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Chemistry Letters Vol.37, No.11 (2008)
A Novel One-step Photocatalytic Synthesis of Benzo[d]oxazol-2(3H)-one
with C-doped TiO2 Nanoparticle
Huqun Wang,1 Zhimin Zhang,ꢀ1 and Wenfu Chang2
1School of Chemistry and Chemical Engineering, Shanxi University, Taiyuan 030006, P. R. China
2Institute of Molecular Science, Shanxi University, Taiyuan 030006, P. R. China
(Received July 31, 2008; CL-080745; E-mail: zhimin@sxu.edu.cn)
A novel approach was proposed to synthesize benzo[d]oxa-
zol-2(3H)-one by photoreduction of o-nitrophenol and cycliza-
tion with urea using C-doped TiO2 nanoparticles as photocata-
lyst which was prepared by a modified sol–gel method using glu-
cose as carbon source.
was added to the solution. The reaction mixture was centrifuged
at 20 min after irradiation to separate the catalyst and the com-
pound benzo[d]oxazol-2(3H)-one was isolated as the major
product. HPLC measurement was performed by Agilent 1100
liquid chromatography equipped with a UV detector and an au-
to-sampler with MeOH/H2O/THF (38/10/18 in volume) as elu-
ent to detect the product. The product was isolated and purified.
1
Wide attention has recently been devoted to photocatalytic
applications for organic synthetic chemistry, such as oxidation,1
reduction,2 addition,3 polymeration,4 amino acid,5 alkylation,6
and cyclization7 reactions. Benzo[d]oxazol-2(3H)-ones have at-
tracted considerable attention as a result of their medicinal prop-
erties and some interesting efficacy of antiviral, analgesic, anti-
inflammatory, chemo-preventive, anticancerous, antibacterial,
anti-mycotic, and antiprotooal,8 have been reported. Benzo-
[d]oxazol-2(3H)-one and its derivatives have been synthesized
by many methods,9 many of which show several limitations in-
cluding long reaction time, harsh reaction conditions, poisonous
reagents, and generating dangerous pollutants for the environ-
ment. We recently discovered a mild and one-pot synthesis of
benzo[d]oxazol-2(3H)-one during a successful attempt based
new active-TiO2 catalytic systems. Compared to the correspond-
ing TiO2, the use of C-doped TiO2 nanoparticles has shown that
their photocatalytic activity is superior and has also received
considerable attention.10
Further analysis was performed by FT-IR and H NMR spectra
measurement.12
(b)
(a)
Figure 1. XRD patterns of (a) as-synthesized TiO2 and (b) C-
TiO2 samples prepared using sol–gel method.
Shown in Figure 1 are X-ray powder diffraction (XRD) pat-
terns of TiO2 and C-TiO2 powder samples prepared, collected
using a Model D/Max 2550V and Cu anticathode radiation.
From the intensity ratios between the diffraction appearing at
2ꢀ ¼ 25:5ꢁ (anatase 101) one may conclude that the TiO2 depos-
ited at 350 ꢁC consists almost completely of the anatase phase
and no other crystal phase can be detected. The average crystal-
line size of C-TiO2 was calculated using the Scherrer equation.
Pure TiO2 had a particle size of 10.3 nm; doped TiO2, about
6.8 nm. Crystalline of C-doped TiO2 showed smaller size than
undoped-TiO2 at the same calcinations temperature.
Shown in Figure 2 are XPS spectra of the as-synthesized
C-TiO2 sample. The XPS survey spectra analysis indicated the
presence of Ti, O, and C on the surface of C-modified TiO2. It
can be seen from Figure 2 that the C 1s peaks fitted to two differ-
ent peaks are found at 284.6, 287.99, and 294.15 eV. The first
signal at 284.6 eV is assigned to the C 1s peaks related to the
C–C or C–H bonds. The other signal can be attributed to C–O
and C=O bonds. According to the literature,11 the XPS peak
at 288.6 eV indicated the presence of C–O bonds and carbon
might substitute for some of the lattice titanium atoms and form
a Ti–O–C structure. The characteristic doublet Ti 2p3=2 and
Ti 2p1=2 are at 461.8 and 467.5 eV, respectively. All of these val-
ues indicate that TiO2 is the main constituent of the as-deposited
C-modified TiO2. The O 1s peak of XPS spectra presented in
Figure 2 can be decomposed into two contributions. The main
peaks at 530.25 eV and a shoulder at 533.21 eV were assigned
The anatase TiO2 and C-TiO2 particles were prepared by a
simple modified sol–gel process with glucose as carbon source
and tetrabutyltitanate as a precursor respectively. Tetrabutyltita-
nate (8.4 mL) and glacial acetic acid (1.2 mL), which prevents
the precipitation of oxides and stabilizes the solutions, were dis-
solved in 30 mL of ethanol. After 1 h, nitric acid was added to
adjust the pH 3. During the hydrolysis process, the mole ratio
.
of H2O, C2H5OH, and C6H12O6 H2O was maintained at
13:21:1. Then the process consisted of evaporation of the sol-
vent, drying at 100 ꢁC for 8 h and finally calcination at 350 ꢁC
for 4 h. The photocatalytic synthesis of benzo[d]oxazol-2(3H)-
one was carried out in a self-designing reactor of 250 mL capaci-
ty with a refluxing device. The suspending solution, which was
composed of an ratio (1:1.2) of o-nitrophenol (1 mmol) and urea
and 500 mg of C-TiO2 along with 20 mL of methanol solvent in
the photoreactor was irradiated using a 500-W high-pressure
mercury lamp (356 nm) under magnetic stirring at refluxing tem-
perature in Scheme 1. After irradiation for 7.5 min, nitric acid
OH
O
OH
+
OH OH
O
C-TiO2
+
O
+
NH2CNH2
hv, methanol
N
H
NO2
NH2
N
N
4.5%
52.5%
1.6%
Scheme 1. Synthesis of benzo[d]oxazol-2(3H)-one with nano-
particle C-TiO2 in methanol.
Copyright Ó 2008 The Chemical Society of Japan