chemistry of phenol

• a phenol is an aromatic benzene ring attached to a hydroxyl (-OH) group
• C6H5OH (phenol) + Na -> C6H5NaO (sodium phenoxide) + 1/2 H2

  C6H5OH (phenol) + NaOH -> C6H5NaO (sodium phenoxide) + H2O
• phenol solubility

  phenols are not particularly soluble. the phenyl is non-polar, whilst the OH is polar.

  but the phenyl is very large and dominating.

  sodium salts of phenols (sodium phenoxide) are very soluble, so the solid phenol dissolves on addition of NaOH
• phenol acidity

  weakly acidic as it only partially ionises in water

  C6H5OH -> (partial ionisation) C6H5O- (phenoxide ion) + H+
• benzene + Br2 (aq) -> (r.t) no reaction


  phenol + 3Br2 (aq) -> (r.t no catalyst) 2,4,6 - tribromophenol + 3HBr

  the electrophilic substitution in phenol is far more effective than in benzene.

  the reason is the concentration of electron in the ring has increased, as a consequence of -OH group
• in phenol the lone pair of electrons on the oxygen (p-orbital) is partially delocalised into the ring. the electron density increases and the Br2 is more polarised.
• phenol is less soluble in water than alcohols due to presence of the non-polar benzene ring
• how is phenol more reactive than benzene?

  this is due to the p-orbital electrons from the oxygen of the hydroxyl group adding to the delocalised electrons of the aromatic ring

  so the π-system of the aromatic ring becomes more nucleophilic

  the increase in electron density allows the aromatic ring in phenol to be more susceptible to electrophilic attack as it can induce a dipole in non polar molecules