Everything about Nitrous Acid totally explained
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Nitrous acid (molecular formula
HNO2) is a weak and monobasic
acid known only in
solution and in the form of
nitrite salts.
Nitrous acid is used to make
diazides from amines; this occurs by nucleophilic attack of the amine onto the
nitrite, reprotonation by the surrounding solvent, and double-elimination of water. The diazide can then be liberated as a
carbene.
Structure
In the gas phase, the planar nitrous acid molecule can adopt both a
cis and a
trans form. The
trans form predominates at room temperature, and
IR measurements indicate it's
more stable by around 2.3 kJ mol
−1..
Preparation
Nitrous acid can be prepared by adding any mineral acid to
sodium nitrite.
Decomposition
Nitrous acid rapidly decomposes into
nitrogen dioxide,
nitric oxide, and
water when in solution.
2HNO
2 → NO
2 + NO + H
2O
It also decomposes into
nitric acid and
nitrous oxide and water.
4HNO
2 → 2HNO
3 + N
2O + H
2O
Chemistry
Nitrous acid is used to prepare
diazonium salts:
» HNO
2 +
ArNH
2 + H
+ → ArN
2+ + 2 H
2O
Such salts are widely is used in
organic synthesis, for example, for the
Sandmeyer reaction and in the preparation
azo dyes, brightly-colored compounds that are the basis of a qualitative test for
anilines. Nitrous acid is used to destroy toxic and potentially-explosive
sodium azide. For most purposes, nitrous acid is usually formed
in situ by the action of mineral acid on
sodium nitrite:
» NaNO
2 + HCl → HNO
2 + NaCl
2 NaN
3 + 2 HNO
2 → 3 N
2 + 2 NO + 2 NaOH
Atmosphere of the earth
Nitrous acid is involved in the
ozone budget of the the lower
atmosphere: the
troposphere. The
heterogenous reaction of
nitrous oxide (NO
2) and water produces nitrous acid. When this reaction takes place on the surface of atmospheric
aerosols, product readily
photolyses to
hydroxyl radicals.
Further Information
Get more info on 'Nitrous Acid'.
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