Elimination Reactions
Chemistry: AQA A Level, topic 5.5.4
Elimination Reactions of Alcohols
So far we’ve seen how we can oxidise alcohols to get aldehydes, ketones and carboxylic acids. We can also get alkenes from alcohols.
,w_800.png)
Dehydration
- Dehydration reactions are just elimination reactions where water is eliminated.
- The equation in the image shows how we can get an alkene from an alcohol via a dehydration reaction under acidic conditions.
Mechanism of ethanol dehydration
- Note the action of the acid catalyst.
- Note how the positively charged alkane collapses to form the alkene in the final step.
The action of the acid catalyst
- The reaction needs an acid catalyst.
- This catalyst protonates the -OH group to make it easier to eliminate the group.
- The acid catalyst is reformed when the H+ is lost as the alkene forms in the last step.
Why do this?
- It turns out that we’re actually pretty good at producing alcohols without using crude oil.
- This means we can get alkenes without cracking the alkanes from crude oil.
- This means we can polymerise the alkenes and make polymers without using crude oil.
Test yourself on Elimination Reactions
What happens to the alcohol in the first step of the mechanism?
What is a good use of the alkenes produced from this reaction?