3.11 Amines

• Primary aliphatic amines can be prepared by the reaction of ammonia with halogenoalkanes and by the reduction of nitriles.
• Aromatic amines, prepared by the reduction of nitro compounds, are used in the manufacture of dyes.
• • Amines are weak bases.
  • The difference in base strength between ammonia, primary aliphatic and primary aromatic amines.
  • Students should be able to: • explain the difference in base strength in terms of the availability of the lone pair of electrons on the N atom.
• Primary aromatic amines are weakest base because (3 marks)

  • Lone or electron pair on N
  • Delocalised or spread into ring in U
  • Less available to accept protons or less able to donate to H+
• Primary aliphatic amines are strongest bases because

  • Positive inductive effect - R group increases electron density / donates electrons / pushes electrons / has positive inductive effect
  • LONE PAIR! on N
• Ammonia and methylamine - Give a method to distinguish these solutions and give its observation [2 marks]

  • Use a pH meter
  • Methylamine would have a higher pH

  Explain:

  • Because of positive inductive effect / alkyl groups pushing electrons / electrons releasing / donating
  • Lone pair on N more easily given out
  • So gives out e- more easily
  • = stronger base
  • = Higher pH
• The use of quaternary ammonium salts as cationic surfactants.

  • Bactericide
  • Detergent
  • Fabric softener / conditioner
  • Hair conditioner
• Give a use of amine

  • MAKING dyes (in specification)
  • MAKING quaternary ammonium salts
  • MAKING cationic surfactants
  • MAKING (All the uses of cationic surfactants)
• The reduction of nitro compounds

  • Reducing agent: Sn (Tin) and HCl