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The amino group is one of the most important functionalities in organic synthesis and in nature.

The amino group is one of the most important functionalities in organic synthesis and in nature. Amines are a class of organic compounds that contain the functional group -NH 2 . The structure of amine is R-NH 2 , where R in the case of aliphatic amine is an alkyl group or for aromatic amines is an aryl group.

To find the presence of amine functional group in the given organic compound.

Amines are classified as primary, secondary and tertiary amines. Primary amines is the one in which the nitrogen atom is bonded to one hydrocarbon atom and two hydrogen atoms. Secondary amines is bonded with two hydrocarbon atom and one hydrogen atom. Tertiary amines are amines in which all the hydrogen atoms are replaced by hydrocarbon atoms.

The following are the tests carried to identify the presence of amino group present in the organic compound.

Amines are organic compounds which is basic in nature, so they dissolve in mineral acids like hydrochloric acid. But this test is not a confirmation test for amines.

The chemical reaction is given below.

C 6 H 5 NH 2 + HCl → C 6 H 5 NH 3 + Cl –

Note: If it is soluble in mineral acid then it may be an amine.

Amines are basic in nature. So it turns red litmus paper blue. This test is also not a confirmation test for amines.

The chemical reaction is given below.

CH 3 -CH 2 -NH 2 + H 2 O → CH 3 -CH 2 -NH 3 + + OH –

Note: The change in the colour of red litmus paper shows the given organic compound is a base. (may be amine)

This test is also called isocyanide test, because when amines are treated with chloroform in the presence of alkali, isocyanide is formed. Both aliphatic and aromatic amines gives positive for this test. Secondary and tertiary amines do not give this test.

The chemical reaction is given below.

R-NH 2 + 3KOH + CHCl 3 → RNC(isocyanide) + 3KCl + 3H 2 O

Note: An unpleasant odor confirms the presence of primary amine.

This test can be used to identify primary, secondary and tertiary amines. An aromatic primary amine reacts with nitrous acid forms a diazonium salt and at higher temperatures the formed diazonium compounds undergoes decomposition.

C 6 H 5 NH 2 + HNO 2 → C 6 H 5 -N=N + Cl – (diazonium compound)

Primary aliphatic amines react with nitrous acid to give nitrogen gas, which is seen as bubbles.

R-NH 2 + HONO → R-OH + H 2 O + N 2 ↑

Secondary amines react with nitrous acid to form a yellow oily nitrosamine.

Tertiary amines react with nitrous acid to form soluble nitrite salts.

Note: Nitrosamines are highly carcinogenic substances.

This test is performed in order to confirm the presence of aromatic amines. Aromatic amines forms a diazonium salts when treated with HNO 2 . These diazo compounds couple with phenols like β-naphthols forms an orange azo dye which is insoluble in water.

The chemical reaction is given below.

C 6 H 5 NH 2 + HNO 2 → C 6 H 5 -N=N + Cl –

Note: The presence of red orange dye conforms the presence of aromatic amines.

The reagent used in this test is benzene sulfonyl chloride. Amines reacts with benzene sulfonyl chloride in the alkaline medium.

Primary amines reacts with benzene sulfonyl chloride to produce substituted sulfonamide which contains an acidic hydrogen and dissolve in basic medium.

A secondary amine forms a substituted sulfonamide which is insoluble in alakali because it does not have acidic hydrogen.

A tertiary amine forms a substituted sulfonamide which is insoluble in alkali because it does not have an acidic hydrogen.

Secondary amines: Precipitate in test tube but does not dissolve in concentrated hydrochloric acid.

Tertiary amines: Precipitate in the test tube but dissolves in concentrated HCl.

The given organic compound contains ___________ [aliphatic or aromatic (primary/secondary/tertiary)] amines.

The test conducted by Hinsberg is used to recognize the difference between ethylamine and diethylamine. When the aqueous potassium hydroxide and benzene sulphonyl chloride are treated with ethyl amine, it provides a clear solution (potassium salt) as the output of the reaction.

Aryl diazonium salts are ionic crystalline solids that are colorless. That is why it is soluble in polar solvents like water.

Isocyanides are destroyed by adding concentrated hydrochloric acid and thrown the mixture into sink.

Hinsberg test is used to distinguish between primary, secondary and tertiary amines.

The reagent used in Hinsberg test is benzene sulfonyl chloride.

If it is soluble in mineral acid then it may be an amine

An unpleasant odor confirms the presence of primary amine.

Appearance of bubbles shows the presence of primary amines, yellow oily liquid shows the presence of secondary amines and formation of nitrite salts conforms the presence of tertiary amines.

The presence of red orange dye conforms the presence of aromatic amines.