Amines

• Primary aliphatic amines act as Bronsted-Lowry Bases because the lone pair of electrons on the nitrogen is readily available for forming a dative covalent bond with a H+ and so accepting a proton.
• Primary aliphatic amines are stronger bases than ammonia as the alkyl groups are electron releasing and push electrons towards the nitrogen atom and so make it a stronger base.
• Primary aromatic amines such as phenylamine do not form basic solutions because the lone pair of electrons on the nitrogen delocalise with the ring of electrons in the benzene ring. This means the N is less able to accept protons.
• Amines as bases react with acids to form ammonium salts.
• Addition of NaOH to an ammonium salt will convert it back to the amine
• Ammonium salts (ionic) will be solid crystals, if the water is evaporated, because of the strong ionic interactions.
• Primary amines can be formed by the nucleophilic substitution reaction between haloalkanes and ammonia.
• Reaction with ammonia forming primary amine;

  Haloalkane +ammonia --> primary amine

  CH3CH2Br + 2NH3 ---> CH3CH2NH2 + NH4Br
• Reaction with ammonia forming primary amine:

  • Excess ammonia dissolved in ethanol is the reagent
  • In the first step of the mechanism the nucleophile attacks the haloalkane to form an intermediate.
  • In the second step of the mechanism a second ammonia removes a proton from the intermediate (acts as base) to form the amine.
• Using an excess of ammonia can limit further substitution reactions and will maximise the amount of primary amine formed
• Amines will react with haloalkanes in the same nucleophilic substitution reactions that ammonia does.
• A primary amine will react with a haloalkane to form a secondary amine
• Reacting secondary amines with haloalkanes form a tertiary amine
• Reducing nitroarenes to aromatic amines

  Reagent: Sn and concentrated HCl

  Conditions: Heating

  Mechanism: reduction
• Sodium hydroxide solution is added to the product of the first stage of the reaction.