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 I aqueous solution I 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) I-2(nb) + 2e(-) reversible arrow 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 reversible arrow 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. (C) 2002 Published by Elsevier Science B.V.