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Electrochemical Oxidation of σ ‐Complex‐Type Intermediates in Aromatic Nucleophilic Substitutions
Author(s) -
Moutiers Gilles,
Pinson Jean,
Terrier François,
Goumont Régis
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20010417)7:8<1712::aid-chem17120>3.0.co;2-g
Subject(s) - adduct , chemistry , oxidizing agent , acetonitrile , electrochemistry , nucleophile , redox , radical ion , medicinal chemistry , proton , nitro , ion , ring (chemistry) , photochemistry , electrode , organic chemistry , catalysis , physics , quantum mechanics , alkyl
A series of σ ‐adducts ( 1 H − … 7 H − ) derived from the addition of 2‐nitropropenide ion to various nitrobenzofuroxans and nitrobenzofurazans have been oxidized electrochemically. The results show that the rearomatization of the carbocyclic ring of these adducts as well as that of a few additional 4,6‐dinitrobenzofuroxan adducts ( 8 H − a – c ) is associated with much higher oxidation potentials than found for the same process in the dinitro‐ and trinitrobenzene series. Especially high E ° values are measured for the oxidation of the 2‐nitropropenide 4,6‐dinitro‐ and 4‐nitro‐6‐trifluoromethylsulfonylbenzofuroxan adducts 1 H − and 4 H − in acetonitrile: E °( 1 H − )=1.15 V versus SCE; E °( 4 H − )=1.33 V versus SCE. These values fit well with the available evidence that the chemical oxidation of these adducts requires the use of very strong oxidizing agents to proceed efficiently. The mechanism for the oxidation process has been established. It is shown to involve transfer of two electrons and liberation of one proton per σ ‐complex precursor with no evidence whatsoever for the intermediacy of radical anionic species.