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AQA Content

Outline the mechanism for the elimination of water from alcohols.

Specification Notes

Alkenes can be formed from alcohols by acid-catalysed elimination reactions.
Alkenes produced by this method can be used to produce addition polymers without using monomers derived from crude oil.


Dehydration: The formation of alkenes by the removal of water

An alcohol is converted into an alkene by dehydration in the presence of an acid and heat.
The reaction is catalysed by an acid (sulfuric or phosphoric) at high temperature (160°C).

For ethanol:
1. The alcohol is protonated
2. The carbon-oxygen bond undergoes heterolysis
3. The water leaves forming a carbocation
4. The carbocation loses hydrogen to the conjugate base of the acid to form an alkene and the reformed acid


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