Formation kinetics of an aluminium(III)-ethylenedinitrilotetraactate-fluoride mixed ligand complex

摘要

The formation kinetics of the [Al(edta)F](2-) mixed ligand complex has been studied using potentiometric and F-19 NMR methods. The rate equation is -dc(F)/dt = d[Al(edta)F2-]/dt = k(1)[Al(edta)(-)][F-] + k(2)[Al(edta)(-)][HF], where k(1) = 20.7 +/- 0.3 M-1 s(-1) and k(2) = 471 +/- 93 M-1 s(-1) at 298 K, the activation parameters for the main reaction path (k(1)) being Delta H double dagger = 49.2 +/- 0.9 kJ mol(-1), Delta S double dagger = -54.6 +/- 2.8 J K-1 mol(-1) studied in the range of pH 4.6-6.0, T = 283-328 K and I = 1 M NaNO3 medium. An associative interchange (I-a) mechanism can be proposed for the reaction. The stability constant, K-AledtaF = [Al(edta)F2-]/[Al(edta)(-)][F-], was redetermined from the kinetic curves: log K = 4.63 +/- 0.01 at 298 K, Delta H= -25.1 +/- 0.5 kJ mol(-1) and Delta S = 4.6 +/- 1.5 J K-1 mol(-1). The initial rate of the reaction can be used as a kinetic method to determine the aluminium concentration using a fluoride-selective electrode. [References: 45]