Polymer Immobilized Bimetallic Nanoparticle Catalysts for Selective Hydrogenation of Quinones and Integration of Quinone-hydrogenation and Its Derivatization Using Sequential and Continuous-flow Systems

Abstract

Several single metal and bimetallic nanoparticle catalysts immobilized on polymer supports have been developed for selective hydrogenation of quinones to hydroquinones. Au-Pt bimetallic nanoparticle catalyst showed the best reactivity and selectivity for this purpose. Though slight over-reduction proceeded under batch conditions, higher reactivity, selectivity, and robustness of the catalysts were confirmed under continuous-flow conditions with polydimethylsilane-supported catalysts. Various direct derivatizations of quinones, such as methylation, acetylation, trifluoromethanesulfonylation, and benzoylation were successfully performed under sequential-flow conditions to afford the desired products in good to excellent yields. Especially, air-sensitive hydroquinones, such as anthrahydroquinones and naphthohydroquinones, could be successfully generated and derivatized under closed sequential-flow conditions without decomposition. This sequential-flow systems showed various benefits of flow systems; suppression of over reactions by controlling residence time, facile use of unstable intermediates, continuous production and robustness of the system.