Spectrophotometric studies of chelate formation of lanthanum and thorium with picramine azo dyes

Abstract

0,O'-Dihydroxypicramine azo dyes form water-soluble yellowish pink complexes with thorium and lanthanum in the pH ranges 1.5-4 and 6-9 respectively. The compositions of the complexes determined by continuous variations and molar ratio methods were found to be 1 : 2 in thorium-Picramine CA and 1 : 1 in lanthanum-Picramine R systems. The order of the formation constant of thorium-Picramine CA complex is 10¹¹ and that of lanthanum-Picramine R is 10⁵. The free energy changes of formation are also calculated.