12.5: Nitrosation
- Page ID
- 433312
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Nitrosation - Nitroso Compounds
In organic chemistry, nitrosamines (or more formally N-nitrosamines) are organic compounds with the chemical structure R2N−N=O, where R is usually an alkyl group. They feature a nitroso group (-N=O) bonded to a deprotonated amine.
Most nitrosamines are carcinogenic. In foods, nitrosamines are produced from the reaction of nitrites and secondary amines, which are often present in proteins. Their formation can occur only under certain conditions, including strongly acidic conditions such as that of the human stomach. High temperatures, as in frying, can also enhance the formation of nitrosamines. There are significant levels of nitrosamines in many foodstuffs, especially meat and cheese products preserved with nitrite compounds. Tobacco specific nitrosamines (TSNAs) comprise one of the most important groups of carcinogens in tobacco products, particularly cigarettes and fermented dipping snuff.
Nitrosation reaction mechanisms begin with addition of a strong acid to sodium nitrite (NaNO2). Nitrous acid is formed, but it reacts further with acid to make water and the nitrosonium cation.
The nitrosonium cation is electron deficient. Its nitrogen has only three pairs of electrons in the valence shell, so it is a very good electrophile, very susceptible to attack by a nucleophile.
When the nucleophile is an amine, the product (after loss of an H+ from the amine nitrogen) is called an N-nitrosoamine.
The nitrosonium ion can also be attacked by an enolate nucleophile, similar to other reactions earlier in this chapter. In this case, the nitroso group is attached to an alpha carbon, and the product is known as a nitrosoalkane.