Abstract
Time-resolved kinetic studies involving the reactions of alloxan (A.H2O) with the reducing species superoxide and carbon dioxide radical anions and the reaction of dialuric acid (HA−) with sulphate radicals showed that the same radical (AH.) was formed either by the one-electron reduction of alloxan or by the one-electron oxidation of dialuric acid. A mechanism including several reversible reactions was proposed and validated. A detailed kinetic analysis yields the following bimolecular rate constants: k(A.H2O + ) < 105m−1 s−1, k(A.H2O + O2−)=(3.4±0.5)×106m−1 s−1, k(HA−+
)=(8±1)×107m−1 s−1 and k(AH.+AH.)=(1.7±0.8)×108m−1 s−1. From these values, the redox potentials E°(A.H2O,H+/AH.)=(−290±20) mV, E°(AH./HA−)=(277±20) mV and E°(A.H2O,H+/HA−)=(−15±20) mV, were obtained.