Studies on Brilliant Green and Solochrome Red B: I. The acid-base properties

The acid-base properties of Brilliant Green and Solochrome Red B have been studied in an attempt to apply them as metallochromic or chromophoric indicators. The thermodynamic pK values 4.93 and 2.62 corresponding to the ionization of the hydrogen sulfate group and to the protonation of the second diethylamino group in Brilliant Green, and 3.46, 5.80, 7.22, and 13.30 corresponding to the ionization of the two sulfonic, the carboxylic, and the phenolic groups in Solochrome Red B, respectively, were computed from results of potentiometric and spectrophotometric measurements.