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

To study the radiolysis of the extractant composition based on solutions of dicyclohexano-18-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.