Mechanism of 2-quinizarinsulphonic acid reduction on a mercury electrode

Abstract

The reduction of the 1,4-dihydroxyanthraquinone-2-sulphonic acid (quinizarinsulphonic acid) at a dropping mercury electrode has been investigated. The reduction takes place in two monoelectronic steps and show E1/2 values vs. sce (E1/2)1 = −0.380 V and (E1/2)2 = −1.045 V at pH 4.60. The first wave is diffusion controlled, while the second wave is kinetically controlled. The reagent captures one electron and one proton to form the semiquinonic system. The semiquinone is dimerized. The dimer captures one electron and one proton, per molecule, to form the hydroquinone. The reaction orders, together with Tafel's slopes, have been calculated.