Kinetics of complexation of nickel (II) and copper (II) with some azophenol derivatives in aqueous nonionic surfactant solution

The kinetics of formation of 11 complexes of nickel(II) and copper(II) ions with some azophenol derivatives in aqueous and micellar solution of a nonionic surfactant, Triton X-100, have been studied by a stopped-flow spectrophotometric method. Second order rate constants for the reactions were determined at 298 K and ionic strength 0.1 (NaClO₄) in aqueous solution. In the surfactant solution, the pseudo-first-order rate constants for the complexation reactions,k_obs, decreased with increasing the concentration of Triton X-100. This observation was explained by the assumption that the chelating reagents distribute between the micelle of the surfactant and bulk aqueous phase and rate-controlling reactions occur only in the bulk aqueous phase. On the basis of the relation betweenk_obs and the concentration of the surfactant, the partition constants of the reagents between micellar and aqueous phases were determined.