Amines are derivatives of ammonia with replacement of hydrogen atoms with alkyl or aryl groups.
Amines exhibit hydrogen bonding which influence their physical properties.
Nomenclature of some Alkylamines and Arylamines:
Preparation of Amines
(i) By Reduction of nitro compounds
(iii) 
(ii) By Ammonolysis of alkyl halides
(iii) By Reduction of nitriles
(iv) By Reduction of amides
(v) By Gabriel phthalimide synthesis
(vi) By Hoffmann bromamide degradation reaction
(vii) By Alcohols reaction with Ammonia
(viii) By Iodides reaction with Ammonia
Chemical Properties of Amines
Basic Strength of Amines:
Amines are basic in nature because they can undergo protonation due to the presence of lone pair of electrons on nitrogen atom of —NH2 group.
The order of basicity of amines in the gaseous phase follows the expected order:
Tertiary amine > Secondary amine > Primary amine > NH3
The order of basic strength in case of methyl substituted amines and ethyl substituted amines in aqueous solution is as follows:
(C2H5)2NH > (C2H5)3N > C2H5NH2 > NH3
(CH3)2NH > CH3NH2 > (CH3)3N > NH3
Reactions of Amines
(i) Alkylation:
(It is same as preparation method “by Ammonolysis of alkyl halides”)
(ii) Acylation:
Benzoylation:
(iii) Carbylamine reaction:
(iv) Reaction with nitrous acid
(a) Primary aliphatic amines
(b) Aromatic amines
(v) Reaction with arylsulphonyl chloride
Hinsberg’s reagent, Benzenesulphonyl chloride (C6H5SO2Cl), reacts with primary and secondary amines.
Tertiary amines do not react with benzenesulphonyl chloride.
(vi) Electrophilic substitution reactions for aniline
(a) Bromination:
For p-monosubstituted aniline derivative, the -NH2 group is converted to more sterically hindered amide group by acetylation with acetic anhydride which prevents substitution at o-position.
(b) Nitration:
Direct nitration of Aniline gives primarily a mixture of p- and m- derivatives.
The p-nitro derivative can be obtained as the major product by protecting the –NH2 group by acetylation reaction with acetic anhydride,
(c) Sulphonation:
(vii) Diazotisation:
(vii) Coupling reactions:
Few reactions of ethyl amine
Identification of primary, secondary and tertiary amines:
|
|
Test |
Primary amine |
Secondary amine |
Tertiary amine |
|
1. |
Action with HNO2 |
Alcohol is formed and N2 is evolved. |
Nitroso-amine is formed which with phenol and conc. H2SO4 gives green colour (Liebermann Test). |
In cold, nitrite salt is formed which on heating gives nitroso-amine. This nitroso-amine gives Liebermann test. |
|
2. |
Action with CHCl3 and alc. KOH. |
Isocyanide with offensive odour is formed. (Carbylamine reaction) |
No reaction. |
No reaction. |
|
3. |
Action with CS2 and HgCl2 (Mustard oil reaction). |
Forms N-substituted isothiocyanate which has smell like that of mustard oil. |
No reaction. |
No reaction. |
|
4. |
Action with acetyl chloride. |
Acetyl derivative is formed. |
Acetyl derivative is formed. |
No reaction. |
|
5. |
Action with CH3I. |
Three molecules of CH3I on reaction with primary amine give quaternary salt. |
Two molecules of CH3I on reaction with secondary amine give quaternary salt. |
Only one molecule of CH3I reacts with tertiary amine and formation of quaternary salt takes place. |
|
6. |
Action with Hinsberg reagent (C6H5SO2Cl). |
Mono alkyl sulphonamide derivative is formed which is soluble in KOH. |
Dialkyl sulphonamide derivative is formed which is insoluble in KOH. |
No reaction. |