Calixarene‐Based Picolinamide Extractants for Selective An/Ln Separation from Radioactive Waste

Eleven novel ligands having picolinamide or thiopicolinamide binding groups at the upper or lower rim of calix[4]‐, calix[6]‐ and calix[8]arenes have been synthesised. The conformational properties of some of these ligands were studied in solution by means of NMR spectroscopy and in the solid state by X‐ray diffraction. Their ability to extract Am III or Eu III from water to NPHE ( o‐ nitrophenyl hexyl ether) was tested at different concentrations of LiNO 3 , HNO 3 and of a lipophilic dicarbollide anion (BrCosan). The data show a high cooperation between binding sites of the calixarene ligands in comparison to data obtained with the model ligand N‐ butyl picolinamide ( 19 ). Some of these ligands show very high distribution coefficients for Am 3+ ( D Am > 300) and good Am/Eu selectivity at pH ≥ 3, which open up interesting perspectives for their application in the treatment of low acidity radioactive waste. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)