Methods for the study of the kinetics of photographic processes. III. Oxidative dye formation in solution

three different methods of investigation of the kinetics of oxidative dye formation in solution are presented, that is, the photometric observation of dye formation in homogeneous solution, the change of zero current potential due to the consumption of oxidized developing compound, and the electrochemical formation and determination of residual quinonediimine. The advantage and disadvantage of these procedures are discussed, and the limitations applying these different methods are demonstrated. Stopped-flow experiments with optical detection of the dye allow the determination of rate constants for coupling between quinonediimine and a variety of soluble couplers, if the dye formation occurs more rapidly than the coupling. But the reaction conditions differ tremendously of the situation in photographic materials during the development? The coupling, i.e. the formation of the leuco dye, can be followed by recording either the zero current potential or the current potential curves at a stationary electrode. As the potential depends on the kind of species and its concentration, the zero current potential method only yields reliable data under very limited conditions. Only by means of cyclic voltammmetry the consumption of quinonediimine can be determined under conditions similar to those during the photographic development. A thorough study of kinetics of oxidative dye formation should include several independent methods.