Thioacetamide, thioacetamide S-oxide (1), and thiopivalamideS-oxide (8) were oxidized with H2O2in H218O to generate the corresponding amides with at least 50%18O incorporation; hydrolysis of theS-oxides to the amides or18O exchange with the amides occurs much more slowly. When1and trifluorothioacetamide (6) were oxidized with three and four equivalents of H2O2, respectively, in the presence of benzylamine,N-acetylbemylamine (5) andN-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 anS,S-dioxide or trioxide intermediate as the major pathway; a minor pathway may involve the intermediacy of an oxathiiraneS-oxide (3) or dioxide (4) species. Understanding is added to the behavior ofS-oxides in aqueous solution, as well as to thermal stability in deuterochloroform. Also reported are studies of the preparation and properties of someN,N-dialkyl derivatives of8, of reduction of1with NADH or NADPH, and of generation and trapping of species related to sulfoxylate ion.