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Other Epoxidation Methods

Other Epoxidation Methods: Halcon Reaction

General procedure

Because of the activating and directive influence of OH groups, allylic alcohols are important starting materials for the Halcon reaction. Good yields are obtained by using catalytic amounts of VO(acac)2 and tert-butyl hydroperoxide as epoxidation agent.

In the first step, the allylic alcohol forms a complex with the metal compound in which the allylic alcohol is coordinated to the metal atom through the hydroxy group. In case of cyclic alcohols, epoxidation with tert-butyl hydroperoxide takes place cis to the hydroxy group. Acyclic alcohols form two different epoxides. The (Z) isomer preferentially adds to the oxygen atom in anti position to the OH group while the (E) isomer forms the syn derivative.

Epoxidation of the (Z) isomer
Epoxidation of the (E) isomer

Industrial application: Preparation of propylene oxide

Propylene (other olefins as well) is reacted in non-aqueous solvents with tert-butyl hydroperoxide in the presence of catalytic amounts of MoOL4-, V5+- or Ti2+complexes.

Technical synthesis of propylene oxide.
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