UNIT 13 AMINES
- Amines can be considered as derivatives of ammonia obtained by replacement of hydrogen atoms with alkyl or aryl groups. Replacement of one hydrogen atom of ammonia gives rise to a structure of the type R-NH2, known as the primary amine. Secondary amines are characterized by the structure R-NH or R-NHR’. Tertiary amines have the structure R3N, RNR’R” or R2NR’.
- Secondary and tertiary amines are known as simple amines if the alkyl or aryl groups are the same and mixed amines if the groups are different.
- Like ammonia, all three types of amines have one unshared electron pair on nitrogen atom due to which they behave as Lewis bases.
- Amines are usually formed from nitro compounds, halides, amides, imides, etc. They exhibit hydrogen bonding which influences their physical properties.
- In alkylamines, a combination of electron releasing, steric and H-bonding factors influence the stability of the substituted ammonium cations in protic polar solvents and thus affect the basic nature of amines.
- Alkyl amines are stronger bases than ammonia. In aromatic amines, electron releasing and withdrawing groups, respectively increase and decrease their basic character.
- Reactions of amines are governed by availability of the unshared pair of electrons on nitrogen. Influence of the number of hydrogen atoms at nitrogen atom on the type of reactions and nature of products is responsible for identification and distinction between primary, secondary and tertiary amines.
- Aryldiazonium salts, usually obtained from arylamines, undergo replacement of the diazonium group with a variety of nucleophiles to provide advantageous methods for producing aryl halides, cyanides, phenols and arenes by reductive removal of the diazo group.
- Coupling reaction of arlydiazonium salts with phenols or arylamines give rise to the formation of azo dyes.