Journal of Catalysis, Vol.196, No.2, 339-344, 2000
Titanium-catalyzed heterogeneous oxidations of silanes, chiral allylic alcohols, 3-alkylcyclohexanes, and thianthrene 5-oxide: A comparison of the reactivities and selectivities for the large-pore zeolite Ti-beta, the mesoporous Ti-MCM-41, and the layered alumosilicate Ti-ITQ-2
A comparative study of silane oxidation, olefin epoxidation, and thianthrene 5-oxide sulfoxidation with the oxidants Ti-beta /H2O2, Ti-MCM-41/t-BuOOH, and Ti-ITQ-2/t-BuOOH provides the catalytic reactivity order Ti-beta > Ti-MCM-41 > Ti-ITQ-2. The steric constraints of the narrow channels make the Ti-beta zeolite the most selective. For the more open structures of the Ti-MCM-41 and Ti-ITQ-2 hosts, such steric constraints are less pronounced and, therefore, a lower selectivity is exhibited by these heterogeneous catalysts. Both activate t-BuOOH for oxygen transfer through a transition structure analogous to the homogeneous Ti(Oi-Pr)(4)/t-BuOOH oxidant. (C) 2000 Academic Press.