Hyponitrous acid is a chemical compound with formula 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.
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), 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, should not be considered as the anhydride of .
The cis acid is not known, but its sodium salt can be obtained.
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.
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:
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