Amines

Physical properties

• boiling point

  • increases with molecular mass

  • amines have higher boiling points than corresponding alkanes because of their intermolecular hydrogen bonding

• solubility

  • lower mass compounds are soluble in water due to hydrogen bonding

  • solubility decreases as the molecule gets heavier

  • soluble in organic solvents

Amines as bases

• amines behave as bases in their chemical reactions as the lone pair of electrons on the nitrogen atom can accept a proton

• when an amine accepts a proton a dative covalent bond is formed between the lone pair of electrons on the nitrogen and the proton

• neutralise acids to make salts

Aliphatic amines

• nucleophilic substitution of halogenoalkanes

• conditions

  • ethanol as solvent

    • prevents H2O being substituted instead to make alcohols

  • warm gently

  • NH3 in excess

    • reduces further substitution of the amine group

• forms in two stages

  • salt

  • amine

Formation of primary amines

• ammonia has a lone pair of electrons on the nitrogen

• allows ammonia to act as a nucleophile in a substitution reaction with a haloalkane

• produces ammonium salt

• aqueous alkali is then added to generate amine from salt

Formation of aromatic amines

• reduction of nitrobenzene

• heated under reflux with tin and hydrochloric acid

• forms ammonium salt then reacted with excess NaOH

• produces phenylamine

• tin and hydrochloric acid act as reducing agent