Actinide complexes ethers

The actinides have a high degree of specificity for neutral and anionic oxygen-containing organic molecules. The actinide complexes with O -donor ligands that are most widely studied include alkoxides, aryloxides amide, carboxylates, and oxalates. Complexes with alcohols, ethers, esters, ketones, aldehydes, ketoenolates, and carbamates have also been reported. 

Actinide ions form complex ions with a large number of organic substances (12). Their extractabiUty by these substances varies from element to element and depends markedly on oxidation state. A number of important separation procedures are based on this property. Solvents that behave in this way are thbutyl phosphate, diethyl ether [60-29-7J, ketones such as diisopropyl ketone [565-80-5] or methyl isobutyl ketone [108-10-17, and several glycol ether type solvents such as diethyl CeUosolve [629-14-1] (ethylene glycol diethyl ether) or dibutyl Carbitol [112-73-2] (diethylene glycol dibutyl ether). 

Table 23 Ether Complexes with Actinide(IV) Compounds...

Table 48 Some Complexes of Actinide(IV) Compounds with Crown Ethers and Cryptands...

In the second project, gathering nine teams from six EC countries, more than 150 new extractants were prepared and studied, and the target was reached for the decategorization of waste. Dialkoxy calix[4]arene-crown-6 for cesium, octaamide calix[8] arenes, and CMPO-like calixarenes for actinides display much higher complexing and extracting abilities than other classical extractants, crown ethers, or dicarbollides proposed and sometimes used for this purpose. 

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... 

Membrane-based separation methods are popular in chemical industry for effluent treatment, desalination, and gas purification. However, their application for separation of actinides relevant to nuclear industry is still at infancy stage. The past few decades saw the use of exotic reagents such as crown ethers, calrxarenes for the selective complexation and removal of actinides... 

As in the presence of aqua complexes, the presence of crown ethers facilitates the crystallization of actinide halide solvate complexes in this manner ThCl4(EtOH)3(H20) 18-crown-6 and ThCl4(MeOH)2(H20)2 15-crown-5 have been isolated. " ... 

Crystallization of complex halides from solution containing crown ethers results not in the complexation of the actinide by the ether oxygen atoms, but rather in the isolation of [AnXg] " salts in which the crown appears to act as a crystallization aid. " ... 

In many cases, synergists are added to HTTA extraction systems to enhance the separation of actinide ions. One example is the addition of the crown ethers (CE) dibenzo-18-crown-6, dicyclo-hexyl-18-crown-6, dibenzyl 24-crown-8, and benzyl-15-crown-5. These crown ethers have been shown to synergistically enhance extraction into benzene and the increase follows Eu > 1102 " > Th". The extraction equilibrium for crown ether/HTTA systems for the separation of Th is shown in Equation (23). The binding of the crown ether in the extracted complex seems to be a function of crown ether basicity and steric effects2 ... 

The extraction of trivalent actinides with /3-diketones in the presence of crown ethers has also been investigated. Trifluoroacetylacetone(HTFA), HTTA, benzoyltrifluoroacetone(HBFy, and 2-napthoyltrifluoroacetone (HNFA) have all been used with 18-crown-6 to remove Am and Cm from perchlorate media into 1,2-dichloroethane. It has been shown that the mechanism of extraction for all of the /3-diketones (HA) is the formation of a cationic complex via a synergistic ion-pair extraction (SIPE) as shown in Equation (66) ... 

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