Nucleophile Assistance of Electron-Transfer Reactions between Nitrogen Dioxide and Chlorine Dioxide Concurrent with the Nitrogen Dioxide Disproportionation

Abstract

The reaction of chlorine dioxide with excess NO(2)(-) to form ClO(2)(-) and NO(3)(-) in the presence of a large concentration of ClO(2)(-) is followed via stopped-flow spectroscopy. Concentrations are set to establish a preequilibrium among ClO(2), NO(2)(-), ClO(2)(-), and an intermediate, NO(2). Studies are conducted at pH 12.0 to avoid complications due to the ClO(2)(-)/NO(2)(-) reaction. These conditions enable the kinetic study of the ClO(2) reaction with nitrogen dioxide as well as the NO(2) disproportionation reaction. The rate of the NO(2)/ClO(2) electron-transfer reaction is accelerated by different nucleophiles (NO(2)(-) > Br(-) > OH(-) > CO(3)(2-) > PO(4)(3-) > ClO(2)(-) > H(2)O). The third-order rate constants for the nucleophile-assisted reactions between NO(2) and ClO(2) (k(Nu), M(-2) s(-1)) at 25.0 degrees C vary from 4.4 x 10(6) for NO(2-) to 2.0 x 10(3) when H(2)O is the nucleophile. The nucleophile is found to associate with NO(2) and not with ClO(2) in the rate-determining step to give NuNO(2)(+) + ClO(2)(-). The concurrent NO(2) disproportionation reaction exhibits no nucleophilic effect and has a rate constant of 4.8 x 10(7) M(-1) s(-1). The ClO(2)/NO(2)/nucleophile reaction is another example of a system that exhibits general nucleophilic acceleration of electron transfer. This system also represents an alternative way to study the rate of NO(2) disproportionation.

Anion-Catalyzed Dissolution of NO2 on Aqueous Microdroplets

“…Strong NO 3 -signals (m/z ) 62), however, develop on aqueous NaOH microdroplets above pH ∼ 10. Since the aerial surfaces of aqueous electrolyte solutions as a rule are negatively charged relative to the bulk, that is, anions approach the interface closer than cations, 44,45 this finding actually implies that OH -is able to catalyze the disproportionation of NO 2 29 and prompted us to explore the possibility that other anions X -could also promote reaction 1. Figure 1A also shows the mass spectrum acquired from 1 mM NaCl microdroplets at pH 7.0 sprayed into NO 2 (g)/N 2 under identical conditions.…”

27 Mechanisms of reactions in solution

“…under conditions which avoid other reactions, to yield ClO 2 2 and NO 3 2 . 87 The reaction was accelerated by a wide range of nucleophiles, with NO 2 2 (k nuc ~4.4 6 10 6 M 22 s 21 ) having the most effect, H 2 O (k nuc ~2.0 6 10 3 M 22 s 21 ), the least and Cl 2 having no apparent effect. The overall mechanism is given by Scheme 5…”

Chlorine Dioxide-Facilitated Oxidation of the Azo Dye Amaranth

“…Margerum et al during their studies on the oxidation of nitrogen dioxide with chlorine dioxide under alkaline conditions have suggested a catalytic role for hydroxide ion with a preferential binding to NO 2 , yielding ClO 2 À and NO 3 À as products. 34 If the assumption is valid, then in the presence of [OH À ], the plot of k 0 /[ClO 2 ] versus [OH À ] should give a straight line. Such a linear curve should have an intercept equal to k 1 and a slope equal to k OH À .…”