Reactivity of solvated electrons in tetrahydrofuran

Abstract

The rates of reaction of solvated electrons (e^–_s) with 23 solutes have been measured in tetrahydrofuran at 22±1 °C. The values range form (1.5±0.4)× 10⁹ dm³ mol^–1 s^–1 for phenol to (1.56±0.01)× 10¹¹ dm³ mol^–1 s^–1 for benzonitrile. It is concluded that the diffusion-controlled rate constant for reactions of e^–_s in this solvent is ca. 1.7 × 10¹¹ dm³ mol^–1 s^–1, which indicates that the sum of the reaction radii of e^–_s and the solute is ca. 1.67 nm. This value is close to the value of 1.38 nm, estimated for the maximum reaction radius of e^– in the gas phase. The effect of ΔG^⊖ for the reaction on the rate constant is investigated and evidence is presented for an inversion in the rate in the highly exergonic region, although a few solutes deviate from the general trend. The temperature dependence of the rate constants for five solutes has been measured and the values of the activation energy lie in the range 11.7–15.4 kJ mol^–1. It is concluded that the rate constants for the electron-scavenging process qualitatively conform to the predictions of quantum-mechanical theories for electron-transfer reactions.