Peroxide
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A peroxide is a compound containing an oxygen-oxygen bond. Superoxides, dioxygenyls, ozones and ozonides compound are considered separately.
[edit] Colloquial meaning
In common usage, peroxide is an aqueous solution of hydrogen peroxide (HOOH or H2O2) sold for use as a disinfectant or mild bleach. The usual peroxide used in commercial applications is a dilute solution containing traces of stabilisers, and is sold in either brown glass, or brown opaque polyethylene bottles to minimise the rate of decomposition. The concentrations sold are generally either 3% (either weight of volume) or 6% (w/v); these are sometimes described as "10 volume" and "20 volume", respectively. This refers to the relative volume of oxygen gas produced, at STP, or the ideal state of gas, from the complete decomposition of the peroxide. 6% (w/v) hydrogen peroxide is strong enough to bleach skin, causing white blotches caused by tiny bubbles of oxygen. Hydrogen peroxide is also used to bleach hair.
Due to the presence of catalase in blood, peroxide is only marginally effective in disinfecting open wounds, but excellent for bleaching blood stains. It is also often used as a disinfectant in the dairy industry because, after application, it leaves absolutely no harmful residues.
[edit] Organic chemistry
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 radicals of the form:
- RO·
This makes them useful as catalysts for some types of polymerisation, such as the polyester resins used in glass-reinforced plastics. MEKP (methyl ethyl ketone peroxide) is commonly used for this purpose.
However, the same property also means that organic peroxides can accidentally initiate explosive polymerisation in materials with unsaturated chemical bonds. Since peroxides can form spontaneously in some materials, some caution must be exercised with such "peroxide-forming materials." Triacetone triperoxide 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 ethers 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 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.[1]
[edit] Inorganic chemistry
In inorganic chemistry, peroxide is the anion O22−. It is highly basic, and present in ionic compounds such as alite[citation needed], the primary constituent of Portland cement clinker. Pure peroxides (containing only cations and the peroxide anions) are usually formed by burning alkali metals or alkaline earth metals in air or oxygen. Sodium peroxide Na2O2 is a typical example.
The peroxide ion contains two electrons more than the oxygen molecule. These two electrons, according to the molecular orbital theory, complete the two π* antibonding orbitals. This has as result a weakening of the bond strength of the peroxide ion and a greater length for the bond O-O : Li2O2 130 pm to BaO2 147 pm. Furthermore, the peroxide ion is diamagnetic.
The peroxides of the alkali metals and Ca, Sr and Ba are 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 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 oxides, peroxides and superoxides 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 submarines), through the reaction:
- 2Na2O2 + 2CO2 → 2Na2CO3 + O2
[edit] See also
- catalase
- oxygen
- ozone
- peroxidases
- hydrogen peroxide
- carbamide peroxide
- sodium percarbonate
- calcium peroxide
- magnesium peroxide
- potassium monopersulfate
- sodium perborate monohydrate
- ozonide, O3−
- superoxide, O2−
- oxide, O2−
- dioxygenyl, O2+
| Functional group | |
|---|---|
| Chemical class: Alcohol • Aldehyde • Alkane • Alkene • Alkyne • Amide • Amine • Azo compound • Benzene derivative • Carboxylic acid • Cyanate • Disulfide • Ester • Ether • Haloalkane • Imine • Isocyanide • Isocyanate • Ketone • Nitrile • Nitro compound • Nitroso compound • Peroxide • Phosphoric acid • Pyridine derivative • Sulfone • Sulfonic acid • Sulfoxide • Thioester • Thioether • Thiol • Toluene derivative |
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