Oxidation with Oxygen without a Catalyst

The processes without an external catalyst can be subdivided in accordance with the nature of the initiating step. Thermal, photocatalytic, and radical-catalyzed procedures may be differentiated. 

In recent years there has been an increase in the number of studies dealing with 

A number of theoretical studies have appeared on the mechanism of the oxirane-forming reaction of olefins and 0( P). A kinetic investigation of the reaction of oxirane and the 0( P) atom has shown that H-abstraction occurs rather than insertion to form a dioxetane intermediate, The thermal and photochemical epoxidation of propylene in the presence of sulfur dioxide and acetonitrile have been reported.  

Photooxidation suitable for the epoxidation of aromatic olefins also occurs with a-diketones (benzil, biacetyl), benzophenone, benzoin, and a-ketoacids, Isotopic mechanistic studies point to a reaction via a biradical. Photooxidation with an a-diketone or a-ketoacid recently has been interpreted in terms of a photochemical a-cleavage leading to an acylperoxy radical, which can effectively transfer an oxygen atom to olefins. Vinylallenes have similarly been photooxidized in the presence of biacetyl.  

Thermally initiated epoxidation with dienones proceeds selectively (Eq. 45) Q O 

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