CHEMICAL TEST : HINSBERG’S TEST
Purpose : Used to differentiate classes of amines. Reagent and condition : Benzene sulphonyl chloride in excess KOH followed by acidification A mixture of amine and benzenesulphonyl chloride is shaken in excess potassium hydroxide and then acidified after the reaction has taken place. Each class of amine gives rise to a different observation in the test.
CLASS KOH in excess Addition of acid Hinsberg’s Test 3° amine 2° amine 1° amine precipitate clear solution two layers formed precipitate precipitate clear solution Observations :
PRIMARY AMINES Primary amines reacts with benzenesulphonyl chloride to form Nsubstituted benzenesulphonamides which react with excess potassium hydroxide to form water soluble potassium salts (clear solution). Acidification of this solution will, in the next stage, cause insoluble Nsubstituted sulphonamide to form a precipitate in water.
R N H + | H | | 1° amine Cl – S O O= = – S O O= = R N | H | – S O O= = R N | KOH K+ − water soluble salt (clear solution) HCl – S O O= = R N | H | water insoluble (precipitate) General equation: Class KOH excess Addition of H+ 1 o amine Clear solution Precipitate Observation :
SECONDARY AMINES Secondary amines reacts with benzenesulphonyl chloride in aqueous potassium hydroxide to form insoluble N,N-disubstituted sulphonamides that precipitate after the first stage. These precipitates do not dissolve in excess potassium hydroxide because they do not have acidic hydrogen. Acidification of this mixtures shows no visible result.
R N H + | R’ | | 2° amine Cl – S O O= = – S O O= = R N | R’ KOH | water insoluble (precipitate) HCl water insoluble (precipitate) General equation: Observation : Class KOH excess Addition of H+ 2 o amine Precipitate Precipitate No Reaction
TERTIARY AMINES Secondary amines reacts with benzenesulphonyl chloride in aqueous potassium hydroxide to form insoluble N,N-disubstituted sulphonamides that precipitate after the first stage. These precipitates do not dissolve in excess potassium hydroxide because they do not have acidic hydrogen. Acidification of this mixtures shows no visible result.
R N R” + | R’ | | 3° amine Cl – S O O= = No Reaction KOH water soluble salt (clear solution) HCl Two layers formed General equation: Observation : Class KOH excess Addition of H+ 3 o amine Two layers formed Clear solution R N R” | R’ | | | HCl− +
EXERCISE: Methanamine, N-methylmethanamine and N,N-dimethylmethanamine canbe differentiated from each other by using Hinsberg’s Test. State the observation and write the reaction equation involved of each amine.
CH3 N H + | H | | methanamine (1° amine) Cl – S O O= = – S O O= = CH3 N | H | – S O O= = CH3 N | KOH K+ − water soluble salt (clear solution) HCl – S O O= = CH3 N | H | water insoluble (precipitate) Class KOH excess Addition of H+ 1 o amine Clear solution Precipitate Observation : ANSWER :
CH3 N H + | CH3 | | N-methylmethanamine 2° amine Cl – S O O= = O O= = CH3 N | CH3 KOH | water insoluble (precipitate) HCl water insoluble (precipitate) Observation : Class KOH excess Addition of H+ 2 o amine Precipitate Precipitate No Reaction ANSWER : S |
CH3 N CH3 + | CH3 | | Cl – S O O= = No Reaction KOH water soluble salt (clear solution) HCl Two layers formed Observation : Class KOH excess Addition of H+ 3 o amine Two layers formed Clear solution CH3 N CH3 | CH3 | | | HCl− + N,N-dimethylmethanamine (3° amine) ANSWER :