S. Rayati, E. Bohloulbandi / C. R. Chimie 17 (2014) 62–68
63
Table 1
The specification of the MWCNT-COOH used in this study.
Outside diameter
Inside diameter
5–10 nm
Length
ꢂ 30
COOH content
2%
Specific surface area
2
1
0–20 nm
m
m
>200 m /g
In the present research,
a
metalloporphyrin was
described above and dried in air before being used in
the next run.
immobilized onto the surface of functionalized multi-wall
carbon nanotubes and used as a catalyst for alkene
oxidation by hydrogen peroxide and acetic anhydrides
as activators under ultrasonic irradiation conditions.
3. Results and discussion
3
.1. Preparation and characterization of the catalyst,
2
. Experimental
[Mn(THPP)OAc@MWCNT]
2.1. Instruments and reagents
The specification of multi-wall carbon nanotubes
containing carboxylic acid groups (MWCNT–COOH), which
was used as the support, is listed in Table 1. Scheme 1
shows the preparation route for [Mn(THPP)OAc@MWCNT].
The covalent bonding between the metalloporphyrin and
the nanotubes was carried out by ester bond formation
between the porphyrin hydroxyl groups and the carboxylic
acid of the nanotube using TBTU (2-(1H-benzotriazole-1-
Chemicals were purchased from Merck or Fluka
chemical companies. Meso-tetrakis(4-hydroxyphenyl)por-
phyrin, (H THPP), was prepared according to the literature
28] . [Mn(THPP)OAc] and [Mn(THPP)OAc@MWCNT] were
2
1
[
prepared and characterized according to the already
reported procedures [26,29]. FT–IR spectra were obtained
ꢀ1
on an ABB Bomem: FTLA 2000–100 in the 400–4000 cm
yl)-1,1,3,3-tetramethyluronium tetrafluoroborate) as
a
range using spectral grade potassium bromide. Micro-
structure observations were conducted with a scanning
electron microscope (SEM). Gas chromatography (GC)
analyses were conducted on a Shimadzu chromatograph
model GC-14B) equipped with a flame ionization detector
FID) and a capillary column SAB-5 (phenyl methyl
siloxane 30 m ꢁ 320 mm ꢁ 0.25 mm). In the GC experi-
ments, n-octane was used as an internal standard. The
reactions were submitted to ultrasonic irradiation at
highly effective uronium salt that has been used as an
activation agent for carboxylic acids for the preparation of
0
esters [30,31] in the presence of DIPEA (N,N -diisopropy-
lamine) [32].
(
(
The prepared catalyst was characterized by elemental
analysis, FT–IR spectroscopy and scanning electron micro-
scopy (SEM). The nitrogen content of the catalyst was
determined by CHN analysis, which showed a value of 0.8%
for the Mn catalyst. Based on this value, the manganese
porphyrin content of the catalyst obtained was about
2
96 W (WUC-A03H, DAIHAN). The temperature reached
to 30 8C during sonication.
357 mmol per gram of the catalyst. The Mn content of the
catalyst was also measured by atomic absorption spectro-
scopy; the results proved comparable to data obtained by
CHN analysis.
2
.2. General heterogeneous oxidation procedure
Catalytic experiments were carried out in a 5-mL test
The most informative spectroscopic data, which con-
firmed the covalent anchoring of Mn(THPP)OAc on the
functionalized MWCNT, were obtained by comparison of the
IR spectra of MWCNT–COOH and [Mn(THPP)OAc@MWCNT].
The C5O stretching band of the carboxylic acid group of
tube. In a typical procedure, to a cyclooctene solution in
ethanol (0.05 mmol) were added 1.25 mol of catalyst,
.12 mmol of imidazole, 0.2 mL of H (30%) and 0.2 mL of
m
0
2 2
O
acetic anhydride. The reaction mixture was maintained
under ultrasonic irradiation for 30 min. Then, the reaction
products were monitored at periodic time intervals using
gas chromatography. The oxidation products were identi-
fied by comparison with authentic samples (retention
times in GC).
ꢀ1
MWCNT–COOH appeared at 1642 cm . When porphyrin
was attached to MWCNT–COOH, an ester vibration was
ꢀ1
observed at 1709 cm . These observations clearly confirmed
the attachment of the manganese porphyrin to the MWCNT.
The scanning electron micrograph of MWCNT–COOH
(
Fig. 1a) shows the morphology of the MWCNT used
in this study. Comparison of SEM images of
Mn(THPP)OAc@MWCNT] (Fig. 1b) and of the carbon
2
.3. Catalyst reuse and stability
[
The reusability of [Mn(THPP)OAc@MWCNT] was inves-
nanotube clearly indicates that the manganese porphyrin
has been supported on the nanotubes.
tigated in the multiple sequential epoxidation of cyclooc-
tene, as described above. At the end of each reaction, the
catalyst was separated from the reaction mixture by
simple filtration. After isolation, the solid catalyst was
washed with ethanol, separated from the solvent as
3
.2. Catalytic oxidation of cyclooctene
The catalytic activity of the heterogeneous catalyst was
investigated in the oxidation of cyclooctene with hydrogen
peroxide and acetic acid or acetic anhydride as an activator
1
H
2
THPP: UV–vis (DMF):
(ppm)): 8.88 (s, 8H,
phenyl), 7.19–7.22 (d, 8H, m-phenyl).
l
max (nm): 422, 517, 555, 594, 647. 1H NMR
(
Table 2). The results show that in the absence of an
(
MeOD, 500 MHz,
d
b
-pyrrole), 7.99–8.02 (d, 8, o-
activator, the reaction proceeds with only 3% conversion,