Electron-transfer reactions and associated conformational changes, the effect of disproportionation on the reduction of bianthrone at elevated temperatures

Bianthrone exists in two forms which are in thermochromic equilibrium. Earlier studies have shown that the twisted high temperature B-form is more readily reduced than the doubly-folded, low temperature. A-form, At room temperature the A-form is reduced in an ECE sequence: A → A^XXX → B^XXX → B^2- At higher temperature the reaction can proceed by prior conversion of A to B followed by reduction, i,e. a CEE scheme A → B → B^XXX B^2-. In the present paper it has been found that the disproportionation/reproportionation (DISP/REP) equilibrium (B^2- + B ⇌ 2B^XXX) has a pronounced effect on the cyclic voltammograms. Results for the reduction of bianthrone in bezonitrile have been quantitatively interpreted in terms of the CEE scheme with associated DISP/REP equilibrium. The values of equilibrium and rate parameters obtained are in excellent agreement with previous studies.