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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:

Since this reaction is not reversible, N2O should not be considered as the anhydride of H2N2O2.³

The cis acid is not known,⁴ but its sodium salt can be obtained.⁵

Preparation

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

Spectroscopic data indicate a trans configuration for the resulting acid.⁶

It can also be synthesized from hydroxylamine and nitrous acid:

Biological aspects

In enzymology, a hyponitrite reductase is an enzyme that catalyzes the chemical reaction:⁷

References

1. Wiberg, Egon; Holleman, Arnold Frederick (2001). Inorganic Chemistry. Elsevier. ISBN 0-12-352651-5. 0-12-352651-5 ↩

2. 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. 0-08-029214-3 ↩

3. Wiberg, Egon; Holleman, Arnold Frederick (2001). Inorganic Chemistry. Elsevier. ISBN 0-12-352651-5. 0-12-352651-5 ↩

4. Wiberg, Egon; Holleman, Arnold Frederick (2001). Inorganic Chemistry. Elsevier. ISBN 0-12-352651-5. 0-12-352651-5 ↩

5. 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. 978-0-13-175553-6 ↩

6. 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. 978-0-13-175553-6 ↩

7. "ENZYME - 1.7.1.5 Hyponitrite reductase". http://enzyme.expasy.org/EC/1.7.1.5 ↩