Kinetics of hydrogen isotope exchange reactions - XXIX. Radiation-induced tritiation of 1, 4-dioxan in aqueous solutions

Abstract

Under the influence of tritium β-radiation, 1, 4-dioxan undergoes hydrogen exchange with the solvent water. The inhibition of the reaction by known electron scavengers (Ag+, Cu2+, Ni2+, Co2+, Zn2+, H+3O and also by species with high reactivity towards hydroxyl radicals but negligible reactivity towards solvated electrons (N-3, Br-, SCN-) has been examined in detail. γ-Irradiation similarly induces hydrogen exchange. The action of scavengers is interpreted as requiring the involvement of two separately scavengeable primary radiolysis products in the sequence of reactions leading to exchange. Evidence is presented that the reactions of these species occur in spur regions, and the scheme RH + OH˙→ R˙ + H2Oe-aq→ R-HTO→ RT is considered to explain the main features of the mechanism. The presence of electron scavengers, even at high concentration, does not totally inhibit the exchange, and a secondary exchange route, involving a lower valency state of inhibitor cations, is considered responsible for the ‘unscavengeable’ portion of the reaction, by providing an alternative exchange route, e. g. R˙ + Ni+→ R-+ Ni2+HTO→ RT Analogies are drawn between the exchange reaction and other radiation-induced reactions that are thought to involve spur processes (such as the formation of H2O2as a molecular product in the radiolysis of water). Some implications of the present results for the interpretation of radiation-chemical studies in water-alcohol mixtures are indicated.