Aromatic anions and free radicals in the pulse radiolysis of aqueous solutions of benzonitrile

Abstract

Hydrated electrons, hydrogen atoms and hydroxyl radicals react with benzonitrile with rate constants of 1.7 × 10¹⁰, 3.1 × 10⁸ and 8.5 × 10⁹ M^–1 s^–1 respectively. In alkaline solutions the hydrated electrons form an anion with a sharp absorption maximum at 315 nm and a broad one at 400 nm. This anion protonates with pK_a 7.2 and at pH 4 the reduced species present has an absorption maximum near 300 nm. A different form of the reduced species is seen at pH 3. In strongly acid solutions, H atoms add to benzonitrile yielding a mixture of isomers exhibiting an absorption maximum at 348 nm. Hydroxyl radicals (in neutral solution) add to benzonitrile yielding adducts showing an absorption maximum at 343 nm. The various adducts disappear in second-order reactions, with 2k= 1.1 × 10⁹ M^–1 s^–1 for mutual reactions of H adducts and for reactions of H adducts with OH adducts.