Acetonylperoxyl Radicals, CH3COCH2O2: A Study on the y-Radiolysis and Pulse Radiolysis of Acetone in Oxygenated Aqueous Solutions

Abstract Hydroxyl radicals from the radiolysis of N 2 O/O 2 (4:1)-saturated aqueous solutions of acetone (10 −3 mol dm −3 ) react with the solute by H-abstraction thereby forming acetonyl radicals. As shown by pulse radiolysis, the acetonyl radicals rapidly add oxygen (k = 3 x 10 9 dm 3 mol −1 s −1 ) thereby forming acetonylperoxyl radicals which decay by second-order kinetics (2 k = 8 x 10 8 dm 3 mol −1 s −1 ). Under steady-state radiolysis conditions (0.24 Gy s −1 ) the products (G values in parentheses) are methylglyoxal (2.5), hydroxyacetone (0.5), form aldehyde (1 .6), acids (1 .7), carbon dioxide (0 .5), organic (hydro)peroxides (0.4), hydrogen peroxide (2 .2), and G (oxygen uptake) has been determined at 5.2. In the decay of the acetonylperoxyl radicals the major process (slightly less than one half) leads in a concerted reaction to two molecules of methyl­ glyoxal and one molecule of hydrogen peroxide. The Russell mechanism which yields one molecule of methylglyoxal, hydroxyacetone and oxygen contributes about one fifth as does the breakdown into two molecules of form aldehyde, one molecule of oxygen and two acetyl radicals. Carbon dioxide, formaldehyde and acetic acid are among the products which result from the acetylperoxyl radicals formed upon oxygen addition to the acetyl radicals. A bout one tenth of the organic peroxyl radicals is converted into hydroperoxides by O 2 ⨪ produced as a byproduct in the water radiolysis.