University of PardubiceFaculty of Chemical Technology

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Novel recyclable polystyrene-supported catalyst for Sharpless epoxidation

Authors: Bartáček Jan | Drabina Pavel | Váňa Jiří | Sedlák Miloš

Year: 2019

Type of publication: ostatní - přednáška nebo poster

Page from-to: nestránkováno

Titles:

Language	Name	Abstract	Keywords
eng	Novel recyclable polystyrene-supported catalyst for Sharpless epoxidation	The Sharpless asymmetric epoxidation is one of the earliest known methods of the enantioselective synthesis. The reaction involves a stereoselective oxygen transfer from organic hydroperoxides to allylic alcohols’ double bond, catalysed by chiral titanium (IV) complexes of enantiopure tartaric acid derivatives (predominantly esters). In our work we have prepared two novel swellable crosslinked polystyrene L-tartrate copolymers. First one is anchored to polystyrene backbone via ester linkage. This catalyst showed up great catalytic activity (up to 99% conversion in 24 h; up to 99 %ee). However, recyclization of such catalyst was not possible due to Lewis acid catalyzed transesterification with alcohols in reaction mixture. This process leads to chiral fragment leaching. As an alternative, another polystyrene with L-tartrate anchored via C-C bond (as ketone) was prepared. Such a structural change did not affected catalytic activity. Series of various allylic alcohols was epoxidized using this catalyst. It is possible to reuse such catalyst at least four times without much activity loss. Precipitation of TiO2 in polymeric matrix was observed and that is the reason of slight deactivation of catalyst during recyclization. This research is key for further development of continuous-flow processes of Sharpless epoxidation.	Sharpless epoxidation; polystyrene-supported catalyst; polystyrene L-tartrate copolymers;