Nitrous acid

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Nitrous acid

General
Systematic name	Dioxonitric(III) acid
Other names	Nitrous acid
Molecular formula	H N O₂
Molar mass	47.0134 g/mol
CAS number	7782-77-6
Properties
Density	? g/cm³
Solubility (water)
Melting point	? °C
Boiling point	? °C
Acid dissociation constant pK_a	3.34
Disclaimer and references

Nitrous acid (molecular formula H N O₂) is a weak 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.

1 Preparation
2 Decomposition
3 Chemistry
4 Atmospheric relevance
5 See also
6 External links

[edit] Preparation

It can be prepared by adding any mineral acid to sodium nitrite.

[edit] Decomposition

It rapidly decomposes into nitrogen dioxide, nitrogen monoxide and water when in solution.

[edit] Chemistry

Nitrous acid can be used to prepare diazonium salts which couple with anilines and phenols to form brightly colored azo compounds in a qualitative test for aromatic amines. This reaction is also used to produce azo-dyes. Nitrous acid is used to destroy toxic and potentially explosive sodium azide solutions. Nitrous acid is usually formed in situ by the action of mineral acid on sodium nitrite.

2HNO_{Subscript text}2------>NO_{Subscript text}2 + NO + H_{Subscript text}2O

[edit] Atmospheric relevance

Nitrous acid is an important atmospheric intermediate. It is produced by the heterogeneous reaction of NO₂ and water on various surfaces such as atmospheric aerosols. It is readily photolysed to produce hydroxyl radicals which are intricately involved in the ozone budget of the troposphere (lower atmosphere).