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 (pKa1 = 7.21, pKa2 = 11.54),[2] and decomposes to nitrous oxide and water with a half life of 16 days at 25 °C at pH 1–3:
- 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:
- 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:
- NH2OH + HNO2 → H2N2O2 + H2O
Biological aspects
In enzymology, a hyponitrite reductase is an enzyme that catalyzes the chemical reaction:[4]
- 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".
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