Hyponitrous acid is a chemical compound with formula or HON=NOH. It is an isomer of
nitramide
Nitramide or nitroamine is a chemical compound with the molecular formula . Substitution reaction, Substituted derivatives are termed nitramides or nitroamines as well. Organyl derivatives of nitramide, and , are widely used as explosives: exam ...
, H
2N−NO
2, and a formal dimer of
azanone, HNO.
Hyponitrous acid forms two series of
salts
In chemistry, a salt or ionic compound is a chemical compound consisting of an assembly of positively charged ions ( cations) and negatively charged ions (anions), which results in a compound with no net electric charge (electrically neutral). ...
, the
hyponitrites containing the
N=NOsup>2− anion and the "acid hyponitrites" containing the
ON=NOsup>− 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 (p''K''
a1 = 7.21, p''K''
a2 = 11.54),
and decomposes to
nitrous oxide
Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, or factitious air, among others, is a chemical compound, an Nitrogen oxide, oxide of nitrogen with the Chemical formula, formula . At room te ...
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
In organic chemistry, ethers are a class of compounds that contain an ether group, a single oxygen atom bonded to two separate carbon atoms, each part of an organyl group (e.g., alkyl or aryl). They have the general formula , where R and R†...
:
:
Spectroscopic data indicate a ''trans'' configuration for the resulting acid.
It can also be synthesized from
hydroxylamine and
nitrous acid
Nitrous acid (molecular formula ) is a weak and monoprotic acid known only in solution, in the gas phase, and in the form of nitrite () salts. It was discovered by Carl Wilhelm Scheele, who called it " phlogisticated acid of niter". Nitrous ac ...
:
:
Biological aspects
In
enzymology
An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...
, a
hyponitrite reductase is an
enzyme
An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...
that
catalyzes the
chemical reaction
A chemical reaction is a process that leads to the chemistry, chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an Gibbs free energy, ...
:
:
References
{{Nitrogen compounds
Pnictogen oxoacids
Nitrogen oxoacids
Oxidizing acids
Hyponitrites