phenol

• phenol is an organic compound containing a hydroxyl group (-OH) directly bonded to an aromatic ring
• simplest member of phenols is C6H5OH
• phenol is less soluble in water than alcohols due to the presence of the non-polar benzene ring
• When dissolved in water, phenol partially dissociates forming the phenoxide ion and a proton
• Phenol's ability to partially dissociate to produce protons, means it is classified as a weak acid.
• Phenol is more acidic than alcohols but less acidic than carboxylic acids.
• phenol undergoes electrophilic substitution reactions
• phenol reacts with sodium hydroxide to form the salt (sodium phenoxide) and water in a neutralisation reaction
• The reactions of phenol take place under milder conditions and more readily than the reactions of benzene.
• Bromination of phenol

  • Phenol reacts with an aqueous solution of bromine (bromine water)
  • Forms white precipitate of 2,4,6-tribromophenol
  • Reaction decolourises the bromine water (orange to colourless)
  • With phenol, a halogen carrier catalyst is not required and the reaction is carried out at room temperature
• Nitration of phenol

  • Phenol reacts readily with dilute nitric acid at room temperature
  • A mixture of 2-nitrophenol and 4-nitrophenol is formed
• Bromine and nitric acid react more readily with phenol than they do with benzene
• Phenol is nitrated with dilute nitric acid rather than needing concentrated nitric and sulfuric acids as with benzene
• • The increased reactivity is caused by a lone pair of electrons from the oxygen p-orbital of the -OH group being donated into the pi system of phenol
  • The electron density of the benzene ring in phenol is increased which attracts electrophiles more strongly than with benzene therefore more susceptible to attack
• For bromine, the electron density in the phenol ring structure is sufficient to polarise bromine molecules and so no halogen carrier catalyst is required
• • Lone pair of electrons on the oxygen atom of the -OH group in phenol is delocalised into the ring
  • This increases the electron density in the ring in phenol
  • Phenol is more able to polarise bromine than benzene
  • In benzene all the electrons are delocalised throughout the structure and benzene is not able to polarise bromine
• reactions of phenol

  • nitration
  • bromination
  • neutralisation
• because phenol has hydrogen bonds it is soluble in water and a solid @ RTP
• phenol is a weak acid
• C6H5O- is a phenoxide ion
• -OH group directs substitution to occur at positions 2, 4, 6

  • -NH2 has the same effect
• • oxygen lone pair p-orbital can overlap with pi electron cloud of benzene ring i.e. delocalise
  • increases electron density of pi electron cloud
• -NO2 group directs electrophiles to position 3, 5 on a benzene ring

  • withdraws electrons from ring
  • lowers electron density at 2, 4, 6