RADIATION-CHEMISTRY OF ALCOHOLS .22. HYDROXYL RADICAL-INDUCED OXIDATION OF 2-METHYL-2-PROPANOL IN OXYGENATED AQUEOUS-SOLUTION - PRODUCT AND PULSE-RADIOLYSIS STUDY

The reactions of the 2-methyl-2-hydroxypropylperoxyl radical were investigated by 7 and pulse radiolysis of aqueous oxygenated solutions of 2-methyl-2-propanol. The products and their G values [in brackets] on γ radiolysis of a N2O/O2 (80/20 v/v) saturated solution at 20 °C are formaldehyde (I [1.3]), acetone (II [1.6]), 2-methyl-2-hydroxypropionaldehyde (III [2.0]), 2-methyl-2,3-propanediol (IV [0.5]), an organic peroxide, very likely di(2-methyl-2-hydroxypropyl) peroxide (V [0.7]), and hydrogen peroxide (VI [2.0]). Two major decay processes for the 2-methyl-2-hydroxypropylperoxyl radical are proposed: (i) formation of O2 and two 2-methyl-2-hydroxypropyloxyl radicals which either combine (product V), disproportionate (products III and IV), or fragment (products I and 2-hydroxypropyl-(2) radicals), and (ii) formation of VI and III. The 2-hydroxypropyl-(2) radicals add oxygen to give the corresponding peroxyl radicals which rapidly eliminate HO2(product II). The HO2- radicals largely disproportionate (products VI and O2). At pH 9.4 the rate of the formation of O2-· (pKa(HO2·) = 4.75) is determined by the bimolecular decay of the primary peroxyl radicals. The rate constant of the latter reaction was obtained pulse conductometrically as 2k = (8 ± 2) × 108 M-1 s-1. Competition among the different modes of reaction is evident from the effect of deuterium substitution and temperature on the distribution of products yields. © 1979 American Chemical Society.