Iron(III) porphyrin covalently supported onto magnetic amino-functionalized nanospheres as catalyst for hydrocarbon and herbicide oxidations

Article abstract of DOI:10.1590/S0103-50532012005000005

This work describes the covalent immobilization of an ironporphyrin, 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin iron(III) chloride (FeTFPP), onto maghemite/silica magnetic nanospheres covered with aminofunctionalized silica. The resulting material (γ-Fe₂O₃/SiO ₂-NHFeP) was characterized by diffuse reflectance infrared spectroscopy (DRIFTS) and UV-Vis absorption spectroscopy. The catalytic activity of this magnetic ironporphyrin was investigated in the oxidation of hydrocarbons (styrene, (Z)-cyclooctene and R-(+)-limonene) and an herbicide (simazine) by hydrogen peroxide or 3-chloroperoxybenzoic acid. Hydrocarbon and simazine oxidation reaction products were analyzed by gas chromatography (GC) and high performance liquid chromatography (HPLC), respectively. This catalytic system proved to be efficient and selective for hydrocarbon oxidation, leading to high product yields from styrene (89percent), cyclooctene (71percent) and R-(+)-limonene (86percent). Simazine oxidation was attained with 100percent selectivity for a dechlorinated product (OEAT), while several oxidation products were obtained for the same catalyst in homogeneous media. The catalyst can be easily recovered through application of an external magnetic field and washed after reaction. Catalyst reuse experiments for R-(+)-limonene oxidation have shown that the catalytic activity is kept at 90percent after 10 consecutive reactions. ?2012 Sociedade Brasileira de Qui?mica.

Full text of DOI:10.1590/S0103-50532012005000005

J. Braz. Chem. Soc., Vol. 23, No. 8, 1411-1420, 2012.
Printed in Brazil - ©2012 Sociedade Brasileira de Química
0
103 - 5053 $6.00+0.00
Article
A
Iron(III) Porphyrin Covalently Supported onto Magnetic Amino-Functionalized
Nanospheres as Catalyst for Hydrocarbon and Herbicide Oxidations
a
a
a
Joicy S. dos Santos, André L. Faria, Patrícia M. da Silva Amorin,
a
b
c
Franco M. La Luna, Kely L. Caiado, Débora O. C. e Silva,
b
,a
Patrícia P. C. Sartoratto and Marilda D. Assis*
a
Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto,
Universidade de São Paulo, Av. Bandeirantes, 3900, 14040-901 Ribeirão Preto-SP, Brazil
b
Instituto de Química, Universidade Federal de Goiás, 74001-970 Goiânia-GO, Brazil
c
Laboratório de Microscopia Eletrônica, Instituto de Ciências Biológicas,
Universidade de Brasília, 70910-900 Brasília-DF, Brazil
Este trabalho descreve a imobilização por ligação covalente de uma ferroporfirina, cloreto
de 5,10,15,20-tetraquis(pentafluorofenil)porfirinaferro(III) (FeTFPP), sobre nanoesferas
de maguemita cobertas com sílica aminofuncionalizada. O material resultante (nomeado
γ-Fe O /SiO -NHFeP) foi caracterizado por espectroscopia no infravermelho por refletância
2
3
2
difusa (DRIFTS) e espectroscopia de absorção UV-Vis. A atividade catalítica desta ferroporfirina
magnética foi investigada em reações de oxidação de hidrocarbonetos (estireno, (Z)-cicloocteno e
R-(+)-limoneno) e de um herbicida (simazina), utilizando-se peróxido de hidrogênio ou ácido
metacloroperbenzóico. Os produtos das reações de oxidação de hidrocarbonetos e simazina
foram analisados por cromatografia em fase gasosa (GC) e cromatografia líquida de alta resolução
(HPLC), respectivamente. Este sistema catalítico provou ser eficiente e seletivo na oxidação dos
hidrocarbonetos, levando a altos rendimentos na oxidação do estireno (89%), cicloocteno (71%) e
(
1
+)-limoneno (86%). Na oxidação da simazina catalisada pelo γ-Fe O /SiO -NHFeP, obteve-se
2
3
2
00% de seletividade para um produto desalogenado (OEAT), enquanto a mesma reação em meio
homogêneo levou à formação de diversos produtos de oxidação. O catalisador pode ser facilmente
recuperado pela aplicação de um campo magnético externo e lavado ao final das reações. Nos
estudos de reutilização do catalisador para a oxidação do (+)-limoneno, a atividade catalítica foi
mantida em 90%, mesmo após 10 reações consecutivas.
This work describes the covalent immobilization of an ironporphyrin, 5,10,15,20-
tetrakis(pentafluorophenyl)porphyrin iron(III) chloride (FeTFPP), onto maghemite/silica magnetic
nanospheres covered with aminofunctionalized silica. The resulting material (γ-Fe O /SiO -
2
3
2
NHFeP) was characterized by diffuse reflectance infrared spectroscopy (DRIFTS) and UV-Vis
absorption spectroscopy. The catalytic activity of this magnetic ironporphyrin was investigated
in the oxidation of hydrocarbons (styrene, (Z)-cyclooctene and R-(+)-limonene) and an herbicide
(
simazine) by hydrogen peroxide or 3-chloroperoxybenzoic acid. Hydrocarbon and simazine
oxidation reaction products were analyzed by gas chromatography (GC) and high performance
liquid chromatography (HPLC), respectively. This catalytic system proved to be efficient and
selective for hydrocarbon oxidation, leading to high product yields from styrene (89%), cyclooctene
(71%) and R-(+)-limonene (86%). Simazine oxidation was attained with 100% selectivity for
a dechlorinated product (OEAT), while several oxidation products were obtained for the same
catalyst in homogeneous media. The catalyst can be easily recovered through application of an
external magnetic field and washed after reaction. Catalyst reuse experiments for R-(+)-limonene
oxidation have shown that the catalytic activity is kept at 90% after 10 consecutive reactions.
Keywords: magnetic nanospheres, magnetic ironporphyrin, hydrocarbon oxidation, limonene,
simazine
*e-mail: mddassis@usp.br

1
412
Iron(III) Porphyrin Covalently Supported onto Magnetic Amino-Functionalized Nanospheres
J. Braz. Chem. Soc.
Introduction
research laboratories. Anchoring of metalloporphyrins
onto magnetic nanospheres offers the advantage of
increasing catalyst stability, enhancing selectivity and
even reducing costs, because these catalysts are very
Magnetic nanospheres have been the focus of many
research areas because of their potential application in
biochemistry, smart materials and catalysis. For catalytic
purposes, functionalized magnetic nanoparticles have been
pointed out as alternatives to conventional supports because
they are promptly available and robust, not to mention
that they confer stability to the catalyst. Their magnetic
properties provide a unique way for catalyst recovery and
reuse since they can be separated from the reaction medium
by application of a magnetic field. Several works have
reported on the use of magnetic nanospheres in catalysis,
1,2
4,22
expensive.
In this sense, as part of our ongoing studies on
bioinspired catalysts, in this work, a MeP, namely
5,10,15,20-tetrakis(pentafluorophenyl)porphyrin iron(III)
chloride (FeTFPP, Figure 1), was immobilized onto the
surface of maghemite magnetic nanospheres covered
with aminofunctionalized silica by covalent binding. The
resulting material was used as catalyst for alkene (styrene,
cycloocteneandR-(+)-limonene)andsimazine(anherbicide)
oxidations by hydrogen peroxide or 3-chloroperoxybenzoic
acid.
3,4
1-8
1,4,8
either as catalyst or as support for a number of catalysts.
Recently, researchers have studied the immobilization
of a manganese porphyrin onto a magnetic polymer for
4
cyclohexane hydroxylation, giving rise to a new class of
supports for cytochrome P450 biomimetic models. The
P450 are a class of enzymes responsible for countless
oxidation reactions, ranging from steroid biosynthesis
9
to xenobiotic metabolism. Synthetic metalloporphyrins
(MePs) have been employed over the last three decades and
are considered the best biomimetical models of these
1
0,11
enzymes.
Many MeP-based catalytic systems have been
investigated for the oxidation of various substrates,
12-16
especially alkene epoxidation and alkane hydroxylation.
The best catalytic systems have also been utilized in the
oxidation of drugs, herbicides and other substrates, with
good efficiencies.
Figure 1. Chemical structure of 5,10,15,20-tetrakis(pentafluorophenyl)
porphyrin iron(III) chloride (FeTFPP).
1
7-20
The design and refinement of these bioinspired
catalytic systems have progressed with the synthesis
of MePs with increasing number of substituents in
Experimental
Materials
2
1
11
the porphyrin ring and the use of various oxidants.
Although these refinements have resulted in more
efficient and stable catalysts, their high cost still make
their application difficult, even in fine chemistry. In order
to overcome this drawback, immobilization of these
catalysts onto solid supports has been proposed, aiming
at their separation from the reaction medium, thereby
enabling its reuse. Many materials have been employed
All reagents were commercially available and of
analytical grade purity unless otherwise stated. Hydrogen
peroxide (30% wt., provided by Fluka) was stored at
5 °C and titrated periodically. 3-Chloroperoxybenzoic acid
(m-CPBA, 70%) was purchased fromAcros Organics. The
hydrocarbons (Z)-cyclooctene, styrene and R-(+)-limonene
(Acros) were purified on a short activated basic alumina
column (Merck) immediately before use. Simazine (CEET,
99%) was acquired from Supelco. The free-base porphyrin
5,10,15,20-tetrakis(pentafluorophenyl)porphyrin was
obtained from MidCentury. Metal insertion into this free
2
2-25
as MePs supports,
some of which have afforded good
turnovers in recycling reactions. Nevertheless, part of
the solid catalyst is always lost during the separation and
washing procedures. In this context, MeP immobilization
onto magnetic nanospheres is an innovative approach
since it allows for combination of the biomimetic
properties of MePs with the easy recovery of the supported
complex by simple application of an external magnetic
field originated from a small, commercially available,
inexpensive magnetic stirring bar, commonly utilized in
26
base was carried out by applying the method ofAdler et al.
FeCl ⋅4H O and FeCl ⋅6H O were supplied by Fluka and
2
2
3
2
Acros, respectively. Ammonium hydroxide solution was
provided by Nuclear. Tetraethoxysilane (TEOS) and
(3-aminopropyl)trimethoxysilane (APTS) were purchased
from Acros.

Vol. 23, No. 8, 2012
Santos et al.
1413
Synthesis and characterization of the ironporphyrin
immobilized onto magnetic nanospheres covered with
aminopropylsilica, γ-Fe O /SiO -NHFeP
chromatograph equipped with two LC-10AS solvent
pumps, an SPD-M 10 A VP spectrophotometric detector
(λ = 230 nm) coupled to a CTO-10 A VP column oven,
a CL-10A VP system controller and an injector with a
20 µL loop. The device was connected to a diode array
spectrophotometer.
2
3
2
The magnetic nanoparticles covered with amino
functionalized silica, γ-Fe O /SiO -NH , were synthesized
2
3
2
2
5,6
as previously described by an adaptation of the Stöber
2
7
method, and characterized by transmission electron
microscopy (TEM).
Oxidation reactions
The catalyst γ-Fe O /SiO -NHFeP was prepared by
mixing 400 mg of nanospheres with a solution containing
.04 mg of 5,10,15,20-tetrakis(pentafluorphenylporphyrin)
iron(III) chloride in 5 mL ethyleneglycol. The mixture was
Oxidation reactions were accomplished in 3 mL
vials with a screw cap. The initially employed catalyst/
oxidant/substrate molar ratio was of 1:500:1000, achieved
2
3
2
5
-5
-5
through addition of 5 × 10 mol substrate, 2.5 × 10 mol
oxidant and a mass of the solid material enough to transfer
maintained under reflux with N bubbling at 110 ºC for
2
-8
2
4 h. The solid was isolated by application of a magnetic
5 × 10 mol FeP catalyst to the vial.Acetonitrile (ACN) was
employed as solvent, and the final volume was completed
to 1.5 mL with solvent. Reactions were maintained under
mechanic stirring at room temperature. Catalyses were run
using 3-chloroperoxybenzoic acid (m-CPBA) or hydrogen
peroxide (H O ) as oxidants. Styrene, (Z)-cyclooctene and
field and was submitted to Soxhlet extraction with
dichloromethane for 24 h and methanol for another 24 h
to extract the ironporphyrin that was just adsorbed onto
the support or was immobilized by coordinative binding
through the iron center, leaving only the covalently attached
ironporphyrin on the support. The amount of FeP that was
leached from the solid was determined in the extraction
solvents by UV-Vis spectroscopy, using the absorbance
of the Soret band characteristic of this FeP (420 nm). The
composite was characterized by diffuse reflectance infrared
spectroscopy (DRIFTS) and UV-Vis spectroscopy.
2
2
R-(+)-limonene were employed as substrates. For the
reuse studies, the catalyst was separated from the reaction
medium by application of a magnetic field using a small
magnetic bar.After isolation, the solid catalyst was washed
with acetonitrile, separated from the solvent as described
above and dried in air before addition of new amounts of
substrate and oxidant.
Equipment
Hydrocarbon oxidation products were analyzed by
gas chromatography (GC). The yields are based on the
added oxidant and determined after 4 h reaction, using
bromobenzene as internal standard. Control reactions
were carried out using the magnetic nanoparticles without
catalyst, γ-Fe O /SiO -NH . No products were detected in
Diffuse reflectance spectra (DRIFTS) were obtained on
a Bomem MB 100 spectrometer equipped with a DRIFT
collector accessory, using the system resolution set at
-1
4
cm and a total 128 scans, with the samples dispersed
2
3
2
2
in KBr pellets (1%). UV-Vis analyses were performed on
a Hewlett-Packard 8452 diode array spectrophotometer
using a quartz cell with optical path of 1 cm. The
transmission electron microscopy (TEM) images were
obtained using a JEOL-1011 microscope at 80 keV.
Diffuse reflectance (DR UV-Vis) spectra were analyzed
on Ocean Optics USB 4000 equipment using an optic
fiber vertically positioned 1.5 cm from the sample.Atomic
absorption analyses were performed on a Perkin Elmer
spectrophotometer (model AAnalyst 200).
these cases.
Simazine oxidation was performed using a catalyst/
oxidant/substrate molar ratio of 1:60:60, achieved by
-6
-5
addition of 4 × 10 mol substrate, 7.5 × 10 mol oxidant and
-7
2.5 × 10 mol metalloporphyrin to the reaction vessel. A
mixture of methanol and dichloromethane 1:1 (v/v) was
employed as solvent. The final volume was completed to
1.5 mL with solvent, and the reactions were kept under
mechanic stirring for 4 h at room temperature. Reactions
were run by using 3-chloroperoxybenzoic acid (m-CPBA)
or hydrogen peroxide (H O ) as oxidant. When m-CPBA
Gas chromatographic (GC) analyses were conducted
on a Shimadzu chromatograph (model GC-2010)
equipped with an AOC-20i auto-injector, flame ionization
detector and capillary column RTX-Wax (dimensions of
2
2
was employed, the unreacted oxidant was removed from
the reaction medium before product analysis, via extraction
with an aqueous (10%) Na SO solution. Separation of
2
4
3
0 m × 0.320 mm × 0.25 µm) from Agilent Technologies.
simazine from its oxidation products was accomplished by
HPLC and conducted in a C LiChrospher column (Merck)
Nitrogen was used as the carrier gas.
18
High performance liquid chromatographic (HPLC)
analyses were accomplished on a Shimadzu liquid
with 5 µm particle size (125 × 4 mm). The mobile phase
consisted of methanol and 0.1% trifluoroacetic acid (TFA),

1
414
Iron(III) Porphyrin Covalently Supported onto Magnetic Amino-Functionalized Nanospheres
J. Braz. Chem. Soc.
followed by a gradient ranging from MeOH/TFA
Figure 2 depicts the scheme relative to the preparation
5
1
:95 (v/v) to MeOH/TFA 50:50, at a flow rate of
mL min . The total elution time was 35 min. The mobile
of γ-Fe O /SiO –NHFeP. Steps a and b have been
2
3
2
-1
5,6
previously described and involve the coverage of the
maghemite nanoparticles with silica (Figure 2, a), and
its functionalization with the amine group (Figure 2, b)
following covalent attachment of the ironporphyrin through
nucleophilic aromatic substitution of the para-fluorine
atoms in the pentafluorophenyl group, as described
for immobilization of this ironporphyrin onto other
phase was purged with helium. Reaction products were
analyzed by comparison of their retention times with
standard solutions of the authentic metabolites. Product
yields or conversions were determined from calibration
curves and were based on the added herbicide. Fractions
were collected for identification of unknown products by
mass spectrometry and comparison with similar products
32-34
aminofunctionalized materials
(Figure 2, c).
28
previously identified for other catalytic systems.
The amount of iron in γ-Fe O /SiO –NH dry
2
3
2
2
-4
nanospheres was determined to be 5.18 × 10 mol Fe per g
of composite, as evidenced by atomic absorption
spectrophotometry. The average diameter of the
maghemite nanoparticles inside the silica nanospheres
was 10 nm as calculated from the X-ray diffraction data
of the γ-Fe O nanoparticles (not shown). Figure 3 shows
Results and Discussion
Synthesis and characterization of the solid catalyst,
γ-Fe O /SiO –NHFeP
2
3
2
2
3
FeTFPP (Figure 1) is a second-generation ironporphyrin
that is commercially available and has been reported to
be a good catalyst for hydrocarbon, drug and herbicide
TEM image of the γ-Fe O /SiO –NH nanospheres. The
2
3
2
2
morphology of the nanospheres is uniform with the
presence of spherical maghemite nanoparticles with
average diameter of 318 nm. The material consists of
multicore maghemite-silica particles with a thick silica
shell covered by a thin amino-functionalized silica layer,
1
2-20
oxidation.
The modification of phenyl groups with
electron-withdrawing or bulky substituents has been
found to enhance MeP catalytic activity by creating
a cage around the metal-oxo, thus avoiding catalyst
5
as previously described.
29,30
self-degradation or formation of inactive µ-oxo dimers.
The content of the immobilized ironporphyrin (loading)
in the nanospheres was determined by UV-Vis spectroscopy
Bearing these advantages in mind, this metalloporphyrin
was selected for binding onto magnetic amino-substituted
nanoparticles. Besides these advantageous properties, this
porphyrin also contains para-fluorine phenyl substituents
that enable its covalent attachment to the amino group of
the functionalized nanospheres. This approach results in a
catalyst that is strongly attached to the solid support and
cannot be leached during oxidation reactions in any solvent,
29
from the absorbance of the FeTFPP Soret band at 420 nm.
These measurements were carried out in the supernatant
obtained from the Soxhlet extractions and provided a value
of 11 mg ironporphyrin per g of magnetic nanospheres or
-2
1 × 10 mmol ironporphyrin per g of nanospheres (84% of
the amount of FeP that was initially employed). The solid
catalyst was also characterized by DRIFTS and DR UV-Vis
spectroscopy, which showed a band in 420 nm, confirming
the MeP presence in the material.
31
ranging from water to polar organic ones, while 100%
catalyst recovery can be obtained after the reaction.
Figure 2. Preparation of the γ-Fe O /SiO -NHFeP catalyst.
2
3
2

Vol. 23, No. 8, 2012
Santos et al.
1415
Figure 3. TEM image of γ-Fe O /SiO –NH nanospheres and particle size histogram (DTEM: average diameter).
2
3
2
2
Figure 4 represents the DRIFTS spectra of the
bands associated with Si-O-Si asymmetric stretching can be
-1 35,36
γ-Fe O /SiO –NH and γ-Fe O /SiO -NHFeP nanospheres.
seen at 1058, 1184 and 1309 cm .
weak bands at 2962 and 2890 cm , which can be ascribed
Figure 4 also reveals
2
3
2
2
2
3
2
-1
The spectra were initially registered with the material diluted
in KBr (as usual), but no changes were observed when both
spectra were compared. As an attempt to identify some
vibrational modes associated with the bonds existing in the
complex, the IR measurements were accomplished using
the pure solid without any dilution with KBr. However,
even in this pure sample it was not possible to observe the
IR bands associated with the ironporphyrin complex due to
the low FeTFPP loading in this material. The bands observed
to vibrational modes due to aliphatic (-CH ) stretching of
2
the propyl chain from APTS, proving that functionalization
of the support was indeed achieved.
The catalytic activity of the studied system was
initially investigated for the oxidation of (Z)-cyclooctene,
styrene and R-(+)-limonene. Either H O or m-CPBA
2
2
was used as oxidant. Results were measured in terms of
product yields based on the oxidant. Hydrogen peroxide
was employed for the oxidation of alkenes because it is
considered a “clean oxidant” since it produces water as
the only side-product. m-CPBA is a stable peroxyacid and
is soluble in a variety of commonly used organic solvents,
-1
at 520 and 610 cm can be attributed to Fe-O vibrational
34
modes of the iron oxide. The broad band in the range
-1
of 3500-3000 cm is due to OH stretching of free water
molecules and the silanol remaining groups (SiO-H). The
-1
37
absorptions at 800 and 960 cm can be assigned to Si-O-Si
stretching and Si-OH stretching, respectively. Three other
usually culminating in high epoxidation yields. The
advantage of using alkylhydroperoxides is that they have
excellent solubility in many organic solvents.
(Z)-Cyclooctene is a diagnostic substrate for all new
catalytic systems involving metalloporphyrins since it is
easily oxidized and generally produces the corresponding
31,38
epoxide as the sole product.
Table 1 lists the product
yields from cyclooctene oxidation by m-CPBA and H O
2
2
catalyzed by the supported FeTFPP prepared herein.
Initially, the oxidation reactions were accomplished using
-8
-5
-4
5
.0×10 molcatalyst, 2.5×10 moloxidantand5.0×10 mol
substrate, corresponding to a catalyst/oxidant/substrate molar
ratio of 1:500:10000. To compare and optimize the catalytic
conditions, a molar ratio of 1:250:5000 was also tested.
The reaction conducted at the molar ratio of 1:250:5000
(
catalyst/oxidant/substrate) rendered higher cyclooctene
oxide yields (71% for reactions with m-CPBA).
Product yields are highly dependent on the oxidant,
the best one being m-CPBA (Table 1, entries 2 and 4).
Figure 4. DRIFTS spectra of the γ-Fe O /SiO –NH and γ-Fe O /SiO -
2
3
2
2
2
3
2
NHFeP nanospheres.

1
416
Iron(III) Porphyrin Covalently Supported onto Magnetic Amino-Functionalized Nanospheres
J. Braz. Chem. Soc.
Table 1. Cyclooctene oxidation by m-CPBA and H O catalyzed by
In this scheme, an asymmetric transition that generates
the epoxide (path a) or phenylacetaldehyde (path b) is
represented. The latter is analogous to the well-established
2
2
γ-Fe O /SiO -NHFeP, in acetonitrile medium, after 24 h reaction
2
3
2
Cyclooctene oxide
a
41
Entry
Molar ratio
Oxidant
H O
NIH rearrangement. Moreover, phenylacetaldehyde
b
yield / %
formation is related to the reactivity of the intermediate
species (activated complex, Scheme 1). In other words,
the lower is the reactivity, the longer is the lifetime and
the higher is the probability of hydrogen rearrangement.
This should lead to phenylacetaldehyde production (path
b) and explains why yields for the latter product are lower
as compared to styrene epoxide yields. Because the FeP
is anchored onto the magnetic nanospheres, the steric
effect of the support must disfavor the rearrangement
that is necessary for phenylacetaldehyde production, as
1
2
3
1:250:5000
1:250:5000
1:500:10000
1:500:10000
Nd
71
2
2
m-CPBA
H O
Nd
48
2
2
4
m-CPBA
a
b
-8
Molar ratio: catalyst/oxidant/substrate; 5.0 × 10 mol FeTFPP; Nd: not
detected; control reactions: no products detected.
No product was detected for reactions oxidized by H O ,
2
2
which can be explained by the catalyzed dismutation of
this oxidant in the presence of metal complexes and/or
rd
previously observed for the more robust 3 generation
30
42
ferromagnetic nanoparticles.
metalloporphyrins. As a result, high selectivity for the
Styrene oxidation generally leads to benzaldehyde,
styrene oxide and phenylacetaldehyde as products, which
are used as intermediates for the synthesis of fine chemicals
as well as for production of fragrances, pharmaceuticals and
epoxide is achieved.
4
,6
agrochemicals. This hydrocarbon is extensively studied
because it can generate different products depending on the
3
8
reaction conditions. This special feature can be exploited
so that a better understanding of the reaction mechanisms
involving metalloporphyrins can be obtained.
The results from styrene oxidation catalyzed by
γ-Fe O /SiO -NHFeP are summarized in Table 2 for three
2
3
2
reaction cycles using the same catalyst batch.
The catalyst γ-Fe O /SiO -NHFeP efficiently promoted
2
3
2
styrene oxidation by m-CPBA, reaching 89% total yield
in the first reaction (Table 2, entry 1). Two products were
obtained in this condition, phenylacetaldehyde (18%) and
styrene oxide, the major product (71%). No benzaldehyde
was produced. Control experiments using styrene oxide as
substrate under the same reaction conditions showed that
phenylacetaldehyde is not formed from the rearrangement
of styrene oxide or from the rearrangement that could occur
Scheme 1. Possible reaction paths for oxygen transfer from the
ironporphyrin intermediate to styrene. Adapted from Groves et al.
4
0
The magnetic catalyst was reused in three
consecutive cycles for the oxidation of styrene (Table 2,
entries 2 and 3), and the catalytic activity was maintained.
The reuse reactions were facilitated by easy catalyst
recovery through simple application of a magnetic field.
On the basis of the results obtained for (Z)-cyclooctene
oxidation, the catalytic condition 1:250:5000 catalyst/
oxidant/substrate molar ratio was chosen for investigation
of the R-(+)-limonene oxidation.
39
in the chromatograph injector. In fact, Groves and Mayer
proposed a mechanism accounting for the parallel formation
of styrene oxide and phenylacetaldehyde in systems
involving metalloporphyrins. Scheme 1 displays an adapted
40
scheme to explain the results obtained in the present study.
Table 2. Styrene oxidation by m-CPBA catalyzed by γ-Fe O /SiO -NHFeP, in acetonitrile medium, after 24 h of reaction
2
3
2
Product yield / %
a
Entry
Cycle
Total yield / %
Phenylacetaldehyde
Styrene epoxide
1
2
1
2
3
18
13
18
71
74
79
89
87
97
3
a
-8
b
Molar ratio: 1:500:10000 (catalyst/oxidant/substrate), 5.0 × 10 mol FeTFPP; control reactions: no products detected.

Vol. 23, No. 8, 2012
Santos et al.
1417
IV
•+
Limonene is naturally found in orange peels, which is
species oxoferryl porphyrin π-cation radical, Fe (O)P or
V
the main source of R-(+)-limonene, while the major source
oxomanganylporphyrin, Mn (O)P. However, the major
43
of S-(-)-limonene is lime peels. Oxygen-functionalized
limonene derivatives (Figure 5) are important for food
additives and for the pharmaceutical and agrochemical
problem regarding the use of ROOH with manganese and
ironporphyrins is avoidance of the thermodynamically
favored homolysis of the peroxide bond. O-O bond
homolytic cleavage gives a less reactive intermediate
4
3
industries, the reason why the development of methods
for the selective oxidation of this alkene has been the object
IV
•
(Me (OH)P) and generates an alkoxyl radical RO , which is
43-46
of intense research.
able to abstract a hydrogen atom from a saturated C-H bond
but is unable to produce epoxides from olefinic substrates.
30
Because the R-(+)-limonene oxidation catalyzed by
γ-Fe O /SiO -NHFeP produced epoxide as the major
2
3
2
product, it can be suggested that the high-valent metal oxo
IV
•+
species, Fe (O)P , is the main catalytic species operating
in this system. Low carveol and carvone yields can be
explained by the difficulty in oxidizing the less reactive
aliphatic C–H bonds as compared to the easily oxidized
C=C leading to limonene epoxides.
The main advantage of the catalytic system studied
herein is the facile catalyst recovery and washing,
achieved by simply using a small magnetic bar to keep
the catalyst inside the reaction vial, while the reaction
medium or washing solvent is transferred to or from the
vial. To evaluate this catalyst property and its stability in
consecutive reactions, reuse experiments were conducted
after isolation of the solid using a magnetic bar (Figure 5),
its washing with acetonitrile (three times) and addition of
new substrate and oxidant charges. Figure 5 shows that 90%
of the catalytic activity is kept in 10 consecutive reactions,
proving the stability of the ironporphyrin in these reaction
conditions and its easy, 100% recovery at the end of each
reaction.
Figure 5. Oxidation of limonene by m-CPBA catalyzed by
γ-Fe O /SiO -NHFeP in acetonitrile (using a 1:250:5000 catalyst/oxidant/
2
3
2
substrate molar ratio) in 10 consecutive reactions.
Limonene oxidation was very effectively and selectively
catalyzed by γ-Fe O /SiO -NHFeP, generating limonene
2
3
2
oxide as the major product, as normally observed for
4
4,46
limonene oxidation catalyzed by metalloporphyrins,
together with traces of carveol and carvone (Table 3). Once
again, oxidation reactions were largely dependent on the
employed oxidant: 75% limonene conversion was reached
after 4 h and 86% conversion was obtained after 24 h in
reactions oxidized by m-CPBA. The reactions oxidized by
H O afforded poor results.
Simazine(CEET, 6-chloro-2,4-ethylamino-1,3-5-triazine)
is a herbicide belonging to the class of s-triazines, which is
used in agriculture to control annual grasses and broadleaf
weeds. It is mainly applied to maize, citrus, apples,
4
7,48
sorghum and sugar cane crops.
Simazine degrades
49,50
relatively slowly in soil and is moderately persistent.
2
2
When alkyl peroxides, such as m-CPBA, are
Table 4 lists the chemical structures of simazine and
its possible oxidation products and abbreviations. The
employed as oxidants, heterolytic cleavage of the O-O
bond is expected upon peroxide coordination to the
metalloporphyrin central metal ion, giving rise to the active
5
1
nomenclature developed by Cook and Hütter and
5
2
complemented elsewhere is employed herein for the
Table 3. R-(+)-limonene oxidation by m-CPBA and H O catalyzed by γ-Fe O /SiO -NHFeP
2
2
2
3
2
Product yield / %
Carvone
Nd
Entry
Oxidant
Time / h
Total yield / %
a
Epoxide / %
Carveol
traces
1
3
m-CPBA
4
4
75
2
75
2
H O
traces
traces
2
2
6
H O
24
5
traces
traces
5
2
2
a
-8
Mixture of epoxides; Nd: not detected; solvent: acetonitrile; molar ratio: 1:250:5000 (catalyst/oxidant/substrate), 5.0 × 10 mol FeTFPP; control reactions:
no products obtained.

1
418
Iron(III) Porphyrin Covalently Supported onto Magnetic Amino-Functionalized Nanospheres
J. Braz. Chem. Soc.
Table 4. Chemical structure of simazine and its metabolites
Abbreviation Compound
R1
R2
R3
CEET
CEAT
CAAT
OAAT
OEAT
OEET
6-chloro-2,4-diethylamino-2,4-diamino-1,3,5-triazine
6-chloro-2-ethylamino-4-amino-1,3,5-triazine
6-chloro-2,4-diamino-1,3,5-triazine
-Cl
-CH CH
-CH CH
2
3
2
3
-Cl
-CH CH
-H
2
3
-Cl
-H
-H
–H
-H
-H
6-hydroxy-2,4-diamino-1,3,5-triazine
-OH
-OH
-OH
6-hydroxy-2-ethylamino-4-amino-1,3,5-triazine
6-hydroxy-2,4-diethylamino-1,3,5-triazine
-CH CH
2
3
-CH CH
-CH CH
2
3
2
3
Table 5. Simazine conversion and relative product selectivity obtained in simazine oxidation by m-CPBA or H O , catalyzed by metalloporphyrins, in
2
2
DCM/MeOH and standard conditions, after 4 h of reaction
Relative selectivity / %
a
CEET
Entry
Catalyst
Oxidant
conversion / %
OEAT
0
CEAT
18
OEET
ODDT
ODET
1
3
4
Fe(TFPP)Cl
Fe(TFPP)Cl
m-CPBA
13
-
11
19
-
58
6
22
< 1
12
H O
-
75
2
2
γ-Fe O /SiO -NHFeP
m-CPBA
100
100
-
-
-
2
3
2
6
γ-Fe O /SiO -NHFeP
H O
2
-
-
-
-
< 1
2
3
2
2
a
Catalyst/oxidant/substrate molar ratio of 1:60:60.
identification of s-triazine compounds: A amino, C chloro,
D acetamido, E ethylamino, O hydroxyl, I isopropyl and T
for the triazine ring.
catalytic system proved to be highly efficient and selective
for hydrocarbon oxidation, leading to high yields of
products from styrene (89%), (Z)-cyclooctene (71%) and
R-(+)-limonene (86%) oxidation using two oxidants.
The high selectivity for epoxide suggests that the high
In order to extend the applicability of the studied magnetic
catalytic system, it was also evaluated for the oxidation of
the herbicide simazine by H O or m-CPBA. Reactions
IV
•+
valent metal-oxo intermediate (Fe (O)P ) must be the
main catalytic species involved in this system. Reuse
experiments in the oxidation of R-(+)-limonene show that
catalytic efficiency is kept after 10 consecutive reactions
since the same high catalytic yields are achieved. The solid
catalyst is easily recovered (100%) and washed at the end
of each reaction. The high applicability of this catalytic
magnetic system has been also demonstrated for an inert
substrate such as the herbicide simazine, giving a 100%
selectivity for production of a dechlorinated product.
This specificity for one oxidized product shows the great
beneficial role of the support in determining the reaction
mechanism. Remembering the chemical inertness of this
herbicide, which is highly persistent in the environment,
as well as the facility in isolating the catalyst for reuse,
this catalytic system has great potential application in
fine chemistry.
2
2
were carried out in conditions previously optimized for
28
other catalytic systems. Table 5 presents these results and
also those obtained for the same catalyst in homogeneous
system. Although the catalytic yields decreased for the
γ-Fe O /SiO -NHFeP-catalyzed reactions as compared to
2
3
2
those obtained with the same FeP in homogeneous medium,
the solid catalyst led to a 100% selectivity, producing OEAT
only (Table 4), while many different products were obtained
28
in homogeneous medium (Table 5, entries 1-3). These
results attest for another beneficial property of this support:
the reaction proceeds through a mechanism involving one
catalytic species only, whereas competitive catalytic species
act when the catalyst is free in solution.
Conclusions
FeTFPP was successfully and strongly immobilized
onto amino-functionalized magnetic nanospheres. This
This magnetically separable material also eliminates
the requirement of catalyst filtration after the reaction

Vol. 23, No. 8, 2012
Santos et al.
1419
completion, which is an additional eco-friendly attribute
of this synthetic protocol.
19. Chauhan, S. M. S.; Kumari, P.; Tetrahedron Lett. 2007, 48,
5035.
2
0. Gotardo, M. C. A. F.; Moraes, L. A. B.; Assis, M. D.; J. Agric.
Food Chem. 2006, 12, 10011.
Acknowledgments
2
1. Gonsalves, A. M. D. A. R.; Pereira, M. M.; J. Mol. Catal. A:
Chem. 1996, 113, 209.
We thank Fundação de Amparo a Pesquisa do
Estado de São Paulo (FAPESP), Conselho Nacional de
Desenvolvimento Científico e Tecnológico (CNPq) and
Coordenação de Aperfeiçoamento de Pessoal de Nível
Superior (CAPES) for financial supports and Cynthia Maria
de Campos Prado Manso for the article revision.
22. Faria, A. L.; Mac Leod, T. C. O.; Assis, M. D.; Catal. Today
2008, 133-135, 863.
23. Mata, G.; Trujillano, R.; Vicente, M. A.; Korili, S. A.; Gil, A.;
Belver, C.; Ciuffi, K. J.; Nassar, E. J.; Ricci, G. P.; Cestari, A.;
Nakagaki, S.; Microporous Mesoporous Mater. 2009, 124, 218.
2
4. Machado, G. S.; Arízaga, G. G. C.; Wypych, F.; Nakagaki, S.;
J. Catal. 2010, 274, 130.
References
2
5. Zucca, P.; Sollai, F.; Garau, A.; Rescigno, A.; Sanjust, E.;
J. Mol. Catal. A: Chem. 2009, 306, 89.
1
2
3
4
5
6
. Yan, N.; Xiao, C.; Kou, Y.; Coord. Chem. Rev. 2010, 254,
179.
. Polshettiwar,V.; Baruwati, B.;Varma, R. S.; Green Chem. 2008,
1, 127.
1
26. Adler, D. A.; Longo, F. R.; Shergali, W.; Kampas, F.; Kim, J.;
J. Inorg. Nucl. Chem. 1970, 32, 2443.
1
27. Stöber, W.; Fink, A.; Bohn, E.; J. Colloid Interface Sci. 1968,
26, 62.
. Oppeneer, P. M.; Panchmatia, P. M.; Sanyal, B.; Eriksson, O.;
Ali, M. E.; Surf. Sci. 2009, 84, 18.
28. Santos, J. S.; Palaretti, V.; Faria, A. L.; Crevelin, E. J.; Moraes,
L. A. B.; Assis, M. D.; Appl. Catal., A 2011, 408, 163.
29. Smith, K. M. In Porphyrins and Metalloporphyrins; Falk, J. E.;
Smith, K. M., eds.; Elsevier Scientific Publishing Company:
Amsterdam, Netherlands, 1975, ch. 1.
. Fu, B.; Yu, H. C.; Huang, J. W. ; Zhao, P.; Liu, J. ; Ji, L. N.;
J. Mol. Catal. A: Chem. 2009, 298, 74.
. Sartoratto, P. P. C.; Caiado, K. L.; Pedroza, R. C.; da Silva, S. W.;
Morais, P. C.; J. Alloys Compd. 2007, 434-435, 650.
. Almeida, M. P. S.; Caiado, K. L.; Sartoratto, P. P. C.;
Cintra e Silva, D. O.; Pereira, A. R.; Morais, P. C.; J. Alloys
Compd. 2010, 500, 149.
30. Meunier, B.; Robert, A.; Pratviel, G. In The Porphyrin
Handbook, vol. 4; Kadish, K. M.; Smith, K. M.; Guilard, R.,
eds.; Academic Press: New York, 2000, ch. 31.
7
8
9
. Kang,Y. S.; Risbud, S.; Rabolt, J. F.; Stroeve, P.; Chem. Mater.
31. Assis, M. D.; Lindsay-Smith, J. R.; J. Chem. Soc., PerkinTrans. 2
1998, 2221.
1
996, 8, 2209.
. Sreedhar, B.; Kumar,A. S.; Reddy, P. S.; Tetrahedron Lett. 2010,
1, 1891.
32. Battioni, P.; Bartoli, J. F.; Mansuy, D.; Byun, Y. S.; Traylor,
T. G.; J. Chem. Soc., Chem. Commun. 1992, 1051.
33. Doro, F. G.; Smith, J. R. L.; Ferreira, A. G.; Assis, M. D.;
J. Mol. Catal. A: Chem. 2000, 164, 97.
5
. de Montellano, P. R. O. In Cytochrome P-450: Structure,
nd
Mechanism and Biochemistry, 2 ed.; Plenum Publishers: New
York, 2005, ch. 1.
34. Faria, A. L.; Airoldi, C.; Doro, F. G.; Fonseca, M. G.; Assis,
M. D.; Appl. Catal. A 2004, 268, 217.
1
1
1
0. Mansuy, D.; Ann. Pharm. Fr. 2011, 69, 62.
1. Mansuy, D.; Catal. Today 2008, 138, 2.
35. Tartaj, P.; Morales, M. P.;Veintemillas-Verdaguer, S.; Gonzalez-
Carreño, T.; Serna, C. J.; J. Phys. D: Appl. Phys. 2003, 36, 182.
36. Sakka, S. In Handbook of Sol-Gel Science and Technology:
Processing, Characterization and Aplications, vol. 2; Kluwer
Academic Publisher: New York, 2005, ch 3.
2. Groves, J. T.; Nemo, T. E.; Myers, R. S.; J. Am. Chem. Soc.
1
979, 101, 1032.
1
3. Vinhado, F. S.; Gandini, M. E. F.; Iamamoto,Y.; Silva,A. M. G.;
Simões, M. M. Q.; Neves, M. G. P. M. S.; Tomé, A. C.; Rebelo,
S. L. H.; Pereira,A. M.V. M.; Cavaleiro, J.A. S.; J. Mol. Catal. A:
Chem. 2005, 239, 138.
37. Swern, D. In Organic Peroxides, vol. 2; Swern, V. D., ed.;
Wiley-Interscience: New York-London, 1971; ch. 10.
38. Mahajan, S. S.; Sharma, M. M.; Sridha, T.; Ind. Eng. Chem.
Res. 2005, 44, 1390.
1
4. Solati, Z.; Hashemi, M. ; Ebrahimi, L.; Catal. Lett. 2011, 141,
1
63.
1
5. Huanga, G.; Luob, Z.; Xiang, F.; Caob, X.; Guob,Y.; Jiang,Y.;
J. Mol. Catal. A: Chem. 2011, 340, 60.
39. Groves, J. T.; Myers, R. S.; J. Am. Chem. Soc. 1983, 105, 5791.
40. Groves, J. T.; Haushalter, R. C.; Nakamura, M.; Nemo, T. E.;
Evans, B. J.; J. Am. Chem. Soc. 1981, 103, 2884.
41. Lindsay-Smith, J. R.; Shaw, B. A. J.; Jeffrey, A. M.; Jerina,
D. M.; J. Chem. Soc., Perkin Trans. 2 1977, 1583.
42. Guedes, A. A.; Santos, A. C. M.; Assis, M. D.; Kinet. Catal.
2006, 47, 555.
1
1
6. Zhou, X.; Ji, H.; Chem. Eng. J. 2010, 156, 411.
7. Mac Leod, T. C. O.; Faria,A. L.; Barros,V. P.; Queiroz, M. E. C.;
Assis, M. D.; J. Mol. Catal. A: Chem. 2008, 296, 54.
8. Rebelo, S. L. H; Pereira, M. M.; Monsanto, P.V.; Burrows, H. D.;
J. Mol. Catal. A: Chem. 2009, 297,35.
1

1
420
Iron(III) Porphyrin Covalently Supported onto Magnetic Amino-Functionalized Nanospheres
J. Braz. Chem. Soc.
4
4
4
3. Cubillos, J. ;Vásquez, S. ; Correa, C. M. ; Appl. Catal., A 2010,
49. Chu, W.; Rao, Y.; Hui, W.Y.; J. Agric. Food Chem. 2009, 57,
6944.
3
73 , 57.
4. Skrobot, F. C.; Valente, A. A.; Neves, G.; Rosa, I.; Rocha, J.;
Cavaleiro, J. A. S.; J. Mol. Catal. A: Chem. 2003, 201, 211.
5. Oliveira, P.; Machado, A.; Ramos, A. M.; Fonseca, I.; Braz
Fernandes, F.M.; Rego, A. M. B.; Vital, J.; Microporous
Mesoporous Mater. 2009, 120, 432.
50. Min, L.; Xiaomei, X.; J. Environ. Sci. 2008, 20, 195.
51. Cook, A. M.; Hütter, R.; J. Agric. Food Chem. 1981, 29, 1135.
52. Néulieu, S.; Kerhoas, L.; Einhorn, J.; Environ. Sci. Technol.
2000, 34, 430.
4
6. Brulé, E.; Miguel,Y. R.; Hii, K. K.; Tetrahedron 2004, 60, 5913.
7. Hauswirth, J. W.; Wetzel, L. T. J. In Triazine Herbicides: Risk
Assessment; Ballantine, L. G.; McFarlland, J. E.; Hackett, D. S.,
eds;American Chemical Society:Washington DC, 1998, ch. 29.
8. Berns,A.E.;Bertmer,M.;Schaffer,A.;Meier,R.J.;Vereecken,H.;
Lewandowski, H.; Eur. J. Soil Sci. 2007, 58, 882.
Submitted: February 2, 2012
Published online: July 3, 2012
4
FAPESP has sponsored the publication of this article.
4