Metallindikatoren VII. Die Aciditätskonstanten und der Eisenkomplex des N,N′‐Äthylen‐bis‐(o‐hydroxyphenyl‐glycins (EHPG))

The acidity constants of N, N′‐Ethylene‐bis‐(o‐hydroxyphenyl‐glycine) (= EHPG)have been determined. The stability constant of the 1:1 complex with trivalent iron has been determined from optical measurements of the equilibrium with trimethylene‐diamine‐tetraacetic acid. Among the studied ligands EHPG forms the stablest 1:1 complex with iron(II1). This red complex can be used in acid solution as indicator for the complexometric titration of iron.