Q.An organic compound (A) with molecular formula $C_2H_7N$ reacts with nitrous acid to form compound (B) which is unstable. Hence compound (B) gets converted to compound (C). Compound (C) is used as a substitute for petrol. Identify compounds (A), (B) and (C).

The molecular formula $C_2H_7N$ points to ethylamine, whose reaction with nitrous acid produces a short-lived aliphatic diazonium salt that immediately breaks down to release nitrogen gas and form ethanol — the same alcohol widely blended with or substituted for petrol.

Identifying A: the molecular formula $C_2H_7N$ corresponds to a saturated amine with the general formula $C_nH_{2n+3}N$ (for $n=2$: $C_2H_7N$), i.e. a primary aliphatic amine, ethylamine, $C_2H_5NH_2$ (A).

Formation of B: unlike aromatic primary amines (which give a relatively stable diazonium salt in the cold), aliphatic primary amines react with nitrous acid (from $NaNO_2+HCl$) to form an aliphatic diazonium salt that is highly unstable even at low temperature: $C_2H_5NH_2 + HNO_2 \rightarrow C_2H_5N_2^+Cl^-\ (B,\ \text{ethanediazonium chloride, unstable}) + H_2O$

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