Electrometric Studies on the Composition and Stability of Thallium (III) Complexes of β-Mercapto-Propionic Acid

The Tl(III) complexes of β-Mercapto propionic acid have been investigated by potentiometric and conductomotric titration techniques in aqueous 0·1 M KNO₃ . It was found that Tl(III) forms two colour· less complexes; 1 : 1, predominating at pH 4·0-5·0 and another 1 : 2 at pH 6·0-8·5. The stability constants of these complexes have been determined at three different temperatures by applying Calvin and Melchior's extension of Bjerrum's method. The log K values (final) for 1 : 1 and 1 : 2 complexes computed by alternative methods at 20, 30 and 40° have been found to be 10·13±0·09, 10·54±0·03, 10·83±0·13 and 7·96±0·22, 8·21 ±0·10, 8·58±0·09 respectively. The values of overall changes in ΔG, ΔH and ΔS accompanying the reaction have also been evaluated at 30° and found to be -25·9 k-cal/mole, 27·8 k-cal/mole and -6·2 cal/deg/mole respectively.