3.3.11 Amines

• You can differ primary, secondary and tertiary amines:

  Primary:

  shows 2 peaks between 3300-3500

  Secondary:

  Shows 1 peak between 3300-3500

  Tertiary:

  shows no peak
• Alkyl groups push electron density towards the nitrogen atom via the inductive effect.

  This makes the lone pair of electrons on the nitrogen atom more available.

  This makes the primary amine a stronger base than ammonia as it is Bette at accepting protons.
• Aromatic amines are weaker bases than ammonia.

  The lone pair of electrons on the nitrogen atom are less available because they are delocalised with the benzene ring
• If you want a high yield of primary amine use excess ammonia.

  If you want a higher yield of quaternary ammonium salt use excess haloalkane so it increases then chance of further substitution.
• There are two methods to make a primary amine:

  1. Nucleophilic Substitution to make amine
  2. Making the nitrile -> then Reduction with LiAH4 in ether

  Disadvantage of 1:

  The 1° produced can act as a nucleophile and further substitution will take place producing 1°, 2°, 3° which requires separation.

  Disadvantage of 2:

  KCN / NaCN is toxic

  Lower yield of product as it is a 2 step process

  Advantage of 1:

  Only one product is made
• As the length of the alkyl group increases the amine becomes a stronger base due to more electron density being pushed towards the N . This makes the lone pair more avaliable and so is better at accepting protons and it is a stronger base
• Why do we use excess ammonia if we want to produce an primary amine?

  To reduce the chance of further substitution because the primary alcohol produced has a lone pair of electrons on the nitrogen and can be used as a nucleophile
• Produced when there is an excess of of haloalkane and ammonia Quarternary ammonium salt - used as a cationic surfactant in fabric softeners
• What are the two ways to form a primary Amine:

  1. Haloalkane + excess ammonia
  2. Reduction of nitriles
• Disadvantage of forming a primary amine via Nucleophilic substitution of an haloalkane with excess NH3:

  The primary amine produced can act as a nucleophile and further substitution will take place, producing a mixture of products, which requires separation.
• Advantages and Disadvantages of forming a primary amine via the reduction of nitriles:

  Advantages:

  > Only one product is made

  Disadvantages:

  > KCN/HCN is toxic

  > Lower yield of product as it is a 2 step process
• Nitriles are reduced to form amines

  Nitriles need a strong reducing agent

  > LiAlH4

  > hydrogen gas and nickel catalyst
• Base strength of 1° ,2° ,3° Amines

  From primary to tertiary amines there are more alkyl groups which push electron density towards the N via the inductive effect making the lone pair of electrons more available therefore better at accepting protons and a stronger base