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

Abstract

The reactions of the 2-methyl-2-hydroxypropylperoxyl radical were investigated by ..gamma.. and pulse radiolysis of aqueous oxygenated solutions of 2-methyl-2-propanol. The products and their G values (in brackets) on ..gamma.. radiolysis of a N/sub 2/O/O/sub 2/(80/20v/v) saturated solution at 20/sup 0/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 perioxide (VI(2.0)). Two major decay processess for the 2-methyl-2-hydroxypropylperoxyl radical are proposed: (i) formation of O/sub 2/ 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 HO/sub 2/ (product II). The HO/sub 2/ radicals largely disproportionate (products VI and O/sub 2/). At pH 9.4 the rate of the formation of O/sub 2/ . (pK/sub a/(HO/sub 2/) = 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 10/sup 8/M/sup -1/s/sup -1/. Competition among the different modes of reaction is evident from the effect of deuterium substitutionand temperature on the distributionmore » of product yields.« less