The electrochemical reduction of a series of alkyltriphenylphosphonium cations is studied in media of low proton availability as a function of the alkyl group, initial concentration, nature and water content of the solvent, and electrolysis potential. With reference to previous work on Ph4P+ and on phosphoniums giving rise to stable ylides, a general pict ure of the mechanisms is drawn with emphasis on the following points: (1) interference of the starting cation as an acid in the reaction process leading to ylide or phosphine oxide formation and to Hofmann degradation;(2) competition between the two-electron pathway involving the above-mentioned reactions and the one-electron pathway leading to dimerization and/or disproportionation of the initially expelled radical; (3) factors determining the competition between the one-electron and the two-electron pathway and the various reactions inside each of them; (4) orientation of cleavage in electrochemical reduction and phosphine oxide formation.
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