Electrochemistry of ferrocene in anionic, cationic and nonionic micellar solutions. Effet of the micelle solubilization of the half-wave potentials

Abstract

The redox properties of the ferrocene/ferricinium Fc/Fc + couple were studied in aqueous 0.1 M NaCl solution of sodium dodecylsulphate (SDS), N-cetyltrimethylammonium bromide (CTAB) and polyoxyethylene-23 lauryl ether (Brij 35). Solubilities of ferrocene were measured by spectrophotometry and by limiting current measurements in direct current voltammetry. The reversible half-wave potentials were determined by cyclic and differential pulse voltammetry. The results are discussed on the basis of the micelle solubilization equilibrium of both the reductant Fc and the oxidant Fc +. Indeed, diffusion coefficient ratios of the oxidant to the reductant, measured by coulometry, show that the micelle solubilization of the electrogenerated ferricinium cation Fc + must also be considered in the nonionic and the anionic micellar solutions. Thus in every solution studied, a standard potential of Fc/Fc + in water may be obtained from the experimental values of the half-wave potentials, the partition coefficients of Fc and Fc + and the ratio of their diffusion coefficients. The behaviour of ferrocene in the SDS solutions and the effect produced by the addition of pentanol seem to confirm that SDS forms micelles with a less ordered structure than the other surfactants studied. The invariance of the half-wave potentials of ferrocene in pure SDS solutions whatever the surfactant and ferrocene concentrations suggests the use of this solute-solvent couple as a reference potential system.