3.11 Amines

• What are amines?


  Nitrogen containing organic compounds derived from ammonia where one or more of the hydrogen atoms has been replaced by another group.
• What is a primary amine?

  An ammonia molecule with one of the hydrogen atoms replaced by an alkyl or aryl group
• What is a secondary amine?

  An ammonia molecule with two of the hydrogen atoms replaced
• What is a tertiary amine?

  An ammonia molecules with three of the the hydrogen atoms replaced
• What is the name of a molecule where the lone pair on the tertiary amine is used for bonding?

  Quaternary ammonium salt
• What are the two ways of preparing aliphatic amines?

  -nucleophilic substitution of a halogenoalkane

  -reduction from a nitrile
• What are the conditions for nucleophilic substitution of halogenoalkanes?

  Excess ammonia (dissolved in ethanol to stop water protonating the NH3) and warmed in a sealed vessel
• Why use excess ammonia?

  Ensures the main product is primary amine however a mixture of primary, secondary and tertiary amines as well as quaternary salts are produced
• Why are a mixture of amines produced during nucleophilic substitution?


  Primary amine produced can act as a nucleophile to form a secondary amines and so on (further substitution)
• What is used to reduce a nitrile?


  Strong reducing agent such as LiAlH4 and dry ether followed by addition of DILUTE acid at room temperature
• Give a general equation to show the reduction of a nitrile.


  R-CN + 4[H] -> R-CH2NH2
• What difference is there to the carbon chain when producing a nitrile?

  Carbon chain increases by one more carbon than the substituted haloalkane
• Why is reduction of a nitrile favoured to nucleophilic substitution?


  Only produces a primary amine compared to a mixture of amines
• What are aromatic amines used in?


  The manufacture of dyes and therefore are important organic reagents
• Why can't aromatic amines be produced from nucleophilic substitution?

  The electron dense ring repels the lone pair on the nucleophile
• How are aromatic amines prepared?

  Reduction of nitrobenzene using Sn and concentrated HCl under reflux which produces C6H5NH3+Cl- salt
• How is the aromatic amine then released? Give an equation

  Adding NaOH

  C6H5NH3+Cl- + NaOH -> C6H5NH2 + H2O + NaCl
• Give an overall equation for the preparation of aromatic amines.


  C6H5NO2 + 6[H] -> C6H5NH2 + 2H2O
• What are bases?


  Proton acceptors
• Why are amines and ammonia Brønsted-Lowry bases?

  They have a lone pair that can be used to accept a proton
• What does the strength of the base depend on?

  The availability of the lone pair on the nitrogen atom which depends on the electron density of the nitrogen
• Why are aliphatic amines stronger bases?

  Alkyl groups are electron repelling, pushing the electrons towards the nitrogen atom in the amine known as the inductive effect. As a result the lone pair is more available for bonding and therefore a stronger base.
• Why are tertiary amines stronger bases then primary amines?

  More alkyl groups bonded to the nitrogen = more inductive effect = more available lone pair = stronger base
• Why are aryl groups weaker bases?

  Aryl groups causes the lone pair on the nitrogen atom to be delocalised into the benzene ring making it less available for bonding and therefore a weaker base
• What is the relative base strength of amines from strongest to weakest?

  Tertiary amine -> secondary amine -> primary amine -> ammonia -> phenyl amine
• What are the nucleophilic properties of amines?


  Can act as nucleophile and therefore can react with halogenoalkanes during nucleophilic substitution
• What are quaternary ammonium salts used for?

  Surfactants (added to liquid to reduce surface tension) such as hair and fabrics etc and Alison known as canonic surfactants
• What other mechanism can amines be used in?

  Nucleophilic addition-elimination