OXIDATION OF KETONES, ALDEHYDES, AND CARBOXYLIC ACIDS

Aliphatic ketones are oxidized in both acetonitrile and trifluoracetic acid at potentials less positive than required for the analogous hydrocarbons. The oxidation process is irreversible in both solvents, and cyclic voltammetry peak potentials are around 2.7 V vs. sce . Loss of an electron from the carbonyl oxygen lone pair is considered to be the first stage in the reaction. Ketones react with electrochemically generated halogens to form the α-halogenocompound. In the presence of potassium hydroxide and potassium iodide, more stable enolate is formed from the ketone and this reacts with the electrochemically generated iodine. The electrochemical oxidation of aldehydes to the carboxylic acid, catalyzed by bromide or iodide ions, is an extensively exploited process. It is the preferred route for the oxidation of reducing sugars to the aldonic acid and replaces the older technique where bromine in stoichiometric amount was used as the oxidizing agent. The reaction is carried out in aqueous solution in an undivided cell at a graphite anode using an electrolyte of sodium bromide containing suspended calcium carbonate. The oxidation of alkylcarboxylates is one of the first organic electrochemical reactions to be investigated.