β-Thioxo-ketones. Part 5. Photo-induced enol–enethiol interconversion of β-thioxo-ketones

Thioacetylacetone, which exists in 2-methylbutane–methylcyclohexane (5 : 1) solution at 95 K exclusively as the intramolecularly hydrogen-bonded enol tautomer, is converted upon irradiation at 353 nm into the corresponding enethiol tautomer, characterized by its absorption at 288 nm. The reverse process takes place upon irradiation of the enethiol tautomer at 288 nm. Both processes are successively repeatable. Other isomeric and/or tautomeric forms have not been observed. Monothiodibenzoylmethane behaves similarly upon photolysis at 95 K.