Brominate phenol with aqueous bromine
Use aqueous Br₂ to replace ring hydrogens at positions 2, 4 and 6, forming 2,4,6-tribromophenol.
A Level; Cambridge International Chemistry 9701, 2028–2030 syllabus, Topic 32. Distinguish phenol (–OH directly on an aromatic ring) from an alcohol (–OH on an aliphatic carbon). Use the specified reagents, temperatures and products; phenol reactions are limited to those listed in the syllabus. Written practice is self-checked
Before you begin
- Recognise alcohols and phenols, aromatic substitution, acids and bases, and diazonium ions from the preceding organic topics.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is the product of phenol with aqueous Br₂?
What you will learn
- Recall bromine water as the phenol bromination reagent
- Predict 2,4,6-tribromophenol
- Contrast phenol conditions with catalytic benzene bromination
Phenol's activated ring undergoes multiple substitution
Phenol reacts with aqueous Br₂ to form 2,4,6-tribromophenol. The –OH group directs bromination to the two ortho positions (2 and 6) and the para position (4).
Each Br replaces one ring hydrogen. The –OH remains attached directly to the ring, and the product contains three bromine atoms at the stated positions.
Aqueous bromine distinguishes the phenol reaction
For phenol, the syllabus specifies Br₂(aq) and 2,4,6-tribromophenol. Benzene ring bromination instead uses Br₂ with AlBr₃ catalyst. Phenol's –OH group activates the ring, so an added Lewis-acid catalyst is not the specified phenol condition.
Do not predict monobromination of phenol when asked for the syllabus product. Check all positions directed by –OH that are available on the ring.
Pause and explain
Which positions are brominated in the named product?
Worked example
What product forms when phenol reacts with aqueous bromine?
Show the worked solution
- Use Br₂(aq).
- –OH directs to positions 2, 4 and 6.
- Replace those three ring hydrogens with Br.
Answer 2,4,6-tribromophenol forms.
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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.
Write the name and reagent for the syllabus bromination of phenol.
Give me a hint
Give aqueous bromine and all three positions.
Compare my reasoning
- Use Br₂(aq).
- –OH directs to 2, 4 and 6.
- Name the product with three bromines.
Aqueous Br₂ forms 2,4,6-tribromophenol.
Look for these in your work
- Reagent correct
- Positions correct
- Product named
Why does phenol give tribromination with aqueous Br₂ while benzene bromination uses a catalyst?
Give me a hint
Compare electron density in the two rings.
Compare my reasoning
- –OH donates electron density into phenol's aromatic ring.
- This activates the ring toward electrophilic substitution.
- Benzene lacks that activating –OH group and uses AlBr₃.
Phenol's –OH activates the ring, so aqueous bromine can produce substitution at 2, 4 and 6; benzene uses AlBr₃ to activate Br₂.
Look for these in your work
- –OH donation stated
- Activation linked
- Benzene contrast made
A proposed phenol product has Br at position 3 only. Explain why it conflicts with the syllabus reaction.
Give me a hint
Use the directing effect and product count.
Compare my reasoning
- Phenolic –OH directs to positions 2, 4 and 6.
- Aqueous bromine substitutes at those three sites.
- The named product is tribrominated, not a single meta product.
The specified reaction gives 2,4,6-tribromophenol; –OH directs to ortho/para sites, not position 3 alone.
Look for these in your work
- Director used
- All three positions named
- Product count corrected
Common mistakes
- Using AlBr₃ as the specified phenol condition
- Naming only bromophenol
- Putting bromine at meta position 3
- Forgetting there are three bromine substituents
What can you explain now?
What is the product of phenol with aqueous Br₂?
Compare with the explanation
2,4,6-tribromophenol
Phenol's –OH activates and directs three ring substitutions.
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Make it stick
How do the brominating reagent and –OH directing effect identify the phenol product?
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