Synthesis Of Manganese Oxides And Their Catalytic Performance For C-N Coupling

Carbon-nitrogen bond(C-N)construction is a very important reaction in the fields of organic synthesis,drug design,and catalysis.Catalytic C-N coupling with aromatic aldehydes/alcohols and aminophenols as raw materials has become one of the main ways to synthesize benzoxazoles.However,The reaction often relies on noble metal homogeneous catalytic systems and harsh reaction conditions limit its industrial application.Transition metal oxides are widely used in the catalysis of fine organic reactions,especially oxidation reactions,due to their strong oxidizing properties and hydrothermal stability.This thesis uses the characteristics of similar atomic radii of N and O atoms,and the possibility of strong interaction between N and manganese oxygen species to construct a new type of nitrogen-doped manganese oxide(N-Mn O_x)catalyst.The thesis mainly studied the regulation of N-Mn O_x structure by urea as the N source,and the catalytic performance of the synthesized catalyst for the synthesis of typical benzoxazole.The N-Mn O_x catalyst was characterized in detail by XRD,SEM,XPS,TEM,IR,TG and other methods,and the relationship between the structure and performance of the catalyst was obtained,and the following main research results were obtained.Three kinds of N-Mn O_x catalysts including N-Mn O₂,N-Mn₅O₈ and N-Mn₃O₄,and N-Mn O₂with different N contents were synthesized.Under the same hydrothermal conditions,when N=0.25?0.125?0.025 mol catalyst particles form a spherical structure with a diameter of about 7.91-10.2nm,the main synthesis of N-Mn O₂ catalyst;N=0.0125?0.01 mol catalyst has a flower-like morphology,with a diameter of about 17.3-21.6 nm,mainly Synthesis of N-Mn₅O₈ catalyst;N=0.0025 mol,the catalyst has a flower-like morphology and a diameter of about 30.9 nm.The main synthesis of N-Mn₃O₄ catalyst is.The catalytic performance of N-Mn O_x catalyst for the synthesis of benzoxazole by C-N coupling using 4-methylbenzaldehyde and 2-aminophenol as raw materials was studied.The results show that manganese oxide is an effective catalyst for the synthesis of benzoxazole,and the catalytic performance of N-Mn O_x is significantly improved after N doping.Under the mild reaction conditions of room temperature and air,the N-Mn O_x catalyst exhibits excellent catalytic performance and good universality.It can achieve high-efficiency catalysis for 10 benzoxazoles,and the conversion frequency(TOF)value can reach 0.91 h^-1.After the catalyst was recycled 10times,the yield of the target product was still higher than 90%,indicating that N-Mn O_x is a potential catalyst for the synthesis of benzoxazole via C-N coupling.N-Mn O₂ catalysts with different nitrogen doping amounts were prepared and their catalytic performance for the synthesis of benzoxazole by C-N coupling of benzyl alcohol and o-aminophenol was studied.The results show that,when the nitrogen content(feeding ratio mole fraction)is greater than 0.025,the N-Mn O₂ catalyst has high-efficiency catalytic performance for the reaction,good recycling ability and universal applicability to different functional groups.Combining the characterization of GC-MS and IR,the intermediate of the C-N coupling reaction was obtained,and a reasonable mechanism of the C-N coupling reaction was proposed.