Anodic oxidation homomediatory systems

The oxidation potential of the substrate S in Figure 2 is beyond the range accessible by the electrochemical method so that direct electron transfer from S to the anode hardly occurs, and also the high oxidation potential necessary for the direct oxidation of S causes unexpected side reactions involving oxidation of the solvent or supporting electrolyte. However, when a compound Mrxi (a reduced form of M) which may be oxidized at a sufficiently lower potential than S is added to the reaction system, the oxidation of Mied to Mox (an oxidized form of M) will take place prior to the oxidation of S. Provided that Mox is able to oxidize S to product P, the oxi tion of S will be achieved at a potential lower than that necessary for its direct oxidation. Oxidation of S with Mox may be effected in two ways, namely by direct electron transfer (homogeneous electron transfer) from S to Mox in solution or by chemical oxidation of S with Mox. The former system is called a homomediatory system and the latter a heteromediatory (or chemomediatory) system. The compound M is called a mediator or an electron carrier, since M mediates electron transfer between S and the anode. When Mox oxidizes S in solution, Mox is reduced to Mrxi... [Pg.807]

Big Chemical Encyclopedia