Regioselective epoxidation of different types of double bonds over large-pore titanium silicate Ti-β

Regioselective epoxidation of different types of double bonds located within the cyclic and acyclic parts of bulky olefins has been investigated using large-pore titanium silicate Ti-β in the presence of dilute aqueous H2O2 as oxidant under mild liquid-phase conditions. Our experimental results revealed that side-chain vinylic double bonds are selectively epoxidized than those in the cyclohexene-ring. The epoxidation tendency of various bulky olefins with different positional and/or geometric isomers over Ti-β follows the order: terminal –CC– > ring –CC– ≈ bicyclic ring –CC– > allylic C − H bond. Unlike 4-vinyl-1-cyclohexene, epoxidation of an equimolar mixture of cyclohexene and 1-hexene under identical conditions using Ti-β exhibits completely different selectivity and product distributions. Steric factor and accessibility of reactants to active Ti-sites are responsible for the observed regioselectivity of bulky alkenes.

Graphical abstractRegioselective epoxidation of double bonds in cyclic and acyclic fractions of the bulky olefins has been investigated over large-pore Ti-β. Experimental results suggested side-chain vinylic double bonds selectively epoxidize here.Figure optionsDownload full-size imageDownload high-quality image (52 K)Download as PowerPoint slide