Reactivity of nitric oxide with simple short-lived radicals in aqueous solutions

The kinetic parameters and spectral properties of the products of the reaction of nitric oxide (NO) with (SCN)₂^-, Br₂^-, CO₂^-, CO₃^-⋅, and ethyl alcohol radicals were studied by the pulse radiolysis technique. The rate constants for the reaction of NO with these radicals are k[NO + (SCN)₂^-] = (4.3 ±0.1) x 10⁹M^-1s^-1, k[NO + CO₂-] = (2.9 ± 0.5) x 10⁹M^-1s-¹, k[NO + C0₃^-⋅] = (3.5 ± 0.5) x 10⁹M^-1s^-1, and k[NO + ethanol radicals] = (3.0 ± 1.0) x 109M-1s-1. (SCN)₂^-radical forms an adduct that decomposes by first-order processes to yield ultimately NO₂^-. The CO₃^-⋅radical reacts with NO by O-transfer with the direct formation of NO₂^-. The CO₂^-radical reacts with NO forming the NOCO₂^- transient which reacts with excess NO yielding N₂O₂^-. The ethanol radical-NO adducts rearrange to yield ultimately oximes/hydroxamic acids. Preliminary studies of the reaction of NO with Br₂^-show that, while NOBr₂^-is formed at a rate similar to that of NO(SCN)₂^-, k(NO + Br₂^-) = (4.8 ± 0.4) x 10⁹M^-1s^-1), the corresponding NOBr transient decays by a very complex mechanism that is currently being studied in greater detail. Mechanisms by which the various NO—adducts decay are discussed.