Organic Electrosynthesis - Fundamentals and Applications of Organic Electrochemistry - page 204

6.3 Solid-Supported Mediators
Although mediators have many advantages as
explained in Chapter 2 , 3 , and 5 , they have to be
removed from the electrolytic solution after
electrolysis. However, mediators have never
been recovered after electrolysis for a long time.
Quite recently, disposal-type mediators have
become a problem from GSC, particularly atom
economical aspect. In order to overcome such
problems, easily separable and recyclable
mediators have been developed.
At an early stage of this approach, a
cross-linked poly-4-vinylpyridine
hydrobromide as a solid-supported mediatory
system was developed [9]. As shown Eq. 6.2 ,
Br − derived from the solid base is anodically
oxidized in an aqueous electrolytic solution to
generate hypobromide ion, BrO − , which
oxidizes alcohols to give ketones, and then Br −
is regenerated. Thus, the mediator can be easily
recovered as the HBr salt of the solid base.
(6.2)
Since N -oxyl radicals as represented by TEMPO
generally show reversible redox properties, as
shown in Eq. 6.3 , they are useful mediators for