The Kinetics and Mechanism of Ion Exchange

Ion exchange on soils and soil constituents has been known since Aristotle s time. It was rediscovered as base exchange by soil scientists in the nineteenth century (Thompson, 1850 Way, 1850), and since that time a voluminous amount of research has appeared in the scientific literature. However, most of these studies, particularly in the soil and environmental sciences, have dealt with equilibrium aspects of ion exchange, and only recently have studies appeared on the kinetics and mechanisms of exchange phenomena. 

Within solution inorganic chemistry, there would be no apparent reason to obtain NMR spectra at high pressures in structural characterization studies. It prevails that most applications of hp NMR spectroscopy relate to solvent exchange reactions on solvated metal ions their mechanisms often have direct bearing upon the kinetics and mechanisms of substitution of one or more solvent molecules from a metal center by other ligands. The first part of the results section provides ample illustration of the value of high-pressure measurements on transition metal and lanthanide ions, fully... 

Kinetics and mechanism of water exchange at iron(III), in the form of Fe aq and of FeOtf aq, have been much studied recently. It is now clear that water exchange at the former takes place by an associative mechanism, at the latter by a dissociative mechanism. Rate constants, " activation enthalpies and entropies, and activation volumes have been obtained from variable-temperature and variable-pressure 0 nmr experiments. The activation volumes for water exchange at Fe Caq) and at FeOH (aq) are -5.4 and 4-7.0 cm moL respectively the former is almost exactly the same as that reported for the isoelectronic Mn (aq) ion. If acidic (HCIO4) aqueous solutions containing iron(III) are heated for a time, then water exchange at the polynuclear product is over a... 

It appears,therefore, that in order to study the "true" role of lithium chloride on the kinetics and mechanism of the anionic polymerization of lactams, it is advisable to useasa catalyst of the reaction a metal lactamate which does not undergo chemical exchanges with Li ions. 

J. A Fee Copper Proteins - Systems Containing the Blue" Copper Center. - M.F.Dunn Mechanisms of Zinc Ion Catalysis in Small Molecules and Enzymes. - W. Schneider Kinetics and Mechanism of Metalloporphyrin Formation. - M. Orchin, D. M. Bollinger Hydro gen-Deuterium Exchange in Aromatic Compounds. 

The above studies have clearly shown that p-jump relaxation measures chemical kinetics and thus one derives the actual rate constants. The implications these types of measurements have for ascertaining mechanisms of ion exchange and of catalytic reactions on soil constituents is tremendous. The application of p-jump relaxation to studying ion exchange kinetics of NH on zeolite (Ikeda et al., 1984b) and the adsorption/ desorption of Pb2+ on y-Al203 (Hachiya et al., 1979) is presented below,... 

---