Prepare a secondary amine from a halogenoalkane and a primary amine
Heat a halogenoalkane with a primary amine in ethanol in a sealed tube or under pressure to form a secondary amine.
A Level; Cambridge International Chemistry 9701, 2028–2030 syllabus, Topic 34. Use the stated reagents, conditions and product scope. Written practice is self-checked This online lesson cannot demonstrate supervised laboratory skills.
Before you begin
- Recall nucleophilic substitution, reduction, acyl-chloride addition–elimination, acid–base equilibria and covalent bonding.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which amine reacts with a halogenoalkane in the secondary-amine preparation route?
What you will learn
- Use a primary amine as the nucleophile
- Recall ethanol and heating in a sealed tube or under pressure
- Recognise the two carbon groups attached to nitrogen
Alkylate nitrogen once more
A primary amine can react with a halogenoalkane in ethanol when heated in a sealed tube or under pressure. The nitrogen attacks the halogenoalkane carbon and replaces its halogen, producing a secondary amine.
For example, methylamine plus bromoethane can give ethylmethylamine, CH₃NHCH₂CH₃. Nitrogen is now bonded to two carbon groups and one hydrogen.
Keep the second alkyl group on nitrogen
The carbon chain from the halogenoalkane becomes attached to nitrogen; the primary amine's existing alkyl group stays there too.
Further alkylation may occur with excess halogenoalkane. The syllabus asks for the route to secondary amines; describe the intended product without claiming that higher alkylation is impossible.
Pause and explain
How many carbon groups are bonded directly to nitrogen in a secondary amine?
Worked example
Predict the amine formed from methylamine and bromoethane under the syllabus conditions.
Show the worked solution
- Methylamine already has one carbon group on N.
- The ethyl group from bromoethane replaces the N–H hydrogen after substitution.
- Nitrogen is now bonded to methyl and ethyl groups.
Answer Ethylmethylamine, CH₃NHCH₂CH₃, a secondary amine.
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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 product class and structure from CH₃NH₂ + CH₃CH₂Br.
Give me a hint
Add the ethyl group to the nitrogen already bonded to methyl.
Compare my reasoning
- Keep the N–CH₃ bond.
- Replace the halogen with an N–CH₂CH₃ bond.
- Retain one N–H bond.
CH₃NHCH₂CH₃, ethylmethylamine, a secondary amine.
Look for these in your work
- Both carbon groups retained
- C–N formed
- Secondary class
Describe the solvent and conditions for the primary-amine alkylation route.
Give me a hint
Distinguish it from the ammonia route by the nucleophile.
Compare my reasoning
- Use a primary amine and halogenoalkane.
- Use ethanol.
- Heat in a sealed tube or under pressure.
React the primary amine with a halogenoalkane in ethanol, heated in a sealed tube or under pressure.
Look for these in your work
- Primary amine
- Ethanol
- Sealed/pressure condition
A student calls CH₃NHCH₂CH₃ a primary amine because it contains one N–H bond. Correct the classification.
Give me a hint
Classify by the number of carbon groups attached to N.
Compare my reasoning
- Nitrogen is attached to CH₃ and CH₂CH₃.
- It has two carbon groups and one hydrogen.
- That is a secondary amine.
It is secondary: two carbon groups are bonded to nitrogen, even though one N–H bond remains.
Look for these in your work
- Carbon groups counted
- N–H distinguished
- Class corrected
Common mistakes
- Using ammonia instead of a primary amine
- Dropping the first amine's carbon group
- Calling the product primary
- Leaving out pressure or the sealed tube
What can you explain now?
Which amine reacts with a halogenoalkane in the secondary-amine preparation route?
Compare with the explanation
A primary amine
The product nitrogen retains two carbon groups.
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Make it stick
How does a primary amine plus a halogenoalkane produce a secondary amine?
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