Diiodomethane or methylene iodide, commonly abbreviated "MI", is an organoiodine compound. Diiodomethane is a very dense 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 very high refractive index of 1.741, and a surface tension of 0.0508 N·m−1.Website of Krüss (8.10.2009)
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 for installing the CH2 group. In the Simmons–Smith reaction, it is a source of methylene.Two cyclopropanation reactions: , In fact the Simmons–Smith reaction does not produce free carbene but proceeds via Zn-CH2I intermediates.
Diiodomethane is also a source of the equivalent of . The synthesis of Fe2(CH2)(CO)8 illustrates this reactivity: Na2Fe2(CO)8 + CH2I2 → Fe2(CH2)(CO)8 + 2NaI
Solvent for NMR spectroscopy
Diiodomethane exhibits exceptional solvation properties toward halide-containing organometallic complexes. Examples include cis-[PdCl2(CNCH2Ph)2] (38 mg/mL), trans-[PtI2(NH2iPr)2] (21 mg/mL), [Pd(acac)2] (38 mg/mL), and [CuI2(CNXyl)4] (109 mg/mL). The effect is attributed to strong halogen bonding between the iodine atoms of the solvent and the halide ligands of some of these solutes.
Preparation Diiodomethane can be prepared from the widely available solvent dichloromethane by the action of sodium iodide in acetone in the Finkelstein reaction: CH2Cl2 + 2 NaI → CH2I2 + 2 NaCl
It can also be prepared by reducing iodoform with elemental phosphorus or sodium arsenite: CHI3 + Na3AsO3 + NaOH → CH2I2 + NaI + Na3AsO4
Safety Alkyl iodides are alkylating agents, which are potential mutagens.
References
External links Diiodomethane data sheet New particle formation from photooxidation of diiodomethane