Oxidative Reaction of Thiosulfate with Hydrogen Peroxide by Freezing

Abstract

In order to investigate the characteristics of the oxidative reactions of low-valence sulfur compounds with H2O2 in the freezing process, a Na2S2O3 aqueous solution was mixed with a H2O2 aqueous solution, followed by freezing at −15 °C. After the designated time had passed, the concentrations of sulfur compounds were measured. The oxidation of thiosulfates was accelerated due to the freeze-concentration effect. The maximum reaction rate of the freezing reaction (−15 °C) was about 20-times faster than that in an aqueous solution (25 °C). In the aqueous-phase reaction, thiosulfates were transformed to tetrathionates as intermediates, or directly to sulfates, and all sulfur compounds were finally oxidized to sulfates. On the other hand, the tetrathionates and sulfates transformed by the freezing reaction were preserved in ice for a long time. The maximum amounts of the tetrathionates formed by freezing were about twice those in the aqueous-phase reaction. Once tetrathionates were formed by the freezing reaction, most of the formed tetrathionates coexisting with high concentrations of H2O2 were not transformed to sulfate, regardless of whether or not the sample was re-frozen. This observation is probably attributable to the difference in the pH value when tetrathionates are formed.

Freeze-Induced Reactions: Formation of Iodine−Bromine Interhalogen Species from Aqueous Halide Ion Solutions

“…Oxidation of nitrous acid, Fe(II), sulfide ions, thiosulfate ions, or formaldehyde by hydrogen peroxide has previously been shown to be accelerated when dilute solutions of these species are frozen. ,, As a proof of principle that the freeze-induced formation of dibromoiodide is not contingent on the presence of acidified nitrous acid as oxidant, it was replaced with hydrogen peroxide.…”

“…As observed in the case where X = Cl − , it was shown that the freezing process itself can lead to unexpected chemical behavior . Previous reports in the literature have shown that a variety of reactions are in fact accelerated as a result of the freezing process. − In particular, a number of atmospherically relevant autoxidation reactions, such as those involving nitrite, iodide, sulfide, or sulfite ions, are known to be promoted when dilute solutions are frozen. − ,− Indeed, an acceleration of reaction rates up to 10 5 times above those at room temperature have been reported in the literature . When a solution of dilute electrolytes is frozen, it is known that some species are incorporated more readily into the ice than others, the so-called Workman−Reynolds effect. , The concentrations of electrolytes in the liquid phase may increase dramatically as liquid water is removed to the growing solid phase and, as the freezing front advances, the remaining liquid becomes trapped between grain boundaries, leading to the formation of unfrozen, liquid-phase “micropockets”.…”

Cyanide Formation in Freezer Stored Foods: Freezing of a Glycine and Nitrite Mixture

“…In particular, these effects are further suppressed under freezing conditions. However, some reactions are accelerated under freezing conditions. − Reactions in ice are mainly explained by the freeze-concentration effect, which is generally experienced to be very sweet in partially frozen fruit juice destined for human consumption.. When an aqueous solution is frozen, the solutes in the aqueous solution are rejected by the ice crystals and are concentrated around each small ice crystal.…”

Acceleration and Reaction Mechanism of the N-Nitrosation Reaction of Dimethylamine with Nitrite in Ice

“…Therefore, we store foodstuffs in a refrigerator or a freezer to slow down the deterioration process. However, it is not always the case because some reactions in aqueous solution are accelerated by freezing. − For example, denitrification of ammonium nitrite and oxidation of nitrite are reported to be accelerated by freezing. Regardless of these reports, reactions accelerated by freezing are little known.…”