Oxidise a secondary alcohol to a ketone
Distil a secondary alcohol with an acidified oxidising agent to obtain a ketone.
Section 17 · Carbonyl compounds
AS Level; Cambridge International Chemistry 9701, 2025–2027 syllabus. Distinguish aldehydes from ketones by structure and evidence; state reagent, condition and observation. Written practice is self-checked
Before you begin
- Use carbonyl structures, alcohol oxidation and reduction from Topics 13 and 16, nucleophiles and curly arrows, and the organic reaction patterns from Topic 15.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What product forms when a secondary alcohol is oxidised?
What you will learn
- Recognise secondary alcohol oxidation
- Use acidified oxidant and distillation
- Locate the ketone carbonyl
A secondary alcohol gives a ketone
Heat a secondary alcohol with acidified K₂Cr₂O₇ or acidified KMnO₄ and distil to produce a ketone.
Propan-2-ol → propanone: CH₃CH(OH)CH₃ + [O] → CH₃COCH₃ + H₂O. The carbon that carried OH becomes the carbonyl carbon.
Use the structure to identify the product
The carbonyl carbon in a ketone is attached to two carbon groups. The carbon skeleton is retained while C–OH and a neighbouring C–H are oxidised to C=O.
Do not predict an aldehyde from a secondary alcohol. Tertiary alcohols do not oxidise under the syllabus conditions.
Pause and explain
Where is the C=O group in the product from butan-2-ol?
Worked example
Predict the product and conditions for oxidation of butan-2-ol.
Show the worked solution
- The OH-bearing carbon has two carbon neighbours, so the alcohol is secondary.
- Oxidation changes that carbon into C=O.
- Distil the product with an acidified oxidising agent.
Answer Butan-2-ol + [O] → butan-2-one + H₂O; acidified K₂Cr₂O₇ or KMnO₄, heat and distil.
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.
Write the equation for oxidising cyclohexanol to cyclohexanone.
Give me a hint
Replace the C–OH site with C=O.
Compare my reasoning
- Cyclohexanol is secondary.
- The carbon skeleton remains a six-membered ring.
- Use [O] and show water.
Cyclohexanol + [O] → cyclohexanone + H₂O; acidified K₂Cr₂O₇ or KMnO₄, heat and distil.
Look for these in your work
- Ketone named
- Ring preserved
- Conditions stated
What carbonyl product forms from pentan-3-ol?
Give me a hint
Locate the OH-bearing carbon before changing the functional group.
Compare my reasoning
- The OH is at C3.
- Oxidation keeps the C=O at C3.
- The product is pentan-3-one.
Pentan-3-one.
Look for these in your work
- Carbonyl position retained
- Ketone named
- Skeleton preserved
A student predicts pentanal from pentan-2-ol. Explain the error.
Give me a hint
Check whether the alcohol is primary or secondary.
Compare my reasoning
- Pentan-2-ol has two carbon groups attached to its OH-bearing carbon.
- It is secondary, not primary.
- Oxidation gives pentan-2-one.
Pentan-2-ol is secondary and gives pentan-2-one; an aldehyde comes from a primary alcohol.
Look for these in your work
- Alcohol class corrected
- Product class corrected
- Position retained
Common mistakes
- Calling the product an aldehyde
- Moving the carbonyl to a different carbon
- Using a reducing agent
What can you explain now?
What product forms when a secondary alcohol is oxidised?
Compare with the explanation
A ketone
The OH-bearing carbon becomes an internal carbonyl carbon.
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Make it stick
How does the carbon bearing OH determine the ketone product from a secondary alcohol?
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