Amines

• Amines


  A class of organic compound of general formula: RNH2, where R is an alkyl or aryl group
• Amine structure


  • Similar to ammonia (NH3), with nitrogen sp3 hybridised
  • Bond angle larger than in ammonia due to greater Van der Waals repulsion
• Ammonia


  Trigonal bipyramidal, with nitrogen sp3 hybridised
• Amine nitrogen


  Also sp3 hybridised
• IUPAC nomenclature for amines


  • Select longest continuous carbon chain as root name
  • Change ending e in alkane to amine
  • Number position of amino group
  • Name other substituents in alphabetical order
• Aromatic and heterocyclic amines


  • Aniline
  • 3-ethylaniline
  • N,N-diethylaniline
  • 4-methylaniline
• Nitrogen heterocycles


  • Pyrrole
  • Pyrrolidine
  • 1-methylpyrrolidine
  • Imidazole
  • Indole
  • Pyridine
  • 2-methylpyridine
  • Piperidine
  • Indole
• Amine classification


  • Primary (RNH2)
  • Secondary (RNHR')
  • Tertiary (RNR'R'')
  • Quaternary (R4N+)
• Amine physical properties


  • Polar molecules with dipole moments
  • Hydrogen bond donors and acceptors
  • Tertiary amines have lower boiling points than primary/secondary
  • Amines soluble in alcohols and lower molecular weight ones in water
  • Characteristic fishy odour
• Amine basicity


  • Amines can act as nucleophiles and bases
  • Basicity expressed by basicity constant Kb
• Amine preparation from alkyl halides

  1. Alkyl halide reacts with NH3 to form quaternary ammonium salt

  2. Deprotonation yields amine
• Amine preparation from nitriles


  Reduction of nitriles using LiAlH4
• Amine preparation from Schiff bases and oximes


  Reduction with LiAlH4
• Reaction of aliphatic amines with acid chlorides

  Forms amides
• Reaction of amines to form diazonium compounds

  Primary amines react with cold nitrous acid
• Reactions of diazonium compounds


  Hydrolysis, Sandmeyer reaction, displacement by cyanide, displacement by hydrogen
• Amines as leaving groups

  Reaction with methyl iodide to form quaternary ammonium salts
• Hoffmann elimination


  Quaternary ammonium hydroxide heated to eliminate alkene
• Reactions of amines with aldehydes and ketones


  Form carbinolamines which dehydrate to Schiff bases