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volumetric flask containing the supernatant solution, and the com-
bined supernatant and washing solutions were analyzed by UV–vis
spectroscopy, to determine the FePor loading on the support. Next,
the solid containing immobilized FePor, absolute ethanol, and
cationic MnPor (1.90 mol) were placed in the glass flask, and the
immobilization process described above was repeated. The solid
containing both FePor and MnPor, designated FeMn-Hallo, was
extensively washed with ethanol and characterized by PXRD, FTIR,
textural analysis, and UV–vis spectroscopy in the solid state.
2.4. Oxidation of cyclooctene, cyclohexane, and n-heptane by
PhIO catalyzed by FeMn-Hallo
Fig. 1. Structure of the anionic FePor [Fe(TDFSPP)H4]Cl = [tetra proton – 5, 10,
15, 20 - tetrakis (2,6-difluoro-3-sulfonatophenyl) porphyrinate iron(III)] chloride;
and of the cationic MnPor [Mn(TMPyP)Cl4]Cl = [5,10,15,20-tetrakis-1-methyl-4-
pyridylporphyrinate manganese(III) tetrachloride salt] chloride.
The oxidation reactions were carried out in a thermostatic glass
vessel (2.0 mL) equipped with a magnetic stirrer bar [6,8]. FeMn-
Hallo (3.0 mg) and PhIO (0.22 mol) were suspended in the solvent
(0.200 mL of dichloromethane/acetonitrile 1:1, v/v); the substrate
(cyclooctene, cyclohexane, or n-heptane) was added to the reaction
mixture, to give a constant metalloporphyrin/oxidant/substrate
molar ratio of 1:20:2000. The oxidation reaction was allowed to
proceed for 1 h, under magnetic stirring. At the end of this period,
sodium sulfite was added to the reaction mixture, to quench the
reaction and to eliminate excess PhIO. The reaction products were
separated from FeMn-Hallo by centrifugation and transferred to
a volumetric flask. Next, FeMn-Hallo was washed several times
with methanol and acetonitrile, to extract any reaction product
that might have been retained in the solid catalyst. The solution
containing the final reaction products and the solvents from the
FeMn-Hallo washing process were combined and analyzed by gas
chromatography. Product yields were quantified on the basis of
PhIO; high-purity n-octanol (99.9%) was the internal standard.
Control reactions were also conducted using the same procedure
described above in the case of (a) the substrate, (b) substrate + PhIO,
and (c) substrate + PhIO + raw halloysite (without FePor or MnPor).
For comparison purposes, raw halloysite containing only FePor
or only MnPor was also prepared; the resulting solids were
designated Fe-Hallo and Mn-Hallo, respectively, and were used
as oxidation catalysts. The corresponding metalloporphyrins in
homogeneous solution, FePor and MnPor, were also investigated
as catalysts (homogeneous catalysis), at the same reagent molar
ratio, using an experimental procedure similar to that described
for heterogeneous catalysis.
in Fig. 1, in an attempt to produce a solid that combines the catalytic
activity of the two metalloporphyrin catalysts while offering the
commonly reported advantages of single metalloporphyrin immo-
bilization.
2. Experimental
2.1. Reagents
Analytical grade chemicals were purchased from Aldrich, Sigma,
pressure, and kept at 0 ◦C; its purity was periodically controlled
by iodometric titration [19]. The raw halloysite mineral clay was
obtained from Matauri Bay, New Zealand, by Imerys Tableware New
˚
Zealand Ltd. [14]. This source shows a very pure halloysite 7.0 A,
without apparent contamination by kaolinite or other crystalline
materials [17].
The anionic free base porphyrin H4[H2(TDFSPP)] and its cor-
responding anionic iron(III) complex (designated FePor) were
synthesized, purified, and characterized following a previously
described methodology [11,12,15,20]. The tosylate salt of the
cationic free base porphyrin [H2(TMPyP)]4+ was purchased from
Aldrich; the corresponding cationic manganese(III) complex (des-
ignated MnPor) was synthesized, purified, and characterized using
the Kobayashi methodology, as previously reported [14,21]. The
UV–visible (UV–vis) spectra of FePor and MnPor in ethanol dis-
played Soret bands at 390 nm (ε = 28 × 103 L mol−1 cm−1) and
460 nm (ε = 19 × 103 L mol−1 cm−1), respectively.
Catalyst reuse tests were performed for all the substrates. At
the end of the first use, FeMn-Hallo was separated and extensively
washed with water, methanol, and acetonitrile, in this sequence.
The combined solvents from the washing procedure were ana-
lyzed by UV–vis spectroscopy, to verify whether metalloporphyrin
leached from the support. The solid recovered at the end of this
process was washed, dried at 100 ◦C, and reused in a further reac-
tion.
2.3. Simultaneous immobilization of FePor and MnPor onto
halloysite
2.5. Characterization of Fe-Hallo, Mn-Hallo, and FeMn-Hallo
microscopy (TEM), powder X-ray diffraction analysis (PXRD), and
Fourier Transform Infrared spectroscopy (FTIR).
TEM analyses were carried out in a JEOL-JEM 1200–100 kV sys-
tem, using a drop of the powder suspension of the sample deposited
onto copper grids covered with amorphous carbon parlodium,
which was evaporated at room temperature.
For the PXRD measurements, self-oriented films were placed on
neutral glass sample holders. PXRD patterns were obtained in the
reflection mode on a Shimadzu XRD-6000 diffractometer operating
FePor and MnPor were immobilized onto halloysite following a
procedure based on a pressurized system, as previously described
by our research group [14]. Briefly, the anionic FePor (1.59 mol)
was placed in a glass flask containing 100 mg of raw halloysite;
then, absolute ethanol was added. The system was sealed, inserted
into a Teflon® capsule, and placed in a steel reactor; the final system
was kept in an oven at 130 ◦C, for 48 h. The resulting suspension
was centrifuged, the supernatant was quantitatively transferred
to a volumetric flask, and the obtained solid was exhaustively
washed with ethanol. The washing solutions were added to the
˚
at 40 kV, 40 mA, using Cu K␣ radiation (ꢀ = 1.5418 A) and a dwell
time of 2◦ min−1
.
FTIR spectra were recorded on a Biorad 3500 GX spectropho-
tometer in the range between 400 and 4000 cm−1, using KBr pellets.
KBr was crushed with a small amount of the solids, and the spectra