| Abstract
| - The role of lauric acid (LAH) in the transport of copper(II) through a permeation liquid membrane (PLM) comprising 1,10-didecyldiaza-18-crown-6 (22DD) and lauricacid (ratio 1:1) in 1:1 v/v toluene/phenylhexane has beeninvestigated by determining the stoichiometry of metalextraction and of the metal complex formed in the organicphase by performing 1H NMR and liquid/liquid andliquid/membrane extraction measurements. In the absence of copper(II), the 1H NMR data suggest that thereis a strong interaction between the proton of LAH and thenitrogen of the 22DD macrocycle but no interactionbetween the aliphatic long chains of LAH and 22DD.Thus, in the organic solution, the two compounds areassociated as (22DD-H)+−LA-, the laurate being awayfrom (22DD-H)+. The signal intensity of the acidic protonwas found to decrease when the metal Pb(II) was incorporated by the carrier after its extraction from the aqueousphase. Additionally, liquid/liquid as well as liquid/membrane extraction results reveal that Cu(II) extractionproceeds via the loss of two protons from the organicphase. The Cu(II) is found to be located in the 22DDcavity and the stoichiometry of the complex in the organicphase is (22DD-Cu)2+−2LA-. Metal extraction is governed by 22DD and laurate acts only as counteranion.An unexpected feature was observed in the liquid/liquidextraction which was that, at low 22DD and LAH concentrations, the slope for log(Kp) = f(pH) was 2 whereas itwas much lower at high carrier concentration. Thisunexpected result seems to stem from impurities presentin 22DD: only 0.1 mol % of impurity can indeed influencethe exchange ratio of Cu(II) and H+. This type of anomaly,however, is not found in the normal procedure of liquid/membrane extraction possibly due to the lower carrier/metal molar ratio which is used in the classical PLMconditions.
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