Formation of Nitrosamines

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Moreover, secondary amines exhibit a much higher loading capacity for CO2 compared to primary amines. Tertiary amines have the disadvantage that they react very slowly with carbon dioxide and thus require large columns.
In the case of gas scrubbing in the chemical industry, there is usually no occurrence of the problem since the nitrosating substance (nitrogen dioxide, or nitrogen monoxide which is to be oxidized to nitrogen dioxide) is generally not present, as a result of which there is also no possibility of nitrosation. In some operations, for example the tire industry, inhibitors are deliberately added to the operation in order to prevent the formation of the N-nitroso components. In the food industry, there are some known and effective inhibitors, for example selenium. However, the acidic medium present therein differs distinctly from the alkaline conditions in the CO2 deposition.
In an advantageous configuration, the secondary amine is an amino acid salt. In a further advantageous configuration, the salt of vitamin C is sodium ascorbate. Amino acid salts have the advantage over other amines, such as alkanolamines, sterically hindered amines or amino acids, that they do not have any noticeable vapor pressure. The inventive solvent can be employed particularly advantageously in the case of amino acid salts, since the subsequent purification or the destruction of the stable nitrosamines is much more difficult in the case of amino acid salts than in comparison to conventional amines such as the alkanolamines or sterically hindered amines. In the case of alkanolamines, one option is distillation for the purification. Due to the lack of vapor pressure, in contrast, this is not possible for amino acid salts. These can be separated from the nitrosamines only by crystallization of the salt.

Reaction of Amines with Nitrous Acid

Nitrous acid (HNO₂ or HONO) reacts with aliphatic amines in a fashion that provides a useful test for distinguishing primary, secondary and tertiary amines.

1°-Amines + HONO (cold acidic solution) Nitrogen Gas Evolution from a Clear Solution 2°-Amines + HONO (cold acidic solution) An Insoluble Oil (N-Nitrosamine) 3°-Amines + HONO (cold acidic solution) A Clear Solution (Ammonium Salt Formation)

Nitrous acid is a Brønsted acid of moderate strength (pK_a = 3.3). Because it is unstable, it is prepared immediately before use in the following manner:
Under the acidic conditions of this reaction, all amines undergo reversible salt formation:
This happens with 3º-amines, and the salts are usually soluble in water. The reactions of nitrous acid with 1°- and 2°- aliphatic amines may be explained by considering their behavior with the nitrosonium cation, NO⁽⁺⁾, an electrophilic species present in acidic nitrous acid solutions.

Primary Amines

Secondary Amines

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