Hyponitrous acid

Names
Preferred IUPAC name Diazenediol
Systematic IUPAC name N-(Hydroxyimino)hydroxylamine
Other names Hyponitrous acid dimer
Identifiers
CAS Number	14448-38-5
3D model (JSmol)	Interactive image
3DMet	B00354
ChEBI	CHEBI:14428
ChemSpider	55636
Gmelin Reference	141300
KEGG	C01818
PubChem CID	61744
CompTox Dashboard (EPA)	DTXSID40896989
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
Conjugate base	Hyponitrite
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	explosive when dry
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 a chemical compound with formula H
₂N
₂O
₂ or HON=NOH. It is an isomer of nitramide, H₂N−NO₂; and a formal dimer of azanone, HNO.

Hyponitrous acid forms two series of salts, the hyponitrites containing the [ON=NO]²⁻ anion, and the "acid hyponitrites" containing the [HON=NO]⁻ anion.^[1]

Structure and properties

There are two possible structures of hyponitrous acid, trans and cis. trans-Hyponitrous acid forms white crystals that are explosive when dry. In aqueous solution, it is a weak acid (pK_a1 = 7.21, pK_a2 = 11.54),^[2] and decomposes to nitrous oxide and water with a half life of 16 days at 25 °C at pH 1–3:

${\displaystyle {\ce {H2N2O2 -> H2O + N2O))}$

Since this reaction is not reversible, N
₂O should not be considered as the anhydride of H
₂N
₂O
₂.^[1]

The cis acid is not known,^[1] but its sodium salt can be obtained.^[3]

Preparation

Hyponitrous acid (trans) can be prepared from silver(I) hyponitrite and anhydrous HCl in ether:

${\displaystyle {\ce {Ag2N2O2 + 2 HCl -> H2N2O2 + 2 AgCl))}$

Spectroscopic data indicate a trans configuration for the resulting acid.^[3]
It can also be synthesized from hydroxylamine and nitrous acid:

${\displaystyle {\ce {NH2OH + HNO2 -> H2N2O2 + H2O))}$

Biological aspects

In enzymology, a hyponitrite reductase is an enzyme that catalyzes the chemical reaction^[4]

${\displaystyle {\ce {H2N2O2 + 2 NADH + 2 H+ <-> 2 NH2OH + 2 NAD+))}$