Potassium Iodide

Potassium Iodide is known as Potassium Salt of Hydriodic Acid [HI], available in white crystalline powder form. It is an inorganic compound and has Molecular Formula KI. Its Ionic form is K⁺ I^-, and iodide ion being mild reducing agent, it can be easily oxidized to Iodine by powerful oxidizing agent like chlorine. With elemental iodine it forms I₃ (tri iodide), the salts of tri iodide are highly water soluble. On long exposure to air Potassium Iodide becomes yellow due to liberation of Iodine.
Potassium Iodide is more readily soluble in water. The solubility in water increases with the increase in temperature ie. (140 gms. /100 ml @ 20°c, 206 gms/ 100 ml @ 100°c). It is slightly soluble in ether, ammonia. It absorbs water less readily than Sodium Iodide and hence convenient to use. It is produced industrially by treating Iodine with Potassium Hydroxide. It can also be prepared by the action of Potassium Bicarbonate on Hydriodic acid.
It finds its applications mainly in organic synthesis for the preparation of Aryl iodides [Sandmeyer Reaction] from Aryl amine. Aryl amines are first diazotized by the action of Nitrous acid to obtain Arene diazonium salts which are then iodinated by using Potassium iodide to obtain Aryl Iodide.
It is used as a key raw material in the synthesis of Iodo alkanes such as Methyl iodide and also in the preparation of Silver Iodide which is used in Photography for high speed photographic films.
Other applications include : Preparation of Potassium Iodate which is obtained by the oxidation of Potassium Iodide with Potassium chlorate or Potassium bromate. It is useful in the treatment of radiation poisoning resulting from nuclear accidents and also as a nutritional supplement for iodine in poultry feeds.