Peroxide
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A '''peroxide''' is a compound containing an [[oxygen]]-oxygen [[chemical bond|single bond]]. The simplest stable peroxide is [[hydrogen peroxide]]. [[Superoxide]]s, [[dioxygenyl]]s, [[ozone]]s and [[ozonide]]s compound are considered separately.
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== Organic chemistry ==
{{main|Organic peroxide}}
In [[organic chemistry]], '''peroxide''' is a specific [[functional group]] or a molecule containing an oxygen-oxygen single bond (R-O-O-R'). When the other oxygen bears a hydrogen, it is called a '''hydroperoxide''' (R-O-O-H). The radical HOO· is known as [[hydroperoxide]] radical, and is thought to be involved in [[combustion]] of hydrocarbons in air.
Organic peroxides tend to decompose easily to [[free radical]]s of the form:
:RO·
This makes them useful as [[catalyst]]s for some types of [[polymerisation]], such as the [[polyester]] [[resin]]s used in [[glass-reinforced plastic]]s. [[MEKP]] ([[methyl ethyl ketone peroxide]]) is commonly used for this purpose.
However, the same property also means that organic peroxides can accidentally initiate explosive polymerization in materials with unsaturated [[chemical bond]]s. Since peroxides can form spontaneously in some materials, some caution must be exercised with such "peroxide-forming materials." [[Triacetone triperoxide]] (TATP) and [[hexamethylene triperoxide diamine]] are explosive organic peroxide compounds; TATP may be formed accidentally as a waste product in some reactions. In addition, many liquid [[ether]]s in the presence of [[air]], light, and [[metal]] slowly (over a period of months) form ether peroxides (e.g., [[diethyl ether peroxide]]), which are extremely unstable. As a consequence, it is recommended that ether be stored over potassium hydroxide, which not only destroys peroxides but also acts as a powerful [[desiccation|desiccant]]. Extreme care must be taken with samples showing signs of crystal growth or precipitates.
TATP is an easily synthesized, inexpensive, explosive compound that is difficult to detect by normal screening methods. Consequently, it is an explosive favored by terrorists. TATP was used in the 2005 London Underground bombings and the 2001 "shoe bomber." In 2002, a simple [[mass spectroscopy]] screening method was developed.[http://pubs.acs.org/isubscribe/journals/cen/84/i04/html/8404scic.html]
== Inorganic chemistry ==
In [[inorganic chemistry]], '''peroxide''' is the [[anion]] O<sub>2</sub><sup>2−</sup>. It is highly basic, and present in ionic compounds. Pure peroxides (containing only cations and the peroxide anions) are usually formed by burning [[alkali metal]]s or [[alkaline earth metal]]s in [[air]] or [[oxygen]]. [[Sodium peroxide]] Na<sub>2</sub>O<sub>2</sub> is a typical example.
The peroxide ion contains two [[electron]]s more than the oxygen molecule. These two electrons, according to the [[molecular orbital]] theory, complete the two π* [[antibonding orbital]]s. This has as result a weakening of the [[bond strength]] of the peroxide ion and a greater length for the bond O-O : Li<sub>2</sub>O<sub>2</sub> 130 pm to BaO<sub>2</sub> 147 pm. Furthermore, the peroxide ion is [[diamagnetic]].
The peroxides of the alkali metals and Ca, Sr and Ba are [[Ion|ionic]]. The peroxides of a number of electropositive metals such as Mg, the lanthanides and the uranyl-ion show an intermediary character, between ionic and [[covalent]]. The peroxides of metals such as Zn, Cd and Hg are mainly covalent.
Peroxides are powerful [[Oxidizing agent|oxidizers]], and usually fairly unstable. Ionic peroxides react with water and diluted acids to form hydrogen peroxide. Organic compounds are oxidized to carbonates, even at normal temperatures. Sodium peroxide is a powerful oxidator of metals, such as iron.
The [[oxide]]s, '''peroxides''' and [[superoxide]]s are closely related, forming a chain of oxygen ions of progressively higher [[oxidation number]].
[[Barium peroxide]] is used in [[pyrotechnics]] and [[tracer ammunition]], and was once used in the manufacture of hydrogen peroxide. [[Sodium peroxide]] is used as a [[carbon dioxide]] absorber and oxygen regenerator (e.g. in some [[submarine]]s), through the reaction:
:2Na<sub>2</sub>O<sub>2</sub> + 2CO<sub>2</sub> → 2Na<sub>2</sub>CO<sub>3</sub> + O<sub>2</sub>
== See also ==
* [[catalase]]
* [[oxygen]]
* [[ozone]]
* [[peroxidases]]
* [[hydrogen peroxide]]
* [[carbamide peroxide]]
* [[sodium percarbonate]]
* [[calcium peroxide]]
* [[magnesium peroxide]]
* [[potassium monopersulfate]]
* [[sodium perborate monohydrate]]
* [[ozonide]], O<sub>3</sub><sup>−</sup>
* [[superoxide]], O<sub>2</sub><sup>−</sup>
* [[oxide]], O<sup>2−</sup>
* [[dioxygenyl]], O<sub>2</sub><sup>+</sup>
{{Functional Groups}}
[[Category:Anions]]
[[Category:Oxygen compounds]]
[[Category:Peroxides| ]]
[[bs:Peroksidi]]
[[de:Peroxide]]
[[es:Peróxido]]
[[fr:Peroxyde]]
[[hr:Peroksidi]]
[[id:Peroksida]]
[[it:Perossido]]
[[lt:Peroksidas]]
[[nl:Peroxide]]
[[ja:過酸化物]]
[[nds:Peroxid]]
[[pl:Nadtlenki]]
[[pt:Peróxido]]
[[ru:Пероксиды]]
[[sr:Пероксид]]
[[sh:Peroksid]]
[[fi:Peroksidi]]
[[sv:Peroxid]]
[[uk:Перекис]]
[[zh:过氧化物]]