Abstract

M. K. Paliwal, Meena and O. D. Gupta*

The reduction of As(III) and Sb(III) with tyrosine is investigated polarographically in aqueous medium. As(III) and Sb(III) both formed 1:1, 1:2 and 1:3 complex species. The stability constants of As(III) and Sb(III) with tyrosine were measured by the method of DeFord and Hume. The reduction of the system in each case is quasireversible and diffusion controlled, involving three electrons. The thermodynamic parameters have been determined. The stability constants of these species at 300K for As(III) are logβ1 = 2.96, logβ2 = 5.14, logβ3 = 7.82 and at 310 K are logβ1 = 2.50, logβ2 = 4.91, logβ3 = 6.78 and thermodynamic parameters free energy (Kcal mol–1), enthalpy (Kcal mol–1) and entropy (cal mol–1 deg–1) are -3.88, -35.94 and -0.10 (MX1 ), -6.74, -40.65 and -0.11 (MX2), -10.26, -36.89 and -0.08 (MX3) respectively. The stability constants of these species at 300K for Sb(III) are logb1 = 2.07, logβ2 = 4.60 logβ3 = 6.68 and at 310 K are logβ1 = 2.20, logβ2 = 4.32, logβ3 = 6.63 and thermodynamic parameters free energy (Kcal mol–1), enthalpy (Kcal mol–1) and entropy (cal mol–1 deg–1) are -2.71, - 45.22 and -0.14 (MX1 ), -6.04, -39.96 and -0.11 (MX2 ), -8.77, -42.23 and -0.11 (MX3), respectively. The Mathematical Mihailov’s method has also been applied for the comparison of stability constants values obtained by graphical method.

Polarography; Dropping mercury electrode; Arsenic; Antimony; Tyrosine; Stability constant; DeFord and Hume’s method; Mihailov’s method; Thermodynamic parameters

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