TEMPERATURE EFFECTS ON THE ONE-ELECTRON REDUCTION POTENTIALS OF NITROARYL COMPOUNDS

Pulse radiolysis was used to establish one-electron transfer equilibria between radical cations of methyl or benzyl viologens (V2+) and nitroaryl compounds (ArNO2): a nitroimidazole (misonidazole or metronidazole), 4-nitrobenzoate or nitrofurazone. The equilibrium constants in water at pH 8 were estimated over the temperature range ∼5 to 75°C. The difference E in mid-point one-electron reduction potentials between the nitro compounds and the viologens varied with temperature T; increasing temperature made the nitro compounds apparently less electron-affinic compared to the effects of temperature on the viologen potential. Values of δdelta;E)δT were in the range -0.7 to -1.1mV K-1 at 25°C. If δ[E(V2+/V-+)]/δT =-0.9mV K-1 for methyl viologen then δ[E(ArNO2/ArNOδ]/δT is about -2rnV K-1 for these compounds. © 1991 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.