Photooxidation Photo-oxygenation

Santamaria, J. and Jroundi, R., Electron transfer activation — a selective photooxidation method for the preparation of aromatic aldehydes and ketones. Tetrahedron Lett., 32, 4291, 1991. Bokobza, L. and Santamaria, J., Exciplex and radical ion intermediates in electron transfer reactions. Solvent effect on the photo-oxygenation of 1,4-dimethylnaphthalene sensitized by 9,10-dicyanoan-thracene,/. Chem. Soc., Perkin Trans. 2, 269, 1985. 

The 02 ion appears to play an important role in a number of photooxidation reactions (see Section VI,C) for example, the photo-oxidation of alkenes over TiOz. However, it seems likely that OJ is not, in many cases, active in the oxidation step but further conversion occurs to give a mononuclear species, not detected directly, which then oxidizes the adsorbed hydrocarbons. Photo-oxidation of lattice oxygen in the M=0 systems (e.g., V2Os supported on PVG) gives rise to an excited charge transfer state such as V4 + -0 . This excited state can react as O- either by addition to a reactant molecule or by an abstraction reaction (see Section V of Ref. /). In the presence of oxygen, 03 is formed which then reacts further with organic molecules. 

The photoimaging process occurs via a photooxidation process photo-initiated by residual transition metal impurities in the presence of oxygen and terminated by coupling of polymer-bound radicals. Photoinduced cross-linking thus requires generation of a critical, and large, concentration of free radicals. 

The Photo-oxidation of Methoxy Substituted Phenols. As we are now aware of the fact that there are several routes to form phenols in the chemical reactions of lignin, we have looked into the nature of free radical induced photooxidation of phenols (IS). There is no doubt that photolysis of methoxy phenols in solutions or in solid state produces yellow products. Molecular oxygen has often been shown to be a necessary reactant in the oxidation, although the radical nature of the mechanism is not understood (16). 

Recently Fermin et al. [31] have used IMPS to study the photo-evolution of oxygen on /i-Ti02 and have concluded that the response is consistent with a Case II type mechanism involving OH ads intermediates. The same work showed that the OHads intermediate is also involved in the photooxidation of formic acid. 

An alternative explanation for the photooxidation of aqueous perchloric acid to give oxygen has been postulated [102], This mechanism involves a photo reaction in which hydroxyl radicals are formed. The proposed reaction scheme is as follows ... 

---