Use Friedel–Crafts alkylation
Use chloromethane and aluminium chloride with heat to attach a methyl group to benzene.
A Level; Cambridge International Chemistry 9701, 2028–2030 syllabus, Topic 30. Follow the listed reagents, catalysts, temperatures and reaction scope for benzene and methylbenzene. Directing effects are limited to –NH₂, –OH, –R, –NO₂, –COOH and –COR. Written practice is self-checked
Before you begin
- Use the Topic 29 model of benzene as a planar aromatic ring with a delocalised π system, and recognise electrophiles, nucleophiles and organic functional groups.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which product is formed by Friedel–Crafts alkylation of benzene with CH₃Cl?
What you will learn
- Recall CH₃Cl, AlCl₃ and heat as the specified conditions
- Predict methylbenzene from benzene alkylation
- Recognise electrophilic substitution as the reaction family
Attach an alkyl group to the ring
Friedel–Crafts alkylation of benzene uses CH₃Cl and AlCl₃ with heat. The methyl group replaces a hydrogen on the aromatic ring, producing methylbenzene.
The aromatic ring is the site of reaction. Do not confuse the product with chloromethylbenzene: that compound has chlorine on the side chain and is made by side-chain halogenation under light.
Track the atoms and scope
The simplified overall equation is C₆H₆ + CH₃Cl → C₆H₅CH₃ + HCl, with AlCl₃ and heat. Chlorine leaves the alkylating reagent and combines with the displaced ring hydrogen.
This is the syllabus example using CH₃Cl. Do not assume all alkylation substrates or catalysts are required from this outcome alone.
Pause and explain
What does AlCl₃ do in the specified Friedel–Crafts example?
Worked example
Predict the product when benzene reacts with CH₃Cl and AlCl₃ on heating.
Show the worked solution
- CH₃Cl supplies the methyl group.
- The methyl group replaces one ring hydrogen.
- The product is methylbenzene, with HCl as by-product.
Answer Methylbenzene forms: C₆H₆ + CH₃Cl → C₆H₅CH₃ + HCl, using AlCl₃ and heat.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Complete the product side: C₆H₆ + CH₃Cl → ?
Give me a hint
Substitute one ring hydrogen with CH₃ and account for Cl.
Compare my reasoning
- Attach CH₃ to the ring.
- The ring loses one H.
- H and Cl form HCl.
C₆H₅CH₃ + HCl.
Look for these in your work
- Methylbenzene formed
- Substitution counted
- By-product balanced
State the complete syllabus conditions for this methylation of benzene.
Give me a hint
Include reagent, catalyst and heating.
Compare my reasoning
- Use CH₃Cl.
- Use AlCl₃ as catalyst.
- Heat the mixture.
CH₃Cl, AlCl₃ catalyst and heat.
Look for these in your work
- Reagent named
- Catalyst named
- Condition named
Explain why CH₃Cl/AlCl₃ gives methylbenzene rather than chloromethylbenzene.
Give me a hint
Locate which atom group the reagent transfers to the ring.
Compare my reasoning
- The reagent acts as an alkylating reagent.
- A methyl group replaces a ring H.
- The chlorine is not retained on the side chain product.
It transfers CH₃ to the aromatic ring, replacing ring H; the product is methylbenzene, while Cl leaves as HCl.
Look for these in your work
- Transferred group identified
- Substitution site identified
- Product distinction explained
Common mistakes
- Putting chlorine on the methyl side chain
- Leaving out AlCl₃
- Forgetting heat
- Calling the reaction addition across the aromatic ring
What can you explain now?
Which product is formed by Friedel–Crafts alkylation of benzene with CH₃Cl?
Compare with the explanation
Methylbenzene
The methyl group substitutes for a ring hydrogen.
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Make it stick
How do the reagent, catalyst and product identify Friedel–Crafts alkylation?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.