• Phenols can undergo many types of reactions as both the?electron-rich benzene ring?and the?polar -OH?group can participate in chemical reactions
• Some of the reactions of phenols include:
  • With bases
  • With reactive metals
  • With diazonium salts
  • Nitration
  • Bromination

Reactions of the -OH group in phenols

• The -OH group in phenols has a?slightly acidic character
• It can therefore act as an?acid?and take part in?acid-base reactions

Reaction with bases

• Phenols are?only slightly soluble?in water due to the large non-polar benzene ring
• However, they do dissolve in alkaline solutions and undergo?acid-base?reactions with?bases?to form a?soluble salt?and?water

Phenols are weak acids and undergo acid-base reactions in alkaline solutions

Reaction with reactive metals

• Molten phenols?react?vigorously?with reactive metals such as?sodium?(Na)
• This is also an?acid-base?reaction
• Now, a soluble salt is formed and?hydrogen gas?is given off

Molten phenols react vigorously with reactive metals to form a soluble salt and hydrogen gas

Reaction with diazonium ions

• Diazonium ions?are very reactive compounds containing an -N₂⁺?group
• When phenols are?dissolved?in sodium hydroxide (NaOH), a solution of?sodium phenoxide?is obtained
• This solution is cooled in?ice?and?cold diazonium ion?is added to the sodium phenoxide
• After the reaction has occurred, a?yellow-orange?solution or precipitate of an?azo compound?is formed
• These are compounds in which?two benzene?rings are linked by a?nitrogen bridge

Azo compounds are formed from the reaction of phenols with diazonium ions

Reactions of the aromatic ring in phenols

• Phenols react more?readily?with?electrophiles?compared to benzene
• This is because one of the lone pairs of electrons on the oxygen atom in -OH overlaps with the π bonding system
• This increases the?electron density?of the benzene ring making it more?susceptible?to?electrophilic attack
• The -OH group in phenols is?activating?and?directs?incoming electrophiles to the?2, 4, and 6 positions

Nitration

• Phenols can undergo?electrophilic substitution?reactions when reacted with?dilute nitric acid?(HNO₃) at?room temperature?to give a mixture of?2-nitrophenol?and?4-nitrophenol
  • When?concentrated HNO₃?is used, the product will be 2,4,6-trinitrophenol instead
• A hydrogen atom in the benzene ring is?substituted?by a nitro (-NO₂) group
• This is also known as the?nitration?of phenol

Phenols undergo nitration when reacted with dilute HNO₃?at room temperature

Bromination

• Phenols also undergo?electrophilic substitution?reactions when reacted with?bromine water?at?room temperature
• Phenol?decolourises?the?orange?bromine solution to form a?white precipitate?of 2,4,6-tribromophenol
• This is also known as the?bromination?of phenol

Phenols undergo bromination when reacted with bromine water at room temperature