Methods for Organic Electrosynthesis - Fundamentals and Applications of Organic Electrochemistry - page 60

4.2 Mechanism of Organic
Electrode Reactions
In the case of organic electrode reactions,
electron transfer generally does not take place
cleanly, and pre and/or post reactions usually
accompany the transfer. This is quite different
from inorganic electrode reactions. An organic
electrode reaction consists of an electron
transfer step as well as several chemical and
physical steps.
Figure 4.2 illustrates each elementary reaction
step of substrate S forming product P via
intermediate I . In step (a), mass transport of S
from the bulk of an electrolytic solution to the
electrode surface takes place by diffusion or
migration. In step (b), pre-reactions such as
desolvation, dissociation and/or deprotonation
of S take place to form intermediate I .
However, such pre-reactions do not always take
place. In step (c), the intermediate I adsorbs on
the surface of the electrode to form
intermediate I ad . In step (d), electron transfer
between I ad and an electrode generates
intermediate I ′ ad . In step (e), desorption of I ′ ad
followed by subsequent chemical reaction (f)
proceeds to provide a product P that diffuses to
the bulk of the electrolytic solution, and then
the sequential reaction is completed.
Intermediate I may undergo an electron
transfer reaction without an adsorption step (c)
and also the order of sequential steps (e) and (f)