Y. Li et al.
were limited to benzene, the substituted benzenes were not
applicable for the hydroxylation. Photocatalytic oxidation
of substituted aromatic compounds was reported, but the
efficiency was not high enough [15, 16]. Phenols with one
or more functional groups are valuable organic intermedi-
ates related to resins, plastics, pharmaceuticals, and agro-
chemicals in the chemical industry [17–20]. Recently, the
hydroxylation of substituted benzenes to the corresponding
phenols with H O was reported using divanadium-
CN, NO , COOH, CF , and COCH are applicable for the
2
3
3
hydroxylation with O . Aromatic halides (F, Cl and Br) can
2
also be oxygenated to the corresponding phenols (see
Scheme 1). The catalyst VOSiW was characterized by
Fourier transform infrared spectra (FT-IR), X-ray diffrac-
tion (XRD) and electron spin resonance (ESR), which
provided some information for the catalyst structure with
the catalytic reactivity.
2
2
substituted phosphotungstate as catalyst, but the catalyst
system was still limited to the benzenes with electron-
donor groups [17]. It is still a demanding challenge to the
hydroxylation of benzenes with electron-withdrawing
2 Experimental Section
2.1 Materials and Methods
groups. The benzenes with F, Cl, Br and NO have been
2
oxidized to the corresponding monophenols by H O with
2
All reagents were purchased from Aladdin Reagent Com-
pany, Sigma–Aldrich Company and Alfa-Aesar Company
without further purification. H PW O (PW), H PMo
12
2
the vanadium peroxocomplexes, however, the conversion
of the substrate was low (\3 %) [21]. Lei et al. [22]
reported the Cu-catalyzed hydroxylation of electron-defi-
cient arenes with air in the presence of NaOtBu. The
ketone-directed Pd-catalyzed hydroxylation of aryl ketones
had been reported and the catalyst exclusively activate the
ortho-position [23]. The Pd-catalyzed ortho-hydroxylation
of benzoic acids with molecular oxygen was developed
with high selectivity and good yields [24]. Moreover, the
ortho-hydroxylation of nitrobenzene to the ortho-nitro-
phenol with molecular oxygen using H PMo V O POM
3
12 40
3
O40 (PMo) and H SiW O (SiW), purchased commer-
4 12 40
cially, were dried before used. Fourier transform infrared
(FT-IR) spectra were recorded on a Nicolet 360 FT-IR
-
1
instrument (KBr discs) in the 4,000–400 cm
region.
XRD patterns were collected on the Bruker D8 Advance
powder diffractometer using Ni–filtered Cu Ka radiation
source at 40 kV and 20 mA, from 5° to 80° with a scan rate
of 0.5°/min. BET surface areas were measured at the
temperature of liquid nitrogen using a Micromeritics
ASAP2010 analyzer. The samples were degassed at 150 °C
5
10 2 40
catalyst was developed, and the formation of a H PMo
5
10
-
3
V O –nitrobenzene complex was stated to be responsible
2 40
to vacuum of 10 Torr before analysis. The amount of
vanadium species was measured using a Jarrell-Ash 1100
inductively coupled plasma–atomic emission spectrometry
(ICP–AES spectrometer). ESR spectra were recorded on a
Bruker EMX-10/12 spectrometer at the X-band. Thermo-
gravimetry (TG) analysis was carried out with a STA409
instrument under dry air at a heating rate of 10 °C/min.
Elemental analyses were performed on a CHN elemental
analyzer (FlashEA 1112).
for the ortho-hydroxylation [25]. However, all the catalyst
systems were applicable with limited substrates, and the
development of catalysts applicable widely for the
hydroxylation of aromatics is still highly desirable.
Recently, we reported the SiO encapsulated H PMo
10
2
5
V O POM catalyst, which was reusable and highly active
2 40
and selective for the hydroxylation of benzene with
hydrogen peroxide [26]. And we are still seeking immo-
bilized catalysts for the hydroxylation of aromatics. Lately,
molecularly defined Fe and Co complexes with N con-
tained ligands were doped in activated carbon by pyrolysis
as heterogeneous catalysts for the hydrogenation and oxi-
dation reactions [27–29]. The ligand 1,10-phenanthroline
can be linked into the surface of the activated carbon
through pyrolysis of the complexes with 1,10-phenanthro-
line, and they were highly stable and were used as excellent
supports for metal oxides. Moreover, the pyrolysis of
2.2 Catalyst Preparation
H PW O (1.44 g, 0.5 mmol) and vanadium oxytrichlo-
3 12 40
ride oxide (VOCl , 0.086 g, 0.5 mmol) were dissolved in
3
absolute ethyl alcohol (20 mL) under argon atmosphere
with stirring for 6 h. 1,10-Phenanthroline hydrate (0.3 g,
1.5 mmol) was dissolved in 10 mL absolute ethyl alcohol,
protonated 1,10-phenanthroline gave
a quite stable
N-doped carbon material, which maybe used as a good
support for catalysts [30]. Here, vanadium catalysts sup-
ported on N-doped carbon materials are reported as cata-
lysts for the hydroxylation of functional aromatics to the
corresponding phenols with O . It is widely applicable for
2
the VOSiW catalyzed hydroxylation of aromatics, and
various benzenes with electron-withdrawing groups such as
Scheme 1 The hydroxylation of substituted aromatic compounds
with O
2
1
23