Nitroxyl

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^-, (pKa = 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, H₂N₂O₂, which is then dehydrated to nitrous oxide N₂O. Therefore, HNO is generally prepared in situ for example with the compounds such as Angeli’s salt (Na₂N₂O₃) and Piloty’s acid (PhSO₂NHOH) when it is needed.