Abstract
The hydrogen-isotope exchange reaction between each of six species of monosubstituted benzoic acids and tritiated water vapaor (gas-solid reaction) has been observed in the range between 40 and 80°C. Each reaction kinetics was analyzed with the A″-McKay plot method, and the rate constant (i.e., “the acidity based on kinetic logic”) for each material was obtained. The comparison of“the acidities” among the monosubstituted benzoic acids clarified the following evidences. (1) When the degree of the electron-attractive effect of the substituent included in a monosubstituted benzoic acid is high, the reactivity of the compound is also high. (2) The higher is the temperature, the greater is the reactivity of monosubstituted benzoic acid. (3) The temperature dependence of the reaction constant (ρ) is considerably small for the reaction under consideration. (4) Monosubstituted benzoic acids used in this work seem to follow the Hammett rule.
The ρ obtained in the gas-solid reaction in the present work is about 1/4 of the ρ obtained previously by the reaction (liquid-solid reaction) between one of liquid compounds and tritiated poly (vinyl alcohol) . This suggests that the effect of the substituent on the reactivity is much smaller in the gas-solid reaction than that in the liquid-solid reaction.
