Primary amines react with benzene sulphonylchloride  and form an organic compound “A”. “A” is soluble in 

$$\begin{gathered} \mathrm{Ph}-{\mathrm{SO}}_2\mathrm{Cl} + \mathrm{H}-\mathrm{NHR} \to \mathrm{Ph}-{\mathrm{SO}}_2-\mathrm{NH}-\mathrm{R}; \\ \mathrm{Hinsberg} \mathrm{reagent} \end{gathered}$$

Sulphonyl group is strong electron withdrawing group,H - attached to Nitrogen is acidic and thus soluble in alkali;

$\mathrm{N}-\mathrm{alkyl} \mathrm{benzene} \mathrm{sulphonamide}.... {\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{SO}}_2\mathrm{N}\underset{-}{\mathrm{H}}-\mathrm{R}$