Elimination Reactions of Alcohols (Oxford AQA International A Level Chemistry): Revision Note

Elimination Reactions of Alcohols

• Alcohols can also undergo dehydration to form alkenes

• Alcohol vapour is passed over a hot (600 C) catalyst of aluminium oxide (Al₂O₃) powder or pieces of porous pot

  • Excess hot, concentrated sulfuric acid or phosphoric acid is used as a catalyst

• Phosphoric(V) acid is used an alternative dehydrating agent

Dehydration of an alcohol

• This is an example of an elimination reaction

  • Elimination reactions involve a small molecule being formed as a by-product

  • The water molecule is formed from the -OH group of the alcohol and the H⁺ from the acid catalyst

  • The neighbouring hydrogen is then lost as a H⁺ ion, which regenerates the acid catalyst

Dehydration of propan-1-ol mechanism

• Alkenes produced by this method can be used to produce addition polymers without using monomers derived from crude oil

Isomeric alkenes

• Dehydration of longer chain alcohols can produce a mixture of alkenes which can exhibit E / Z isomerism