Pulse radiolysis studies of electron transfer in aqueous quinone solutions

Abstract

The transient absorption spectra observed on pulse radiolysis of neutral aqueous solutions containing p-benzoquinone and excess methanol, ethanol, isopropanol and formate, saturated with nitrous oxide are reported. The spectra are analogous to those obtained in solutions containing excess t-butanol and N₂, O₂, nicotinamide adenine dinucleotide or thymine and are attributed to the semiquinone radical-anion formed by electron transfer reactions with bimolecular rate constants k=ca. 10⁹-10¹⁰ M^–1 s^–1. This assignment is supported by measurements of the acid dissociation constant of the absorbing product (pK_a= 4.1) in solutions containing excess acetone and isopropanol.