3.11 amines

• What type of base are primary aliphatic amines?

  Brønsted-Lowry 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.
• Are primary aliphatic bases strong or weak?

  Weak as they only partially dissociate to produce a low conc of hydroxide ions.
• Is ammonia a good base?

  No it is a very weak base. Primary aliphatic amines are better as the alkyl groups are electron releasing and push electrons towards the nitrogen atom and so making the lone pair of electrons on the nitrogen more readily available.
• Are primary or secondary amines better base? Why?

  Secondary amines are stronger bases than primary amines because they have more alkyl groups that are substituted onto the N atom in place of H atoms. Therefore more electron density is pushed onto the N atom (as the inductive effect of alkyl groups is greater than that of H atoms).
• Are tertiary amines better bases than primary and secondary? Why?

  The tertiary amines and corresponding ammonium salts are less soluble in water and this makes them less strong bases than the secondary amines.
• Are aromatic amines good bases?

  No, 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.
• Order the amine derivatives in their order of weak to strong basic behaviour.

  Aromatic amines < ammonia < primary amines < tertiary amines < secondary amines
• amines react with acids to form?

  ammonium salts - ionic compounds that are water soluble. When water evaporates they will form crystals.
• What happens when you add NaOH to an ammonium salt?

  It will convert back into the amine
• What are ammonium salts used for?

  Ammonium salts aka cationic surfactants reduce the surface tension of liquids as the positive nitrogen is attracted toward negatively charged surfaces such as glass, hair, fibres and plastics. This helps in their uses as fabric softeners, hair conditioners and sewage flocculants.
• What are the two ways to turn make an amine from a haloalkane? Which is preferred and why?

  Nucleophilic substitution with an excess of ammonia dissolved in ethanol.

  
  

  Nucleophilic substitution from haloalkane to a nitrile with KCN in aqueous ethanol and heat under reflux. Then reduce this with either LiAlH4 or H2 with a nickel catalyst.

  
  

  The second step is preferred as the first method can have further substitutions which limits the yield of primary amine. However the second method could also have a reduced yield as it requires two steps and KCN is toxic.
• when reacting primary amines with haloalkanes what can be produced

  secondary, tertiary, and ammonium salts
• Give an equation for the reduction of nitrobenzene to form phenylamine. Use [H] to represent the reducing agent.

  C6H6NO2 + 6[H] = C6H5NH2 + 2H2O
• when reducing nitrobenzene to phenylamine why is an aqueou solution obtained?

  because it forms an ion and therefore an ionic salt which is soluble