On the reactant concentration and the reaction kinetics in the Villermaux-Dushman protocol

Abstract

The optimum choice of acid and buffer in the iodide/iodate reaction system known as the Villermaux-Dushman protocol has been under debate for several years. In this paper, the phosphate buffer recently suggested by Pinot et al. is for the first time compared to the established boric acid buffer over a large range of concentrations. The results show that the resulting triiodide yield is a function of the phosphate buffer concentration, which is not the case for boric acid buffer. Furthermore, the evaporation and reactive oxidation of iodine species was identified to significantly influence the sample treatment after mixing, while the dismutation of iodine is less influential. Additionally, a comparison of different hydrochloric, sulfuric, and perchloric acid concentrations was conducted. The catalytic effect of chloride on the Dushman reaction was for the first time quantified within a Villermaux-Dushman protocol, as was the incomplete dissociation of sulfuric acid during the mixing process. Interestingly, it can be found that the presence of chloride and sulfate influences the obtained triiodide yield to the same extent. Finally, this study takes a closer look on the investigation of Dushman kinetics as part of a Villermaux-Dushman protocol and elucidates the role of chemical attenuation for these investigations.