Tertiary amines do not react with benzenesulphonyl chloride, providing a basis for distinguishing between primary, secondary, and tertiary amines. This property is employed for the separation of amine mixtures. Nowadays, p-toluenesulphonyl chloride is commonly used in place of benzenesulphonyl chloride.

The reaction of benzenesulphonyl chloride with secondary amines yields N,N-diethylbenzenesulphonamide, which lacks acidic hydrogen and is insoluble in alkali due to the absence of a hydrogen atom attached to the nitrogen.

Benzenesulphonyl chloride reacts with primary amines to form sulphonamides, such as N-ethylbenzenesulphonyl amide. The sulphonyl group imparts acidity to the hydrogen attached to nitrogen, making it soluble in alkali.

Aromatic amines react with nitrous acid at low temperatures to form diazonium salts, a crucial class of compounds employed in the synthesis of various aromatic compounds. Secondary and tertiary amines exhibit different reactions with nitrous acid.

Primary aliphatic amines, when treated with nitrous acid, form unstable aliphatic diazonium salts that quantitatively release nitrogen gas and alcohols. The quantitative evolution of nitrogen is used for the estimation of amino acids and proteins.