Editing Iodine (section)

===Organoiodine compounds===
{{main|Organoiodine compound}}
[[File:IBXAcid.png|thumb|right|Structure of the oxidising agent [[2-Iodoxybenzoic acid|2-iodoxybenzoic acid]]]]
Organoiodine compounds have been fundamental in the development of organic synthesis, such as in the [[Hofmann elimination]] of [[amine]]s,<ref>{{cite journal | title = Beiträge zur Kenntniss der flüchtigen organischen Basen | journal = [[Annalen der Chemie und Pharmacie]] | volume = 78 | issue = 3 | year = 1851 | pages = 253–286 | vauthors = Hofmann AW | doi = 10.1002/jlac.18510780302 | url = https://zenodo.org/record/1427040 | access-date = 30 June 2019 | archive-date = 1 December 2022 | archive-url = https://web.archive.org/web/20221201072415/https://zenodo.org/record/1427040 | url-status = live }}</ref> the [[Williamson ether synthesis]],<ref>{{cite journal | title = Theory of Aetherification | journal = Philosophical Magazine | volume = 37 | issue = 251 | pages = 350–356 | year = 1850 | doi = 10.1080/14786445008646627 | vauthors = Williamson A | url = https://zenodo.org/record/1431121 | access-date = 29 September 2020 | archive-date = 9 November 2022 | archive-url = https://web.archive.org/web/20221109194527/https://zenodo.org/record/1431121 | url-status = live }} ([http://web.lemoyne.edu/~giunta/williamson.html Link to excerpt]. {{Webarchive|url=https://web.archive.org/web/20190423075534/http://web.lemoyne.edu/~giunta/williamson.html |date=23 April 2019 }})</ref> the [[Wurtz reaction|Wurtz coupling reaction]],<ref>{{cite journal | title = Ueber eine neue Klasse organischer Radicale | vauthors = Wurtz A | journal = [[Annalen der Chemie und Pharmacie]] | volume = 96 | issue = 3 | pages = 364–375 | year = 1855 | url = https://zenodo.org/record/1427074 | doi = 10.1002/jlac.18550960310 | access-date = 30 June 2019 | archive-date = 3 February 2023 | archive-url = https://web.archive.org/web/20230203205851/https://zenodo.org/record/1427074 | url-status = live }}</ref> and in [[Grignard reagent]]s.<ref>{{cite journal | vauthors = Grignard V | title = Sur quelques nouvelles combinaisons organométaliques du magnésium et leur application à des synthèses d'alcools et d'hydrocabures | journal = Comptes rendus de l'Académie des Sciences | year = 1900 | volume = 130 | pages = 1322–25 | url = http://gallica.bnf.fr/ark:/12148/bpt6k3086n/f1322.table | author-link = Victor Grignard | access-date = 2 October 2016 | archive-date = 8 August 2019 | archive-url = https://web.archive.org/web/20190808225609/https://gallica.bnf.fr/ark:/12148/bpt6k3086n/f1322.table | url-status = live }}</ref>

The [[carbon]]–iodine bond is a common functional group that forms part of core [[organic chemistry]]; formally, these compounds may be thought of as organic derivatives of the [[Iodide|iodide anion]]. The simplest [[Organoiodine chemistry|organoiodine compounds]], [[Organoiodine chemistry|alkyl iodides]], may be synthesised by the reaction of [[Alcohol (chemistry)|alcohol]]s with [[phosphorus triiodide]]; these may then be used in [[nucleophilic substitution]] reactions, or for preparing [[Grignard reagent]]s. The C–I bond is the weakest of all the carbon–halogen bonds due to the minuscule difference in electronegativity between carbon (2.55) and iodine (2.66). As such, iodide is the best [[leaving group]] among the halogens, to such an extent that many organoiodine compounds turn yellow when stored over time due to decomposition into elemental iodine; as such, they are commonly used in [[organic synthesis]], because of the easy formation and cleavage of the C–I bond.<ref>{{Ullmann | vauthors = Lyday PA | title = Iodine and Iodine Compounds | doi = 10.1002/14356007.a14_381}}</ref> They are also significantly denser than the other organohalogen compounds thanks to the high atomic weight of iodine.<ref name="blanksby">{{cite journal | vauthors = Blanksby SJ, Ellison GB | title = Bond dissociation energies of organic molecules | journal = Accounts of Chemical Research | volume = 36 | issue = 4 | pages = 255–263 | date = April 2003 | pmid = 12693923 | doi = 10.1021/ar020230d | url = http://www.colorado.edu/chem/ellison/papers/Blanksby_Acct_Chem_Res_2003.pdf | access-date = 25 October 2017 | url-status = dead | citeseerx = 10.1.1.616.3043 | archive-url = https://web.archive.org/web/20090206144739/http://colorado.edu/chem/ellison/papers/Blanksby_Acct_Chem_Res_2003.pdf | archive-date = 6 February 2009 }}</ref> A few organic oxidising agents like the [[Hypervalent organoiodine compounds|iodanes]] contain iodine in a higher oxidation state than −1, such as [[2-Iodoxybenzoic acid|2-iodoxybenzoic acid]], a common reagent for the oxidation of alcohols to [[aldehyde]]s,<ref>{{ OrgSynth | title = Dess–Martin periodinane: 1,1,1-Triacetoxy-1,1-dihydro-1,2-benziodoxol-3(1''H'')-one | vauthors = Boeckman Jr RK, Shao P, Mullins JJ | year = 2000 | volume = 77 | pages = 141 | collvol = 10 | collvolpages = 696 | prep = v77p0141 }}</ref> and [[iodobenzene dichloride]] (PhICl<sub>2</sub>), used for the selective chlorination of [[alkene]]s and [[alkyne]]s.<ref>{{cite journal | vauthors = Jung ME, Parker MH | title = Synthesis of Several Naturally Occurring Polyhalogenated Monoterpenes of the Halomon Class(1) | journal = The Journal of Organic Chemistry | volume = 62 | issue = 21 | pages = 7094–7095 | date = October 1997 | pmid = 11671809 | doi = 10.1021/jo971371 }}</ref> One of the more well-known uses of organoiodine compounds is the so-called [[Haloform reaction|iodoform test]], where [[iodoform]] (CHI<sub>3</sub>) is produced by the exhaustive iodination of a [[Ketone|methyl ketone]] (or another compound capable of being oxidised to a methyl ketone), as follows:<ref name="March">{{March6th}}</ref>

{{block indent|[[Image:Iodoform synthesis.svg|450px]]}}

Some drawbacks of using organoiodine compounds as compared to organochlorine or organobromine compounds is the greater expense and toxicity of the iodine derivatives, since iodine is expensive and organoiodine compounds are stronger alkylating agents.<ref>{{cite web|publisher = Oxford University|title = Safety data for iodomethane|url = http://msds.chem.ox.ac.uk/IO/iodomethane.html|access-date = 12 December 2008|archive-date = 10 August 2010|archive-url = https://web.archive.org/web/20100810211004/http://msds.chem.ox.ac.uk/IO/iodomethane.html|url-status = dead}}</ref> For example, [[iodoacetamide]] and [[iodoacetic acid]] denature proteins by irreversibly alkylating [[cysteine]] residues and preventing the reformation of [[disulfide]] linkages.<ref>{{cite journal | vauthors = Polgár L | title = Deuterium isotope effects on papain acylation. Evidence for lack of general base catalysis and for enzyme–leaving-group interaction | journal = European Journal of Biochemistry | volume = 98 | issue = 2 | pages = 369–374 | date = August 1979 | pmid = 488108 | doi = 10.1111/j.1432-1033.1979.tb13196.x | doi-access = free }}</ref>

Halogen exchange to produce iodoalkanes by the [[Finkelstein reaction]] is slightly complicated by the fact that iodide is a better leaving group than chloride or bromide. The difference is nevertheless small enough that the reaction can be driven to completion by exploiting the differential solubility of halide salts, or by using a large excess of the halide salt.<ref name="March" /> In the classic Finkelstein reaction, an [[Organochlorine chemistry|alkyl chloride]] or an [[Organobromine chemistry|alkyl bromide]] is converted to an [[Organoiodine chemistry|alkyl iodide]] by treatment with a solution of [[sodium iodide]] in [[acetone]]. Sodium iodide is soluble in acetone and [[sodium chloride]] and [[sodium bromide]] are not.<ref>{{cite journal | vauthors = Ervithayasuporn V, Ervithayasuporn V, Pornsamutsin N, Pornsamutsin N, Prangyoo P, Prangyoo P, Sammawutthichai K, Sammawutthichai K, Jaroentomeechai T, Jaroentomeechai T, Phurat C, Phurat C, Teerawatananond T, Teerawatananond T | title = One-pot synthesis of halogen exchanged silsesquioxanes: octakis(3-bromopropyl)octasilsesquioxane and octakis(3-iodopropyl)octasilsesquioxane | journal = Dalton Transactions | volume = 42 | issue = 37 | pages = 13747–13753 | date = October 2013 | pmid = 23907310 | doi = 10.1039/C3DT51373D | s2cid = 41232118 }}</ref> The reaction is driven toward products by [[Law of mass action|mass action]] due to the precipitation of the insoluble salt.<ref>{{cite journal | vauthors = Streitwieser A | year = 1956 | title = Solvolytic Displacement Reactions at Saturated Carbon Atoms | journal = [[Chemical Reviews]] | volume = 56 | pages = 571–752 | doi = 10.1021/cr50010a001 | issue = 4}}</ref><ref>{{cite journal | title = The Effect of the Carbonyl and Related Groups on the Reactivity of Halides in S<sub>N</sub>2 Reactions | vauthors = Bordwell FG, Brannen WT | journal = [[Journal of the American Chemical Society]] | year = 1964 | volume = 86 | pages = 4645–4650 | doi = 10.1021/ja01075a025 | issue = 21}}</ref>