What is "hyponitrous acid"

Hyponitrous \Hy`po*ni"trous\, a. [Pref. hypo- + nitrous.] (Chem.) Containing or derived from nitrogen having a lower valence than in nitrous compounds.

Hyponitrous acid (Chem.), an unstable nitrogen acid, NOH, whose salts are produced by reduction of the nitrates, although the acid itself is not isolated in the free state except as a solution in water; -- called also nitrosylic acid.

n. (context inorganic compound English) The unstable compound HNO

n. an explosive white crystalline weak acid (H2N2O2)

Hyponitrous acid is the chemical compound HNO. This can be formulated as HON=NOH and is an isomer of nitramide, (HN−NO). It forms white crystals that are explosive when dry.

Hyponitrous acid is a weak acid (pK = 7.21, pK = 11.54) in aqueous solution and decomposes to NO and water with a half-life of 16 days at 25 °C at pH 1–3.

HNO → HO + NO

Hyponitrous acid forms two series of salts, the "acid hyponitrites" containing [HON=NO] anion and hyponitrites containing the [ON=NO] anion.

The hyponitrite ion [ON=NO] can be prepared in aqueous solution by two methods. One method uses organic nitrites to synthesize the sodium salt:

RONO + NHOH + 2 EtONa → NaNO + ROH + 2 EtOH

Another method is by the reduction of sodium nitrite with sodium amalgam:

2 NaNO + 4 Na(Hg) + 2 HO → NaNO + 4 NaOH + 4 Hg

The insoluble silver salt can be precipitated from the solution by the addition of silver nitrate:

NaNO + 2 AgNO → AgNO + 2 NaNO

The free acid is then prepared from silver(I) hyponitrite and anhydrous HCl in ether:

AgNO + 2 HCl → HNO + 2 AgCl

There are two possible structures of hyponitrous acid, trans and cis, and the solid NaNO·5HO is confirmed to be the trans form. Spectroscopic data also indicate a trans configuration of the free acid. The cis form can be prepared as the sodium salt NaNO by heating NaO with gaseous NO.