Immobilized catalysts for alkene oxidation
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Tertiary butyl substituted and unsubstituted Schiff base systems containing N,O donor ligands (Salicylaldimines) with aminotriethoxysilane tail were synthesized and complexed to Copper and Cobalt acetate. The ligands were characterized by FTIR and 1 HNMR Spectroscopy. The complexes were characterized by elemental analysis, ESI-Mass spectrometry and IR spectroscopy Mesoporous silica supports (SBA-15 and MCM-41) were synthesized and characterized by Xray diffraction, BET surface analysis and SEM. The tertiary butyl substituted and unsubstituted copper and cobalt salicylaldimine complexes were immobilized on amorphous (Davisil silica gel) and mesoporous supports (SBA-15 and MCM-41). Immobilized catalysts were characterized with Atomic Absorption Spectroscopy, X-ray diffraction, BET surface analysis, IR spectroscopy and SEM. Immobilized catalysts were tested for cyclohexene oxidation using molecular oxygen as cooxidant and hydrogen peroxide as oxidant. In this study the effect of metal, reaction time, nature of oxidant (hydrogen peroxide tertiary butyl hydroperoxide), substituents on the ligand and substrate concentration were investigated. Allylic products were obtained at relatively high cyclohexene conversion. In addition to the above, homogeneous systems were compared with heterogeneous analogues. The former were found to have better selectivity than their heterogeneous analogues although there appears to be no significant difference in the activity.