Amines — Class 12 Chemistry

Amines are derivatives of ammonia in which one, two or three hydrogen atoms are replaced by alkyl or aryl groups, giving primary, secondary and tertiary amines respectively. The nitrogen is hybridised and pyramidal with an unshared electron pair, which makes amines behave as Lewis bases and nucleophiles. They are named by common (alkylamine) and IUPAC (alkanamine) systems. Amines are prepared by reduction of nitro compounds, nitriles and amides, by ammonolysis of alkyl halides, by the Gabriel phthalimide synthesis (for primary amines) and by the Hoffmann bromamide degradation. Primary and secondary amines form intermolecular hydrogen bonds, raising their boiling points. The basic strength of amines depends on the interplay of the inductive effect, solvation and steric hindrance; aliphatic amines are stronger bases than ammonia while aromatic amines like aniline are weaker because the nitrogen lone pair is delocalised into the ring. Amines undergo alkylation, acylation, the carbylamine test (for primary amines), reaction with nitrous acid and electrophilic substitution. Aromatic primary amines react with nitrous acid at low temperature to give diazonium salts, which are valuable intermediates: their diazo group can be replaced by halides, cyanide, hydroxyl and other groups, or retained in coupling reactions that yield azo dyes.