Nitrous acid, and amines

Nitrous acid is a weak acid. A strong acid can dehydrate nitrous acid to produce ni-trosonium ion and water. 

Most reactions with amines and nitrous add involve the nitrosonium ion. 

Primary amines react with nitrous add to form diarxifiiitm salts. Aliphatic (nonaromatic) amines form extremely unstable salts that decompose spontaneously to form nitrogen gas. Aromatic amines also form unstable diazonium salts, but at temperatures bedow 5°C they decompose very slowly, 

The reaction, called diazotization of an amine goes as follows Nitrous acid is pro-tonated by a strong acid to form the nitrosonium ion, Nitrosonium ion reacts with the primary amine to form AAnihosoammomum, an unstable compound., V-ni-trosoammonium deprotonates to form AAnitrosoamine. W-nitrosoamine tautomerizes to diazenol. In die presence of acid, diazenol dehydrates to diazonium 

This reaction is pretty long, When thinking about nitrous acid and primary amines, just think diazonium ion, and remember that only aromatic amines work. 

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A -Nitroso derivatives, prepared from secondary amines and nitrous acid, are cleaved by reduction (H2/Raney Ni, EtOH, 28°, 3.5 h CuCl/concd. HCl"). Since many V-nitroso compounds are carcinogens, and because some racemization and cyclodehydration of V-nitroso derivatives of V-alkyl amino acids occur during peptide syntheses, V-nitroso derivatives are of limited value as protective groups. 

We have seen that Af-nitroso compounds are formed from secondary amines and nitrous acid ... 

An indirect method of hydrolyzing some amides utilizes nitrous acid. Primary amides are converted easily to carboxylic acids by treatment with nitrous acid. These reactions are very similar to that which occurs between a primary amine and nitrous acid (Section 23-10) ... 

Undoubtedly the same reaction occurs with aliphatic primary amines and nitrous acid. With aryl amines, however, the diazonium ion is stabilized by the resonance forms,... 

Griess diazo reaction. Formation of aromatic diazonium salts from primary aromatic amines and nitrous acid or other nitrosating agents. 

Since the synthesis of N-nitroso compounds is accomplished through reaction of secondary amines and nitrous acid, it was demonstrated that nitrosamines could be produced biochemically by the naturally acidic conditions in the stomach with ingestion of secondary amines (2). The nitrosating agent would be formed by the reaction of gastric juice with nitrite compounds that are widely used as food preservatives and for food color enhancement (2). Vitamin C was found to be a potent inhibitor of this reaction (I). 

When nihous acid reacts with amines, the products are very useful. We will soon see that these products can be used in a large number of synthetic transformations. So, let s make sure that you are comfortable with the reactions between amines and nitrous acid. 

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