Assembly Of Methyltrioxorhenium And Nickel Chloride On Mcm-41 And Their Catalytic Performances On The Oxidation Of Alkenes

Three di-nitrogen schiff base ligands were synthesized by the condensation of 2-pyridinecarboxaldehyde with aniline and its derivatives and their structures were characterized by FT-IR,1H NMR,13C NMR. The effects of the in situ coordination of methyltrioxorhenium (MTO) with schiff bases on the epoxidation of alkenes with 30% H2O2 as oxidant were studied. The results revealed that the ligand with an electron-withdrawing carboxy group has suitable coordination capacity and acidity, therefore, it can largely increase the selectivity of epoxides without concomitancy of the obvious decrease of reaction rate in the epoxidation of olefins catalyzed by MTO. For example, when the molar ratio of the schiff base I to MTO was 2 and the reaction was run at 10 oC for 4 h, the conversion of cyclohexene and the selectivity of the epoxide reached 94.6% and 99.0%, respectively. However, the ligands without electron-withdrawing group decreased the catalytic activity of MTO, though they could increase the selectivity of epoxides in some degree.MCM-41 reacted with bis(3-(triethoxysilyl)propyl)amine to give MCM-41-I which was functionalized with amino groups. Then the dinitrogen schiff base ligand was attached to MCM-41-I by employing amidation reaction to give MCM-41-II. The dinitrogen schiff base ligand supported on MCM-41 coordinated with MTO to bring about assembling of MTO on MCM-41, which give the heterogenized catalyst. The catalyst was characterized by means of FT-IR, DR UV-vis, XRD, N₂ adsorption and atomic absorption analysis. The catalytic experimental results showed that the heterogenized catalyst has poor catalytic performance in the epoxidation of alkenes with aqueous 30% H₂O₂ as oxidant.Nickel chloride hexahydrate (NiCl₂·6H₂O) was empolied as a catalyst to the oxidation of styrene to benzaldehyde with tert-butyl hydroperoxide (TBHP) as an oxidant. The effects of solvent, reaction temperature, oxidants, loading amounts of catalyst and oxidant were investigated throughly. Results showed that the styrene conversion could reach 89.5% with a benzaldehyde selectivity of 79.1% at 40 ?C for 34 h with acetonitrile as solvent.A heterogenized catalyst was obtained by the coordination of nickel chloride hexahydrate (NiCl₂·6H₂O) with amino groups attached on MCM-41. The catalyst was applied to the oxidation of styrene to benzaldehyde with tert-butyl hydroperoxide (TBHP) as an oxidant. The effects of reaction temperature, loading amounts of catalyst and oxidant were investigated. The yield of benzaldehyde can reach up to 54%. The recycle of the catalyst was also studied and the results showed the catalyst can run for six times without large loses of the yield of benzaldehyde.