Organoiodine compounds are
organic compounds
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The s ...
that contain one or more
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
–
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 ...
bond
Bond or bonds may refer to:
Common meanings
* Bond (finance), a type of debt security
* Bail bond, a commercial third-party guarantor of surety bonds in the United States
* Chemical bond, the attraction of atoms, ions or molecules to form chemical ...
s. They occur widely in organic chemistry, but are relatively rare in nature. The
thyroxine
File:Thyroid_system.svg, upright=1.5, The thyroid system of the thyroid hormones T3 and T4
rect 376 268 820 433 Thyroid-stimulating hormone
rect 411 200 849 266 Thyrotropin-releasing hormone
rect 297 168 502 200 Hypothalamus
rect 66 216 386 25 ...
hormones are organoiodine compounds that are required for health and the reason for government-mandated
iodization of salt.
Structure, bonding, general properties
Almost all organoiodine compounds feature iodide connected to one carbon center. These are usually classified as derivatives of I
−. Some organoiodine compounds feature iodine in higher oxidation states.
The C–I bond is the weakest of the carbon–
halogen
The halogens () are a group in the periodic table consisting of five or six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In the modern IUPAC nomenclature, this group is ...
bonds. These bond strengths correlate with the
electronegativity
Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the d ...
of the halogen, decreasing in the order F > Cl > Br > I. This
periodic order also follows the
atomic radius
The atomic radius of a chemical element is a measure of the size of its atom, usually the mean or typical distance from the center of the nucleus to the outermost isolated electron. Since the boundary is not a well-defined physical entity, there ...
of halogens and the length of the carbon-halogen bond. For example, in the molecules represented by CH
3X, where X is a halide, the carbon-X bonds have strengths, or
bond dissociation energies
The bond-dissociation energy (BDE, ''D''0, or ''DH°'') is one measure of the strength of a chemical bond . It can be defined as the standard enthalpy change when is cleaved by homolysis to give fragments A and B, which are usually radical s ...
, of 115, 83.7, 72.1, and 57.6 kcal/mol for X = fluoride, chloride, bromide, and iodide, respectively.
Of the halides, iodide usually is the best
leaving group In chemistry, a leaving group is defined by the IUPAC as an atom or group of atoms that detaches from the main or residual part of a substrate during a reaction or elementary step of a reaction. However, in common usage, the term is often limited t ...
. Because of the weakness of the C–I bond, samples of organoiodine compounds are often yellow due to an impurity of I
2.
A noteworthy aspect of organoiodine compounds is their high density, which arises from the high atomic weight of iodine. For example, one millilitre of
methylene iodide
Diiodomethane or methylene iodide, commonly abbreviated "MI", is an organoiodine compound. Diiodomethane is a colorless liquid; however, it decomposes upon exposure to light liberating iodine, which colours samples brownish. It is slightly solu ...
weighs 3.325 g.
Industrial applications
Few organoiodine compounds are important industrially, at least in terms of large scale production. Iodide-containing intermediates are common in
organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...
, because of the easy formation and cleavage of the C–I bond. Industrially significant organoiodine compounds, often used as disinfectants or pesticides, are
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 ...
(CHI
3),
methylene iodide
Diiodomethane or methylene iodide, commonly abbreviated "MI", is an organoiodine compound. Diiodomethane is a colorless liquid; however, it decomposes upon exposure to light liberating iodine, which colours samples brownish. It is slightly solu ...
(CH
2I
2), and
methyl iodide
Iodomethane, also called methyl iodide, and commonly abbreviated "MeI", is the chemical compound with the formula CH3I. It is a dense, colorless, volatile liquid. In terms of chemical structure, it is related to methane by replacement of one h ...
(CH
3I). Although methyl iodide is not an industrially important product, it is an important intermediate, being a transiently generated intermediate in the
industrial production
Industrial production is a measure of output of the industrial sector of the economy. The industrial sector includes manufacturing, mining, and utilities. Although these sectors contribute only a small portion of gross domestic product (GDP), the ...
of
acetic acid
Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...
and
acetic anhydride
Acetic anhydride, or ethanoic anhydride, is the chemical compound with the formula (CH3CO)2O. Commonly abbreviated Ac2O, it is the simplest isolable anhydride of a carboxylic acid and is widely used as a reagent in organic synthesis. It is a col ...
. The potential for methyl iodide to replace the ubiquitous dependence on methyl bromide as a soil fumigant has been considered, however limited information is available on environmental behavior of the former. Ioxynil (3,5-diiodo-4-hydroxybenzonitrile), which inhibits photosynthesis at photosystem II, is among the very few organoiodine herbicides. A member of the hydroxybenzonitrile herbicide class, ioxynil is an iodinated analog of the brominated herbicide,
bromoxynil
Bromoxynil is an organic compound with the formula HOBr2C6H2CN. It is classified as a nitrile herbicide, and as such sold under many trade names. It is a white solid. It works by inhibiting photosynthesis. It is moderately toxic to mammals.
Pr ...
(3,5-dibromo-4-hydroxybenzonitrile).
Iodinated and brominated organic compounds are of concern as environmental contaminants owing to very limited information available on environment fate behavior. However, recent reports have shown promise in biological detoxification of these classes of contaminants. For example, Iodotyrosine deiodinase is a mammalian enzyme with the unusual function of aerobic
reductive dehalogenation
In organochlorine chemistry, reductive dechlorination describes any chemical reaction which cleaves the covalent bond between carbon and chlorine via reductants, to release chloride ions. Many modalities have been implemented, depending on the a ...
of iodine- or bromine-substituted organic substrates. Bromoxynil and ioxynil herbicides have been shown to undergo a variety of environmental transformations, including reductive dehalogenation by
anaerobic
Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to:
* Anaerobic adhesive, a bonding a ...
bacteria.
Polyiodoorganic compounds are sometimes employed as X-ray
contrast agent
A contrast agent (or contrast medium) is a substance used to increase the contrast of structures or fluids within the body in medical imaging. Contrast agents absorb or alter external electromagnetism or ultrasound, which is different from radiop ...
s, in
fluoroscopy
Fluoroscopy () is an imaging technique that uses X-rays to obtain real-time moving images of the interior of an object. In its primary application of medical imaging, a fluoroscope () allows a physician to see the internal structure and functio ...
, a type of
medical imaging
Medical imaging is the technique and process of imaging the interior of a body for clinical analysis and medical intervention, as well as visual representation of the function of some organs or tissues (physiology). Medical imaging seeks to rev ...
. This application exploits the X-ray absorbing ability of the heavy iodine nucleus. A variety of agents are available commercially, many are derivatives of 1,3,5-triiodo
benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, ...
and contain about 50% by weight iodine. For most applications, the agent must be highly soluble in water and, of course, non-toxic and readily excreted. A representative reagent is
Ioversol
Ioversol (INN; trade name Optiray) is an organoiodine compound that is used as a contrast medium. It features both a high iodine content, as well as several hydrophilic groups. It is used in clinical diagnostics including arthrography, angiocar ...
(Figure to right), which has water-solubilizing
diol
A diol is a chemical compound containing two hydroxyl groups ( groups). An aliphatic diol is also called a glycol. This pairing of functional groups is pervasive, and many subcategories have been identified.
The most common industrial diol is e ...
substituents. Typical applications include
urography
Pyelogram (or pyelography or urography) is a form of imaging of the renal pelvis and ureter.
Types include:
* #Intravenous pyelogram, Intravenous pyelogram – In which a contrast solution is introduced through a vein into the circulatory system.
...
and
angiography
Angiography or arteriography is a medical imaging technique used to visualize the inside, or lumen, of blood vessels and organs of the body, with particular interest in the arteries, veins, and the heart chambers. Modern angiography is performe ...
.
Organoiodine lubricants can be used with
titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...
,
stainless steel
Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's corros ...
s, and other metals which tend to seize up with conventional lubricants: organoiodine lubricants can be used in
turbine
A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating e ...
s and
spacecraft
A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, p ...
, and as a cutting oil in
machining
Machining is a process in which a material (often metal) is cut to a desired final shape and size by a controlled material-removal process. The processes that have this common theme are collectively called subtractive manufacturing, which utilizes ...
.
File:Methyl iodide.svg, Methyl iodide
Iodomethane, also called methyl iodide, and commonly abbreviated "MeI", is the chemical compound with the formula CH3I. It is a dense, colorless, volatile liquid. In terms of chemical structure, it is related to methane by replacement of one h ...
, precursor to synthetic acetic acid.
File:Erythrosine.svg, Erythrosine
Erythrosine, also known as Red No. 3, is an organoiodine compound, specifically a derivative of fluorone. It is a pink dye which is primarily used for food coloring. It is the disodium salt of 2,4,5,7-tetraiodofluorescein. Its maximum absorbanc ...
, a common food dye.
File:Iodoversol.png, Ioversol
Ioversol (INN; trade name Optiray) is an organoiodine compound that is used as a contrast medium. It features both a high iodine content, as well as several hydrophilic groups. It is used in clinical diagnostics including arthrography, angiocar ...
, an organoiodine compound used as an X-ray contrast agent
A contrast agent (or contrast medium) is a substance used to increase the contrast of structures or fluids within the body in medical imaging. Contrast agents absorb or alter external electromagnetism or ultrasound, which is different from radiop ...
.
File:Thyroxine-2D-skeletal.png, Thyroxine
File:Thyroid_system.svg, upright=1.5, The thyroid system of the thyroid hormones T3 and T4
rect 376 268 820 433 Thyroid-stimulating hormone
rect 411 200 849 266 Thyrotropin-releasing hormone
rect 297 168 502 200 Hypothalamus
rect 66 216 386 25 ...
(T4), a hormone
A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...
.
File:Triiodothyronine.svg, Triiodothyronine
Triiodothyronine, also known as T3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate.
Production of T3 and its prohormone thyroxine ( ...
(T3), another thyroid hormone.
Biological role
In terms of human health, the most important organoiodine compounds are the two
thyroid hormone
File:Thyroid_system.svg, upright=1.5, The thyroid system of the thyroid hormones T3 and T4
rect 376 268 820 433 Thyroid-stimulating hormone
rect 411 200 849 266 Thyrotropin-releasing hormone
rect 297 168 502 200 Hypothalamus
rect 66 216 386 25 ...
s
thyroxine
File:Thyroid_system.svg, upright=1.5, The thyroid system of the thyroid hormones T3 and T4
rect 376 268 820 433 Thyroid-stimulating hormone
rect 411 200 849 266 Thyrotropin-releasing hormone
rect 297 168 502 200 Hypothalamus
rect 66 216 386 25 ...
("T
4") and
triiodothyronine
Triiodothyronine, also known as T3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate.
Production of T3 and its prohormone thyroxine ( ...
("T
3"). Marine natural products are rich sources of organoiodine compounds, like the recently discovered
plakohypaphorine Plakohypaphorines are halogenated indolic non-proteinogenic amino acids named for their similarity to hypaphorine (''N,N,N''-trimethyltryptophan). First reported in the Caribbean sponge
Sponges, the members of the phylum Porifera (; meaning ...
s from the sponge ''
Plakortis simplex''.
The sum of
iodomethane
Iodomethane, also called methyl iodide, and commonly abbreviated "MeI", is the chemical compound with the formula CH3I. It is a dense, colorless, volatile liquid. In terms of chemical structure, it is related to methane by replacement of one h ...
produced by the marine environment, microbial activity in
rice paddies
A paddy field is a flooded field of arable land used for growing semiaquatic crops, most notably rice and taro. It originates from the Neolithic rice-farming cultures of the Yangtze River basin in southern China, associated with pre-Aust ...
, and the burning of biological material is estimated to be 214
kilotonne
TNT equivalent is a convention for expressing energy, typically used to describe the energy released in an explosion. The is a unit of energy defined by that convention to be , which is the approximate energy released in the detonation of a m ...
s per year.
The volatile iodomethane is broken up by oxidation reactions in the atmosphere and a global iodine cycle is established.
More than 3000 organoiodine compounds have been identified.
Methods for preparation of the C–I bond
From I2
Organoiodine compounds are prepared by numerous routes, depending on the degree and regiochemistry of iodination sought as well as the nature of the precursors. The direct iodination with is employed with unsaturated substrates:
:
This reaction is used to determine the
iodine number
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 ...
, an indicator of the unsaturation of fats and related samples.
From I− sources
The iodide anion is a good nucleophile and will displace chloride, tosylate, bromide and other leaving groups, as 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 ...
.
Alcohols can be converted to the corresponding iodides using
phosphorus triiodide
Phosphorus triiodide (PI3) is an inorganic compound with the formula PI3. A red solid, it is a common misconception that PI3 is too unstable to be stored; it is, in fact, commercially available. It is widely used in organic chemistry for convertin ...
. Illustrative is the conversion of
methanol
Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a ...
to
iodomethane
Iodomethane, also called methyl iodide, and commonly abbreviated "MeI", is the chemical compound with the formula CH3I. It is a dense, colorless, volatile liquid. In terms of chemical structure, it is related to methane by replacement of one h ...
:
:PI
3 + 3 → 3 + ""
For bulky alcohol substrates, the
methiodide In organic chemistry, a methiodide is a chemical derivative produced by the reaction of a compound with methyl iodide. Methiodides are often formed through the methylation of tertiary amines:
: R3N + CH3I → (CH3)R3N+I−
Whereas the parent am ...
of triphenylphosphite has been used.
:
3(C6H5O)3P">H3(C6H5O)3Psup>+I
− + ROH → RI + CH
3(C
6H
5O)
2PO + C
6H
5OH
Aromatic iodides may be prepared via a
diazonium salt
Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group where R can be any organic group, such as an alkyl or an aryl, and X is an inorganic or organic anion, such as a halide.
General properti ...
by treatment with potassium iodide:
:
C6H5N2+ + KI -> C6H5I + K+ + N2
From I+ sources
Benzene can be iodinated with a combination of iodide and
nitric acid
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...
.
[
] Iodine monochloride
Iodine monochloride is an interhalogen compound with the formula . It is a red-brown chemical compound that melts near room temperature. Because of the difference in the electronegativity of iodine and chlorine, this molecule is highly polar ...
is a reagent that is sometimes used to deliver the equivalent of "".
See also
*
Organofluorine compound
Organofluorine chemistry describes the chemistry of the organofluorines, organic compounds that contain the carbon–fluorine bond. Organofluorine compounds find diverse applications ranging from oil and water repellents to pharmaceuticals, refri ...
s
*
Organochlorine compound
An organochloride, organochlorine compound, chlorocarbon, or chlorinated hydrocarbon is an organic compound containing at least one covalent bond, covalently bonded atom of chlorine. The chloroalkane class (alkanes with one or more hydrogens subst ...
s
*
Organobromine compound
Organobromine compounds, also called organobromides, are organic compounds that contain carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons avai ...
s
*
Iodane
Iodane generally refers to any organic derivative of iodine. Without modifier, ''iodane'' is the systematic name for the parent hydride of iodine, HI. Thus, any organoiodine compound with general formula RI (e.g., iodomethane , or iodobenzene ) i ...
s
*
Periodinane Periodinanes also known as λ5-iodanes are organoiodine compounds with iodine in the +5 oxidation state. These compounds are described as hypervalent because the iodine center has more than 8 valence electrons.
Periodinane compounds
The λ5-iodane ...
s
References
{{ChemicalBondsToCarbon