Electrochemical behaviour of azo dyes in acid/ethanol media

Abstract

The electrochemical reduction of four azo dyes in acid media was studied by differential-pulse polarography, cyclic voltammetry and constant-potential coulometric methods. All of the electro-reductions of the azo groups are irreversible one-step and 4-electron reduction at pH < 2. Ortho and para electron withdrawing substituents (e.g. -CO 2Bu-n) cause the azo groups to be more easily reduced than meta analogues. In compounds containing both azo and nitro groups, the azo group is reduced prior to the nitro group. The dyes are very useful in silver dye bleach photographic materials.