Sulphonated alizarin fluorine blue. Part II. Fundamental solution chemistry and an improved isolation procedure

Abstract

Sulphonated alizarin fluorine blue {3-[N N-di(carboxymethyl)aminomethyl]-1,2-dihydroxyanthraquinone-5-sulphonic acid}, or its monopotassium salt, shows promise as a general reagent for metals and as a positive absorptiometric reagent for fluoride. An improved purification procedure for the reagent is described. The acid-dissociation constants are pK₁= 0·5; pK₂= 1·4; pK₃= 2·5; pK₄= 5·8; pK₅= 10·0; and pK₆= 12·3. Detailed pH-absorption spectrum graphs and pH-absorbance graphs are given, together with the distribution diagram and the likely ionisation scheme. The following solubilities at 20 °C have been deduced: H₅A, 4 × 10^–5M; K⁺.H₄A^–, 5·6 × 10^–3M; and K₂⁺.H₃A^2–, >4·4 × 10^–2M.