React an acyl chloride with a primary or secondary amine
Primary and secondary amines react with acyl chlorides at room temperature to form substituted amides.
A Level; Cambridge International Chemistry 9701, 2028–2030 syllabus, Topic 33. Focus on the named compounds, reagents and conditions in each outcome; apply the specified reaction type rather than extending it to unlisted cases. Written practice is self-checked
Before you begin
- Recall carboxylic acids, esters, phenols, alcohols, halogenoalkanes and electrophilic/nucleophilic reaction ideas from earlier topics.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What product class forms when a primary amine reacts with an acyl chloride?
What you will learn
- Predict amides from primary and secondary amines
- Keep the amine substituents on nitrogen
- Account for HCl capture by excess amine
The amine nitrogen joins the acyl group
A primary or secondary amine reacts with an acyl chloride at room temperature to form an amide. A primary amine R′NH₂ gives RCONHR′; a secondary amine R′₂NH gives RCONR′₂.
One amine molecule supplies nitrogen to the amide. Another molecule can accept HCl, giving an ammonium chloride salt in a balanced equation with excess amine.
Check the nitrogen substitution level
A primary amine has one carbon group and two hydrogens on nitrogen; after acylation, the amide nitrogen retains one H. A secondary amine has two carbon groups and one H; its product nitrogen has two carbon groups and no H.
The syllabus limits this outcome to primary or secondary amines. Do not extend the product prediction to tertiary amines, which have no N–H bond for this amide-forming substitution as presented here.
Pause and explain
What does methylamine contribute to N-methylethanamide?
Worked example
Predict the amide formed from ethanoyl chloride and methylamine.
Show the worked solution
- Methylamine is a primary amine.
- Attach nitrogen to the ethanoyl carbonyl carbon.
- Keep one H and the methyl group on nitrogen.
Answer N-methylethanamide, CH₃CONHCH₃, forms; excess methylamine can form its ammonium chloride salt.
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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.
Predict the amide from propanoyl chloride and ethylamine.
Give me a hint
Keep the ethyl group on nitrogen and preserve the propanoyl fragment.
Compare my reasoning
- Ethylamine is primary.
- Replace acyl Cl with NHCH₂CH₃.
- The product retains one N–H.
N-ethylpropanamide, CH₃CH₂CONHCH₂CH₃.
Look for these in your work
- Propanoyl part
- Ethyl on N
- One N–H retained
Compare the nitrogen in the products from methylamine and dimethylamine.
Give me a hint
Count carbon substituents and remaining N–H bonds.
Compare my reasoning
- Methylamine gives an amide with one methyl and one N–H.
- Dimethylamine gives an amide with two methyl groups on nitrogen.
- Both products contain the acyl carbonyl.
Methylamine forms CH₃CONHCH₃; dimethylamine forms CH₃CON(CH₃)₂.
Look for these in your work
- Primary amine product
- Secondary amine product
- Carbonyl preserved
A response changes propanoyl chloride to propanamide when the reagent is ethylamine. Correct the nitrogen substituent.
Give me a hint
The amine-derived alkyl group remains on nitrogen.
Compare my reasoning
- Ethylamine contributes an ethyl group.
- The amide nitrogen retains one H from the primary amine.
- The product is N-ethylpropanamide.
The product is N-ethylpropanamide, CH₃CH₂CONHCH₂CH₃, not unsubstituted propanamide.
Look for these in your work
- Amine fragment retained
- N–H count
- Name corrected
Common mistakes
- Removing the amine’s carbon substituent
- Leaving two hydrogens on a primary-amine-derived amide nitrogen
- Calling the product an amine rather than an amide
- Forgetting amine can neutralise HCl
What can you explain now?
What product class forms when a primary amine reacts with an acyl chloride?
Compare with the explanation
An amide
The amine nitrogen bonds to the acyl carbon.
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Make it stick
How do primary and secondary amines differ in the amide products they form?
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