Elimination Reactions
Chemistry: AQA A Level, topic 5.3.2
Elimination Reactions
When a halogenoalkane is reacted with hydroxide ions, you can get an alcohol via substitution. But there is another reaction that can happen - elimination - which produces an alkene.
Elimination mechanism
- The image shows the mechanism for the elimination reaction of a halogenoalkane to form an alkene.
- All the steps happen at the same time - it is a one step process.
Elimination
- Hydroxide ions are nucleophiles, but they are also bases.
- They can take a proton off of a halogenoalkane if the next-door carbons have protons on them.
- This results in formation of an alkene.
Which reaction?
- Hydroxide reacting with a halogenoalkane can either eliminate to produce an alkene or substitute to produce an alcohol.
- Both are very possible.
- To promote the elimination reaction, we can:
- Use ethanol as the solvent rather than water.
- Heat the reaction under reflux conditions.
- Reflux involves using a reflux condenser to condense gases back into the reaction flask.
Test yourself on Elimination Reactions
Where does the hydroxide ion attack the halogenoalkane in the elimination mechanism?