Biomimetic epoxidation of alkenes with sodium periodate catalyzed by tetraphenylporphyrinatomanganese(III) chloride supported on multiwall carbon nanotubes

Article abstract of DOI:10.1007/s11243-011-9555-2

The biomimetic epoxidation of alkenes catalyzed by tetraphenylporphyrinatomanganese(III) chloride, [Mn(TPP)Cl], immobilized on multiwall carbon nanotubes modified with 4-aminopyridine and 4-aminophenol is reported. These heterogenized catalysts were used as efficient and reusable catalysts for epoxidation of a variety of cyclic and linear alkenes with sodium periodate under mild conditions. The catalysts, [Mn(TPP)Cl@amine-MWCNT], were characterized by physico-chemical and spectroscopic methods. The effect of ultrasonic irradiation on these catalytic systems was also investigated. The catalysts were reused several times without loss of their activity. Springer Science+Business Media B.V. 2011.

Full text of DOI:10.1007/s11243-011-9555-2

Transition Met Chem (2012) 37:45–53
DOI 10.1007/s11243-011-9555-2
Biomimetic epoxidation of alkenes with sodium periodate
catalyzed by tetraphenylporphyrinatomanganese(III) chloride
supported on multiwall carbon nanotubes
•
Maryam Zakeri Majid Moghadam Iraj Mohammadpoor-Baltork
•
•
•
Shahram Tangestaninejad Valiollah Mirkhani
•
•
Ahmad Reza Khosropour Mohammad Alizadeh
Received: 10 August 2011 / Accepted: 17 October 2011 / Published online: 8 November 2011
Ó Springer Science+Business Media B.V. 2011
Abstract The biomimetic epoxidation of alkenes cata-
lyzed by tetraphenylporphyrinatomanganese(III) chloride,
[Mn(TPP)Cl], immobilized on multiwall carbon nanotubes
modified with 4-aminopyridine and 4-aminophenol is
reported. These heterogenized catalysts were used as effi-
cient and reusable catalysts for epoxidation of a variety of
cyclic and linear alkenes with sodium periodate under mild
conditions. The catalysts, [Mn(TPP)Cl@amine-MWCNT],
were characterized by physico-chemical and spectroscopic
methods. The effect of ultrasonic irradiation on these cat-
alytic systems was also investigated. The catalysts were
reused several times without loss of their activity.
P-450 and metalloporphyrin complexes are able to oxidize
organic compounds.
Homogenous metalloporphyrins readily undergo
decomposition during the oxidation reaction, which leads
to the formation of l-oxo catalytically inactive dimers in
solvent. Hence, immobilizing these expensive catalysts on
to a solid organic or inorganic support can overcome this
problem [11, 12]. Although the reactivity of this heterog-
enized catalyst is often lower than the homogenized
counterpart, recovery and reusability of the catalyst makes
it cost-effective.
Manganese porphyrins can be immobilized on variety of
supports via different methods, including coordination
bonding, covalent anchorage, electrostatic interactions,
encapsulation and intercalation. In the last two decades,
several manganese porphyrins have been successfully
attached to different supports and investigated for catalytic
activity in organic reactions. Previously, our research
group reported the catalytic activity of manganese por-
phyrins immobilized on silica, polystyrene, ion-exchange
resins and zeolite. Recently, we reported the preparation of
tetrakis(p-aminophenyl)porphyrinatomanganese(III) chlo-
ride, [Mn(TNH2PP)Cl], supported on multiwall carbon
nanotubes via covalent attachment. All of them were used
for alkene epoxidation with NaIO4 [9, 10, 13–22].
Carbon nanotubes (CNTs) offer an ideal opportunity as
a support because of their large specific surface area, water
insolubility and chemical inertness. These long tubes have
attracted a lot of attention from researchers around the
world [23–25].
Introduction
Catalytic oxidation of hydrocarbons in organic liquid phase
by oxo metalloporphyrins, in which the metal possesses
high oxidation number, has attracted much attention by
mimicking the function of monooxygenase enzymes like
cytochrome P-450. In the presence of single oxygen donors
such as iodosylbenzene [1, 2], hypochlorites [3, 4], amine
N-oxides [5], alkyl hydroperoxides [6], hydrogen peroxide
[7, 8] and sodium periodate [9, 10], natural cytochrome
Electronic supplementary material The online version of this
article (doi:10.1007/s11243-011-9555-2) contains supplementary
material, which is available to authorized users.
The use of ultrasound to improve the catalytic activity of
metalloporphyrins has been reported [26–30]. The ability
of ultrasound to create highly reactive surfaces and to
increase mass transfer makes it a particularly elegant
technique for activation of the catalyst. The main effect of
M. Zakeri Á M. Moghadam (&) Á I. Mohammadpoor-Baltork Á
S. Tangestaninejad Á V. Mirkhani Á A. R. Khosropour Á
M. Alizadeh
Department of Chemistry, Catalysis Division,
University of Isfahan, Isfahan 81746-73441, Iran
e-mail: moghadamm@sci.ui.ac.ir
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Transition Met Chem (2012) 37:45–53
O
precipitate was assumed to be the chlorinated multiwall
carbon nanotubes, MWCNT-COCl, and used without
further purification.
[Mn(TPP)Cl@amin-MWCNT]
CH3CN/ H2O/ NaIO4
Magnetic stirring or
Modification of MWCNT-COCl with amines
Scheme 1 Epoxidation of alkenes with NaIO4 in the presence of
[Mn(TPP)Cl@amin-MWCNT]
The MWCNT-COCl (1 g) and Et3N (3 mL) were added to
a solution of 4-aminopyridine (Apy) or 4-aminophenol
(AP) (0.5 g) in dimethylformamide (DMF) (20 mL) and
heated at 80°C for 72 h. Then, the solid was filtered off,
washed with CH3CN and dried at 60°C. CHN analysis
for Apy-MWCNT: C:87.8%, H:1.8%, N:2.9% and of
AP-MWCNT: C:89.2%, H:1.9%, N:1.8%.
ultrasound in liquids is cavitation, which involves numerous
tiny gas bubbles called cavitation bubbles. The collapse of
the bubbles generates high temperature and pressures at the
center of the bubbles. These local effects produce a variety of
radicals and highly active intermediates, which initiate other
secondary chemical reactions in the bulk liquid. These rad-
icals can react with contaminants to form by-products [31].
In the present work, the preparation, characterization
and investigation of catalytic activity of [Mn(TPP)Cl]
supported on functionalized multiwall carbon nanotubes in
the epoxidation of alkenes with sodium periodate is
reported (Scheme 1).
Supporting of Mn(TPP)Cl on amine modified
MWCNTs
To a solution of Mn(TPP)Cl (1 g) in toluene (50 mL),
amine modified MWCNTs (5 g) was added and refluxed
for 72 h. At the end of the reaction, the mixture was
cooled; the catalysts were filtered off and washed thor-
oughly with toluene, methanol, and ether, successively, and
dried in vacuum for several hours.
Experimental
General procedure for alkene epoxidation with NaIO4
catalyzed by [Mn(TPP)Cl@amine-MWCNT]
under agitation with magnetic stirring
All materials were of the commercial reagent grade.
Alkenes were obtained from Merck chemical company and
passed through a column containing active alumina to
remove the peroxidic impurities. Tetraphenylporphyrin
was prepared and metallated according to the literature
[32, 33]. FT-IR spectra were obtained with potassium
bromide pellets in the range 400–4,000 cm-1 with a Perkin
Elmer version 10.00 spectrometer. Scanning electron
micrographs of MWCNT were taken on a Philips XL 30
SEM instrument. Gas chromatography experiments (GC)
were performed with a Shimadzu GC-16A instrument
using a 2 m column packed with silicon DC-200 or Car-
bowax 20 m. In the GC experiments, n-decane was used as
an internal standard. The ICP analyses were performed on
an ICP-Spectrociros CCD instrument. The diffuse reflec-
tance ultraviolet–visible spectra of solids were determined
on a UV–Vis Shimadzu model 265 spectrophotometer.
MWCNTs (multiwall carbon nanotubes with diameters
between 20 and 30 nm containing -COOH groups, purity
96%) were purchased from Shenzen NTP Factory (China).
The products were identified by comparison of their
retention times with known samples.
All of the reactions were carried out at room temperature
under air. To a mixture of alkene (0.5 mmol), [Mn(TPP)-
Cl@APy-MWCNT] (250 mg) or [Mn(TPP)Cl@AP-MW-
CNT] (300 mg) and CH3CN (5 mL), a solution of NaIO4
(1 mmol) in H2O (5 mL) was added. The progress of the
reaction was monitored by GC. Since different alkenes
have different reactivity toward oxidation, the reactions
were continued until no further progress was observed. At
the end of the reaction, the reaction mixture was diluted
with Et2O (20 mL) and filtered. The catalysts were thor-
oughly washed with Et2O and the combined washings and
filtrate were purified on a silica gel plate to obtain the pure
product.
General procedure for alkene epoxidation with NaIO4
catalyzed by [Mn(TPP)Cl@amin-MWCNT]
under ultrasonic irradiation
All reactions were carried out at room temperature in a
40-mL glass reactor. 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. The operating frequency was 24 kHz
and the output power was adjustable from 0 to 400 W
manually. The total volume of the solution was 10 mL. The
Chlorination of MWCNT-COOH
The MWCNT-COOH (1 g) and SOCl2 (10 mL) were
mixed and refluxed for 1 h. Then the reaction mixture was
cooled and the SOCl2 was evaporated. The resulting
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Transition Met Chem (2012) 37:45–53
47
temperature was maintained at 25 °C during sonication.
A solution of NaIO4 (1 mmol in 5 mL H2O) was added
to a mixture of alkene (0.5 mmol) in CH3CN (5 mL).
After addition of catalyst, [Mn(TPP)Cl@APy-MWCNT]
(250 mg) or [Mn(TPP)Cl@AP-MWCNT] (300 mg), the
mixture was sonicated. Progress of the reaction was followed
by GC. At the end of reaction, the reaction mixture was
diluted with Et2O (20 mL) and filtered. The catalyst was
thoroughly washed with Et2O and the combined washing and
filtrates were purified on a silica gel plate to obtain the pure
product.
washed with Et2O and dried carefully before using it in the
next run.
Results and discussion
Preparation and characterization of the catalysts,
[Mn(TPP)Cl@APy-MWCNT] and [Mn(TPP)Cl@AP-
MWCNT] and investigation of their catalytic activity
in the epoxidation of alkenes with NaIO4
under agitation with magnetic stirring and ultrasonic
irradiation
Catalyst reuse and stability
The specifications of multiwall carbon nanotubes contain-
ing carboxylic acid groups, MWCNT-COOH, which was
used as support, are listed in Table 1. Scheme 2 shows the
preparation procedure for immobilization of [Mn(TPP)Cl]
on amine modified MWCNTs. The amine modified
MWCNT, amine-MWCNT, was prepared by covalent
attachment of 4-aminopyridine and 4-aminophenol to
MWCNT-COCl via an amide linkage. In the next step, the
Mn(TPP)Cl was reacted with amine-MWCNT to obtain the
catalysts via axial ligation. The prepared catalysts were
characterized by elemental analysis, scanning electron
microscopy, and FT-IR and diffuse reflectance UV–vis
spectroscopic methods. The nitrogen content of the sup-
ports was determined by CHN analysis which showed
The reusability of the catalysts was investigated in the
multiple sequential epoxidation of cyclooctene as descri-
bed above. At the end of each reaction, the catalyst was
separated from the reaction mixture by simple filtration,
Table 1 The specification of MWCNT-COOH used in this study
MWCNT-COOH
Outside
diameter
Inside
diameter
Length
COOH
content
Specific surface
area
20–30 nm
5–10 nm
30 lm
1.5%
[110 m2/g
SOCl2
Reflux, 1 h
COCl
COOH
DMF, 120oC
Et3N, 72 h
N
H2N
H2N
OH
O
C
O
C
NH
OH
N
HN
N
N
Mn
N
N
Toluene, 72 h
Toluene, 72 h
O
O
C
C
N
N
H
H
N
N
N
O
N
Mn
N
N
Mn
N
N
N
Scheme 2 Preparation of [Mn(TPP)Cl@amin-MWCNT]
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48
Transition Met Chem (2012) 37:45–53
Table 2 Characteristics of the prepared catalysts
Catalyst
N (%) Mn content FT-IR spectrum (cm-1
(mmol/g)
)
UV–Vis peak (nm)
C=O C–N N–H Porphyrin units
Soret band Q bands
C-Hpyrrol C-HPh C=N C-HPh
APy-MWCNT]
AP-MWCNT]
[Mn(TPP)Cl]
2.92
1.79
–
–
1655 1397 3439
1633 1395 3446
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
752
1176
1160
1173
1240 2920
1226 2923
1232 2921
477.5
466
469
582,617
574,612
570,610
[Mn(TPP)Cl@APy-MWCNT] 2.94
[Mn(TPP)Cl@AP-MWCNT] 1.
0.076
0.069
1653 1397 3448 797
1634 1400 3444 799
values of 2.92% and 1.79% for APy-MWCNT and AP-
MWCNT, respectively. Based on these values, the nitrogen
contents of the supports, which were available for attach-
ment of manganese porphyrin, were obtained as about
1.04 and 1.28 mmol per gram of the APy-MWCNT and
AP-MWCNT, respectively. The Mn content of the cata-
lysts, measured by ICP analysis, were obtained 0.076 and
0.069 mmol/g of catalyst for [Mn(TPP)@APy-MWCNT]
and [Mn(TPP)@AP-MWCNT], respectively (Table 2).
The most informative spectroscopic data, which con-
firmed the anchoring of the Mn(TPP)Cl on the functional-
ized MWCNT, were obtained by FT-IR spectra of,
[Mn(TPP)Cl], amine-MWCNT and [Mn(TPP)Cl@amine-
MWCNT] Fig. S1 (see the Supplementary Data). In the FT-
IR spectrum of APy-MWCNT, the C=O stretching band of
the amide group was observed at 1,655 cm-1. The C–N and
the N–H stretching bands of amide groups present at 1,397
and 3,439 cm-1, respectively (Fig. S1B), which confirmed
the anchoring of 4-aminopyridine to acylated multiwall
carbon nanotubes. The FT-IR spectrum of the supported
catalyst, [Mn(TPP)Cl@APy-MWCNT], exhibits the char-
acteristic bands of the porphyrin units at 797 (C-HPyrrole),
1160 (C-HPh), 1226 (C = N) and 2923 cm-1 (C-HPh) (Fig.
S1C). These observations proved the coordination of
[Mn(TPP)Cl] to MWCNT. The FT-IR spectrum of 4-ami-
nophenol modified MWCNT (Fig. S1D) shows the bands of
the amide linkage at 1,633, 1,395 and 3,446 cm-1 corre-
sponding to C=O, C–N and N–H stretching bands,
respectively. The porphyrin units of the catalyst, [Mn(TPP)
Cl@AP-MWCNT], are observed at 799, 1,173, 1,232 and
2,921 cm-1 (Fig. S1E). The UV–vis spectroscopy was
employed in the diffuse reflectance mode for characteriza-
tion of the supported catalysts. The diffuse reflectance of the
MWCNT-bound porphyrin resembles the solution coun-
terpart spectrum (Fig. 1) with a slight shift. The presence of
Soret and Q bands of manganese porphyrin in the supported
catalysts clearly indicated the presence of the metallopor-
phyrin on the surface of the MWCNT (Fig. 2; Table 2).
Since the MWCNT shows no absorption peak in its diffuse
reflectance spectrum, it is confirmed that [Mn(TPP)Cl] has
been supported on the MWCNT. The SEM images of the
Fig. 1 The UV–Vis spectrum of homogeneous [Mn(TPP)Cl]
[Mn(TPP)Cl@APy-MWCNT] and [Mn(TPP)Cl@AP-
MWCNT] showed that the nanotubes are aggregated and
have retained their nanotube nature (Fig. 3).
The prepared catalysts were used for the epoxidation of
olefins with sodium periodate at room temperature. First,
the reaction parameters such as catalysts amount, kind of
solvent and oxidant were optimized in the epoxidation of
cyclooctene.
In order to optimize the catalysts amount, different
quantities of each catalyst were used in the epoxidation of
cyclooctene (0.5 mmol) with NaIO4 (1 mmol). The best
results were obtained with 250 mg (0.019 mmol) of
[Mn(TPP)Cl@APy-MWCNT] and 300 mg (0.020 mmol)
of [Mn(TPP)Cl@AP-MWCNT] catalysts (Table 3).
The ability of different single oxygen donors such as
NaIO4, H2O2, NaOCl, tert-BuOOH and n-Bu4NIO4 was
investigated in the epoxidation of cyclooctene. The results,
which are summarized in Table 4, showed that NaIO4 is
the best oxygen source because this oxidant, which is inert
in the absence of catalyst, can give good oxidation con-
version in CH3CN/H2O.
In order to choose the reaction media, different solvents
were checked in the epoxidation of cyclooctene with
NaIO4. Among the different mixtures of acetonitrile, ace-
tone, methanol, ethanol (single phase systems),
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Transition Met Chem (2012) 37:45–53
49
Fig. 3 The SEM image of: a [Mn(TPP)Cl@APy-MWCNT] and
b [Mn(TPP)Cl@AP-MWCNT]
Table 3 Optimization of the catalysts amount in the epoxidation of
cyclooctene with NaIO4
Catalyst Epoxide yield
amount (%)a after 2.5 h
Epoxide yield
(%)a after 3 h
[Mn(TPP)Cl@APy-MWCNT] [Mn(TPP)Cl@AP-MWCNT]
(mg)
0
4
68
76
98
98
–
2
49
67
80
94
94
100
200
250
300
350
Fig. 2 Diffuse reflectance UV–Vis spectra of:
b [Mn(TPP)Cl@APy-MWCNT], c [Mn(TPP)Cl@AP-MWCNT]
a
MWCNT
Reaction conditions: cyclooctene (0.5 mmol), oxidant, catalyst,
CH3CN/H2O (5 mL/5 mL)
dichloromethane and chloroform (two phase systems with n-
Bu4NBr as phase transfer catalyst), the 1:1 mixture of ace-
tonitrile: water was chosen as the reaction medium, because
the higher catalytic activity was observed in this experi-
mental condition (Table 5). The higher catalytic activity in
acetonitrile/water mixture is attributed to polarity of solvent
and solubility of NaIO4 and alkene in this medium.
a
GC yield based on the starting alkene
is due to the bundled agglomerates of MWCNT that
aggregate slowly and let the catalysts to suspend without
setting down for
a
long period of time. The
[Mn(TPP)Cl@APy-MWCNT] and [Mn(TPP)Cl@AP-
MWCNT] were found as efficient catalysts for epoxidation
of alkenes with NaIO4 (Tables 6 and 7). In these heterog-
enized catalytic systems, the oxidation of cyclooctene
The supported catalysts were used for epoxidation of
olefins with NaIO4 under optimized conditions. During the
reaction, the catalysts were suspended in the solvent. This
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50
Transition Met Chem (2012) 37:45–53
Table 4 The effect of oxidant on the epoxidation of cyclooctene catalyzed by [Mn(TPP)Cl@amine-MWCNT] at room temperature
Row
Oxidant
Solvent
Epoxide yield (%)a after 2.5 h
[Mn(TPP)Cl@APy-MWCNT]b
Epoxide yield (%)a after 3 h
[Mn(TPP)Cl@AP-MWCNT]c
1
2
3
4
5
6
7
NaIO4
CH3CN/H2O
CH3CN/H2O
CH3CN
98
90
25
74
35
36
5
94
89
45
67
28
42
6
Oxone (KHSO5)
NaOCl
tert-BuOOH
(n-Bu)4NIO4
H2O2
CH3CN
CH3CN
CH3CN
No oxidant
CH3CN
Reaction conditions: cyclooctene (0.5 mmol), oxidant (1 mmol), CH3CN/H2O (5 mL/5 mL)
a
GC Yield based on the starting alkene
b
250 mg (0.019 mmol) of the catalyst
c
300 mg (0.020 mmol) of the catalyst
Ultrasonic irradiation can alter the reactivity observed
during the heterogeneous catalysis of a variety of reactions.
The chemical effect of ultrasonic irradiation is due to
several acoustic phenomena, of which cavitation is the
most important. The acoustic cavitation has important
effects such as local increasing in temperature and pres-
sure, the propagation of oxidation catalysts, and the for-
mation of intense liquid microflows [34]. The mechanical
effects of ultrasound offer an opportunity to overcome the
following types of problem associated with conventional
solid/metal reactions: break-up of the surface structure
allows penetration of reactants and/or release of materials
from surface, degradation of large solid particles due to
shear forces induced by shock waves and microstreaming
leads to reduction of particle size and increase of surface
area and accelerated motion of suspended particles leads to
better mass transfer [35].
Table 5 The effect of solvent on the epoxidation of cyclooctene
catalyzed by [Mn(TPP)Cl@amine-MWCNT] at room temperature
Row
Solvent
Epoxide yield
(%)a after 2.5 h
[Mn(TPP)Cl@
APy-MWCNT]b
Epoxide yield
(%)a after 3 h
[Mn(TPP)Cl@
AP-MWCNT]c
1
2
3
4
5
6
7
8
CH3CN/H2O (1:1)
CH3CN/H2O (1:2)
CH3CN/H2O (2:1)
CH3COCH3/H2O
CH3OH/H2O
98
87
64
75
63
46
27
18
96
90
67
73
59
52
32
14
CH3CH2OH/H2O
CH2Cl2/H2O
CCl4/H2O
Reaction conditions: cyclooctene (0.5 mmol), NaIO4 (1 mmol), sol-
vent/H2O (5 mL/5 mL)
a
GC Yield based on the starting alkene
Therefore, all the reactions were exposed to ultrasonic
irradiation. The obtained results are summarized in
Tables 6 and 7. These results clearly showed that the
reaction times were reduced and the TOFs increased in the
system under US irradiation.
b
250 mg (0.019 mmol) of the catalyst
c
300 mg (0.020 mmol) of the catalyst
produced 94–96% of cyclooctene oxide. The cyclohexene
was oxidized in high yield and selectivity to cyclohexene
oxide and no by-product was observed. In the epoxidation of
styrene and a-methylstyrene, the major products were sty-
rene oxide and a-methylstyrene oxide and only small
amounts of benzaldehyde and acetophenone were produced,
respectively. In the case of linear alkenes such as 1-octene
and 1-dodecene, the corresponding epoxides were obtained
in high yields with 100% selectivity.
In the alkene epoxidation with NaIO4 in the presence of
[Mn(TPP)Cl@APy-MWCNT] and [Mn(TPP)Cl@AP-
MWCNT], cyclooctene was epoxidized in 99 and 95%
yield with 100% selectivity, but the reaction time
decreased to 15 and 20 min, respectively. The yields in the
case of linear alkenes increased and the reaction times were
greatly decreased.
To confirm the break-up of the agglomerates by US
irradiation, a sample of each catalyst was sonicated for
30 min and used in the epoxidation of cyclooctene with
NaIO4 under agitation with magnetic stirring. It was
observed that the reaction times reduced from
150–180 min to 90–100 min. The blank experiment in the
The results obtained by this method were compared with
some of those reported previously in the oxidation of
cyclohexene with NaIO4. As can be seen in Table 8, the
present method is superior in term of selectivity while the
TOFs are comparable with the others.
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Transition Met Chem (2012) 37:45–53
51
Table 6 Epoxidation of
Entry Alkene
Conversion (%)a Epoxide yield (%)a Time/min TOF (h-1
)
alkenes with NaIO4 catalyzed
by [Mn(TPP)Cl@APy-
MWCNT] under agitation with
magnetic stirring (MS) and
under ultrasonic irradiation
(US)
MS
98
US
99
MS
98
US
99
MS US MS
US
1
2
150 15 10.26 103.66
120 10 13.04 163.61
100
87b
85d
100
89c
86d
100
70
100
72
3
4
180 20
180 20
7.50
7.42
70.60
68.22
67
76
Reaction conditions: alkene
(0.5 mmol), NaIO4 (1 mmol),
catalyst (250 mg), CH3CN/H2O
(5 mL/5 mL)
a
GC yield based on starting
5
71
78
71
78
180 25
6.19
49.08
alkene
b
17% benzaldehyde was
produced
c
18% benzaldehyde was
produced
6
7
73
60
72
56
73
60
72
56
180 30
180 30
6.37
5.23
37.69
29.32
d
The by-product is
acetophenone
Table 7 Epoxidation of
Entry Alkene
Conversion (%)a Epoxide yield (%)a Time/min TOF (h-1
)
alkenes with NaIO4 catalyzed
by [Mn(TPP)Cl@AP-MWCNT]
under agitation with magnetic
stirring (MS) and under
MS
94
US
95
MS
94
US
95
MS US MS
US
1
180 20 7.56 69.53
ultrasonic irradiation (US)
2
3
4
98
85b
82d
98
83c
79d
98
66
65
98
67
58
120 15 11.83 94.63
180 25
180 25
6.84 48.19
6.60 45.87
Reaction conditions: alkene
(0.5 mmol), NaIO4 (1 mmol),
catalyst (300 mg), CH3CN/
H2O (5 mL/5 mL)
a
GC yield based on starting
5
68
71
68
71
180 25
5.47 41.22
alkene
b
%19 benzaldehyde was
produced
c
% 16 benzaldehyde was
produced
6
7
64
52
68
56
64
52
68
56
210 30
210 30
4.42 32.85
4.19 27.05
d
The by-product is
acetophenone
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52
Transition Met Chem (2012) 37:45–53
Table 8 The comparison of the results obtained for the oxidation of
cyclohexene with NaIO4 catalyzed by manganese porphyrins with
those obtained by the recently reported catalysts
Table 9 The results of catalysts recovery and the amount of man-
ganese leached in the epoxidation of cyclooctene with sodium
periodate
Row Catalyst
Selectivity TOF Ref.
(h-1
Run
[Mn(TPP)Cl@
APy-MWCNT]a
[Mn(TPP)Cl@
AP-MWCNT]b
(%)
)
Yield
(%)c
Mn leached
(%)d
Yield
(%)c
Mn leached
(%)d
1
2
3
4
5
6
7
8
9
MnTPPS-PSMP
83
85
83
79
77
64
53
74
17.5
9.4
[36]
[13]
MnTPyP-CMP
Mn(Br8TPPS)-Ad-400
MnTPPS-Ad
14.09 [37]
15.71 [38]
1
2
3
4
5
98
96
96
90
90
1.4
0.5
0
94
92
88
85
85
1.4
0.4
0
Mn(TNH2PP)-PSA
Mn(TPP)-PSI
6.5
[39]
[30]
16.6
0
0
MnP-NaY
9.10 [2]
0
0
[Mn(TNH2PP)Cl-MWCNT]
18.4
[9]
Reaction conditions: alkene (0.5 mmol), NaIO4 (1 mmol), CH3CN/
H2O (5 mL/5 mL)
Mn(TPP)Cl-APy-MWCNT 100
13.04 Present
work
a
250 mg (0.019 mmol) of the catalyst
10
Mn(TPP)Cl-AP-MWCNT 100
11.83 Present
work
b
300 mg (0.020 mmol) of the catalyst
c
GC yield based on the starting alkene
d
Determined by atomic absorption spectroscopy
and [Mn(TPP)@AP-MWCNT] was investigated in the
multiple sequential epoxidation of cyclooctene with NaIO4.
At the end of the each reaction, the catalysts were separated
by simple filtration, washed with Et2O and dried carefully
before using in the next run. After using of the catalysts for
five consecutive times, the epoxide yields were 90 and 85%
for [Mn(TPP)@Apy-MWCNT] and [Mn(TPP)@AP-
MWCNT], respectively (Table 9). The filtrates were col-
lected for determination of Mn leaching. The results showed
that after two first runs, no manganese was detected in the
filtrates by atomic absorption spectrometry. The nature of the
recovered catalysts has been followed by FT- IR (Fig S2) and
DR UV–Vis (Fig. S3). The results indicated that the catalysts
after reusing several times, showed no change in their
structures. The catalytic activity of the separated solution
was also investigated. In this manner, after separation of the
each catalyst, fresh cyclooctene and oxidant were added to
the solution. Execution of the oxidation reaction under
the same reaction conditions, as with catalyst, showed
that the obtained results were the same as those for blank
experiments.
Fig. 4 Comparison of systems under US irradiation and MS in the
epoxidation of cyclooctene with NaIO4 catalyzed by [Mn(TPP)Cl@
APy-MWCNT]
absence of catalysts, under ultrasonic irradiation, showed
that the ultrasonic irradiation is much less efficient in the
oxidation reactions with sodium periodate. When these
reactions were carried out under reflux conditions, the
reaction times decreased. These observations showed that
another part of the ultrasonic effect is production of hot
spots due to cavitation phenomenon.
Figure 4 shows a comparison between systems under
US irradiation and under agitation with magnetic stirring,
which indicates the effect of ultrasonic irradiation on the
catalytic activity of [Mn(TPP)Cl@APy-MWCNT] in the
epoxidation of cyclooctene with NaIO4.
Conclusion
In conclusion, manganese(III)tetraphenylporphyrin immo-
bilized on MWCNTs modified with amines were used as
heterogenized catalysts for efficient epoxidation of alkenes
with NaIO4 under mechanical stirring and ultrasonic irra-
diation. The ultrasonic irradiation increased the perfor-
mance of the catalysts. The catalysts could be recovered
several times by simple filtration and reused without sig-
nificant loss of their catalytic activity.
The reusability of a heterogeneous catalyst is of great
importance from synthetic and economical points of view.
The homogeneous [Mn(TPP)Cl] cannot be recovered even
one time, in contrast, the MWCNT supported catalysts can
be filtered and reused several timeswithout significant lossof
its activity. The reusability of [Mn(TPP)@Apy-MWCNT]
123

Transition Met Chem (2012) 37:45–53
53
Acknowledgments We acknowledge the support of this work by
Center of Excellence of Chemistry of University of Isfahan (CECUI).
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