Hydrolyse nitriles to carboxylic acids
Hydrolyse a nitrile with dilute acid or dilute alkali; acidify the alkaline route to release the acid.
Section 19 · Nitrogen compounds
AS Level; Cambridge International Chemistry 9701, syllabus for 2028–2030. Classification of amines is not tested at AS Level. Cyanides, hydrogen cyanide and pressurised reactions are hazardous: these examples teach exam chemistry, not practical instructions. Written practice is self-checked
Before you begin
- Use nucleophilic substitution and addition, carbonyl compounds, functional-group names and balanced equations from Topics 13–18.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is the organic product in alkaline solution after nitrile hydrolysis?
What you will learn
- Recall acid and alkaline hydrolysis routes
- Recognise the carboxylate intermediate after alkaline hydrolysis
- Track the nitrile carbon into the carboxyl group
Hydrolysis changes the nitrile group
Nitriles can be hydrolysed with dilute acid or dilute alkali to form a carboxylic acid. In alkaline solution the organic product is a carboxylate ion; acidification then gives the free carboxylic acid.
The nitrile carbon becomes the carboxyl carbon, so the carbon skeleton is retained. Propanenitrile gives propanoic acid. Do not remove the nitrile carbon when counting the acid chain.
Show the work-up when alkali is used
For the alkaline route, write both stages: nitrile hydrolysis produces a carboxylate, then acidification protonates the carboxylate to form –COOH. If dilute acid is used for hydrolysis, state that acid route directly.
Hydroxynitrile hydrolysis also converts –CN to –COOH while retaining the hydroxy group, giving a hydroxycarboxylic acid. This is a useful link across the topic sequence, not a separate required reaction type.
Pause and explain
What does acidification do after alkaline hydrolysis?
Worked example
Describe an alkaline route from butanenitrile to butanoic acid.
Show the worked solution
- Hydrolyse the nitrile with dilute alkali.
- The product in alkaline solution is butanoate.
- Acidify to convert –COO⁻ into –COOH.
Answer Heat butanenitrile with dilute alkali, then acidify the butanoate to obtain butanoic acid.
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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.
Give a dilute-acid route to convert ethanenitrile into ethanoic acid.
Give me a hint
Use acid hydrolysis and keep both carbons in the product.
Compare my reasoning
- Start with CH₃CN.
- Hydrolysis converts –CN to –COOH.
- The two-carbon skeleton remains.
Hydrolyse ethanenitrile with dilute acid to form ethanoic acid.
Look for these in your work
- Dilute acid stated
- Nitrile hydrolysis identified
- Product chain length retained
A learner hydrolyses propanenitrile with dilute NaOH but reports propanoic acid as the immediate product. What is missing?
Give me a hint
Check the ionic form in alkaline solution.
Compare my reasoning
- Hydroxide leaves the acid deprotonated.
- The intermediate is propanoate.
- Add dilute acid after hydrolysis.
Acidify the propanoate solution to obtain propanoic acid.
Look for these in your work
- Intermediate corrected
- Acidification added
- Reason linked to carboxylate
Hydrolyse 2-hydroxypropanenitrile. Predict the product and explain which carbon becomes the carboxyl carbon.
Give me a hint
Only the nitrile group is hydrolysed; retain the OH and the carbon skeleton.
Compare my reasoning
- The –CN carbon becomes –COOH.
- The existing OH group remains on the adjacent carbon.
- Count three carbons in the acid product.
2-hydroxypropanoic acid, CH₃CH(OH)COOH. The nitrile carbon becomes the carboxyl carbon.
Look for these in your work
- Nitrile carbon tracked
- OH group retained
- Correct acid named
Common mistakes
- Stopping at the carboxylate when the question asks for the acid
- Losing one carbon during hydrolysis
- Calling hydrolysis a reduction
- Acidifying before the nitrile has hydrolysed
What can you explain now?
What is the organic product in alkaline solution after nitrile hydrolysis?
Compare with the explanation
A carboxylate
Alkali leaves the acid as its carboxylate ion until acidification.
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Make it stick
What intermediate appears in alkaline hydrolysis, and how does the nitrile carbon affect the product name?
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