Laboratory test for amines

Two distinct laboratory tests for amines are described here. (a) Testing for the amine's basic character: all three classes of amine -- primary, secondary and tertiary alike -- are basic compounds, so the aqueous solution of any water-soluble amine turns red litmus paper blue, exactly as any other base would. More specifically, this basic character is detected in the laboratory by reacting the amine with an aqueous solution of a strong mineral acid such as HCl: even a WATER-INSOLUBLE amine dissolves readily into this aqueous HCl, because the reaction forms a water-soluble substituted-ammonium chloride salt; adding excess aqueous NaOH to that salt afterwards regenerates the original, insoluble free amine again (the amine is 'salted out' of solution as the strong base NaOH out-competes it for the proton). (b) The diazotization reaction, also called the orange-dye test, is specific to AROMATIC primary amines: 1-2 mL of concentrated HCl is added to a sample of the aromatic primary amine, followed by aqueous sodium nitrite solution added WHILE COOLING; the resulting solution is then transferred into a test tube already containing a solution of beta-naphthol dissolved in NaOH. Formation of an ORANGE dye specifically indicates the presence of an aromatic primary amino group. It is important to note that the temperature of every solution and reaction mixture involved in this test is deliberately maintained near 0 degrees …