International A LevelChemistryOxford AQARevision NotesOrganic ChemistryAlcoholsElimination Reactions of Alcohols

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

Revision Note

Philippa Platt

Written by: Philippa Platt

Reviewed by: Stewart Hird

Elimination Reactions of Alcohols

  • Alcohols can also undergo dehydration to form alkenes

  • Alcohol vapour is passed over a hot (600 degreeC) 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

Dehydration of Alcohols
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

Dehydration of propan-1-ol mechanism

A diagram to show the mechanism for the dehydration of propan-1-ol
Water is lost when propan-1-ol is dehydrated to form propene

  • 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

A diagram to show the formation of isomeric alkenes from alcohols
Isomeric alkenes can be formed during the dehydration of specific alcohols

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    Philippa Platt

    Author: Philippa Platt

    Expertise: Chemistry

    Philippa has worked as a GCSE and A level chemistry teacher and tutor for over thirteen years. She studied chemistry and sport science at Loughborough University graduating in 2007 having also completed her PGCE in science. Throughout her time as a teacher she was incharge of a boarding house for five years and coached many teams in a variety of sports. When not producing resources with the chemistry team, Philippa enjoys being active outside with her young family and is a very keen gardener

    Stewart Hird

    Author: Stewart Hird

    Expertise: Chemistry Lead

    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 Topic Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.