OXIDATION REACTION OF L-ASCORBIC-ACID BY DICYANOBIS(1,10-PHENANTHROLINE)IRON(III) IN DIMETHYL-SULFOXIDE AT ELEVATED PRESSURES - EVIDENCE FOR ADIABATIC ELECTRON-TRANSFER

Kinetic measurements of the oxidation reaction of L-ascorbic acid by d icyanobis(1,10-phenanthroline)iron(III) were carried out at elevated p ressures. The activation volume corresponding to the one-electron oxid ation process of L-ascorbic acid was -0.5+/-1.3 cm(3) mol(-1). The rea ction mechanism was analyzed by using the volume cross relation based on the Stranks-Hush-Marcus theory. Estimation of the reaction volume o f the ascorbic acid radical/ascorbic acid couple revealed that the oxi dation reaction of ascorbic acid proceeds through a simple adiabatic p rocess in DMSO, while an electron transfer followed by a rapid ring-cl osure reaction within the ascorbic acid radical was suggested for the reactions in aqueous solution.