Electrochemical Methods for Degradation of Orange II (Sodium 4-(2-Hydroxy-1-naphthylazo)benzenesulfonate)

In divided flow-through cells, reductive electrolysis of Orange II (1) was first order in both substrate and applied current and gave the products of reductive cleavage at the azo linkage in essentially quantitative yield. Oxidative electrolysis was also pseudo-first-order and led to mineralization. At a boron-doped diamond anode, the rate of disappearance of 1 closely tracked the loss of total organic carbon from solution. In undivided cells oxidation and reduction occurred simultaneously; under acidic conditions the reduction products (anilines) were rather persistent because they were present as ammonium ions, but under alkaline conditions the anilines were mineralized along with the starting material. When chloride ion was present in the supporting electrolyte, electrochemical oxidation afforded hypochlorite, and the disappearance of 1 proceeded by way of hypochlorination.