Question

Arene diazonium salt results from the reaction of nitrous acid with which of the following

• A. Primary alcohol
• B. Secondary amine
• C. Primary aromatic amine
• D. Aldehyde

Answer 1

Answer: (C)

Primary aromatic amine

Answer 2

Arene diazonium salts are formed by the reaction of primary aromatic amines with nitrous acid (HNO₂). This reaction is known as diazotization. Nitrous acid is typically generated in situ by reacting sodium nitrite (NaNO₂) with a strong acid like hydrochloric acid (HCl) at low temperatures (0-5°C).

The general reaction is:

$\qquad \text{Ar-NH}_2 + \text{HNO}_2 + \text{HCl} \xrightarrow{0-5^\circ C} \text{Ar-N}_2^+\text{Cl}^- + 2\text{H}_2\text{O}$

For example, aniline (a primary aromatic amine) reacts as follows:

$\qquad \text{C}_6\text{H}_5\text{NH}_2 + \text{NaNO}_2 + 2\text{HCl} \xrightarrow{0-5^\circ C} \text{C}_6\text{H}_5\text{N}_2^+\text{Cl}^- + \text{NaCl} + 2\text{H}_2\text{O}$

Therefore, the compound that reacts with nitrous acid to form an arene diazonium salt is a primary aromatic amine.