Potential step generating cathodic

Figure 2. Potential step generating (a) cathodic and (b) anodic ECL.

A more useful chronoamperometric method involves a double potential step (somewhat reminiscent of the previously discussed reversal electrolysis). In this case, for instance for a reduction process, a first cathodic potential step is applied according to the preceding criteria (such that instantaneously COx(0,0 — 0), followed at a time x by the application of a second anodic potential step which causes the species Red previously generated at times < x to be instantaneously reoxidised (such that CRed(0,0 — 0). 

The use of a redox mediator such as azobenzene has introduced a further sophistication in that it has allowed the cathodic potential in the second step of the procedure to be substantially reduced, until only the mediator remained electroactive. Thus the first step is the electroreductive generation of RSe or RTe then the haloketone, the acidic species such as fluorene, and the azobenzene redox mediator are added and the potential reduced for the second step. By this means isolated yields of 86%... 

Intermolecular addition of radicals, generated by photo-electrochemical catalysis, to activated alkenes can also be brought about. The reaction of 66 is used as a key step in one synthesis of the insect pheromone, brevicomin [219]. The reaction of a secondary radical from 67 occurs at low cathode potentials and without photochemical assistance [219]. This illustrates the equiibrium between a secondary al-kylcobalt(m) species and the radical - cobalt(ii) pair. The carbon radical is eventually captured by reaction with the alkene. Further steps in the synthesis lead to four isomers of the pheromone, multistriatin, each of which is a pure enantiomer since... 

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