Reactivity of sulfur nucleophiles towards S-nitrosothiols

Rate constants have been measured for the reactions of a range of S-nitroso thiols with the following sulfur-centred nucleophiles: sulfite ion, thioure a, thiocyanate ion, thiosulfate ion, thiomethoxide ion and sulfide ion. Man y of the reactions were very fast and were followed in a stopped-flow spect rophotometer. For the sulfite reaction the reactive species over the pH ran ge 4-8 was shown to be exclusively SO32-. For two RSNO species the reactivi ty sequence was established as: SO32- > MeS- > S2O32 >> SC(NH2)(2) > SCN-. The reaction with sulfide ion was also rapid and generated a fairly stable yellow species (lambda(max) 410 nm), which was probably the nitrosodisulfid e ion ONSS-, but the absorbance-time data were too complex for a simple kin etic analysis. This reaction could have some potential as an analytical pro cedure for the determination of RSNO species. The kinetic results are discu ssed in terms of the factors affecting nucleophilicity and are compared wit h the corresponding reactions of other nitrosating species.