Unsensitized photooxidation

Type I mechanism, which does not involve the singlet oxygen reaction, is the another mechanism for the photosensitized oxidation of flavor compounds. Benzophenone-sensitized photooxidation of tetrahydrofuran leads to formation of the a-hydroperoxide (Scheme 27) (Schench et al, 1963), which is the same product formed in the unsensitized photooxidation of tetrahydrofuran as demonstrated in Scheme 11. 

Synthesis of Camphoric Anhydride via Unsensitized Photooxidation of Camphorquinone.56-17... 

The mechanism of the unsensitized photoreaction with oxygen is similar to that of photoreaction without oxygen. Both of them involve free radical or biradical formation. Photooxidation without sensitizer generally gives a more complex result than sensitizer photooxidation, probably because of co-occurrence of the photoreaction of the substrate itself, oxidation of the initial photoproduct, or further photochemical transformation of the photooxdation product (Matsuura and Saito, 1976). 

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