A Level · Cambridge (CIE) · 9701

Reduce carboxylic acids to primary alcohols

LiAlH₄ reduces a carboxylic acid to the corresponding primary alcohol.

Carboxylic acids and derivatives · Cambridge 9701 AS Chemistry · 18.1

AS Level; Cambridge International Chemistry 9701, 2025–2027 syllabus. Track the carbon skeleton, name reagents and conditions, and show products and observations. Written practice is self-checked

Before you begin

Use alcohol oxidation and carbonyl chemistry from Topics 16–17, functional-group names, acid–base equations and balanced reaction formulae.

Work on paper. Try each question before revealing help, and explain why your method works.

Quick readiness check

Which reagent is specified to reduce a carboxylic acid to a primary alcohol?

What you will learn

Recall LiAlH₄ as the reducing agent
Predict a primary alcohol
Track carbon count through reduction

Carboxylic-acid reactions: a reactive metal gives carboxylate salt and H₂; an alkali gives salt and water; a carbonate gives salt, water and CO₂; LiAlH₄ reduces the acid to a primary alcohol. Products and gases distinguish the reaction types.

Reduction changes –COOH to –CH₂OH

LiAlH₄ reduces a carboxylic acid to a primary alcohol. Use dry ether for the reduction, then aqueous work-up to release the alcohol.

The carbon skeleton is retained: ethanoic acid gives ethanol; butanoic acid gives butan-1-ol.

Reduction reverses the oxidation level

A primary alcohol can be oxidised to an aldehyde and then a carboxylic acid. LiAlH₄ takes a carboxylic acid back to the primary alcohol.

Do not use NaBH₄ for this syllabus transformation; LiAlH₄ is the named reducing agent for carboxylic acids here.

Pause and explain

What alcohol forms from propanoic acid after LiAlH₄ reduction?

Put the idea to work

Worked example

Predict the product when pentanoic acid is reduced with LiAlH₄.

Show the worked solution

LiAlH₄ reduces –COOH to –CH₂OH.
The product is primary because –OH is at the end carbon.
Retain all five carbons.

Answer Pentan-1-ol (after aqueous work-up).

Try a topic test

Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.

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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.

1 · Guided

Predict the product and reagent for reducing 2-methylpropanoic acid.

Give me a hint

Replace the acid group with a terminal primary alcohol group.

Compare my reasoning

Use LiAlH₄.
Retain the branched carbon skeleton.
Name the terminal alcohol.

2-methylpropan-1-ol; LiAlH₄ then aqueous work-up.

Look for these in your work

Reagent correct
Branch retained
Primary alcohol named

2 · Independent

Why does butanoic acid form butan-1-ol rather than butan-2-ol?

Give me a hint

Track the carbon that carried –COOH.

Compare my reasoning

The carboxyl carbon remains in the chain.
It becomes the terminal carbon attached to –OH.
The product alcohol is primary.

Reduction converts the terminal –COOH carbon into –CH₂OH, giving butan-1-ol.

Look for these in your work

Carbon tracked
Position retained
Alcohol class correct

3 · Transfer

Complete the reversible functional-group sequence: propan-1-ol → propanoic acid → ?

Give me a hint

The last arrow is reduction of a carboxylic acid.

Compare my reasoning

Use LiAlH₄ for acid reduction.
The carbon skeleton stays three-carbon.
The terminal acid group returns to –CH₂OH.

Propan-1-ol, after LiAlH₄ reduction and work-up.

Look for these in your work

Reagent inferred
Skeleton retained
Product class stated

Common mistakes

Naming a secondary alcohol
Using NaBH₄ as the specified reagent
Changing the carbon chain length

Recall without your notes

What can you explain now?

Which reagent is specified to reduce a carboxylic acid to a primary alcohol?

Compare with the explanation

LiAlH₄

Lithium aluminium hydride is the syllabus reagent.

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Make it stick

Which reagent reduces a carboxylic acid, and what class and position of alcohol result?

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.

Keep learning Chemistry

Check the official syllabus 2028–2030

Course scope and assessment

Four hundred and forty-two original lessons map the published learning outcomes across AS Chemistry Topics 1–22 and A Level Topics 23–37, with guided, independent and transfer practice and explained answers. Every numbered subject-content topic and listed outcome tag now has a mapped lesson sequence. Topic 32 maps all 12 hydroxy-compound outcome tags in 11 lessons; Topic 33 maps all 15 carboxylic-acid and derivative outcome tags in 16 lessons; Topic 34 maps all 22 nitrogen-compound outcome tags in 20 lessons; Topic 35 maps all 12 polymerisation outcome tags in 16 lessons; Topic 36 maps all four organic-synthesis outcome tags in 14 lessons; Topic 37 maps all 22 chromatography and NMR outcome tags in 18 lessons. Cambridge's 2028–2030 Version 1 syllabus states that there are no significant changes which affect teaching from the preceding edition; the routes are aligned to that edition. This is 37 of the 37 numbered subject-content topics. Full cumulative exam assessment, Paper 3 laboratory competence, Paper 5 investigation practice and human subject-teacher review remain outstanding. Written practice is self-checked and does not certify exam readiness.