Amine oxidation. Part 13. Electrochemical oxidation of some substituted tertiary alkylamines

Abstract

The anodic oxidation of some polyamines and amino-alcohols has been studied by linear sweep voltammetry at a glassy-carbon electrode in basic aqueous methanol. Although most of the substrates show one oxidation wave, a few show two. It is concluded that the second, less anodic wave comes from the oxidation of substrate diffusing to the anode, whereas substrate adsorbed to the anode gives rise to the more anodic wave. In general the introduction of an electron-withdrawing heteroatom substituent into a tertiary amine destabilises the aminium radical forming in the potential-determining step and raises the oxidation peak potential, the magnitude of this effect being related to the separation between the substituent and the oxidation centre. In some of the substrates through-bond or through-space interactions occur. These effects, which stabilise the forming aminium radical and lower the E_p value, are superimposed on the inductive or field effects.