Priyanka Anandgaonker et al. / Chinese Journal of Catalysis 35 (2014) 196–200
use of TiO2 nanoparticles has received considerable attention in
on an 400 MHz FT‐NMR spectrometer with CDCl3 as a solvent.
The chemical shift values are recorded as δ (ppm units) relative
to tetramethylsilane (Me4Si) as an internal standard.
green synthetic organic chemistry [34–38] and the pho‐
to‐degradation of carcinogenic dyes [39] and pesticides [40].
The synthesis of transition metal nanoparticles by the elec‐
trochemical reduction method was originally reported by Reetz
et al [41], who showed that it gave metal nanoparticles with a
narrow size distribution. The cluster size was found to de‐
crease with an increase in current density [42]. The solid
product exhibited electronic, paramagnetic, optical and cata‐
lytic properties that were significantly better than those of the
bulk material, which was due to its extremely small size and
large surface area. In the present work, TiO2 nanoparticles
were prepared by the electrochemical reduction method and
their catalytic activity was tested for the synthesis of azlactone.
2.3. Typical reaction procedure
A mixture of an aromatic or heteroaromatic aldehyde (2
mmol), hippuric acid (2 mmol), acetic anhydride (6 mmol) and
100 mg of TiO2 nanoparticles in 5 ml ethanol was heated with
constant stirring at 120 °C. At first the mixture became almost
solid and then with increase in temperature, it gradually turned
into a deep yellow colored liquid. The progress of reaction was
monitored by TLC. After completion of the reaction, 30 ml of
hot ethanol was added to the flask to separate out the catalyst.
After cooling, the yellow color product was filtered and washed
with ice cold ethanol and then with hot water, and dried and
recrystallized to afford pure crystals of the desired compound.
The products (3a–3m) were confirmed by comparison with
2. Experimental
2.1. Catalyst preparation
1
standard samples using the IR, H NMR and C13NMR spectra
All chemicals were purchased from Aldrich and S. D. Fine
Chemicals Suppliers and used as received. The purity of the
substrates and the reaction monitoring were determined by
thin layer chromatography (TLC) and visualization under ul‐
traviolet (UV) light. In the initial experiment we used a titanium
metal sheet (1 cm 1 cm) as anode and a platinum sheet (1 cm
1 cm) as the cathode. The two electrodes were 1 cm apart.
Tetrabutyl ammonium bromide (TBAB, 0.01 mol/L) in an ace‐
tonitrile and tetrahydrofuran solution (4:1) was the electrolyte.
Upon applying a current density of 10 mA/cm2, we obtained >
95% of the titanium dioxide clusters getting stabilized by
TBAB. Electrolysis was carried out in nitrogen atmosphere. The
titanium dioxide nanoparticles were white in color. Since the
material was insoluble in the solvent used, the work up only
needed simple decantation. The decanted solid product was
washed with dry THF three to four times to remove excess
tetrabutyl ammonium bromide and dried in a vacuum desicca‐
tor. The dried sample was calcined at 550 °C and stored in
closed glass vials under ambient conditions.
and melting points.
2.4. Spectral data of representative compounds
3a. Bright yellow needles. 1H NMR (CDCl3, ppm) δ =
8.22–8.17 (m, 4H, ArH), 7.55–7.61 (m, 3H, ArH), 7.22–7.39 (m,
3H, Ar‐H and –CH=); 13C NMR ( 101MHz, CDCl3) δ = 110.0,
125.6, 128.4, 128.8, 128.9, 131.2, 131.8, 132.4, 133.3, 133.5,
163.6, 167.6; IR (KBr) ν = 3322, 2930, 1795, 1655, 1165 cm–1.
1
3c. Yellow needles. H NMR (CDC13, ppm) δ = 7.16 (s, 1H,
–CH=), 7.40–7.64 (m, 5H, Ar‐H), 7.85 (d, 1H, Ar‐H), 8.00 (d, 1H,
Ar‐H), 8.19 (d, 1H, Ar‐H), 8.30 (s, 1H, Ar‐H); 13C NMR (101 MHz,
CDCl3) δ = 125.39, 128.06, 128.58, 129.01, 129.87, 131.12,
31.25, 131.70, 134.02, 134.42, 135.84, 190.25; IR (KBr): ν =
3322, 2930, 1799, 1657, 1165 cm–1.
3f. Bright yellow solid. 1H NMR (CDCl3, ppm) δ = 8.19–8.16
(m, 2H), 8.10 (d, J = 8.1 Hz, 2H), 7.62–7.52 (dd, J = 10.5 Hz, 4.6,
2H), 7.28 (d, J = 8.0 Hz, 2H), 7.23 (s, 1H), 2.42 (s, 3H, CH3); 13
C
NMR (101 MHz, CDCl3) δ = 21.3, 125.6, 128.6, 128.9, 129.6,
132.1, 132.3, 133.1, 133.3, 133.6, 139.0, 163.5, 167.7; IR (KBr) ν
= 3432, 2922, 1791, 1654, 1160 cm–1.
2.2. Catalyst characterization
3h. Orange solid. 1H NMR (CDCl3, ppm) δ = 3.87 (s, 3H, CH3),
7.12 (d, 2H, J = 8.4 Hz, ArH), 7.35 (s, 1H, –CH=), 7.62–7.74 (m,
3H, ArH), 8.12 (d, 2H, J = 8.4 Hz, ArH), 8.32 (d, 2H, J = 8.4 Hz,
ArH); IR (KBr) ν = 3432, 2938, 1789, 1654, 1162 cm–1.
3g. Yellow needles. 1H NMR (CDCl3, ppm) δ = 7.39 (d, 1H, J =
7.6 Hz, ArH), 7.48 (s, 1H, –CH=), 7.53–7.66 (m, 4H, ArH), 8.17(d,
2H, J = 7.6 Hz, ArH), 8.90 (d, 1H, J = 8.4 Hz, ArH); IR (KBr) ν =
3448, 3088, 1798, 1658, 1170 cm–1.
The titanium dioxide nanoparticles were characterized by
UV‐Vis spectrophotometry, XRD, TEM, and SEM‐EDS tech‐
niques. The wavelength of absorbance was determined by a
UV‐Vis spectrophotometer [JASCO 503] using a quartz cuvette
and an acetonitrile/tetrahydrofuran solution as reference. The
IR spectra were recorded on a FT‐IR spectrometer [JASCO,
FT‐IR/4100, Japan] using dry KBr as the standard reference.
The XRD patterns of the TiO2 nanoparticles were recorded on a
Bruker 8D advance X‐ray diffractometer using Cu Kα radiation
of wavelength 0.154 056 nm. To study the morphology of TiO2
nanoparticles, SEM analysis was carried out with a JEOL
(JSM‐6330 LA) equipment operated at 20.0 kV and 1.0 nA. The
elemental compositions of the TiO2 nanoparticles were exam‐
ined using a energy dispersive spectrometer (EDS). The TEM
analysis was carried out with a Philips Model CM200 equip‐
3. Results and discussion
3.1. SEM‐EDS results
SEM analysis was carried out to study the morphology of the
TiO2 nanoparticles. It can be seen from Fig. 1(a) that the TiO2
powders have a uniform size and can be classified as nanopar‐
ticles. The EDS spectrum was used to analyze the composition
1
ment operated at 20–200 kV. H NMR spectra were recorded