Photocyclization Reaction of some 2-Methyl-4-phenyl- Substituted Aldehyde Thiosemicarbazones. Mechanistic Aspects

Irradiation of 2-methyl-4-phenyl- substituted benzaldehyde thiosemicarbazones led with good yields to the corresponding Δ2-1,2,4-triazoline-5-thione derivatives through the formation of stable 1,2,4-triazolidine-5-thione intermediates. The relative quantum yields of photocyclization at 313 nm were analysed by means of the Hammett equation and ρ values determined. We interpreted the results in terms of the mechanism of photocyclization of 2-methyl-4-phenyl-substituted benzaldehyde thiosemicarbazones.