[Mn(TPPS)] immobilized on ionic liquid-modified silica as a heterogeneous and reusable catalyst for epoxidation of alkenes with NaIO4 under ultrasonic irradiation

Article abstract of DOI:10.1007/s13738-016-0820-3

Effective epoxidation of alkenes using sodium periodate was accomplished with Manganese (III) tetrakis(p-sulfonatophenyl)porphyrin, [C₄₄H₂₆N₄O₁₂S₄Na₄], supported on ionic liquids-modified silica, Im-SiO₂, under ultrasonic irradiation conditions is reported. This heterogeneous catalyst, [Mn(TPPS)@SiO₂-Im] was characterized by elemental analysis, scanning electron microscopy (SEM), FT-IR and UV–Vis spectroscopic methods. The synthesized hybrid catalyst was applied for efficient epoxidation of various alkenes with sodium periodate in acetonitrile under ultrasonic irradiation conditions. This solid catalyst can be easily recovered by simple filtration and reused several time without apparent loss of its catalytic activity.

Full text of DOI:10.1007/s13738-016-0820-3

J IRAN CHEM SOC
DOI 10.1007/s13738-016-0820-3
ORIGINAL PAPER
[Mn(TPPS)] immobilized on ionic liquid-modified silica
as a heterogeneous and reusable catalyst for epoxidation
of alkenes with NaIO4 under ultrasonic irradiation
Robabeh Hajian1 · Shahram Tangestaninejad2 · Majid Moghadam2 ·
Valiollah Mirkhani2 · Iraj Mohammadpoor-Baltork2
Received: 21 July 2015 / Accepted: 17 January 2016
© Iranian Chemical Society 2016
Abstract Effective epoxidation of alkenes using
sodium periodate was accomplished with Manganese (III)
tetrakis(p-sulfonatophenyl)porphyrin, [C44H26N4O12S4Na4],
supported on ionic liquids-modified silica, Im-SiO2, under
ultrasonic irradiation conditions is reported. This heteroge-
neous catalyst, [Mn(TPPS)@SiO2-Im] was characterized by
elemental analysis, scanning electron microscopy (SEM),
FT-IR and UV–Vis spectroscopic methods. The synthe-
sized hybrid catalyst was applied for efficient epoxidation of
various alkenes with sodium periodate in acetonitrile under
ultrasonic irradiation conditions. This solid catalyst can be
easily recovered by simple filtration and reused several time
without apparent loss of its catalytic activity.
have been potentially employed as good catalysts for epoxi-
dation of alkenes [5–7]. It was establish that when metal-
loporphyrins were used as catalysts, organic compounds
could be oxidized by oxygen donors such as iodosylarenes,
hypochlorites, alkylhydroperoxides, hydrogen peroxide and
periodates [8–12]. However, the cost of synthesis and recov-
ery of homogeneous porphyrins are drawbacks of these
catalysts. Moreover, the intermolecular self-aggregation
due to π–π stacking and the tendency to oxidation led to
deactivation, destruction of metalloporphyrin in such sys-
tems. One of the best manners to overcome these problems
is their immobilization on solid supports [13–15]. There-
fore, immobilization of metalloporphyrins on solid supports
can provide catalysts, which are easier to handle, and may
demonstrate improved selectivities and activities due to the
support environment. Among various methods employed
to anchor metalloporphyrins to supports, the one based on
making use of electrostatic interactions between an ionic
metalloporphyrin and counterionic groups on the surface of
the carrier is of particular attraction. The main advantage of
such an approach is the existence of strong interactions pre-
venting leaching of the active centres from the support and a
simplicity of the catalyst preparation, which is based on ion
exchange procedures [16, 17].
Ionic liquids typically consist of organic nitrogen-con-
taining heterocylic cations and inorganic anions and are liq-
uid at room temperature. Due to their unique physicochemi-
cal properties such as negligible vapor pressure, wide liquid
temperature range, excellent thermodynamic stability, wide
electrochemical window, tunable polarity and amphiphilic-
ity, good solvent behavior for inorganic, organic and even
polymeric materials, excellent designable space through the
changing of components, and so on, they have found many
applications in the fields of synthesis, catalysis and extrac-
tion to function as new media and liquid materials [18, 19].
Keywords Immobilized ionic liquid · Sodium periodate ·
Epoxidation · [Mn(TPPS)] · Heterogeneous catalyst ·
Ultrasonic irradiation
Introduction
Over the past three decades, epoxidation of alkenes cata-
lyzed by metalloporphyrins catalyst with oxygen donors has
been extensively studied to mimic the cytochrome P-450
chemistry [1–3]. The main target in this domain is design-
ing selective, stable, and high turnover catalytic systems
[4]. Among the metalloporphyrins, manganese porphyrins
* Robabeh Hajian
rhajian@yazd.ac.ir
1
Department of Chemistry, Yazd University, 89195-741 Yazd,
Iran
2
Catalysis Division, Department of Chemistry, University
of Isfahan, 81746-73441 Esfaha¯n, Iran
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J IRAN CHEM SOC
were obtained on a D8 Advanced Bruker using Cu Kα radia-
tion (2θ = 5°–60°). Gas chromatography experiments (GC)
were performed with a Shimadzu GC-16A instrument using
a 2 m column packed with silicon DC-200 or Carbowax
20 m. In GC experiments, n-decane was used as internal
standard. A UP 400S ultrasonic processor equipped with a
3 mm wide and 140 mm long probe, which was immersed
directly into the reaction mixture, was used for sonication.
Scheme 1 Epoxidation of alkenes with NaIO4 catalyzed by
[Mn(TPPS)@SiO2-Im]
Supported ionic liquid catalyst consists of immobilized cata-
lytic species residing in an ionic liquid layer immobilized
on a solid support. On the other hand, supported ionic liquid
catalysis is a concept that combines the advantages of ionic
liquids with those of heterogeneous catalysts [20]. Ionic liq-
uids supported catalysts supply the hydrophobic environment
for organic reactions. Immobilization or supporting of ionic
liquids can be performed in many different manners, such
as simple impregnation, grafting, polymerization sol–gel
method, encapsulation or pore trapping, among others and
dilution with molecular solvent [21–23]. Some supported
ionic liquid metalloporphyrins have been reported in the lit-
erature [24–26]. Previously, we have reported the use of sup-
ported manganese (III) porphyrins in the oxidation of organic
compounds with NaIO4 [10, 27, 28]. In addition, we have
explored an ionic liquids supported porphyrin by immobilisa-
tion of [Mn(TPPS)] on poly(4-styrylmethyl)pyridinium chlo-
ride (PSMP) [29]. Ultrasound had been prosperously utilized
in the past to improve the selectivity as well as conversion of
the desired product by increasing the rates of the reactions by
manifolds [30–34]. It also delays catalyst deactivation [33].
Herein, the preparation and characterization of
[Mn(TPPS)] supported on ionic liquid-modified SiO2,
[Mn(TPPS)@SiO2-Im], and its catalytic activity in the alk-
ene epoxidation with NaIO4 under ultrasonic irradiation
conditions are reported (Scheme 1).
Preparation of ionic liquid-modified silica, SiO2-Im
The 3-chloropropyl functionalized silica, SiO2, was used
as purchased. To a suspension of SiO2 (1 g) in CH3CN
(20 mL), was added N-methylimidazole (10 mmol) and
stirred under refluxed condition for 48 h. After the reaction
was completed, the SiO2-Im was filtered, washed consecu-
tively with water and acetone, and dried under vacuum at
70 °C over night [36].
Preparation of Mn(TPPS) immobilized on ionic
liquid-modified silica Mn(TPPS)@SiO2-Im
To a solution of Mn(TPPS) (0.5 g) in acetone/water
(v/v:1/1) was added SiO2-Im (4 g) and refluxed for
24 h. Finally, the catalyst was filtered and dried at room
temperature.
General procedure for epoxidation of alkenes
with NaIO4 catalyzed by [Mn(TPPS)@SiO2-Im]
under ultrasonic irradiation conditions
All of the reactions took place under ultrasonic irradiation
in a 25 mL flask. A solution of NaIO4 (460 mg, 2 mmol
in 5 mL H2O) was added to a mixture of alkene (1 mmol),
imidazole (0.1 mmol) and the [Mn(TPPS)@SiO2-Im]
(330 mg, 0.02 mmol) in acetonitrile (5 mL). The mixture
was exposed to ultrasonic irradiation. The progress of the
reactions was monitored by GC. At the end of the reaction,
the catalyst was filtered and washed with Et2O (20 mL).
The organic layer was separated, concentrated and after
chromatography on a short column of silica gel the pure
Experimental
Measurement and analysis
1
All chemicals were commercial reagent grade and obtained
from Merck and Fluka. Manganese (III) tetrakis(p-sul-
fonatophenyl)porphyrin was prepared according to the lit-
erature [35]. The prepared catalyst was characterized by
elemental analysis, scanning electron microscopy (SEM),
FT-IR and UV–Vis spectroscopic methods. FT-IR spectra
were obtained as potassium bromide pellets in the range
400–4000 cm−1 with a Jasco Impact 6300D spectrometer.
Scanning electron micrographs (SEM) of the catalyst and
support were taken on a SEM Philips XL 20 instrument.
UV–Vis spectra were obtained in rang 200–800 cm−1 with a
Jasco V-670 spectrometer. Powder X-ray diffraction patterns
product was obtained. IR and H-NMR spectral data con-
firmed the identities of the products.
Results and discussion
Preparation and characterization of catalyst,
Mn(TPPS)@Im-SiO2
The preparation route for catalyst is shown in Scheme 2.
In the first step, 3-chloropropyl functionalized silica gel
was reacted with N-methylimidazole at 80 °C to produce
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J IRAN CHEM SOC
the supported ionic liquid. Elemental analysis was car-
ried out for ionic liquid support and respective catalyst.
The nitrogen content of the SiO2-Im was about 0.86 %.
According to this value, 0.31 mmol of the ionic liquid
fragment has been grafted per gram of the SiO2-Im. The
amount of Mn was measured by ICP. The value showed
that the catalyst loading is about 0.06 mmol/g. The FT-IR
spectrum of SiO2-Im (Fig. 1) showed the characteris-
shifted to lower frequency (1633 cm−1) by immobilisa-
tion of [Mn(TPPS)]. The appearance of metalloporphy-
rin bands in the IR spectra of the supported catalyst con-
firmed that Mn(TPPS) had been supported on the surface
of silica (Fig. 2). Diffuse reflectance (DR) UV–Vis spec-
tra of [Mn(TPPS)@SiO2-Im] showed the Soret band at
474 nm and Q bands at 544, 580, 612 and 680 nm. This
absorption bands were appeared in the UV–Vis spectra of
[Mn(TPPS)@SiO2-Im] and since pure SiO2-Im shows no
UV absorption peak in these area (Fig. 3). These obser-
vations clearly proved the presence of Mn(TPPS) on the
tic band of the parent ionic liquid (νC=N) at 1637 cm−1
.
After anion exchange with metalloporphyrin anion, the
C=N stretching band in supported catalyst (Fig. 2) is
Scheme 2 Preparation of
Mn(TPPS)@SiO2-Im
Fig. 1 FT-IR spectrum of
SiO2-Im
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J IRAN CHEM SOC
Fig. 2 FT-IR spectrum of
Mn(TPPS)@SiO2-Im
Fig. 3 DR UV–Vis spectra of:
a SiO2-Im and b Mn(TPPS)@
SiO2-Im
Fig. 4 Scanning electron
micrographs of: a SiO2-Im and
b Mn(TPPS)@SiO2-Im
support. The SEM images of SiO2-Im and [Mn(TPPS)@
SiO2-Im] are shown in Fig. 4. The SEM image of
[Mn(TPPS)@SiO2-Im] is clearly different from that of
SiO2-Im. This different can be attributed to the supporting
of Mn(TPPS) on the surface of SiO2-Im.
Catalytic activity
The catalytic activity of supported Mn(TPPS) metal-
loporphyrin was tested by investigating the conversion
of cyclooctene to cyclooctene oxide in the presence of
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J IRAN CHEM SOC
Table 1 The effect of solvent on the epoxidation of cis-cyclooctene
catalyzed by [Mn(TPPS)@SiO2-Im] under ultrasonic irradiation con-
ditions
and benzaldehyde was produced as by-product. In the
oxidation of α-methylstyrene, the major product was
α-methylstyreneoxide (62 %), while acetophenone was
produced as minor products. Epoxidation of limonene
with 100 % conversion and 100 % epoxide selectivity,
was led to 67 % of 1,2-epoxide, 33 % of 8,9-epoxide.
Control experiments indicate that in the absence of the
catalyst was also investigated and it was observed that the
amount of product is negligible.
Entry
Solvent
Epoxide (%)a
Time (min)
1
2
3
4
5
6
CH2Cl2
CHCl3
20
15
10
10
10
10
10
10
(CH3)2CO
CH3OH
C2H5OH
CH3CN
67
55
60
100
Catalyst reuse and stability
Reaction condition: cis-cyclooctene (1 mmol), catalyst (330 mg,
0.02 mmol), solvent (5 mL), NaIO4 (2 mmol in 5 mL H2O), imida-
zole (0.1 mmol)
The reusability of a supported catalyst is one of the
most important benefits of heterogeneous catalysts,
a
GC yield based on the starting cyclooctene
Table 2 Oxidation of alkenes with NaIO4 catalyzed by [Mn(TPPS)@SiO2-Im] under ultrasonic irradiation conditions
Substrate
Product
Time (min)
Conversion (%)a
Epoxide selecꢀvity (%)
TOF (h−1
)
1
2
3
10
5
100
100
100
100
100
73
312.6
602.4
151.5
O
O
O
O
20
H
O
O
4
5
20
22
75
83
113.6
135.1
(67 % exo)
100
O
O
(33 % endo)
O
6
15
100
100
200
Reaction conditions: alkene (1 mmol), NaIO4 (2 mmol in 5 mL H2O), catalyst (330 mg, 0.02 mmol), imidazole (0.1 mmol), acetonitrile (5 mL)
a
GC yield based on the starting alkene
sodium periodate. The reactions were continued until
no further progress was observed. In order to choose the
reaction media, the various organic solvents were exam-
ined in the epoxidation of cis-cyclooctene. Among the
dichloromethane, chloroform, acetonitrile, methanol,
ethanol and acetone, acetonitrile was selected as reaction
media because the highest epoxide yield was observed
(Table 1). The catalytic activity of this catalyst was inves-
tigated in the epoxidation of different olefins (Table 2).
The reactions were continued until no further progress
was observed. In the epoxidation of cis-cyclooctene,
indene and α-pinene were completely converted to their
corresponding epoxides with 100 % selectivity. In the
case of styrene, the major product was epoxide 73 %,
because metalloporphyrins are often expensive to pur-
chase or prepare. Therefore, heterogenization of homo-
geneous catalysts makes them useful for commercial
applications. In order to investigate the recyclability
of the heterogeneous catalyst, we selected cyclooctene
as a model substrate due to its relative unreactive alk-
ene. The stability of the [Mn(TPPS)@SiO2-Im] cata-
lyst was monitored using multiple sequential oxidation
of cyclooctene with sodium periodate under ultrasonic
irradiation conditions. To assess stability and reusabil-
ity, the catalyst was separated from the reaction mixture
after each experiment, washed thoroughly with acetoni-
trile and n-hexane successively and dried before being
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J IRAN CHEM SOC
the same reaction conditions [37]. As shown in Table 3, the
TOF (h−1) for supported ionic liquid catalyst, [Mn(TPPS)@
SiO2-Im], were higher than that of supported catalyst
[Mn(TPPS)-SiO2].
Conclusion
In this summary, we have designed an efficient olefins
epoxidation system with sodium periodate under ultrasonic
irradiation conditions in which [Mn(TPPS)-SiO2] has been
immobilized on ionic liquid-modified silica. The major
advantage of ionic liquid-supported catalyst was recover-
able and reusable.
Fig. 5 The results obtained from catalyst reuse and stability in the
oxidation of cyclooctene with NaIO4 by [Mn(TPPS)@SiO2-Im]
under ultrasonic irradiation conditions
Fig. 6 FT-IR spectrum of
recovered Mn(TPPS)@SiO2-Im
Table 3 Comparison of TOF (h−1) obtained in the presence of
Mn(TPPS)@SiO2-Im with Mn(TPPS)@SiO2 for the epoxidation of
olefins with NaIO4 under ultrasonic irradiation conditions
used in the subsequent run. The catalyst was sequen-
tially reused several times with some loss of its cata-
lytic activity (Fig. 5). The filtrates were used for deter-
mination of the catalyst leaching by atomic absorption
spectroscopy (AAS). The results showed that in two
first runs some catalyst is leached from support (3.6 %
in the first run and 0.95 % in the second run), but in the
next runs no leaching was observed. The FT-IR spec-
troscopy of the recovered catalyst after using for ten
times showed no change in its IR spectrum (Fig. 6),
which illuminated the fact that the catalytic activity of
the catalyst did not change significantly, as compared
with fresh catalyst.
Substrate
TOF (h−1
)
Mn(TPPS)@SiO2-Ima
Mn(TPPS)@SiOb2
Cyclooctene
Styrene
312.6
151.5
113.6
90.7
133.8
106.2
α-Methylstyrene
a
Reaction conditions: alkene (1 mmol), catalyst (0.026 mmol), oxi-
dant (2 mmol), CH3CN (10 mL), H2O (10 mL)
b
Reaction condition: alkene (1 mmol), catalyst(0.02 mmol), NaIO4
(2 mmol), CH3CN (5 mL), H2O (5 mL), imidazole (0.1 mmol)
To demonstrate the effectiveness of ionic-liquid support-
ing on the catalytic activity of Mn(TPPS), some of the results
obtained by [Mn(TPPS)@SiO2-Im] was compared with our
previously reported systems such as [Mn(TPPS)-SiO2] under
Acknowledgments The support of this work by the Center of
Excellence of Chemistry of University of Isfahan (CECUI) is
acknowledged.
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