Reaction of Superoxide with Nitric Oxide to Form Peroxonitrite in Alkaline Aqueous Solution

摘要

Although aqueous superoxide often acts as a one-electron reductant or less frequently as an oxidant, it rarely undergoes covalent bond formation with simple organic or inorganic compounds in water, perhaps owing to its poor nucleophilicity in this solvent. In this communication we show, however, that superoxide can react with nitric oxide to form the peroxonitrite anion in deaerated aqueous solution at pH 12-13: O2(-) + NO = -OONO. This reaction represents one of the few examples of a radical-radical coupling of O2(-) with another odd-electron species to form a diamagnetic product. The reaction also may be of significance in natural waters or prove useful for trapping and measuring low levels of superoxide in aqueous systems. Peroxonitrite exhibits a broad absorption spectrum with a maximum at ca. 300nm. Although stable for hours in 0.1 M base, at lower pH it rapidly protonates and subsequently rearranges to nitrate.