Hyponitrous acid
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Names | |||
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Preferred IUPAC name
Diazenediol | |||
Systematic IUPAC name
N-(Hydroxyimino)hydroxylamine | |||
Other names
Hyponitrous acid dimer
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Identifiers | |||
3D model (JSmol)
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3DMet | |||
ChEBI | |||
ChemSpider | |||
141300 | |||
KEGG | |||
PubChem CID
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CompTox Dashboard (EPA)
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Properties | |||
H2N2O2 | |||
Molar mass | 62.0282 g/mol | ||
Appearance | white crystals | ||
Hazards | |||
Occupational safety and health (OHS/OSH): | |||
Main hazards
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explosive when dry | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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]
References
- ^ a b c Wiberg, Egon; Holleman, Arnold Frederick (2001). Inorganic Chemistry. Elsevier. ISBN 0-12-352651-5.
- ^ a b c 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.
- ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.