THE ELECTROCHEMICAL REDUCTION OF 2-ETHYL ANTHRAQUINONE

The electrochemical reduction of 2-ethyl anthraquinone (EAQ), an alternate step in the production of hydrogen peroxide, is shown to be feasible in a two-phase system consisting of a mixture of ethyl benzene and tributyl phosphate, and aqueous sodium hydroxide. The initial reduction product on the most effective cathode material, lead, is the sodium salt of the hydroquinone (Na2EAHQ). In this system the reactant, EAQ, has very low solubility in the aqueous phase whereas the product, Na2EAHQ, is similarly insoluble in the organic phase. The results of this investigation may be of interest to the study of other systems with these solubility characteristics. Electrolysis was carried out under well-defined conditions of vigorous turbulence in a cell in which a rotating cylindrical cathode was separated from the cylindrical anode by a coaxial Nafion membrane. At a rotational rate of 2000 rpm, about equal volumes of the organic and aqueous phases could be suspended in the cell while keeping the aqueous phase continuous. Current-voltage behavior was mass-transfer limited and hence was a function of rate of rotation, organic/aqueous phase ratio, and EAQ concentration in the organic phase. The maximum cathodic limiting current density achieved was 30 mA/cm2. Current efficiencies approached 100% for the reduction of EAQ when operating at 50% of the limiting current. The electrochemical reaction was shown to take place at the three-phase boundary: organic/aqueous/lead. A flow-through porous-electrode cell, using lead-plated, reticulated vitreous carbon for the cathode, was constructed to promote more intimate contact between the reactant and the electrode. The maximum current density for EAQ reduction achieved in this cell was 177 mA/cm2 based on the projected cathode area.