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目前应用于酸碱滴定的目测指示剂数目很多,但变色域较窄、变色敏锐的指示剂为数还甚少,因此人们往往采用混合指示剂使其变色明显敏锐。溴代苯并噻唑偶氮间羟基苯甲酸用作酸碱指示剂,在滴定终点时有一近无色到红色的突变。颜色转变十分敏锐,可与混合指示剂相媲美,是一个较理想的酸碱指示剂。该试剂由韩希清、张谦、张有贤等合成,其合成及应用至今尚未见报导(合成方法及分析特性另文报告)。该试剂为暗红色结晶,微溶于水,易溶子乙醇、丙酮等有机溶剂,其离解平衡可表示如下:
At present, there are many visual indicator used in acid-base titration, but the number of indicators with narrower discoloration and sharp discoloration is very small. Therefore, people often use the mixed indicator to change the color obviously. Bromobenzothiazole Azo-hydroxybenzoic acid is used as an acid-base indicator with a nearly colorless to red mutation at the end of the titration. Color change is very sharp, comparable with the mixed indicator, is an ideal acid-base indicator. The reagent was synthesized by Han Xichun, Zhang Qian, Zhang Youxian et al. The synthesis and application of this reagent have not been reported until now (report of synthesis method and analysis of other properties). The reagent is dark red crystal, slightly soluble in water, easily soluble ethanol, acetone and other organic solvents, the dissociation equilibrium can be expressed as follows: