Carbon tetraiodide is a
tetrahalomethane Tetrahalomethanes are fully halogenated methane derivatives of general formula CBrkCllFmInAtp, where:k+l+m+n+p=4Tetrahalomethanes are on the border of inorganic and organic chemistry, thus they can be assigned both inorganic and organic names by IU ...
with the molecular formula CI
4. Being bright red, it is a relatively rare example of a highly colored
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
derivative
In mathematics, the derivative of a function of a real variable measures the sensitivity to change of the function value (output value) with respect to a change in its argument (input value). Derivatives are a fundamental tool of calculus. ...
. 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
In crystallography, the tetragonal crystal system is one of the 7 crystal systems. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a squar ...
crystal structure (''a'' 6.409, ''c'' 9.558 (.10
−1 nm)).
It has zero
dipole moment due to its symmetrically substituted
tetrahedral
In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the ...
geometry.
Properties, synthesis, uses
Carbon tetraiodide is slightly reactive towards water, giving
iodoform
Iodoform (also known as triiodomethane and, inaccurately, as carbon triiodide) is the organoiodine compound with the chemical formula C H I3. A pale yellow, crystalline, volatile substance, it has a penetrating and distinctive odor (in older ch ...
and I
2. It is soluble in nonpolar organic solvents. It decomposes thermally and photochemically to
tetraiodoethylene, C
2I
4. 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
Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to P Ph3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists ...
(PPh
3) and carbon tetraiodide. Alcohols are converted in and to iodide, by a mechanism similar to the
Appel reaction
The Appel reaction is an organic reaction that converts an alcohol into an alkyl chloride using triphenylphosphine and carbon tetrachloride. The use of carbon tetrabromide or bromine as a halide source will yield alkyl bromides, whereas using carbo ...
. 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