Compounds of Carbon Containing Nitrogen: Chemical Properties of Amines (For CBSE, ICSE, IAS, NET, NRA 2022)

Doorsteptutor material for competitive exams is prepared by world's top subject experts: get questions, notes, tests, video lectures and more- for all subjects of your exam.

Chemical Properties of Amines

Ring Substitution in Aromatic Amines

You know that – group is a strong activating and ortho-, para- directing group for electrophilic aromatic substitution reactions. This directive influence can be explained by the following resonating structures of aniline.

Ring Substitution in Aromatic Amines

Some important ring substitution reactions of aromatic amines are halogenation, nitration and Sulphonation.

Halogenation

Aniline on treatment with an aqueous solution of bromine gives 2,4, 6 - tribromo aniline.

Amines: Halogenation

Nitration

Nitration of aniline is carried out on the acetylated amine (acetanilide) rather than on the free amine itself. There are two reasons for this.

  • The free amine is very susceptible to oxidation and thus much of it is lost in the form of a black-sticky material which is formed as result of its oxidation.
  • The free amine is very reactive but acetyl the group protects it and reduces its reactivity.

The nitration of aniline with the protection of the amino group is shown below:

Amines: Nitration

Sulphonation

Sulphonation is carried out in the presence of sulphuric acid. The amino group in aniline is a basic group. Therefore, an acid-base reaction takes place to form anilinism hydrogen sulphate salt. This salt undergoes rearrangement at a high temperature to give sulphonic acid.

Amines: Sulphonation

Diazonium Salts

The reactions of diazonium salts are very important synthetically because the diazonium group can be replaced by a variety of other groups such as .

These reactions are given below:

The Sandmeyer Reaction

In this reaction, the arene diazonium salts are reacted with cuprous bromide, cuprous chloride and cuprous cyanide in the presence of , and , respectively.

The Sandmeyer Reaction

Replacement of Diazonium Group by – I Group

In this reaction, the diazonium salt is treated with potassium iodide to give the product in which diazonium group has been replaced by – I group.

Replacement of Diazonium Group by -I

Replacement of Diazonium Group by – F Group

The diazonium salt is first treated with fluoroboric acid and the diazonium fluoroborate precipitated is isolated and dried. It is then heated until it starts decomposing to give the aryl fluoride product.

Replacement of Diazonium Group by -F

Replacement of Diazonium Group by – OH Group

If cuprous oxide is added to a dilute solution of the diazonium salt containing a large excess of cupric nitrate, then the diazonium group is replaced by a hydroxyl group.

Replacement of Diazonium Group by -OH

Replacement of Diazonium Group by a Hydrogen Atom

The reaction of diazonium salts with hypo phosphorous acid replaces the diazonium group by a hydrogen atom.

Replacement of Diazonium Group by a Hydrogen Atom

Coupling Reactions of Arene Diazonium Salts

Arene diazonium salts react with phenols and tertiary aryl amines to give azo compounds which are known azo dyes. This reaction is called diazo coupling reaction.

Coupling Reactions of Arene Diazonium Salts

Developed by: