Question

Explain why a secondary amine forms a nitrosamine rather than a diazonium ion when it reacts with a nitrosonium ion.

Short answer

The nitrosamine generated from the secondary amine cannot form a diazonium ion when the nitrogen-nitrogen double bond is formed. The nitrogen cannot lose its positive charge by losing a proton.

Step-by-step solution

Azo linkage

The electrophilic substitution reaction between a highly activated aromatic ring and an arene diazonium ion creates the azo linkage (N=N).

The reaction is significantly favored when the electron-withdrawing group is present on the arene-diazonium ion and the electron-donating group is on the aromatic ring.

Explanation of why a secondary amine forms a nitrosamine rather than a diazonium ion when it reacts with a nitrosonium ion

The nitrosamine generated from the secondary amine cannot form a diazonium ion when the nitrogen-nitrogen double bond is formed. The nitrogen cannot lose its positive charge by losing a proton. Hence, the reaction stops at the nitrosamine.