Peroxide
Peroxide has three distinct meanings:
In common usage,
peroxide is an
aqueous solution of
hydrogen peroxide (HOOH or H
2O
2) 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
opaque polyethylene bottles to minimise the rate of decomposition. The
concentrations sold are generally either 3% (w/v) 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.
In
organic chemistry,
peroxide is a specific
functional group or a molecule containing that functional group.
ROOR'
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
desiccation. Extreme care must be taken with samples showing signs of crystal growth or precipitates.
In
inorganic chemistry,
peroxide is the
anion O
22−, usually formed by burning
alkali metals or
alkaline earth metals in
air or
oxygen.
Hydrogen peroxide H
2O
2 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 : Li
2O
2 130 pm to BaO
2 147 pm. Furthermore, the peroxide ion is
diamagnetic.
The peroxides of the alkali metals and Ca, Sr and Ba are . 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:
2Na
2O
2 + 2CO
2 â†' 2Na
2CO
3 + O
2*
catalase*
oxygen*
ozone*
peroxidases*
sodium percarbonate*
calcium peroxide*
magnesium peroxide*
potassium monopersulfate*
sodium perborate monohydrate*
ozonide, O
3−*
superoxide, O
2−*
oxide, O
2−*
dioxygenyl, O
2+
