Cesium-137 Extraction from Nitric Acid Media with Calix[4]arene-сrown-6 Ether Solutions in Bis(tetrafluoropropyl) Carbonate

The physicochemical and extraction properties of calixarene crown ethers, 1,3-alt-bis(octyloxy)-calix[4]arene-crown-6 (II) and its derivatives with o-phenylene (I), methylenepropoxy (IV) and methylene(2,2,3,3-tetrafluoropropoxy) (III) substituents in the crown ether ring, were studied. Solutions of compound II in bis(2,2,3,3-tetrafluoropropyl) carbonate (BK-1) effectively extract cesium from 3 M nitric acid already at a concentration of 0.001 M. The introduction of substituents into the crown ether ring significantly reduces the efficiency of the cesium extraction but increases the solubility of calixarene crown ethers in bis(2,2,3,3-tetrafluoropropyl) carbonate. Data on the solubility of calixarene crown ethers in water and 3 M nitric acid, on the distribution between the organic and aqueous phases, and on the rate of the reaction with nitric acid were obtained. Calixarene crown ether I with an o-phenylene substituent reacts with 3 M nitric acid approximately 2 times faster than dibenzo-21-crown-7 does. The other calixarene crown ethers studied do not react with nitric acid under the similar conditions. Quantum chemical modeling, including optimization of the structure geometry and calculation of vibrational frequencies, was performed for the molecules of calixarene crown ethers, DB21C7, and their complexes with the cesium cation. The calculated ΔG0 values for the complexation of ligands with the cesium cation correlate well with the experimental logDCs (except for compound III with a fluorinated substituent). Solutions of calixarene crown ethers in bis(2,2,3,3-tetrafluoropropyl) carbonate exhibit selectivity for cesium and extract neither 152Eu nor 241Am from nitric acid media.