Organoiodine compound

Last updated • 4 min readFrom Wikipedia, The Free Encyclopedia

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 health and the reason for government-mandated iodization of salt.

Contents

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. [1]

The CI bond is the weakest of the carbon halogen bonds. These bond strengths correlate with the electronegativity of the halogen, decreasing in the order F > Cl > Br > I. This periodic order also follows the atomic radius of halogens and the length of the carbon-halogen bond. For example, in the molecules represented by CH3X, where X is a halide, the carbon-X bonds have strengths, or bond dissociation energies, of 115, 83.7, 72.1, and 57.6 kcal/mol for X = fluoride, chloride, bromide, and iodide, respectively. [2] Of the halides, iodide usually is the best leaving group. Because of the weakness of the C–I bond, samples of organoiodine compounds are often yellow due to an impurity of I2.

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 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, because of the easy formation and cleavage of the CI bond. Industrially significant organoiodine compounds, often used as disinfectants or pesticides, are iodoform (CHI3), methylene iodide (CH2I2), and methyl iodide (CH3I). [3] Although methyl iodide is not an industrially important product, it is an important intermediate, being a transiently generated intermediate in the industrial production of acetic acid and acetic anhydride. 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. [4] 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 (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 of iodine- or bromine-substituted organic substrates. [5] Bromoxynil and ioxynil herbicides have been shown to undergo a variety of environmental transformations, including reductive dehalogenation by anaerobic bacteria. [6]

Polyiodoorganic compounds are sometimes employed as X-ray contrast agents, in fluoroscopy, a type of medical imaging. 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-triiodobenzene 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 (Figure to right), [7] which has water-solubilizing diol substituents. Typical applications include urography and angiography.

Organoiodine lubricants can be used with titanium, stainless steels, and other metals which tend to seize up with conventional lubricants: organoiodine lubricants can be used in turbines and spacecraft, and as a cutting oil in machining. [8]

Biological role

In terms of human health, the most important organoiodine compounds are the two thyroid hormones thyroxine ("T4") and triiodothyronine ("T3"). [9] Marine natural products are rich sources of organoiodine compounds, like the recently discovered plakohypaphorines from the sponge Plakortis simplex .

The sum of iodomethane produced by the marine environment, microbial activity in rice paddies, and the burning of biological material is estimated to be 214 kilotonnes per year. [10] 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. [11]

Methods for preparation of the CI 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 I2 is employed with unsaturated substrates:

RHC=CH2 + I2 → RHIC-CIH2

This reaction is used to determine the iodine number, 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.

Alcohols can be converted to the corresponding iodides using phosphorus triiodide. Illustrative is the conversion of methanol to iodomethane: [12]

PI3 + 3 CH
3
OH
→ 3 CH
3
I
+ "H
3
PO
3
"

For bulky alcohol substrates, the methiodide of triphenylphosphite has been used. [13]

[CH3(C6H5O)3P]+I + ROH → RI + CH3(C6H5O)2PO + C6H5OH

Aromatic iodides may be prepared via a diazonium salt by treatment with potassium iodide: [14]

From I+ sources

Benzene can be iodinated with a combination of iodide and nitric acid. [15] Iodine monochloride is a reagent that is sometimes used to deliver the equivalent of "I+".

See also

Related Research Articles

Iodine Chemical element, symbol I and atomic number 53

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 114 °C (237 °F), and boils to a violet gas at 184 °C (363 °F). The element was discovered by the French chemist Bernard Courtois in 1811 and was named two years later by Joseph Louis Gay-Lussac, after the Ancient Greek Ιώδης 'violet-coloured'.

Ketone Class of organic compounds having structure RCOR

In chemistry, a ketone is a functional group with the structure R2C=O, where R can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond). The simplest ketone is acetone (R = R' = methyl), with the formula CH3C(O)CH3. Many ketones are of great importance in biology and in industry. Examples include many sugars (ketoses), many steroids (e.g., testosterone), and the solvent acetone.

Haloalkane Group of chemical compounds derived from alkanes containing one or more halogens

The haloalkanes are alkanes containing one or more halogen substituents. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely used commercially. They are used as flame retardants, fire extinguishants, refrigerants, propellants, solvents, and pharmaceuticals. Subsequent to the widespread use in commerce, many halocarbons have also been shown to be serious pollutants and toxins. For example, the chlorofluorocarbons have been shown to lead to ozone depletion. Methyl bromide is a controversial fumigant. Only haloalkanes that contain chlorine, bromine, and iodine are a threat to the ozone layer, but fluorinated volatile haloalkanes in theory may have activity as greenhouse gases. Methyl iodide, a naturally occurring substance, however, does not have ozone-depleting properties and the United States Environmental Protection Agency has designated the compound a non-ozone layer depleter. For more information, see Halomethane. Haloalkane or alkyl halides are the compounds which have the general formula "RX" where R is an alkyl or substituted alkyl group and X is a halogen.

In chemistry, halogenation is a chemical reaction that entails the introduction of one or more halogens into a compound. Halide-containing compounds are pervasive, making this type of transformation important, e.g. in the production of polymers, drugs. This kind of conversion is in fact so common that a comprehensive overview is challenging. This article mainly deals with halogenation using elemental halogens (F2, Cl2, Br2, I2). Halides are also commonly introduced using salts of the halides and halogen acids. Many specialized reagents exist for and introducing halogens into diverse substrates, e.g. thionyl chloride.

Acyl halide Chemical compound

An acyl halide is a chemical compound derived from an oxoacid by replacing a hydroxyl group with a halide group.

Halocarbon compounds are chemicals in which one or more carbon atoms are linked by covalent bonds with one or more halogen atoms resulting in the formation of organofluorine compounds, organochlorine compounds, organobromine compounds, and organoiodine compounds. Chlorine halocarbons are the most common and are called organochlorides.

Phosphorus triiodide Chemical compound

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 converting alcohols to alkyl iodides. It is also a powerful reducing agent. Note that phosphorus also forms a lower iodide, P2I4, but the existence of PI5 is doubtful at room temperature.

In the Ullmann condensation or Ullmann-type reaction is the copper-promoted conversion of aryl halides to aryl ethers, aryl thioethers, aryl nitriles, and aryl amines. These reactions are examples of cross-coupling reactions.

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 hydrogen atom by an atom of iodine. It is naturally emitted by rice plantations in small amounts. It is also produced in vast quantities estimated to be greater than 214,000 tons annually by algae and kelp in the world's temperate oceans, and in lesser amounts on land by terrestrial fungi and bacteria. It is used in organic synthesis as a source of methyl groups.

Sulfonium

A sulfonium ion, also known as sulphonium ion or sulfanium ion, is a positively charged ion (a "cation") featuring three organic substituents attached to sulfur. These organosulfur compounds have the formula [SR3]+. Together with a negatively charged counterion, they give sulfonium salts. They are typically colorless solids that are soluble in organic solvent.

Lithium iodide Chemical compound

Lithium iodide, or LiI, is a compound of lithium and iodine. When exposed to air, it becomes yellow in color, due to the oxidation of iodide to iodine. It crystallizes in the NaCl motif. It can participate in various hydrates.

Alpha-Haloketone

In organic chemistry, an α-haloketone is a functional group consisting of a ketone group or more generally a carbonyl group with an α-halogen substituent. α-haloketones are alkylating agents. Prominent α-haloketones include phenacyl bromide and chloroacetone.

Neopentyl alcohol Chemical compound

Neopentyl alcohol is a compound with formula (CH3)3CCH2OH. It is a colorless solid. The compound is one of the eight isomers of pentyl alcohol.

Meerwein arylation

The Meerwein arylation is an organic reaction involving the addition of an aryl diazonium salt (ArN2X) to an electron-poor alkene usually supported by a metal salt. The reaction product is an alkylated arene compound. The reaction is named after Hans Meerwein, one of its inventors who first published it in 1939.

Diiodomethane Chemical compound

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 soluble in water, but soluble in organic solvents. It has a relatively high refractive index of 1.741, and a surface tension of 0.0508 N·m−1.

Bromoxynil Chemical compound

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.

Organobromine compounds, also called organobromides, are organic compounds that contain carbon bonded to bromine. The most pervasive is the naturally produced bromomethane.

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 is a substituted iodane. However, as used in the context of organic synthesis, the term iodane more specifically refers to organoiodine compounds with nonstandard bond number, making this term a synonym for hypervalent iodine. These iodine compounds are hypervalent because the iodine atom formally contains more than the 8 electrons in the valence shell required for the octet rule. When iodine is ligated to an organic residue and electronegative ligands, hypervalent iodine compounds occur with a +3 oxidation number as iodine(III) or λ3-iodanes, or as a +5 oxidation number as iodine(V) or λ5-iodanes, or as a +7 oxidation number as iodine(VII) or λ7-iodanes.

Sulfenyl chloride

A sulfenyl chloride is a functional group with the connectivity R–S–Cl, where R is alkyl or aryl. Sulfenyl chlorides are reactive compounds that behave as sources of RS+. They are used in the formation of RS–N and RS–O bonds. According to IUPAC nomenclature they are named as alkyl thiohypochlorites, i.e. esters of thiohypochlorous acid.

In organometallic chemistry, metal–halogen exchange is a fundamental reaction that converts a organic halide into an organometallic product. The reaction commonly involves the use of electropositive metals and organochlorides, bromides, and iodides. Particularly well-developed is the use of metal–halogen exchange for the preparation of organolithium compounds.

References

  1. Alex G. Fallis, Pierre E. Tessier, "2-Iodoxybenzoic acid (IBX)1" Encyclopedia of Reagents for Organic Synthesis, 2003 John Wiley doi : 10.1002/047084289X.rn00221
  2. Blanksby SJ, Ellison GB (April 2003). "Bond dissociation energies of organic molecules". Acc. Chem. Res. 36 (4): 255–63. CiteSeerX   10.1.1.616.3043 . doi:10.1021/ar020230d. PMID   12693923.
  3. Phyllis A. Lyday. "Iodine and Iodine Compounds". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a14_381.
  4. Allard, A.S. and A. H. Neilson 2003 Degradation and transformation of organic bromine and iodine compounds: comparison with their chlorinated analogues. The Handbook of Environmental Chemistry 3:1-74.
  5. McTamney, P.M. and S.E. Rokita 2010. A mammalian reductive deiodinase has broad power to dehalogenate chlorinated and brominated substrates. J Am Chem Soc. 131(40): 14212–14213.
  6. Cupples, A. M., R. A. Sanford, and G. K. Sims. 2005. Dehalogenation of Bromoxynil (3,5-Dibromo-4-Hydroxybenzonitrile) and Ioxynil (3,5-Diiodino-4-Hydroxybenzonitrile) by Desulfitobacterium chlororespirans. Appl. Env. Micro. 71(7):3741-3746.
  7. Ulrich Speck, Ute Hübner-Steiner "Radiopaque Media" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. doi : 10.1002/14356007.a22_593
  8. "Key Lubrication Ingredient: Iodine Moves to Space Age", Schenectady Gazette, November 17, 1965.
  9. Gribble, G. W. (1996). "Naturally occurring organohalogen compounds - A comprehensive survey". Progress in the Chemistry of Organic Natural Products. 68 (10): 1–423. doi:10.1021/np50088a001. PMID   8795309.
  10. N. Bell; L. Hsu; D. J. Jacob; M. G. Schultz; D. R. Blake; J. H. Butler; D. B. King; J. M. Lobert & E. Maier-Reimer (2002). "Methyl iodide: Atmospheric budget and use as a tracer of marine convection in global models". Journal of Geophysical Research. 107 (D17): 4340. Bibcode:2002JGRD..107.4340B. doi:10.1029/2001JD001151. S2CID   18327103.
  11. V.M. Dembitsky; G.A. Tolstikov . (2003). "Naturally occurring organohalogen compounds - A comprehensive survey". Nauka Press, Novosibirsk.
  12. King, C. S.; Hartman, W. W. (1933). "Methyl Iodide". Organic Syntheses . 13: 60. doi:10.15227/orgsyn.013.0060.
  13. H. N. Rydon (1971). "Alkyl Iodides: Neopentyl Iodide and Iodocyclohexane". Organic Syntheses. 51: 44. doi:10.15227/orgsyn.051.0044.
  14. Lucas, H. J.; Kennedy, E. R. (1939). "Iodobenzene". Organic Syntheses. 19: 55. doi:10.15227/orgsyn.019.0055.
  15. F. B. Dains and R. Q. Brewster (1929). "Iodobenzene". Organic Syntheses . 9: 46. doi:10.15227/orgsyn.009.0046.