Localization of radiation damages in X-rays irradiated cis-syn-cis-dicyclohexano-18-crown-6 and its inclusion complex with BaCl2

For the first time, structures of radical intermediates generated upon low temperature (77 K) X-rays radiolysis of “free” dicyclohexano-18-crown-6 (cis-syn-cis-isomer, DCH18C6) and its inclusion complex with barium chloride (DCH18C6·BaCl2) were identified using EPR spectroscopy. A set of radicals originated from polyether and cyclohexyl rings was detected in DCH18C6·BaCl2 complex and “free” crown ether DCH18C6 irradiated at 77 K. Cyclohexyl, macrocyclic OCHCH2 and acyclic CHC(H)O radicals were suggested to be formed at early stages of radiolysis in both investigated compounds, and the fraction of macrocyclic OCHCH2 radicals was predominant immediately after irradiation at 77 K. Additionally, an effect of barium cation on post-radiation reactions of the radicals in irradiated DCH18C6·BaCl2 complex upon its subsequent thermal annealing at temperature above 333 K was found. In particular, the analysis of EPR spectrum of the irradiated complex annealed at 333–413 K implied a presence of signal from acyclic cyclohexanonyl radicals, which may presumably resulted from rearrangement of cyclic α-alkoxycyclohexyl radical precursors. This post-radiation reaction may contribute to accumulation of acyclic radiolytic products in the irradiated complex when comparing with radiolysis of free DCH18C6. The results obtained are essential for understanding the peculiarities of radiation resistance of extraction and sorption systems based on the crown ether under real conditions of radioactive waste reprocessing.

► The mode of radiation damage of DCH18C6 and its complex with BaCl2 was characterized. ► Both cyclic and acyclic radicals were identified as paramagnetic intermediates stabilized at 77 K. ► The macrocylic OCHCH2 radicals resulted from deprotonation of the primary radical cations. ► Macrocylic radicals were the major paramagnetic intermediates in both investigated substances. ► A mechanism of cyclohexanonyl radical formation was proposed for DCH18C6·BaCl2 complex.