| Abstract: | The rate of the isotope exchange reaction between iron(II) and iron(III) perchlorates has been measured in a solvent mixture containing a 3:2 mole ratio of water to dimethyl sulfoxide over the temperature range from 25° to ?98°C. In this temperature range, the reactants can diffuse together faster than they can undergo isotope exchange. The activation enthalpy and entropy for the acid-independent reaction were 6.0 ± 1.2 kcal/mole and ?38 ± 17 cal/deg mole, respectively. Below ?22°C, the acid-dependent exchange reaction did not contribute significantly to the exchange. In liquid media at ?112° and ?117°C and in a solid glass at ?136°C, no isotope exchange was observed over the period of a calculated half-life for the reaction. At these temperatures, the rate at which the reactants diffuse together is slower than the calculated rate of isotope exchange. In a solid glass at ?196°C, no isotope exchange was observed over the period of one week. |
