Carbon tetraiodide is a tetrahalomethane with the molecular formula . Being bright red, it is a relatively rare example of a highly colored methane derivative. It is only 2.3% by weight carbon, although other methane derivatives are known with still less carbon.
The tetrahedral molecule features CâÂÂI distances of 2.12 ñ 0.02 à. The molecule is slightly crowded with short contacts between iodine atoms of 3.459 ñ 0.03 à, and possibly for this reason, it is thermally and photochemically unstable.
Carbon tetraiodide crystallizes in tetragonal crystal structure (a 6.409, c 9.558 (.10<sup>âÂÂ1</sup> nm)).
It has zero dipole moment due to its symmetrically substituted tetrahedral geometry.
Carbon tetraiodide is slightly reactive towards water, giving iodoform and I<sub>2</sub>. It is soluble in nonpolar organic solvents. It decomposes thermally and photochemically to , C<sub>2</sub>I<sub>4</sub>. Its synthesis entails AlCl<sub>3</sub>-catalyzed halide exchange, which is conducted at room temperature:
The product crystallizes from the reaction solution.
Carbon tetraiodide is used as an iodination reagent, often upon reaction with bases. Ketones are converted to 1,1-diiodoalkenes upon treatment with triphenylphosphine (PPh<sub>3</sub>) and carbon tetraiodide. Alcohols are converted in and to iodide, by a mechanism similar to the Appel reaction. In an Appel reaction, carbon tetrachloride is used to generate alkyl chlorides from alcohols.
Manufacturers recommend that carbon tetraiodide be stored near . As a ready source of iodine, it is an irritant. Its LD<sub>50</sub> on rats is 18 mg/kg. In general, organic compounds should be considered toxic, with the narrow exception of small perfluoroalkanes (essentially inert due to the strength of the CâÂÂF bond).