Ultrasound promoted preparation of Mn(III)-porphyrin nanoparticles: An efficient heterogeneous catalyst for oxidation of alkenes, alkanes and sulfides

Article abstract of DOI:10.1142/S1088424615501060

In the present research meso-tetrakis(4-carboxyphenyl)porphyrinatomanganese(III) acetate (Mn(TCPP)OAc) nanoparticles have been prepared for the first time without any stabilizing agent or supporting matrix under ultrasonic irradiation. Scanning electron microscopy (SEM) was used to characterize and investigate the nanocatalyst. Rapid, efficient, facile and highly selective oxidation of a wide range of olefins by tetra-n-butylammonium hydrogen monopersulfate over the prepared manganese nanocatalyst was investigated. Also oxidation of sulfides and alkanes in the presence of the (Mn(TCPP)OAc) nanoparticles were studied. The catalyst is recovered by filtration and reused at least five times.

Full text of DOI:10.1142/S1088424615501060

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2015; 19: 1232–1237
DOI: 10.1142/S1088424615501060
Published at http://www.worldscinet.com/jpp/
Ultrasound promoted preparation of Mn(III)-porphyrin
nanoparticles: An efficient heterogeneous catalyst
for oxidation of alkenes, alkanes and sulfides
Saeed Rayati*◊, Fatemeh Nejabat and Nasireh Naghashian
Department of Chemistry, K.N. Toosi University of Technology, P.O. Box 16315-1618, Tehran 15418, Iran
Received 29 September 2015
Accepted 11 November 2015
ABSTRACT: In the present research meso-tetrakis(4-carboxyphenyl)porphyrinatomanganese(III)
acetate (Mn(TCPP)OAc) nanoparticles have been prepared for the first time without any stabilizing
agent or supporting matrix under ultrasonic irradiation. Scanning electron microscopy (SEM) was used
to characterize and investigate the nanocatalyst. Rapid, efficient, facile and highly selective oxidation of a
wide range of olefins by tetra-n-butylammonium hydrogen monopersulfate over the prepared manganese
nanocatalyst was investigated. Also oxidation of sulfides and alkanes in the presence of the (Mn(TCPP)
OAc) nanoparticles were studied. The catalyst is recovered by filtration and reused at least five times.
KEYWORDS: ultrasonic irradiation, oxidation, heterogeneous nanocatalyst, manganese porphyrin,
nanoparticles.
has been reported by Drain [21]. They have investigated
INTRODUCTION
the effect of particle size on the catalytic activity and
Inorganic nanoparticles with various capping groups
selectivity in the oxidation reactions, while they could
or supported on mesoporous materials, polymers or
not study the reusability of the catalyst [22–24].
carbon nanotubes are widely used as catalyst and many
In our present research, in order to overcome to this
publications have been reported in the literature [1–7].
problem, we have used ultrasonic irradiation for production
Synthetic metalloporphyrin complexes which are
of Mn-porphyrin nanoparticles (Mn(TCPP)OAc) by a
introduced to be as model of cytochrome P-450 enzyme
simple, rapid and cheap method without any supporting
have been used as homogeneous catalysts in oxidation
matrix. The prepared nanocatalyst has been used in
reactions [8–12], but their high cost and difficult recovery
oxidation of various alkenes, alkanes and sulfides with tetra-
from the reaction medium limited their use especially in
industrial processes. Immobilization onto solid supports
is a good strategy to overcome this problem [13–19]. On
n-butylammonium hydrogen monopersulfate (TBAO).
the other hand, the properties of nanoscaled particles are
different from those of bulk materials composed of the
same atoms or molecules. Gong and co-workers have
reported the synthesis and characterization of porphyrin
colloidal nanoparticles for the first time [20] and then
RESULTS AND DISCUSSION
Characterization of the bulk and nano complexes
by scanning electron microscopy (SEM)
production of porphyrin based nanoparticles using
different stabilizers such as (polyethylene)glycol(PEG)
Scanning electron microscopy (SEM) was used for
comparison of Mn(TCPP)OAc-nano and bulk complexes
(Fig. 1). The results show that nanoparticles were well-
distributed and the average particle size was from 30 to
60 nm for Mn(TCPP)OAc-nano (Fig. 2). These data
confirms that sonication causes a significant decrease in
the particle size. On the other hand, sonication may limited
◊ SPP full member in good standing
*Correspondence to: Saeed Rayati, tel: +98 2122-850-266,
fax: +98 2122-853-650, email: rayati@kntu.ac.ir or srayati@
yahoo.com
Copyright © 2015 World Scientific Publishing Company

ULTRASOUND PROMOTED PREPARATION OF MN(III)-PORPHYRIN NANOPARTICLES 1233
Fig. 1. The SEM images of (a) bulk, (b) nano-Mn(TCPP)OAc
Fig. 3. The influence of the molar ratio of oxidant/alkene on the
oxidation of cyclooctene. The molar ratio of Mn(TCPP)OAc-
nano:ImH:cyclooctene:TBAO is 1:50:70:X. Time: 20 min
Fig. 2. The particle size distribution for Mn(TCPP)OAc
nanoparticles
Table 1. Experiments on catalytic oxidation of
cyclooctenea
Entry
Catalyst
Conversion, %
2 min 20 min
1
2
3
none
0
11
18
0
33
65
MnTCPP-bulk
MnTCPP-nano
Fig. 4. The effect of solventon catalytic oxidation of cyclo-
octene with TBAO. The molar ratio of Mn(TCPP)OAc:
ImH:alkene:TBAO is 1:50:70:70. Reaction time: 20 min
a The molar ratio of the catalyst:ImH:cycloo-
ctene:TBAO is: 1:30:70:70.
Also catalytic efficiency of the nano-sized catalysts is
considerably more than bulk ones (Table 1).
the tendency of Mn(TCPP)OAc molecules for aggregation
which can definitely control Mn(TCPP)OAc particle size.
The effect of ultrasound irradiation on the particle
size of Mn(TCPP)OAc confirmed by SEM (Fig. 1) and
also the effect of particle size on the catalytic activity of
Mn(TCPP)OAc investigated and presented in Table 1.
In order to find the suitable reaction conditions,
the effect of different parameters that may affect the
conversion of the reaction were studied. The molar ratio
of the ImH/catalyst and oxidant/alkene and solvent are
the factors that have been evaluated. The ImH/catalyst
Heterogeneous catalytic epoxidation of olefins
The catalytic performance of Mn(TCPP)OAc was
investigated in the epoxidation of olefins with TBAO
at room temperature. Blank experiment shows that the
existence of a catalyst is essential for oxidation reaction.
Copyright © 2015 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2015; 19: 1233–1237

1234 S. RAYATI ET AL.
Table 2. Epoxidation of olefins using TBAO catalyzed by Mn(TCPP)OAc
in CH2Cl2
ratios were examined (Fig. 3). The highest
conversion was obtained in 1:1 oxidant/alkene
molar ratio. Lower conversion in higher molar
ratios may be due to the catalyst degradation.
The influence of different solvents on
the oxidation of cyclooctene was studied
using Mn(TCPP)OAc-bulk and Mn(TCPP)
OAc-nano as catalyst. The results which are
presented in Fig. 4 show higher conversions
for dichloromethane and chloroform while
the oxidation reaction in dichloromethane
shows the highest difference between bulk
and nano complexes.
a
Entry
Alkene
Product
Conversion
(selectivity), %
Nano
Bulk
1
2
70 (100)
50 (100)
O
18 (100)
4 (100)
O
In order to establish the general applicability
of this catalytic system, and also to determine
the importance of particle size in the catalytic
activity of Mn(TCPP)OAc, under the optimized
conditions, different olefins were subjected to
oxidation in the presence of the catalytic amount
of Mn(TCPP)OAc (nano and bulk) with TBAO
(Table 2). Cyclooctene, cyclohexene, 1-octene,
trans-stilbene, styrene, indene, 4-chlorostyrene
and 4-methoxystyrene converted to the related
epoxide as the sole product. Nevertheless,
in the oxidation of 4-methylstyrene and
a-methylstyrene, some related benzaldehyde
was obtained as by product.
p
h
p
h
O
3
25 (93)
100 (100)
94 (100)
6 (70)
29 (100)
28 (100)
p
h
p
h
O
4
5
O
Cl
Cl
O
6
7
98 (85)
75 (86)
Me
Me
O
Heterogeneous oxidation of alkanes
100 (100)
55 (100)
Oxidation of saturated hydrocarbons using
Mn(TCPP)OAc/TBAO/ImH catalytic system
has been studied (Table 3). However the
product yield is not high, but comparison of
the obtained conversion in Table 3, clearly
demonstrate the effect of particle size on
catalytic activity.
MeO
MeO
Me
Me
O
8
100 (64)
68 (50)
9
96 (100)
4 (100)
70 (100)
0
Heterogeneous oxidation of sulfides
O
In order to show the significance of particle
size in the catalytic activity of Mn(TCPP)OAc
on the oxidation of different substrate, oxidation
of various sulfides with TBAO in the presence
of Mn(TCPP)OAc nano and bulk complexes
was investigated and the results are presented
in Table 4.
10
5
5
O
a The molar ratio of catalyst:ImH:Alkene:TBAO is 1:50:70:70. Reaction time:
20 min.
molar ratio is an important parameter that may affect the
conversion of the reaction especially in the presence of
Homogeneous epoxidation of cyclooctene
Mn-porphyrins. In the absence of imidazole no significant
product was observed. Higher conversions were obtained
by increasing the amount of imidazole and the highest
conversion was obtained in 1:50 Cat./ImH molar ratio.
In order to investigate the effect of oxidizing agent in the
oxidation of cyclooctene, different oxidant/alkene molar
Homogeneous catalytic epoxidation of cyclooctene
with TBAO in methanol led to only 38% conversion of
cyclooctene to its corresponding epoxide. This may be
due to the aggregation [27, 28] between Mn(TCPP)OAc
molecules.
Copyright © 2015 World Scientific Publishing Company
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ULTRASOUND PROMOTED PREPARATION OF MN(III)-PORPHYRIN NANOPARTICLES 1235
Table 3. Oxidation of alkanes using TBAO catalyzed by
Mn(TCPP)OAc in dichloromethanea
Entry
Alkane
Product
Conversion
(selectivity), %
Bulk
Nano
OH
1
2
13 (83)
38 (95)
OH
23 (100)
36 (100)
Fig. 5. Recycling of the catalytic system for the epoxidation of
cyclooctene with TBAO by Mn(TCPP)OAc-nano complex. The
molar ratio of Catalyst:ImH:Cyclooctene:TBAO is 1:30:70:70.
Reaction time: 20 min
OH
6 (80)
11 (62)
8 (100)
3
4
O
the heterogeneous Mn(TCPP)OAc nano particles can be
separated easily and reused multiple times. For each of the
repeated reactions, after the completion of the reaction, the
solid catalyst was separated by centrifugation for 15 min,
washed with dichloromethane (3 × 2 mL) and dried at
80°C for 20 h and irradiated with ultrasonic waves for
40 min in dichloromethane and used for next run. The
MnTCPP-nano was consecutively reused five times
(Fig. 5). 40% conversion was obtained after five catalytic
cycles which is valuable result especially in the presence
of heterogeneous catalyst without any supporting matrix.
A decrease in the conversion of cyclooctene after five
times may be due to the catalyst degradation.
2 (100)
O
2 (100)
6 (55)
5
a The molar ratio of catalyst:ImH:Alkane:TBAO is 1:50:35:70.
Reaction time: 20 min.
Table 4. Oxidation of various sulfides with TBAO catalyzed
by Mn(TCPP)OAc
Comparison of this catalytic system with previously
reported systems shows that the reaction conditions are
much easier and this catalytic system is cheaper with respect
to the heterogeneous catalysts with various capping groups
or imbedded into polymers or other matrix [7, 14, 16].
Entry
Sulfide
Conversion (selectivity
to sulfoxide), %a
Bulk
Nano
s
Proposed mechanism
1
52 (100)
71 (76)
Although the difference in the catalytic activity of
MnTCPP(OAc)-nano and bulk for oxidation of various
substrate is completely clear, but the oxidation reactions
show no significant differences in the selectivity of
products (Tables 2, 3 and 4), which may be related to the
same mechanism for both nano and bulk catalysts.
In the proposed catalytic cycle, TBAO will be activated
by coordination to the Mn-center (Scheme 1, I) [29, 30].
It seems that a six coordinate species (Scheme 1, II) or
a high-valent metal-oxo species (Scheme 1, III) as active
oxidation species are responsible for an effective oxidation.
S
2b
68 (88)
82 (90)
3b
4
83 (75)
96 (59)
61 (82)
s
S
49 (100)
a The molar ratio of catalyst:ImH:Alkene:TBAO is 1:50:70:70
based on 0.0015 mmol of catalyst. Reaction time: 2 min.
b Temperature: 0°C.
EXPERIMENTAL
Catalyst reuse and stability
Instruments and reagents
The reusability of a heterogeneous catalyst is
significant in the catalytic systems. The homogeneous
Mn(TCPP)OAc cannot be recovered even once while
The reactions were irradiated with ultrasound 296 W
(WUC-A03H, DAIHAN). Scanning electron microscopy
Copyright © 2015 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2015; 19: 1235–1237

1236 S. RAYATI ET AL.
H
-
OSO3
+
O
Mn
-
H
OSO3
+
O
ImH
O
Mn
II
ImH
ImH
TBAO
MnIII
OAc
MnIII
ImH
I
O
Mn
III
ImH
O
O
Mn
ImH
Scheme 1. Proposed mechanism for oxidation of cyclooctene
1
(SEM) images were obtained on a Hitachi S-1460
field emission scanning electron microscope using Acc
voltage of 15 kV. The oxidation products were analyzed
with a gas chromatograph (Shimadzu, GC-14B) equipped
421, 515, 549, 592, 646. H NMR (500 MHz; DMSO;
Me4Si): dH, ppm 8.69 (8H, br, b-pyrrole), 8.31–8.33 (8H,
d, o-phenyl), 8.08–8.11 (8H, d, m-phenyl).
Preparation of the [Mn(TCPP)OAc]. The Mn(III)-
porphyrincomplex was prepared according to the
literature method [26]. In brief, H2TCPP (0.3 mmol) and
Mn(OAc)2.4H2O (1.5 mmol) were added to 15 mL DMF
and the reaction mixture was refluxed for 3 h. Then the
solvent was evaporated under reduced pressure and the
crude residue was washed with water and dried in air.
UV-vis (DMF): lmax, nm 477, 577, 609.
Preparation of the [Mn(TCPP)OAc] nanoparticles
under ultrasonic irradiation. The Mn(TCPP)OAc
(0.003 mmol or 0.0015 mmol for using in the catalytic
experiment of hydrocarbon or sulfide respectively)
was added to dichloromethane (1 mL) in a 5 mL test
tube. The test tube was fixed in ultrasound batch and
irradiated with ultrasonic waves for 40 min. Mn(TCPP)
OAc is completely insoluble in dichloromethane and
the suspension of Mn-porphyrins was observable during
the irradiation. However because of the absence of any
stabilizing agent, at the end of ultrasonic irradiation,
Mn(TCPP)OAc quickly precipitated, while it is in nano
scale. Mn(TCPP)OAc nanoparticles were used directly
in the catalytic experiments. UV-vis spectra was used to
1
with a SAB-5 capillary column. H NMR spectrum
was obtained in dimethyl sulfoxide (DMSO) solutions
with a Bruker FT-NMR 500 (500 MHz) spectrometer.
The electronic absorption spectra were recorded on a
single beam spectrophotometer (Cam Spec-M330) in
DMF and CH2Cl2. Tetra-n-butylammonium hydrogen
monopersulfate was prepared freshly according to the
literature [25].
Synthesis
Preparation of the meso-tetrakis(4-carboxyphenyl)
porphyrin (H2TCPP). Meso-tetrakis(4-carboxyphenyl)-
porphyrin was prepared and characterized by standard
method [26]. Freshly distilled pyrrole (4.5 mmol) and
terephthalaldehydic acid (4.5 mmol) were mixed in
propionic acid (200 mL). The solution was refluxed for
2 h. Then the desired dark purple solution was cooled
to room temperature and filtered to yield the purple
crystals. The products were washed with warm water and
methanol and finally dried in air. UV-vis (DMF): lmax, nm
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J. Porphyrins Phthalocyanines 2015; 19: 1236–1237

ULTRASOUND PROMOTED PREPARATION OF MN(III)-PORPHYRIN NANOPARTICLES 1237
checked and confirmed insolubility of Mn(TCPP)OAc in
dichloromethane even after ultrasonic irradiation.
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General heterogeneous oxidation procedure
General procedure for oxygenation of alkenes and
alkanes. In a typical procedure for oxidation of alkenes
or alkanes, substrate (0.21 mmol) and imidazole (0.15
mmol) were added to dichloromethane (1 mL) including
Mn-porphyrin nanoparticles (0.003 mmol) and finally,
freshly prepared TBAO (0.21 mmol or 0.42 mmol for
alkenes or alkanes respectively) was added. The reaction
mixture was stirred for 20 min at 25°C. The resulting
solution was directly analyzed by GC.
General procedure for oxygenation of sulfides. In
a typical procedure for oxidation of sulfides, substrate
(0.12 mmol) and imidazole (0.075 mmol) were added
to a dichloromethane solution (3 mL) including
Mn-porphyrin nanoparticles (0.0015 mmol) and finally,
freshly prepared TBAO (0.11 mmol) was added. The
reaction mixture was stirred for 2 min and was directly
analyzed by GC.
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CONCLUSION
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In conclusion, use of this highly efficient catalytic
system is a suitable path for biomimetic oxidation of
alkenes, alkanes and sulfides withTBAO. Highly selective
epoxidation of olefins such as cyclooctene, cyclohexene,
1-octene, indene and some substituted styrene were
obtained. The use of ultrasonic irradiation conditions
without any stabilizing agent to prepare heterogeneous
nanocatalysts is of our interest. Finally, Mn(TCPP)OAc
nanocatalyst is a reusable catalyst in oxidation reactions.
Acknowledgements
The financial support of this work by K.N.
Toosi University of Technology research council is
acknowledged.
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