S. Ghorbani, R. Parnian and E. Soleimani
Journal of Organometallic Chemistry 952 (2021) 122025
and high catalytic activity in oxidation reactions of benzyl alco-
hols to the corresponding carbonyl compounds in the presence of
hydrogen peroxide in ethanol as solvent at 60 °C. Easy separation,
high stability, reusability, and excellent selectivity without any over
oxidation are advantages of this heterogeneous catalyst. These ad-
vantages are beneficial, where an alcoholic group should be selec-
tively oxidized to its aldehyde, especially in the total synthesis of
drug molecules.
separated by centrifugation, washed with ethanol, and dried in an
oven at 60 °C. Finally, to ensure complete removal of CTAB and
other organic components, the resulting white solid product was
calcined at 550 °C for 5 h in air.
4.2.3. Preparation of modified HMSNs (HMSNs∼Cl)
The chloro modified HMSNs (HMSNs∼Cl) were prepared us-
ing a post-modification method with 3-chloropropyltriethoxysilane
(CPTES). In brief, 0.2 g of prepared HMSNs were mixed with 10 mL
4
. Experimental
of dry toluene by ultrasonic treatment, then 0.6 mL CPTES was
added to the mixture. The mixture was stirred for 24 h under
reflux at 110 °C. After cooling, the mixture was centrifuged and
washed thoroughly twice with ethanol and distilled water to re-
move unreacted CPTES. The resultant HMSNs∼Cl was dried under
vacuum at 60 °C for 24 h.
4
.1. General remarks
The chemicals were purchased from Fluka, SigmaAldrich, and
Merck companies and were used without further purification. All
reactions were monitored by TLC. Infrared spectra were recorded
using a Ray Leigh Wqf510 FT-IR instrument. Transition electron
microscopy (TEM) analysis was performed using a Zeiss-EM10C
4.2.4. Synthesis of pyrazolone-based ligand (Pyra)
A solution of hydrazine hydrate (2 mmol), ethyl acetoacetate
(2 mmol), and acetic acid (2 equiv.) in water/EtOH (2:1) was stirred
at 70 °C. After 15 min, 4-hydroxybenzaldehyde (1 mmol) was
added, and the mixture was stirred at 70 °C for 12 h. After com-
pletion of the reaction, as indicated by TLC, the precipitated solid
was filtered and washed with the mixture of water/ethanol (1:1)
(
Germany) operated at 100 kV V electron beam accelerating volt-
age. Emission scanning electron microscopy (SEM) and energy-
dispersive X-ray (EDX) were performed on a TESCAN- MIRA3 op-
erated at 26 kV with the electron gun filament: tungsten. XRD
patterns were recorded using an STOE STADI-P diffractometer with
˚
ꢀ
monochromatic Cu-Ka radiation (wavelength = 1.54060 A). To de-
to obtain the 4,4 -((4-hydroxyphenyl)methylene)bis(3-methyl-1H-
termine the organic content in a sample, thermogravimetric anal-
pyrazol-5-ol) as a pure white powder in 90% yield. Mp 267–270 °C.
IR (KBr) (ʋmax/cm 1): 3403, 2924, 1709, 1595, 1483. MS, (m/z):
301(M+1), 299, 267, 241, 203, 186, 115. 1H NMR (300 MHz, DMSO-
d ): ẟ (ppm) 2.12 (6 H, s, 2 CH ), 4.78 (1H, s, CH), 5.54 (2NH, and
−
yses were investigated using an STA PT-1000 Linseis instrument
Germany) at a heating rate of 10 °C min 1 under air atmosphere.
−
(
The amount of Pd NPs loaded on the nanocatalyst was determined
by Perkin Elmer Optima 7300D inductively coupled plasma (ICP).
The specific surface area (BET method), total pore volume, and
mean pore diameter (BJH method) were measured using an N2
adsorption-desorption isotherm by using a BEISORP Mini Microtrac
Bel Crop instrument.
6
H
3
3OH exchanged with water of DMSO-d ), 6.67 (2H, d, 3JHH = 8.4
6
Hz, HAr), 7.00 (2H, d, 3JHH = 8.4 Hz, HAr). C NMR (75 MHz,
13
DMSO-d ): ẟ (ppm)10.3 (CH ), 31.9 (CH), 104.8, 114.6, 128.3, 133.3,
6
C
3
140.1, 155.1, 161.1(C-Ar). Anal. Calcd. for C15H16 N O : C, 59.99; H,
4
3
5.37; N, 18.66. Found: C, 59.96; H, 5.33; N, 18.71.
4
.2. Preparation of catalyst
4.2.5. Functionalization of the modified HMSNs (HMSNs∼Pyra)
ꢀ
The
4,4 -((4-hydroxyphenyl)methylene)bis(3-methyl-1H-
4
.2.1. Synthesis of silica-coated magnetite NPs (Fe O @CTAB/SiO
2
pyrazol-5-ol) (0.3 g, 1 mmol) was added into a suspension of
HMSNs∼Cl (0.2 g) in dry DMF (50 mL). The reaction mixture was
refluxed at 140 °C in an oil bath for 24 h. The resulting precipitate
was centrifuged and washed with DMF, followed by distilled
water, ethanol, and acetone. Finally, the HMSNs∼Pyra was dried at
100 °C for 24 h.
3
4
NPs)
Magnetite (Fe O ) NPs were prepared according to the re-
3
4
ported procedure (co-precipitation) [78]. Briefly, 10 mmol (2.7 g)
of FeCl .6H O and 5 mmol (1.0 g) of FeCl .4H O were dissolved in
3
2
2
2
130 mL deionized water under nitrogen gas with vigorous stirring.
Then, NH3 (25%) was added to the solution until the pH of the so-
lution reached 11, the orange color of the solution changed to black
immediately. Stirring was continued for 1 h at 60 °C. The resul-
tant magnetite precipitate was separated from the solution using
a magnet, washed several times with deionized water and ethanol,
and left to dry in the air. Subsequently, Fe O @CTAB/SiO NPs were
4.2.6. Preparation of Pd/HMSNs∼Pyra/Pd NPs
To a stirred solution of Pd(OAc)2 (0.134 g, 0.6 mmol) in wa-
ter (30 mL) was added HMSNs∼Pyra (0.3 g). The mixture was
stirred for 0.5 h to form a brown mixture, and then a solution
of NaBH4 (0.11 g, 3 mmol) in EtOH (10 mL) was added. The color
of the mixture immediately turned to black. After stirring for 6 h
at 60 °C, the product was obtained by centrifugation, washed
with EtOH twice, and dried at 70 °C overnight to give dark gray
Pd/HMSNs∼Pyra/Pd nanocatalyst. The amount of Pd loaded on the
0.1 g of Pd/HMSNs∼Pyra/Pd NPs was 0.153 mmol (16.27 wt%), as
detected by ICP.
3
4
2
synthesized by coating a mesoporous silica layer on the surface of
Fe O NPs (sol-gel method) [79]. Typically, 0.1 g Fe O4 NPs and
3
4
3
0
.60 g CTAB were dispersed in a mixture of ethanol (60 mL) and
water (100 mL) by ultrasonic treatment for 30 min. Then, 6.0 mL
ammonia solution (25%) was added to the mixture, followed by the
addition of TEOS solution (3.0 mL in 20 mL ethanol) slowly under
stirring and left at 30 °C for 24 h. After magnetic separation, the
final product (Fe O @CTAB/SiO NPs) was washed with water and
4.3. General procedure for oxidation of benzyl alcohols using
3
4
2
ethanol and dried under vacuum.
Pd/HMSNs∼Pyra/Pd nanocatalyst
4
.2.2. Preparation of hollow mesoporous silica NPs (HMSNs)
To
Pd/HMSNs∼Pyra/Pd nanocatalyst (0.02 g, 3.06 mmol%) in ethanol
(5 mL), H O (3 equiv.) was added dropwise under stirring at
a
mixture of benzylic alcohol (1.0 mmol) and
HMSNs were prepared after removing both Fe O NPs and CTAB
3
4
templates in a single step by acid treatment. Fe O @CTAB/SiO NPs
3
4
2
2
2
were dispersed in acidic ethanol (HCl, 37%) and then heated at
0 °C. After a while, the color of the solution turned from dark
brown to bright yellow due to the dissolution of the Fe O NPs
room temperature. The reaction was continuously stirred at 50 °C
for an appropriate reaction time. After completing the reaction,
as indicated by TLC, the reaction mixture was centrifuged, and
the nanocatalyst was separated. Then, the remaining solution was
analyzed by the GC-MS method to obtain the yield and selectivity
8
3
4
[
91]. The mixture was stirred continuously overnight for the com-
plete removal of the templates. The resultant white HMSNs were
9