Amines

• Draw the structures of primary, secondary and tertiary amines and a quartenary ammonium ion.

  A) ammonia

  B) primary

  C) secondary

  D) tertiary

  E) quarternary ammonium ion

  
• How do you name amines?

  -amine or amino-
• Why are amines so reactive?

  The lone pair of electrons on the Nitrogen - due to polar N-H bond
• What shape are amines around the N? Bond angle?

  Trigonal pyramidal, 107 degrees due to lone pair on N
• What kind of intermolecular forces do they have?

  Hydrogen bonding due to polar N-H bond and lone pair of electrons on N atom
• Do amines have intermolecular forces which are stronger than or weaker than alcohols? Why?

  Weaker, as N has a lower electronegativity than O -> weaker hydrogen bonding
• How can / when do amines act as bases?

  The lone pair on the nitrogen atom accepts a proton
• How can / when do amines act as nucleophiles?

  When they bond with an electron-deficient C atom (donate lone pair from N)
• Draw a mechanism for the basic action of an amine with water.

  A) NH3+

  B) OH-

  
• What is the product from the basic action of an amine with water?

  RNH3+ - ammonium ion, which forms a salt with an anion
• Write an equation for methylamine reacting with HCl.

  CH3NH2 + HCl -> CH3NH3+Cl-

  methylamine + hydrochloric acid -> methylammonium chloride
• In order to be the strongest base, what must a particular amine have (out of a setof amines)?

  Greatest electron density around the N atom, making it a better electron pair donor (attracts protons more)
• What affect do alkyl groups have on electron density and base strength?

  Positive inductive effect - increase electron density around N -> stronger base
• Place the following in order of base strength (in general): NH3, primary amine, secondary amine, phenylamine.

  secondary amine > primary amine > NH3 > phenylamine
• Draw a mechanism for the nucleophilic substitution of NH3 with RCH2Br to form primary amines.

  A) NH3

  B) NH3+

  
• How can primary amines then form secondary, tertiary amines and quartenary ammonium ions?

  Multiple substitutions; primary amine is a nucleophile that attacks the original haloalkane
• What are the problems with this method?

  Not efficient as low yield of primary amine due to multiple substitutions
• How would you maximise the yield of the primary amine?

  Use excess ammonia
• What type of mechanism is the reaction of a haloalkane with a cyanide ion?

  Nucleophilic substitution
• What conditions does this reaction (haloalkane + cyanide ion) require? What is the product formed?

  • Ethanol as a solvent
  • A nitrile is formed
• How do you get from a nitrile to a primary amine? (name of reaction type and reagents/catalysts).

  Reduction using hydrogen / nickel catalyst
• Why is this a purer method of synthesisng amines?

  Only the primary amine can be formed
• What conditions are needed to form nitrobenzene from benzene?

  Concentrated H2SO4 and HNO3 to form the NO2+ ion for electrophilic attack
• How do you form an ammonium chloride salt from nitrobenzene? What conditions are needed?

  Reduce the nitrile using tin / HCl -> forms an ammonium salt with Cl- ions

  Room temperature
• Equation for the reaction of nitrobenzene -> phenylamine.

  C6H5NO2 + 6[H] -> C6H5NH2 + 2H2O
• What mechanism is used for forming amides from acyl chlorides and amines?

  Nucleophilic addition/elimination
• Draw a mechanism for the reaction of ethanoyl chloride with ethanamine.

  A) slightly positive

  B) slightly negative

  C) slightly negative

  D) O-