Synthesis of mesoporous SBA-15/ionic liquid nanocomposites for the selective oxidation of 2,3,6-trimethylphenol

Abstract

We report the grafting of ILs onto mesoporous silica SBA-15 nanomaterial with a larger surface area of 737.96 m²/g and an interpore distance of 10.68 nm for selective oxidation of 2,3,6-trimethylphenol (TMP). IL, 1-(3-triethoxysilylpropyl)-3-methylimidazolium chloride was grafted with concentration of 1.0, 2.0, 4.0, 6.0, 8.0 and 10.0 mmol onto SBA-15 via a sol-gel method to obtain IL-SBA-15 nanocomposites. The appearance of vibration bands of C­−H (~2900 cm^-1), C=C (~1630 cm^-1) and C=N bonds (~1570 cm^-1) in the FTIR spectra indicates that the ILs were successfully grafted on the surface of SBA-15. The total surface area, total pore volume and BJH pore size distribution of all IL-SBA-15 nanocomposites decreasing with the increasing amount of IL from 393.27 to 354.39 m²/g which indicated that the pore channel and/or surface of SBA-15 were occupied by IL without significant reduction of the quality. It was found that the grafted amount of IL on SBA-15 nanocomposites increased from 0.60 to 0.97 mmol/g when amount of ILs content in the mixture was increased from 1.0 to 10.0 mmol. The IL-SBA-15 nanocomposites were tested as a heterogeneous catalyst for oxidation reaction of 2,3,6-TMP to 2,3,5-trimethylbenzoquinone (TMBQ), employing tert-butyl hydroperoxide (TBHP) as an oxidant at 80 °C for 24 hours. All IL-SBA-15 nanocomposites gave 100% selectivity towards 2,3,5-TMBQ in which IL-SBA-15 with 1.0 mmol of IL gave the highest conversion of TMP (37%).