Electrochemistry of electron transfer probes. alpha-aryloxyacetoveratronesand implications for the mechanism of photo-yellowing of pulp

Standard potentials (E degrees) of a series of substituted alpha-aryloxyace toveratrone derivatives have been determined from a correlation of the C-13 NMR chemical shifts of the carbonyl group and a similar correlation (E deg rees vs. C-13 NMR shifts) within a series of alpha-anilinoacetoveratrones. Using these potentials the rate constants for fragmentation of the radical anions were determined by digital simulation of the voltammetric waves. The rate contants for C-O cleavage in the radical anions correlate with the pK (a) of the corresponding phenols. The fragmentations are all in the activat ed region of a general free energy relationship for this class of compound (alpha=0.5). The standard potential and rate constant for fragmention of th e alpha-guaiacoxyacetoveratrone radical anion also were determined. This sp ecies is a model compound for one of the lignin substructures. The implicat ion of these results on the currently accepted mechanism for photoyellowing of lignin rich paper is discussed.