Choose between aldehyde and carboxylic-acid oxidation routes
Use the alcohol class and oxidation conditions to select the intended carbonyl or acid product.
A Level; Cambridge International Chemistry 9701, 2028–2030 syllabus, Topic 36. Routes use reactions listed in the syllabus and state the relevant reagents and conditions. Check every intermediate and possible by-product; no route implies a practical procedure. Written practice is self-checked
Before you begin
- Use the functional-group reactions from Topics 13–19 and 29–35, including their reagents, conditions, products and limitations.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which condition favours isolating an aldehyde from a primary alcohol?
What you will learn
- Distinguish oxidation of primary and secondary alcohols
- Use distillation or reflux to select a product
- Apply the distinction in a synthesis route
Conditions determine the oxidation endpoint
Oxidising a primary alcohol with acidified potassium dichromate(VI) or potassium manganate(VII) can form an aldehyde when the product is distilled off. Reflux allows further oxidation to the carboxylic acid.
A secondary alcohol oxidises to a ketone under the syllabus oxidation conditions. A tertiary alcohol does not undergo this oxidation in the stated syllabus context.
Build the condition into the route arrow
If a route needs an aldehyde intermediate, name distillation so it can be removed before further oxidation. If the target is the acid, name reflux for the primary-alcohol oxidation.
The same alcohol and oxidising reagent can lead to different products depending on the condition. An answer that gives only ‘oxidise’ is incomplete when the endpoint matters.
Pause and explain
What product forms when a secondary alcohol is oxidised with acidified dichromate?
Worked example
Choose conditions to convert butan-1-ol to butanal and then to butanoic acid.
Show the worked solution
- Use acidified dichromate or manganate for both oxidation steps.
- Distil during the aldehyde-forming step.
- Use reflux to continue oxidation to the acid.
Answer Butan-1-ol → butanal by controlled oxidation with distillation; further oxidation under reflux gives butanoic acid.
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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.
State the reagent and condition to prepare propanal from propan-1-ol.
Give me a hint
Choose the oxidation endpoint that prevents the aldehyde being oxidised further.
Compare my reasoning
- Use acidified K₂Cr₂O₇ or KMnO₄.
- Distil the aldehyde as it forms.
- Do not reflux if propanal is the target.
Oxidise propan-1-ol with acidified dichromate(VI) or manganate(VII) and distil to obtain propanal.
Look for these in your work
- Oxidant correct
- Distillation stated
- Aldehyde endpoint protected
The target is butanoic acid from butan-1-ol. Why should the route use reflux?
Give me a hint
Compare the aldehyde intermediate with the desired acid.
Compare my reasoning
- Primary alcohol oxidation first gives an aldehyde.
- Reflux allows further oxidation.
- The carboxylic acid is the target.
Reflux allows the primary alcohol/aldehyde oxidation sequence to continue to butanoic acid instead of distilling off butanal.
Look for these in your work
- Intermediate recognized
- Condition justified
- Target linked
A route claims propan-2-ol gives propanal on oxidation. Correct the product class.
Give me a hint
Classify the alcohol carbon bearing –OH.
Compare my reasoning
- Propan-2-ol is a secondary alcohol.
- Secondary alcohol oxidation gives a ketone.
- The product is propanone, not propanal.
Propan-2-ol oxidises to propanone; propanal is the oxidation product expected from a primary alcohol such as propan-1-ol.
Look for these in your work
- Alcohol class correct
- Ketone product
- Aldehyde contrast
Common mistakes
- Refluxing when the aldehyde is the desired product
- Distilling when the desired product is the acid
- Predicting an aldehyde from a secondary alcohol
- Claiming a tertiary alcohol oxidises under these conditions
What can you explain now?
Which condition favours isolating an aldehyde from a primary alcohol?
Compare with the explanation
Distillation
Distilling the aldehyde away limits further oxidation.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
How do alcohol class and distillation versus reflux determine the oxidation product?
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.