Voltammetry of tetra-alkyl ammonium salts at platinum in sulphur dioxide solution: Oxidation of the halides

Abstract

The polarographic or voltammetric behaviour of a selected group of tetra-alkyl ammonium halides and related compounds in liquid sulphur dioxide was investigated, using a stationary disk platinum indicating micro-electrode and a silver/silver-bromide reference electrode with compensation for the IR drop of the solution. The electrochemical oxidation-reduction patterns are characteristic of the natures of the cation and anion composing the compound.Generally, good reproducible polarograms are obtained. The anodic patterns indicate that the oxidation of each halogen ion can occur in multiple stages, although the bromides generally show only a single anodic wave. The order of ease of electrolytic oxidation in sulphur dioxide is iodide (easiest), bromide and chloride.Sulphur dioxide solutions of the tetra-alkyl ammonium salts show a characteristic cathodic discharge potential in the range of -0[middle dot]3 to -0[middle dot]6 V vs Ag/AgBr. If the sulphur dioxide is insufficiently purified, two cathodic waves appear, which are apparently due to a non-condensable gas other than oxygen, sulphur trioxide or water.