Hypohalite Ion Catalysis of the Disproportionation of Chlorine Dioxide

Abstract

The disproportionation of chlorine dioxide in basic solution to give ClO2- and ClO3- is catalyzed by OBr- and OCl-. The reactions have a first-order dependence in both [ClO2] and [OX-] (X = Br, Cl) when the ClO2- concentrations are low. However, the reactions become second-order in [ClO2] with the addition of excess ClO2-, and the observed rates become inversely proportional to [ClO2-]. In the proposed mechanisms, electron transfer from OX- to ClO2(k1OBr- = 2.05 +/- 0.03 M(-1) x s(-1) for OBr(-)/ClO2 and k1OCl-= 0.91 +/- 0.04 M(-1) x s(-1) for OCl-/ClO2) occurs in the first step to give OX and ClO2-. This reversible step (k1OBr-/k(-1)OBr = 1.3 x 10(-7) for OBr-/ClO2, / = 5.1 x 10(-10) for OCl-/ClO2) accounts for the observed suppression by ClO2-. The second step is the reaction between two free radicals (XO and ClO2) to form XOClO2. These rate constants are = 1.0 x 10(8) M(-1) x s(-1) for OBr/ClO2 and = 7 x 10(9) M(-1) x s(-1) for OCl/ClO2. The XOClO2 adduct hydrolyzes rapidly in the basic solution to give ClO3- and to regenerate OX-. The activation parameters for the first step are DeltaH1(++) = 55 +/- 1 kJ x mol(-1), DeltaS1(++) = - 49 +/- 2 J x mol(-1) x K(-1) for the OBr-/ClO2 reaction and DeltaH1(++) = 61 +/- 3 kJ x mol(-1), DeltaS1(++) = - 43 +/- 2 J x mol(-1) x K(-1) for the OCl-/ClO2 reaction.

Kinetics of the Benzaldehyde-Inhibited Oxidation of Sulfite by Chlorine Dioxide

“…• (eq 12) is very fast, with a rate constant of k ClOx = 7 × 10 9 M −1 s −1 having been reported by Wang and Margerum. 30 Likewise, the reaction of HOCl with SO 3 2− (eq 13) is very fast, with k hypo = 7.6 × 10 8 M −1 s −1 . 31 Scheme 2 requires that Cl − and ClO 3 − be produced in equal yields, in agreement with our capillary electrophoresis results.…”

“…The forward and reverse rate constants for association of benzaldehyde with sulfite (eq 7) are well-established; here we adopt the values reported by Olson et al: k fBA = 0.71 M –1 s –1 and k rBA = 1.5 × 10 –4 s –1 . Electron-transfer oxidation of SO 3 •– by ClO 2 • to form SO 3 as in eq 11 has been proposed previously, , and electron transfer from SO 3 •– is often suggested for reactions where SO 3 2– undergoes one-electron oxidation: examples include the reactions of [Os­(bpy) 3 ] 3+ , [Ru­(NH 3 ) 4 phen] 3+ , [IrCl 6 ] 2– , [Cu III (H –3 G 4 )] − , and [Fe­(phen) 3 ] 3+ . − The reaction of ClO • with ClO 2 • (eq 12) is very fast, with a rate constant of k ClOx = 7 × 10 9 M –1 s –1 having been reported by Wang and Margerum . Likewise, the reaction of HOCl with SO 3 2– (eq 13) is very fast, with k hypo = 7.6 × 10 8 M –1 s –1 …”

Kinetics of the Two-Stage Oxidation of Sulfide by Chlorine Dioxide

“…Most surprisingly, our calculation showed that, under our experimental condition, although the direct tetrasulfide–chlorine dioxide reaction proceeds steadily, tetrasulfide can very efficiently catalyze the decomposition of chlorine dioxide. The catalytic effect of hypohalite ions on the decomposition of chlorine dioxide is well-known, , but to our knowledge, this is the first time that sulfur species is reported to catalyze the disproportionation of • ClO 2 . Unfortunately, the preparation of a pure tetrasulfide solution is still not resolved completely, and it may also contain certain amounts of other polysulfides.…”

“…The pH of sodium sulfide solutions was regulated between 12.6 and 13.5 by sodium hydroxide, and the ionic strength was adjusted to 1.0 M by the addition of the necessary amount of sodium sulfate. The ionic strength of the chlorine dioxide stock solution was also controlled at 1.0 M by sodium sulfate, but it did not contain any sodium hydroxide to avoid the well-known alkaline disproportionation of chlorine dioxide . When the effect of the chlorite ion was studied, the initial chlorine dioxide stock solution contained the necessary amount of sodium chlorite as well.…”

Reactivity of Inorganic Radicals in Aqueous Solution

“…ClO 2 disproportionates, but only with the assistance of nucleophiles. [23][24][25] Three pathways are found in the mechanism. The first path has a rate law that is first order in [ClO 2 ] and [OH À ] and yields ClO 2 À þ ClO 3 À ; it is inferred to have addition of OH À to ClO 2 as the rate-limiting step with disproportionation occurring in a rapid reaction of this adduct with ClO 2 .…”