Carbon tetraiodide

Carbon tetraiodide is $CI 4$ , 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.^[2] 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 tetragonal crystal structure (a 6.409, c 9.558 (.10⁻¹ nm)).^[3]

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

Properties, synthesis, uses

$CI 4$ is slightly reactive towards water, giving iodoform and $I 2$ . Otherwise it is soluble in nonpolar organic solvents. It decomposes thermally and photochemically to tetraiodoethylene, $I 2 C=CI 2$ . Its synthesis entails $AlCl 3$ -catalyzed halide exchange, which is conducted at room temperature:^[4]

CCl 4 + 4 EtI \to CI 4 + 4 EtCl

The product crystallizes from the reaction solution.

$CI 4$ is used as an iodination reagent, often upon reaction with bases.^[5] Ketones are converted to 1,1-diiodoethenes upon treatment with $PPh 3$ and $CI 4$ . 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 $CI 4$ be stored near 0 °C (32 °F). As a ready source of iodine, it is an irritant. LD50: 178 mg.kg⁻¹. 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

↑ "Tetraiodomethane - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 27 March 2005. Identification and Related Records. Retrieved 29 February 2012.
↑ Finbak, Chr.; Hassel, O. "Kristallstruktur und Molekülbau von $CI 4$ und $CBr 4$ " Zeitschrift für Physikalische Chemie (1937), volume B36, page 301-8
↑ Pohl, S. "Die Kristallstruktur von $CI 4$ " Zeitschrift für Kristallographie (1982), volume 159, page 211-216 http://www.oldenbourg-link.com/doi/abs/10.1524/zkri.1982.159.1-4.211[]
↑ McArthur, R. E.; Simons, J. H., “Carbon Tetraiodide” Inorganic Syntheses 1950, volume III, 37–39
↑ P. R. Schreiner, A. A. Fokin, “Carbon Tetraiodide” in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2005; John Wiley & Sons, Ltd

Halomethanes

Monosubstituted	CH₃F CH₃Cl CH₃Br CH₃I

Disubstituted	CH₂F₂ CH₂ClF CH₂BrF CH₂FI CH₂Cl₂ CH₂BrCl CH₂ClI CH₂Br₂ CH₂BrI CH₂I₂

Trisubstituted	CHF₃ CHClF₂ CHBrF₂ CHF₂I CHCl₂F CHBrClF CHClFI CHBr₂F CHBrFI CHFI₂ CHCl₃ CHBrCl₂ CHCl₂I CHBr₂Cl CHBrClI CHClI₂ CHBr₃ CHBr₂I CHBrI₂ CHI₃

Tetrasubstituted	CF₄ CClF₃ CBrF₃ CF₃I CCl₂F₂ CBrClF₂ CClF₂I CBr₂F₂ CBrF₂I CF₂I₂ CCl₃F CBrCl₂F CCl₂FI CBr₂ClF C*BrClFI CClFI₂ CBr₃F CBr₂FI CBrFI₂ CFI₃ CCl₄ CBrCl₃ CCl₃I CBr₂Cl₂ CBrCl₂I CCl₂I₂ CBr₃Cl CBr₂ClI CBrClI₂ CClI₃ CBr₄ CBr₃I CBr₂I₂ CBrI₃ CI₄

* Chiral compound.

Inorganic compounds of carbon and related ions

Compounds	CBr₄ CCl₄ CF CF₄ CI₄ CO CO₂ CO₃ COS CS CS₂ CSe₂ C₃O₂ C₃S₂ SiC

Carbon ions	Carbides [:C≡C:]^2–, [::C::]^4–, [:C=C=C:]^4– Cyanides [:C≡N:]^– Cyanates [:O-C≡N:]^– Thiocyanates [:S-C≡N:]^– Fulminates [:C≡N-O:]^– Thiofulminates [:C≡N-S:]^–

Oxides and related	Oxides Metal carbonyls Carbonic acid Bicarbonates Carbonates

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Carbon tetraiodide

Properties, synthesis, uses

Safety considerations

References

Further reading