Hyponitrous acid

Hyponitrous acid
Preferred IUPAC name
Systematic IUPAC name
Other names
Hyponitrous acid dimer
3D model (Jmol) Interactive image
3DMet B00354
ChemSpider 55636
KEGG C01818
PubChem 61744
Molar mass 62.0282 g/mol
Appearance white crystals
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 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.[1]

Hyponitrous acid is a weak acid (pKa1 = 7.21, pKa2 = 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.[1]

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.[1]

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:[2]

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

Another method is by the reduction of sodium nitrite with sodium amalgam:[3]

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(I) 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.[2] 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.[2]


  1. 1 2 3 Wiberg, Egon; Holleman, Arnold Frederick (2001). Inorganic Chemistry. Elsevier. ISBN 0-12-352651-5.
  2. 1 2 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.
  3. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.
This article is issued from Wikipedia - version of the 4/12/2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.