EFFECTS OF FLUOROCARBON AND HYDROCARBON ANIONIC MICELLES ON THE KINETICS OF WATER REPLACEMENT IN THE PALLADIUM(II) AQUOCOMPLEX OF 1,1,7,7-TETRAETHYLDIETHYLENETRIAMINE BY MONOALKYLTHIOUREAS

The effect of sodium perfluorooctanoate (NaPFO), sodium perfluorononan oate (NaPFN) and sodium decyl sulfate (SDeS) micelles on the kinetics of water replacement in the cationic palladium(II) complex [Pd(Et(4)di en)(H2O)](2+), where Et(4)dien = Et(2)N(CH2)(2)NH(CH2)(2)NEt(2), by th e nucleophiles methyl-, ethyl- and butylthiourea has been studied in a queous acidic solutions at 25 degrees C and ionic strength 0.03 mol dm (-3) (0.06 mol dm(-3) with SDeS). The micellar aggregates promote the substitution reactions reaching a maximum rate just beyond the critica l micelle concentrations, which have been estimated experimentally by surface tension and conductivity measurements. The binding constants o f the nucleophiles calculated from the present kinetic data, together with those obtained previously in the presence of sodium dodecyl sulfa te (SDS), indicate that the capacity of the micelles to solubilize the thioureas increases in the order SDeS < SDS approximate to NaPFO < Na PFN. Moreover, for each surfactant used, solubilization is favoured by an increase in the hydrophobic character of the substrates. The estim ated free energies of transfer of the thioureas from aqueous to micell ar pseudo-phase show that the affinity of the hydrogenated micelles to ward the substrate CH2 group is larger than that of the fluorinated on es. The possible solubilization sites and reaction rates in the micell ar pseudophases are also discussed.