Ether complexes, solvent extraction

Those in which solvent molecules are directly involved in formation of the ion association complex. Most of the solvents (ethers, esters, ketones and alcohols) which participate in this way contain donor oxygen atoms and the coordinating ability of the solvent is of vital significance. The coordinated solvent molecules facilitate the solvent extraction of salts such as chlorides and nitrates by contributing both to the size of the cation and the resemblance of the complex to the solvent. 

The theory and development of a solvent-extraction scheme for polynuclear aromatic hydrocarbons (PAHs) is described. The use of y-cyclodextrin (CDx) as an aqueous phase modifier makes this scheme unique since it allows for the extraction of PAHs from ether to the aqueous phase. Generally, the extraction of PAHS into water is not feasible due to the low solubility of these compounds in aqueous media. Water-soluble cyclodextrins, which act as hosts in the formation of inclusion complexes, promote this type of extraction by partitioning PAHs into the aqueous phase through the formation of complexes. The stereoselective nature of CDx inclusion-complex formation enhances the separation of different sized PAH molecules present in a mixture. For example, perylene is extracted into the aqueous phase from an organic phase anthracene-perylene mixture in the presence of CDx modifier. Extraction results for a variety of PAHs are presented, and the potential of this method for separation of more complex mixtures is discussed. 

Cyclodextrin-modified solvent extraction has been used to extract several PAHs from ether to an aqueous phase. Data evaluation shows that the degree of extraction is related to the size of the potential guest molecule and that the method successfully separates simple binary mixtures in which one component does not complex strongly with CDx. The most useful application of cyclodextrin-modified solvent extraction is for the simplification of complex mixtures. The combined use of CDx modifier and data-analysis techniques may simplify the qualitative analysis of PAH mixtures. 

Various types of research are carried out on ITIESs nowadays. These studies are modeled on electrochemical techniques, theories, and systems. Studies of ion transfer across ITIESs are especially interesting and important because these are the only studies on ITIESs. Many complex ion transfers assisted by some chemical reactions have been studied, to say nothing of single ion transfers. In the world of nature, many types of ion transfer play important roles such as selective ion transfer through biological membranes. Therefore, there are quite a few studies that get ideas from those systems, while many interests from analytical applications motivate those too. Since the ion transfer at an ITIES is closely related with the fields of solvent extraction and ion-selective electrodes, these studies mainly deal with facilitated ion transfer by various kinds of ionophores. Since crown ethers as ionophores show interesting selectivity, a lot of derivatives are synthesized and their selectivities are evaluated in solvent extraction, ion-selective systems, etc. Of course electrochemical studies on ITIESs are also suitable for the systems of ion transfer facilitated by crown ethers and have thrown new light on the mechanisms of selectivity exhibited by crown ethers. 

Consequently, the red-complex is extracted with either solvents possessing donor oxygen atoms, such as 3-methyl butanol. However, Mo (VI) may also be extracted with diethyl ether-an oxygenated solvent, because it yields the maximum percentage extractive with 7.0 M NH4 SCN as could be seen from the following Table 27.2. 

The p-tolylphosphine complex is prepared in a similar manner, except that its greater solubility in THF and diethyl ether precludes precipitation with diethyl ether. The product is isolated by removing the THF/diethyl ether reaction solvent under vacuum and extracting the residue with toluene (dried by distillation from sodium). The toluene extracts are filtered and diluted with an equal volume of hexane (dried by distillation from sodium). Upon slow cooling, fine red needles are deposited. 

The distribution ratios (D s) for crown-ether-based extraction processes using conventional solvents depend on two major factors (1) the thermodynamic driving force for cafion complexation by a crown efher and (2) the solvation of fhe cafion and counfer anion by the organic solvent [1,4] the former factor is usually thermodynamically favored (see Equation 10.3). Difficulties in increasing the solvent-extraction efficiency of conventional solvent-extraction systems using crown ethers as extractants lie in the... 

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. 

Figure 5. Solvent extraction of the complex by diethyl ether...

Solvent extraction technique has been used in the synthesis of tris chelates of l,l,l,5,5,6,6,7,7,7-decafluoro-2,4-heptanedione. An aqueous solution of lanthanide chloride is equilibrated with an ether solution of ammonium diketonate, with the condition of an excess of lanthanide in the aqueous phase to prevent the formation of the tetrakis complex [46]. 

Actinide ions form complex ions with a large number of organic substances (12). Their extractability by these substances varies from element to element and depends markedly on oxidation state. A number of important separation procedures are based on this property7. Solvents that behave in this way are tributyl phosphate, diethyl ether [60-29-7 ], ketones such as diisopropyl ketone [565-80-5] or methyl isobutyl ketone [108-10-1 /, and several glycol ether type solvents such as diethyl Ceflosolve [629-14-1] (ethylene glycol diethyl ether) or dibutyl Carbitol [112-73-2] (dietliylene glycol dibutyl ether). 

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