Convert phenylamine to phenol through a diazonium salt
Diazotise phenylamine below 10°C using HNO₂ or NaNO₂ with dilute acid, then warm the salt with water to form phenol.
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
At what temperature is phenylamine diazotised?
What you will learn
- Recall diazotisation reagents and temperature
- Identify the diazonium salt intermediate
- Describe warming the salt with water to obtain phenol
Form the diazonium salt cold
React phenylamine with HNO₂, or generate it using NaNO₂ and dilute acid, below 10°C. This forms a benzenediazonium salt.
Keep the salt-forming stage below 10°C. The condition applies to diazotisation, not to the later conversion to phenol.
Warm the salt with water
Further warming of the diazonium salt with H₂O gives phenol and nitrogen gas. The route is phenylamine → diazonium salt below 10°C → warm with water → phenol.
This route also appears in the Topic 32 phenol outcomes. Here the focus is the preparation starting from phenylamine and the exact order of conditions.
Pause and explain
What is done after forming the diazonium salt?
Worked example
Describe the conversion from phenylamine to phenol.
Show the worked solution
- Use HNO₂ or NaNO₂ plus dilute acid below 10°C.
- Form a diazonium salt.
- Warm the salt with water to produce phenol.
Answer Diazotise phenylamine below 10°C, then warm the diazonium salt with water to form phenol.
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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 the reagents and conditions in order for phenylamine → phenol.
Give me a hint
Separate the cold diazotisation from the warm hydrolysis.
Compare my reasoning
- Use HNO₂ or NaNO₂/dilute acid.
- Keep the salt-forming stage below 10°C.
- Warm the diazonium salt with water.
Phenylamine → diazonium salt below 10°C → warm with H₂O → phenol.
Look for these in your work
- Reagents
- Cold stage
- Warm stage
A student writes ‘warm phenylamine with water below 10°C to make phenol’. Correct the intermediate and assign each condition.
Give me a hint
The cold condition belongs to diazonium formation.
Compare my reasoning
- First react phenylamine with HNO₂ or NaNO₂/dilute acid.
- Form the diazonium salt below 10°C.
- Then warm that salt with water.
Form a diazonium salt below 10°C using nitrous acid; afterwards warm the salt with water to form phenol.
Look for these in your work
- Nitrite step
- Intermediate
- Conditions in order
Why is a diazonium salt named as an intermediate rather than the final product here?
Give me a hint
Check what the question asks to prepare.
Compare my reasoning
- The target is phenol.
- The diazonium salt is made in the cold first stage.
- Warming it with water completes the route.
The diazonium salt is an intermediate; warming it with water converts it into phenol.
Look for these in your work
- Target identified
- Intermediate role
- Final step
Common mistakes
- Warming before diazonium formation
- Omitting dilute acid when using NaNO₂
- Stopping at the diazonium salt
- Using NaOH to convert the salt into phenol
What can you explain now?
At what temperature is phenylamine diazotised?
Compare with the explanation
Below 10°C
The diazonium salt is formed cold.
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Make it stick
Which step must be below 10°C, and which step must be warmed with water?
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.