Photo-oxygenation of 4H-pyran-4-thiones and 4H-thiopyran-4-thiones: reactivity and kinetic characterization

Methylene Blue-sensitized photo-oxygenation of the 4H-pyran-4-thiones and 4H-thiopyran-4-thiones gives the corresponding ketones. The relative reactivity (β=k1/k2) of these thioketones to dye-sensitized oxygenation has been determined. The reactivity of the thioketones is the same or higher than that of tetramethylethylene. The quenching of the oxygenation by β-carotene suggests that the reactive species is singlet oxygen for the dyesensitized photo-oxygenation.