Iodine Monochloride in Acetic Acid Solution (WIJS)

Iodine monochloride is a reddish-brown interhalogen solution produced by combining iodine and chloride halogens in a 1:1 molar ratio. This can be expressed by the equation: I2 + Cl2 → 2 ICl.

As chlorine gas is injected into an iodine solution, one observes the brown color of iodine gradually turn to the amber color of iodine monochloride. If excess chlorine is injected, it will enter a reversible reaction, converting the iodine monochloride into iodine trichloride.

As a solid, iodine monochloride is soluble in Hydrofluoric and Hydrochloric acids, but reacts with pure water to form HCl and HI.

Iodine monochloride is a reagent with many uses in organic synthesis. It can be used as a source of electrophilic iodine in the synthesis of certain aromatic iodides. It also cleaves the bonds of C-Si. Iodine monochloride will also add to the double bond in alkenes yielding chloro-iodo alkanes.

The Wijs solution, iodine monochloride dissolved in acetic acid, is widely used to determine the iodine value of a substance. An ‘Iodine Value’ is a measure of the number of double bonds present in fats and oils. It can also be used to make pure iodates, by reacting with a chlorate and releasing chlorine gas as byproduct.