Hydroxyl radical-induced oxidation of 2-methyl-2-propanol in oxygenated aqueous solution. A product and pulse radiolysis study

The reactions of the 2-methyl-2-hydroxypropylperoxyl radical were investigated by γ 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(80/20v/v) saturated solution at 200C 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 perioxide (VI[2.0]). Two major decay processess for the 2-methyl-2-hydroxypropylperoxyl radical are proposed: (i) formation of O2 and two 2-methyl-2-hydroxpropyloxyl 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 . (pK/sub a/(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) X 108M-1s-1. Competition among the different modes of reaction is evident from the effect of deuterium substitutionand temperature on the distribution of product yields