Thiono Compounds, 7. Oxidation of Thioamides in Relation to Adverse Biological Effects1

Thioacetamide, thioacetamide S-oxide (1), and thiopivalamide S-oxide (8) were oxidized with H2O2 in H2 18O to generate the corresponding amides with at least 50% 18O incorporation; hydrolysis of the S-oxides to the amides or 18O exchange with the amides occurs much more slowly. When 1 and trifluorothioacetamide (6) were oxidized with three and four equivalents of H2O2, respectively, in the presence of benzylamine, N-acetylbemylamine (5) and N-benzyltrifluoroacetamide (7) were isolated in respective yields of 17% and 37%. These results are interpreted as evidence for an oxidative desulfurization mechanism involving nucleophilic attack at the carbon atom of an S,S-dioxide or trioxide intermediate as the major pathway; a minor pathway may involve the intermediacy of an oxathiirane S -oxide (3) or dioxide (4) species. Understanding is added to the behavior of S-oxides in aqueous solution, as well as to thermal stability in deuterochloroform. Also reported are studies of the preparation and properties of some N,N-dialkyl derivatives of 8, of reduction of 1 with NADH or NADPH, and of generation and trapping of species related to sulfoxylate ion.