VARIABLE-PRESSURE KINETIC AND EQUILIBRIUM STUDY OF THE COMPLEXATION OF THE BERYLLIUM(II) ION WITH 4-ISOPROPYLTROPOLONE IN ACIDIC AQUEOUS-SOLUTION

Kinetics and equilibria for the formation and dissociation of the 1:1 complex of the beryllium (II) ion with 4-isopropyltropolone (Hipt) in acidic aqueous solution have been studied spectrophotometrically at various temperatures and pressures at an ionic strength of 0.100 M ((Na,H)ClO4). Equilibrium measurements gave the following results: K = [Be(ipt)+][H+][Be2+]-1[Hipt]-1 = 1.17 +/- 0.06 (25.0-degrees-C), DELTA-H-degrees = 2.4 +/- 0.3 kJ mol-1, DELTA-S-degrees = 9.2 +/- 1.1 J K-1 mol-1, DELTA-V-degrees = +5.3 +/- 0.2 cm3 mol-1 (25.0-degrees-C). The reaction volumes for the proton dissociation of Hipt and for the complexation of Be2+ with ipt- are -8.2 +/- 0.5 and +13.5 +/- 0.6 cm3 mol-1, respectively, at 25.0-degrees-C. The rate constants and activation parameters for formation and dissociation of the complex are as follows: k(f) = 58.1 +/- 0.5 M-1 s-1 (25.0-degrees-C), k(r) = 49.8 +/- 0.5 M-1 s-1 (25.0-degrees-C), DELTA-H(f)-double-ending-dagger = 38.1 +/- 0.4 kJ mol-1, DELTA-H(r)-double-ending-dagger = 35.7 +/- 0.4 kJ mol-1, DELTA-S(f)-double-ending-dagger = -83.5 +/- 1.3 J K-1 mol-1, DELTA-S(r)-double-ending-dagger = -92.7 +/- 1.2 J K-1 mol-1, DELTA-V(f)-double-ending-dagger = -7.1 +/- 0.2 cm3 mol-1 (25.0-degrees-C), DELTA-V(r)-double-ending-dagger = -12.4 +/- 0.2 cm3 mol-1 (25.0-degrees-C). The negative values of entropy and volume of activation indicate that the reaction proceeds with an associative mode of activation.