Question

Which of the following statement about primary amines is false?

• A. Alkyl amines are stronger bases than aryl amines
• B. Alkyl amines react with nitrous acid to produce alcohols
• C. Aryl amines react with nitrous acid to produce phenols
• D. Alkyl amines are stronger bases than ammonia

Hint:

Primary aromatic amines with nitrous acid first form diazonium salts at \(0-5^\circ C\).

Answer 1

The Correct Option is C

Concept:
Primary amines are of two types: \[ \text{Primary aliphatic amines} \] and \[ \text{Primary aromatic amines} \] Their reactions with nitrous acid are different. Aliphatic primary amines react with nitrous acid to form alcohols with evolution of nitrogen gas. Aromatic primary amines react with nitrous acid at low temperature to form diazonium salts.

Step 1: Check statement (A).
Alkyl amines are stronger bases than aryl amines. This is true because in alkyl amines, the alkyl group increases electron density on nitrogen by \(+I\) effect. In aryl amines, the lone pair on nitrogen is delocalized into the benzene ring, so basicity decreases.

Step 2: Check statement (B).
Alkyl amines react with nitrous acid to give alcohols. General reaction: \[ RNH_2+HNO_2 \rightarrow ROH+N_2+H_2O \] So statement (B) is true.

Step 3: Check statement (C).
Aryl amines react with nitrous acid at \(0-5^\circ C\) to produce diazonium salts first. Example: \[ C_6H_5NH_2+HNO_2+HCl \rightarrow C_6H_5N_2^+Cl^-+2H_2O \] The immediate product is not phenol. Phenol can be formed later by hydrolysis of diazonium salt. So the direct statement is false.

Step 4: Check statement (D).
Alkyl amines are generally stronger bases than ammonia because alkyl groups increase electron density on nitrogen. So statement (D) is true. Hence, the false statement is: \[ \boxed{(C)\ \text{Aryl amines react with nitrous acid to produce phenols}} \]