AQA · A-Level · Chemistry
Course version: 7405 · Version from Sept 2016
Oxidation of alcohols: Secondary alcohols can be oxidised to ketones.
A secondary alcohol has just one hydrogen on the carbon carrying the hydroxyl group, so it can be oxidised once and no further.
Checked against the AQA 7405 specification (opens in a new tab) on .
- Point 3 of 6
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A secondary alcohol has just one hydrogen on the carbon carrying the hydroxyl group, so it can be oxidised once and no further. Propan-2-ol gives propanone: CH₃CH(OH)CH₃ + [O] → CH₃COCH₃ + H₂O. The ketone that results has no hydrogen on its carbonyl carbon, so oxidising it again would mean breaking a carbon–carbon bond, which acidified dichromate cannot do. That makes the reaction convenient: you can heat under reflux without any risk of going too far, then distil the ketone out afterwards. AQA has tested this directly by asking which statement is not true of both primary and secondary alcohols, the answer being that both are easily oxidised to carboxylic acids; secondary alcohols are not.
What earns the marks
- The equation using [O], with water as the second product.
- Naming the ketone product, such as propanone from propan-2-ol.
- Stating that the ketone is not oxidised further by this reagent.
- The reason, that the carbonyl carbon carries no hydrogen atom.
Common mistakes and how to put them right
Oxidising the ketone on to a carboxylic acid, which acidified dichromate cannot do.
Leaving the water out of the equation.
Saying distillation is needed to stop the reaction at the ketone.
Naming the product of oxidising propan-2-ol as propanal rather than propanone.
Exam tips
- Check the carbonyl carbon in your product: no hydrogen on it means the oxidation has finished.
- Name aldehydes with the ending -al and ketones with -one, and check which the carbon skeleton allows.
- Use reflux freely for a secondary alcohol; there is no over-oxidation to guard against.
Try the lesson
The start of the Oxidation of alcohols: Secondary alcohols can be oxidised to ketones. lesson, made from checked teaching notes for this specification point.
Have a go first
What type of organic compound is formed when a secondary alcohol is oxidised?
Listen
A secondary alcohol has just one hydrogen on the carbon carrying the hydroxyl group, so it can be oxidised once and no further. Propan-2-ol gives propanone: CH₃CH(OH)CH₃ + [O] → CH₃COCH₃ + H₂O. The ketone that results has no hydrogen on its carbonyl carbon, so oxidising it again would mean breaking a carbon–carbon bond, which acidified dichromate cannot do. That makes the reaction convenient: you can heat under reflux without any risk of going too far, then distil the ketone out afterwards. AQA has tested this directly by asking which statement is not true of both primary and secondary alcohols, the answer being that both are easily oxidised to carboxylic acids; secondary alcohols are not. A strong answer earns marks for these points. the equation using [O], with water as the second product. naming the ketone product, such as propanone from propan-2-ol. stating that the ketone is not oxidised further by this reagent. the reason, that the carbonyl carbon carries no hydrogen atom. Exam tip: Check the carbonyl carbon in your product: no hydrogen on it means the oxidation has finished.
Key words
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secondary alcohol oxidation
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ketone product
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no further oxidation
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hydrogen on the carbonyl carbon
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See every definition
- secondary alcohol oxidation
- A secondary alcohol has just one hydrogen on the carbon carrying the hydroxyl group, so it can be oxidised once and no further.
- ketone product
- The ketone that results has no hydrogen on its carbonyl carbon, so oxidising it again would mean breaking a carbon–carbon bond.
- no further oxidation
- Acidified dichromate cannot oxidise the ketone further, because that would mean breaking a carbon–carbon bond.
- hydrogen on the carbonyl carbon
- The ketone that results has no hydrogen on its carbonyl carbon, which is why it is not oxidised further.
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