1^o Aliphatic Amine

1^o Aromatic Amine

2^o Amine

3^o Aliphatic Amine

3^o Aromatic Amine

Amino Acid

Procedure

Dissolve 0.5 mL or 0.5 g of unknown in 1.5 mL of conc. HCl diluted with 2.5 mL of water, and cool the solution to 0^oC in a beaker of ice. Dissolve 0.5 g of sodium nitrite in 2.5 mL of water and add this solution dropwise, with shaking, to the cold solution of the amine hydrochloride. Continue the addition until the mixture gives a positive test for nitrous acid. The test is carried out by placing a drop of the solution on starch-iodide paper; a blue color indicates the presence of nitrous acid. If the test is positive, move 2 mL of the solution to another test tube, warm gently, and examine for evolution of gas.

Positive Test

1^o aliphatic amines- rapid bubbling upon addition of sodium nitrite is a positive test.

1^o aromatic amines- rapid bubbling after addition of sodium nitrite (with heating) is a positive test.

2^o amines- pale yellow oil with no evolution of gas is a positive test.

3^o aliphatic amines- immediate positive test for nitrous acid with no evolution of gas is a positive test.

3^o aromatic amines- dark-orange solution or orange solid, when treated with base turns green is a positive test.

Complications

Compounds having a methylene group adjacent to a carbonyl group give a positive test.

Alkyl mercaptans yield red thionitroso compounds.

Nitrous acid will react with amides and phenols.