5.5.3 Aromatic Amines

• Phenylamine is an organic compound consisting of a benzene ring and an amine (NH₂) functional group
  • Phenylamine is sometimes known as aminobenzene and aniline
• Nitrobenzene, C₆H₅NO₂, can be reduced to phenylamine, C₆H₅NH₂, according to the following two-stage reaction:

The two-stage reduction reaction of nitrobenzene to phenylamine

Stage 1 - Reduction of nitrobenzene

• Nitrobenzene, C₆H₅NO₂, is reacted with tin, Sn, and concentrated hydrochloric acid, HCl
  • Tin and hydrochloric acid act as reducing agents
• The reaction mixture is heated under reflux in a boiling water bath
• The phenylammonium ions, C₆H₅NH₃⁺, are protonated due to the acidic conditions

Stage 2 - Formation of phenylamine

• • The phenylammonium ions, C₆H₅NH₃⁺, are deprotonated by the addition of excess sodium hydroxide solution, NaOH (aq)

• Azo (or diazonium) compounds are organic compounds that have an R₁-N=N-R₂ group
• They are often used as dyes and are formed in a coupling reaction between the diazonium ion and an alkaline solution of phenol

Azo compounds are characterized by the presence of an R₁-N=N-R₂ group

Coupling of benzenediazonium chloride with phenol in NaOH

• Azo compounds can be formed from the coupling reaction of a benzenediazonium chloride salt with alkaline phenol
• Making an azo dye is a multi-step process

Formation of Azo Compounds Table

Reaction mechanism of the formation of azo compounds

• The delocalised electrons in the π bonding systems of the two benzene rings are extended through the -N=N- which acts as a bridge between the two rings
• As a result of the delocalisation of electrons throughout the compound, azo compounds are very stable