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-beta 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-beta follows the order: terminal -C=C- > ring -C=C- approximate to bicyclic ring -C=C- > allylic C-H bond. Unlike 4-vinyl-1-cyclohexene, epoxidation of an equimolar mixture of cyclohexene and 1-hexene under identical conditions using Ti-beta 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. (C) 2010 Elsevier B.V. All rights reserved.