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.

Quick Facts Names, Identifiers ...

Carbon tetraiodide

Carbon tetraiodide crystals (left) Solution in Et2O (right)
Names
Preferred IUPAC name Tetraiodomethane[1]
Identifiers
CAS Number	507-25-5 Y
3D model (JSmol)	Interactive image
Beilstein Reference	1733108
ChemSpider	10055 Y
ECHA InfoCard	100.007.335
EC Number	208-068-5
PubChem CID	10487
RTECS number	FG4960000
UNII	E22GNX36ZQ Y
CompTox Dashboard (EPA)	DTXSID0060145
InChI InChI=1S/CI4/c2-1(3,4)5 Y Key: JOHCVVJGGSABQY-UHFFFAOYSA-N Y
SMILES IC(I)(I)I
Properties
Chemical formula	CI4
Molar mass	519.629 g·mol−1
Appearance	Dark violet crystals
Density	4.32 g mL−1
Magnetic susceptibility (χ)	-136·10−6 cm3/mol
Structure
Crystal structure	Tetragonal
Molecular shape	Tetrahedral
Dipole moment	0 D
Thermochemistry
Heat capacity (C)	0.500 J K−1 g−1
Std enthalpy of formation (ΔfH⦵298)	384.0–400.4 kJ mol−1
Std enthalpy of combustion (ΔcH⦵298)	−794.4–−778.4 kJ mol−1
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	toxic
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H315, H319, H335
Precautionary statements	P261, P305+P351+P338
Related compounds
Other anions	Carbon tetrafluoride Carbon tetrachloride Carbon tetrabromide
Other cations	Silicon tetraiodide Germanium tetraiodide Tin(IV) iodide
Related alkanes	Methane Methyl iodide Diiodomethane Iodoform Ethane Ethyl iodide
Related compounds	Pimagedine Guanidine
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

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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]

${\displaystyle {\ce {CCl4 + 4 EtI -> CI4 + 4 EtCl}}}$

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).