16
S. PAKVOJOUD ET AL.
diffractometer with Cu-Kα radiation was employed to obtain the X-ray powder diffrac-
tion (XRD) patterns of the powder samples at room temperature. A Zeiss Sigma VP-500
FE-SEM instrument was used to take scanning electron micrographs and EDX spec-
tra. TEM images were recorded using a Zeiss-EM10C transmission electron microscope.
The N adsorption–desorption isotherms (BET) were recorded at 77 K on a BELSORP
2
Mini instrument. Thermal gravimetric analysis (TGA) was performed with a Rheometric
SCIENTIFIC STA 1500 instrument. The thin-layer chromatography (TLC) on silica-gel
polygram SILG/UV 254 plates was carried out to check the reactions progress. A Philips
GC-PU 4600 instrument equipped with a flame ionization detector (FID) was employed
for the gas chromatography analyses.
4
.2. Synthesis of KIT-6
The mesoporous silica KIT-6 was prepared according to the procedure of Ref. [42]. A solu-
tion containing 4 g of P123 (as structure-directing agent) and 7.9 g of HCl (35 wt%) in 144 g
distilled water was prepared and stirred mechanically for 2 h at 35°C. Subsequently, 4 g of
n-butanol was added as the co-solvent to the above-mentioned mixture with the continu-
ous agitating at 35°C for 2 h. Afterwards, 8.6 g of tetraethylorthosilicate (TEOS) was added
to the resulted clear solution, followed by stirring at 35°C for 24 h and keeping in an oven
of 100°C for 24 h. Then the white solid precipitate was filtered and, without washing, dried
at 100°C overnight. Finally, the obtained product was calcined at 550°C for 5 h with the
heating ramp of 2°C/min in the furnace in the open air.
4
.3. Preparation of Pd-isatin Schiff base@KIT-6 catalyst
First, a mixture of 3-aminopropyltriethoxysilane (0.268 g, 1.2 mmol) and KIT-6 (1 g) in
dry toluene (25 mL) was agitated and refluxed in N environment for 24 h. The resulted
2
white solid KIT-6-pr-NH was filtered, washed with toluene and then dried at 100°C for
2
4
h [43]. Subsequently, a solution of isatin (0.147 g, 1 mmol) in absolute methanol (25 mL)
was added to a suspension of freshly prepared KIT-6-pr-NH (1 g) in methanol (50 mL).
2
This mixture was actively agitated under reflux for 24 h. The achieved light brown solid
isatin Schiff base@KIT-6 was filtered, washed carefully with methanol and dried at 90°C
for 4 h. Finally, a mixture of isatin Schiff base@KIT-6 (1 g) and Pd(OAc) (0.224 g, 1 mmol)
2
in absolute methanol (25 mL) was prepared and magnetically stirred at room temperature
for 24 h. Afterwards, the obtained light green solid catalyst was filtered and washed with
methanol using a Soxhlet apparatus and then dried at 90°C for 6 h. Based on the ICP results,
the Pd content in the catalyst was determined about 0.24 mmol per gram of the supported
catalyst.
4
.4. General procedure for the oxidation of sulfides to sulfoxides with tert-butyl
hydroperoxide catalyzed by Pd-isatin Schiff base@KIT-6
The catalyst (20 mg), sulfide (1 mmol) and tert-BuOOH (70% aqueous solution, 3 mmol)
were mixed in ethanol (2 mL) inside a test tube. Then, the reaction mixture was magneti-
cally stirred at room temperature. The reaction progress was checked by gas chromatogra-
phy (GC) or thin-layer chromatography (TLC). After completion of the reaction, the solid