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Nitrous acid
General
Systematic name	Dioxonitric(III) acid
Other names	Nitrous acid
Molecular formula	HNO2
Molar mass	47.0134 g/mol
CAS number	10102-44-0
Properties
Density	? g/cm3
Solubility (water)
Melting point	? °C
Boiling point	? °C
Acid dissociation constant pKa	3.34
Chemical infobox

Nitrous acid (molecular formula HNO₂) 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.

Preparation

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

Decomposition

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

Atmospheric relevance

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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).

See also

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• Demjanov rearrangement
• Nitric acid (HNO₃)
• Tiffeneau-Demjanov rearrangement

External links

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Nitrites | Acids | Nitrogen metabolism

Азотиста киселина | Kyselina dusitá | Salpetrige Säure | Ácido nitroso | Nitrita acido | Acide nitreux | Salpeterig zuur | 亜硝酸 | Kwas azotowy(III) | Азотистая кислота | Salpetersyrlighet | Азотиста кислота | 亚硝酸