Cationic extractants

Figure 1 shows the mechanistic picture developed by C. M. Starks (1,2) for Hquid—Hquid PTC in a graphical form. The catalyst cation extracts the more hpholilic anion Y from the aqueous to the nonpolar organic phase where it is present in the form of a poorly solvated ion pair Y ]. This then reacts rapidly with RX, and the newly formed ion pair X ] returns to the aqueous phase for another exchange process X — Y . In practice most catalyst cations used are rather lipophilic and do not extract strongly into the aqueous phase so that the anions are exchanged at the phase boundary. 

Figure 10.6 Effect of 1-alkyl group variation of ionic liquids on efficiency of competitive metal cation extraction from aqueous solutions by DCH18C6 (0.1 M) in [C CjIm][Tf2N], (Reproduced from the American Chemical Society from Luo, H. M., Dai, S., Bonnesen, RV., Anal Chem., 76, 2773-2779, 2004. With permission.)...

The value of A ex is, of course, fixed for any given cation-extracting agent-solvent system. Analytically important distribution coefficients, D, can be varied by changing the concentration of ligand relative to that of the metal and more significantly by adjusting the pH for 50% extraction D = 1 and equation (21) reduces to... 

Baaden, M., Berny, F., Madic, C., Schurhammer, R., Wipff, G. 2003. Theoretical studies on lanthanide cation extraction by picolinamides Ligand-cation interactions and interfacial behavior. Solvent Extr. IonExch. 21 (2) 199-220. 

Following the recommendation of Reinhoudt,23 in almost the majority of cases, nitrophenyl alkyl ethers were used as diluents for the extraction tests by the Cadarache group, because they are able to dissolve calixarenes at relatively high concentration. Moreover, the basicity as well the dielectric constant of these diluents improves cation extraction by better solvation of the associated nitrate anions (Table 4.3). 

Electrospray Ionization/Mass Spectrometry (ES/MS), a soft-ionization desorption technique using polar solvents such as water, methanol, or acetonitrile, was used for direct measurement of cations in solution. The first measurements carried out with mono or bis(crown-6) calix[4]arenes from an equimolar cation-extractant solution confirm that the calixarenes mono(crown-6) extract only one cesium cation. On the contrary, in the same conditions, bis(crown-6) calix[4]arenes can extract two cesium cations for a ratio Cs/BC6 equal to 2.5. The binuclear complex (composed of two cesium cations) is the major species. Cesium/sodium selectivity measurements implementing various mono or bis(crown-6) calix[4]arenes were in agreement with liquid/liquid results.42... 

To increase the distribution ratios, a solution of lithium nitrate 1M was used. This salt, which has a common anion with europium and americium to be extracted but a cation which is usually negligibly extracted by other calixarenes, should increase the distribution ratios according to the relation Du = A (JU "[N03- ". It seems that these calixarenes, as several nitrogen ligands do, present a certain affinity for this lithium cation. The lipophilic dicarbollide anion (BrCosan), which is known to facilitate cation extraction, was implemented and led to a strong increase of the extraction of cations from 10 3 M HN03 solutions. Under these conditions, only thiopicolinamide was not able to significantly extract trivalent actinides.187... 

R. Diss and G. Wipff. Lanthanide cation extraction by malonamide ligands From liquid-liquid interfaces to microemulsions. A molecular dynamics study. Phys. Chem. Chem. Phys., 7(2) 264—272, 2005. 

B. Coupez, C. Boehme, and G. Wipff. Importance of interfacial phenomena and synergistic effects in lanthanide cation extraction by dithiophosphinic ligands A molecular dynamics study. J. Phys. Chem. B, 107(35) 9484-9490, 2003. 

Vayssiere, P., Wipff, G. (2003), Importance of Counterions in Alkali and Alkaline Earth Cation Extraction by 18-Crown-6 Molecular Dynamics Studies at the Water / SC-CO2 Interface, Phys. Chem. Chem. Phys. 5, 2842-2850. 

Cation Extraction from GLC Detector Comments water column conditions LD Ref ... 

Cation Extraction from water GLC column conditions Detector Comments LD Ref. 

The sample Is dissolved In HC1 and excess HC1 is evaporated off. The soln. is diluted with HsO to 0.5 mg Sc/ml concentration and extracted with an equal volume of 0.5 M TTA in benzene by stirring for 10 min (Sc and more extractable cations are removed). Then the aqueous phase Is adjusted to pH 5 with NaOH and again extracted with 0.5 M TEA soln. (Sc and all cations extractable between pH 1 and pH 5 are removed). Then the Bqueous phase Is adjusted to pH 6.2 and extracted with 0.5 M TTA. The Ca+s Is extracted Into benzene phase and back-extracted with BgO. Yield Is > 99. ... 

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