Epoxidation of olefins was carried with an excellent yield by dioxiranes generated in situ by reaction of ketone with H 2O 2 in the presence of NaHCO 3 in mixed solvent of acetonitrile and water. The catalytic activity of various ketones on epoxidation was studied for the first time. It is found that the ketone with electron withdrawing group has an excellent catalytic activity and trifluromethyl ketone has the highest catalytic activity. Some bulky ketones with electron withdrawing group show a very low catalytic activity. For olefins, the electron withdrawing group decreased the reactivity of the olefin and the electron donating group increased the reactivity, but the steric factor has little effect on the reactivity of olefins.
