Synthesis of N-(2-pyridyl)-N'-(4-phenylsulfonic acid)-C-phenyl formazan and its reactions with metal ions

Abstract

A water-soluble formazan compound was synthesized. The acid dissociation constant of this compound was pK_a2=4.48 and pK_a3=11.83. The color reactions of this reagent with some metal ions were investigated and the stability constants of the complexes were obtained. The compositions of the complexes in the excess of metals were 1:1 for Cu, Zn, Ni and Co, and those in the excess of the reagent were 1:2 for Zn, Ni and Co, and 1:1 for Cu. Cu also formed a 1:2 complex at pH>8. The stability constants were determined by spectrophotometric and potentiometric methods. The values obtained by the former method were log K^A_CuA=15.50, logK^A_ZnA=8.4, logK^A_NiA=11.75 and logK^A_CoA=14.67. The reagent was applied as a metal indicator for the photometric titration of Cu with EDTA.