Formation and reactivity of pyridylperoxyl radicals in solution

2-Pyridyl radicals were produced by the reaction of 2-chloro- or 2-bromopyridine with solvated electrons (k approximately 10¹⁰ L mol^-1 s^-1) and reacted rapidly with oxygen (k = 2.2 × 10⁹ L mol^-1 s^-1) to produce the 2-pyridylperoxyl radical. This radical exhibits optical absorption in the visible range, with λ_max at 440 nm. 2-Pyridylperoxyl radical is a fairly strong oxidant, which reacts with 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate ion) (ABTS), chlorpromazine, and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox C) by one-electron oxidation. The rate constants k for these reactions, determined from the rate of formation of the one-electron oxidation as a function of substrate concentration, vary between 2 × 10⁶ and 2 × 10⁹ L mol^-1 s^-1 in various mixtures. For each substrate, a good correlation was found between log k and the cohesive pressure of the solvent or solvent mixture, as found before for CCI₃O₂ radical reactions in nearly neat solvents. 3-Bromo, 3-chloro- and 4-chloropyridine also reacted rapidly with solvated electrons, but their radical anions underwent protonation on the nitrogen in competition with the dehalogenation process. Therefore, no pyridylperoxyl radicals were formed from these species in aqueous solutions and only partial yield was found in neat methanol.