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

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 NO3−, Cl−, Br−, F− and ClO4− 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) I2(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) I2(nb)+2X−(nb)+2e−⇄2I−(nb)+2X−(aq) (X−=Cl−, Br−, possibly in the form of I2X−). 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 I2X−(nb) ions in nitrobenzene.