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Radical elimination can be viewed as the reverse of radical addition. In radical elimination, an unstable radical compound breaks down into a spin-paired molecule and a new radical compound. Shown below is an example of a radical elimination reaction, where a benzoyloxy radical breaks down into a phenyl radical and a carbon dioxide molecule. [7]
Hydroxyl radical (HO·) is generated by Fenton reaction of hydrogen peroxide with ferrous compounds and related reducing agents: Fe(II) + H 2 O 2 → Fe(III)OH + HO· In its fleeting existence, the hydroxyl radical reacts rapidly irreversibly with all organic compounds. superoxide (O − 2) is produced by reduction of O 2. [4]
These reactions can happen due to the free radicals having an unpaired electron in their valence shell, making them highly reactive. [1] Radical additions are known for a variety of unsaturated substrates, both olefinic or aromatic and with or without heteroatoms. Free-radical reactions depend on one or more relatively weak bonds in a
Radical reactions must be carried out under inert atmosphere as dioxygen is a triplet radical which will intercept radical intermediates. Because the relative rates of a number of processes are important to the reaction, concentrations must be carefully adjusted to optimize reaction conditions.
Therefore, it is important that the other components of the polymerization (initiator, catalyst, ligand, and solvent) are optimized in order for the concentration of the dormant species to be greater than that of the propagating radical while being low enough as to prevent slowing down or halting the reaction. [8] [9]
Here, the new radical is generated on the polymer chain, which can further undergo a similar type of reaction to generate more styrene molecules. This process is known as the radical mediated depolymerization of polystyrene. Radical elimination reactions are found in enzyme-catalyzed pathways.
The hydroxyl radical has a very short in vivo half-life of approximately 10 −9 seconds and a high reactivity. [5] This makes it a very dangerous compound to the organism. [6] [7] Unlike superoxide, which can be detoxified by superoxide dismutase, the hydroxyl radical cannot be eliminated by an enzymatic reaction.
It is the reactions of the radical species that are responsible for the changes observed following irradiation of a chemical system. [ 2 ] Charged radiation species (α and β particles) interact through Coulombic forces between the charges of the electrons in the absorbing medium and the charged radiation particle.