3.5.5 Elimination Reactions of Alcohols

Elimination Reaction of Alcohols

• Alcohols can also undergo dehydration to form alkenes
  • This is an example of an elimination reaction
  • Elimination reactions involve a small molecule leaving the parent molecule as a byproduct
  • In this case, the small molecule is a water molecule
  • The water molecule is formed from the -OH group and a hydrogen atom from the adjacent carbon atom

• Alcohol vapour is passed over a hot catalyst of aluminium oxide (Al₂O₃) powder or pieces of porous pot
  • Excess hot, concentrated sulfuric acid or phosphoric acid is used as a catalyst

Dehydration of ethanol using aluminium oxide as a catalyst forms ethene gas, which can be collected over water

• The reaction and mechanism for the dehydration of propan-1-ol is shown below

Dehydration of propan-1-ol mechanism