Solvent effects on reactivity of solvated electrons with ammonium nitrate in 2-propanol/water mixed solvents

Abstract

The solvent effects on reactivity of solvated electrons ( e s − ) with ammonium nitrate were studied in 2-propanol/water mixed solvents as a function of solvent composition and temperature. The kinematic viscosities and densities of these mixed solvents were measured as a function of solvent composition and temperature, and the electrical conductances of ammonium nitrate in the mixed solvents were also measured. The measured rate constants of the nearly diffusion controlled reaction were examined according to the Smoluchowski-type models. These models are useful in evaluating the effects of bulk solvents on reactivity of solvated electrons with charged solutes. In the region of 80–100 mol% water, the rate constants for the reaction [ e s − + ( N O 3 − ) s ] increase with the decrease of viscosity. This indicates that the reaction rates in these solvents correspond well to the Smoluchowski–Stokes model. However in the region of 0–20 mol% water, the rate constant for the reaction [ e s − + ( N H 4 + ) s ] increases with the increase of viscosity. This phenomenon is attributed to the high values of the effective reaction radius ( κR r) for the reaction [ e s − + ( N H 4 + ) s ] in these solvents. The values of κR r (10 −10 m) in the region of 0–20 mol% water are 4.8–5.7, whereas 2.3–2.6 in the region of 80–100 mol% water at 298 K. With the exception of the region from 100 to 93 mol% water, the effective diffusion radius ( R d) decreases with the increase of water content. The activation energies of reaction ( E 2) display having higher values than those of viscosity ( E η ) and conductance ( E Λ 0 ) in the 2-propanol-rich region, while they become lower than both of E η and E Λ 0 in the water-rich region, and converge to similar values in almost pure water.