4520-08-5Relevant articles and documents
Outer-sphere dissociative electron transfer to organic molecules: A source of radicals or carbanions? Direct and indirect electrochemistry of perfluoroalkyl bromides and iodides
Andrieux, Claude P.,Gélis, Laurence,Medebielle, Maurice,Pinson, Jean,Savéant, Jean-Michel
, p. 3509 - 3520 (2007/10/02)
As an example of the general problem posed in the title, the reduction of CF3Br, CF3I, C6F13I, and C8F17I by outer-sphere heterogeneous (glassy-carbon electrodes) and homogeneous (aromatic anion radicals) reagents is investigated, in aprotic solvents containing tetralkylammonium salts, by cyclic voltammetry and preparative-scale electrolysis. A RF. chemistry is thus triggered in all cases with the exception of CF3Br where a mixed RF./RF- chemistry is obtained by direct electrochemical reduction or by electron transfer from aromatic anion radicals having a close reduction potential. Quantitative analysis of the reduction kinetics of RFX (X = Br, I) and of RF. led to the following conclusions. RFX most likely undergoes a concerted electron-transfer-bond-breaking reduction involving a substantial overpotential (ca. 1.5 V for C-Br and 1.0 V for C-I), mainly governed by the C-X bond dissociation energy. RF. radicals are strongly stabilized by interaction with the solvent but are nevertheless easier to reduce than alkyl radicals on thermodynamical grounds, exhibiting however a high intrinsic barrier of the same order as for alkyl radicals. Unlike alkyl radicals, but similar to aryl radicals, RF. radicals are good H-atom scavengers and do not couple with aromatic anion radicals.
