Amines and their Derivatives | Organic Chemistry 3

Amines and their derivatives are studied in this chapter: name, properties and synthesis of amines, Hofmann elimination, Mannich reaction

Nomenclature of Amines

Amines:

Derivatives of ammonia NH3, in which one, two or three of the H have been replaced by alkyl or aryl groups
 

Nomenclature:

The -ane ending of the corresponding alkane is replace by -anamine. The rules for naming alcohols  also apply to amines
For secondary and tertiary amines:
- largest alkyl group = main chain
- other alkyl groups = substituents named as prefixes preceded by N-
The amine functional group has the lowest order of priority of all functional groups (except alkene and alkyne). The prefixe amino- is used when the amine is a substituent

 

Properties of Amines

Properties:

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

 Alkanamine is tetrahedral

 

Comparison with alcohols:

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
 

Absorption spectroscopy:

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:

  1. Nucleophilic substitution:


     
  2. Deprotonation:


     
  3. Subsequent alkylations
     


Amines from azides:

 


Amines by reductive amination:

Mechanism:

  1. Condensation:


     
  2. Reduction:


     


Amines from carboxylic amides:

 


Amines from nitriles:

Hofmann Elimination


Mechanism:

Mannich Reaction


Mechanism:

The Mannich reaction can be thought of as a variation of the aldol condensation

  1. Iminium ion formation:


     
  2. Carbon-carbon bond formation:


     
  3. Deprotonation: