Abstract
An empirical rate law model consisting of 6 protonation equilibria and 12 redox reactions is proposed for the oscillatory reaction between S2" and H202. The 14 species whose concentrations are explicitly taken into consideration are S2~, HS", H2S, HOSH, S42", HS4“, S82", HS03", S032", H202, H02~, H+, and OH". The key to the pH-regulated oscillatory behavior is the H+-autocatalysis in the overall reaction HS" + 4H202 —» S042' + 4H20 + H+ that results from the more rapid oxidation by H202 of the protonated than of the unprotonated form of the sulfite intermediate in this pathway. Simulations give excellent qualitative agreement with both the closed system behavior and the oscillations observed in a flow reactor, though some quantitative discrepancies remain.