COMPLEXATION KINETICS OF 5-ALKYLOXYMETHYL-8-QUINOLINOLS AT LIQUID-LIQUID INTERFACES AS STUDIED BY DYNAMIC INTERFACIAL TENSIOMETRY

The effect of alkyl chain length of chelating reagents on the complexa tion kinetics of 8-quinolinol (HQ) and 5-alkyloxymethyl-8-quinolinol ( HC(n)Q; n = 1, 2, 3, 5, 8) with transition metal ions(M2+: Ni2+, Zn2+) at liquid-liquid interfaces is studied by dynamic interfacial tensiom etry. A decrease in the dynamic interfacial tension is caused by the i nterfacial adsorption of a 1:1 complex (M(C(n)Q)(+)) The interfacial c omplexation kinetics for Zn2+ is controlled by the diffusion of ligand s from the bulk organic phase to the interface. For Ni2+, the kinetics is also diffusion-controlled for the ligands with short alkyl chains; however, it is controlled by the complexation reaction at the interfa ce for those having longer alkyl chains. The interfacial complexation rate is found to be faster for Zn2+ than for Ni2+, and it correlates c losely with the partition coefficient of the ligands. For the reaction -controlled complexation kinetics, a new procedure for calculating the interfacial complexation rate constant (k(1)) is proposed, and hi val ues for the reaction with Ni2+ at the heptane-water interface are calc ulated as 1.7 x 10(-5) m s(-1) M-1 (1M = 1 mol dm(-3)) for HC(5)Q and 2.2 x 10(-5) m s(-1) M-1 for HC(8)Q.