Chemistry:Hyponitrous acid

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Hyponitrous acid
Tautomer wireframe models of hyponitrous acid
Hyponitrous acid Ball and Stick (Tautomer 1).png
Hyponitrous acid Ball and Stick (Tautomer 2).png
Names
Preferred IUPAC name
Diazenediol
Systematic IUPAC name
N-(Hydroxyimino)hydroxylamine
Other names
Hyponitrous acid dimer
Identifiers
3D model (JSmol)
3DMet
ChEBI
ChemSpider
141300
KEGG
Properties
H2N2O2
Molar mass 62.0282 g/mol
Appearance white crystals
Conjugate base Hyponitrite
Hazards
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
Tracking categories (test):

Hyponitrous acid is a chemical compound with formula H2N2O2 or HON=NOH. It is an isomer of nitramide, H2N−NO2.

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 (pKa1 = 7.21, pKa2 = 11.54), and decomposes to nitrous oxide and water with a half life of 16 days at 25 °C at pH 1–3:

H2N2O2H2O + N2O

Since this reaction is not reversible, N2O should not be considered as the anhydride of H2N2O2.[1]

The cis acid is not known,[1] but its sodium salt can be obtained.[2]

Preparation

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

Ag2N2O2 + 2 HCl → H2N2O2 + 2 AgCl

Spectroscopic data indicate a trans configuration for the resulting acid.[2]
It can also be synthesized from hydroxylamine and nitrous acid:

NH2OH + HNO2H2N2O2 + H2O

Biological aspects

In enzymology, a hyponitrite reductase is an enzyme that catalyzes the chemical reaction[3]

H2N2O2 + 2 NADH + 2 H+ ↔ 2 NH2OH + 2 NAD+

References

  1. 1.0 1.1 1.2 Wiberg, Egon; Holleman, Arnold Frederick (2001). Inorganic Chemistry. Elsevier. ISBN 0-12-352651-5. 
  2. 2.0 2.1 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. https://archive.org/details/inorganicchemist00hous_159. 
  3. "ENZYME - 1.7.1.5 Hyponitrite reductase". http://enzyme.expasy.org/EC/1.7.1.5.