Hyponitrous acid
| Hyponitrous acid | |
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Diazenediol |
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N-(Hydroxyimino)hydroxylamine |
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Other names
Hyponitrous acid dimer |
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| Identifiers | |
| CAS number | 14448-38-5 |
| PubChem | 61744  |
| ChemSpider | 55636 |
| KEGG | C01818 |
| ChEBI | CHEBI:14428 |
| Gmelin Reference | 141300 |
| 3DMet | B00354 |
| Jmol-3D images | Image 1 |
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| Properties | |
| Molecular formula | H2N2O2 |
| Molar mass | 62.0282 g/mol |
| Appearance | white crystals |
| Hazards | |
| Main hazards | explosive when dry |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 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 (pk1 = 7.21, pK2= 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
As this reaction is not reversible, N2O should not be considered as the anhydride of H2N2O2.[1]
Hyponitrous acid forms two series of salts, the "acid hyponitrites" containing [HON=N]− 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 to give the silver salt:[3]
- 2 NaNO2 + 4 NaHg + 2 H2O + 2 AgNO3 → Ag2N2O2 + 2 NaNO3 + 4 NaOH + 4 Hg
Addition of Ag+(aq) ions precipitates Ag2N2O2 from solution. The free acid is then prepared from silver 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 d Egon Wiberg, Arnold Frederick Holleman (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 Edition. Pearson. p. 468. ISBN 978-0-13-175553-6.
- ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth–Heinemann. ISBN 0080379419.
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