamen-
tal research, functionalization of ILs with various
groups has been attempted with particular interest in
catalysis. Recently, the metal-containing ILs were
found to be promising catalytic materials, which have
the textural porosities of ionic liquids and simultane-
ously the advantages of the catalytic properties of metal
*Corresponding author. Email: xingrr@126.com
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Article
Wang et al.
salts/oxides.37,38 Among the metal-containing ionic
liquids, chlorometallate ILs are often employed as
Lewis-acidic catalysts.39,40 Very recently, the iron chlo-
ride ionic liquid/SBA-15 was applied as a catalyst for
the oxidation of benzyl alcohol with hydrogen peroxide
(H2O2).41
O
H
[BBIM]Br-SnCl2
OH
H2O2, 65ºC, 15min
N
N
H2O2 is a clean and environmentally friendly
oxidant because it can produce highly active oxygen
species, and is widely applied in liquid-phase oxida-
tion reactions.42 Moreover, this oxidant is also readily
available and is much cheaper and safer than most
other organic and inorganic oxidants owing to pro-
duction of only water during the oxidation processes.6
Compared to other transition- and noble metal salts,
tin(II) dichloride is commercially inexpensive and eas-
ily obtainable, and can be applied directly as a cata-
lyst in various organic transformations or modified
on the various carriers used as the heterogeneous
catalysts.43–48 To the best of our knowledge, little
work have been reported on the tin-containing 1,3-di-
n-butylimidazolium bromide ([BBIM]Br) IL and its
application to the oxidation of benzyl alcohol to
benzaldehyde. In this work, we report a simple and
inexpensive protocol for the efficient oxidation of
benzyl alcohol with H2O2 in the presence of the
[BBIM]Br–SnCl2 as a separable and reusable catalyst
under solvent-free conditions (Scheme 1). The Sn spe-
cies of the catalyst can be coordinated with the imid-
azole ring of the [BBIM]Br. All the preparation
methods used are simple, cost-effective, and less time
consuming.
SnCl2 Br
[BBIM]Br-SnCl2
Scheme 1. Catalytic oxidation of benzyl alcohol to
benzaldehyde.
selectivity of benzaldehyde. However, the [BBIM]Br–
SnCl2, with the advantages of both the IL and the
metal salt, significantly enhanced the catalytic activity
and led to complete conversion and a selectivity of
95.1% (Table 1, entry 5), indicating a clear synergic
effect in comparison with a single species. The oxida-
tion of benzyl alcohol did not effectively take place
using the [BBIM]Br–FeCl2 or [BBIM]Br–CuCl as the
catalyst at the temperature range 0–65ꢀC (Table 1,
entries 6 and 7). At the beginning of the reaction, the
rapid self-decomposition of H2O2 was observed. It is
speculated that isolated iron(II) or copper(I) species
was responsible this phenomenon. That means that
the oxygen released during the H2O2 decomposition
process played no role in the oxidation of benzyl alco-
hol, leading to the extremely low conversion of benzyl
alcohol. The [BBIM]Br–AgCl displayed very low
activity with a conversion of 2.1% (Table 1, entry 8).
In this reaction, there was no obvious self-
decomposition of H2O2. So the very low conversion
meant that there was no synergic effect between
[BBIM]Br–AgCl and H2O2. These findings implied
that the metal species of the catalyst played a key role
in the oxidation reactions using H2O2 as an oxidant
under solvent-free conditions. On the basis of the
above results, [BBIM]Br–SnCl2 was chosen as the
model catalyst for further investigation.
RESULTS AND DISCUSSION
Catalytic performance of various catalysts
We first investigated the catalytic performance of
various metal-containing ILs in the oxidation of ben-
zyl alcohol using H2O2 as the oxidant under solvent-
free conditions. The results are summarized in
Table 1. The oxidation reaction did not occur over
[BBIM]Br (Table 1, entry 1), indicating that it was
catalytically inactive. SnCl2 was also found to be of
very low activity with a conversion of 2.6% (Table 1,
entry 2). The oxidation of benzyl alcohol was cata-
lyzed by the introduction of [BBIM]Br followed by
SnCl2 or by the introduction of SnCl2 followed by
[BBIM]Br, respectively (Table 1, entries 3 and 4), and
both gave low conversion of benzyl alcohol and poor
Optimization of oxidation conditions
The nature of the solvents can have a dramatic effect
on the catalytic activity. So the effect of the solvents on
the catalytic performance of [BBIM]Br–SnCl2 in the oxi-
dation of benzyl alcohol with H2O2 was investigated. In
Table 2, the effect of no solvent, organic solvents, and
2
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Efficient and Reusable Sn(II)-containing Imidazolium-based Ionic Liquid
Table 1. Comparison of the catalytic activity of various metal-containing ionic liquid catalysts1
Entry
Catalyst
T/ꢀC
Conv. /(%)2
Sel. /(%)2
1
2
3
4
5
6
7
8
[BBIM]Br
SnCl2
[BBIM]Br + SnCl2
65
65
65
65
4.6
2.6
31.5
36.4
100
5
Trace
Trace
67.1
55.2
95.1
Trace
Trace
Trace
3
SnCl2 + [BBIM]Br4
[BBIM]Br–SnCl2
[BBIM]Br–FeCl2
[BBIM]Br–CuCl
[BBIM]Br–AgCl
65
0–65
0–65
65
Trace
2
1 Reaction conditions: benzyl alcohol (1.5 mmol), catalyst (0.11 g), H2O2 (30%, 2 mmol), 65ꢀC, 15 min.
2 GC analysis.
3 By introduction of [BBIM]Br followed by SnCl2.
4 By introduction of SnCl2 followed by [BBIM]Br.
water on the conversion and selectivity is summarized.
The reaction system exhibited the lowest catalytic activity
with a conversion of 16% in water. Organic solvents
including dimethyl sulfoxide (DMSO), ethanol, acetoni-
trile (CH3CN), dichloromethane (CH2Cl2), and dimethyl-
formamide (DMF) used in the oxidation reaction did not
show any appreciable performance in comparison with
the solvent-free system, which gave a complete conversion
and a selectivity of 95.1%. It is speculated that the high
catalytic performance of [BBIM]Br–SnCl2 under solvent-
free condition is due to the significant ability to solubilize
H2O2 and then form easily Sn peroxo complex (I) species
(see the following mechanism). This is beneficial to the
reaction of the substrates.
when 0.06 g of the catalyst was used for the oxidation
of benzyl alcohol at the same conditions, the catalyst
gave a conversion of 69% and a selectivity of 90%,
respectively, which is due to the fewer catalytic sites
within a lower amount of the catalyst. On increasing
the catalyst dose from 0.06 to 0.11 g, the complete con-
version of benzyl alcohol and the highest selectivity of
95.1% were obtained. On increasing the catalyst dose
further in the range 0.11–0.6 g, complete conversion of
benzyl alcohol was still obtained, but the selectivity of
benzaldehyde decreased slightly. This indicates that an
excess amount of the catalyst led to further oxidation of
benzaldehyde to benzoic acid.49 The results led to the
optimum catalyst dose as 0.11 g.
The catalyst dose can significantly affect both the
conversion and selectivity in the oxidation reaction of
benzyl alcohol to benzaldehyde. As Figure 1 shows,
It is well known that the reaction temperature
influences greatly the reaction rate and the catalytic
properties of the catalysts. Therefore, the effect of the
reaction temperature ranging from 45 to 75ꢀC was
investigated for the oxidation benzyl alcohol to benzal-
dehyde with H2O2. The results are shown clearly in
Figure 2. On increasing the reaction temperature from
45 to 65ꢀC, the conversion of benzyl alcohol increased
significantly from 20.5 to 100%, and the selectivity of
benzaldehyde increased from 84.7 to 95.1%. However,
the selectivity of benzaldehyde gradually reduced to be
87.1% at complete conversion when the reaction tem-
perature was increased from 65 to 75ꢀC. The result
shows that a higher temperature is disadvantageous to
a higher selectivity of benzaldehyde, which could be
further oxidized to benzoic acid.
Table 2. Effects of various solvents on the oxidation of
benzyl alcohol1
Conv.
/(%)2
Sel.
Entry Catalyst
Solvent
/(%)2
1
2
3
4
5
6
7
[BBIM]Br–
SnCl2
–
100
16
46
95.1
84
81
50
80
H2O
CH2Cl2
Ethanol 34
DMF
DMSO
18.8
67.5
85
62
CH3CN 38
1 Reaction conditions: benzyl alcohol (1.5 mmol), catalyst
(0.11 g), H2O2 (30%, 2 mmol), 65ꢀC, 15 min, solvent (1 mL).
2 GC analysis.
The amount of H2O2 applied in the reaction is a
vital factor influencing the progress of benzyl alcohol
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Wang et al.
Conversion
Selectivity
benzyl alcohol was unchanged, but the selectivity of
benzaldehyde decreased slightly. This implied that a
small amount of benzaldehyde may be further oxidized
to benzoic acid by the excess amount of H2O2 and cata-
lyst. The above results suggested that 2 mmol of H2O2
was optimal for the oxidation reaction.
100
80
60
40
20
0
The effect of reaction time was also investigated.
As seen in Figure 4, benzyl alcohol conversion
increased from 75 to 100%, and the selectivity of benz-
aldehyde increased from 86 to 95.1% as the reaction
time was increased from 10 to 15 min. However, when
the reaction time was further increased from 15 to
30, 45, and 60 min, respectively, a slight decrease of the
selectivity of benzaldehyde was observed. The results
showed that the optimum reaction time was 15 min.
0.06
0.11
0.2
0.4
0.6
Catalyst Mass (g)
Fig. 1. Effect of the catalyst dose on the oxidation
reaction of benzyl alcohol to benzaldehyde.
Study of various alcohols
Reaction
conditions:
benzyl
alcohol
(1.5 mmol), H2O2 (30%, 2 mmol), 65ꢀC.
To investigate the generality of the catalytic activ-
ity of [BBIM]Br–SnCl2, it was further applied to the
oxidation reactions of a range of benzyl alcohols and
their derivatives under the optimized conditions. As
seen from Table 3, benzyl alcohols with the electron-
donating or -withdrawing substituents were converted
to the corresponding aldehydes with high conversion
and selectivity by prolonging the reaction time or
increasing the reaction temperature, indicating that the
catalyst [BBIM]Br–SnCl2 shows good catalytic activity
for substituted aromatic alcohols. It is worth noting that
the inactive benzhydrol would be also be suitable to the
system and gave excellent conversion (>99%) and selec-
tivity (99%), suggesting that the steric hindrance of the
substituent groups has no effect on the catalytic activity.
Unfortunately, the inactive phenethyl alcohol and cyclo-
hexanol showed a low reaction activity and gave lower
selectivity even when the reaction time was increased.
oxidation. As is shown in Figure 3, the influence of the
amount of H2O2 was investigated by varying the
amount of H2O2 from 1 to 6 mmol. As expected, as
the amount of H2O2 was increased from 1 to 2 mmol,
the conversion of benzyl alcohol increased from 48.5 to
100%, and the selectivity of benzaldehyde increased
from 89.3 to 95.1%. With further increase of the
amount of H2O2 from 2 to 6 mmol, the conversion of
100
80
60
Conversion
Selectivity
40
Reusability of the catalyst
From the viewpoint of practical application, recy-
clability of the catalyst is very important. Recycling
experiments of the oxidation reaction of benzyl alcohol
with H2O2 under solvent-free conditions were per-
formed. As shown in Figure 5, even after the sixth cycle
of the oxidation reaction, [BBIM]Br–SnCl2 showed sim-
ilar catalytic activity and gave 100% conversion and
93.5% selectivity. These results confirmed that [BBIM]
Br–SnCl2 was a robust and reusable material and can
20
45
50
55
60
65
70
75
Temperature (°C)
Fig. 2. Effect of the temperature on the oxidation
reaction of benzyl alcohol to benzaldehyde.
Reaction
conditions:
benzyl
alcohol
(1.5 mmol), catalyst (0.11 g), H2O2 (30%,
2 mmol).
4
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Efficient and Reusable Sn(II)-containing Imidazolium-based Ionic Liquid
3430 cm−1 in the spectra of fresh and used samples is
assigned to the O H stretching vibration of the
adsorbed water. The absorption bands at around 3137,
2931, and 2874 cm−1 are associated with the stretching
vibration of the C H bonds. The bands at 3080, 2966,
1331, and 1168 cm−1 are assigned to the stretching
vibration of the C N bonds. The bands at 1632 and
1563 cm−1 are attributed to the C N stretching. The
bands at 1464 and 1378 cm−1 correspond to CH2 and
CH3 bending vibration, respectively. The bands ran-
ging from 883 to 1111 cm−1 are attributed to C H
bending vibration. The results show that no structural
transformation or change in chemical performance had
taken place in the catalyst after the oxidation reac-
tions. The results further proved that [BBIM]Br–SnCl2
was a stable and reusable material for oxidation
reactions.
100
80
Conversion
Selectivity
60
40
1
2
3
4
5
6
H2O2 (mmol)
Fig. 3. Effect of the amount of H2O2 on the oxida-
tion reaction of benzyl alcohol to benzalde-
hyde. Reaction conditions: benzyl alcohol
(1.5 mmol), catalyst (0.11 g), 65ꢀC.
Possible mechanism of the oxidation reaction
Based on the above experimental results and pre-
vious literature,48,50 a possible mechanism for the oxi-
dation of benzyl alcohol to benzaldehyde is proposed
(Scheme 2). In the oxidation reaction, the Sn species of
the catalyst coordinate with the imidazole ring of the
ionic liquid and react with the oxidant H2O2 via coordi-
nating to oxygen to form Sn peroxo complex
(I) species, which then react with the benzyl alcohol to
form the transition state (II). The transition state
(II) further removes a molecule of H2O to form the
transition state (III), which would be transformed into
the desired product of benzaldehyde, and complete the
catalytic cycle, simultaneously. During the oxidation
reaction, [BBIM]Br–SnCl2 transferred successfully the
H2O2 from an aqueous solution into an organic reac-
tion phase. It helped proceeding with the oxidation
reaction. The [BBIM]Br–SnCl2 catalyst showed high
catalytic activity and stability due to the Sn species
coordinating to the imidazole ring of [BBIM]Br, which
prevented it from leaching from the catalyst.
maintain excellent conversion and selectivity even after
the six cycles of the oxidation reactions.
The reused catalyst was further characterized by
Fourier transform infrared (FT-IR) spectroscopy to
evaluate its chemical properties. Figure 6 shows the
FT-IR spectra of fresh and used catalysts. The FT-IR
spectrum of the reused catalyst was completely consist-
ent with that of fresh one. The band appearing at
100
80
Conversion
Selectivity
60
40
CONCLUSION
10
20
30
40
50
60
In summary, a simple, durable, economical, recy-
clable, and highly efficient catalytic oxidation system
with [BBIM]Br–SnCl2 and H2O2 has been developed,
which could effectively oxidize benzyl alcohol and its
derivatives to the corresponding aldehydes under mild
reaction conditions, such as atmospheric pressure, as
Time (min)
Fig. 4. Effect of the reaction time on the oxidation
reaction of benzyl alcohol to benzaldehyde.
Reaction
conditions:
benzyl
alcohol
(1.5 mmol), catalyst (0.11 g), H2O2 (30%,
2 mmol), 65ꢀC.
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Article
Wang et al.
1
Table 3. Catalytic properties of [BBIM]Br–SnCl2 in the oxidation of various alcohols with H2O2
Entry
1
Alcohols
Products
Time/min
Conv. /(%)2
100
Sel. /(%)2
95.1
15
2
3
4
5
6
7
60
71
99
87
99
99
99
99
153
160
15
90
91
50
15
98
15
>99
8
9
604
604
20
32
40
30
1 Reaction conditions: alcohol (1.5 mmol), catalyst (0.11 g), H2O2 (30%, 2 mmol), 65ꢀC.
2 GC analysis.
3 The reaction was carried out using H2O2 (30%, 3.5 mmol).
4 The reaction was carried out at 85ꢀC.
well as solvent-free and base-free conditions. Moreover,
the catalytic system may offer many advantages, such
as simplicity of operation, high yields, stability, excel-
lent recyclability, and easy isolation of products.
(GC-MS) using an Agilent 7890B-7000C instrument
with an HP-5-MS capillary column. Their amounts were
quantified on an Agilent 7890B GC equipped with a
DB-1701 (30 m × 0.32 mm × 0.25 μm) capillary col-
umn and a flame ionization detector ( FID), using dode-
cane as the internal standard to calculate the conversion
and selectivity of the reaction. Elemental analysis was
performed on a Perkin-Elmer Series-II 2400 CHNS/O
analyzer, inductively coupled plasma (ICP) analysis on
a Perkin-Elmer Optima 8000DV, and ion chromatogra-
phy on a Thermo-Fisher ICS-5000+, respectively.
EXPERIMENTAL
All chemicals used in the experiments were pur-
chased from commercial sources and used without fur-
ther purification. All reagents were of analytical grade.
1H NMR spectra were recorded on a Bruker 400 MHz
spectrometer using DMSO-d6 as the solvent with tetra-
methylsilane (TMS) as the internal standard. FT-IR
spectra were recorded on a Bruker VERTEX 80 FT-IR
spectrometer using the KBr pellets. All products were
identified using gas chromatography-mass spectrometry
Synthesis of [BBIM]Br–SnCl2
First, the synthesis of [BBIM]Br was carried out
by modifying the procedure reported previously.51,52
6
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Efficient and Reusable Sn(II)-containing Imidazolium-based Ionic Liquid
Conversion
Selectivity
H
H
O-O
Sn2+
H2O2
OH
100
80
60
40
20
0
[BBIM]BrCl2
(I)
H
H
O
O
H
O
Sn2+
N
C
N
H2
SnCl
2Br
(II)
[BBIM]BrCl2
H2O
[BBIM]Br-SnCl2
H2O
H
O
CH
H
Sn2+
C
O
H
O
[BBIM]BrCl2
(III)
1
2
3
4
5
6
Recycle times
Scheme 2. Possible mechanism for the oxidation of
benzyl alcohol to benzaldehyde.
Fig. 5. Reusability of the catalyst. Reaction condi-
tions: benzyl alcohol (1.5 mmol), catalyst
(0.11 g), H2O2 (30%, 2 mmol), 15 min, 65ꢀC.
and SnCl2 in toluene at 95ꢀC for 24 h. The obtained tin-
containing ionic liquid, denoted as [BBIM]Br–SnCl2,
was dried in vacuum at 80ꢀC for 24 h. The molar
ratios of [BBIM], Br, Cl, and Sn of [BBIM]Br–SnCl2
Fifty mmol of 1-bromobutane was dissolved in 30 mL
of toluene, and 50 mmol of 1-butylimidazole was
slowly added to the above mixture solution, which was
stirred and refluxed at 80ꢀC for 24 h. The resulting vis-
cous liquid was cooled to room temperature, and then
washed three times with ethyl acetate (50 mL). After
the removal of the solvent by heating of the solution
under vacuum at 80ꢀC, the product [BBIM]Br was
obtained. The tin-containing ionic liquid was synthesized
by reaction with a certain amount of the [BBIM]-Br
1
were 1:1:1:0.5. H NMR: δ 0.90 (t, J = 7.2 Hz, 6H,
CH3), 1.25 (sept, J = 7.2 Hz, 4H, CH3CH2(CH2)
2N), 1.79 (pent, J = 7.2 Hz, 4H, NCH2CH2), 4.19
(t, J = 7.2 Hz, 4H, NCH2), 7.84 (s, 2H, NCHCHN),
9.32 (s, 1H, NCHN).
General procedure for the oxidation reactions
The liquid-phase oxidation of alcohol reactions
was performed in a glass flask with a reflux condenser
and a magnetic stirrer. In a typical experiment,
1.5 mmol of benzyl alcohol and 0.11 g of [BBIM]Br–
SnCl2 were stirred at 65ꢀC, and then 2 mmol of the
aqueous solution of H2O2 (30%) was slowly added
dropwise into the reaction system. After the reaction at
65ꢀC for 15 min, the products were extracted with ether
or ethyl acetate (3 × 10 mL), and then identified using
GC-MS. The remaining [BBIM]Br–SnCl2 catalyst was
recovered by the decantation of water produced in the
reaction and concentrating under vacuum. The next run
was carried out under optimized reaction conditions.
a
b
4000
3500
3000
Wavenumber (cm–1
2500
2000
1500
1000
ACKNOWLEDGMENTS
)
This work was supported by the Qian-Lan Project
of Jiangsu Province, the Natural Science Foundation of
Jiangsu Province (No. BK20140460), the University
Fig. 6. FT-IR spectra of (a) fresh and (b) reused
catalysts.
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Article
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