Reactions of Intermediates Formed in Electrode Processes

As an analogy of an electrochemical process at the cathode, consider a solution of an anion radical (NT) salt in an inert solvent in the presence of an excess of the substrate (M) from which the anion radical is derived. The following primary reactions are then possible  

Only the dimerization process is considered, even if it is easily seen that the scheme may be expanded to include formation of trimers, tetramers, etc., and polymers. Thus, even in a system as simple as this the formation of MM can occur via two pathways due to the intervention of the electron transfer reaction (Eq. (40) ). This reaction scheme has been demonstrated for the radical anion from 1,1-diphenylethylene 112 (see 14.4). 

A further complication is the possibility of disproportionation of the anion radical via electron transfer  

The protonation of anion radicals and dianions derived from aromatic hydrocarbons has been studied in some detail by Hoijtink and co-workers 113-11 s). it was shown that apart from the reactions given above (Eqs. (42)—(46)) other disproportionation equilibria also play an important role. These are different for different anion radicals, making the whole picture very complex. Kinetic studies on the disproportionation of the nitrobenzene anion radical and some of its derivati-ves 116,u 7) jlave s 10wn that in aqueous solution at a pH 11.5, reaction (41) is of great importance, whereas the protonated radical ion and the radical ion are the kinetically active species in the pH interval between 3.2 and 11.5. 

The discussion above has some interesting repercussions for cathodic processes. The reaction sequence depicted in Eqs. (47) - (49) will 

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