Kinetics of Complexation of Uranium with 2-(5-Bromo-2-Pyridylazo)-5-(Diethylamino) Phenol (Br-PADAP) in a 1:1 Water-Ethanol Medium |
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Authors: | Neetika Rawat P. K. Mohapatra V. K. Manchanda |
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Affiliation: | (1) Radiochemistry Division, B.A.R.C., Trombay, Mumbai, 400085, India |
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Abstract: | 2-(5-Bromo-2-pyridylazo)-5-(diethylamino) phenol (Br-PADAP) forms a 1:1 complex with the uranyl ion in the presence of sulphosalicylic acid, which acts as stabilizer for this complex in the triethanol amine/perchloric acid buffer system. A change in the stoichiometry of the complex was seen at pH<5. Kinetic measurements were carried out using stopped-flow spectrophotometer in the presence of an excess concentration of U(VI) in the pH range 6.5 to 8. The dependence of the pseudo-first-order rate constant, k(obs), on the concentrations of U(VI), ligand and hydrogen ion showed that Br-PADAP reacts with UO2(OH)+ to form an intermediate species (equilibrium constant = 1.28×104mol.dm−3) that then rearranges (rate constant = 5.6×10−2s−1) to form the product species. UO2(OH)+ is present in equilibrium with the unreactive species UO2(OH)2, as well as with the unreactive sulfosalicylic acid complex. |
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Keywords: | Uranium(VI) Kinetics Stopped-flow spectrophotometry Bromo-PADAP |
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