Nitroxyl

Nitroxyl 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.