METHODS FOR THE STUDY OF THE KINETICS OF PHOTOGRAPHIC PROCESSES .3. 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 obse rvation of dye formation in homogeneous solution, the change of zero c urrent potential due to the consumption of oxidized developing compoun d, and the electrochemical formation and determination of residual qui nonediimine. The advantage and disadvantage of these procedures are di scussed, and the limitations applying these different methods are demo nstrated. Stopped-flow experiments with optical detection of the dye a llow the determination of rate constants for coupling between quinoned iimine and a variety of soluble couplers, if the dye formation occurs more rapidly than the coupling. But the reaction conditions differ tre mendously of the situation in photographic materials during the develo pment. The coupling, ie. the formation of the leuco dye, can be follow ed by recording either the zero current potential or the current poten tial curves at a stationary electrode. As the potential depends on the kind of species and its concentration, the zero current potential met hod only yields reliable data under very limited conditions. Only by m eans of cyclic voltammetry the consumption of quinonediimine can be de termined under conditions similar to those during the photographic dev elopment. A thorough study of kinetics of oxidative dye formation shou ld include several independent methods.