Role of proton transfer in the electrochemical reduction mechanism of salicylideneaniline

The electrochemical reduction mechanism of salicylideneaniline has been investigated by cyclic voltammetry, controlled potential electrolysis and coulometry. The main reduction product, characterised by HPLC, IR, ¹H NMR in X-ray diffractometry, is an anionic dimer, present in two diastereoisomeric forms, together with the conjugate base of the substrate. The latter stems from an intermolecular proton transfer from the substrate to a basic reduction intermediate. Kinetic analysis of the voltammetric results has allowed the electrode reaction mechanism to be fully characterised, showing in particular that the rate-determining step is the coupling between two anionic radicals, promoted by intramolecular H-bridging.