Kinetics and mechanism of the oxidation of hydroxylamine by aqueous chlorine

Cooper, John N.; Margerum, Dale W.

doi:10.1021/ic00078a004

Cited by 10 publications

(8 citation statements)

References 2 publications

(2 reference statements)

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“…Both the LiClO 4 and LiCl solutions were standardized by passing a known amount through a Dowex 50W-X8 cation-exchanger and titrating against a KHP standardized NaOH solution. Stock solutions of NaOCl were prepared by bubbling Matheson high-purity Cl 2 gas, prewashed in 0.1 M KMnO 4 and then in concentrated H 2 SO 4 , into a 0.6 M NaOH solution. This solution was then diluted with an additional volume of NaOH to raise the pH to 12.…”

Section: Methodsmentioning

confidence: 99%

Oxidation of Coordinated Ammonia to Nitrosyl in the Reaction of Aqueous Chlorine with cis-[Ru(bpy)₂(NH₃)₂]²⁺

Assefa

Stanbury

1997

J. Am. Chem. Soc.

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Rapid-scan stopped-flow kinetic studies show that the multielectron oxidation of coordinated ammonia in cis-[Ru(bpy)2(NH3)2]2+ by acidic (pH 0.5−1.3) aqueous chlorine provides the nitrosyl complex cis-[Ru(bpy)2(NH3)(NO)]3+ as the final product. The first step in this process involves the metal-centered oxidation of cis-[Ru(bpy)2(NH3)2]2+ to cis-[Ru(bpy)2(NH3)2]3+, and the rate law for this process is −d[Ru(II)]/dt = 2k 1[Ru(II)][Cl2] with the second order rate constant, k 1, as (1.1 ± 0.1) × 103 M-1 s-1. Independent studies conducted on the cis-[Ru(bpy)2(NH3)2]3+ complex show that conversion to the nitrosyl complex follows an A → B → C type consecutive pathway with k slow and k fast components, respectively. In the pH range of 0.5−2.8, the k slow process follows a competitive pathway where both Cl2 and HOCl react with deprotonated coordinated ammonia. The rate law for the k slow process has the form k slow = {(k 2[H+][Cl-] + k 3 K Cl)/(K Cl + [H+][Cl-])}([Cl2]tot/[H+]), where K Cl corresponds to the equilibrium constant for the hydrolysis of Cl2. The rate constant k 2, corresponding to the Cl2 term, is 6.5 ± 0.3 s-1 while the rate constant k 3, corresponding to the HOCl reaction, is 2.0 ± 0.2 s-1. The k fast process involves further oxidation of intermediate B by Cl2. The intermediate of this reaction is speculated as either a nitrene, nitrido, or chloroamine complex. The kinetic studies indicate that the conversion of this unidentified intermediate to the final nitrosyl complex proceeds through a fast preequilibrium, involving deprotonation of the intermediate, followed by a direct attack by Cl2. The rate law corresponding to the k fast process has the form k fast = [k 4 K int[Cl2]tot[H+][Cl-]]/[{K int + [H+]}{[H+][Cl-] + K Cl}], the equilibrium constant K int for the deprotonation process is 0.11 ± 0.04 M, and the rate constant k 4 is (7.8 ± 1.5) × 102 M-1 s-1.

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Section: Methodsmentioning

confidence: 99%

Oxidation of Coordinated Ammonia to Nitrosyl in the Reaction of Aqueous Chlorine with cis-[Ru(bpy)₂(NH₃)₂]²⁺

Assefa

Stanbury

1997

J. Am. Chem. Soc.

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“…There have been a few publications disagreeing with the hypotheses involving this species, but these are much fewer in number and are found mainly in the inorganic chemistry literature. 19,20 One goal in the present study was to determine the chlorine species that is present (and responsible for the extremely rapid oxidation) at pH values below 5 in aqueous free-chlorine solutions. Raman spectroscopy was chosen as the primary analytical tool because it provided several advantages for this investigation.…”

Section: Introductionmentioning

confidence: 99%

Monitoring the Speciation of Aqueous Free Chlorine from pH 1 to 12 with Raman Spectroscopy to Determine the Identity of the Potent Low-pH Oxidant

et al. 2006

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The speciation of aqueous free chlorine above pH 5 is a well-understood equilibrium of H2O + HOCl <==> OCl- + H3O+ with a pKa of 7.5. However, the identity of another very potent oxidant present at low pH (below 5) has been attributed by some researchers to Cl2(aq) and by others to H2OCl+. We have conducted a series of experiments designed to ascertain which of these two species is correct. First, using Raman spectroscopy, we found that an equilibrium of H2O + H2OCl+ <==> HOCl + H3O+ is unlikely because the "apparent pKa" increases monotonically from 1.25 to 2.11 as the analytical concentration is increased from 6.6 to 26.2 mM. Second, we found that significantly reducing the chloride ion concentration changed the Raman spectrum and also dramatically reduced the oxidation potency of the low-pH solution (as compared to solutions at the same pH that contained equimolar concentrations of Cl- and HOCl). The chloride ion concentration was not expected to impact an equilibrium of H2O + H2OCl+ <==> HOCl + H3O+, if it existed. These observations supported the following equilibrium as pH is decreased: Cl2(aq) + 2H2O <==> HOCl + Cl- + H3O+. The concentration-based equilibrium constant was estimated to be approximately 2.56 x 10(-4) M2 in solutions whose ionic strengths were approximately 0.01 M. The oxidative potency of the species in low pH solutions was investigated by monitoring the oxidation of secondary alcohols to ketones. These and other results reported here argue strongly that Cl2(aq) is the correct form of the potent low-pH oxidant in aqueous free-chlorine solutions.

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“…Work by Margerum's group suggests the same intermediate. In that work, the mechanism involved a reaction between NH 2 OH and Cl 2 to produce the same NHClOH species proposed here [22]. However, unlike those conditions, where the concentration of Cl 2 was in large excess relative to that of the NH 2 OH, here a large excess of NH 2 OH relative to the NH 2 Cl exists, and no subsequent chlorination of the intermediate is possible.…”

Section: Discussionmentioning

confidence: 85%

“…Careful inspection of the two proposed transition states yields a consequential observation. There are two equivalent protons on NH 2 OH that can be transferred to form the N Cl N transition state, while there are three equivalent protons on NH 3 [ [21,22]. The lack of any absorbance change at 350 nm indicates a lack of formation of NO − 2 , thus Scheme 1 assumes the formation of N 2 O from HNO.…”

Section: Discussionmentioning

confidence: 99%

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Kinetics and mechanism of the reduction of monochloramine by hydroxylamine and hydroxylammonium ion

Robinson¹,

Hoppe²,

Paslay³

et al. 2005

Int J of Chemical Kinetics

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The kinetics and mechanism by which monochloramine is reduced by hydroxylamine in aqueous solution over the pH range of 5-8 are reported. The reaction proceeds via two different mechanisms depending upon whether the hydroxylamine is protonated or unprotonated. When the hydroxylamine is protonated, the reaction stoichiometry is 1:1. The reaction stoichiometry becomes 3:1 (hydroxylamine:monochloramine) when the hydroxylamine is unprotonated. The principle products under both conditions are Cl -, NH + 4 , and N 2 O. The rate law is given byAt an ionic strength of 1.2 M, at 25 • C, and under pseudo-first-order conditions, k + = (1.03 ± 0.06) ×10 3 L · mol −1 · s −1 and k 0 = 91 ± 15 L · mol −1 · s −1 . Isotopic studies demonstrate that both nitrogen atoms in the N 2 O come from the NH 2 OH/NH 3 OH + . Activation parameters for the reaction determined at pH 5.1 and 8.0 at an ionic strength of 1.2 M were found to be H ‡ = 36 ± 3 kJ · mol -1 and S ‡ = −66 ± 9 J · K −1 · mol −1 , and H ‡ = 12 ± 2 kJ · mol −1 and S ‡ = −168 ± 6 J · K −1 · mol −1 , respectively, and confirm that the transition states are significantly different for the two reaction pathways. C 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: [124][125][126][127][128][129][130][131][132][133][134][135] 2006

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Kinetics and mechanism of the oxidation of hydroxylamine by aqueous chlorine

Cited by 10 publications

References 2 publications

Oxidation of Coordinated Ammonia to Nitrosyl in the Reaction of Aqueous Chlorine with cis-[Ru(bpy)₂(NH₃)₂]²⁺

Oxidation of Coordinated Ammonia to Nitrosyl in the Reaction of Aqueous Chlorine with cis-[Ru(bpy)₂(NH₃)₂]²⁺

Monitoring the Speciation of Aqueous Free Chlorine from pH 1 to 12 with Raman Spectroscopy to Determine the Identity of the Potent Low-pH Oxidant

Kinetics and mechanism of the reduction of monochloramine by hydroxylamine and hydroxylammonium ion

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Kinetics and mechanism of the oxidation of hydroxylamine by aqueous chlorine

Cited by 10 publications

References 2 publications

Oxidation of Coordinated Ammonia to Nitrosyl in the Reaction of Aqueous Chlorine with cis-[Ru(bpy)2(NH3)2]2+

Oxidation of Coordinated Ammonia to Nitrosyl in the Reaction of Aqueous Chlorine with cis-[Ru(bpy)2(NH3)2]2+

Monitoring the Speciation of Aqueous Free Chlorine from pH 1 to 12 with Raman Spectroscopy to Determine the Identity of the Potent Low-pH Oxidant

Kinetics and mechanism of the reduction of monochloramine by hydroxylamine and hydroxylammonium ion

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Oxidation of Coordinated Ammonia to Nitrosyl in the Reaction of Aqueous Chlorine with cis-[Ru(bpy)₂(NH₃)₂]²⁺

Oxidation of Coordinated Ammonia to Nitrosyl in the Reaction of Aqueous Chlorine with cis-[Ru(bpy)₂(NH₃)₂]²⁺