Very Fast, in Cage, Recombination of a Radical with a Nucleophile. Arylazo Sulfides in SRN1 Aromatic Nucleophilic Substitutions

Article abstract of DOI:10.1021/jo00062a007

The cyclic voltammograms of (E)-(4-cyanophenyl)azo (1a) and (E)-(4-nitrophenyl)azo phenyl sulfide (1b) as well as of (E)- and (Z)-(4-cyanophenyl)azo tert-butyl sulfide <(E)-1c and (Z)-1c> evidence an extremely effective recombination between the aryl radical and the thiolate anion originating from the decomposition of the radical anions of the azo sulfides.Solvent changes and the addition of CN^- as an "external" nucleophile point to a cage effect as the cause of such efficient S_RN1 reactions leading to the corresponding aryl phenyl or aryl tert-butyl sulfides 2a-c.In the case of (4-cyanophenyl)azo tert-butyl sulfide <(E)-1c and (Z)-1c>, trapping by the "external" nucleophile is more efficient with the (E)-isomer than with the (Z)-isomer, and the possible causes of this effect are discussed.