Question

Which of the following amines will give most easily \(\mathrm{N}_2\) gas on treatment with \(\mathrm{NaNO}_2 + \mathrm{HCl}\) at 275 K:

• A. \(\mathrm{C}_2\mathrm{H}_5\mathrm{NH}_2\)
• B. \(\mathrm{C}_6\mathrm{H}_5\mathrm{NHCH}_3\)
• C. \(\mathrm{C}_6\mathrm{H}_5\mathrm{NH}_2\)
• D. \(\left(\mathrm{CH}_3\right)_3\mathrm{N}\)

Hint:

For amine reactions with \(\mathrm{NaNO}_2 + \mathrm{HCl}\):

- Primary aliphatic: Unstable diazonium, releases \({N2}\).

- Primary aromatic: Stable diazonium salt, \({N2}\) with further reaction.

- Secondary/tertiary: No \({N2}\) evolution.

Answer 1

The Correct Option is C

The reaction of amines with \(\mathrm{NaNO}_2\) and \(\mathrm{HCl}\) at low temperatures (e.g., 275 K, or 2°C) forms diazonium salts or other products, depending on the amine type. The evolution of \(\mathrm{N}_2\) gas is characteristic of diazonium salt formation and subsequent decomposition.
Step 1: Reaction with \(\mathrm{NaNO}_2 + \mathrm{HCl}\) 
- Primary aliphatic amines (\({RNH2}\)): Form diazonium ions (\({RN2^+}\)), which are unstable and decompose to alcohols, releasing \({N2}\): \[ {RNH2 + NaNO2 + HCl -> RN2^+ -> ROH + N2 + H^+} \] - Primary aromatic amines (\({ArNH2}\)): Form stable diazonium salts (\({ArN2^+Cl^-}\)) at low temperatures, which do not immediately release \({N2}\) unless heated or reacted further: \[ {ArNH2 + NaNO2 + HCl -> ArN2^+Cl^-} \] - Secondary amines (\({R2NH}\)): Form N-nitrosoamines, no \({N2}\) evolution: \[ {R2NH + NaNO2 + HCl -> R2N-NO} \] - Tertiary amines (\({R3N}\)): Aliphatic tertiary amines form ammonium salts or nitrosamines; aromatic tertiary amines may form p-nitroso derivatives, no \({N2}\). 
Step 2: Analyze options 
- (A) \(\mathrm{C}_2\mathrm{H}_5\mathrm{NH}_2\): Primary aliphatic amine, forms unstable diazonium ion, releases \({N2}\) to form ethanol. 
- (B) \(\mathrm{C}_6\mathrm{H}_5\mathrm{NHCH}_3\): Secondary amine, forms N-nitrosomethylaniline, no \({N2}\). 
- (C) \(\mathrm{C}_6\mathrm{H}_5\mathrm{NH}_2\): Primary aromatic amine, forms stable benzenediazonium chloride at 275 K, which does not release \({N2}\) immediately but can decompose with heat or reagents (e.g., \({H3PO2}\)), releasing \({N2}\). 
- (D) \(\left(\mathrm{CH}_3\right)_3\mathrm{N}\): Tertiary aliphatic amine, forms trimethylammonium chloride or nitrosamine, no \({N2}\). 
Step 3: Interpret “most easily \(\mathrm{N}_2\) gas” 
The question likely assumes conditions where diazonium salts decompose to release \({N}_2\). Aliphatic diazonium ions (from \({C2H5NH2}\)) are highly unstable and release \({N2}\) readily at 275 K. Aromatic diazonium salts (from \({C6H5NH2}\)) are stable at 275 K but decompose under additional conditions (e.g., warming). Since aromatic diazonium salts are commonly tested for \({N2}\) evolution in subsequent reactions, \({C6H5NH2}\) is often the intended answer in such questions. 
Step 4: Conclusion 
Assuming standard organic chemistry context, \(\mathrm{C}_6\mathrm{H}_5\mathrm{NH}_2\) forms a diazonium salt most readily associated with \({N2}\) evolution in follow-up reactions, matching option (C).