text: Dioxiranes are generated by combining the ketone precursor with a buffered aqueous solution of KHSO. The volatile dioxiranes DMD and TFD are isolated via distillation of the crude reaction mixture. Baeyer-Villiger oxidation may compete with dioxirane formation. Once isolated, dioxiranes are kept in solutions of the corresponding ketones and dried with molecular sieves. Air-free technique is unnecessary unless the substrate or product is air-sensitive or hydrolytically labile, and most oxidations are carried out in the open air in Erlenmeyer flasks.
  Oxidations with in situ generated dioxiranes are more convenient than isolation methods, provided the substrate is stable towards hydrolysis. Reactions can either be carried out in truly biphasic media with mechanical stirring, or in a homogeneous medium derived from water and a miscible organic solvent, such as acetonitrile. Asymmetric epoxidations are commonly carried out under the latter conditions. Some ketone catalysts are more persistent under slightly basic homogeneous conditions.