Autocatalytic Oxidation of Trithionate by Iodate in a Strongly Acidic Medium

Abstract

The trithionate-iodate reaction has been studied spectrophotometrically in an acidic medium at 25.0 ± 0.1 °C in phosphoric acid/dihydrogen phosphate buffer, monitoring the absorbance at 468 nm at the isosbestic point of the iodine-triiodide ion system and at I = 0.5 M ionic strength adjusted by sodium perchlorate. The main characteristics of the title system are very reminiscent of those found recently in the pentathionate-iodate and the pentathionate-periodate reactions, the systems paving the way for classifying clock reactions. Thorough analysis revealed that the direct trithionate-iodate reaction plays a subtle role only to produce a trace amount of iodide ion via a finite sequence of reactions, and once its concentration reaches a certain level, then the reaction is almost exclusively governed by the trithionate-iodine and iodide-iodate reactions. The title reaction, as expected, was experimentally proven to be autocatalytic with respect to iodide ion. A simple three-step Landolt-type kinetic model is proposed to describe adequately the most important kinetic features of the title system that can easily be extended to a feasible sequence of elementary and quasi-elementary reactions.

Multichannel Feeding Module-HPLC Integrated System for Online Species Tracking and Kinetic Analysis

“…Therefore, the above comparative test has verified the ability and accuracy of the upgraded HPLC integrated system for the kinetic experiments. A mean value k ave = 0.0057 min –1 is slightly lower than that reported in the literature ( k = 0.015 min –1 at pH = 8.0), probably because of the different compositions of buffer solutions …”

“…A mean value k ave = 0.0057 min −1 is slightly lower than that reported in the literature (k = 0.015 min −1 at pH = 8.0), 4 probably because of the different compositions of buffer solutions. 29 The Application Thiourea is a sulfur-containing compound that displays many kinds of nonlinear phenomena (autocatalysis, oscillation, and chaos) during oxidation because of the formation of different intermediates. 4,5,30 The change in the oxidation state of sulfur is a key cause of these nonlinear phenomena.…”