An amine on reaction with benzenesulphonyl chloride produces a compound insoluble in alkaline solution. This amine can be prepared by ammonolysis of ethyl chloride. The correct structure of amine is:

The behaviour of an amine with benzenesulphonyl chloride is known as the Hinsberg test.

Hinsberg test summary:
  • Primary amine $$\left(1^{\circ}\right)$$ → forms a sulphonamide that still contains an $$N-H$$ bond; this product is acidic and therefore dissolves in aqueous alkali as its salt.
  • Secondary amine $$\left(2^{\circ}\right)$$ → forms an $$N,N$$-disubstituted sulphonamide that has no acidic hydrogen; the product is therefore insoluble in alkali.
  • Tertiary amine $$\left(3^{\circ}\right)$$ → does not give a sulphonamide (no reaction under these conditions).

The question states that “a compound insoluble in alkaline solution” is obtained. Hence the unknown amine must be a secondary amine.

Next, the amine “can be prepared by ammonolysis of ethyl chloride ( $$C_2H_5Cl$$ )”. When ethyl chloride is treated with excess alcoholic ammonia, the first product is ethylamine: $$C_2H_5Cl + NH_3 \;\xrightarrow{alc.}\; C_2H_5NH_2 + HCl$$

The freshly formed ethylamine can react further with another molecule of ethyl chloride to give a secondary amine:

$$C_2H_5Cl + C_2H_5NH_2 \;\xrightarrow{}\; \left(C_2H_5\right)_2NH + HCl$$

The secondary amine produced in this way is diethylamine, structural formula $$\left(C_2H_5\right)_2NH$$, which may also be written as $$CH_3CH_2NHCH_2CH_3$$.

Now match this structure with the options:

  • Option A: $$CH_3CH_2NH_2$$ - primary amine (ruled out).
  • Option B: $$CH_3CH_2CH_2NHCH_3$$ - secondary amine, but one group is methyl rather than ethyl; it cannot arise solely from ethyl chloride.
  • Option C: $$CH_3CH_2NHCH_2CH_3$$ - secondary amine with two ethyl groups (diethylamine).
  • Option D: $$\mathrm{C_6H_5NHCH_2CH_2CH_3}$$ - primary aromatic amine (ruled out).

Only Option C satisfies both conditions: it is secondary and it is obtainable from ethyl chloride via ammonolysis.

Therefore, the correct structure of the amine is given in Option C.