What happens when a primary aliphatic amine, such as ethylamine (CH3CH2NH2), reacts with nitrous acid (HNO2, generated from NaNO2 + HCl) at room temperature?

Answer and explanation

Correct answer: D. Forms an unstable diazonium salt that decomposes quantitatively to release N2 and alcohol

  1. Step 1: Primary aliphatic amines react with nitrous acid () at 0–5°C to form aliphatic diazonium salts: .
  2. Step 2: Unlike aromatic diazonium salts (which are resonance-stabilized by the benzene ring at 273–278 K), primary aliphatic diazonium salts lack resonance stabilization and are extremely unstable.
  3. Step 3: They decompose spontaneously and quantitatively even at 0°C, liberating nitrogen gas () and forming carbocations that react with water to yield alcohols, alkenes, and alkyl chlorides.
  4. Step 4: The quantitative evolution of gas is used in the Van Slyke method for estimating amino acids and proteins.
Answer
It forms an unstable aliphatic diazonium salt that decomposes quantitatively to evolve nitrogen gas (N2) and produce ethanol
Why not the others: 'It forms a stable crystalline diazonium chloride...' describes aromatic amines (aniline), not aliphatic amines; 'It forms a yellow oily nitrosoamine...' is characteristic of secondary amines (Liebermann's nitroso test); 'It precipitates as metallic sodium...' is nonsensical.

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