Application of the Refined Model of Nonhomogeneous Kinetics to the Reactions of Electrons during the γ Radiolysis of Ethanol and 2-Propanol. Energies and Entropies of Activation of the Reactions of Solvated Electrons with Alcohols and with Water

Abstract

The yields of nitrogen and hydrogen from the radiolysis of solutions of nitrous oxide in ethanol and in 2‐propanol at temperatures from about − 100° to + 140° have been calculated by the refined model of the nonhomogeneous kinetics of ionic reactions in irradiated alcohols. The calculated yields agree satisfactorily with those measured experimentally. The value $\mathrm{G(}\mathrm{total\; ionization}\text{)=\hspace{0.17em}4.3}$ was assumed for both liquids. In “absolutely pure” ethanol the values of $\mathrm{G(}{\mathrm{H}}_2)$ and ${\mathrm{G(e}}_{\mathrm{solv}}^{-}{)}_{\mathrm{fi}}$ were estimated to be, respectively, 5.3 and 1.7 at − 112°, 5.3 and 1.5 at + 25°, 6.3 and 1.4 at 90°, and 6.9 and 1.2 at 145°. For the decomposition of the solvated electron $e_{\mathrm{solv}}^{-}\to {\mathrm{RO}}_{\mathrm{solv}}^{-}\mathrm{\hspace{0.17em}+\hspace{0.17em}}\mathrm{H}$ [Eq. (8)] in ethanol at 25°, $k_8{\text{\hspace{0.17em}=\hspace{0.17em}1\hspace{0.17em}×\hspace{0.17em}10}}^5{\sec }^{\text{−1}}{E}_8\text{∼4.6}\mathrm{kcal}/\mathrm{mole}$ , and ${\mathrm{\Delta S}}_8^{†}\text{∼−21}\mathrm{cal}/\mathrm{deg}·\mathrm{mole}$ . In “absolutely pure” 2‐propanol the values of $\mathrm{G(}{\mathrm{H}}_2)$ and ${\mathrm{G(e}}_{\mathrm{solv}}^{-}{)}_{\mathrm{fi}}$ were estimated to be, respectively, 4.1 and 1.2 at −85°, 4.9 and 1.3 at + 25°, and 5.4 and 1.0 at 140°. For the decomposition of the solvated electron in 2‐propanol at 25°, $k_8{\text{\hspace{0.17em}=\hspace{0.17em}3\hspace{0.17em}×\hspace{0.17em}10}}^5{\sec }^{\text{−1}}{\mathrm{,\; E}}_8\text{∼6.3}\mathrm{kcal}/\mathrm{mole}$ , and ${\mathrm{\Delta S}}_8^{†}\text{≈\hspace{0.17em}−\hspace{0.17em}14}\mathrm{cal}/\mathrm{deg}·\mathrm{mole}$ . In each of the liquids methanol, ethanol, 1‐propanol, 2‐propanol, and water, Reaction (8) has an activation energy approximately equal to that of dielectric relaxation, which is also approximately equal to that of diffusion. It is concluded that Reaction (8) is approximately thermoneutral and that the enthalpy of solvation of RO⁻ is more than 70 kcal/mole more negative (exothermic) than that of the electron in each of the five liquids. The activation energy $E_8$ might be used either to rearrange the solvent molecules about the reaction site or for the migration of the electron to a suitably oriented site. The large negative entropy of activation is related to the specific structure required by the transition state to increase the solvation energy of the negative species by more than 70 kcal/mole.