Abstract
Chelation reactions of thorium(IV) with 3,3′-bis[N,N′-di(carboxymethyl) aminomethyl]- o-cresolsulphonphthalein (xylenol orange; DCAC) and 1-( o-arsonophenylazo)-2-naphthol-3,6-disulphonic acid (thoron; APANS) have been investigated in aqueous media at 35° at an ionic strength of 0·1 M (KNO 3) employing a pH-titration technique. Evidence is presented of the formation of the monoprotonated 1:1 metal-ligand species. These species liberate hydrogen ions at pH ≈ 4·5, and finally the nonprotonated species interacts with hydroxyl ions to form mono- and dihydroxo species. The equilibrium constants have been evaluated, and the probable co-ordination sites of ligands involved in the complexes have been suggested.
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