Amines

• functional group NH2
• 4 types:

  • primary
  • secondary
  • tertiary
  • quaternary
• quaternary ammonium salts are used for:

  • shampoo
  • laundry detergent
  • washing up liquid
• how quaternary ammonium salts clean oil:

  • water and oil don't mix
  • the non polar tail is attracted to the oil
  • the polar head is attracted to the water
  • this allows the water and oil to mix , it traps the oil between the cationic surfactants and removes the grease
• what determines the strength of the base?

  • availability of the lone pair
  • higher electron density, lone pair is more readily available
  • electron density is dependant on the type of group attached to the nitrogen
• how amines act as a base:

  • lone pair of electrons allows them to accept a proton
  • a proton bonds to an amine via a dative covalent bond - both electrons in the bond are provided by the lone pair on the nitrogen.
• weakest to strongest amine bases:

  weakest - aromatic amine

  middle - ammonia

  strongest - primary amines
• aromatic amines are the weakest base:

  • electrons are delocalised into the benzene ring
  • decreases electron density on nitrogen
  • the lone pair on nitrogen is less available
• alkyl groups increase the strength of a base:

  • release electrons onto the nitrogen
  • electron density of nitrogen increases
  • lone pair is more available
• amines can be made in two ways:

  • reacting haloalkanes with excess ammonia
  • reducing a nitrile
• disadvantage of nucleophilic substitution when making an amine:

  • the primary amine produced is a nucleophile as it has a lone pair
  • therefore it keeps reacting with the haloalkane until a quaternary ammonium salt is formed
  • to stop this, a large excess of ammonia used
• nucleophilic substitution to make amines:

  • excess ammonia
  • heat under reflux
  • high pressure
• reduction of a nitrile to make ammonia:

  • formation of a nitrile from a haloalkane
  • reduction of nitrile with lithium aluminium hydroxide (LiAlH4) in ether
  • R-CN + 4[H] -----> R-CH2-NH2
  • this can also be done with a nickel catalyst and heat:
  • R-CN + 2H2 -----> R-CH2-NH2
• • amines react with acyl chlorides and anhydrides to produce an amide and a molecule of HCl or a carboxylic acid
  • a second molecule of the amine reacts with the HCl/carboxylic acid to form a salt
• amines react with acids and acid derivatives to form salts
• preparation of aromatic amines:

  • reduction of nitrogen compounds
  • nitrobenzene is heated under reflux with tin and conc HCl to form an ammonium salt
  • NaOH is added to the ammonium salt to give the amine
  • nitrobenzene + 6[H] -----> phenylamine + 2H2O
• quaternary ammonium salt example:

  • hydrocarbon tail is called cationic surfactant

  A) polar head

  B) non-polar hydrocarbon tail

  
• amide structure:

  A) R group

  B)

  C) NH2

  D)

  
• non aromatic amines are called aliphatic amines
• it is cheaper to use catalytic hydrogenation (nickel catalyst + H2) to make an amine than using LiAlH4 in ether
• LiAlH4 is a strong reducing agent
• aromatic amines are used to make dyes and pharmaceuticals
• justify the statement that it is better to prepare primary amines from nitriles than from haloalkanes

  • with haloalkanes the product is a nucleophile so further reactions occur
  • with nitriles there is no further reaction