CIE A Level Chemistry (9701) 2019-2021

Revision Notes

7.4.2 Reactions of Phenol

Reactions of Phenol

  • 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

 

Hydroxy Compounds - Acid-base Reaction of Phenols, downloadable AS & A Level Chemistry revision notes

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

 

Hydroxy Compounds - Reaction of Phenols with Sodium, downloadable AS & A Level Chemistry revision notes

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

Hydroxy Compounds - Reaction with Diazonium Ions, downloadable AS & A Level Chemistry revision notes

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

Hydroxy Compounds - Nitration, downloadable AS & A Level Chemistry revision notes

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

Hydroxy Compounds - Bromination, downloadable AS & A Level Chemistry revision notes

Phenols undergo bromination when reacted with bromine water at room temperature

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
Close

Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now
Already a member?
Go to Top