Polarography of Halides in Dimethylformamide. II. The Iodide Ion, the Triiodomercurate Ion, and Mercuric Iodide

Abstract The polarographic behavior of the iodide ion, the triiodomercurate ion, and mercuric iodide at the dropping mercury electrode was investigated in dimethylformamide, using d.c. polarography, controlled potential electrolysis, and oscillographic polarography with a multi-triangular voltage sweep. The iodide ion gives two well-defined anodic waves: the first wave corresponds to the reversible oxidation of mercury to the triiodomercurate ion, and the second, to the reversible oxidation of mercury to mercuric iodide. A maximum arises on the reduction wave of the triiodomercurate ion, but it is suppressed by the addition of a small amount of polyvinyl chloride. The oscillographic polarograms and electrocapillary curves suggested that the iodide ion, like the triiodomercurate ion and mercuric iodide, is strongly adsorbed on the dropping mercury electrode. The maximum on the wave due to the reduction of the triiodomercurate ion to mercury and the iodide ion was ascribed to the convection of the mercury drop, which was itself probably caused by the abrupt desorption of the iodide ion formed successively with an increase in the negative potentials. The adsorption phenomena of the corresponding bromides and chlorides are also discussed.