Kinetic Studies of the Reaction of Nitrous Acid with Iodide Ion in the Presence of Molecular Oxygen in an Acid Solution

Abstract

The kinetics of the reaction between nitrous acid and iodide ion were studied in the presence of molecular oxygen (O2) in an acid solution (pH 1.9—3.1); much larger amounts of the triiodide ion than expected from the amounts of nitrous acid were formed under conditions of the iodide ion in excess over nitrous acid. The initial rates for the formation of I2 and I3− increased proportionally with increasing both the O2 and nitrous acid contents, and increased greatly with decreasing the pH in the solution. The reaction rate was also decreased by bubbling either air or O2 through the reacting solution, depending on the bubbling velocity. A chain mechanism is proposed to account for the results obtained in the dark: 2HNO2 + 2I− + 2H+ → 2NO + I2 + 2H2O; 2NO + O2 → 2NO2; 2NO2 N2O4; N2O4 + 2I− + 2H+ → 2HNO2 + I2; I2 + I− I3−. The rate-determining step was the reaction of NO with O2. The addition of trace amounts of copper(II) or iron(II) ion enhanced the formation of I2 and I3− due to the occurrence of reactions of I− with the metal ions. Such an acceleration effect by the metal ions, however, could be diminished by the addition of ethylenediaminetetraacetic acid. Although the rate of the reaction of HNO2 with I− was not greatly changed by the irradiation of visible light during the initial period of reaction, it was greatly accelerated after some formation of I2 and I3−, being dependent on not only the light intensity, but also on the concentrations of H+ and I− ions. The effects of the metal ions as well as visible light are also accounted for by the above-mentioned mechanism.

Great Enhancement in the Oxidation Ability of Dilute Nitric Acid in Nanoscale Water-Droplets of Reverse Micelle Systems

“…Light over the reaction vessel and ambient oxygen had no apparent effects on the Br À oxidation; whereas, it has been reported that air, or oxygen gas, affected the oxidation of I À into I 3 À . 20,21 Dilute nitric acid with concentration in the 0.25-2.5 mol dm À3 (in 1.0 vol % H 2 O) range produced almost the half-amount Br 2 molecules to each HNO 3 molecules. Considering the amount of the product, the formation of Br 2 (or Br 3 À ) seems to follow the reaction in Eq.…”

“…8 we observed that a rather strong yellow-color developed only when (dilute) nitric acid was present in Br À ion rich conditions; the possibility of formation of yellow-colored cobalt(II) and cobalt(III) complexes was denied by our careful examination of many cobalt complexes. Kimura et al 20,21 have reported the reactions of nitrous and phosphinic acids with the iodide ion in the presence of molecular oxygen in acidic solutions.…”

Reduction of iodine by hydroxylamine within the pH range 0.7-3.5

“…The reactive medium must contain some nitrogen monoxide resulting from reaction (R-4) or, more hypothetically, from the dismutation of nitrous acid in acidic medium (this reaction being much slower than reaction (R-3) [14]). The catalysis of reaction (R-9) by nitrogen monoxide has been reported by Eguchi et al [15,16], whose results were confirmed by Kimura et al [17]. It occurs according to the following mechanism: the sum of (R-11), (R-12) and (R-4) resulting in (R-9).…”

Sensitive determination of nitrite by means of a Landolt-type reaction in fluorescent aggregates of a binaphthyl-based amphiphile

“…The mechanism of iodine formation in the blank test is not completely clear, since even solutions deaerated by bubbling argon gas, revealed some presence of iodine under longer irradiation of the sample at excitation wavelength. Probably a trace amount of oxygen is sufficient for an initial formation of iodine whose concentration further increases as a result of chain photochemical reactions involving free iodine radicals [14]. On the other hand, no clear effect of the deaeration on the reaction rate of iodide with NO2 has been observed, although a catalytic effect of oxygen on reaction (1) was observed in classical systems containing KI at high concentration (0.1 M) [ 14,15].…”

“…Probably a trace amount of oxygen is sufficient for an initial formation of iodine whose concentration further increases as a result of chain photochemical reactions involving free iodine radicals [14]. On the other hand, no clear effect of the deaeration on the reaction rate of iodide with NO2 has been observed, although a catalytic effect of oxygen on reaction (1) was observed in classical systems containing KI at high concentration (0.1 M) [ 14,15]. These differences probably result from the application of a micellar system, in which the concentration effect favours the reacting anions over neutral oxygen molecules.…”