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sorption analysis was measured at 77 K using a [5.0.0.3] Belsorp,
BEL Japan, Inc. instrument. Before measurements, the samples
were outgassed at 100 ꢀC for 4 h. Using the Brunauer–Emmett–
Teller (BET) method and Barrett–Joyner–Halenda (BJH) anal-
yses the specic surface area and the pore size distributions,
respectively, were obtained from the desorption branch of the
isotherms. Transmission electron microscopy (TEM) and High
Resolution TEM (HR-TEM) were performed with a Philips
Tecnai F20 operating at 200 kV. For this purpose, the crystal
powders were dispersed in isopropyl alcohol using ultrasound
and a few drops of the suspension were deposited on a sample
holder consisting of a copper grid covered with holey carbon
lm. The chemical composition was determined on several
crystal grains by means of energy dispersive spectrometry (EDS)
by using an EDAX Phoenix spectrometer equipped with an ultra-
thin window detector and TIA analysis soware. 1H-NMR
spectra were recorded on a Bruker AC 400 spectrometer.
Chemical shis (d) were expressed in parts per million (ppm)
and were referenced to deuterated solvents with tetramethylsi-
lane as the internal standard. Coupling constants were
expressed in Hertz (Hz). Melting points (M.P.) were measured
on an Electrothermal 9100 apparatus and were uncorrected.
Mass spectra were recorded on a Shimadzu GCMS-QP5050
mass spectrometer operating at an ionization potential of 70 eV.
IR spectra were measured on a Perkin-Elmer 783 infrared
spectrophotometer.
2-Benzylidenemalononitrile (2a). White crystals, (146 mg,
95%). M.P. ¼ 84–85 ꢀC. 1H NMR (CDCl3, 400 MHz) d: 7.93 (d, J ¼
7.8 Hz, 2H, Ar), 7.79 (s, 1H, ¼CH), 7.64 (d, J ¼ 7.5 Hz, 1H, Ar),
7.55 (d, J ¼ 7.2 Hz, 2H, Ar). IR (KBr) n: 2223 (CN), 1591 (C]C)
cmꢂ1; MS (70 eV) m/z: 154 (M+).
2-(4-Methoxybenzylidene)malononitrile (2b). Yellow crystals,
1
ꢀ
(168 mg, 91%). M.P. ¼ 112–114 C, H NMR (CDCl3, 400 MHz)
d: 7.91 (d, J ¼ 8.8 Hz, 2H, Ar), 7.65 (s, 1H, ]CH), 7.01 (d, J ¼ 8.8
Hz, 2H, Ar), 3.92 (s, 3H, Me); IR (KBr) n: 2225 (CN), 1560 (C]C)
cmꢂ1; MS (70 eV) m/z: 184 (M+).
2-(4-Methylbenzylidene)malononitrile (2c). Pale yellow crys-
ꢀ
tals, (153 mg, 91%). M.P. ¼ 132–133 C, 1H NMR (CDCl3, 400
MHz) d: 7.83 (d, J ¼ 8.2 Hz, 2H, Ar), 7.64 (s, 1H, ]CH), 7.50 (d,
J ¼ 9.8, 2H, Ar), 2.45 (s, 3H, Me); IR (KBr) n: 2228 (CN), 1584 (C]
C) cmꢂ1; MS (70 eV) m/z: 168 (M+).
(2,4-Dimethylbenzylidene)malononitrile (2f). Yellow crys-
1
ꢀ
tals, (200 mg, 91%). M.P. ¼ 143–145 C, H NMR (CDCl3, 400
MHz) d: 8.26 (d, J ¼ 8.8 Hz, 1H, Ar), 8.18 (s, 1H, ¼CH), 6.61 (dd,
J ¼ 8 Hz, J ¼ 2 Hz, 1H, Ar), 3.93 (s, 3H, Me), 3.92 (s, 3H, Me); IR
(KBr) n: 2220 (CN), 1600 (C]C) cmꢂ1; MS (70 eV) m/z: 182 (M+).
2-(3-Nitrobenzylidene)malononitrile (2h). White crystals,
(187 mg, 94%). M.P. ¼ 101–102 ꢀC, 1H NMR (CDCl3, 400 MHz) d:
8.66 (s, 1H), 8.49 (d, J ¼ 7.0 Hz, 1H), 8.34 (d, J ¼ 7.9, 1H), 7.88 (s,
1H), 7.82 (t, J ¼ 7.7 Hz, 1H); IR (KBr) n: 2233 (CN), 1533 (C]C)
cmꢂ1; MS (70 eV) m/z: 199 (M+).
2-(2-Chlorobenzylidene)malononitrile (2l). White crystals,
(177 mg, 94%). M.P. ¼ 87–89 ꢀC, 1H NMR (CDCl3, 400 MHz) d:
8.28 (s, 1H, ]CH), 8.20 (d, J ¼ 7.8 Hz, 1H, Ar), 7.55–7.59 (m, 3H,
Ar); IR (KBr) n: 2232 (CN), 1590 (C]C) cmꢂ1; MS (70 eV) m/z: 188
(M+).
2.3 Preparation of zirconia nanoparticles
In a typical synthesis, 3 mmol of ZrOCl2$8H2O, 3 mmol of oleic
acid and 8.4 mL of oleylamine were mixed in a 25 mL three-neck
ask equipped with a magnetic stirrer, a condenser, and a
thermocouple.ꢀ The resulting mixture was degassed and dehy-
drated at 120 C for 30 min under vacuum. This mixture was
3. Results and discussion
3.1 Characterization
then heated to 300 ꢀC under an N2 ow and aged at this Fig. 1 compares the XRD patterns of zirconia nanoparticlꢀes –
temperature for 1 h. The turbid mixture was then cooled to before and aer annealing at temperatures of 400 or 600 C –
room temperature by removing the heat source. The white with those of bulk zirconia. The XRD pattern obtained before
precipitate was retrieved by centrifugation and dried aer annealing (Fig. 1a) displays broad peaks which complicate the
washing with methanol and toluene three times. In the case of identication of the crystal phase. Rietveld renement was
the annealed samples, the white solid was calcined in a furnace performed to identify the zirconia polymorph and a good t was
ꢀ
ꢀ
at 400 C or 600 C for 2 h.
obtained for the tetragonal phase with lattice parameters a ¼
˚
˚
3.463 A and c ¼ 5.092 A (ESI†). The decreased size of the unit cell
compared with standard values25 (a ¼ 3.61 A and c ¼ 5.27 A) is
related to the partial reduction of ZrO2 and the formation of
oxygen vacancies which play an important role in stabilizing the
˚
˚
2.4 General procedure for the Knoevenagel condensation of
aldehydes and malononitrile
In a typical condensation reaction, ZrO2 (0.02 g) was added to a tetragonal structure in nanocrystalline zirconia.26 The size of
stirred solution of the corresponding aldehyde (1 mmol) and the crystalline grains obtained by Rietveld renement was
malononitrile (1.2 mmol) in ethanol (5 mL). The reaction estimated to be below 2 nm. As shown in Fig. 1d, the bulk
mixture was reuxed for specied times until thin layer chro- zirconia standard (purchased from Merck) only exhibits the
matography (TLC) indicated the complete disappearance of the monoclinic phase. Crystallites of these sizes are more correctly
starting material (eluent, n-hexane–EtOAc, 5 : 1). The catalyst characterized as clusters. Their atomic structure should be
was isolated by ltration. The product was crystallized in compared to those of bulk samples with caution, coming from
ethanol and no further purication was required.
the knowledge that substantial structural differences can exist
The structure of the products was conrmed by IR, 1H-NMR (in both the bulk and the surface structure).27 The XRD patterns
and mass spectra and comparison with authentic samples obtained from the annealed samples (cf. Fig. 1b and c) indicate
prepared by previously reported methods.16–24 Selected data for a mixture of phases in various ratios. The phase content was
typical products are given below.
estimated from XRD data by the Rietveld method and the
22354 | RSC Adv., 2013, 3, 22353–22359
This journal is ª The Royal Society of Chemistry 2013