RING-CHAIN TAUTOMERISM OF N-SUBSTITUTED THIOSEMICARBAZONES

The condensation products from 4,4-dimethyl- and Z4,4-trimethylthiosemicarbazides and aldehydes or ketones, as well as those from 2-methyl- and 2,4-disubstituted thiosemicarbazides and aldehydes have the thiosemicarbazone structure, while ketones react with 2-methyl- or 2,4-dialkylthiosemicarbazides to form 1,2,4- triazolidine-3-thiones. Both thiosemicarbazones and 1,2,4- triazolidine- 3-thiones in trifluoroacetic acid solution yield 1,3,4-thiadiazolidine-2-iminium salts. Their deprotonation by pyridine leads to thiosemicarbazones, including otherwise inaccessible 2-methyl- and 2,4-disubstituted ketone thiosemicarbazones. The mass-spectrometric investigation of these compounds also suggests presence of their tautomers in the gas phase.