Studies On The Polymer Functionalized Fe₃O₄ Nano Magnetic Composite Materials And Their Application In Alcohol Selective Oxidation Catalysis

The oxidation of alcohols into corresponding aldehydes and ketones is a crucial transformation in organic chemistry, with both academic and industry relevance. To obtain suitable green, efficient, recoverable aerobic oxidation catalysts has been a significant challenge. Fe₃O₄ magnetic composite particles are novel functional materials and expected to exhibit new functional properties for a wide range of applications. Loading suitable homogenous catalytic center onto the magnetic particles via chemical functional modification would be a feasible way to obtain separable and reuseable catalysts.In this work, polymer-functionalized-Fe₃O₄ magnetic composite particles were synthesized. The nano Fe₃O₄ was prepared by co-precipitation process, followed by polymer modification via suspension polymerization. Then, the epoxyl of GMA was modified by -NH₂ functional group via ring-opening reaction, and subsequently -NH₂ group reacted with salicylaldehyde via condensation reaction. Salen-modified magnetic particles were obtained, which was facilely connected with metal ions via coordination bonds. These magnetic catalysts were characterized by IR, EA, TGA, XRD, TEM and VSM. The results showed that the magnetic catalysts have an average size of 30 run. Polymer functionalized groups and catalytic centers were successfully connected onto the surface of the Fe₃O₄ magnetic materials via suspension polymerization, ring-opening, condensation and coordination etc, chemical reactions. The composite catalysts have reasonable magnetic response, with saturation magnetizatic intensity of 22. 8 emu/g, residual magnetizatic intensity of 2.49 emu/g and coercive force of 47.2 Oe, respectively.These polymer-functionalized-Fe₃O₄ magnetic composite particles were applied as catalysts for the selective oxidation of alcohols to aldehyde and ketones. Some important variables for the catalytic selective oxidation of alcohols, e. g. substrate species, types of oxidant, reaction time, temperature have been optimized. The effect of co-catalysts, e. g. 2, 2,6,6- tetramethyl - piperidyl - 1 - oxyl (TEMPO) and anhydrous potassium carbonate, have been investigated as well; The effect of ligands, substitute groups, and the monomer ratio for the polymerization have also been investigated. Comparative studies on these heterogeneous magnetic catalysts and homogeneous catalyst which has the same catalytic center have been carried out. The results showed that the optimized condition for the selective oxidation of alcohols to aldehyde and ketones catalyzed by the polymer-functionalized-Fe₃O₄ magnetic composite particles were at reaction temperature of 60℃, 30% hydrogen peroxide as oxidant, with reaction time at 2.5 hours. This kind of magnetic catalyst had the best catalytic properties on the substrates with benzyl alcohol or substitute benzyl alcohols. 1 mmol of 4 kinds of studied benzyl alcohol and substitute benzyl alcohols can be 100 % converted to corresponding aldehydes without other unfavorable by-products catalyzed by 0.02 g of the present magnetic catalyst in the optimized reaction conditions. The literature reported co-catalyst, e g., TEMPO and anhydrous potassium carbonate had no obvious effect on the reaction as promoters. The effect of the types of Schiff base ligands and substitute groups did not significantly affect the catalytic properties of the present magnetic catalysts. The ratio of the monomer GMA used in the polymerization process had significant effect on the catalytic properties of the present magnetic catalysts. The highest catalytic properties were obtained when 0.023 mol GMA/1 g Fe₃O₄ used in polymerization, in which the conversion of benzyl alcohol reached to 100%. This may be related to the properties of GMA, i.e. the amount of GMA directly affect the amount of the reactive site for conjection to -NH₂ and furtherly for the catalytic center. The studied benzyl alcohol and substitute benzyl alcohols can be oxidated to corresponding aldehyde and ketones with 100 % conversion and selectivities over the present nano-magentic catalysts, which was much higher than those catalyzed by the corresponding homogeneous catalyst with 41% conversion.