I. Kinetics of Reactions of Electrons during Radiolysis of Liquid Methanol. II. Reaction of Electrons with Liquid Alcohols and with Water

Publisher Website
Google Scholar
Abstract
The gamma radiolysis of liquid methanol has been studied over the temperature range from its melting point ( − 98°) to its critical temperature (240°). The value of G(H2) varies from 4.95 at −98° to 5.45 at 25° and 8.0 at 240°. Sulfuric acid and nitrous oxide were added as electron scavengers at −97°, 25°, and 150°. The nitrogen and hydrogen yields were calculated as functions of the nitrous oxide concentration at each of the three temperatures. The calculations were based on a proposed mechanism. Homogeneous kinetics were used for the reactions of the free ions and nonhomogeneous kinetics were used for the reactions in spurs. At −97°, G(total ionization) = 4.6 and the value is assumed to be independent of temperature. The yield of free ions is G(esolv−)fi = 2.0 ± 0.2, independent of temperature from −97° − 150°. The reaction esolv−→CH3Osolv−) + H has a rate constant of 4.6 × 105 sec− 1 at 25° and an activation energy equal to that of dielectric relaxation (3.7 kcal/mole); the entropy of activation of the reaction is −21 cal/deg·mole. In each of the liquids methanol, ethanol, isopropanol, and probably also water, the reaction esolv−→ROsolv− + H has an activation energy approximately equal to that of dielectric relaxation and has a large negative entropy of activation. The large negative entropy of activation indicates that the transition state has a relatively specific structure. It is suggested that solvated electrons are liquid-structure breakers in water and relatively weak structure formers in the alcohols.