OXIDATION OF ALCOHOLS, AMINES AND AMIDES

The chapter describes the process of oxidation of alcohols, amines, and amides. Early electrochemical processes for the oxidation of alcohols to ketones or carboxylic acids used platinum or lead dioxide anodes, usually with dilute sulphuric acid as an electrolyte. The majority of amines show an irreversible oxidation wave on cyclic voltammetry in acetonitrite at a platinum electrode. An electron is lost from the nitrogen lone pair and the resulting radical-cation loses a proton from the α-position. Proton loss is assisted by overlap in the transition state between the p -orbital containing an unpaired electron on nitrogen and the stretching σ-orbital of the carbon-hydrogen bond. Amines are stable to electrochemical oxidation in acid solution because the nitrogen lone pair is protonated and inaccessible for reaction. However, this is not the case for N-acetylamines, which are oxidizable at a lead dioxide anode in aqueous sulphuric acid. The primary electron transfer step involves the amide function and leads to a radical-cation, which loses a proton from the carbon atom adjacent to nitrogen. Electrochemical oxidation of amides and urethanes in methanol containing an inert electrolyte has been developed into a useful procedure for the generation of α -methoxy derivatives.