Acetonylperoxyl Radicals, CH3C0CH20 2: A Study on the y-Radiolysis and Pulse Radiolysis of Acetone in Oxygenated Aqueous Solutions

Hydroxyl radicals from the radiolysis of N20 / 0 2 (4:l)-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 109 dm3m ol_1s_1) thereby forming acetonylperoxyl radicals which decay by second-order kinetics (2 k = 8 x 10* dm3mol 's -1). Under steady-state radiolysis conditions (0.24 G y s “1) the products (G values in parentheses) are methylglyoxal (2 .5). hydroxyacetone (0.5), formaldehyde (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 m olecules of m ethyl­ glyoxal and one m olecule of hydrogen peroxide. The Russell mechanism which yields one m olecule of m ethylglyoxal. hydroxyacetone and oxygen contributes about one fifth as does the breakdown into two m olecules of formaldehyde, 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. About one tenth o f the organic peroxyl radicals is converted into hydroperoxides by OJ produced as a byproduct in the water radiolysis.