Equilibria of protolysis and complexing reactions between pyrocatechol violet and rare earth, yttrium and scandium ions in aqueous solutions

Determination of pyrocatechol violet (PCV) ionization constants and study of its complexing with rare earth(3), Y3+ and Sc3+ ions in aqueous solutions were conducted. Four ionic species of PCV form one by one during its protolytic dissociation in aqueous solutions at pH 2-12. Forms H3R- and H2R2- give overlapping absorption band maxima (440 nm). PCV forms metal complexes with a component ratio of 1:1 which exist as protonated and deprotonated species. The dependence of the complex stability constant on the inverse rare earth ion radius has a shape of a two-peak curve with a bend corresponding to Cd3+