Comparison of Monohydrogenphosphates in Reactivity Observed with Hydrogen-Isotope Exchange in a Liquid-Solid System

Hydrogen-isotope exchange reaction (liquid-solid reaction) between ethanol and a monohydrogenphosphate (solid) labeled with tritium has been observed to reveal the effect of the metal ion contained in monohydrogenphosphate on the reactivity of the salt. The sample materials used are six species of monohydrogenphosphates. The reaction was analyzed with the A"-McKay plot method, and the rate constants were obtained for those materials. By comparing the results obtained in this work with those obtained previously (gas-solid reaction), the following three facts have been confirmed. (1) Both the rate constant of monohydrogenphosphate and its temperature dependence are large when electronegativity of the metallic element in the salt is large. (2) The rate constant observed for liquid-solid reaction of monohydrogenphosphate (with OH group in ethanol) is 3 χ 10 times that in gas-solid reaction. (3) When a reaction starts and then proceeds too fast to be observed in a liquid-liquid system, the reaction may be slowed down to an experimentally observable rate in a liquid-solid system or in a gas-solid system.