Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Diazotization is the process of converting primary aromatic amines into diazonium salts by treating them with nitrous acid () at low temperatures ().
Nitrous acid is highly unstable and is therefore produced in situ by the reaction of sodium nitrite () with a mineral acid like or .
The reaction must be carried out at to . If the temperature rises, the diazonium salt decomposes, reacting with water to form phenol and evolving gas.
Aromatic diazonium salts are relatively stable due to the dispersal of the positive charge over the benzene ring through resonance.
Primary aliphatic amines react with nitrous acid to form highly unstable aliphatic diazonium salts, which decompose immediately to yield a mixture of alcohols, alkenes, and alkyl halides, with the evolution of gas.
📐Formulae
💡Examples
Problem 1:
Explain why aniline does not form a stable diazonium salt at room temperature.
Solution:
At room temperature (above ), the benzenediazonium salt formed is thermally unstable. It reacts with the water present in the reaction mixture via a nucleophilic substitution reaction: .
Explanation:
The diazonium group () is an excellent leaving group. The kinetic energy at room temperature is sufficient to break the bond, leading to the formation of phenol and the release of nitrogen gas.
Problem 2:
How is nitrous acid prepared during the diazotization reaction?
Solution:
Nitrous acid () is prepared in the reaction flask (in situ) by reacting sodium nitrite () with cold dilute hydrochloric acid (): .
Explanation:
Since is an unstable weak acid that decomposes easily, it cannot be stored and must be generated freshly at the time of the reaction.