The Hinsberg reagent is

Benzenesulphonyl chloride $\left({C}_{6}{H}_{5}{SO}_{2}Cl\right)$, which is also known as Hinsberg's reagent, reacts with primary and secondary amines to form sulphonamides.

The Hinsberg test is based on the production of sulfonamides. An amine interacts with benzene sulfonyl chloride in the Hinsberg test. Due to the inability of tertiary amines to form stable sulfonamides, any product produced is either a primary or secondary amine. If the resulting sulfonamide dissolves in aqueous sodium hydroxide solution, it is a primary amine. It is a secondary amine if the sulfonamide is insoluble in aqueous sodium hydroxide and hydrogen chloride.