amines

• CH3NH2 +H2O ⇌ CH3NH3+ +OH-


  Primary aliphatic amine reaction with water
• NH3 (aq) +H2O (l) ⇌ NH4+ (aq) +OH- (aq)

  Ammonia reaction with water
• 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
  • They are weak bases as only a low concentration of hydroxide ions is produced
• Primary aliphatic amines


  • Stronger bases than ammonia 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
• Primary aromatic amines


  • Do not form basic solutions because the lone pair of electrons on the nitrogen delocalise with the ring of electrons in the benzene ring, making the N less able to accept protons
• Amines as bases

  React with acids to form ammonium salts
• Addition of NaOH to an ammonium salt


  Converts it back to the amine
• Ionic salts formed


  Compounds are soluble in the acid
• Secondary amines


  • Stronger bases than primary amines because they have more alkyl groups that are substituted onto the N atom in place of H atoms, pushing more electron density onto the N atom
• Tertiary amines


  • Less strong bases than secondary amines because the tertiary amines and corresponding ammonium salts are less soluble in water
• Order of base strength

  • Aromatic amines < ammonia< primary amines< tertiary amines< secondary amines
• Forming a primary amine in a one step reaction of halogenoalkanes with ammonia


  1. Ammonia dissolved in ethanol is the initial nucleophile

  2. In the first step, the nucleophile attacks the halogenoalkane to form an intermediate

  3. In the second step, a second ammonia removes a proton from the intermediate (acts as base) to form the amine
• Reaction forming a secondary amine

  1. The primary amine formed has a lone pair of electrons on the nitrogen and will react further with the halogenoalkane

  2. Either ammonia or the amine can remove a proton from the intermediate (acts as base) to form the amine
• Reaction forming a tertiary amine

  The same reaction mechanism occurs with the secondary amine reacting to form a tertiary amine
• Reaction forming a quaternary ammonium salt

  1. Only the first step of the mechanism occurs when forming the quaternary salt

  2. Using an excess of the halogenoalkane will promote the formation of the quaternary salt
• Quaternary ammonium salts


  Can be used as cationic surfactants, as the positive nitrogen is attracted toward negatively charged surfaces such as glass, hair, fibres and plastics
• Using a large excess of ammonia will maximise the amount of primary amine formed
• Using an excess of the halogenoalkane will promote the formation of the quaternary salt
• Preparing amines from nitriles in a 2 step reaction


  1. Step 1: Convert halogenoalkane to nitrile by using KCN in aqueous ethanol (heat under reflux)

  2. Step 2: Reduce nitrile to amine by using LiAlH4 in ether or by reducing with H2 using a Ni catalyst
• Reducing nitroaromatics to aromatic amines

  1. Reagent: Sn and HCl or Fe and HCl

  2. Conditions: Heating

  3. Mechanism: Reduction
• The ionic salt C6H5NH3+Cl- will be formed, which can be reacted with NaOH to give phenylamine
• Catalytic hydrogenation (H2 using a Ni catalyst) can also be used to reduce nitroaromatics to aromatic amines
• Reaction of aliphatic amines and phenylamine with acyl chlorides and acid anhydrides

  Forms amides in a nucleophilic addition-elimination reaction