From 4-nitrotoluene and 4,4′-dinitrobibenzyl to E-4,4′-dinitrostilbene: an electrochemical approach

Abstract

The dianions formed by the electroreduction of Z-O₂NC₆H₄CHCHC₆H₄NO₂, E-O₂NC₆H₄CHCHC₆H₄NO₂, O₂NC₆H₄CH₂–CH₂C₆H₄NO₂ or O₂NC₆H₄CMeH–CMeHC₆H₄NO₂, as well as the anion radical arising from 4-nitrotoluene, are stable, in the time scale of cyclic voltammetry (DMF + 0.10 M NBu₄BF₄). However, in the electrolysis time scale (from minutes to hours), only the dianion O₂NC₆H₄CMeH–CMeHC₆H₄NO₂²⁻ remains stable, since the reduced species, Z-O₂NC₆H₄CHCHC₆H₄NO₂²⁻, O₂NC₆H₄CH₂–CH₂C₆H₄NO₂²⁻ or O₂NC₆H₄Me˙⁻, evolve to form the E-O₂NC₆H₄CHCHC₆H₄NO₂²⁻ dianion. This intermediate is recovered as the neutral species E-O₂NC₆H₄CHCHC₆H₄NO₂ with concomitant water reduction after the work-up with water, as demonstrated by combined electrolysis, cyclic voltammetry experiments, UV-spectroelectrochochemistry and theoretical calculations. Bulk electrolysis under optimized conditions (ACN + 0.10 M NBu₄BF₄) provides 40% and 67% isolated yields of E-4,4′-dinitrostilbene from 4-nitrotoluene and 4,4′-dinitrobibenzyl, respectively.