Mechanism and dynamics of methyl and ethyl orange transfer across the water/1,2-dichloroethane interface

The mechanism of methyl (MO) and ethyl orange (EO) transfer across the water/1,2-dichloroethane (DCE) interface was studied from thermodynamic and kinetic points of view. Ionic partition diagrams were constructed from the appropriate acid/base equilibrium and formal transfer potentials. In situ spectroscopic studies suggest that the transfer of the anionic species from water to DCE takes place mainly via the non-hydrogen bonded form. On the other hand, the transfer of the anions from DCE to water with a pH smaller than the pK(a) involves the protonation of MO during the transfer step. The rate of ion transfer was studied by chronoabsorptometry and potential modulated reflectance. It was confirmed that the transfer of both anions is a potential dependent process, giving a standard apparent rate constant of the order of 10(-2) cm s(-1) and a transfer coefficient of 0.5. Kinetic data are discussed within the framework of existing model for ion transfer at ITIES, Theoretical aspects of chronoabsorptometry for the study of ion transfer kinetics are also outlined. (C) 1998 Elsevier Science Ltd. All rights reserve