Electron spin resonance studies. Part 68. Addition versus overall one-electron abstraction in the oxidation of alkenes and dienes by SO4–˙, Cl2–˙, and ˙OH in acidic aqueous solution
- 1 January 1984
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 2
- No. 11,p. 1809-1815
- https://doi.org/10.1039/p29840001809
Abstract
E.s.r. spectroscopy has been employed to characterize radicals formed by the reaction of alkenes, dienes, and some substituted derivatives with SO4 –˙(generated photolytically), Cl2 –˙(from Cl– and SO4 –˙ or ˙OH, and ˙OH (from TiIII–H2O2 in a flow system). For some substrates (e.g. HOCH2CHCH2, butadiene) the appropriate SO4 –˙ and chlorine-atom adducts are detected, whereas for others (e.g. cyclopentadiene) only hydroxyl adducts are characterized. It is suggested that the reaction mechanism involves formation of the appropriate chlorine-atom and sulphate adducts, with subsequent rapid hydrolysis: this may involve production and rapid hydration of an incipient radical-cation. It is found that Cl2 –˙ is more effective than SO4 –˙ in achieving overall one-electron oxidation. The regioselectivities of ˙OH attack on alkenes and of the hydration of alkene radical-cations are contrasted and rationalized. Finally, cyclization reactions of pent-4-en-1-ol (with Cl2 –˙, ˙OH–H+) and hex-4-en-1-ol (CI2 –˙, ˙OH–H+, SO4 –˙) are rationalized in terms of rapid internal nucleophilic attack on a transient alkene radical-cation.Keywords
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