Extraction and complexation of alkali, alkaline earth, and F-element cations by calixaryl phosphine oxides

A series of new calixarene derivatives with phosphine oxide groups on the l ower rim and, for comparison, a series of noncalixarene phosphine oxides ha ve been synthesised. Their extraction power for alkali and alkaline earth c ations from aqueous metal picrate solution into dichloromethane have been d etermined as well as the stability constants in methanol of the 1:1 complex es of several members of the calixarene series. Important selectivity trend s are revealed by both methods. The extraction power from aqueous nitrate s olutions (1M in HNO3) towards europium(III), as a model for trivalent actin ides, and thorium(Iv), as a model for tetravalent actinides, has been studi ed in detail for eight symmetrical calixarene derivatives, which differ in either calixarene size (4, 5, 6 or 8), the substituent at the upper rim (te rt-butyl or hydrogen) or the number of methylene groups separating the phen olic oxygen atoms from the phosphorus atoms (1 or 2). The stoichiometry of the extracted species was characterised by a classical log - log plot analy sis. All the calixarenes tested are far better extractants than typical non calixarene extractants, for example, TOPO and CMPO, currently in use in the treatment of radioactive waste; they extract thorium better than europium. The influence of the nitric acid concentration and of the sodium nitrate c oncentration in the aqueous phase on the extraction efficiency was also exa mined in order to assess the possible application of these compounds for th e decategorisation of liquid nuclear waste. Several thorium complexes have been characterised by their stability constants in methanol.