What are Amines?
Amines are an important class of organic compounds derived by replacing one or more hydrogen atoms of ammonia molecules with an alkyl or aryl group(s). In nature, they occur among proteins, vitamins, alkaloids and hormones. These are classified on the basis of the presence of replaceable hydrogen atoms. When one of the three hydrogen atoms is replaced by an alkyl or aryl group, the amine is primary. If two hydrogens of ammonia are replaced, the secondary amine is formed. The tertiary amine is formed when all hydrogens of ammonia are replaced by an alkyl or aryl group. Cyclic amines are secondary or tertiary amines forming a cyclic structure. In amines, nitrogen undergoes sp3 hybridisation and the shape is pyramidal due to the presence of lone pair of electrons on nitrogen.
Chemical properties of amines
The difference in electronegativity of hydrogen and nitrogen atom and the presence of a lone pair of electrons on the nitrogen atom makes the amine reactive. The number of hydrogen atoms attached to nitrogen determines the course of action for the amine. This is the reason why primary, secondary and tertiary amines undergo different reactions. Amines behave like nucleophiles due to the presence of unshared electrons. Following are the reactions of amines:
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Basicity of amines:
Being basic in nature, they react with acids to form salts.
Amine salts on reaction with bases like NaOH regenerate the parent amine.
Amine salts are water-soluble but insoluble in organic solvents such as alcohol and ether. This reaction is the basis for the separation of amines from non-basic organic compounds which are insoluble in water. The reaction between amines and mineral acids forms ammonium salts which clearly depicts the basic nature of amines.
Basicity of amines depends on the groups attached to them, solvation effect and steric hindrance
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Acylation:
Aliphatic and aromatic, primary and secondary amines react with acid chlorides, anhydrides and esters by the process of nucleophilic substitution reaction. This is known as acylation. Amides are the end products of acylation. The reactions are carried out in the presence of a stronger base as compared to amines. For example Pyridine. To remove the HCl formed during the reaction, equilibrium moves to the right-hand side.
This article covers the basic details of the acylation reaction of amines. For any further queries on topics like classification and nomenclature of amines install, BYJU’S – The Learning App.
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