Extraction alkaline earth cations

Figure 3 shows that the ability of these ligands to extract alkaline earth cations depends strongly on the nature of the two remaining alkoxy groups which, in turn, determine the stereochemistry around the binding region. 

Bond, A.H., Chiarizia, R., Huber, V.J. et al. 1999. Synergistic solvent extraction of alkaline earth cations by mixtures of di-n-octylphosphoric acid and stereoisomers of dicyclohexano-18-crown-6. Anal. Chem. 71 (14) 2757-2765. 

Several classes of synthesized calixarenes bearing several moieties (ether, ester, and amide derivatives), were tested for the extraction of strontium picrates (from aqueous solutions into dichloromethane).128 Only a few of them show appreciable extraction levels. The p-i-butyl calix[6]arene hexa(di-/V-ethyl)amide (CA4) shows a very high extraction level of alkaline earth cations with respect to alkali metal cations. Moreover, dealkylation of the calix[6]arene hcxa(di-/V-cthyl)amidc (CA5) decreases the extraction of both sodium and strontium. As this decrease is much more important for sodium than for strontium, the Sr/Na selectivity, which increases from 3.12 to 9.4, is better than that achieved for DC18 derivative under the same conditions (8.7). These results were confirmed by extraction of strontium (5 x 10 4 M) from 1 M HN03 solutions, where it was found that p-t-butyl calix[4]arene tetra(di-N-ethyl) amide (CA2) (10 2 M in NPOE) extracts only sodium (DNa = 12.3, DSl < 0.001). 

Extraction data for alkali and alkaline earth cations showed that the replacement of two distal tertiary amides of the p-tert-butyl calix[4]arene tctra(di-/V-cthyl)amide (CA2) by secondary or primary amides (CA1) leads to a sharp decrease of the extraction of these cations. 

In the early 1990s, there existed several classes of extractants for actinides (CMPO), for cesium and more generally alkali cations, and for strontium and alkaline earth cations (crown ethers and cosan). The combination of these extractants and the grafting of these functions on calixarene platforms have led to new classes of extremely efficient and selective extractants, in particular calixarene-crown, which are presently applied in the United States to treat the huge amounts of waste at the SRS. Calixarenes/ CMPO, crown ethers/cosan, CMPO/cosan, and more recently calixarenes/CMPO/ cosan are promising compounds. It is desirable that these studies, conducted at the international level, continue in particular to obtain a better understanding of the complex mechanisms of extraction of these compounds.127187... 

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. 

Analogous compounds 8 a —c with more than one sulfur atom in the ring have also been prepared by Akabori [26] and the synthesis led to ring-expanded products 9 and 10, probably by the route illustrated in Scheme 6-3. All the polyoxathiaferro-cenophanes showed little or no ability to extract hard alkali or alkaline earth cations... 

The common disadvantage of crown ethers as extractants of amino compounds is the interference from hard metal ions, such as alkali and alkaline earth cations. This may cause problems in extraction-based analytical and technological applications, as these metals, particularly sodium and potassium, are often present in (bio)media of interest. For illustration. Fig. 1 shows the influence of alkali metals on the extraction-photometric determination of benzylamine with DC18C6 and picrate [56,70]. 

McGregor, W. McKervey, M.A. Schwing-Weill, M.-J. Vetrogon. V. Wechsler, S. Extraction and solution thermodynamics of coinplexation of alkali and alkaline-earth cations by calix[4]arene amides. J. Chem. Soc., Perkin 21. Trans., 2 Phys. Org. Chem. 1995, 3. 453-461. 

Abstract. Crown ethers derived from tartaric acid present a number of interesting features as receptor frameworks and offer a possibility of enhanced metal cation binding due to favorable electrostatic interactions. The synthesis of polycarboxylate crown ethers from tartaric acid is achieved by simple Williamson ether synthesis using thallous ethoxide or sodium hydride as base. Stability constants for the complexation of alkali metal and alkaline earth cations were determined by potentiometric titration. Complexation is dominated by electrostatic interactions but cooperative coordination of the cation by both the crown ether and a carboxylate group is essential to complex stability. Complexes are stable to pH 3 and the ligands can be used as simultaneous proton and metal ion buffers. The low extractibility of the complexes was applied in a membrane transport system which is a formal model of primary active transport. 

Subsequent to any decomposition, but also in the case of liquid samples such as water and urine, the analytes of interest are generally present in dilute solution together with a large excess of foreign ions (e.g.. alkali-metal and alkaline-earth cations). Separation and concentration of the analytes may be necessary to improve the limit of detection and exclude interference. Useful techniques in this regard include liquid-liquid extraction. solid-phase extraction, special precipitation reactions, and electrolytic deposition. 

Fig. 3 Extraction of alkaline earth cations by ligands 15-17 from water to dichloromethane.

An extraction efficiency of RTILs over conventional solvents was definitely observed for a series of cations in presence of neutral complexing agents (Dietz, 2006 Murding Tang, 2010). At the same time, unlike for molecular solvents the Dm values for alkali and alkaline earth cations M in numerous RTIL/water systems in the presence of different crown ethers declined as HNQs concentration in aqueous phase increased, then the Dm dependence passed a minimum at c.a. 1 mol/ dmP concentration and started to increase as nitric acid concentration increased up to 3 mol/dm3 (EHetz, 2006 Egorov et al, 2010). Our group has demonstrated that the pH-dependence of crown-ether assisted extraction from water into RTIL phase correlates well with the relative distribution of a crown (Vendilo, et al, 2009), Fig. 1,2... 

On the other hand, Bartsch et al. have studied cation transports using crown ether carboxylic acids, which are ascertained to be effective and selective extractants for alkali metal and alkaline earth metal cations 33-42>. In a proton-driven passive transport system (HC1) using a chloroform liquid membrane, ionophore 31 selectively transports Li+, whereas 32-36 and 37 are effective for selective transport of Na+ and K+, respectively, corresponding to the compatible sizes of the ring cavity and the cation. By increasing the lipophilicity from 33 to 36, the transport rate is gradually... 

The general trend is similar for the four hosts, although some discrepancy appears along these data. In spite of some systematic errors arising from the extraction method, it must be underlined for example the discrepancy of data for Ag. The silver(I) cation is much better extracted by the thioether-substituted host 12g probably because Ag can interact not only with the phosphorylated binding sites of the cavitand, but also with the thioether functionality of the lower rim. Furthermore, it must be pointed out that the Hpophihcity of the host can interfere in the extraction process. For both al-kahne and alkaline-earth picrate salts, the extractability increases with the... 

The guest cations hitherto examined cover broadly uni- to trivalent and inorganic to organic ions that include alkali, alkaline earth, heavy and transition metal ions, as well as (ar)alkyl ammonium and diazonium ions. As to the complex stoichiometry between cation and ligand, both 1 1 stoichiometric and 1 2 sandwich complexes are analyzed. The solvent systems employed also vary widely from protic and aprotic homogeneous phase to binary-phase solvent extraction. 

The selective cation binding properties ol crown ethers and cryptands have obvious commercial applications in the separation of metal ions and these have recently been reviewed (B-78MI52103.79MI52102, B-81MI52103). Many liquid-liquid extraction systems have been developed for alkali and alkaline earth metal separations. Since the hardness of the counterion is inversely proportional to the extraction coefficient, large, soft anions, such as picrate, are usually used. 

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