Diiodomethane

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Diiodomethane

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Template:Longitem	1696892
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MeSH	methylene+iodide
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Template:Longitem	Template:Chembox Elements/molecular formula
Molar mass	Template:Chem molar mass
Appearance	Colorless liquid
Density	3.325 g mL−1 (3325 kg/m3)
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Template:Longitem	23 μmol Pa−1 kg−1
Template:Longitem	−93.10·10−6 cm3/mol
Template:Longitem	Tetragonal
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Template:Longitem	133.81 J K−1 mol−1
Template:Longitem	67.7–69.3 kJ mol−1
Template:Longitem	−748.4 to −747.2 kJ mol−1
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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.

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. 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 Template:Chem2. The synthesis of Fe₂(CH₂)(CO)₈ illustrates this reactivity:

Na₂Fe₂(CO)₈ + CH₂I₂ → Fe₂(CH₂)(CO)₈ + 2NaI

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.

External links

• Diiodomethane data sheet
• New particle formation from photooxidation of diiodomethane