Prepare phenylamine from benzene through nitrobenzene
Nitrate benzene to nitrobenzene, reduce with hot tin and concentrated HCl, then add aqueous NaOH to release phenylamine.
A Level; Cambridge International Chemistry 9701, 2028–2030 syllabus, Topic 34. Use the stated reagents, conditions and product scope. Written practice is self-checked This online lesson cannot demonstrate supervised laboratory skills.
Before you begin
- Recall nucleophilic substitution, reduction, acyl-chloride addition–elimination, acid–base equilibria and covalent bonding.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is the intermediate when benzene is converted to phenylamine by the syllabus route?
What you will learn
- Describe the nitration and reduction sequence
- Recall hot Sn/concentrated HCl and NaOH work-up
- Explain why alkali is added after acidic reduction
Make nitrobenzene, then reduce
First nitrate benzene to nitrobenzene using the nitration conditions studied in the arenes topic. Then heat nitrobenzene with tin and concentrated HCl to reduce –NO₂ to –NH₃⁺ in the acidic mixture.
Add aqueous NaOH after reduction to neutralise the acid and release free phenylamine, C₆H₅NH₂, from its protonated salt.
Keep the stages in order
The route is benzene → nitrobenzene → phenylamine. Hot Sn/concentrated HCl performs the reduction; NaOH is added afterwards as the work-up.
Do not add NaOH first or name nitrobenzene as the final product. The nitration step requires the standard concentrated acid mixture; the syllabus outcome focuses on the route and the specified reduction reagents.
Pause and explain
Why is aqueous NaOH added after hot Sn/concentrated HCl?
Worked example
Outline the preparation of phenylamine from benzene.
Show the worked solution
- Nitrate benzene to nitrobenzene.
- Reduce with hot Sn/concentrated HCl.
- Add aqueous NaOH to liberate phenylamine.
Answer Benzene → nitrobenzene by nitration → reduction with hot Sn/concentrated HCl → NaOH(aq) work-up → phenylamine.
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Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
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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.
Put these route steps in order: NaOH(aq), nitration of benzene, hot Sn/concentrated HCl.
Give me a hint
Nitration creates the nitro group that is reduced.
Compare my reasoning
- Make nitrobenzene by nitration.
- Reduce with hot Sn/concentrated HCl.
- Add NaOH(aq) to free phenylamine.
Nitration → hot Sn/concentrated HCl reduction → NaOH(aq) work-up.
Look for these in your work
- Intermediate formed
- Reduction second
- Alkali last
Explain why the product after reduction is treated with NaOH.
Give me a hint
The reduction takes place in concentrated acid.
Compare my reasoning
- The amino group is protonated in the acidic mixture.
- NaOH neutralises the acid.
- Free phenylamine is released.
NaOH neutralises the acid and deprotonates the phenylammonium salt to release C₆H₅NH₂.
Look for these in your work
- Acidic salt
- Neutralisation
- Free base
A student stops after reducing nitrobenzene in HCl and claims the mixture contains only neutral phenylamine. Refine the work-up description.
Give me a hint
Consider the protonation state in concentrated acid.
Compare my reasoning
- Phenylamine is protonated in the acidic medium.
- Add aqueous NaOH after reduction.
- This releases the neutral amine.
The acidic mixture contains phenylammonium ions; adding NaOH is needed to liberate free phenylamine.
Look for these in your work
- Protonation
- Work-up
- Neutral product
Common mistakes
- Reversing nitration and reduction
- Leaving out the NaOH work-up
- Using tin without the acidic medium
- Stopping at nitrobenzene
What can you explain now?
What is the intermediate when benzene is converted to phenylamine by the syllabus route?
Compare with the explanation
Nitrobenzene
Benzene is nitrated before reduction.
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Make it stick
What is the full sequence from benzene to free phenylamine?
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.