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| In [[chemistry]], '''radical initiators''' are substances that can produce [[radical (chemistry)|radical species]] under mild conditions and promote [[radical reaction]]s.<ref>{{JerryMarch}}</ref> These substances generally possess weak bonds—bonds that have small [[bond dissociation energy|bond dissociation energies]]. Radical initiators are utilized in industrial processes such as [[polymer]] synthesis. Typical examples are [[halogen]] [[molecule]]s, [[azo compound]]s, and [[organic peroxide|organic and inorganic peroxides]]s.<ref>{{March6th}}</ref>
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| ==Major types of initiation reaction==
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| *[[Halogen]]s undergo the [[homolysis (chemistry)|homolytic fission]] relatively easily. [[Chlorine]], for example, gives two chlorine radicals (Cl•) by irradiation with [[ultraviolet|ultraviolet light]]. This process is used for [[Free-radical halogenation|chlorination]] of [[alkane]]s.
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| *[[Azo compound]]s (R-[[nitrogen|N]]=[[nitrogen|N]]-R') can be the precursor of two [[carbon]]-centered radicals (R• and R'•) and [[nitrogen]] gas upon heating and/or by irradiation. For example, [[Azobisisobutyronitrile|AIBN]] and [[ABCN]] yield isobutyronitrile and cyclohexanecarbonitrile radicals, respectively.
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| :[[Image:AIBN-radical-2D.png|400px|AIBN initiator]]
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| *[[Organic peroxide]]s each have a peroxide bond (-[[oxygen|O]]-[[oxygen|O]]-), which is readily cleaved to give two [[oxygen]]-centered radicals. The oxyl radicals are unstable and believed to be transformed into relatively stable [[carbon]]-centered radicals. For example, [[Di-tert-butyl peroxide|di-''tert''-butyl peroxide]] (<sup>''t''</sup>[[butyl|Bu]][[oxygen|OO]]<sup>''t''</sup>[[butyl|Bu]]) gives two ''t''-butanoyl radicals (<sup>''t''</sup>[[butyl|Bu]][[oxygen|O]]•) and the radicals become [[methyl]] radicals ([[carbon|C]][[hydrogen|H]]<sub>3</sub>•) with the loss of [[acetone]]. [[Benzoyl peroxide]] (([[phenyl|Ph]][[carbon|C]][[oxygen|OO]])<sub>2</sub>) generates benzoyloxyl radicals ([[phenyl|Ph]][[carbon|C]][[oxygen|OO]]•), each of which loses [[carbon dioxide]] to be converted into a [[phenyl]] radical ([[phenyl|Ph]]•). [[Methyl ethyl ketone peroxide]] is also common, and [[acetone peroxide]] is on rare occasions used as a radical initiator, too.
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| *Inorganic peroxides function analogously to organic peroxides. Many polymers are often produced from the alkenes upon initiation with [[peroxydisulfate]] salts. In solution, peroxydisulfate dissociates to give sulfate radicals:<ref name = Ullmann>{{Ullmann | title = Peroxo Compounds, Inorganic | author = Harald Jakob, Stefan Leininger, Thomas Lehmann, Sylvia Jacobi, Sven Gutewort | doi = 10.1002/14356007.a19_177.pub2}}</ref>
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| :: [O<sub>3</sub>SO-OSO<sub>3</sub>]<sup>2-</sup> <math>\overrightarrow{\leftarrow}</math> 2 [SO<sub>4</sub>]<sup>-</sup>
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| The sulfate radical adds to an alkene forming radical sulfate esters, e.g. <sup>.</sup>CHPhCH<sub>2</sub>OSO<sub>3</sub><sup>-</sup>, that add further alkenes via formation of C-C bonds. Many styrene and fluoroalkene polymers are produced in this way.
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| * In atom transfer radical polymerization (ATRP) carbon-halides reversibly generate organic radicals in the presence of [[transition metal]] [[catalyst]].
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| [[Image:ATRP general.png|thumb|600px|General ATRP Reaction. <span style="color: blue">A.</span> Initiation. <span style="color: blue">B.</span> Equilibrium with dormant species. <span style="color: blue">C.</span>Propagation]]
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| ==Safety==
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| Some radical initiators such as [[azo compound]]s and [[peroxide]]s are often unstable. They are often stored cold.
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| ==References==
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| {{Reflist}}
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| {{DEFAULTSORT:Radical Initiator}}
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| [[Category:Radical initiators| ]]
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27 year old Market Study Analyst Rusty Golden from Chase, has many passions that include bonsai trees, property developers house for sale in singapore singapore and fish keeping. Discovers the charm in traveling to destinations across the entire world, recently only returning from Armenian Monastic Ensembles of Iran.