ddlivermto srohentgncd8ce0oea8noa cads have therformula: ouble bonds bec of the 只 婚一· 2openingofoxagyclopropaneswthwaterpwoducesang CH TmsoCeaYtaeloeeGroamee8beocncrease ” CH 12-11 Vicna Osmium 8 8 Peroxycarboxylic acids deliver oxygen atoms to double bonds. Peroxycarboxylic acids have the general formula: These compounds react with double bonds because one of the oxygen atoms is electrophilic. The resulting products are an oxacyclopropane and a carboxylic acid. This reaction is referred to as an “epoxidation.” The older common name of an oxacyclopropane was an “epoxide.” Commonly used peroxycaraboxylic acids for this reaction are meta-chloroperoxybenzoic acid (MCPBA) which is somewhat shock sensitive, and magnesium monoperoxyphthalate (MMPP). The mechanism of this epoxidation reaction involves a cyclic transition state: The peroxycarboxylic acid reactivity with double bonds increases with alkyl substitution, allowing for selective oxidations: Hydrolysis of oxacyclopropanes furnishes the products of anti dihydroxylation of an alkene. Ring opening of oxacyclopropanes with water produces anti vicinal diols. Vicinal Syn Dihydroxylation with Osmium Tetroxide 12-11 The reaction of osmium tetroxide with alkenes yields syn vicinal diols in a two step process: The reaction mechanism involves the concerted addition of the osmium tetroxide to the π bond of the alkene: Catalytic amounts of osmium tetroxide in the presence of an oxidizing agent (H2O2) to regenerate the spent osmium tetroxide are often used, due to the expense and toxicity of OsO4