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Abstract
Dark stability of the magenta dye image obtained from 2-equivalent 3-acylamino-5-pyrazolone couplers was investigated from the viewpoint of the reaction of the magenta dye with the residual coupler.
A correlation was found between the reaction rate and the pKa values of the starting 3acylamino-5-pyrazolone couplers, i.e., the couplers with the lowest pKa values showed the least reactivity. This observation suggests that the reaction proceeds via an ionic reaction mechanism rather than by a radical reaction mechanism.
The use of couplers with low pKas for colour negative film makes it possible to remove formaldehyde from the stabilizing bath in colour negative processing.