Irradiation of adamantanethione (λ 500 nm) gives the dimer, a 1,3-dithietane. In the presence of olefins thietanes are obtained in a regiospecific, nonstereospecific reaction. The regiospecificity is that expected with the formation of the more stable possible biradical intermediate. In one case, that of a-methylstyrene, support for the intermediacy of the biradical comes from the isolation of an "ene" product and proof that the latter is formed by intramolecular hydrogen transfer. It is shown that the reactive state of the thione is 3(n, π*) and that Φisc ∼ 1. Rate constants for dimerization and the addition to ethyl vinyl ether and acrylonitrile have been obtained, and the inefficiency in dimerization and cycloaddition (Φ ∼ 10-4) shown to be due to reversion in an intermediate or intermediates to regenerate starting material, and not to a slow reaction. In the case of dimerization, trapping of the thione triplet by thione is diffusion controlled. The mechanism of addition is discussed and the intervention of complexes suggested.
ASJC Scopus subject areas
- Colloid and Surface Chemistry