Exchange of Methanol between Solvated Cations and Solvent. I

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Abstract
The exchange of methanol between solvated Li+, Cd++, and Mg++, and the solvent has been studied by the isotope dilution technique at —82.5° and —96.9°C. Even at —96.9°C the exchange is complete for Li+ and Cd++ within the time of sampling, 0.5 min. However, the exchange for solvated Mg++ is observable. At —82.5° and —96.9°C the half‐lives for the isotopic exchange are 3.7 and 64 min, respectively. The activation energy ΔH‡ is 12.5±2.0 kcal/mole and the entropy of activation ΔS‡ is +(4±4) eu. The ``kinetic solvation number'' of Mg++ with respect to methanol as determined by the isotope dilution technique is less than six, where six is the coordination number of Mg++ in these solutions. The defect is caused by residual water which both displaces methanol from the coordination sphere and labilizes it for exchange.