Radical initiator

Main types of initiation reaction

• Halogens undergo homolytic fission relatively easily. Chlorine, for example, gives two chlorine radicals by irradiation with ultraviolet light. This process is used for chlorination of alkanes.
• Azo compounds can be the precursor of two carbon-centered radicals and nitrogen gas upon heating and/or by irradiation. For example, AIBN and ABCN yield isobutyronitrile and cyclohexanecarbonitrile radicals, respectively.
• Organic peroxides each have a peroxide bond, 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 gives two t-butoxy radicals and the radicals become methyl radicals with the loss of acetone. Benzoyl peroxide ₂) generates benzoyloxyl radicals, each of which loses carbon dioxide to be converted into a phenyl radical. Methyl ethyl ketone peroxide is also common, and acetone peroxide is on rare occasions used as a radical initiator, too.
• 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:

• In atom transfer radical polymerization carbon-halides reversibly generate organic radicals in the presence of transition metal catalyst.

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