Kinetics and mechanism of redox reactions of Np and Pu ions with several organic rednctants

Abstract

The paper discusses specific features pertaining to reactions of single electron oxidants of Np(VI) and Pu(IV) with organic nitrogen containing reductants such as substitution derivatives of hydrazine and hydroxylamine, nitriles, guanidines, oximes and aziridines. The oxidation rates of derivatives of hydrazine as well as hydrazine nitrite in HNO3 solutions obey the first order equations in relation to oxidation and reduction while the reaction order relative to H** ions is equal or close to minus 1. The reactions of this type are limited by the slow stage of the interaction between the uncharged molecule of a reductant and ions of NpO22+ or Pu4+. The oxidation mechanism of derivatives of hydroxylamine depends on the types of oxidants and reductants. The key specific features of the reactions of Pu(IV) are its second order relative to Pu(IV) and retardation by its product Pu(III) ions. These specific features find explanation in the mechanism of the reactions. As distinct from reactions of Pu(IV) reactions of Np(VI) are of the first order in relation to each reagent. General mechanisms of those reactions are also typical of Np(VI) and Pu(IV) reactions with acetaldoxime, diaziridine and aminoguanidine. The reactions of Np(VI) and Pu(IV) with the studied nitrogen containing organic reductants obey the isokinetic ratio: the activation enthalpy of those reactions increases in proportion to the activation enthropy. © 2002 Atomic Energy Society of Japan.