Rapid reaction of sulfide with hydrogen peroxide and formation of different final products by freezing compared to those in solution

Abstract

The reaction of sulfide with hydrogen peroxide in an aqueous solution at pH 9 produces thiosulfate, sulfite, and an unknown sulfur compound as intermediates, and, finally, all sulfides convert to sulfate (Chen and Gupta, Environ Lett 1973, 4, 187-200; Yokosuka et al., Nihon Kagaku Kaishi 1975, 11, 1901-1909; Hoffmann, Environ Sci Technol 1977, 11, 61-66; Ràbai et al., J Phys Chem 1992, 96, 5414-5419). This reaction was found to be accelerated by freezing The decomposition rate of sulfide by H2O2 in freezing at - 15°C was about 5 times faster than the maximum decomposition rate in solution at 25°C. The decomposition of sulfide by freezing obeys zero-order kinetics, and the rate coefficient was 11.9 mol dm-3 min-1 at a freezing rate of 0.83 cm3 min-1. Zero-order kinetics is one of the characteristics of freezing rate-controlled reactions. Thiosulfate, sulfite, and an unknown sulfur compound were also observed as intermediates in the reaction by freezing. The decomposition of thiosulfate obeys first-order kinetics, and the rate coefficient was 0.0496 min-1 at - 15°C. The rate coefficient in freezing at - 15°C is about 47 times faster than that in solution at 25°C. Sulfide, thiosulfate, and sulfite were consumed after 90 min. However, the unknown sulfur compound was not oxidized and was preserved in ice for a long time even in the presence of an excess of hydrogen peroxide. The concentration of an unknown sulfur compound in the frozen sample can be changed by changing the concentration of H2O2 and the pH of the solution. Freezing could be used for rapid preparation and preservation of unstable substances in solution.