Chemical aspects of the radiation stability of macrocyclic extractants designed for 90Sr separation

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Distribution of benzo-substituted crown-ethers between chloroform and water: effects of macrocycle ring size and lithium chloride

Small size benzo-substituted crown ethers are attractive complexing agents for lithium isotope separation by solvent extraction. Low transfer of the crown ethers from solvent to water is a key point for applicability of the extractants. In the present study, 9- and 12-membered crown ethers were synthesized, and their distribution between chloroform and water was studied. Polyether ring size, benzene substituents and addition of LiCl to water were found to effect on distribution constants. Low losses of the macrocycles were observed at single-stage contact with aqueous phase. However, these losses should be taken into account in the design of multistage processes for the preparation of highly enriched lithium isotopes.     

Radiation chemical synthesis of polyethylene oxide hydrogel containing DCH18C6 crown ether: A new approach

Polyethylene oxide hydrogels containing physically immobilized dicyclohexano-18-crown-6 were prepared by radiation chemical synthesis. Doses of gel formation were found to depend on the molecular weight of the polyethylene oxide and were about 20 and 4 kGy for M_w of 10⁵ and 3·10⁶, respectively. An increase in the crown ether concentration resulted in the decrease of the efficiency of hydrogel formation, whereas the effect of polymer concentration was less pronounced. It was found that dicyclohexano-18-crown-6 immobilized in the PEO hydrogel showed relatively high resistance toward washout in aqueous media.This revised version was published online in November 2005 with corrections to the Cover Date.     

Radical products of γ-radiolysis of 12-crown-4 at 77 K

Paramagnetic products of γ-radiolysis of 12-crown-4 and its solutions in CFCl₃ and CFCl₂CF₂Cl at 77 K were studied by ESR spectroscopy. It was found that the ESR spectra of 12-crown-4 irradiated with γ-rays at 77 K contained superimposing signals of at least two species, the radicals resulting from macrocycle opening -?H-C(H) = O and macrocyclic radicals -O-?H-CH₂-, which are formed with nearly equal yields. It was shown that -O-?H-CH₂-radicals rapidly decayed at temperatures above 140 K. However, the -?H-C(H)=O radicals are stable almost up to the matrix softening temperature. The radical cations of 12-crown-4 are not stabilized in the matrices of Freon 11 and Freon 113, since they undergo transformation to macrocyclic radicals -O-?H-CH₂-via the deprotonation reaction.     

Radical channels of radiation destruction of macrocyclic component of strontium-selective extractants based on ionic liquids

Russian Chemical Bulletin - To study the radiolysis of the extractant composition based on solutions of dicyclohexano-18-crown-6 (DCH18C6) in ionic liquids containing the...     

Radiolysis of aqueous DCH18C6 solutions at 77 K

Low-temperature (77 K) γ- and X-ray radiolysis of aqueous DCH18C6 solutions was studied by ESR-spectroscopy. OH radicals, trapped electrons and macrocyclic radicals -CH₂-CH-O- resulting from H-atom abstraction from methylene groups of polyether ring were identified as predominant radiolysis products. Increasing the crown ether concentration in aqueous solution leads to the growth of relative yields of the trapped electron and macrocyclic radicals as well as the decrease of that of hydroxyl radical. Neither radical products of macrocycle rupture nor H-atom abstraction from cyclohexane rings were observed.     

Radiolysis of aqueous solutions of poly(vinyl alcohol) at 77 K

Paramagnetic products of low-temperature X-ray radiolysis of aqueous poly(vinyl alcohol) solutions (2.5 and 5% by weight) were studied by ESR spectroscopy. Experimental spectra were ascribed to a superposition of signals from hydroxyl radicals and –CH₂?^?C(OH)–CH₂? macroradicals (C_α-macroradicals), respectively. No ESR signals corresponding to trapped electrons were observed that was attributed to the peculiarities of microheterogenous structure of the frozen aqueous polymer solutions. Annealing at 115 K resulted in partial conversion of OH radicals to C_α-macroradicals. It was suggested that main part of hydroxyl radicals was stabilized in phase of polycrystalline ice while macroradicals were formed in “mixed” water–polymer phase. The radiation–chemical yields of paramagnetic species stabilized in the systems under study were determined.     

Radiolysis of Aqueous Solutions of Poly(ethylene oxide) at 77 K

Low-temperature (77 K) γ-radiolysis of aqueous solutions of poly(ethylene oxide) was studied by ESR spectroscopy. Trapped electrons, hydroxyl radicals, and -CH₂-ĊH-O- radicals were identified as principal paramagnetic products of radiolysis. It was shown that an increase in the polymer concentration in solution led to a growth in number of trapped electrons and -CH₂-ĊH-O- macroradicals. The decay of hydroxyl radicals occurring at 110–115 K was accompanied by the formation of -CH₂-ĊH-O- macroradicals and partial recombination of hydroxyl radicals. Action of visible light resulted in virtually quantitative transformation of trapped electrons into -CH₂-ĊH-O- macroradicals. The radiation-chemical yields of the species trapped at 77 K were estimated and the scheme of radiation-induced chemical processes was suggested.__________Translated from Khimiya Vysokikh Energii, Vol. 39, No. 4, 2005, pp. 243–249.Original Russian Text Copyright © 2005 by Zakurdaeva, Nesterov, Feldman.