Hydroxy! Radical-Induced Oxidation of Diisopropyl Ether in Oxygenated Aqueous Solution. A Product and Pulse Radiolysis Study

Abstract

In the radiolysis of N2O/O2(4:1 )-saturated aqueous solutions of diisopropyl ether(10-3 moldm-3), OH radicals abstract H-atoms, thereby producing radicals at C(2) (1 ≈ 78%) and to a lesser extent at C(l) (2 ≈ 22%) which are converted by oxygen into the corresponding peroxyl radicals 3 and 4. Some O2 radicals are formed by the reaction of radiolytically produced H atoms with oxygen. Methyl radicals formed in the course of the bimolecular decay of 3 and 4 give rise to methylperoxyl radicals 5. At high dose rate as delivered by 2.8 MeV electron pulses the products (G values in parentheses) are: isopropyl acetate (2.6), acetone (1.1), isopropanol (1.1), 2-isopropoxypropanal (1.4, estimated), formaldehyde (2.0), organic hydroperoxides (0.4), organic acids (0.5) and hydrogen peroxide (1.9). At low dose rates (≤ 0.39 Gy s-1 ) G(acetone) is considerably increased and is no longer balanced by an equivalent yield of isopropanol. This is thought to be due to an intramolecular H-abstraction of radical 3. Pulse radiolysis studies revealed that 3, 4 and 5 decay by second order kinetics. At the early stages the bimolecular decay is faster (2k ≈ 6 × 107 dm3mol-1s-1 ) than toward the end (2k ≈ 2 × 107 dm3moI-1s-1) . It is suggested that the faster decay at the beginning is due to a preponderance of termination by the primary peroxyl radical 4 with the tertiary peroxyl radical 3 while at later stages termination is mainly governed by the reaction of 3-1-3 which produces 5. The rate constants k(5 + 3) and k(5 + 5) are very likely much higher than 2k(3 + 3), hence 2k(3 + 3 ) < 2 × 107 dm3mol-1s-1 . In O2-saturated solutions O2 plays a considerable role in the termination reactions, and organic hydroperoxides which are unimportant in N2O/O2-saturated solutions at high dose rates are now the major products.