Iodoform Reaction (CIE AS Chemistry)

• Tri-iodomethane (also called iodoform) is a yellow precipitate 
• It is formed from the reaction of iodine in an alkaline solution with methyl ketones
  • Methyl ketones are compounds that have a CH₃CO-group
  • Ethanal also contains a CH₃CO- group and therefore also forms a yellow precipitate with iodoform

• The reagent is heated with an alkaline solution of iodine
• This reaction involves a halogenation and hydrolysis step
  • In the halogenation step, all three H-atoms in the -CH₃ (methyl) group are replaced with iodine atoms, forming a -CI₃ group
  • The intermediate compound is hydrolysed by an alkaline solution to form a sodium salt (RCO₂^- Na⁺) and a yellow precipitate of CHI₃

The iodoform reaction

The reaction of ethanal with iodoform results in the formation of a yellow CHI₃ precipitate