Olefin epoxidation with tert-butyl hydroperoxide catalyzed by functionalized polymer-supported copper(II) Schiff base complex

Article abstract of DOI:10.1007/s00706-011-0641-0

A new polymer-supported Cu(II) Schiff base complex has been synthesized and characterized by elemental (including metal) analysis, FT-IR spectroscopy, UV-Vis diffuse reflectance spectroscopy, thermogravimetric analysis, and scanning electron microscopy. The catalytic performance of this complex was evaluated in the epoxidation of styrene in acetonitrile/N,N-dimethylformamide (9:1) mixture with 70% tert-butyl hydroperoxide as an oxidizing agent under liquid phase reaction conditions for selective synthesis of styrene oxide. Suitable reaction conditions have been optimized by considering the effects of various reaction parameters such as temperature, reaction time, solvent, oxidant, catalyst amount, and styrene to hydroperoxide molar ratio for the maximum conversion of styrene as well as selectivity of styrene oxide. We have also investigated the epoxidation reaction of various olefins under the optimized reaction conditions. Comparison between catalytic activities of the polymer-supported Cu(II) Schiff base complex and its homogeneous analogue showed that the polymer-supported catalyst was more active. This heterogeneous complex was reused for five times. The selectivity of the heterogeneous catalyst does not change even after five times of reusing. Springer-Verlag 2011.

Full text of DOI:10.1007/s00706-011-0641-0

Monatsh Chem (2012) 143:815–823
DOI 10.1007/s00706-011-0641-0
ORIGINAL PAPER
Olefin epoxidation with tert-butyl hydroperoxide catalyzed
by functionalized polymer-supported copper(II) Schiff base
complex
•
Sk Manirul Islam Anupam Singha Roy Paramita Mondal
•
•
•
•
•
•
Manir Mobarok Brindaban Roy Noor Salam Sumantra Paul
Sanchita Mondal
Received: 20 January 2011 / Accepted: 25 August 2011 / Published online: 23 September 2011
Ó Springer-Verlag 2011
Abstract A new polymer-supported Cu(II) Schiff base
complex has been synthesized and characterized by ele-
mental (including metal) analysis, FT-IR spectroscopy,
UV–Vis diffuse reflectance spectroscopy, thermogravi-
metric analysis, and scanning electron microscopy. The
catalytic performance of this complex was evaluated in the
epoxidation of styrene in acetonitrile/N,N-dimethylform-
amide (9:1) mixture with 70% tert-butyl hydroperoxide as
an oxidizing agent under liquid phase reaction conditions
for selective synthesis of styrene oxide. Suitable reaction
conditions have been optimized by considering the effects
of various reaction parameters such as temperature, reac-
tion time, solvent, oxidant, catalyst amount, and styrene to
hydroperoxide molar ratio for the maximum conversion of
styrene as well as selectivity of styrene oxide. We have
also investigated the epoxidation reaction of various olefins
under the optimized reaction conditions. Comparison
between catalytic activities of the polymer-supported
Cu(II) Schiff base complex and its homogeneous analogue
showed that the polymer-supported catalyst was more
active. This heterogeneous complex was reused for five
times. The selectivity of the heterogeneous catalyst does
not change even after five times of reusing.
Introduction
Oxygenation of organic substrates has been extensively
studied, and olefin oxidation is especially interesting
because of the industrial importance of this type of reac-
tion. Among such oxidation reactions, olefin epoxidation is
extremely important for the preparation of highly func-
tionalized organic compounds, epoxy resins, paints,
perfumes, and surfactants [1–6]. Various epoxides are used
as intermediates in organic synthesis, pharmaceuticals, and
polymer production, and act as precursors for the synthesis
of complex molecules because of the strained oxirane ring
[7]. The traditional procedure for epoxidation of alkenes is
oxidation by peracids [8]. However, peracids are very
expensive, hazardous to handle, and nonselective for the
epoxide formation, and also lead to formation of undesir-
able products, creating a lot of waste material [9, 10]. Alkyl
hydroperoxides are used on a large scale in industrial
epoxidation, for example, in Halcon-Arco and Sumitomo
processes [11]. The recycling of the byproduct, tert-BuOH,
has been realized in the Sumitomo process. In order to
make the epoxidation process cleaner, safer, and more
efficient, the use of catalysts is mandatory. Over the last
few decades, the application of soluble compounds of early
transition metals such as rhenium [12], titanium [13],
vanadium [14], manganese [15], and molybdenum [16] has
been used for alkene epoxidation. Good activities and
selectivities have been pointed out as the main advantages
of homogeneous catalysts. However, some industrial
problems such as corrosion, deposition on the reactor wall,
difficulty in recovery, and separation of the catalyst from
reaction mixtures are associated with these homogeneous
catalysts.
Keywords Epoxidations ꢀ Heterogeneous catalysis ꢀ
Copper(II) complex ꢀ Olefins ꢀ tert-Butyl hydroperoxide
S. M. Islam (&) ꢀ A. S. Roy ꢀ P. Mondal ꢀ M. Mobarok ꢀ
B. Roy ꢀ N. Salam ꢀ S. Paul ꢀ S. Mondal
Department of Chemistry, University of Kalyani, Kalyani,
Nadia 741235, WB, India
In recent years, the design and synthesis of catalyti-
cally active supported metal complexes have received
e-mail: manir65@rediffmail.com
123

816
S. M. Islam et al.
considerable attention because of easy separation of the
product from the reaction medium along with the recov-
ery and reuse of these expensive catalysts. These
heterogeneous catalysts offer several practical advantages
over their homogeneous soluble counterparts [17, 18].
Various approaches have been focused on the incorpo-
ration of metal-based catalysts onto or into inert supports
by different methods, such as organic supports including
polybenzimidazole [19], functionalized polystyrene [20],
ion exchange resins [21], and epoxy resins [22]. Inorganic
oxides with hydroxyl-covered surfaces [23], amorphous
silica [24], modified MCM-41 [25], alumina [26], or
intercalation in clays [27] have been used for immobili-
zation of homogeneous compounds and have been
applied as catalysts for alkene epoxidation. Recently,
anchoring of catalytically active transition metal com-
plexes onto a polymer matrix has received considerable
attention because of their potential advantages in prac-
tical synthesis, i.e., (1) the catalyst is easily separated
from the reaction mixture by filtration, and (2) the
recovered catalyst can be reused. Tangestaninejad et al.
[28] and Sherrington’s group [29] have synthesized
polymer resin immobilized catalysts and have investi-
gated their catalytic activity in alkene epoxidation with
tert-butyl hydroperoxide (TBHP). Transition metal com-
plexes have attracted a lot of attention as possible
oxidation catalysts for the selective oxidation of olefins in
mild conditions [30, 31]. Many catalytic epoxidation
methods, including asymmetric epoxidation, have been
developed [32], but selective epoxidation of alkenes using
heterogeneous catalysts and clean oxidants under mild
conditions is still a challenge [33].
spectroscopic methods (IR, UV–Vis diffuse reflectance
spectroscopy), elemental analysis, thermogravimetric
analysis, and scanning electron microscopy. Catalytic
performance was investigated in liquid phase epoxidation
of styrene as probe reaction. The influences of various
reaction parameters on the conversion of styrene, yield,
and selectivity of styrene oxide have been studied in order
to optimize the reaction conditions. Under optimized
reaction conditions, epoxidation of various olefins was
also investigated. Catalytic activities of polymer-sup-
ported and homogeneous complex were compared. The
results illustrated that the heterogeneous copper catalyst
was more effective for the epoxidation reaction with a
variety of olefin compounds using TBHP as oxidant and
was found to be easily recoverable and recyclable up to
five times.
Results and discussion
Characterization of the polymer-supported Cu(II) Schiff
base complex
The outline for the preparation of polymer-supported
Cu(II) Schiff base complex is given in Scheme 1. Due to
insolubility of the polymer-supported Cu(II) complex in all
common organic solvents, characterization was limited to
the physicochemical properties, chemical analysis, SEM,
TGA, IR, and UV–Vis spectral data. Elemental analysis of
the free ligand and complex supported the formulation of
the complex. Chemical analysis suggested 1.76% Cu in the
immobilized Cu(II) Schiff base complex.
Copper is one of the most important elements in bio-
logical systems. Recently, copper complexes have been
widely used in oxidation reactions under heterogeneous
phase [34–36]. Heterogeneous Schiff base complexes
containing donor atoms such as oxygen and nitrogen have
been investigated for alkene epoxidation [37]. The activity
of polymer-supported Schiff base complexes of transition
metal ions varies with the type of Schiff base ligands,
coordination sites, and metal ions used in their formation.
Therefore, we have decided to prepare a heterogeneous
Cu(II) catalyst bearing an N, O-donor ligand. The synthesis
procedures for the polymer-supported complex combine the
advantages of both homogeneous (activity) and heteroge-
neous (separation, recovery, recycling) catalysts. Therefore,
animmobilizedcatalystallowsovercomingthe problemswith
separation and reuse, and greatly amends the properties of the
catalyst and its commercial value.
Scanning electron micrographs of the polymer-supported
Schiff base ligand and the prepared catalyst were recorded to
understand the morphological changes occurring on the
surface of the polymer matrix. In Fig. 1 the SEM images of
the polymer-anchored Schiff base ligand (a) and the immo-
bilized copper complex on modified polystyrene (b) are
shown. SEM pictures showed a morphological difference
between the free Schiff base ligand and the catalyst. The
presence of copper was also indicated by energy dispersive
spectroscopy analysis of X-rays (EDX).
The mode of attachment of 2-aminophenol and metal
onto the support was confirmed by IR spectral bands. In the
FT-IR spectrum of polymer-bound aldehyde, a new peak
appeared at 1,702 cm-1 that was assigned to carbonyl
group stretching vibration of the aldehyde. In the polymer
bound aldehyde, the sharp C–Cl peak (due to –CH2Cl
groups) at 1,264 cm-1 in the starting polymer was seen as
a weak band or was absent [38]. The formation of the
Schiff base ligand on the polymeric support is indicated by
a peak at 1,624 cm-1 assigned to C=N stretching fre-
quency. This band showed a decrease in intensity and
In this article, we have developed a polymer-supported
Cu(II) Schiff base complex by reacting aldehyde func-
tionalized polymer resins with 2-aminophenol and CuCl2.
The heterogeneous catalyst was characterized by various
123

Olefin epoxidation with TBHP catalyzed
817
Scheme 1
NH2
OH
NaHCO3
DMSO
P
CH2Cl
P
CHO
P
CH
N
MeOH
1
2
HO
PS-amp (3)
EtOH CuCl2
P
CH
Cu
N
O
P
= Polystyrene framework
Cl
OH2
PS-Cu(II)-amp (4)
shifted to lower wave numbers after complexation. It
suggested the coordination of the Schiff base to the central
Cu(II) ion through the azomethine nitrogen. The phenolic
(C–O) stretching frequency was observed in the region of
1,286 cm-1 (of ligand), which shifted to lower frequency
at 1,270 cm-1 in the complex, indicating coordination of
metal through the phenolic oxygen. The complex showed a
characteristic frequency mCu–Cl at 354 cm-1 [39]. In the
complex, bands at 628 cm-1 and 530 cm-1 were assigned to
mCu–O and mCu–N stretching frequencies, respectively [40, 41].
Thermal stability of the polymer-supported Schiff base
ligand and Cu(II) complex was investigated at a heating
rate of 10 °C/min in air over a temperature range of
30–600 °C. It is shown that the thermal stability of the
metal complex was slightly greater than that of its pre-
cursor Schiff base ligand. The complex was stable up to
350 °C, and above this temperature it decomposed.
Thermogravimetric study suggested that the polymer-
supported Cu(II) complex degraded at considerably high
temperature.
The electronic spectrum of the polymer-supported
Cu(II) complex was recorded in diffuse reflectance spec-
trum mode as a MgCO3/BaSO4 disc because of the
solubility limitations in common organic solvents. In the
complex five bands at ca. 310, 380, 446, 485, and 674 nm
were observed. The absorption around 310 nm may be
attributed to p?p* transitions of the phenyl moiety. The
bands at 380 and 446 nm were due to LMCT. The band at
446 nm indicated the phenolic oxygen to copper charge
transfer [42, 43]. In the complex, the bands around at 485
and 674 nm were due to d–d transition, which was assigned
to the square-planar geometry [36, 44, 45]. From the dif-
ferent microanalytical and spectral data, the probable
Fig. 1 FE SEM image of polymer-supported Schiff base (a) and
polymer-supported Cu(II) Schiff base catalyst (b)
123

818
S. M. Islam et al.
structure of the polymer-supported Cu(II) complex may be
described according to Scheme 1.
styrene oxide from the site. So, the deep oxidation of sty-
rene oxide was prevented and the selectivity increases [46].
However, the detailed mechanism is unknown at present.
In this study, the effects of different oxidants such as
TBHP, H2O2, PhIO, and molecular oxygen over this cat-
alyst were examined in the epoxidation reaction of styrene.
The results of this study are given in Table 2. The reaction
showed almost no conversion when molecular oxygen
acted as oxidant. TBHP was the best oxidant among the
three oxidants that were used in catalytic epoxidation
reaction in the present study. Oxidants like H2O2 and PhIO
were clearly less efficient than TBHP, as evident from the
percentage of conversion of styrene. The significant dif-
ference in the styrene oxide yields in case of using tert-
butyl hydroperoxide in comparison to hydrogen peroxide
can be explained by an inhibition effect due to water
formation during epoxidation in case of hydrogen perox-
ide. Hydrogen peroxide was not applicable because this
water strongly blocked the active sites of the metal catalyst
[47].
Catalytic activity in the epoxidation of styrene
Catalytic activities of polymer-supported Cu(II) Schiff
base catalyst were investigated by epoxidation of styrene to
produce styrene oxide. In search of optimal reaction con-
ditions to achieve the maximum yield of styrene oxide, the
effects of solvent, temperature of the reaction, oxidant,
reaction time, reactant ratio (styrene to TBHP), and amount
of catalyst were studied. During the catalytic oxidation
reaction of styrene, two products (styrene oxide and
benzaldehyde) were identified (Scheme 2).
The styrene epoxidation has been examined using dif-
ferent solvents. The selected solvent should possess certain
criteria, such as that it should be stable and should dissolve
the substrate and oxidant. Table 1 shows the influence of
solvent on the conversion of styrene and selectivity of
styrene oxide by using polymer-supported Cu(II) Schiff
base complex as a catalyst. The selectivity of styrene oxide
was in the order ACN [ DMF [ MeOH [ (Me)2CO [
MePh. Results indicate that the epoxidation reaction did
not proceed in toluene solvent. Additionally, poor con-
version and selectivity were found when the reaction was
carried out in acetone medium. The reaction, however,
showed low activity and epoxidation selectivity in metha-
nol; the main product was benzaldehyde. For the present
reaction, the copper catalyst exhibits the highest catalytic
activity and selectivity for styrene oxide in acetonitrile
medium, because it is a polar solvent, has a high dielectric
constant, and dissolves a wide range of chemical com-
pounds. On the other hand, DMF is the next best solvent. It
is a dipolar aprotic solvent with high dielectric constant.
The results suggest the possibility that the combination of
two solvents might result in good activity, yield, and
selectivity because both solvents have a high dielectric
constant and polarity. Now the reaction was examined in
various solvent volume ratios (ACN/DMF). The highest
selectivity (90%) of styrene oxide and conversion of sty-
rene (88%) were achieved for a volume ratio of 9:1 of ACN
to DMF. Both DMF and ACN molecules strongly interact
with the active sites of the catalyst. The affinity of ACN
and DMF to the active site might promote separation of
Table 1 Styrene epoxidation using different solvents
Entry Solvent
Time/h Conversion/%a Selectivity/%a
Styrene Benzaldehyde
oxide
1
2
3
4
5
6
MePh
8
8
8
8
8
0
16
23
67
46
88
0
9
0
91
78
42
56
10
(Me)2CO
MeOH
ACN
22
58
44
90
DMF
ACN/DMF 8
(9:1)
Reaction conditions: catalyst (0.05 g), styrene (5 mmol), solvent
(10 cm3), TBHP (10 mmol), 60 °C
a
Determined by GC
Table 2 Styrene epoxidation using different oxidants
Entry Oxidant Time/h Conversion/%a Selectivity/%a
Styrene Benzaldehyde
oxide
1
None
PhIO
O2
8
8
8
8
8
8
0
17
5
0
59
74
90
17
54
0
41
26
10
83
46
2
3
4
TBHP
H2O2
TBHP
88
35
9
O
5
6b
CHO
Cu catalyst
Reaction conditions: catalyst (0.05 g), styrene (5 mmol), ACN/DMF
(9:1), oxidant (10 mmol), 60 °C
+
TBHP / ACN/DMF (9:1)
a
Determined by GC
b
Without catalyst
Scheme 2
123

Olefin epoxidation with TBHP catalyzed
819
100
90
80
70
60
50
40
30
20
10
0
Liquid phase epoxidation of styrene was carried out with
three different molar ratios of styrene to TBHP. In all
cases, styrene oxide was obtained as the major product
along with small amounts of benzaldehyde as by-product.
It was observed that the highest conversion of styrene
(88%) and selectivity (90%) of styrene oxide were obtained
at a styrene to TBHP molar ratio of 1:2 over the hetero-
geneous copper catalyst at 60 °C in 8 h as shown in Fig. 2.
When the molar ratio of styrene to TBHP was increased
from 1:1 to 1:2, the conversion as well as selectivity of
styrene oxide increased with decreasing the selectivity of
the byproducts. The catalytic activity was found to be
decreased when the styrene to oxidant molar ratio was 1:3;
probably a high oxygen concentration produced by more
oxidants inhibited the reaction [48]. Thus, the optimal
molar ratio of styrene to TBHP is 1:2.
400C
500C
600C
700C
800C
0
2
4
6
8
10
Time/h
Fig. 3 Variation of reaction temperature with conversion of styrene,
yield, and selectivity of styrene oxide with polymer-supported Cu(II)
Schiff base complex with variation of time. Reaction conditions:
styrene (5 mmol), TBHP (10 mmol), catalyst (0.05 g), ACN/DMF
(9:1)
To determine the best temperature, the epoxidation of
styrene has been thoroughly investigated with different
temperatures over polymer-supported Cu(II) Schiff base
complex with time. The epoxidation reaction was carried out
with various reaction temperatures from 40 to 80 °C using
the reactant as a 1:2 molar ratio of styrene to TBHP with
ACN/DMF (9:1) solvent mixture for a duration of 10 h.
Results are shown in Fig. 3. The optimum temperature was
found to be 60 °C. At lower temperatures the conversion of
styrene was low. At a higher temperature, the yield and
selectivity of styrene oxide decrease. Under these reaction
conditions, the conversion increased with time and then
reached a maximum value of 88% at 8 h. When the reaction
time goes on, the conversion is kept almost constant. The
yield and selectivity of epoxide were 79 and 90% at 8 h.
The amount of catalyst was varied from 0.025 to 0.1 g
keeping the molar ratio of styrene:TBHP at 1:2 and the
100
90
80
Conversion
70
Yield
Selectivity
60
50
0.02
0.04
0.06
0.08
0.10
0.12
Weight of catalyst/g
Fig. 4 Effect of catalyst amount with conversion of styrene, yield,
and selectivity of styrene oxide with polymer-supported Cu(II) Schiff
base complex. Reaction conditions: styrene (5 mmol), TBHP
(10 mmol), ACN/DMF (9:1), 60 °C, 8 h
100
Conversion
Yield
Selectivity
80
60
40
20
0
reaction temperature at 60 °C. The reaction was carried out
for 8 h, and the products were analyzed. The results are
presented in Fig. 4. With the increase in catalyst amount
from 0.025 to 0.050 g the conversion of styrene increased
from 76 to 88%. This was due to the availability of more
active sites that favored the accessibility of a large number
of molecules of substrates and oxidant to the catalyst.
Styrene conversion was almost the same with a further
increase of catalyst amount to 0.10 g.
1:2
1:3
1:1
Styrene : TBHP molar ratio
Thus, the required parameters for the epoxidation of
styrene, to get selectively styrene oxide, were as follows:
styrene (5 mmol), TBHP (10 mmol), ACN/DMF (9:1),
catalyst (0.05 g), reaction time (8 h), and temperature
Fig. 2 Variation of styrene to TBHP molar ratio with conversion of
styrene, yield, and selectivity of styrene oxide with polymer-
supported Cu(II) Schiff base complex. Reaction conditions: styrene
(5 mmol), catalyst (0.05 g), ACN/DMF (9:1), 60 °C
123

820
S. M. Islam et al.
Comparison of homogeneous Cu(II)-amp
and heterogeneous PS-Cu(II)-amp in the alkene
epoxidation
(60 °C). The major product, styrene oxide, was formed
with 90% selectivity in the above reaction conditions.
Many efficient heterogeneous copper catalysts have
been reported for the styrene epoxidation with TBHP
[35, 49–53]. However, this catalytic system was superior
to reaction time [50–53], conversion [49, 50], selectivity
[35, 49–51, 53], and reaction temperature [50] in com-
parison to others. The results are summarized in Table 3.
Comparison of this catalyst with the above-reported sys-
tems reveals that the present system gives better yields than
the above-reported catalysts.
In order to examine the effect of supporting on the catalytic
activity of copper complex in the alkene epoxidation with
TBHP, we repeated all the reactions with both types of
catalyst and with same reaction conditions. The obtained
results showed that in the alkene epoxidation the conver-
sion, selectivity, and stability of the heterogeneous catalyst
were better than those of the homogeneous catalyst
(Table 4). On the other hand, the heterogeneous catalyst
can be recovered several times without loss of its activity.
The most important disadvantage of homogeneous Cu(II)-
amp was the catalyst degradation in the presence of oxi-
dant, whereas the heterogenized catalyst can be reused
several times without significant loss of its activity.
Catalytic epoxidation with different olefins
Finally, in order to explore further the catalytic activity and
selectivity of the catalyst, epoxidation of other olefins was
investigated under optimized reaction conditions, which
proved to be best for styrene (Table 4, entry 1). This cat-
alyst efficiently converted both cyclic and linear alkenes to
their corresponding epoxides with TBHP. 1-Hexene and
1-octene as linear alkenes were efficiently converted to
their corresponding epoxides. Cyclic olefins such as
cyclohexene and cyclooctene were also epoxidized in high
yields. First, the ability of the prepared catalyst was
investigated in the epoxidation of cyclooctene. The results
showed that the conversion is 82% with 100% epoxide
selectivity. Epoxidation of cyclohexene occurred with 81%
conversion and 95% epoxide selectivity, and allylic oxi-
dation products (cyclohexene-1-one and cyclohexene-1-ol)
were also detected in the reaction mixture. In the case of
isopropenylbenzene, the corresponding epoxide was
obtained in 85% epoxide selectivity. In the oxidation of a-
pinene, the major product was a-pineneoxide, while ver-
benone and verbenol were produced as minor products.
Limonene selectively epoxidized to the 1,2-epoxy product
with other coproducts. Oxidation of linear alkenes such as
1-hexene and 1-octene were accompanied by allylic
oxidation.
Recyclability and stability
The recyclability of the catalyst is important for the
catalysis reaction. To investigate the reusability of poly-
mer-supported Cu(II) Schiff base complex, the catalyst was
separated by filtration after the first catalytic reaction fin-
ished. For the next reaction cycle, we recovered the catalyst
by washing with solvent and drying under a vacuum, then
subjected it to the second run under the same reaction
conditions. The catalytic run was repeated with further
addition of substrates in appropriate amount under opti-
mum reaction conditions. The nature and yield of the final
products were comparable to that of the original one.
Table 4 (entry 1) illustrates the reusability of the catalyst
for the epoxidation of styrene during five cycles. It was
found that the catalytic activity did not change significantly
after five repeated runs.
To check the leaching of copper metal into the solution
during the reaction, the following experiment was carried
out under the optimum reaction conditions. The reaction
Table 3 Epoxidation of styrene with TBHP catalyzed by a variety of copper catalysts
Catalyst
Reaction conditions
Conversion/%
Selectivity of epoxide/%
Reference
PS-Cu(II)-amp
ACN/DMF(9:1), 60 °C, 8 h
ACN, 40 °C, 8 h
1,2-Dichloroethane, 75 °C, 24 h
ACN, 60 °C, 12 h
ACN, 60 °C, 24 h
ACN, 50 °C, 12 h
88
90
This study
[49]
CuCl16Pc-MCM-41
[Cu(2,2-bipy)(H2btec)]a
HMS-Cu-I
47
25
23.7
89.4
88
71
[50]
63.2
90
[51]
[Cu2L(l1,1-N3)(l1,3-N3)(l1,1,1-N3)]/silica
Cu–S-AMSiO2
[52]
36.2
68.5
21
28.8
52.5
6
[35]
Cu–S-AM(PS)
ACN, 50 °C, 12 h
ACN, 60 °C, 24 h
[35]
CuY
[53]
CuPcY
ACN, 60 °C, 24 h
95
23
[53]
123

Olefin epoxidation with TBHP catalyzed
821
Table 4 Epoxidation of olefins
catalyzed by polymer-supported
Cu(II) Schiff base catalyst
Entry
Olefins
Conversion/%a
PS-Cu(II)-amp
Epoxide yield/%a
PS-Cu(II)-amp
Cu(II)-amp
Cu(II)-amp
1
Styrene
88 (87, 87, 86, 85)b
81
78
75
77
49
44
67
72
67
59
43
35
90 (90, 90, 89, 89)b
72
78
62
56
33
34
59
56
53
47
23
14
2
Cyclooctene
Cyclohexene
a-Methylstyrene
a-Pinene
82
81
84
56
51
76
79
71
66
49
40
82
77
72
43
41
72
67
59
55
45
35
3
4
5
6
Limonene
7
trans-Stilbene
4-Chlorostyrene
4-Methylstyrene
4-Nitrostyrene
1-Hexene
Reaction conditions: catalyst
(1.38 9 10-5 mol), substrate
(5 mmol), ACN/DMF (9:1),
TBHP (10 mmol), 60 °C, 8 h
8
9
10
11
12
a
Determined by GC
b
Catalytic runs to test
recyclability
1-Octene
was stopped after it had proceeded for 3 h with styrene
conversion of 54%. The separated filtrate was allowed to
react for another 5 h under the same reaction condition, but
no further styrene conversion was observed. The UV–Vis
spectroscopy was also used to determine the stability of the
heterogeneous catalyst. The UV–Vis spectra of the reaction
solution, at the first run, did not show any absorption peaks
characteristic of copper metal, indicating that leaching of
copper metal did not take place during the course of the
oxidation reaction. These results suggest that the present
catalyst was heterogeneous in nature.
Experimental
Analytical grade reagents and freshly distilled solvents
were used throughout the experiment. Liquid substrates
were predistilled and dried by appropriate molecular sieve.
Distillation and purification of the solvents and substrates
were done by standard procedures [54]. Chloromethylated
poly(styrene-divinyl benzene) and olefins were supplied by
Sigma-Aldrich Chemical Co. (USA). Copper(II) chloride
and 2-aminophenol were procured from Merck and were
used without further purification.
A Perkin-Elmer 2400 C elemental analyzer was used to
collect microanalytical data (C, H, N). FT-IR spectra of the
samples were recorded on a Perkin-Elmer FTIR 783
spectrophotometer using KBr pellets. Diffuse reflectance
UV–Vis spectra were taken using a Shimadzu UV-2401PC
double-beam spectrophotometer having an integrating
sphere attachment for solid samples. A Mettler Toledo
TGA/SDTA 851 instrument was used for the thermo-
gravimetric (TGA) analysis. Morphologies of the
functionalized polystyrene and complex were analyzed
using a scanning electron microscope ZEISS EVO40
(England) equipped with EDX facility. Copper content in
the catalyst was determined using a Varian AA240 atomic
absorption spectrometer.
Conclusions
In summary, we have successfully anchored the Cu(II) Schiff
base complex into the polymer matrix. This catalyst, which
can be prepared easily, is a heterogeneous and efficient cat-
alyst for epoxidation of linear and cyclic alkenes with TBHP
in acetonitriline/N,N-dimethylformamide mixed solvent
(9:1). The developed heterogeneous catalyst shows high
catalytic activity in styrene epoxidation with conversion
(88%) as well as selectivity of styrene oxide (90%).
Demanding olefins such as limonene can also be epoxidized
with high selectivity. The complex was also applied for the
heterogeneous catalysis of other olefins to their corresponding
epoxides. The results show that the immobilized catalyst is
highly active and selective to the epoxide formation. Hence, a
better catalytic efficiency has been observed in polymer-
supported Cu(II) Schiff base complex. Another important
factor is the stability and recyclability of the catalyst under the
optimized reaction conditions. Leaching tests indicated that
the catalytic reaction is mainly heterogeneous in nature. The
reusability of this catalyst is high; it can be reused five times
without a significant decrease in its initial activity.
Polymer-supported N-(2-hydroxyphenyl)benzaldimine
(PS-amp, 3)
Chloromethylated polystyrene beads (1) were functional-
ized with aldehyde group according to a literature
procedure [55]. The aldehyde-bearing beads (2) were
allowed to swell in 50 cm3 methanol, and a solution of
4.0 g 2-aminophenol in 25 cm3 methanol was added
dropwise over a period of 1 h with constant stirring, and
then it was refluxed for 8 h. After cooling to room
temperature, the reddish brown-colored polymer beads
123

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S. M. Islam et al.
9. Barf GA, Sheldon RA (1995) J Mol Catal A: Chem 102:23
were filtered, washed thoroughly with methanol and
petroleum ether, and dried in a vacuum. Yield: 35%; IR
(KBr): vꢀ ¼ 3,414, 2,924, 1,700, 1,624, 1,509, 1,453,
1,286 cm-1; UV–Vis: kmax = 320–330 nm.
10. Mukaiyama T, Yamada T (1995) Bull Chem Soc Jpn 68:17
11. Bregeault JM (2003) Dalton Trans 17:3289
12. Herrmann WA, Fischer RW, Marz DW (1991) Angew Chem Int
Ed 30:1638
13. Maschmeyer T, Rey F, Sankar G (1995) Nature 378:159
14. Behrens CH, Sharpless KB (1983) Aldrichimica Acta 16:67
15. Mohajer D, Tangestaninejad S (1993) J Chem Soc, Chem Com-
mun 3:240
Polymer-supported N-(2-hydroxyphenyl)benzaldimine
copper(II) chloride complex (PS-Cu(II)-amp, 4)
The polymer-supported Schiff base (2.0 g) was kept in
contact with 10 cm3 methanol in a round-bottom flask. A
methanolic solution of CuCl2 (10 cm3, 1% w/v) was added
over a period of 45 min and was refluxed for 6 h. The
black-colored copper-loaded beads were filtered carefully,
washed with ethanol, and dried in a vacuum. Yield: 20%;
IR (KBr): vꢀ ¼ 3,376 (sh), 2,920, 1,699, 1,605, 1,511, 1,453,
1,270, 628, 530, 354 cm-1; UV–Vis: kmax = 310, 380,
446, 485, 674 nm.
16. Calvante RM, O’Shea VAP, Campos-Martin JM, Fierro JLG,
´
Gutierrez-Puebla E (2004) J Mol Catal A: Chem 214:269
17. Booth RJ, Hodges JC (1999) Acc Chem Res 32:18
18. Gupta KC, Sutar AK (2008) React Funct Polym 68:12
19. Miller MM, Sherrington DC, Simpson S (1994) J Chem Soc
Perkin Trans 2:2091
20. Valodkar VB, Tembe GL, Ram RN, Rama HS (2003) Catal Lett
90:91
21. Kotov SV, Balbolov E (2001) J Mol Catal A: Chem 176:41
¨
22. Arnold U, Fan F, Habicht W, Doring M (2007) J Catal 245:55
23. Jia M, Seifert A, Thiel WR (2004) J Catal 221:319
´
24. Bakala PC, Briot E, Salles L, Bregeault JM (2006) Appl Catal A:
Gen 300:91
25. Karandikar P, Chandwadkar AJ, Agashe M, Ramgir NS, Siva-
sanker S (2006) Appl Catal A: Gen 297:220
26. Handzlik J, Ogonowski J, Stoch J, Mikołajczyk M (2005) Catal
Lett 101:65
27. Gigante B, Corma A, Garcia H, Sabater MJ (2000) Catal Lett
68:113
28. Tangestaninejad S, Habibi MH, Mirkhani V, Moghadam M,
Grivani G (2006) Inorg Chem Comm 9:575
29. Mbeleck R, Ambroziak K, Saha B, Sherrington DC (2007) React
Funct Polym 67:1448
General procedure for catalytic epoxidation reactions
catalyzed by PS-Cu(II)-amp
The liquid phase epoxidation reactions were carried out in
a two-necked round-bottom flask fitted with a water
condenser and placed in an oil bath at different temper-
atures under vigorous stirring. Substrates (5 mmol) were
dissolved in ACN/DMF (9:1) mixed solvent for different
sets of reactions together with 0.05 g catalyst, to which
10 mmol of TBHP (70% in aq. solution) was added. When
the reaction was carried out under O2 atmosphere, oxygen
gas was purged into the flask continuously. The withdrawal
of the reaction mixture was done at regular time intervals
and analyzed with a Varian 3400 gas chromatograph
equipped with a 30 m CP-SIL8CB capillary column and a
flame ionization detector. Chlorobenzene was used as an
internal standard. All reaction products were identified by
using an Agilent GC-MS.
30. Sureshan CA, Bhattacharya PK (1998) J Mol Catal A: Chem
136:285
31. Nam W, Kim HJ, Kim SH, Ho RYN, Valentine JS (1996) Inorg
Chem 35:1045
¨
32. Pietikainen P (1999) Tetrahedron Lett 40:1001
33. Fraile JM, Garcia JI, Mayoral JA, Vispe E (2000) J Catal 189:40
34. Maurya MR, Chandrakar AK, Chand S (2007) J Mol Catal A:
Chem 270:225
35. Karandikara P, Dhany KC, Deshpande S, Chandwadkar AJ,
Sivasanker S, Agashe M (2004) Cat Comm 5:69
36. Srinivas D, Sivasanker S (2003) Catal Surv Asia 7:121
37. Sui Y, Zenga X, Fang X, Fub X, Xiao Y, Chend L, Li M, Chenga
S (2007) J Mol Catal A: Chem 270:61
38. Angelino MD, Laibinis PE (1998) Macromolecules 31:7581
39. Ferraro JR (1971) Low Frequency Vibration of Inorganic and
Coordination Compounds. Plenum Press, New York
40. Sallam SA, Orabi AS (2002) Transition Met Chem 27:447
41. Kandil SS, El-Hefnawy GB (2003) Transition Met Chem 28:168
42. Solomon EI, Sundaram UM, Machonkin TE (1996) Chem Rev
96:2563
43. Burk PL, Osborn JA, Youinou MT, Agnus Y, Louis R, Weiss R
(1981) J Am Chem Soc 103:1273
44. Lever ABP (1984) Inorganic electronic spectroscopy, 2nd edn.
Elsevier, Amsterdam
45. Salavati-Niasari M (2004) J Mol Catal A: Chem 217:87
46. Yonemitsu M, Tanaka Y, Iwamoto M (1998) J Catal 178:207
47. Arends IWCE, Sheldon RA (2002) Topics Catal 19:133
48. Pillai UR, Sahle-Demessie E (2002) Chem Commun 18:2142
49. Karandikar P, Agashe M, Vijayamohanan K, Chandwadkar A
(2004) Appl Catal A: Gen 257:133
50. Brown K, Zolezzi S, Aguirre P, Venegas-Yazigi D, Paredes-
Garcia V, Baggio R, Novak MA, Spodine E (2009) Dalton Trans
8:1422–1427
Acknowledgments S.M.I. acknowledges the Department of Sci-
ence and Technology (DST), Council of Scientific and Industrial
Research (CSIR), and University Grant Commission (UGC), New
Delhi, India for funding.
References
1. McGarrigle EM, Gilheany DG (2005) Chem Rev 105:1563
2. Blaser HU, Pugin B, Spindler F (2005) J Mol Catal A Chem
231:1
3. Shulpin GB (2002) J Mol Catal A: Chem 189:39
4. Backvall JE (2004) Modern oxidation methods. Wiley-VCH,
Weinheim, p 21
5. Haines AH (1985) Methods for the oxidation of organic com-
pounds. Academic Press, New York
6. Xia QH, Ge HQ, Ye CP, Liu ZM, Su KX (2005) Chem Rev
105:1603
7. Yudin AK (2006) Aziridines and epoxides in organic synthesis.
Wiley-VCH, Weinheim, p 185
8. Swern D (ed) (1971) Organic Peroxide, vol 2. Wiley-Interscience,
New York, p 265
123

Olefin epoxidation with TBHP catalyzed
823
51. Mijanuddin M, Jana AD, Drew MGB, Hong CS, Chattopadhyay
B, Mukherjee M, Nandi M, Bhaumik A, Helliwell M, Mostafa G,
Ali M (2009) Polyhedron 28:665
52. Roy P, Dhara K, Manassero M, Banerjee P (2008) Inorg Chem
Comm 11:265
53. Seelan S, Sinha AK, Srinivas D, Srivasankar S (2000) J Mol Catal
A: Chem 157:163
54. Vogel AI (1989) Textbook of practical organic chemistry
(quantitative analysis), 5th edn. Longman, London
55. Frechet JM, Schuerch C (1971) J Am Chem Soc 93:492
123