Primary amines
Introduced| English | Meaning |
|---|---|
| amine/ˈæmaɪn/ | An organic compound derived from ammonia by replacing one or more hydrogen atoms with carbon-containing groups. |
| halogenoalkane/ˈheɪləʊdʒnəʊlkeɪn/ | An alkane derivative in which one or more hydrogen atoms have been replaced by halogen atoms. |
| nucleophilic substitution/ˌnjuːklɪəˈfɪlɪk ˌsʌbstɪˈtjuːʃn/ | A reaction in which an electron-pair donor replaces a leaving group in a molecule. |
| lone pair/ləʊn peə/ | A pair of outer-shell electrons on one atom that is not shared in a covalent bond. |
| nucleophile/ˈnjuːklɪɒfaɪl/ | An electron-pair donor that forms a covalent bond to an electron-deficient centre. |
Organic bases
- An amine 胺 has an –NH₂ group (nitrogen in place of a hydrogen of ammonia).
- We can make a primary amine from a halogenoalkane 卤代烷.
- It happens by nucleophilic substitution 亲核取代.
Amine reaction lab
Classify amine examples by basicity and nucleophilic behaviour.
An amine contains the:
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An amine has an –NH₂ group, where nitrogen replaces a hydrogen of ammonia.
Amines act as bases because the nitrogen lone pair can accept a ______.
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R–NH₂ + H⁺ → R–NH₃⁺.
Making a primary amine
- Heat a halogenoalkane with ammonia dissolved in ethanol, under pressure:
$$\text{C}_2\text{H}_5\text{Br} + \text{NH}_3 \rightarrow \text{C}_2\text{H}_5\text{NH}_2 + \text{HBr}$$
Ammonia's lone pair substitutes for the halogen of a halogenoalkane, giving a primary amine
A primary amine is made by heating a halogenoalkane with:
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Ammonia (in ethanol, under pressure) substitutes the halogen to give the amine.
Match each amine fact.
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Each item links the term to its correct meaning.
The mechanism
- This is a nucleophilic substitution: the lone pair 孤对电子 on ammonia's nitrogen attacks the slightly positive carbon and pushes out the halogen.
- Use an excess of ammonia, or the amine formed reacts again.
Nylon, the first fully synthetic polyamide, was famously first used to make stockings.
The reaction is a nucleophilic substitution because:
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Ammonia is the nucleophile; its nitrogen lone pair attacks the C–X carbon and pushes out the halogen.
Why is an excess of ammonia used?
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The amine is itself a nucleophile and could react again; excess ammonia favours the primary amine.
Amines as nucleophiles 亲核试剂
- The nitrogen lone pair lets amines act as nucleophiles as well as bases.
- This is why they react with halogenoalkanes and acyl chlorides.
You've got it
- an amine has the –NH₂ group
- made by heating a halogenoalkane with NH₃ in ethanol, under pressure
- it is a nucleophilic substitution (ammonia's lone pair attacks); use excess NH₃