Prepare a primary amine from a halogenoalkane and ammonia
Heat a halogenoalkane with ammonia in ethanol under pressure to replace the halogen with an –NH₂ group.
Section 34 · Nitrogen compounds
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
What conditions are used to react a halogenoalkane with ammonia to form a primary amine?
What you will learn
- Recall ammonia in ethanol as the nucleophile
- State heating under pressure as the condition
- Predict a primary amine from the carbon skeleton
Substitute the halogen with –NH₂
Ammonia reacts with a halogenoalkane in ethanol when heated under pressure. The nitrogen lone pair attacks the carbon bonded to the halogen; the halide leaves and a C–N bond forms.
For example, bromoethane can form ethylamine. Excess ammonia favours formation of the primary amine; further alkylation can also occur, so do not imply the reaction mixture must contain only one amine product.
Include every stated condition
When describing this syllabus route, name ammonia, ethanol and heating under pressure (often a sealed vessel). The pressure helps keep the ethanol reaction mixture hot.
A second ammonia molecule may accept the HBr formed, giving an ammonium salt in a fully balanced equation. The key organic product is the primary amine with the same carbon skeleton as the halogenoalkane.
Pause and explain
What happens to the halogen-bearing carbon during substitution?
Worked example
Describe the conversion of bromoethane into ethylamine.
Show the worked solution
- Use ammonia dissolved in ethanol.
- Heat the mixture under pressure.
- Replace Br with NH₂ while retaining two carbon atoms.
Answer Heat bromoethane with ammonia in ethanol under pressure to form ethylamine.
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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.
Complete the organic change: CH₃CH₂Br → ? using ammonia.
Give me a hint
Replace Br with NH₂ and keep the two-carbon chain.
Compare my reasoning
- The carbon skeleton stays CH₃CH₂–.
- Attach NH₂ at the carbon that bore Br.
- Name the product as a primary amine.
CH₃CH₂NH₂, ethylamine.
Look for these in your work
- Two carbons retained
- C–N formed
- Primary amine named
State the reagents, solvent and conditions for preparing a primary amine from a halogenoalkane.
Give me a hint
Include the named solvent and pressure condition.
Compare my reasoning
- Use NH₃ as the nucleophile.
- Dissolve it in ethanol.
- Heat under pressure.
React the halogenoalkane with ammonia in ethanol, heated under pressure.
Look for these in your work
- Ammonia
- Ethanol
- Heat/pressure
A learner predicts propylamine from 1-bromobutane and ammonia. Check the carbon skeleton and classify the product.
Give me a hint
Substitution changes the group attached, not the number of carbons.
Compare my reasoning
- 1-Bromobutane has four carbons.
- Replacing Br with NH₂ preserves all four.
- The resulting primary amine is butan-1-amine.
The product is butan-1-amine, not propylamine; the four-carbon skeleton is retained.
Look for these in your work
- Carbon count
- Substitution site
- Name corrected
Common mistakes
- Using aqueous ammonia as the stated medium
- Omitting pressure
- Changing the carbon-chain length
- Claiming only primary amine forms under all reagent ratios
What can you explain now?
What conditions are used to react a halogenoalkane with ammonia to form a primary amine?
Compare with the explanation
Ammonia in ethanol, heated under pressure
These are the specified conditions.
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Make it stick
Which nucleophile, solvent and conditions prepare a primary amine from a halogenoalkane?
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