Rate of interfacial reactions compared to bulk reactions in liquid-liquid and micellar processes: An attempt to clarify a confusing situation

The complete understanding of the mechanisms of reactions taking place at l iquid-liquid interfaces is a difficult problem. We focus here on one specif ic aspect of this problem: the comparison of the rates of interfacial react ions with those of bulk reactions. Apparently conflicting results exist in the literature (interfacial reactions are sometimes reported to be faster t han bulk reactions whereas the reverse appears to be true in other circumst ances) and we try here to rationalize the interpretation of some typical ex perimental observations. We recall the potential of micellar systems to hel p understand such processes and we show that results obtained from solvent extraction as well as from micellar extraction can in principle be approach ed through the same kind of analysis. The main points discussed here are th e effect of reduction of dimensionality on the rate of reactions, the need to make careful distinction between analysis of global reaction rates and m echanistic rate constants, and the part played by the distribution coeffici ents (between organic phase, aqueous phase, and interface) and by the speci fic interfacial area. Special attention is given to the factors influencing the distribution coefficients and those favoring the interfacial reactions . For this purpose we have selected some data from the literature, includin g some from our own works, that we felt especially demonstrative. Particula r emphasis is finally given to the case of reactions in organized systems s uch as micelles, microemulsions, or vesicles, where the same trends are obs erved. (C) 2001 Academic Press.