Epoxides are important intermediates, widely used in the synthesis of a variety of valuable chemicals.[1]During this presentation, an overview of the chemistry and associated pitfalls of various epoxidation strategies will be provided. We will start with radical autoxidation chemistry, illustrated for different pinene-isomers.[2]The classical Twiggs epoxidation mechanism (involving the addition of peroxyl radicals to the C=C bond and a subsequent rearrangement) will be discussed, and the oxygen pressure dependence will be explained and incorporated into the micro-kinetic modeling of the system. In a second part of the lecture, the homogeneous activation of peroxides by oxidatively stable d0transition metal ions, such as Mo(VI), will be addressed. The dependence of the selectivity on the olefin/peroxide ratio will be explained by the kinetic competition of the peroxo intermediates, and the formation of radicals – which lead to allylic by-products – will be highlighted.[3]In the last part of the lecture, the immobilization of Lewis acidic Ti(IV) sites will be discussed.[4]The structural characterization of the various surfacespecies will be addressed, as will their influence on the catalytic performance under continuous flow conditions. Reference will be made to the current state-of-the-art TS-1 epoxidation catalyst, used in the HPPO process.[1]
[1] F. Cavani, J. H. Teles,ChemSusChem2009,2, 508-534.
[2] a)U. Neuenschwander, F. Guignard, I. Hermans,ChemSusChem2010,3, 75-84, b) U. Neuenschwander, I. Hermans,Phys. Chem. Chem. Phys.2010,12, 10542-10549, c) U. Neuenschwander, E. Meier, I. Hermans,ChemSusChem2011,4, 1613-1621.
[3] Ulrich Neuenschwander, Emanuel Meier, Ive Hermans, submitted.
[4]P. Mania, R. Verel, M. Rolph, I. Hermans, submitted.