The Synthesis And Performance Study Of Magnetic Catalyst Based On Sonogashira Reaction

In recent years, the research and application of magnetic nanocomposite catalyst has attracted widespread attention. The magnetic nanocomposite catalyst not only has the advantage of high selectivity and highly active, but also can be simple separation and recovery by use the applied magnetic field. Thus reducing the production cost, has extensive value for industrial use.In this paper, we used the SiO2@Fe3O4magnetic microspheres, which had obvious core/shell structure. Then taking PdCl2as the palladium source, using three ways of hydrogen, sodium borohydride and hydrazine hydrate reduction to get three kinds of Pd/SiO2@Fe3O4heterogeneous catalyst. XRD、VSM、TEM and BET methods were used to characterize the structure of the Pd/SiO2@Fe3O4catalysts. And performances of the Pd/SiO2@Fe3O4catalysts were evalued with Sonogashira reaction of iodobenzene and phenylacetylene. After the reaction, we used external magnetic field collect the catalyst and investigate its repeated use performance. The results showed that:we used solvothermal proess successfully prepared superparamagnetic Fe3O4nanoparticles,which have particle size distribution of about230～250nm and good dispersivity. Using the sol-gel method to prepare the SiO2@Fe3O4carrier of porous structured, large specific surface area, uniform particle morphology and consistent with a core-shell structure. Reduction by hydrogen, sodium borohydride and hydrazine hydrate can be successfully prepared the Pd (0) nanoparticles.The PdH/SiO2@Fe3O4catalyst, which geted by H2reduction method, has the smaller Pd nanoparticles than the PdB/SiO2@Fe3O4and Pds/SiO2@Fe3O4catalysts. In addition, Pd nanoparticles of sodium borohydride and hydrazine hydrate reduction were all load on the surface of the carrier, unable to enter the channel. While the the Pd nanoparticles of PdH/SiO2@Fe3O4catalyst had two distribution:highly dispersed in the shell surface of the carrier mesopores were4nm-6nm and in the shell mesoporous channel were2nm-3nm.Use the Sonogashira reaction of benzene and phenylacetylene as model to explore its catalytic performance, and the study showed that three kinds of Pd/SiO2@Fe3O4magnetic catalyst all have high catalytic performance for Sonogashira reaction. Wherein the optimal reaction system of PdH/SiO2@Fe3O4catalyst was:DMF as solvent, KOAc as base, in iodobenzene:phenylacetylene molecular ratio of1:1.3, iodobenzene:alkali molecular ratio of1:3, the Pd0.5mol%content of catalyst, reaction1.5h under the condition of130℃, iodobenzene conversion rate can reached99.2%, diphenylacetylene yield up to98.7%. At the same time,2mol%Pd content of the PdB/SiO2@Fe3O4catalyst and Pds/SiO2@Fe3O4catalyst, respectively, react8h and12h also reached more than90%yield.Three kinds of catalysts all had good recovery performance, and conversion rate was not apparent reduced repeating six to seven times.