Electron-transfer reactions and associated conformational changes. The effect of disproportion on the oxidation of dixanthylene at elevated temperatures

Dixanthylene undergoes a change in conformation from the A form to the B form prior to its electrochemical oxidation. The rate of this conformational change increases as the temperature is increased giving rise to larger kinetic currents. However, the current is not simply that from a CEE process but has autocatalytic character. The current increases with time in chronoamperometry and "curve-crossing" is seen in the cyclic voltammograms. The reaction was studied at temperatures from 40 to 60 °C using a platinum electrode and n-butyronitrile as solvent. The chronoamperometric data were analyzed to obtain the equilibrium constant and rate constants for the conformational change. The autocatalysis is caused by the disproportionation-synproportionation reaction occurring with the neutral, cation radical and dication of the B form. An approximate equation valid for early stages of the autocatalysis was derived and the data were also analyzed via comparison to digital simulation. From the analysis, the rate and equilibrium constants for the disproportionation-synproportionation reaction were obtained.