Use nitriles as intermediates to acids or amines
Select hydrolysis or reduction to direct a nitrile intermediate toward a carboxylic acid or a primary amine.
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 transformation converts a nitrile into a primary amine?
What you will learn
- Compare nitrile hydrolysis and reduction
- Select reagents for the intended product
- Track the nitrile carbon through each route
Hydrolysis makes a carboxylic acid
A nitrile can be hydrolysed with dilute acid to produce a carboxylic acid. With dilute alkali, the carboxylate forms first and is followed by acidification to obtain the carboxylic acid.
The nitrile carbon is retained and becomes the carboxyl carbon. This is why forming a nitrile by KCN substitution can extend a carbon chain before hydrolysis.
Reduction makes an amine
A nitrile can be reduced to a primary amine using LiAlH₄ or hydrogen with a nickel catalyst. The nitrile carbon remains in the carbon skeleton as the carbon attached to the new –CH₂NH₂ group.
Hydrolysis and reduction are alternative branches. Do not use an acid-hydrolysis reagent when the target is an amine, or a reducing agent when the target is a carboxylic acid.
Pause and explain
What happens to the nitrile carbon during hydrolysis to a carboxylic acid?
Worked example
Choose reagents to direct propanenitrile toward propanoic acid or propylamine.
Show the worked solution
- Identify hydrolysis as the acid route.
- Identify reduction as the amine route.
- Retain the nitrile carbon in both products.
Answer Hydrolyse propanenitrile with dilute acid to form propanoic acid. Reduce it with LiAlH₄ or H₂/Ni to form propylamine.
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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.
Choose the route and product from butanenitrile if the target is pentanoic acid.
Give me a hint
Check whether the nitrile's total carbon count matches the target acid.
Compare my reasoning
- Butanenitrile has four carbons including the nitrile carbon.
- Hydrolysis retains that carbon and changes –CN to –COOH.
- The target acid therefore has four carbons, not five.
Hydrolysis gives butanoic acid, not pentanoic acid. A five-carbon target would require a five-carbon nitrile first.
Look for these in your work
- Carbon count checked
- Hydrolysis identified
- Target mismatch explained
Give two syllabus reagent systems that reduce a nitrile to a primary amine.
Give me a hint
Name one hydride reagent and one catalytic hydrogenation system.
Compare my reasoning
- LiAlH₄ is one reducing system.
- H₂ with a Ni catalyst is another.
- Both target a primary amine.
LiAlH₄ or H₂/Ni reduces a nitrile to a primary amine.
Look for these in your work
- First system correct
- Second system correct
- Product class correct
A student uses dilute alkali to hydrolyse a nitrile but stops at the carboxylate while the target is a carboxylic acid. What is the missing step?
Give me a hint
Convert the carboxylate to its protonated acid form.
Compare my reasoning
- Alkaline hydrolysis forms a carboxylate salt.
- Add acid after hydrolysis.
- Acidification produces –COOH.
Acidify the carboxylate after alkaline hydrolysis to obtain the carboxylic acid.
Look for these in your work
- Intermediate recognized
- Acidification added
- Target reached
Common mistakes
- Confusing nitrile hydrolysis with reduction
- Dropping the nitrile carbon
- Forgetting acidification after alkaline hydrolysis
- Using a product name inconsistent with chain length
What can you explain now?
Which transformation converts a nitrile into a primary amine?
Compare with the explanation
Reduction with LiAlH₄ or H₂/Ni
Reduction changes –C≡N to –CH₂NH₂.
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Make it stick
How do hydrolysis and reduction send a nitrile toward different target groups?
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.