Carbon tetraiodide

Stereo, skeletal formula of carbon tetraiodide

Names Preferred IUPAC name Identifiers 1733108 ChemSpider ECHA InfoCard 100.007.335 Edit this at Wikidata EC Number RTECS number UNII Properties CI₄ Molar mass 519.629 g·mol⁻¹ Appearance Dark violet crystals Density 4.32 g mL⁻¹ -136·10⁻⁶ cm³/mol Structure Tetragonal Tetrahedral 0 D Thermochemistry 0.500 J K⁻¹ g⁻¹ 384.0–400.4 kJ mol⁻¹ −794.4–−778.4 kJ mol⁻¹ Hazards Occupational safety and health (OHS/OSH): toxic GHS labelling: GHS07: Exclamation mark Warning H315, H319, H335 P261, P305+P351+P338 Related compounds Carbon tetrafluoride
Carbon tetrachloride
Carbon tetrabromide Silicon tetraiodide
Germanium tetraiodide
Tin(IV) iodide

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.

The tetrahedral molecule features C-I distances of 2.12 ± 0.02 Å.^[2] 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)).^[3]

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

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:^[4]

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.^[5] 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.

Manufacturers recommend that carbon tetraiodide be stored near 0 °C (32 °F). 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).

• Sorros H., Hinkam J. B. (1945). "The Redistribution Reaction. XI. Application to the Preparation of Carbon Tetraiodide and Related Halides". Journal of the American Chemical Society . 67 (10): 1643. Bibcode:1945JAChS..67.1642S. doi:10.1021/ja01226a004.