Electrochemical monitoring of proton transfer across liquid/liquid interfaces on the surface of graphite electrodes

Equilibrium partitioning of HClO4 between aqueous solutions and benzonitril e (BN) or nitrobenzene (NB) was measured and used to evaluate the pK(a) of the acid in the two organic solvents. The potential drop across the BN/H2O interface was evaluated from the known potential drop across the NB/H2O int erface and the voltammetrically measured formal potential of a ferrocenium/ ferrocene redox couple confined within thin layers of the two organic solve nts. The voltammetric reduction of tetrachloro-1, 4-benzoquinone in thin la yers of BN was used to monitor changes in the concentration of protons in t he layer during proton-consuming faradaic reactions. The rate of proton tra nsfer from the aqueous to the nonaqueous phase across the BN/H2O interface was shown to be adequate to sustain proton-consuming reactions at the elect rode/BN interface.