Reduction of iodine at the organic liquid | aqueous solution | graphite electrode three-phase arrangement

Abstract

The electrochemistry of the iodine/iodide redox couple was studied at the three-phase arrangement organic liquid | aqueous solution | graphite electrode. A droplet of an organic solvent, e.g. nitrobenzene, containing dissolved iodine was attached to a graphite electrode and immersed in an aqueous electrolyte solution. The reaction mechanism has been studied in the presence of NO 3 −, Cl −, Br −, F − and ClO 4 − ions in the aqueous supporting electrolyte, and for nitrobenzene, tetrachloromethane, and paraffin oil as organic solvents for iodine. The reduction of iodine in the nitrobenzene droplet is either accompanied by a transfer of the iodide ions formed from nitrobenzene to water: (i) I 2(nb)+2e −⇄2I − (aq), or, in the case that the aqueous electrolyte is an alkali chloride or bromide, by a transfer of chloride or bromide ions from nitrobenzene to water: (ii) I 2(nb)+2X − (nb)+2e −⇄2I − (nb)+2X − (aq) (X −=Cl −, Br −, possibly in the form of I 2X −). The second reaction is possible because with chloride and bromide ions a rather fast reactive partition of the aqueous electrolyte into nitrobenzene occurs, due to the formation of I 2X − (nb) ions in nitrobenzene.