Iodoform is obtained by the action of iodine on ethanol (ethyl alcohol), or on propanone (acetone) in the presence of an alkali. This reaction is called haloform reaction, and is commonly known as iodoform test.

• When ethanol is warmed (60°C) with iodine in the presence of an alkali (NaOH, or Na₂CO₃z), iodoform is obtained.

  Step 1:

  NaOH + I₂ NaI + H₂O

  Step 2: Oxidation of ethanol to ethanal (acetaldehyde).

  

  Step 3:Ethanal so formed undergoes iodination.

  

  Step 4: Hydrolysis (cleavage) of Cl₃CHO by alkali.

  Cl₃CHO + NaOH + HCOONa

  Net reaction:

  + HCOONa + 2NaI + 5H₂O + HCOONa + 2NaI + 5H₂O

• Iodoform can also be prepared by warming acetone with iodine in the presence of an alkali. The reactions are

  Step 1:

  2NaOH + I₂ NaOI + NaI + H₂O

  Step 2:Iodination of acetone.

  CH₃.CO.CH₃ + 3NaOI + 3NaOH

  Step 3:Hydrolysis (cleavage) of Cl₃.CO.CH₃ by alkali.

  

  Net reaction:

  

  The reactions for the preparation of iodoform when Na₂CO₃ is used in place of NaOH are as follows:

• when ethanol is used:

  

• when propanone (acetone) is used:

  

• Iodoform is a yellow crystalline solid (hexagonal plates) with characteristic unpleasant odor. It melts at 392 K, (119°C).
• Iodoform is insoluble in water, but soluble in alcohol, chloroform and ether.
• It has antiseptic properties which is due to the liberation of iodine from it.

Iodoform shows chemical behavior similar to that of chloroform, but it is less stable. Some of the typical reactions given by iodoform are:

• Stability.
  On heating, iodoform decomposes to give iodine vapor. Due to the liberation of free iodine iodoform shows antiseptic action. Moisture, air and light also cause the decomposition of iodoform.
• Hydrolysis.
  
  On boiling with alcoholic sodium hydroxide, iodoform gives sodium formate.
  
• Heating with silver powder.
  
  When heated with Ag powder, iodoform gives ethyne (acetylene).
  
• With primary amines:
  
  Carbylamine reaction. Iodoform when heated with a primary amine and alcoholic potash, gives an offensive smelling compound known as carbylamine.
  
• With silver nitrate
  
  Iodoform gives yellow colored precipitate of AgI when heated with alcoholic silver nitrate.

Iodoform is used as an antiseptic. Its antiseptic property is due to the liberated iodine. However, due to its unpleasant smell, it has been replaced by other formulations containing iodine. It is used in the manufacture of certain pharmaceuticals.