Ether coordinative extractant

It is generally agreed that the extracted uranium species is U02(N03)2(TBP)2 in which, in contrast to the species extracted into ether, the extractant molecules are directly coordinated to the metal ion. The extraction of uranium(VI) by neutral organophosphorus compounds increases with the number of C—P bonds (as opposed to C—0—P bonds) and with the increased branching of the substituent alkyl groups, as would be expected from the effect of these changes on the electron-donor properties of the phosphoryl group. The extracted thorium(IV) complex has been formulated as Th(N03)4-2S and as Th(N03)4-3S,2 2 and its composition may depend to some extent on the conditions of extraction. The extraction of thorium (like that of... 

Ethers. Although ethers hold an important historical place in actinide extraction, they are not used extensively at present. They are weak-Lewis-base coordinative extractants, whose chemistry has been adequately covered in earlier reviews (22). 

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 mode of extraction in these oxonium systems may be illustrated by considering the ether extraction of iron(III) from strong hydrochloric acid solution. In the aqueous phase chloride ions replace the water molecules coordinated to the Fe3+ ion, yielding the tetrahedral FeCl ion. It is recognised that the hydrated hydronium ion, H30 + (H20)3 or HgO,, normally pairs with the complex halo-anions, but in the presence of the organic solvent, solvent molecules enter the aqueous phase and compete with water for positions in the solvation shell of the proton. On this basis the primary species extracted into the ether (R20) phase is considered to be [H30(R20)3, FeCl ] although aggregation of this species may occur in solvents of low dielectric constant. 

Oxygen-containing solvents with a strong coordinating ability, such as diethyl ether, methyl /.so-butyl ketone and /.so-amyl acetate, form oxonium cations with protons under strongly acidic conditions, e.g. (R20) H. Metals which form anionic complexes in strong acid can be extracted as ion pairs into such solvents. For example, Fe(III) is extracted from 7 M hydrochloric acid into diethyl ether as the ion pair... 

The efficiency of the extraction depends on the coordinating ability of the solvent, and on the acidity of the aqueous solution which determines the concentration of the metal complex. Coordinating ability follows the sequence ketones > esters > alcohols > ethers. Many metals can be extracted as fluoride, chloride, bromide, iodide or thiocyanate complexes. Table 4.5 shows how the extraction of some metals as their chloro complexes into diethyl ether varies with acid concentration. By controlling... 

J. Lamond, Analyst 74, 560—61(1949) [Small quantities of alcohol in ether may be detd after extracting it from ether by water, followed by testing the aqueous extract by means of ceric ammonium nitrate. The following reaction takes place, producing the red coordination product ... 

The action of H202 on acidic dichromate solutions gives an unstable blue species which can be extracted into ether (equation 128).2,518,1428 On the addition of pyridine the blue compound Crvl0(02)2py crystallizes. The molecules are distorted pentagonal pyramids with sideways-bonded peroxo groups (298) 1429 some workers with less refined data have reported rather different bond distances.1430 In water the blue species is considered to be CrO(62)2(OH2), in ether it is Cr0(02)20Et2, and amines such as aniline, bipy and phen can replace the pyridine. With bidentate bipy the coordination sphere becomes essentially a pentagonal bipyramid (299),... 

While the liquid-liquid extraction of inorganic elements as coordination complexes with thiocyanate ions can be traced back to Skey (1867), the extraction from hydrochloric acid into ether of iron(III) (J. W. Rothe, 1892) or gallium (E. H. Swift, 1924) depends on the formation of solvated acido complexes derived from HMC14 extractions of metal complexes from nitric, thio-cyanic, hydrofluoric, hydrochloric and hydrobromic acids were studied exhaustively by Bock and his collaborators (1942—1956).6... 

Uranyl nitrate has been extracted into solvents such as diethyl ether as the entity [U02(N03)2(H20)4] solvated by two to six molecules of the organic solvent.254-256 The solvation is usually considered to be of the secondary type, in which the solvent molecules are attached by hydrogen bonding to the water molecules in the primary hydration shell. However, IR data have been presented257 258 to support Muller s earlier hypothesis259 that only two of the water molecules are directly bound to the uranyl cation, the remaining coordination sites being occupied by solvent molecules. 

Single-element Separation Extraction of Cs + ion is fairly difficult due to the small charge density of the atomic surface. Thus, calix-crowns were preferentially used for the extraction, because they trap Cs + ion not only by coordinating with the crown ring, but also by interaction with the n-electrons of the phenyl rings of the calixarene (382, 383). On the other hand, many reports appeared concerning extraction of Sr2+ from acidic solutions by crown ethers (384). 

Extraction by solvation involves the displacement of some or all of the water molecules in the coordination sphere of a metal complex by neutral organic donors, conferring high solubility in water-immiscible solvents. Solvating extractants are typically ethers, ketones, or neutral phosphorus(V) molecules containing P=0 units, e.g. the extraction of uranium(VI) from nitrate solutions by tri- -butyl phosphate (TBP). 

Lewis acids readily isomerize both 1,3-dioxolanes and 1,3-oxathiolanes in ether solution. The reaction proceeds by coordination with the oxygen atom in the latter case since 1,3-dithiolanes do not isomerize under the same conditions. With trityl carbonium ion, an oxidative cleavage reaction takes place as shown in Scheme 6. Hydride extraction from the 4-position of 2,2-disubstituted 1,3-dioxolanes leads to an a-ketol in a preparatively useful reaction. 1,3-Oxathiolanes are reported to undergo similar cleavage but no mention of products other than regeneration of the ketone has been made (71CC861). Cationic polymerization of 1,3-dioxolane has been initiated by a wide variety of proton acids, Lewis acids and complex catalytic systems. The exact mechanism of the polymerization is still the subject of controversy, as is the structure of the polymer itself. It is unclear if polymerization... 

The nature of the solvent used in reactions often has a profound effect on how the reaction proceeds. Often we are limited in our choice of solvent by the solubilities of the reactants and products—this can also be to our advantage when trying to separate products, for example, in ether extractions. We have seen so far in this chapter that THF is a good solvent for lithiations because it coordinates to Li, that water is a good solvent for hydrolyses of carboxylic acids because it is a reagent and because it dissolves the carboxylate anion, and that alcohols are a good solvents in reactions such as transesterifications where mass action is needed to drive equilibria over towards products. 

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