Iodine trichloride
Iodine trichloride is an interhalogen compound of iodine and chlorine. It is bright yellow but with time and upon exposure to light it turns red due to decomposition with formation of elemental iodine. In the solid state is present as a planar dimer I2Cl6, with two bridging Cl atoms.
It can be prepared by reacting iodine with an excess of liquid chlorine at −70 °C, or heating a mixture of liquid iodine and chlorine gas to 105 °C. In the molten state it is conductive, which may indicate disproportionation into ions:
It is an oxidizing agent, capable of causing fire on contact with organic materials. That oxidizing power also makes it a useful catalyst for organic chlorination reactions.
Iodine trichloride reacts with concentrated hydrochloric acid, forming tetrachloroiodic acid: