Peroxides are defined as groups of compounds in which two oxygen atoms are joined together by a single covalent bond. They have the typical structure of R-O-O-R where R denotes any kind of atom. The O-O the bond present is called the peroxide group. Usually, the oxygen ion has a 2- oxidation number, but the oxygen atoms in the O-O bond has an oxidation number of 1-. Peroxides are unstable compounds and release oxygen when heated to decomposition. Thus, peroxides are strong oxidising agents. Peroxides can be formed by the direct reaction of an element with oxygen.
Hydrogen peroxide (H2O2) is the most common peroxide found. It is almost colourless and its solutions are colourless as well. It is very dangerous when it comes into contact with organic compounds. However, it is biochemically produced and synthesized inside our bodies as a result of the oxidase enzyme range.
There are a few major classes of peroxides:
Peroxy Acids: Peroxy derivatives of familiar acids, for example, peracetic acid,
Primary Group Peroxides: Compounds with the structure E-O-O-E where E is the main group element,
Metal Peroxides: The main element is a metal, for example, zinc peroxide (ZnO2),
Organic Peroxides: The main element is carbon and the main structure is C-O-O-C or C-O-O-H, for example, tertiary butyl hydroperoxide.
The most common peroxide is hydrogen peroxide (H2O2) which acts as a bleaching agent. Metallic class oxides which contain the divalent -O-O- bond are also considered peroxide. Na2O2 is one such example. It is also used as a bleaching agent. Organic compounds that contain the -O-O- bond or the peroxide anion are also considered peroxides. These kinds of compounds are explosive in nature. Ozone, ozonides and superoxides are also peroxides but tend to be ignored as peroxides due to their specific characteristics.
There are some compounds that resemble the peroxide formula but do not contain the -O-O- bond such as Manganese peroxide (MnO2).
Peroxides have a wide range of purposes in everyday life as well as in our bodies. Inside our bodies, hydrogen peroxide is formed during some kind of biochemical process. Peroxides formed inside our bodies are called peroxisomes. Although it is formed momentarily, it is toxic to our cells, especially the DNA. This characteristic feature of hydrogen peroxide is useful for killing bacteria and pathogens inside our bodies. Peroxisomes are used in the synthesis of compounds that are important for the normal functioning of the brain and the lungs. They are also useful for the synthesis of fatty acids and polyamines.
Plants also use peroxides for signalling defence against pathogens.
Peroxides like hydrogen peroxide are used as bleaching agents and in hair products to lighten hair colour. Peroxides are also used to synthesize drugs and some other chemicals.
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