Diiodomethane or methylene iodide, commonly abbreviated "MI", is an
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. The thyroxine hormones are organoiodine compounds that are required for he ...
. Diiodomethane is a colorless liquid; however, it decomposes upon exposure to light liberating
iodine
Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions 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 relatively high
refractive index
In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium.
The refractive index determines how much the path of light is bent, or ...
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 is what allows objects with a higher density than water such as razor blades and insects (e.g. water striders) to f ...
of 0.0508 N·m
−1.
Website of Krüss
'' (8.10.2009)
Uses
Because of its high
density
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...
, 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 CH
2 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 meth ...
, it is a source of
methylene. In fact the Simmons–Smith reaction does not produce free carbene but proceeds via Zn-CH
2I intermediates.
Diiodomethane is also a source of the equivalent of CH
22+. The synthesis of Fe
2(CH
2)(CO)
8 illustrates this reactivity:
:Na
2Fe
2(CO)
8 + CH
2I
2 → Fe
2(CH
2)(CO)
8 + 2NaI
Preparation
Diiodomethane can be prepared from the widely available solvent
dichloromethane
Dichloromethane (DCM or methylene chloride, methylene bichloride) is an organochlorine compound with the formula . This colorless, volatile liquid with a chloroform-like, sweet odour 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 (I ...
in
acetone
Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour.
Acetone is miscib ...
in the
Finkelstein reaction
The Finkelstein reaction named after the German chemist Hans Finkelstein, is an SN2 reaction (Substitution Nucleophilic Bimolecular reaction) that involves the exchange of one halogen atom for another. It is an equilibrium reaction, but the reac ...
:
[
:CH2Cl2 + 2 NaI → CH2I2 + 2 NaCl
It can also be prepared by reducing ]iodoform
Iodoform (also known as triiodomethane and, inaccurately, as carbon triiodide) is the organoiodine compound with the chemical formula C H I3. A pale yellow, crystalline, volatile substance, it has a penetrating and distinctive odor (in older che ...
with elemental phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
or sodium arsenite
Sodium arsenite usually refers to the inorganic compound with the formula NaAsO2. Also called sodium ''meta''-arsenite, it is the sodium salt of arsenous acid. Sodium ''ortho''-arsenite is Na3AsO3.Greenwood, N. N.; & Earnshaw, A. (1997). Chemistr ...
:
:CHI3 + Na3AsO3 + NaOH → CH2I2 + NaI + Na3AsO4
Safety
Alkyl iodides are alkylating agent
Alkylation is the transfer of an alkyl group from one molecule to another. 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 al ...
s, which are potential mutagens.
References
External links
Diiodomethane data sheet
New particle formation from photooxidation of diiodomethane
{{Halomethanes
Iodoalkanes
Halomethanes
Halogenated solvents