Four-electron reduction of oximes to amines is known to involve pre-protonation but the number of protons was not known. The reduction was supposed to take place by initial cleavage of the N-O bond, but no direct experimental evidence was available. From the shape of i=f(pH) plots and shifts of E1/2 with pH it was concluded that it is the diprotonated form which is reduced (>C=N+H-OH+2). Presence of positive charge on adjacent N and O atoms was supported by pH-dependence of the reduction of nitrones. Some deviations from simple experimental evidence were attributed to the heterogeneity of the electrode process. When conditions are found, where dE1/2/dpH are similar, substituent effects follow Hammett equation. In acidic media separation of two two-electron waves was observed. This is due to a difference in pH-dependence of E1/2 of oximes and resulting imines. The observation of two two-electron waves confirms the formation of imine as an intermediate in the reduction of oximes.
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