MECHANISM AND DYNAMICS OF METHYL AND ETHYL ORANGE TRANSFER ACROSS THEWATER 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 thermodynam ic and kinetic points of view. Ionic partition diagrams were construct ed from the appropriate acid/base equilibrium and formal transfer pote ntials. In situ spectroscopic studies suggest that the transfer of the anionic species from water to DCE takes place mainly via the non-hydr ogen bonded form. On the other hand, the transfer of the anions from D CE 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 b y chronoabsorptometry and potential modulated reflectance. It was conf irmed that the transfer of both anions is a potential dependent proces s, 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 wi thin the framework of existing model for ion transfer at ITIES, Theore tical aspects of chronoabsorptometry for the study of ion transfer kin etics are also outlined. (C) 1998 Elsevier Science Ltd. All rights res erved.