The present paper firstly announces the possibility of using a Schiff base as an acid-base indicator. This surprising phenomenon can be considered as an interest due to the fact that Schiff bases are usually unstable in solutions and definitely undergo hydrolysis. It was found that such a specific observation depends merely upon the chemical structure and type of the substitute of amine that reacts with aldehyde to give the Schiff base. The latter reagent 4[(4-dimethylamino-benzylidene)-amino]-benzene sulfonamide was synthesized from the condensation of sulfanilamide with p-dimethylaminobenzaldehyde. The reagent solution shows a reproducible change in its color due to the addition of acid and base. A UV-Vis spectroscopic characterization and acid-base equilibrium study of the reagent for its possible use as an indicator were investigated. The results show that the reagent is an amphoteric which possesses four ionization constants K_a1, K_a2, K_b1 and K_b2 of weak dibasic and diacidic properties. The value of pK_a2 (9.80) is parallel to the observed transition interval pH 9.5 (yellow) and pH 10.5 (colorless), which is considered to be the indicator exponents pK_i. It was concluded that the benzyl sulfonamide group plays a key role in the stability of the reagent towards hydrolysis and also for indicator characteristics through breaking the conjugation.

中文翻译：

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衍生自磺酰胺的席夫碱作为酸碱指示剂的应用

本论文首先宣布了使用席夫碱作为酸碱指示剂的可能性。由于席夫碱通常在溶液中不稳定并且肯定会发生水解，因此这种令人惊讶的现象可以被认为是一种令人感兴趣的现象。已经发现，这种具体观察仅取决于与醛反应以产生席夫碱的胺的取代基的化学结构和类型。后一种试剂4 [（4-二甲基氨基-亚苄基）-氨基]-苯磺酰胺是由磺酰胺与对氨基苯酚的缩合反应合成的。-二甲基氨基苯甲醛。由于添加了酸和碱，试剂溶液的颜色显示出可再现的变化。对该试剂的紫外可见光谱表征和酸碱平衡研究进行了研究，以探讨其可能用作指示剂。结果表明该试剂是两性的，具有弱的二元和二元酸性的四个电离常数K _a1，K _a2，K _b1和K _b2。pK _a2（9.80）的值与观察到的过渡区间pH 9.5（黄色）和pH 10.5（无色）平行，被认为是指标指数pK _i。结论是，苄基磺酰胺基团在试剂对水解的稳定性以及通过破坏偶联而对于指示剂特性中起关键作用。