Radiation chemical oxidation of benzaldehyde, acetophenone, and benzophenone

Abstract

Radiation chemical reactions of ^•OH, O^•-, and SO₄^•- with benzaldehyde, acetophenone, and benzophenone have been studied using both pulse and steady-state radiolysis techniques. The observed rates for the ^•OH addition (k = (2.6-8.8) × 10⁹ M^-1 s^-1) are higher than those found for the SO₄^•- reaction (k = (0.7-4.0) × 10⁹ M^-1 s^-1). The rate for the reaction of O^•- with benzaldehyde is higher than that found for ^•OH, while a reverse trend is observed in the case of the two ketones. Optical absorption spectra of the intermediate transients formed in the reactions of ^•OH and SO₄^•- with all three compounds are similar with a peak around 370-380 nm. The absorption spectra from the O^•- reaction have shown a major peak at 310 nm and are somewhat different from those obtained in the reaction of ^•OH. The yields of the phenolic products formed in the reaction of ^•OH with benzaldehyde and acetophenone in the presence of 0.1 mM ferricyanide corresponded to only 30% and 50% ^•OH yields, respectively. Benzoic acid is a major product formed with benzaldehyde in the reaction of ^•OH as well as SO₄^•- with G values of 2.1 and 1.3 per 100 eV, respectively. The formation of the exocyclic OH adduct is a major pathway in the reactions of ^•OH (by addition) and of SO₄^•- from hydrolysis of the initially formed radical cation (k = 2.4 × 10⁴ s^-1) with benzaldehyde. The exocyclic OH adduct undergoes disproportionation to give benzoic acid. The formation of the exocyclic OH adduct of acetophenone is possibly hindered owing to the bulky -COCH₃ group.