Reducing Radicals in Nitrate Solutions. The NO₃^2-System Revisited

Abstract

The one-electron reduction product of nitrate, the NO3 2- radical, was reinvestigated because of the contemporary interest in its reactivity in high-level liquid radioactive systems. Indirect observations suggest that the same dianion is produced by the precursor to the solvated electron. The redox potential of the couple NO3 -/NO3 2- was calculated, using several ab initio approaches combined with semiempirical solvation models, to be E° ≈ −1.1 V vs NHE. Using the theoretical prediction to guide the experiment, we find a value of E° = −0.89 V at zero ionic strength. Kinetic and free-energy-relationship arguments are used to question the acid−base equilibria and reaction mode that converts the NO3 2- to the oxidizing NO2 radical. It is proposed that the reaction of the dianion with various general acids is an O2- (i.e., water or OH-) transfer to the acid and not proton transfer to NO3 2-. Implications of the highly negative redox potential of the dianion and the existence of the protonated forms to practical systems are discussed.

Radiation and Chemistry in Nuclear Waste: The NOx System and Organic Aging

“…Using the equilibrium constants determined experimentally we calculate a mid-point potential of E m = -0.89±0.02 V for the N0 3 7N0 3 2 " couple at pH 9.2 and μ = 0. This value is also close to predicted estimates from theoretical calculations (-1.04±0.1 V) (10). At a more commonly encountered ionic strength of μ = 1.0, and at that same pH, we estimate E m = -0.79±0.02 V.…”

Identification of the Non-Pertechnetate Species in Hanford Waste Tanks, Tc(I)−Carbonyl Complexes

“…be generated in high level waste as a result of the radiolytic decomposition of nitrate and nitrite. 22,23 The XANES spectra of Tc(CO) 2 (NO) and fac-Tc(CO) 3 would be similar. Given the similarity of the XANES spectra of the Tc(I) carbonyl complexes, assignment of the non-pertechnetate species to a particular species is not conclusive although Tc(CO) 3 (gluconate) 2-provides an excellent fit to the observed XANES spectrum of the non-pertechnetate species.…”

The low temperature radiolysis of cis-syn-cis- dicyclohexano-18-crown-6 complexes with alkaline earth metal nitrates: An evidence for energy transfer to the macrocyclic ligand

“…Both protonating the dianion NO 3 2− (reaction (9)) (Shkrob et al, 2011;Balcerzyk et al, 2012;Katsumura et al, 1991) and dissociative O 2 À transfer (reaction (10)) (Cook et al, 2001) have been proposed to explain the conversion of NO 3 2− to NO 2 . The resulting NO 2 radical reacts with DCH18C6 via H-atom abstraction from polyether ring to generate the macrocyclic -CH 2 -CḢ-O-radicals (reaction (11) …”