Epoxidation

Epoxides are a type of cyclic ether, characterized by a three-membered ring that consists of two carbon atoms and one oxygen atom. The compact, triangular formation of this structure imparts a high degree of ring strain, which in turn makes epoxides considerably more reactive than other ethers.

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In laboratory synthesis procedures, the Prilezhaev reaction is often used. This method involves the oxidation of an alkene using a peroxyacid, such as meta-chloroperoxybenzoic acid (mCPBA). The mechanism unfolds through what is typically referred to as the “Butterfly Mechanism”. In this mechanism, the peroxide functions as an electrophile, while the alkene serves as a nucleophile. The reaction is concerted, meaning it occurs in a single step without any intermediates. The butterfly mechanism positions the O−O sigma star orbital perfectly for an attack by the C−C pi electrons. As the reaction involves the breaking and forming of two bonds with the oxygen atom in the epoxide, it is a classic example of a coarctate transition state.