Azo compounds (R-N=N-R') can be the precursor of twocarbon-centered radicals (R• and R'•) and nitrogen gas upon heating and/or by irradiation. For example,AIBN andABCN yield isobutyronitrile and cyclohexanecarbonitrile radicals, respectively.
Organic peroxides each have a peroxide bond (-O-O-), 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 (t-BuOOt-Bu) gives twot-butoxy radicals (t-BuO•) and the radicals becomemethyl radicals (CH3•) with the loss ofacetone.Benzoyl peroxide ((PhC)OO)2) generates benzoyloxyl radicals (PhCOO•), each of which losescarbon dioxide to be converted into a phenyl radical (Ph•).Methyl ethyl ketone peroxide is also common, andacetone 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 withperoxydisulfate salts. In solution, peroxydisulfate dissociates to give sulfate radicals:[3]
[O3SO-OSO3]2− ⇌ 2 [SO4]−
The sulfate radical adds to an alkene forming radical sulfate esters, e.g..CHPhCH2OSO3−, that add further alkenes via formation of C-C bonds. Many styrene and fluoroalkene polymers are produced in this way.
