# Oxidation of alcohols

Oxidising an alcohol removes hydrogen and adds a C=O. A primary alcohol gives an aldehyde, and with strong oxidant a carboxylic acid. A secondary alcohol gives a ketone. A tertiary alcohol does not oxidise easily because it has no hydrogen on the carbon.

Chemistry (university) · Part 10: Organic reactions and mechanisms · Card 10 of 10 · Last updated 2026-10-19

## Analogy

Think of removing hydrogen as stripping layers off the carbon until it holds more bonds to oxygen.

## Example

**Alcohol to product**

Primary ethanol → ethanal → ethanoic acid
Secondary propan-2-ol → propanone
Tertiary 2-methylpropan-2-ol → no reaction
Cr₂O₇²⁻ orange → Cr³⁺ green

## In practice

The breathalyser test works because ethanol is oxidised by dichromate, which changes colour from orange to green.

## Practice

### Flashcards

- **Oxidising a secondary alcohol gives what?** A ketone.

### Interview questions

**Describe how to convert ethanol into ethyl ethanoate, and say why the reaction is reversible.**

- Oxidise ethanol to ethanoic acid
- Heat with ethanol and acid catalyst
- Esterification forms water
- Reaction reaches equilibrium, remove water for better yield

## Questions people ask

### How can I stop at the aldehyde and not go on to the acid?

Use a mild oxidant such as PCC in dry solvent, or distil the aldehyde out as it forms, since it boils lower than the alcohol. A strong oxidant in water, such as acidified dichromate with heating under reflux, carries on to the carboxylic acid.

### Why can't tertiary alcohols be oxidised easily?

Oxidation needs a hydrogen on the carbon that holds the OH, so a C=O can form. A tertiary alcohol has three carbon groups on that carbon and no hydrogen. Oxidising it would mean breaking a carbon-carbon bond, which needs harsh conditions.

## Related concepts

- [Nucleophilic acyl substitution](https://studyvisually.com/learn/science/chemistry-university/chemistry-university-part-10/chemistry-university-part-10-concept-9)

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