tetraiodomethane

Carbon tetraiodide is a tetrahalomethane with the molecular formula CI₄. 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.

Structure

The tetrahedral molecule features C-I distances of 2.12 ± 0.02 Å. The molecule is slightly crowded with short contacts between iodine atoms of 3.459 ± 0.03 Å, and possibly for this reason, it is thermally and photochemically unstable.

Carbon tetraiodide crystallizes in tetragonal crystal structure (''a'' 6.409, ''c'' 9.558 (.10⁻¹ nm)).

It has zero dipole moment due to its symmetrically substituted tetrahedral geometry.

Properties, synthesis, uses

Carbon tetraiodide is slightly reactive towards water, giving iodoform and I₂. It is soluble in nonpolar organic solvents. It decomposes thermally and photochemically to tetraiodoethylene, C₂I₄. Its synthesis entails AlCl₃-catalyzed halide exchange, which is conducted at room temperature:

:CCl4 + 4 EtI -> CI4 + 4 EtCl
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 (PPh₃) 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.

Safety considerations

Manufacturers recommend that carbon tetraiodide be stored near . As a ready source of iodine, it is an irritant. Its LD₅₀ on rats is 18 mg/kg. In general, perhalogenated organic compounds should be considered toxic, with the narrow exception of small perfluoroalkanes (essentially inert due to the strength of the C-F bond).

References

Further reading

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{{Iodides

Inorganic carbon compounds
Nonmetal halides
Iodoalkanes
Halomethanes
Reagents for organic chemistry