Elimination Reactions of Alcohols (AQA A Level Chemistry)

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Elimination Reactions

  • 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

Hydroxy Compounds Dehydration of Alcohols, downloadable AS & A Level Chemistry revision notes

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

  • 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

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

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

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Stewart

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Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Exam Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.