OH radical induced oxidation of ethanol in oxygenated aqueous solutions. Part 1.—Formation of acetic acid

Abstract

γ-Irradiation of ethanol (10^–2 mol dm³) in aqueous N₂O + O₂(4 : 1) saturated solution (pH = 6.8) at 0°C leads to the following products (G-values): acetaldehyde (4.0), acetic acid (1.5), glycolaldehyde (0.2), ethylene glycol (0.2), and hydrogen peroxide (1.9).

The G-values of acetaldehyde and acetic acid were determined as a function of ethanol concentration, pH, temperature and dose rate. G(acetic acid) decreases with increasing temperature and pH, and increases with dose rate. The ethanol concentration in the range of 10^–3 to 1 mol dm^–3 has no influence on the G-value. The sum of G(acetic acid) and G(acetaldehyde) is always about 6. At pH = 6.8 a long lived peroxidic intermediate A is observed with a half life of approximately 800 s at 0°C. A is assumed to be 1-hydroxyethyl hydroperoxide (ethanol hydroperoxide). The only source of acetic acid is the proton catalysed decomposition of A at pH > 3.

At low dose rate, A is formed with low yield because the 1-hydroxyethylperoxyl radical decomposes into acetaldehyde and H₂O₂ without forming A.