Radical channels of radiation destruction of macrocyclic component of strontium-selective extractants based on ionic liq
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Radical channels of radiation destruction of macrocyclic component of strontium-selective extractants based on ionic liquids* S. V. Nesterov,a,b O. A. Zakurdaeva,a M. A. Kochetkova,с and I. O. Kuchkinaa аN.
S. Enikolopov Institute of Synthetic Polymer Materials, Russian Academy of Sciences, 70 ul. Profsoyuznaya, 117393 Moscow, Russian Federation. Fax: +7 (495) 718 3404. E-mail: [email protected] bDepartment of Chemistry, M. V. Lomonosov Moscow State University, Build. 3, 1 Leninskie Gory, 119991 Moscow, Russian Federation cMendeleev University of Chemical Technology of Russia, 9 Miusskaya pl., 125047 Moscow, Russian Federation
To study the radiolysis of the extractant composition based on solutions of dicyclohexano18-crown-6 (DCH18C6) in ionic liquids containing the bis(trifluoromethylsulfonyl)imide anion (NTf2–), we synthesized stereoisomeric DCH18C6•Sr(NTf2)2 complexes as a model of the strontium-containing macrocyclic component of this system and studied the mechanism of their destruction in the solid phase. Three main stages of radiation-chemical transformations were found. At the initial stage of radiolysis after ionization of the complex components, a positive charge is transferred from the macrocycle to the anion, which is induced by the lower ionization potential of NTf2– as compared to the crown ether. This results in the radiation protection of the macrocycle due to the blockage of the polyether ring cleavage, which is observed under radiolysis of "free" DCH18C6. The next stage consists in the accumulation of the —O—•CH—CH2— radicals caused by the reaction of the dissociation products of the NTf2– anion with the crown ether. It intensifies the radiation destruction of the polyether ring. At the final stage, the macrocyclic radicals efficiently scavenge SO2, the molecular product of dissociation of the NTf2– anion, with the formation of sulfonyl-type radicals. The discovered channels of radiation-chemical transformations of the macrocycle in the systems including the NTf2– anion should be considered in the design of new radiation-resistant extractants. Key words: dicyclohexano-18-crown-6, bis(trifluoromethylsulfonyl)imide, stereoisomerism, radiolysis, ionization potential, radicals, macrocycle cleavage.
Modern concepts of spent nuclear fuel reprocessing require separate extraction of fission products, in particular 90Sr and 137Cs, minor actinides, noble metals, etc.1 This will significantly decrease the amount of radioactive waste to be disposed and, consequently, their environmental impact. An important stage of such a combined process is the selective extraction of the 90Sr radionuclide. On the one hand, it reduces the specific activity and heat release of the processed solutions. On the other hand, the extracted strontium can be used as an energy source in radioisotope thermoelectric generators, for the production of the 90Y isotope required for radionuclide therapy, and in other areas. Dicyclohexano-substituted crown ethers such as dicyclohexano-18-crown-6 (DCH18C6) and di(tert-butylcyclohexano)-18-crown-6
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