Carbon Tetraiodide, CI₄

Carbon Tetraiodide, CI₄, results from the interchange of chlorine and iodine when carbon tetrachloride reacts with aluminium or boron iodide. It may be prepared by dropping a solution of the tetrachloride in carbon bisulphide on to aluminium iodide at 0° C.:

3CCl₄ + 4AlI₃ = 4AlCl₃ + 3CI₄.

Lantenois prepares this compound by heating lithium iodide with excess of carbon tetrachloride in a vacuum in a sealed tube at 90°-92° C. for five days. The best solvents for carbon tetraiodide are benzene, acetone, and carbon disulphide. It crystallises in dark red, regular octahedra, having a density of 4.32. When exposed to air it begins to decompose, producing carbon dioxide and iodine; it has no melting-point, but from 50° C. onwards decomposes into its elements. Carbon tetraiodide is attacked by hydrogen at 100° C., the chief product being iodoform; alcoholic potassium hydroxide at 30°-40° C. also produces iodoform. Oxygen forms carbonyl iodide with liberation of iodine even in the dark. Carbon tetraiodide is estimated by means of its reaction with 20 per cent, silver nitrate solution, carbon monoxide and dioxide being evolved in the proportion of 3 to 1 by volume.