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

Abstract

There has been steady interest in the aqueous reaction of ClO2• with sulfur(IV) since the 1950s, and a wide variety of rate laws and mechanisms have been proposed. In neutral-to-alkaline media, the reaction is challenging to study because of its great rate. Here it is shown that benzaldehyde can be used as an additive to slow the reaction and make its rates more amenable to study. The rates can be quantitatively modeled by a mechanism that includes reversible binding of sulfur(IV) by benzaldehyde and a rate-limiting mixed second-order reaction of ClO2• with SO3(2-). The latter reaction occurs through parallel electron transfer from SO3(2-) to ClO2• and oxygen-atom transfer from ClO2• to SO3(2-).

The Key Heterolysis Selectivity of Divalent Sulfur–Sulfur Bonds for a Unified Mechanistic Scheme in the Thiosulfatolysis and Sulfitolysis of the Pentathionate Ion

“…Here, K a2 approaches the value for the sulfite equilibrium proposed by Hoffmann, for which the corrected acidity constant c K a2 = 2.43 × 10 –7 m for an ionic strength of 0.5 m . The ionic strength of our buffer solution was 0.075 m ; thus, for the protonation process of sulfite in our present work, we set K a2 = 2.2 × 10 –7 m –1 , which is also approximately the same value as that used in our recent work …”

Kinetics and Mechanism of the Chlorite–Periodate System: Formation of a Short-Lived Key Intermediate OClOIO3 and Its Subsequent Reactions

“…Finally, a word is also in order here to discuss possible alternative pathways instead of invoking the presence of the short-lived intermediate OClOIO 3 . Very recently, Pan and his co-workers confirmed that the sulfite–chlorine dioxide reaction proceeds via parallel oxygen and electron transfer routes . Considering this opportunity here, we also tried to exchange the OClOIO 3 -driven route to the following sequence of reactions: and the measured absorbance–time series were evaluated by steps , , and refining parameters k 1 , k 2 ′ , k –2 ′ , and k 3 ′ .…”

“…Very recently, Pan and his co-workers confirmed that the sulfite−chlorine dioxide reaction proceeds via parallel oxygen and electron transfer routes. 23 Considering this opportunity here, we also tried to exchange the OClOIO 3 -driven route to the following sequence of reactions: In those systems, however, these species form in a rapid preequilibrium established instantaneously but shifted far to the left, meaning that kinetic features of the overall reaction should also depend on the characteristics of their subsequent reactions. In the present system, however, the rate-determining step is the formation of OClOIO 3 ; hence, the kinetic feature of their subsequent reactions is not manifested in the overall kinetics.…”

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

“…The data obtained suggested that approximately 0.3 mM tetrasulfide (ε S 4 2– = 1140 M –1 cm –1 ) formed when 15 mM • ClO 2 was used to oxidize 0.1 M sulfide. Consequently, the major sulfur-containing species of the oxidation has to be sulfate because sulfite , and thiosulfate , are rapidly oxidized further by chlorine dioxide as well and polythionates are not stable species under these experimental circumstances. The appearance of the characteristic absorption band around 260 nm clearly suggests that chlorite ion certainly forms during the course of the first very rapid stage, although it may not be the only chlorine-containing product.…”

“…A plausible possibility of the presence of a branching mechanism is that the reaction starts with parallel electron- and oxygen-atom-transfer processes as an analogy of sulfite and thiosulfate oxidation performed by chlorine dioxide. ,− In these systems, it is shown that the reaction starts with electron transfer from the substrate to chlorine dioxide and with oxygen transfer from chlorine dioxide to the substrate, simultaneously. To check whether the initiation step proceeds or not, we first investigated the effect of the chlorite ion on the measured kinetic curves.…”