HALOGEN SENSITIZED PHOTOREACTIONS

Spectroscopic evidence indicates that reactions photosensitized by fluorine would take place by way of fluorine atoms. Similarly, the sensitizing action of chlorine will practically always be due to chlorine atoms. For bromine, when the wave length is less than 5107 Å, reaction will be by way of bromine atoms. Experiments using wave lengths 5107–6290 Å also probably involve bromine atoms although the possibility of reaction due to excited bromine molecules cannot be wholly ruled out. Iodine atoms are produced in photosensitization experiments involving iodine and wave lengths less than 4989 Å. Experimental evidence also favors the production of iodine atoms using wave lengths up to 6200 Å. Mechanisms in accordance with the above are advanced for a number of chlorine sensitized oxidation reactions. In the oxidation reactions an intermediate compound with a trivalent carbon is formed which reacts with oxygen forming a peroxide, giving rise to a chain reaction. Reactions sensitized by bromine and iodine are also discussed. It appears that all the halogen sensitized gaseous photoreactions thus far known can be explained by chemical mechanisms involving halogen atoms.