Abstract
2-(1, 8-Dihydroxy-3, 6-disulfo-2-naphthylazo)-phcnoxyacetic acid has been synthesized. The acid dissociation constants of the reagent have been determined spectrophotometrically at 25 °C and at an ionic strength of 0.1. The reagent forms a violet 1 : 1 complex with thorium, showing an absorption maximum at 575 mμ in an acidic solution. The apparent stability constant of the thorium complex was measured over the pH range from 1 to 3.5.