Carbon tetraiodide

Carbon tetraiodide is CI₄, a tetrahalomethane. Being bright red, it is a relatively rare example of a highly colored methane derivative. It is only 2% by weight carbon, although other methane derivatives are known with still less carbon.

The tetrahedral molecule features C-I distances of 2.12 ± 0.02 Å. ^[1] The molecule is slightly crowded with short I---I contacts of 3.459 ± 0.03 Å, and possibly for this reason, it is thermally and photochemically unstable. Hexaiodoethane is unknown, probably for the same reason.

Carbon tetraiodide crystallizes in monoclinic crystal structure (a 22.39, b 12.93, c 25.85 (.10^-1 nm), β 125.26°).

It has dipole moment of 0 Debyes due to its symmetrically substituted tetrahedral molecule.

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Properties, synthesis, uses

CI₄ is slightly reactive towards water, giving iodoform and I₂. Otherwise it is soluble in nonpolar organic solvents. It decomposes thermally and photochemically to tetraiodoethylene, I₂C=CI₂. Its synthesis entails AlCl₃-catalyzed halide exchange, which is conducted at room temperature:^[2]

CCl₄ + 4 EtI → CI₄ + 4 EtCl

The product crystallizes from the reaction solution.

CI₄ is used as an iodination reagent, often upon reaction with base. ^[3] Ketones are converted to 1,1-diiodoethenes upon treatment with PPh₃ and CI₄. 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 the chloride from alcohols.

Safety considerations

Manufacturers recommend that CI₄ be stored near 0 °C. As a ready source of iodine, it is an irritant. LD50: 178 mg.kg^–1. In general perhalogenated organic compounds should be considered toxic.

References

1. ^ Finbak, Chr.; Hassel, O. "Kristallstruktur und Molekülbau von CI₄ und CBr₄" Zeitschrift für Physikalische Chemie (1937), volume B36, page 301-8
2. ^ McArthur, R. E.; Simons, J. H., “Carbon Tetraiodide” Inorganic Syntheses 1950, volume III, 37–39
3. ^ P. R. Schreiner, A. A. Fokin, “Carbon Tetraiodide” in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2005; John Wiley & Sons, Ltd

Further reading

Sorros, H., Hinkam J. B. , “The Redistribution Reaction. XI. Application to the Preparation of Carbon Tetraiodide and Related Halides” Journal of the American Chemical Society 1945, 67, 1643. DOI.

See also

• Haloalkane
• Halomethane
• Iodomethane
• Diiodomethane
• Iodoform (Triiodomethane)
• Tetrafluoromethane
• Carbon tetrachloride (Tetrachloromethane)
• Tetrabromomethane