Electrooxidation of β-dicarbonyl compounds using ceric methanesulfonate as mediator:: Some kinetics and spectroscopic studies

beta-Dicarbonyl compounds 2,4-pentanedione (I),1,3-cyclohexanedione (II), 1,3-diphenyl-1,3-propanedione (III), methyl acetoacetate (IV), dimethyl malonate (V), methyl cyanoacetate (VI), and malononitrile (VII) were submitted to electrocatalytic oxidation mediated by Ce-IV anodically generated from cerous methanesulfonate, Ce(CH3SO3)(3). I, II, III, IV, and V decompose yielding their respective carboxylic acids, methyl alcohol and CO2, via a proposed tricarbonylic intermediate. Four electrons per mole are consumed in these reactions. VI and VII proved to be unreactive. The reactivity order found was I congruent to III > II > IV > V. The substrates that form larger quantities of enol in reaction medium (beta-diketones) are the most reactive, followed by the beta-ketoester that forms less enol and the diester that forms no enol. An enol-Ce-IV complex is formed and the electron transfer is postulated as being "inner sphere." (C) 1999 Academic Press.