Hyponitrous acid

Hyponitrous acid

Names
Preferred IUPAC name Diazenediol
Systematic IUPAC name N-(Hydroxyimino)hydroxylamine
Other names Hyponitrous acid dimer
Identifiers
CAS Number	14448-38-5
3DMet	B00354
ChEBI	CHEBI:14428
ChemSpider	55636 N
Gmelin Reference	141300
Jmol 3D model	Interactive image
KEGG	C01818
PubChem	61744
InChI InChI=1S/H2N2O/c3-1-2-4/h(H,1,4)(H,2,3) Key: NFMHSPWHNQRFNR-UHFFFAOYSA-N
SMILES ON=NO
Properties
Chemical formula	H2N2O2
Molar mass	62.0282 g/mol
Appearance	white crystals
Vapor pressure	{{{value}}}
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Hyponitrous acid is the chemical compound H₂N₂O₂. This can be formulated as HON=NOH and is an isomer of nitramide, (H₂N−NO₂). It forms white crystals that are explosive when dry.

Hyponitrous acid is a weak acid (pk₁ = 7.21, pK₂= 11.54) in aqueous solution and decomposes to N₂O and water with a half-life of 16 days at 25 °C at pH 1-3.

H₂N₂O₂→ H₂O + N₂O

Hyponitrous acid forms two series of salts, the "acid hyponitrites" containing [HON=NO]⁻ anion and hyponitrites containing the [ON=NO]²⁻ anion.

The hyponitrite ion [ON=NO]²⁻ can be prepared in aqueous solution by two methods. One method uses organic nitrites to synthesize the sodium salt:

RONO + NH₂OH + 2 EtONa → Na₂N₂O₂ + ROH + 2 EtOH

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

2 NaNO₂ + 4 Na(Hg) + 2 H₂O → Na₂N₂O₂ + 4 NaOH + 4 Hg

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

Na₂N₂O₂ + 2 AgNO₃ → Ag₂N₂O₂ + 2 NaNO₃

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

Ag₂N₂O₂ + 2 HCl → H₂N₂O₂ + 2 AgCl

There are two possible structures of hyponitrous acid, trans and cis, and the solid Na₂N₂O₂•5H₂O 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 Na₂N₂O₂ by heating Na₂O with gaseous N₂O.