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Which of the following statements about primary amines is 'False'?
A
Alkyl amines are stronger bases than ammonia
B
Alkyl amines are stronger bases than aryl amines
C
Alkyl amines react with nitrous acid to produce alcohols
D
Aryl amines react with nitrous acid to produce phenols
Detailed Solution
Alkyl groups release electrons (+I effect) and increase the electron density on nitrogen, so alkyl amines are stronger bases than ammonia (true).
In aryl amines the lone pair on nitrogen is delocalised into the benzene ring, so they are weaker bases than alkyl amines (true).
Primary aliphatic amines react with nitrous acid to give unstable aliphatic diazonium salts, which decompose to alcohols with evolution of nitrogen: $RNH_2 + HNO_2 \rightarrow ROH + N_2 + H_2O$ (true).
Primary aromatic amines react with nitrous acid at 273–278 K to form arenediazonium salts, which are stable at this temperature: $C_6H_5NH_2 + NaNO_2 + 2HCl \rightarrow C_6H_5N_2^+Cl^- + NaCl + 2H_2O$. Phenol is not the product of this reaction.
Hence the false statement is that aryl amines react with nitrous acid to produce phenols.
In aryl amines the lone pair on nitrogen is delocalised into the benzene ring, so they are weaker bases than alkyl amines (true).
Primary aliphatic amines react with nitrous acid to give unstable aliphatic diazonium salts, which decompose to alcohols with evolution of nitrogen: $RNH_2 + HNO_2 \rightarrow ROH + N_2 + H_2O$ (true).
Primary aromatic amines react with nitrous acid at 273–278 K to form arenediazonium salts, which are stable at this temperature: $C_6H_5NH_2 + NaNO_2 + 2HCl \rightarrow C_6H_5N_2^+Cl^- + NaCl + 2H_2O$. Phenol is not the product of this reaction.
Hence the false statement is that aryl amines react with nitrous acid to produce phenols.