10.1002/asia.201700499
Chemistry - An Asian Journal
FULL PAPER
appropriate drying reagents and distilled under nitrogen prior to use. The
Catalytic tests
scorpionate vanadium(IV) complexes [VCl3{κ3-SO3C(pz)3}] (1),[12]
[VOCl2{κ3-HOCH2C(pz)3}] (2)[13] and
(3)[14]
[VOCl2{κ3-MeSO2OCH2C(pz)3}]
In a typical MW-assisted reaction, 2.5 mmol of xylene, 5 mmol of tert-
butyl hydroperoxide (TBHP, 70% aq. solution) and vanadium catalysts 1-
3@CNT (0.16 – 0.80 mol of V supported at CNT, 6.4 × 10-3 – 3.2 × 10-2
mol% vs. substrate) were introduced into a 10 mL glass vessel. In the
experiments with HNO3 (65%, 1.6 – 8.0 mol) this acid was added
immediately before the addition of the catalyst. The mixture was
subjected to microwave irradiation at the desired temperature for the
selected time at 600 rpm stirring speed. At the end of the reaction, the
mixture was cooled down to r.t., the organics extracted with 2.5 mL of
acetonitrile and identified by GC-MS. The V-catalysts were separated by
filtration, washed with acetonitrile, dried with compressed air and reused
in subsequent oxidation cycles.
were synthesized according to reported procedures and
characterized accordingly.
1H and 13C NMR spectra were recorded at ambient temperature on a
Bruker Avance II + 300 (UltraShieldTM Magnet) spectrometer operating at
300.130 and 75.468 MHz for proton and carbon-13, respectively, at
ambient temperature. The chemical shifts are reported in ppm using
tetramethylsilane as an internal reference.
Infrared spectra (4000–400 cm−1) were recorded on a Vertex 70 (Bruker)
instrument in KBr pellets. Far infrared spectra FIR (400-200 cm-1) were
recorded on a Vertex 70 spectrophotometer in CsI pellets.
Elemental analyses were carried out by the Microanalytical Service of the
Instituto Superior Técnico.
For comparison, xylene oxidation reactions were performed in round
bottom flasks under the same reaction conditions but using an oil bath as
heating source (up to 3 mL total volume).
SEM and EDX analyses were carried out on a scanning electron
microscope JEOL 7001F with Oxford light elements EDS detector and
EBSD detector.
Acknowledgements
Reactions under microwave (MW) irradiation were performed in
a
focused Anton Paar Monowave 300 reactor fitted with a rotational system
and an IR temperature detector, using a 10 mL capacity reaction tube
with a 13 mm internal diameter.
Funding from FCT (Fundação para a Ciência e a Tecnologia,
Portugal) (UID/QUI/00100/2013, PTDC/QEQ-ERQ/1648/2014 and
PTDC/QEQ-QIN/3967/201 projects) are acknowledged. APCR
acknowledges FCT for the SFRH/BPD/90883/2012 grant. SACC
GC-MS analyses were performed using a Perkin Elmer Clarus 600 C
instrument (He as the carrier gas), equipped with two capillary columns
(SGE BPX5; 30 m × 0.32 mm × 25 mm), one having an EI-MS (electron
impact) detector and the other one with a FID detector. The temperature
of injection was 330 ºC. The initial temperature (50 ºC) was raised at 5
ºC/min to 300 ºC. Reaction products were identified by comparison of
their retention times with known reference compounds, and by comparing
their mass spectra to fragmentation patterns obtained from the NIST
spectral library stored in the computer software of the mass spectrometer.
acknowledges
FCT
for
Investigator
2013
Program
(IF/01381/2013/CP1160/CT0007), with financing from the European
Social Fund and the Human Potential Operational Program. This
work was financially supported by Project POCI-01-0145-FEDER-
006984 – Associate Laboratory LSRE-LCM funded by FEDER
through COMPETE2020 - Programa Operacional Competitividade e
Internacionalização (POCI) – and by national funds through FCT.
Keywords: xylene • oxidation • C-scorpionate • carbon
nanotubes • vanadium
Support synthesis
Multi-walled carbon nanotubes (CNT) NC3100 from NanocylTM were
treated in reflux with 75 mL of a 5 M nitric acid solution per gram of
carbon material, for 3 h, then separated by filtration and washed with
deionized water until neutral pH, similarly to what is described in
literature.[15, 19] The obtained material was further treated with 75 mL of a
20 mM NaOH aqueous solution (per gram of carbon material) in reflux for
1 h, as in literature.[15, 19b, 20] This material was also separated by filtration
and washed until neutral pH.
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Heterogenisation procedure
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The V complexes were anchored onto CNT (0.15 g) through dissolution
in 25 mL of distilled water with continuous stirring for 24 h, in order to
achieve 0.2 mmol V per gram of CNT. Afterwards, the material was
deposited by gravity and separated by filtration, washed with water and
methanol, and dried overnight at 40 ºC, under vacuum.
Metal loading determination
[9]
M. H. Ab Rahim, M. M. Forde, R. L. Jenkins, C. Hammond, Q. He,
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The loading of V was determined by atomic absorption spectroscopy
(AAS) using a Unicam 939 atomic absorption spectrometer and a V
hollow cathode lamp.
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