Diiodomethane
Diiodomethane or methylene iodide, commonly abbreviated “MI”, is an organoiodine compound. Diiodomethane is a colorless liquid; however, it decomposes upon exposure to light liberating iodine, which colours samples brownish. It is slightly soluble in water, but soluble in organic solvents. It has a relatively high refractive index of 1.741, and a surface tension of 0.0508 N·m−1.[3]
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| Names | |||
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| IUPAC name
Diiodomethane[1] | |||
| Identifiers | |||
3D model (JSmol) |
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| 1696892 | |||
| ChemSpider | |||
| ECHA InfoCard | 100.000.765  | ||
| EC Number |
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| MeSH | methylene+iodide | ||
PubChem CID |
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| RTECS number |
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| UNII | |||
CompTox Dashboard (EPA) |
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| Properties | |||
| CH2I2 | |||
| Molar mass | 267.836 g·mol−1 | ||
| Appearance | Colorless liquid | ||
| Density | 3.325 g mL−1 | ||
| Melting point | 5.4 to 6.2 °C; 41.6 to 43.1 °F; 278.5 to 279.3 K | ||
| Boiling point | 182.1 °C; 359.7 °F; 455.2 K | ||
| 1.24 g L−1 (at 20 °C)[2] | |||
Henry's law constant (kH) |
23 μmol Pa−1 kg−1 | ||
| -93.10·10−6 cm3/mol | |||
| Structure | |||
| Tetragonal | |||
| Tetrahedron | |||
| Thermochemistry | |||
Heat capacity (C) |
133.81 J K−1 mol−1 | ||
Std enthalpy of formation (ΔfH⦵298) |
67.7–69.3 kJ mol−1 | ||
Std enthalpy of combustion (ΔcH⦵298) |
−748.4–−747.2 kJ mol−1 | ||
| Hazards | |||
| Safety data sheet | hazard.com | ||
| GHS pictograms |   | ||
| GHS Signal word | Danger | ||
| H302, H315, H318, H335 | |||
| P261, P280, P305+351+338 | |||
| NFPA 704 (fire diamond) | |||
| Flash point | 110 °C (230 °F; 383 K) | ||
| Related compounds | |||
Related alkanes |
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Related compounds |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |||
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| Infobox references | |||
Uses
Because of its high density, diiodomethane is used in the determination of the density of mineral and other solid samples. It can also be used as an optical contact liquid, in conjunction with the gemmological refractometer, for determining the refractive index of certain gemstones. Diiodomethane is a reagent in the Simmons–Smith reaction, serving as a source of the free radical methylene (carbene), :CH
2.[4]
Preparation
Diiodomethane can be prepared from the widely available solvent dichloromethane by the action of sodium iodide in acetone in the Finkelstein reaction:[5]
- CH2Cl2 + 2 NaI → CH2I2 + 2 NaCl
It can also be prepared by reducing iodoform with elemental phosphorus[6] or sodium arsenite:[5]
- CHI3 + Na3AsO3 + NaOH → CH2I2 + NaI + Na3AsO4
Safety
Alkyl iodides are alkylating agents and contact should be avoided.
References
- "methylene iodide - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 26 March 2005. Identification ad Related Records. Retrieved 27 February 2012.
- http://www.surface-tension.de/LIQUIDS/Diiodomethane3.htm
- Website of Krüss Archived 2013-12-01 at the Wayback Machine (8.10.2009)
- Two cyclopropanation reactions: Smith, R. D.; Simmons, H. E. "Norcarane". Organic Syntheses.; Collective Volume, 5, p. 855, Ito, Y.; Fujii, S.; Nakatuska, M.; Kawamoto, F.; Saegusa, T. (1988). "One-Carbon Ring Expansion Of Cycloalkanones To Conjugated Cycloalkenones: 2-Cyclohepten-1-one". Organic Syntheses.; Collective Volume, 6, p. 327
- Roger Adams; C. S. Marvel (1941). "Methylene Iodide". Organic Syntheses.; Collective Volume, 1, p. 358
- Miller, William Allen (1880). Elements of Chemistry: Chemistry of carbon compounds (5th ed.). London: Longmans Green and Co. p. 154.