Epoxidation of alkenes to form epoxides

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epoxidation mechanism

Peroxy-acids are commonly used epoxidizing agents. They have an extra oxygen atom between the carbonyl group and their acidic hydrogen, and are electrophilic at oxygen. Attack at this position by a nucleophile displaces carboxylate, which is a good leaving group. An example of one such epoxidation reaction is shown below involving ethylene and performic acid. The mechanism is essentially an electrophilic attack, with a proton being transferred from the epoxide oxygen to the carboxylic acid by-product.

Firstly the nucleophilic π bond donates its electrons to the oxygen, breaking the O-O bond to form the new carbonyl bond. The electrons from the old O-H bond make up the second new C-O bond, and the original carbonyl group uses its electrons to pick up the proton. The transition state for the reaction makes the bond-forming and bond-breaking processes much clearer.

V. G. Dryuk, Tetrahedron, 1976, 32, 2855–2866.

A. S. Rao, S. K. Paknikar and J. G. Kirtane, Tetrahedron, 1983, 39, 2323–2367.


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