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;
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:

{\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:

{\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:

{\ce {NH2OH + HNO2 -> H2N2O2 + H2O}}

Biological aspects

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

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

References

^ ^a ^b ^c Wiberg, Egon; Holleman, Arnold Frederick (2001). Inorganic Chemistry. Elsevier. ISBN 0-12-352651-5.
^ Perrin, D. D., ed. (1982) [1969]. Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution. IUPAC Chemical Data (2nd ed.). Oxford: Pergamon (published 1984). Entry 120. ISBN 0-08-029214-3. LCCN 82-16524.
^ ^a ^b Catherine E. Housecroft; Alan G. Sharpe (2008). "Chapter 15: The group 15 elements". Inorganic Chemistry (3rd ed.). Pearson. p. 468. ISBN 978-0-13-175553-6.
^ "ENZYME - 1.7.1.5 Hyponitrite reductase".

[Wiberg&Holleman-1] Wiberg, Egon; Holleman, Arnold Frederick (2001). Inorganic Chemistry. Elsevier. ISBN 0-12-352651-5.

[P82db-2] Perrin, D. D., ed. (1982) [1969]. Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution. IUPAC Chemical Data (2nd ed.). Oxford: Pergamon (published 1984). Entry 120. ISBN 0-08-029214-3. LCCN 82-16524.

[InorgChem-3] Catherine E. Housecroft; Alan G. Sharpe (2008). "Chapter 15: The group 15 elements". Inorganic Chemistry (3rd ed.). Pearson. p. 468. ISBN 978-0-13-175553-6.

[4] "ENZYME - 1.7.1.5 Hyponitrite reductase".

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