- Radical substitution
In
organic chemistry , a radical substitution reaction is asubstitution reaction involving free radicals as areactive intermediate .The reaction always involves at least two steps, and possibly a third. In the first step called initiation a
free radical is created byhomolysis . Homolysis can be brought about by heat or light but also byradical initiator s such asorganic peroxide s orazo compound s. Light is used to create two free radicals from one diatomic species. The final step is called termination in which the radical recombines with another radical species. If the reaction is not terminated, but instead the radical group(s) go on to react further, the steps where new radicals are formed and then react is collectively known as propagation because a new radical is created available for secondary reactions.Radical substitution reactions
In
free radical halogenation reactions radical substitution takes place withhalogen reagents andalkane substrates. Another important class of radical substitutions involvearyl radicals. One example is the hydroxylation ofbenzene byFenton's reagent . Many oxidation and reduction reactions in organic chemistry have free radical intermediates, for example the oxidation ofaldehyde s tocarboxylic acid s withchromic acid .Coupling reaction s can also be considered radical substitutions. Certain aromatic substitutions takes place byradical-nucleophilic aromatic substitution .Auto-oxidation is a process responsible for deterioration of paints and food and lab hazards such asdiethyl ether peroxide .More radical substitutions are listed below:
*TheBarton-McCombie deoxygenation is a way to substitute ahydroxyl group for a proton.
*TheWohl-Ziegler reaction involves the allylic bromination of alkenes.
*TheHunsdiecker reaction converts silver salts of carboxylic acids to alkyl halides.
*The Dowd-Beckwith reaction involves ring expansion of cyclic β-keto esters.
* TheBarton reaction involves synthesis of nitrosoalcohols from nitrites.
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