Flash-photolysis study of the 4-(methyl sulphonate)-benzophenone ketyl radical anion in alcohol-water mixtures

Abstract

Irradiation of sodium 4-(methyl sulphonate)-benzophenone (BzPS), a water-soluble benzophenone, using ultraviolet (UV)-visible light in solutions containing an aliphatic alcohol and water results in the formation of the intermediate ketyl radical anion, BzPS.-. The photochemistry of this species was studied in several alcohol-water solvent systems. The molar extinction coefficient of BzPS.- (measured at its wavelength of maximum absorbance) and the pKa of BzPSH. (the conjugate acid of BzPS.-) in propan-2-ol-water solutions were determined to be (1.1 ± 0.1) × 103 m2 mol-1 and 11.8 ± 0.1, respectively. These values are independent of the solvent alcohol concentration in the range 10-50% (v/v) p..