Primary amines
| English | Chinese | Pinyin |
|---|---|---|
| amine | 胺 | àn |
| halogenoalkane | 卤代烷 | lǔ dài wán |
| nucleophilic substitution | 亲核取代 | qīn hé qǔ dài |
| lone pair | 孤对电子 | gū duì diàn zi |
| nucleophile | 亲核试剂 | qīn hé shì jì |
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:
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 ______.
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:
Ammonia (in ethanol, under pressure) substitutes the halogen to give the amine.
Match each amine fact.
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:
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?
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