Radiation chemistry of crown-compounds

Makhlyarchuk, V.V.; Zatonskii, S.V.

doi:10.1070/rc1992v061n05abeh000958

Cited by 15 publications

(9 citation statements)

References 2 publications

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“…From the results presented in section , it appears that the ground state of radical 2 does not undergo the fragmentation reactions shown in Scheme b. From previous product analysis studies, it is known that in most organic solvents such radicals cross recombine, react with molecular O 2 with the subsequent elimination of a monomer unit, or recombine with inorganic radicals generated in the aqueous phase, yielding the corresponding -Cl and -NO 2 derivatives . In analogy, it may be expected that in ILs, radical 2 can recombine or disproportionate with the anion fragment radicals (such as • CF 3 ) and the R • ( C + ).…”

Section: Discussion and Concluding Remarksmentioning

confidence: 95%

“…Before examining crown ether-containing IL systems (section ), it is important to first consider briefly the known radiation chemistry of neat CEs. − Ionization of unsubstituted CE ( 1 ) causes the formation of a radical cation 1 +• that promptly deprotonates (Scheme a). , The resulting radical 2 can also be generated via H + transfer to an excess electron, homolytic cleavage of the C−H bonds in an electronically excited CE molecule, or hydrogen abstraction by radiolytically generated H • atoms. This radical 2 (most likely, in the excited state precursor, see section ) undergoes C−O fragmentation yielding terminal radical 3 .…”

Section: Introductionmentioning

confidence: 99%

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On the Radiation Stability of Crown Ethers in Ionic Liquids

2011

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Crown ethers (CEs) are macrocyclic ionophores used for the separation of strontium-90 from acidic nuclear waste streams. Room temperature ionic liquids (ILs) are presently being considered as replacements for traditional molecular solvents employed in such separations. It is desirable that the extraction efficacy obtained with such solvents should not deteriorate in the strong radiation fields generated by decaying radionuclides. This deterioration will depend on the extent of radiation damage to both the IL solvent and the CE solute. While radiation damage to ILs has been extensively studied, the issue of the radiation stability of crown ethers, particularly in an IL matrix, has not been adequately addressed. With this in mind, we have employed electron paramagnetic resonance (EPR) spectroscopy to study the formation of CE-related radicals in the radiolysis of selected CEs in ILs incorporating aromatic (imidazolium and pyridinium) cations. The crown ethers have been found to yield primarily hydrogen loss radicals, H atoms, and the formyl radical. In the low-dose regime, the relative yield of these radicals increases linearly with the mole fraction of the solute, suggesting negligible transfer of the excitation energy from the solvent to the solute; that is, the solvent has a "radioprotective" effect. The damage to the CE in the loading region of practical interest is relatively low. Under such conditions, the main chemical pathway leading to decreased extraction performance is protonation of the macrocycle. At high radiation doses, sufficient to increase the acidity of the IL solvent significantly, such proton complexes compete with the solvent cations as electron traps. In this regime, the CEs will rapidly degrade as the result of H abstraction from the CE ring by the released H atoms. Thus, the radiation dose to which a CE/IL system is exposed must be maintained at a level sufficiently low to avoid this regime.

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Section: Discussion and Concluding Remarksmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

On the Radiation Stability of Crown Ethers in Ionic Liquids

2011

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“…Apparently, the dominant process of radiolysis of the majority of crown ethers is the cleavage of the ether bond rather than the abstraction of a hydrogen atom, as was believed earlier. 62 This conclusion is supported by the complexity and multicomponent pattern of the EPR spectra of g-irradiated (at 77 K) crown ethers, which is explained 59,66,69 by the superposition of signals belonging to several paramagnetic species and also by the absence of correlation between the radiation-chemical yields of radical products and of molecular hydrogen, G(R) = 2G(H 2 ) (see Table 1).…”

Section: Radiolysis Of Crown Ethersmentioning

confidence: 89%

Crown ethers in radiochemistry. Advances and prospects

Нестеров¹

2000

Russ. Chem. Rev.

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Methods for the immobilisation of dicyclohexano-and Methods for the immobilisation of dicyclohexano-and non-substituted crown ethers are reviewed. Data on the radiation non-substituted crown ethers are reviewed. Data on the radiation chemistry of these compounds and on the influence of irradiation chemistry of these compounds and on the influence of irradiation on the properties of crown-containing extraction systems pub-on the properties of crown-containing extraction systems published over the last decade are discussed systematically. Examples lished over the last decade are discussed systematically. Examples of the use of crown ethers in different fields of radiochemistry are of the use of crown ethers in different fields of radiochemistry are presented. The bibliography includes 199 references presented. The bibliography includes 199 references. .

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“…The crown ethers have a reputation for high radiation and chemical stability, yet quantitative mechanistic and kinetic information on their radiation chemistry is scarce. Previous reviews include that of Makhlyarchuk and Zatonskii in 1992 [8] and that of Nesterov in 2000. [9] The current review focuses specifically on that chemistry of interest to solvent extraction.…”

Section: The Radiation Chemistry Of Crown Ethersmentioning

confidence: 98%

“…As expected, [23] 0.01 M MC6 was more stable in the aromatic diluent NPOE than in dodecane, with degradation yields of 0.003 and 0.008 mmol J 21 , respectively. [45] The only other work involving the irradiation of calixarenes of which we are aware is that of Feng et al [47] The decomposition of calix [4]-, calix [6]-, and calix [8]arenes following e-beam irradiation of their mixtures with polypropylene in the presence of air was examined by multiple analytical techniques. It was concluded that the calixarene skeleton was not decomposed by doses as high as 20 MGy, but that only modification of phenol and alkyl substituents due to radical addition and hydrogen abstraction reactions occurred.…”

Section: The Radiation Chemistry Of Calixarenesmentioning

confidence: 99%