Amines and their Derivatives | Organic Chemistry 3

The Amines and their Derivatives are studied in this chapter: the naming and properties of amines, their synthesis, the Hofmann elimination, the Mannich reaction.

Naming the Amines

Amines = derivatives of ammonia NH3, in which one, two or three of the H have been replaced by alkyl or aryl groups.

The -ane ending of the corresponding alkane is replace by -anamine. Same rules as alcohols.
For secondary and tertiary amines:
- largest alkyl group = main chain
- other alkyl groups = substituents named by using the letter N-
Amine function has the lowest order of precedence of all functional groups (except alkene and alkyne).
We use prefixe amino- when the amine is a substituent.

 

Properties of Amines

 Alkanamine is tetrahedral

Properties similar to alcohols and ethers.
Amines can:
- serve as nucleophile
- participate in hydrogen bonding (high boiling point + soluble in water)
- be both basic and acidic
 

 

Oxygen is more electronegative than Nitrogen
⇒ Amines are less acidic than alcohols
⇒ Amines are more basic and nucleophilic than alcohols and ethers
⇒ Amines have weaker hydrogen bonding than alcohols


NMR: 1H broad signal and variable δ (1.0-2.5 ppm) 
IR: N-H stretching ⇒ broad band ~ 3250-3500 cm-1

 

Preparation of Amines

Amines by alkylation:
 

 

Mechanism:

Step 1: Nucleophilic Substitution


Step 2: Deprotonation


And then, subsequent alkylation.

 

Amines from azides:
 

 

Amines by reductive amination:
 

 

Mechanism:

Step 1: Condensation


 

Step 2: Reduction

 

Amines from carboxylic amides:
 

 

Amines from nitriles:
 

Hofmann Elimination

 

Mechanism:

Mannich Reaction

Mannich reaction can be considered a variation of the aldol condensation:
 

 

 


Mechanism:
 

Step 1: Iminium ion formation



Step 2: Carbon-carbon bond formation



Step 3: Deprotonation