Hydroxyl Radical-Induced Oxidation of Ethanol in Oxygenated Aqueous Solutions. A Pulse Radiolysis and Product Study

Abstract

γ-Radiolysis of N2O-saturated water or photolysis of aqueous H2O2 provided a source of OH radicals. These radicals react with ethanol by preferentially abstracting an H atom at C-l. In the presence of oxygen these radicals are converted into the corresponding peroxyl radicals. The α-hydroxyethylperoxyl radicals decay by first order kinetics (k = k1 + k2 [OH-]) acetaldehyde and HO2·/H+ +[formula omitted] being the products (k1 (20 °C) = 50 ± 10 s-1, Ea = 66 ± 7 kJ·mol-1, k2 = (4 ± 1) × 109M-1s-1). In competition (favoured by low pH, low temperature and high dose rate) they also decay by second order kinetics (2k3= (7 ± 2) × 108M-1s-1). The most important route in the bimolecular decay leads to acetaldehyde, acetic acid and oxygen (ca. 75%). This route might largely be concerted (Russell mechanism), but there might also be a contribution from the disproportionation of oxyl radicals within the solvent cage. There is also a concerted route that leads to two molecules of acetic acid and to hydrogen peroxide (ca. 10%). Another pathway (ca. 15%) yields two oxyl radicals and oxygen. The former may either decompose into formic acid and methyl radicals (ca. 5%) or rearrange into 1,1 -dihydroxyethyl radicals (ca. 10%). These radicals add oxygen and the resulting peroxyl radicals rapidly decompose into acetic acid and [formula omitted]. The reaction of α-hydroxyethylperoxyl radicals with [formula omitted] radicals appears to be slow (k ≈ 107M-1s-1). © 1983, Walter de Gruyter. All rights reserved.