CMPO-substituted calix[6]- and calix[8]arene extractants for the separation of An 3D /Ln 3D from radioactive waste Francesco Sansone, a Marco Fontanella, a Alessandro Casnati, a, * Rocco Ungaro, a Volker Bo ¨hmer, b, * Mohamed Saadioui, b Karine Liger c and Jean-Franc ¸ois Dozol c a Dipartimento di Chimica Organica e Industriale, Universita`di Parma, V.le G. P. Usberti 17/A, I-43100 Parma, Italy b Fachbereich Chemie, Pharmazie und Geowissenschaften, Abteilung Lehramt Chemie, Johannes Gutenberg-Universit € at, Duesbergweg 10-14, D-55099 Mainz, Germany c CEA/DEN Cadarache, DED/SEP/LCD, 13108 Saint Paul lez Durance, France Received 7 February 2006; revised 12 April 2006; accepted 4 May 2006 Available online 30 May 2006 Abstract—Three calix[6]arene derivatives (1a–c) and two calix[8]arene derivatives (2a,b), with six and eight CMPO residues, respectively, attached to the narrow/lower rim via ether links, were synthesised. Preliminary liquid–liquid extraction studies for Eu(III) and Am(III) from aqueous nitric acid to o-nitrophenylhexyl ether reveal remarkable properties with respect to efficiency and selectivity, especially for the tert- butylcalix[6]arene derivative with a –(CH 2 ) 3 – spacer. Ó 2006 Elsevier Ltd. All rights reserved. 1. Introduction The separation of actinides (An) from lanthanides (Ln) is an urgent and important problem for the management of waste resulting from the reprocessing of fuels of nuclear plants. In fact, spent nuclear fuel contains moderate amounts of long- lived minor actinides (Np, Am, Cm) together with many fis- sion products, among which lanthanides represent one of the major components. 1 The transmutation of actinides into short-lived radionuclides has been proposed for the condi- tioning of such waste, 1–3 which requires their separation from lanthanides. Organophosphorous ligands like CMPO (carbamoylmethyl-phosphine oxide), used in the TRUEX process, phosphine oxides or dialkylphosphoric acids (TAL- SPEAK) are quite efficient extractants for An from acidic media. The introduction of CMPO binding groups onto the lower 4 or upper 5,6 rim of calix[4]arenes (I, II), as well as onto other polyvalent scaffolds, 7,8 increases not only the ex- traction efficiency of trivalent metal ions by more than 2 or- ders of magnitude, but also improves the selectivity, in some cases. 9 The original idea of pre-organising four CMPO func- tional groups on a calix[4]arene fixed in the cone conforma- tion 4,5 was further strengthened by the fact that blocking the calix[4]arene platform in a ‘rigid cone’ led to an increase (about 10-fold) in extraction ability, although not in selectiv- ity. 6 On the other hand, we have recently shown for a series of calixarene-based amide ligands, that not only the effi- ciency of alkali and alkaline-earth metal ion complexation greatly changes, passing from the calix[4]arene to the ca- lix[6]- and calix[8]arene scaffold but also the selectivity HN O P O Ph Ph NH O P O Ph Ph O P O Ph Ph HN O O O O HN O P O Ph Ph HN O P O Ph Ph O P O Ph Ph NH O P O Ph Ph NH HN O P O Ph Ph O O O O O R N O n III 4 : n = 4; R = t-Bu; cone III 6 : n = 6; R = H, t-Bu; OBn, OMe III 8 : n = 8; R = H, t-Bu; OBn, OMe I II Keywords: Actinides/lanthanides separation; CMPO; Calixarenes; Confor- mational properties; Radioactive waste treatment; Actinides complexation. * Corresponding authors. Tel.: +39 0521 905458; fax: +39 0521 905472 (A.C.); tel.: +49 6131 3922319; fax: +49 6131 3925419 (V.B.); e-mail addresses: casnati@unipr.it; vboehmer@mail.uni-mainz.de 0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.tet.2006.05.009 Tetrahedron 62 (2006) 6749–6753