Cations crown ethers

FIGURE 8. Relative intensities of ions corresponding to alkali cationized crown ethers 6a ( ), 6b ( ), 6c (B), 6d (O) and benzo-18-crown-6, 7 (A). Reproduced with permission from Ref. 42... 

From a thermodynamic perspective, the solvation of ionic species (see Equations 10.6 and 10.7), such as crown-ether complexes, NO3, and SO 4, in the ILs, should be much more favored thermodynamically than those of conventional solvent extractions (Equations 10.1 and 10.2). This is one of the key advantages of using ILs in separations involving ionic species. In this case, cationic crown-ether complexes and their counter anions are not expected to form ion pairs, but to be solvated separately by ionic species from the ILs. Therefore, the extraction process using crown ethers in ILs may not be an ion-pair extraction process. 

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... 

We have studied the interactions of the crown ether 4-nitrobenzo-15-crown-5 at the water/dichloroethane interface [78] (Figure 1.11). The variation of the SHG signal from this crown ether as a function of potential across the interface depends dramatically on the presence or absence of sodium ions. The neutral crown ether behaves quite differently from the charges cation-crown ether complex. At the hepatane/water interface, cation binding has been studied using dye-labelled crowns [79]. We are currently investigating the behaviour of other crown ethers at the air/water and solvent/water interfaces. 

Apart from their obvious utility in separating mixtures of cations, crown ethers have found much use in organic synthesis (see the discussion on p. 510). Chiral crown ethers have been used for the resolution of racemic mixtures (p. 138). Although crown ethers are most frequently used to complex cations,... 

Table 4.2 Cation-crown ether complex formation...

Fyles, T.M. Zeng. B. On the assessment of complex cation-crown ether equilibria by electrospray mass spectrometry. Supramol. Chem. 1998. 10. 143-153. 

Polymeric crown ether phases have been thoroughly investigated for their applications in chromatography by Blasius et al. [70-75]. They are characterized by chemical and thermal stability, are compatible with a variety of organic solvents, and are of high capacity. Thus, Blasius et al. separated anions with pure methanol as the mobile phase. Because the stability constants of the cation crown ether complexes depend on the type of solvent, the solvent content in the mobile phase can be used as an additional parameter for optimizing the chromatographic separation. 

In this chapter we have attempted to give the reader an overview of the various techniques that can be used to measure spectra of cold, gas-phase biomolecular ions. The goal has been to provide an appreciation of the various methods for cooling and spectroscopic detection as well as an idea of how they have been combined in creative ways in different laboratories around the world to measure spectra of cold ions. It should be noted that there is nothing that restricts these techniques to biomolecular ions - in fact, applications to molecules such as cation-crown ether complexes [185-187], reaction intermediates [188], and organometallic catalysts [147] have proven to be particularly powerful. 

Figure 12 illustrates an anion transport system with a lanthanide tris(p-diketonate) as the carrier. When the lipophilic lanthanide complex is present in Membrane, a highly coordinated complex is formed with the anion guest at the interface between Aq. I and Membrane, and K(I) cation is extracted into Membrane as the counter-cation. The resulting ternary complex moves across Membrane. At the interface between Membrane and Aq. II, the guest anion is released into Aq. II together with its counter-cation. Crown ether carrier mediates anion transport in a In Chemical Separations with Liquid Membranes Bartsch, R., et al. ... 

Ever since Petersen reported the complexing ability of the crown ether with alkali, alkaline earth and other cations, crown ether became a major subject for researchers. This is due to the fact that crown ether possesses the ability to form complexes with a variety of inorganic salts and also the ability to solubilize these salts in aprotic solvents The complexation between metal cation and crown ether is believed to involve ion-dipole interactions and therefore is similar in nature to ordinary solvation. In addition, crown ether/metal cation complexes can serve as catalysts in reactions involving ionic intermediates. Polymerization of diene with crown ether/metal cation complexes is a typical example of this subject, since this reaction involves ionic intermediates. The detailed information including a brief history, chemical properties of crown ether and its application in the anionic polymerization and copolymerization have been discussed. 

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