Properties of nitroxyl as intermediate in the nitric oxide-hydroxylamine reaction and in trioxodinitrate decomposition

Abstract

The rate of decomposition of trioxodinitrate monobasic anion (HN2O3-) in aqueous solution is unaffected by the presence of hydroxylamine, but the primary product nitroxyl ("0) experiences a competition between dimerization to N 2 0 and reduction to N2. The proportion of N2 increases with pH and with NHzOH concentration; at pH 8, with N H 2 0 H in 10-fold excess over HN203-, the reaction product is more than 97% N2. The reaction between NO and N H 2 0 H produces equimolar amounts of N2 and N 2 0 at pH >13, but the ratio N Z / N 2 0 decreases with pH; at pH 8 the product is almost entirely N20.The rate of reaction declines sharply with decreasing pH. Observations of reaction product ratios are complicated by simultaneous contributions of ",OH disproportionation, which produces N2 and NzO in pH-dependent proportions. Tracer experiments employing 15N180 reactant confirm a previously proposed mechanistic interpretation of the NO-NHzOH reaction in detail: an N-bound H atom is abstracted by NO to form H N O and the radical NHOH. The radical combines with a second N O molecule to form nitrosohydroxylamine, which in turn produces two kinds of N20: I, predominantly 14N15N180, and 11, predominantly I5Nl4Ni6O. The asymmetry of the intermediate is reflected in a higher proportion of I than I1 in the product at high pH, but these proportions become equalized at pH 8, probably because of tautomerism in the intermediate. Nitroxyl is entirely reduced by NHzOH to N2 at high pH but undergoes dimerization to produce a third kind of N 2 0 , predominantly 15N1SNis0, to an extent that increases with decreasing pH. The tracer experiments also provide support for the hypothesis that nitroxyl is a primary product of hydroxylamine disproportionation. Since the nitroxyl produced in "203-decomposition is preferentially reduced to Nz at pH 8 in the presence of ",OH, while the nitroxyl produced in the NO-NH20H reaction is almost entirely consumed by self-reaction at the same pH, different intermediate species are produced in these two reactions. Possible explanations for this difference are discussed.

Disproportionation of hydroxylamine by water-soluble iron(III) porphyrinate compounds

“…Indeed, a radical mechanism has been described for the reaction of free NO with HA, forming N 2 O, Eqs. (6) and (7) [8,40]. Reactions (4)- (6), and (7) support the production of N 2 O and N 2 as unique oxidized nitrogen containing species.…”

“…The same products are obtained by spontaneous HA disproportionation, a reaction that exhibits a strong dependence with pH, described by Eqs. (2) and (3) [8,28].…”

“…Disproportionation reactions of HA [7] have been described either as uncatalyzed [8] or as metal-catalyzed processes [9]. With non-heme transition metal complexes, the products can be N 2 , N 2 O, NH 3 , and even NO + , depending on the metal, ligands, pH and the reaction medium [7,9].…”

The Chemistry of Flammable Gas Generation

“…Under other conditions, the reaction proceeds more rapidly, and considerably more nitrous oxide is formed (Bonner et al 1978). Apparently, nitrosyl anion is produced, and it has several different decomposition pathways, as discussed in Section 4.5.3.1.…”

Study of the Hydroxylammonium Nitrate - Isopropyl Ammonium Nitrate Reaction.

“…Some intermediates of this reaction have been identified and the luminosity that is produced during the reaction has been found to be caused by sodium impurities. Since decomposition of HAN produces the oxidizers that react with the fuel (IPAN) a detailed study was carried ouj 5 Block #20 (abstract) continued an isotopic tracer it was possible to demonstrate that NH was an inter-I mediate in the thermal decomposition of HAN and various radicals such as NH,, NHOH, NOH, NO and NO were responsible for producing the final products in the HAN decomposition which were N 2 0, NO, NO 9 , N 2 and HNO . Some of these are the oxidizers that attack the IPAN to poduce the fiRal products of the HAN-IPAN reaction.…”