Q.How will you distinguish between methylamine, dimethylamine and trimethylamine by Hinsberg's test ?

p-Toluenesulphonyl chloride (Hinsberg's reagent) gives a KOH-soluble sulfonamide with a primary amine but a KOH-insoluble one with a secondary amine.

p-Toluenesulphonyl chloride ($p$-$CH_3C_6H_4SO_2Cl$), also called Hinsberg's reagent, reacts with amines to form sulfonamides, and the solubility of the product in alkali distinguishes primary from secondary amines (the Hinsberg test).

With ethylamine (a primary amine):

$C_2H_5NH_2 + ClSO_2C_6H_4CH_3 \rightarrow C_2H_5-NH-SO_2C_6H_4CH_3 + HCl$

The product, N-ethyl-p-toluenesulphonamide, still has one hydrogen on nitrogen. This N–H has become acidic due to the strongly electron-withdrawing sulfonyl group, so it is readily removed by KOH, and the resulting sodium/potassium salt is soluble in the alkaline solution (clear solution forms).

With diethylamine (a secondary amine):

$(C_2H_5)_2NH + ClSO_2C_6H_4CH_3 \rightarrow (C_2H_5)_2N-SO_2C_6H_4CH_3 + HCl$

…