Evidence from the Reaction between Trioxodinitrate(II) and 15NO That Trioxodinitrate(II) Decomposes into Nitrosyl Hydride and Nitrite in Neutral Aqueous Solution

Abstract

An attempt was made to trap nitrosyl hydride (nitroxyl; HNO, NO- at pH 7) with 15NO in order to decide whether trioxodi-nitrate(II) (Angeli's salt; oxyhyponitrite; Na2N2O3, HN2O3- at pH 7) decomposes in neutral aqueous solution into nitroxyl plus nitrite or into NO plus HONO- as intermediate products. Final products are N2O and nitrite. The reaction of 15NO with nitroxyl was expected to double the yields of both N2O and nitrite relative to those normally produced from trioxodinitrate alone and also to provide N2O with a particular isotopic signature. The yields of N2O and nitrite and the isotope distributions in product N2O and the 15NO pool strongly support the view that trioxodinitrate decomposes into nitroxyl and nitrite. In the trapping of nitroxyl by 15NO, little exchange of 15NO and 14NO- was observed. In addition to the trapping reaction, a fraction of the nitroxyl can partition by dimerization/dehydration to form 14N2O. On the basis of these data and certain rate constants from the literature, a rate constant between 1.8 × 109 and 7.2 × 109 M-1 s-1 is estimated for the dimerization/dehydration of nitroxyl at pH 7.0, 25 °C. The reaction is thus diffusion-controlled or nearly so. The calculation leading to the above rate constant is not free from kinetic ambiguity, but ambiguity could be largely removed if N2O2-, a presumed intermediate in the trapping reaction, were asymmetrical. © 1985, American Chemical Society. All rights reserved.