Chapter 13 - Nitroxyl (HNO) and the nitroxyl anion (NO−)

Abstract

Evidences have been accumulating in recent years, which suggest that the nitroxyl anion NO- or its protonated form HNO (nitroxyl) might be implicated in some of the biological properties associated with nitric oxide. Very little is known about the chemistry of the NO-/HNO system other than the species have only a fleeting existence. The existence of the nitroxyl anion NO- was proposed, as early as 1903, by Angeli. He had synthesized the salt sodium trioxodinitrate, from hydroxylamine and an organic nitrate in basic solution. The salt decomposes in dilute acid solution, yielding finally nitrous oxide and nitrite ions. Nitroxyl is a proposed intermediate here. Reaction occurs via the monoprotonated form of N2O32-. Even though the existence of HNO/NO- has been postulated as a reactive intermediate for over a hundred years, it was not until 1958 that any physical evidence for its existence was obtained, initially by infrared (IR) spectroscopy in the gas phase, and later by ultraviolet (UV) spectroscopy in solution following reduction of nitric oxide by the solvated electron using pulse radiolysis. However, in recent years the HNO/NO- system has been re-investigated with quite far-reaching consequences.