SOLVENT EFFECTS ON THE REACTIVITY OF SOLVATED ELECTRONS WITH AMMONIUM AND NITRATE IONS IN 1-BUTANOL WATER SOLVENTS

Values of the rate constants, k2 (10(6) m3 mol-1 s-1), of solvated electrons, e(s)-, with several re ate salts, in pure water and pure 1-butanol solvents at 298 K are, respectively, as follows: LiNO3, 9.2, 0.19, NH4NO3, 10, 8.3; NH4ClO4, 1.5 x 10(-3), 12 in 20 mol% water; LiClO4, 1.0 X 10(-4), < 1.0 X 10(-4). The value of k2(e(s)- + NO3,s-) in water solvent is 48 times larger than that in 1-butanol solvent, whereas k2(e(s)- + NH4,s+) in water is 10(-4) times smaller than the value in 1-butanol. This enormous reversal of solvent effects on e(s)- reaction rates is the first observed for ionic reactants. The solvent participates chemically in the (e(s)- + NO3,s-) reaction, and the overall rate constant increases with increasing viscosity and dielectric relaxation time. This unusual behavior is attributed to a greatly increased probability of reaction of an encounter pair with increasing duration of the encounter. Effective reaction radii kappaR(r) for (e(s)- + NO3,s-) and (e(s)- + NH4,s+) were estimated with the aid of measured electrical conductances of the salt solutions in all the solvents. Values of kappaR(r) are (2-7) x 10(-10) m, except for NH4,s+ in 100 and 99 mol% water, which are 2.6 and 2.7 x 10(-14) m, respectively. The effective radii of the ions for mutual diffusion increase with increasing butanol content of the solvent, from approximately 50 pm in water to approximately 150 pm in 1-butanol, due to the increasing average size of the molecules that solvate the ions.