Question

Before the advent of modern spectroscopic techniques, such as NMR and IR spectroscopy, chemists typically determined whether a functional group was transformed into another during a reaction by performing chemical tests, where the reagents would react with the new functional group but not the old one (or vice versa) causing an observable reaction to occur, such as gas bubbles or a solid precipitate. Find a chemical test that you could have used to determine whether or not the nitro group on your starting material had been reduced to an amine and describe the test.

Answer 1

The test should show positive only with amines. We use Hinsberg test to determine the presence of amine. The reagent used is benzene sulphonyl chloride.

Procedure : take the reacted compound in a small quantity in a test tube and add 2ml of 25% NaOH, 2 ml of water and 1 ml of benzene sulphonyl chloride. Shake the mixture well and wait for 10 minutes. Cool the mixture under tap water. A precipitate will be formed. Treat the precipitate with conc.HCl

Results: on addition of conc. HCl, precipitate is seen - primary amine

Precipitate formed in the test tube does not dissolve in conc.HCl - secondary amine

Precipitate formed in the test tube dissolves in conc. hCl - tertiary amine