Kinetic electron spin resonance spectroscopy. Part IV. Photoreduction of triplet pyruvic acid and triplet biacetyl in alcoholic solvents

Abstract

The study of the photoreduction of triplet ketones in alcoholic solvents by means of kinetic electron spin resonance spectroscopy has been extended to include the determination of the Arrhenius parameters for the reactions of ³(n,π*) pyruvic acid with methanol, ethanol, propan-2-ol, t-butyl alcohol, and 1-phenylethanol. A competitive quenching method was employed with naphthalene as triplet quencher. Activation energies are between 11 and 22 kJ mol^–1 and pre-exponential factors between 10^8·8 and 10^9·3 l mol^–1 s^–1. Similar studies on the reactions of ³(n,π*) biacetyl provided estimates of the rate constants of the corresponding reactions (ranging from 3·5 × 10³ l mol^–1 s^–1 in ethanol to 6·5 × 10⁴ in 1-phenylethanol). some problems associated with the behaviour of the triplet quencher (acridine) in these systems are discussed.