Preparation Of Amino-Modified Metal-Salen Composites And Their Catalytic Oxidation Performance

Heterogeneous catalysis is part of the field of catalytic chemistry,and the heterogeneous catalytic oxidation among them occupies an important position.Although the homogeneous metal-Salen complex shows high catalytic activity in the reaction system,it has the characteristics of easy synthesis,easy modification,and high yield,so it is widely used in catalytic oxidation reactions.However,it also has the disadvantages of being difficult to recycle and reuse,easy to decompose,easy to fall off the active ingredients,and polluting the environment.Therefore,it is particularly important to make the homogeneous catalyst heterogeneous.Choosing non-toxic and harmless amine-modified chitosan to metal-Salen complex,to a certain extent,not only overcomes the disadvantages of homogeneous metal-Salen complex,but also improves catalytic efficiency,reducing the degree of pollution caused by catalyst emissions,it is an effective method to realize its application.（1）Using 3-aminopropyltriethoxysilane（APS）as an organic ammonia functionalization reagent and chitosan as a carrier,amine-modified chitosan was successfully prepared in N,N dimethylformamide solvent（pr-NH₂-CS）.The condensation reaction of o-phenylenediamine and salicylaldehyde is used to generate Salen ligand（Schiff base）,followed by the addition of manganese acetate and lithium chloride to prepare Salen（Mn）,and finally Salen（Mn）and pr-NH₂-CS in alkaline tetrahydrofuran solution.In the coordination reaction,Salen（Mn）-pr-NH₂-CS composite catalyst was prepared.Through Fourier Infrared Spectroscopy（FT-IR）,Thermal Weightless Analysis（TGA）,UV-visible diffuse reflectance spectroscopy（UV-Vis）,Wide Angle X-ray Powder Diffraction（XRD）,Scanning Electron Microscopy（SEM）and N₂ Adsorption-Desorption Analysis method characterized the composition and surface morphology of the composite catalyst.Using catalytic oxidation of styrene to produce styrene oxide as a probe reaction,under the action of Salen（Mn）-pr-NH₂-CS composite catalyst,the conversion rate of styrene was 90.7%.The yield of the product styrene oxide is 90.7%,and the selectivity is100%.The composite catalyst was used 4 times and showed good stability.（2）Since 3,5-di-tert-butylsalicylic aldehyde has an electron-donating effect compared to salicylaldehyde,the density of the electron cloud increases,thereby increasing the catalytic activity of Salen（Mn）.Therefore,3,5-di-tert-butyl salicylaldehyde was condensed with o-phenylenediamine to produce t-Bu-substituted Salen ligand（t-Bu-Schiff base）,followed by addition of manganese acetate and lithium chloride to prepare another Species of Salen（Mn）complex（t-Bu-Salen（Mn））,finally t-Bu-Salen（Mn）and pr-NH₂-CS are coordinated to prepare t-Bu-Salen（Mn）-pr-NH₂-CS composite catalyst.Through Fourier Infrared Spectroscopy,Thermal Weightless Analysis,UV-visible diffuse reflectance spectroscopy,Wide Angle X-ray Powder Diffraction,Scanning Electron Microscopy and N₂ Adsorption-Desorption Analysis technology analyzes the morphology and structure of the catalyst.The results show that:in the tere-butyl-substituted Salen（Mn）complex,the Salen ligand successfully coordinated with the central manganese ion of manganese acetate,and the nitrogen atom in pr-NH₂-CS formed a coordination bond（Mn-N）with the metal manganese ion and is firmly bonded.Using methylphenyl sulfide oxidation to produce methylphenyl sulfoxide as a probe reaction,under the action of t-Bu-Salen（Mn）-pr-NH₂-CS composite catalyst,the yield of methylphenyl sulfoxide can reach 57.1%,and the composite catalyst can be used for 3times to show good stability.