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Electrochemical Oxidation of σ‐Complex‐Type Intermediates in Aromatic Nucleophilic Substitutions

Gilles Moutiers Dr.

E-mail address:moutiers@chimie.uvsq.fr

SIRCOB, UPRES‐A CNRS 8086 Université de Versailles, Bâtiment Lavoisier 45 Avenue des Etats‐Unis, 78035 Versailles Cedex (France) Fax: (+33) 1‐39‐25‐44‐52

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Jean Pinson Prof.

E-mail address:pinson@paris7.jussieu.fr

Laboratoire d'Electrochimie Moléculaire UMR CNRS no 7591. Université Paris7‐Denis Diderot 2 Place Jussieu, 75251, Paris Cedex 05 (France) Fax: (+33) 1‐44‐27‐76‐25

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François Terrier Prof.

E-mail address:terrier@chimie.uvsq.fr

SIRCOB, UPRES‐A CNRS 8086 Université de Versailles, Bâtiment Lavoisier 45 Avenue des Etats‐Unis, 78035 Versailles Cedex (France) Fax: (+33) 1‐39‐25‐44‐52

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Régis Goumont Dr.

SIRCOB, UPRES‐A CNRS 8086 Université de Versailles, Bâtiment Lavoisier 45 Avenue des Etats‐Unis, 78035 Versailles Cedex (France) Fax: (+33) 1‐39‐25‐44‐52

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Abstract

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 ac) 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.

Number of times cited: 27

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