Complexation equilibria between uranium(VI) and 2-(2’-thiazolylazo)-4,6-dimethylphenol and 2-(4’,5’-dimethyl-2’-thiazolylazo)-4,6-dimethylphenol. Extraction-spectrophotometric determination of uranium

Abstract

2-(2’-Thiazolylazo)-4,6-dimethylphenol (TADMP) and 2-(4’,5’-dimethyl-2’-thiazolylazo)-4,6-dimethylphenol (DMTADMP) have been synthesized and their ionization constants determined by spectrophotometric methods and graphical and numerical calculation methods. Both reagents form UO2R+ and UO2R2 complexes with uranium (TADMP: log β101 = 9.18 ± 0.02, log β102 = 17.64 ± 0.01; DMTADMP: log β101 = 8.38 ± 0.02, log β102 = 18.78 ± 0.14) in a 40% (v/v) ethanol-water medium at I = 0.25 (NaClO4). An extraction-spectrophotometric method for the determination of 1.35-9.45 ppm uranium based on its extraction into toluene with TADMP from a pH 6.5 buffered medium has been developed ( ε = 1.6 . 104 l mol-1 cm-1 at 580 nm), and applied to its determination in sulphuric acid leaching residues.