Polarographic Analysis of Reductive Fading Reactions of 4-Aza-2'-ethyl-4'-Diethylaminophenyl-Quinones
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This paper concerns the effect of substituent groups of phenolic couplers on dark stability of cyan quinonimine dyes deduced from the polarographic analysis of the solutions of two structure types of this class of dyes. These dyes were prepared by oxidative coupling of CD-2 developing agent (2-amino-5-diethylaminotoluene) with m-cresol or a 2-, 5-diacylamino-Pheno1. Polarographic measurements of these dyes were carried out in a mixture of ethanol and Britton-Robinson (borate-acetate-phosphate) buffer solution (volume ratio, 1.5 : 1) as a supporting electrolyte at 20±O.2℃,bubbled with nitrogen gas. Plots of E versus log {i/(i_d-i)} reveal that the leuco dye formations of these dyes are two-electron processes. In the case of the m-cresol dye, the proton number calculated from a plot of pH versus E_<1/2> was 2.8 in the range of pH 6.1〜6.9,and 2.0, pH 7.1〜7.8. Consequently, the fading reaction of the dye can be written as follows : Dye+2e+3H^+ → Leuco Dye・H^+ (Protonated Leuco Dye), in the lower pH region, and Dye+2e+2H^+ → Leuco Dye, in the higher pH region. The half-wave potential of the acylaminophenol dye was much more negative than that of the m-cresol dye. Thus, the fading reaction of the dye does not proceed easily in the presence of a reducing agent. The proton number that the dye required was approximately 2.0 in the pH range 5.9〜7.6. The chemical equation for the redox reaction of the dye can be expressed as follows : Dye+2e+2H^+ → Leuco Dye. The m-cresol dye could be easily reduced and thus fade in the presence of thiosulfate or EDTA-Fe (II), because there was a big difference between the half-wave potential of the dye and these reducing agents. For example, in the faded solution with thiosulfate polarographic waves of the leuco dye and tetrathionate ions were observed separately. Therefore, the leuco dye formation of m-cresol dye in the fading reaction with reducing agent can be written as follows : Dye+2Red.+3H^+ → Leuco Dye・H^++2O_x. in the lower pH region, Dye+2Red.+2H^+ → Leuco Dye+2Ox. in the higher pH region. On the other hand, the half-wave potential of the acylamino-Phenol dye is close to those of the reducing agents. As 21 result, the polarographic waves of the leuco dye and the oxides of the reeucing agents were not observed separately. It is suggested that the cyan dye image formed with an acylaminophenol dye would be much more stable than a m-cresol dye under the reductive conditions. Consequently, some basic information to predict dad stability of cyan quinonimine dye images under reductive conditions can be obtained by measurement of the half-wave potential of dye solutions.
- 東京工芸大学の論文
- 1988-01-15