Diiodomethane or methylene iodide, commonly abbreviated "MI", is an

organoiodine compound Organoiodine chemistry is the study of the synthesis and properties of organoiodine compounds, or organoiodides, organic compounds that contain one or more carbon–iodine bonds. They occur widely in organic chemistry, but are relatively rare ...

. Diiodomethane is a very dense colorless liquid; however, it decomposes upon exposure to light liberating

iodine Iodine is a chemical element; it has symbol I and atomic number 53. The heaviest of the stable halogens, it exists at standard conditions as a semi-lustrous, non-metallic solid that melts to form a deep violet liquid at , and boils to a vi ...

, which colours samples brownish. It is slightly soluble in water, but soluble in organic solvents. It has a very high

refractive index In optics, the refractive index (or refraction index) of an optical medium is the ratio of the apparent speed of light in the air or vacuum to the speed in the medium. The refractive index determines how much the path of light is bent, or refrac ...

of 1.741, and a

surface tension Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension (physics), tension is what allows objects with a higher density than water such as razor blades and insects (e.g. Ge ...

of 0.0508 N·m⁻¹.
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Uses

Because of its high

density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...

, 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 chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

for installing the CH₂ group. In the

Simmons–Smith reaction The Simmons–Smith reaction is an organic cheletropic reaction involving an organozinc carbenoid that reacts with an alkene (or alkyne) to form a cyclopropane. It is named after Howard Ensign Simmons, Jr. and Ronald D. Smith. It uses a me ...

, 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 . 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 Dichloromethane (DCM, methylene chloride, or methylene bichloride) is an organochlorine compound with the formula . This colorless, volatile liquid with a chloroform-like, sweet odor is widely used as a solvent. Although it is not miscible with ...

by the action of

sodium iodide Sodium iodide (chemical formula NaI) is an ionic compound formed from the chemical reaction of sodium metal and iodine. Under standard conditions, it is a white, water-soluble solid comprising a 1:1 mix of sodium cations (Na+) and iodide anions ...

acetone Acetone (2-propanone or dimethyl ketone) is an organic compound with the chemical formula, formula . It is the simplest and smallest ketone (). It is a colorless, highly Volatile organic compound, volatile, and flammable liquid with a charact ...

in the Finkelstein reaction: :CH₂Cl₂ + 2 NaI → CH₂I₂ + 2 NaCl It can also be prepared by reducing

iodoform Iodoform (also known as triiodomethane) is the organoiodine compound with the chemical formula . It is a pale yellow, crystalline, volatile substance, with a penetrating and distinctive odor (in older chemistry texts, the smell is sometimes refe ...

with elemental

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

sodium arsenite Sodium arsenite usually refers to the inorganic compound with the formula NaAsO2. Also called sodium ''meta''-arsenite, it is an inorganic polymer consisting of the infinite chains sO2associated with sodium cations, Na+. The polymer backbone ...

: :CHI₃ + Na₃AsO₃ + NaOH → CH₂I₂ + NaI + Na₃AsO₄

Safety

Alkyl iodides are

alkylating agent Alkylation is a chemical reaction that entails transfer of an alkyl group. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene (or their equivalents). Alkylating agents are reagents for effecting ...

s, which are potential mutagens.

References

External links

Diiodomethane data sheet

New particle formation from photooxidation of diiodomethane
{{Halomethanes Iodoalkanes Halomethanes Halogenated solvents