Amines Chapter Notes Class 12th

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Amines Chapter Notes Class 12th

What is  Amines?

Amines can be considered as derivatives of ammonia obtained by the replacement of hydrogen atoms with alkyl or aryl groups.

Preparation of Amines

Amines Chapter Notes Class 12th
Preparation of Amines

Classification of Amines

On the basis of number of aryl group attached to N amines are classified as primary 1° (R—NH2), secondary or 2° (R2NH) and Tertiary or 3° (R3N).

Physical Properties of Amines-

CH3NH2 is a gas and C2H5NH2 is a vaporisable liquid. Higher amines have odour like fish. Due to tendency to form hydrogen bonds lower molecular weight bearing aliphatic amine are soluble in water. Amine is more polar than alkane but less polar than alcohol.

Basic character of Amines

Aliphatic Amines-

1. All aliphatic amines are more basic than ammonia.

2. In aqueous solutions, the basicity of methylamines follows the order but for ethylamines and all other higher amines, basicity follows the order

3. In gaseous phase, the order of basicity is 3 > 2 > 1 > amine.

4. Greater the value of Kb or smaller the value of pKb, stronger is the base.

Aromatic Amines-

1. All aromatic amines are weaker bases than ammonia.

2. Electron donating groups such as —NH3, —OCH3, —NH2 increases the basicity while electron withdrawing substitutes such as —NH2, —CN, halogens decrease the basicity of amines. The effect of these substitutes is more pronounced at p-than at m-positions.

3. o-substituted anilines are weaker bases than aniline regardless of the nature of the substituent whether electron-donating or electron-withdrawing. This is called ortho effect and is due to steric hindrance.

Halogenation

On reaction of aniline with bromine water 2, 4, 6-tribromoaniline yellow coloured precipitate is obtained. Because NH2 is very reactive group.

Nitration

Nitration of aniline in presence of (CH3CO)2O, we get p-nitroaniline (as major product) mixture.

Sulphonation

Sulphonation of aniline is done by fuming H2SO4 at 180° C to get p-amino benzene sulphonic acid, which is known as sulphonic acid.

Test of Aniline

Azo dye test

Aniline when dissolved in dil. HCl. On mixing β-naphthol to this mixture a orange-red coloured dye is formed.

Reaction with bromine water

On reaction of Aniline with bromine water, a yellow precipitate of 2,4,6-tribromoaniline is obtained.

Diazonium Salt

Those aromatic primary amine salt which have general formula as ArN2X- are known as diazonium salt.

Amines Chapter Notes Class 12th

Amines Chapter Notes Class 12th

 

 

 

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