Iodomethane



Iodomethane
IUPAC name Iodomethane
Other names Methyl iodide, Monoiodomethane, Methyl iodine, MeI, Halon 10001, UN 2644
Identifiers
CAS number 74-88-4
PubChem 6328
EINECS number 200-819-5
RTECS number PA9450000
SMILES CI
InChI InChI=1/CH3I/c1-2/h1H3
Properties
Molecular formula CH3I
Molar mass 141.94 g/mol
Appearance Clear colourless liquid with acrid odor
Density 2.2789 g/cm3 at 20 °C
Melting point

-66.45 °C (206.70 K)

Boiling point

42.43 °C (315.58 K)

Solubility in water 14 g/l at 20 °C
log P 1.51
Vapor pressure 50 kPa at 20 °C

53.32 at 25.3 °C 166.1 kPa at 55 °C

Hazards
EU classification Toxic (T), Carc. Cat. 3
NFPA 704
1
3
1
 
R-phrases R21, R23/25, R37/38, R40
S-phrases S45
Flash point -28 °C
Autoignition
temperature 		352 °C
Explosive limits 8.5 - 66%
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Iodomethane, commonly called methyl iodide and commonly abbreviated "MeI", is the methylation. It is naturally emitted by rice plantations in small amounts.[1]

Chemical properties

Methyl iodide is an excellent substrate for SN2 substitution reactions. It is carboxylic acids:[2]


In these examples, the K2CO3 or Li2CO3) removes the acidic proton to form the carboxylate or phenoxide anion, which serves as the nucleophile in the SN2 substitution.

Iodide is a oxygen atom or the (usually desired) carbon atom. With methyl iodide, C-alkylation nearly always predominates.

MeI is also an important precursor to methyl lithium.

In the hydrolysis. Most acetic acid is prepared by this method.

MeI hydrolyzes at 270 °C forming carbon dioxide.

Preparation

Iodomethane is formed via the phosphorus:[3]

5 H2O

The iodinating reagent is calcium carbonate:[3]

(CH3O)2SO2 + KI → K2SO4 + 2 CH3I

The CH3I can easily be purified by distillation followed by washing with Na2CO3.

Methyl iodide can be formed during nuclear accidents by the reaction of organic matter with the "fission iodine."

Choice of iodomethane as a methylating agent

Iodomethane is an excellent reagent for methylation, but there are some disadvantages to its use. It has a high equivalent weight: one mole of MeI weighs almost three times as much as one mole of methyl bromide), making it more awkward to work with than liquid MeI. Methyl chloride is a poorer methylating reagent than MeI, though it is often adequate.

Iodides are generally expensive relative to the more common chlorides and bromides, though iodomethane is reasonably affordable; on a commercial scale the toxic dimethyl sulfate is preferred, since it is both cheap and liquid. The iodide leaving group in MeI may cause side reactions, as it is a powerful nucleophile. Finally, being highly reactive, MeI is more dangerous for laboratory workers than related chlorides and bromides. When considering alternatives to MeI, it is necessary to consider cost, handling, risk, chemical selectivity, and ease of reaction work-up.

Uses

Besides use as a methylation agent, there have been proposals of its use as a fungicide, bromomethane (which was banned under the Montreal Protocol), and in microscopy due to properties related to refraction index. In a controversial October 2007 decision, the United States Environmental Protection Agency approved its use as a soil fumigant in some cases, although it cannot yet be used in California (a major potential market) due to lack of state approval.[4]

Biological effects

Iodomethane has LD50 for oral administration to rats 76 mg/kg and in the liver it undergoes rapid conversion to S-methylglutathione.[5]

Breathing iodomethane fumes can cause lung, liver, kidney and central nervous system damage. It causes nausea, dizziness, coughing and vomiting. Prolonged contact with skin causes burns. Massive inhalation causes pulmonary edema.

See also

Methylating reagents

References

  1. ^ K. R. Redeker, N.-Y. Wang, J. C. Low, A. McMillan, S. C. Tyler, and R. J. Cicerone (2000). "Emissions of Methyl Halides and Methane from Rice Paddies". Science 290: 966-969. doi:10.1126/science.290.5493.966.
  2. ^ Avila-Zárraga, J. G., Martínez, R. (January 2001). "Efficient methylation of carboxylic acids with potassium hydroxide/methyl sulfoxide and iodomethane". Synthetic Communications 31 (14): 2177 - 2183. doi:10.1081/SCC-100104469.
  3. ^ a b King, C. S.; Hartman, W. W. (1943). "Methyl Iodide". Org. Synth.; Coll. Vol. 2: 399. 
  4. ^ "EPA approves new pesticide despite scientists' concerns", Los Angeles Times, October 6, 2007. 
  5. ^ Johnson, M. K. (1966). "Metabolism of iodomethane in the rat". Biochem. J. 98: 38-43.
  • March, J. (1992). Advanced Organic Chemistry, 4th Edn., New York: Wiley. ISBN 0-471-60180-2. 
  • Sulikowski, G. A.; Sulikowski, M. M. (1999). in Coates, R.M.; Denmark, S. E. (Eds.) Handbook of Reagents for Organic Synthesis, Volume 1: Reagents, Auxiliaries and Catalysts for C-C Bond Formation New York: Wiley, pp. 423–26.
  • Bolt H. M., Gansewendt B. (1993). "Mechanisms of carcinogenicity of methyl halides.". Crit Rev Toxicol. 23 (3): 237-53.
 
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