- Electrochemical Determination of Absolute and Relative Reactivities of Phenyl Chalcogenide Anions toward Aryl Radicals
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Absolute and/or relative reactivities of PhE- anions (E = Se, Te) toward the radicals resulting from the reductive cleavage of 9-bromoanthracene and 2- and 4-bromobenzophenone were determined by electrochemically stimulated SRN1 substitution in MeCN and Me2SO.Cyclic voltammetry and preparative-scale electrolyses were carried out under experimental conditions where the nucleophilic attack (rate constant k2) was competing only with H atom abstraction (rate constant kH) and so k2/kH ratios could be measured.Taking into account results previously published by Saveant et al. concerning kH and the reactivity of PhS- nucleophile toward aryl radicals, the following conclusions were drawn out.The absolute reactivity of PhSeNBu4 toward 9-anthryl radical is 12 times higher in MeCN (k2 = 8.1 x 109 M-1 s-1) than in Me2SO (k2 = 6.8 x 108 M-1 s-1).In Me2SO, the relative reactivities of PhSLi, PhSeLi, and PhTeLi are 1, 1.4, and 3.2.In MeCN the rate k2 is close to the diffusion limit in the nucleophilic attack of PhSeNBu4 and PhSNBu4 upon radicals corresponding to reduction of bromobenzophenone.
- Degrand, Chantal,Prest, Rita
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p. 5242 - 5246
(2007/10/02)
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- Electrochemically induced srn1 substitution in acetonitrile. Synthesis of arenes substituted by phenylseleno- and phenyltelluro groups
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In MeCN, the direct or mediated cathodic reduction of unactivated ArBr (Ar = 4-biphenyl, 2-fluorenyl, 9-anthryl) in the presence of an equivalent of PhE- (E = Se, Te) leads to ArEPh in interesting isolated yields (53-74 %) by SNR1 substitution. The electrochemical synthesis of 9-phenylchalcogenoanthracene proceeds in better yields in MeCN than in DMSO. The 4,4′-disubstituted biphenyl PhSeC6H4C6H4SePh was prepared in 46 % yield in MeCN whereas its synthesis by photostimulation in liquid ammonia failed.
- Degrand, Chantal
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p. 5237 - 5252
(2007/10/02)
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