PULSE-ELECTROLYSIS STOPPED-FLOW METHOD FOR THE ELECTROSPECTROSCOPIC ANALYSIS OF SHORT-LIVED INTERMEDIATES GENERATED IN THE ELECTROOXIDATION OF TRIPHENYLAMINE

A new analytical method was developed for the electrochemical and spectroscopic analyses of short-lived intermediates generated during electrochemical processes. Many-faceted conclusions can be drawn from spectroscopic measurements after pulse electrolysis with a column electrode; e.g. dynamic transformation profiles of absorption spectra correspond to the applied potential. The fundamental characteristics of this method are described in detail. Electrolytic efficiency in the carbon-wool column electrode was evaluated in controlled-potential and controlled-current pulse electrolysis of the tetracyanoquinodimethane anion radical (TCNQ.-). In the controlled-potential operation, 0.11 mM TCNQ.- was electrolyzed quantitatively within 200 ms. Up to 2.2 mM, the controlled-current operation permitted quantitative electrolysis with a 50-ms current pulse. Kinetic analysis of the dimerization reaction of the triphenylamine (TPA) cation radical (TPA.+) was carried out by this method. The pure solution containing only TPA.+ was successfully prepared by pulse electrolysis without any interference by the consecutive reactions. Therefore the absorption coefficient of TPA.+ was easily determined and the dimerization rate constant of TPA.+ was quite simply analyzed by following the absorbance decay of TPA.+. The effect of the parent molecules on the reaction was also clarified by mixing TPA and TPA.+ solutions.