Diiodomethane
Encyclopedia
Diiodomethane or methylene iodide, commonly abbreviated "MI", is a liquid organoiodine compound
. It is insoluble in water, but soluble in ether
and alcohol
. It has a relatively high refractive index
of 1.741, and a surface tension of 0.0508 N·m−1. Diiodomethane is a colorless liquid, however, it decomposes upon exposure to light liberating iodine
, which colours samples brownish.
With its high specific gravity
, diiodomethane is used in the determination of the density of mineral and other solid samples. It is also used as a contact liquid for refractometer
s. Diiodomethane is a reagent
in the Simmons-Smith reaction
, serving as a source of methylene
.
with sodium arsenite
:
Diiodomethane can also be prepared from dichloromethane
by the action of sodium iodide
in acetone in the Finkelstein reaction
:
Organoiodine compound
Organoiodine compounds are organic compounds that contain one or more carbon–iodine bonds. They occur widely in organic chemistry, but are relatively rare in nature...
. It is insoluble in water, but soluble in ether
Ether
Ethers are a class of organic compounds that contain an ether group — an oxygen atom connected to two alkyl or aryl groups — of general formula R–O–R'. A typical example is the solvent and anesthetic diethyl ether, commonly referred to simply as "ether"...
and alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
. It has a relatively high refractive index
Refractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....
of 1.741, and a surface tension of 0.0508 N·m−1. Diiodomethane is a colorless liquid, however, it decomposes upon exposure to light liberating iodine
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
, which colours samples brownish.
With its high specific gravity
Specific gravity
Specific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...
, diiodomethane is used in the determination of the density of mineral and other solid samples. It is also used as a contact liquid for refractometer
Refractometer
A refractometer is a laboratory or field device for the measurement of an index of refraction . The index of refraction is calculated from Snell's law and can be calculated from the composition of the material using the Gladstone-Dale relation....
s. Diiodomethane is a reagent
Reagent
A reagent is a "substance or compound that is added to a system in order to bring about a chemical reaction, or added to see if a reaction occurs." Although the terms reactant and reagent are often used interchangeably, a reactant is less specifically a "substance that is consumed in the course of...
in the Simmons-Smith reaction
Simmons-Smith reaction
The Simmons–Smith reaction is an organic cheletropic reaction in which a carbenoid reacts with an alkene to form a cyclopropane. It is named after Howard Ensign Simmons, Jr. and R. D. Smith...
, serving as a source of methylene
Methylene
Methylene is a chemical species in which a carbon atom is bonded to two hydrogen atoms. Three different possibilities present themselves:* the -CH2- substituent group: e.g., dichloromethane ....
.
Preparation
Although commercially available, it can be prepared by reducing iodoformIodoform
Iodoform is the organoiodine compound with the formula CHI3. A pale yellow, crystalline, volatile substance, it has a penetrating odor and, analogous to chloroform, sweetish taste. It is occasionally used as a disinfectant...
with sodium arsenite
Sodium arsenite
Sodium arsenite is a compound with formula NaAsO2. It is the sodium salt of arsenous acid. It is a crystalline solid consisting of sodium cations, Na+, and catena-arsenite anions, [AsO2], which are infinite -O-As- chains, similar in structure to selenium dioxide, SeO2.It is a pesticide....
:
- CHI3 + Na3AsO3 + NaOH → CH2I2 + NaI + Na3AsO4
Diiodomethane can also be prepared from dichloromethane
Dichloromethane
Dichloromethane is an organic compound with the formula CH2Cl2. This colorless, volatile liquid with a moderately sweet aroma is widely used as a solvent. Although it is not miscible with water, it is miscible with many organic solvents...
by the action of sodium iodide
Sodium iodide
Sodium iodide is a white, crystalline salt with chemical formula NaI used in radiation detection, treatment of iodine deficiency, and as a reactant in the Finkelstein reaction.-Uses:Sodium iodide is commonly used to treat and prevent iodine deficiency....
in acetone in the Finkelstein reaction
Finkelstein reaction
The Finkelstein reaction, named for the German chemist Hans Finkelstein , is an SN2 reaction that involves the exchange of one halogen atom for another...
:
- CH2Cl2 + 2 NaI → CH2I2 + 2 NaCl