Aromatic Amine - Formation
- Phenylamine is an organic compound consisting of a benzene ring and an amine (NH2) functional group
- Phenylamine is sometimes known as aminobenzene or 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
- The combination of tin and hydrochloric acid acts as a reducing agent
- The reaction mixture is heated under reflux in a boiling water bath
- The nitrobenzene has been reduced, in the presence of acid, by gaining electrons from tin
- The tin is oxidised to a mixture of tin(II), Sn2+, and tin(IV), Sn4+
- The reduction reaction of nitrobenzene does not form phenylamine directly
- Due to the acidic conditions, the reduction reaction forms the phenylammonium ion, C6H5NH3+
Stage 2 - Formation of phenylamine
- Excess sodium hydroxide solution, NaOH (aq), is added to the phenylammonium ions, C6H5NH3+
- This causes them to deprotonate and form the desired phenylamine product
- A mixture of tin compounds, including tin(II) hydroxide and tin(IV) hydroxide is also formed from reactions between the sodium hydroxide solution and the tin ions in stage 1
Stage 3 - Purification of phenylamine
- The crude phenylamine product undergoes steam distillation to produce a cloudy distillate
- Sodium chloride is added to the distillate before the mixture is added to a separating funnel
- Ether is added to the separating funnel resulting in an aqueous layer at the bottom and an organic layer, containing the phenylamine, on the top
- The sodium chloride aids separation by increasing the polarity of the aqueous layer causing the phenylamine to "salt out" into the organic layer
- The aqueous layer is discarded and the organic layer is distilled
- The ether will boil off easily and is discarded
- The phenylamine fraction that boils off at 180 - 185 oC is retained and can have its boiling point tested to check the purity of the product