What is "nitroxyl"

nitro- \ni"tro-\pref.

1. A combining form or an adjective denoting the presence of niter.

2. (Chem.) A combining form (used also adjectively) designating certain compounds of nitrogen or of its acids; as nitrohydrochloric, nitrocalcite; also, designating the group or radical NO2, or its compounds, as nitrobenzene ( C6H5.NO2).

   Nitro group, the radical NO2; -- called also nitroxyl.

n. aminoxyl.

Nitroxyl (common name) or azanone (IUPAC name) is the chemical compound HNO. It is well known in the gas phase. In aqueous solution it acts as an acid with the conjugate base NO, ( pK = 11.4). NO is the reduced form of nitric oxide (NO) and is isoelectronic with dioxygen. Nitroxyl can be formed as a reaction intermediate.

Nitroxyl is very reactive towards nucleophiles (especially thiols) and quickly dimerizes to hyponitrous acid, HNO, which is then dehydrated to nitrous oxide NO. Therefore, HNO is generally prepared in situ for example with the compounds such as Angeli’s salt (NaNO) and Piloty’s acid (PhSONHOH) when it is needed.

Nitroxyl donors, known as nitroso compounds, show potential in the treatment of heart failure and ongoing research is focused on finding new molecules for this task. In one study such donor is prepared by organic oxidation of cyclohexanone oxime with lead tetraacetate to form 1-nitrosocyclohexyl acetate:

This compound can be hydrolyzed under basic conditions in a phosphate buffer to HNO, acetic acid and cyclohexanone.

Other studies that have been conducted on HNO precursors include those from Nagasawa et al. in which Piloty's acid is derivatized and produces HNO upon thermal decomposition. Other notable studies on the production of HNO come from Toscano et al. in which cycloadducts of acyl nitroso species (which are known to decompose via hydrolysis to HNO and acyl acid) are synthesized. Upon photolysis these compounds release the acyl nitroso species which then further decomposes.