Kinetics and mechanism of oxidation of hydroxylamine by hexachloroiridate(IV) ion in buffer solutions

Abstract

The oxidation of hydroxylammonium ion by [IrCl6]2− ion in acetic acid – acetate buffer solutions, studied by stopped flow, has the stoichiometric ratio Δ[IrCl6]2−/Δ[NH2OH] = 1. The oxidation involves the species [IrCl6]2− and NH3OH+ although spectral analysis of the spent reaction mixture indicates [IrCl5(OH2)]2− to be the main product (almost to the extent of 80%). This anomaly arises because of the aquation of the reduced product [IrCl6]3−. The rate is retarded both by H+ and Cl− ions and the plots of [Formula: see text] against respective concentrations are linear. The proposed mechanism is given by reactions [i]–[v].[Formula: see text]The values of the rate constants at 25 °C are as follows: k1 = 147 dm3 mol−1 s−1 and 102ketKia = 2.8 s−1. The related activation parameters are [Formula: see text], and,[Formula: see text], and [Formula: see text] and [Formula: see text], respectively. The value of Kipd is 2.91 ± 0.03 mol dm−3 and that of Kipa (= 1/Kipd) is 0.344 ± 0.004 dm3 mol−1; both values are almost independent of temperature.

Kinetic Isotope Effect and Extended pH-Dependent Studies of the Oxidation of Hydroxylamine by Hexachloroiridate(IV): ET and PCET

“…Comparison with Prior Reports . The present stoichiometric data (at low pH) on the reaction NH 2 OH with [IrCl 6 ] 2- are in agreement with those published previously. − The current data on the catalytic effect of transition-metal ions and degradation effect confirm our prior observations of these effects, and the rate law for the uncatalyzed reaction agrees with the limited data in our prior report . Kinetic data in the early reports 13,14 are apparently artifacts arising from catalysis by adventitious metal ions or degraded samples of Ir(IV).…”

“…[12][13][14] The current data on the catalytic effect of transition-metal ions and degradation effect confirm our prior observations of these effects, and the rate law for the uncatalyzed reaction agrees with the limited data in our prior report. 12 Kinetic data in the early reports 13,14 are apparently artifacts arising from catalysis by adventitious metal ions or degraded samples of Ir(IV). This conclusion is strengthened by our new observations that aquo-iridium(III and IV) complexes are catalytic and that [IrCl 5 (H 2 O)]is a very efficient oxidant of hydroxylamine.…”

“…Oxidation of NH 2 OH with metal complexes may have an “outer-sphere” mechanism ([W(CN) 8 ] − and [IrCl 6 ] − ) or involve complex formation (Pt(IV), Ce(IV), and V(V)). In principle, studies of the outer-sphere oxidation of hydroxylamine could be quite revealing regarding the properties of the intermediate free radicals.…”

A coupling process of electrodialysis with oxime hydrolysis reaction for preparation of hydroxylamine sulfate

“… 33 Furthermore, the ionic radius of NH 3 OH + is similar to that of sodium ions. 34 It means that NH 3 OH + can penetrate through the IEMs as easily as sodium ions. NH 2 OH + H 2 O ⇄ NH 3 OH + + OH − …”

Spectrophotometric Kinetic and Mechanistic Investigation of Chlorpromazine Radical Cation with Hexachloroiridate (IV) in Catalyzed Aqueous Acid Medium

“…The oxidation kinetics and mechanistic interest of [IrCl 6 ] 2À which acts as a one equivalent oxidant, is important tool of determining the oxidation kinetics of various organic and inorganic substrates. A covalent bond formation does not possible between the [IrCl 6 ] 2À and reductant, hence this oxidant is inert [48][49][50][51][52] to substitution. Therefore the outer sphere mechanism is involved instead of inner sphere mechanism, so the outer sphere complex is formed from which the reaction product yields after decomposition.…”