Complexation kinetics of 8-quinolinol derivatives with Ni(II) and Zn(II) at the 1,2-dichloroethane-water interface as studied by electrolyte ascending electrode polarography

Complexation kinetics of 8-quinolinol (HQ) and 5-alkyloxymethyl-8-quinolinols (HC_nQ; n = 1, 2, 3, 5, 8) with metal ions M²⁺ (M = Ni, Zn) at the 1,2-dichloroethane (DCE)-water interface is analyzed by dynamic interfacial tensiometry and electrolyte ascending electrode polarography. Polarographic measurements show that the chemical species formed at the interface is a cationic 1:1 complex (M(Q)⁺ or M(C_nQ)⁺). For Zn²⁺, the interfacial complexation is very fast, and its kinetics is controlled by the diffusion of ligands from the bulk DCE phase to the DCE-water interface. On the other hand, for Ni²⁺, the kinetics is interfacial reaction-controlled and is significantly affected by the alkyl chain length of the chelating reagents.