Preparation of Phenylamine
- Phenylamine is an organic compound consisting of a benzene ring and an amine (NH2) functional group
- It can be produced in a three-step synthesis reaction followed by the separation of phenylamine from the reaction mixture
- Step 1- Benzene undergoes nitration with concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4) at 25 to 60 oC to form nitrobenzene
- Step 2 – Nitrobenzene is reduced with hot tin (Sn) and concentrated hydrochloric acid (HCl) under reflux to form an acidic mixture that contains the organic product C6H5N+H3
- Step 3 – Sodium hydroxide (NaOH) is added to the acidic reaction mixture to form phenylamine
- Step 4 – The phenylamine is separated from the reaction mixture by steam distillation
Reactions of Phenylamine
- Both the benzene ring as well as the -NH2 group in phenylamine can take part in chemical reactions
- These reactions include
- The bromination of phenylamine
- Formation of a diazonium salt
Bromination of phenylamine
- Phenylamines react in electrophilic substitution reactions in a similar way as phenols
- The lone pair of electrons on the nitrogen atom in phenylamines donate electron density into the benzene ring
- In phenols, the oxygen atom donates its lone pair of electrons instead
- The delocalisation of the electrons causes an increased electron density in the benzene ring
- The benzene ring, therefore, becomes activated and becomes more readily attacked by electrophiles
- The incoming electrophiles are directed to the 2,4 and 6 positions
- Phenylamines, therefore, react under milder conditions with aqueous bromine at room temperature to form 2,4,6-tribromophenylamine
Formation of diazonium salt
- Diazonium compounds are very reactive compounds containing an -N2+ group
- The amine (-NH2) group of phenylamines will react with nitric(III) acid (HNO3) at a temperature below 10 °C to form diazonium salts
- Since nitric(III) acid is unstable, it has to be made in the test-tube by reacting sodium nitrate (NaNO2) and dilute acid (such as HCl)
- These diazonium salts are so unstable that they will upon further warming with water to form a phenol