CIE AS Chemistry (9701) 2019-2021

Revision Notes

3.5.4 Iodoform Reaction

Iodoform Reaction

  • Tri-iodomethane (also called iodoform) forms a yellow precipitate 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

Carbonyl Compounds Iodoform Test, downloadable AS & A Level Chemistry revision notes

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

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