• Compared to?benzene, phenol?reacts?more readily?with?electrophiles
• This is because?one of the lone pairs?of electrons on the oxygen atom in phenol?overlaps?with the π bonding system of the benzene ring
• As a result, there is now an?increased electron density?in the ring
• The?electron-donating?-OH group in phenol, therefore,?activates?the benzene ring and?directs?incoming?electrophiles?to the 2, 4, and 6 positions
• The increased reactivity of phenol means that different reagents and conditions are used for?electrophilic substitution?reactions of phenols compared to benzene

Nitration

• Nitration is an example of an?electrophilic substitution?reaction
• The nitration of?benzene?requires a mixture of?concentrated?nitric acid (HNO₂) and sulfuric acid (H₂SO₄)?refluxed?with benzene between?25?^oC and 60?^oC
• Since phenol is more reactive, nitration can occur under?milder?conditions?by reacting it with?dilute?nitric acid at?room?temperature
  • If?concentrated?nitric acid is used, 2,4,6-trinitrophenol is formed

Bromination

• Bromination is another example of an?electrophilic substitution?reaction
• Benzene will undergo bromination?only?when reacted with?pure bromine?(not a solution)?and?in the presence of an anhydrous aluminium bromide (AlBr₃)?catalyst?at?room temperature
• Phenol on the other hand readily reacts with?bromine water?in the?absence?of a catalyst

Reagents & conditions for nitration and bromination of phenol & benzene table

• Phenols consist of a hydroxyl (-OH) group attached to a benzene ring
• The?oxygen?atom in this hydroxyl group?donates?electron density into the ring
• One of the lone pairs of the oxygen atom?overlaps?with the π system of the benzene ring and become?delocalised?causing an?increased?electron density in the aromatic ring
• Due to the increased electron density, the benzene ring is now more likely to undergo?electrophilic attack?and becomes?activated
• The incoming electrophiles are?directed?by the hydroxyl group of the phenol to the 2, 4, and 6 positions
• An example is the bromination of phenol
  • The bromine acts as an electrophile and?substitutes?a hydrogen atom in the benzene ring
  • The substitution of the hydrogen atom can occur on the 2, 4, or 6 positions

The hydroxyl group in phenol directs bromination in the 2, 4, and 6 positions