EFFECT OF TEMPERATURE ON SULFIDE PHOTOOXIDATIONS. EVIDENCE FOR A REVERSIBLY FORMED EXCIPLEX

A kinetic study of the reactions of singlet oxygen with pentamethylenesulfide, 1,4-dithiane, and 3-hydroxy-3,4-dimethylpentyl p-methylphenyl sulfide has been conducted as a function of temperature. The total rates of singlet oxygen removal (k T ) and the chemical rates of sulfide disappearance (k r ) have been measured and the physical quenching rates determined from the relationship k T =k r +k q . The activation barriers for the photooxidations are very different from those observed in photooxidations of other substrates and are explained by tighter binding in sulfide/oxyen exciplexes and bimolecular conversions of the exciplexes to products