No abstract

No abstract

Nuclear waste reprocessing is a current topic of great importance. Presently plutonium and uranium are effectively removed from nuclear waste streams by the PUREX process [1]. This leaves a waste stream containing long lived radio-nuclides which are both β and γ emitters as well as α emitters. The latter class of compounds includes the actinides which, if efficiently removed, can be transmuted to non-radioactive or short lived nuclides.Separation of lanthanides and actinides from nuclear waste is presently achieved using the TRUEX process [2] which utilises CMPO 1 (octyl phenyl N,N-diisobutyl carbamoylmethyl phosphine oxide) as the extractant. Although this is rather efficient it shows little discrimination between lanthanides and actinides. We have previously shown that the attachment of four CMPO-like moieties to the wide rim of a calix[4]arene not only greatly enhances extraction [3], but also imparts a selectivity for actinides and lighter lanthanides [4]. This increase in extraction for molecules of type 2 is believed to be due to the co-operative action of the ligating functions, since studies on CMPO 1 have shown three ligands to be required per cation [5]. However, to date the actual composition and conformation of the extracted species are unknown [6]. Abstract. Six new calix[4]arene derivatives 2a -f have been synthesised, bearing CMPO-like functions (-NH-C(O)-CH 2 -P(O)Ph 2 ) at their wide rim. They differ by their alkoxy groups at the narrow rim, comprising all possible combinations of methoxy and syn-propoxy groups including the conformationally mobile tetramethyl ether 2e and the tetrapropyl ether 2f fixed in the cone conformation. Their extraction behaviour for thorium(IV) and several lanthanides(III) from 1M HNO 3 to dichloromethane has been studied and compared also to non cyclic calixarene analogues 6a -e. Surprisingly Calix[4]arenes [7,8] are macrocycles which have been used in numerous ways as a platform for the design of ligands [9]. They contain hydroxyl groups at the narrow rim which are small enough to pass through the annulus. Tetra-O-alkylation with residues greater than ethyl blocks this rotation and fixes the molecule in a certain conformation. However, the tetramethyl ether(s) show a flexibility similar to the parent calix[4]arenes and can assume all four possible conformers ("cone", "partial cone", "1,2 alternate", "1,3 alternate"). In contrast to the parent calix[4]arenes which exist exclusively in the cone-conformation, due to intramolecular hydrogen bonding between their hydroxy groups, the tetramethyl ethers exist as a mixture of conformers where the partial cone is usually preferred [10]. the best extraction results were found for the 1,2-dimethoxy-3,4-dipropoxy derivative 2c among the calixarenes and for the tetramer 6d among the linear compounds. Extraction of americium(III) in comparison to curium(III) and various lanthanides(LaIII), Ce(III), Nd(III), Sm(III), Eu(III)) from 0.1 -3M HNO 3 to NPHE (o-nitrophenyl hexyl ether) was most effective again for 2c. Among these cations,...

No abstract