Hyponitrous acid

 ( Pnictogen Oxoacids ) 

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 containing the ON=NO²⁻ anion and the "acid hyponitrites" containing the HON=NO⁻ anion.

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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 (p K_a1 = 7.21, p K_a2 = 11.54),

(1982). 9780080292144, Pergamon. ISBN 9780080292144

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 .

(2025). 9780123526519, Elsevier. ISBN 9780123526519

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

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

Spectroscopic data indicate a trans configuration for the resulting acid.

(2025). 9780131755536, Pearson. . ISBN 9780131755536

It can also be synthesized from hydroxylamine and nitrous acid:

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Biological aspects In enzymology, a hyponitrite reductase is an enzyme that catalysis the chemical reaction:

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