Radiolysis of Tertiary Butyl Hydroperoxide in Aqueous Solution. Reductive Cleavage by the Solvated Electron, the Hydrogen Atom, and, in Particular, the Superoxide Radical Anion

Abstract

The reactions o f the solvated electron, the H atom, the OH radical and the superoxide radi cal anion with /-butylhydroperoxide (/-BuOOH) have been studied in aqueous solutions using y-radiolysis and pulse radiolysis to generate these radicals.The solvated electron reacts rapidly with r-BuOOH (k = 5 x 109 dm 3 m ol" 1 s~') yielding /-BuO ' and OH in a ratio o f 4:1. The yield o f r-BuO' has been determined by measuring its fragmentation product, acetone.The H atom reacts more slowly with r-BuOOH (k = 5x 107 dm 3 m o l-1 s"1). There is very little H-abstraction from the methyl and the hydroperoxyl groups (about 3%), the main reac tion again being the scission o f the hydroperoxyl function with a branching ratio /-BuO'/'OH o f about unity.The OH radical reacts with /-BuOOH considerably more slowly (k = 8 x 107 dm3 m o l" 1 s ' 1) than with /-butanol (k = 5 X 108 dm3 m o l-1 s"1) with an approximate preference o f 8:1 o f ab stracting a methyl hydrogen over a hydroperoxyl hydrogen atom. The carbon-centered radical undergoes y-cleavage (k ~ 102 s"1) thereby reforming an OH radical. The resulting chain reac tion is rather short (maximum yield G (2-methyl-1,2-epoxypropane), 26 x 10"7 mol / ' at low dose rate) due to H-abstraction at the hydroperoxyl function o f r-BuOOH by the OH radical.The superoxide radical anion also reacts with /-BuOOH by cleaving the hydroperoxyl func tion. Its reactivity is, however, rather low (k = 5 dm3 m ol" 1 s"1).

Determination of •OH, O2•-, and Hydroperoxide Yields in Ozone Reactions in Aqueous Solution

“…These yields were independent of the Fe(CN) 6 4concentration (0.4-4 mM) and were not affected by an addition of tertiary butanol. This indicates that no • OH are formed in this electron-transfer reaction (confirming the earlier 62 conclusion) and that the HC(O)O • radical undergoes the otherwise very fast 1,2-H-shift (cf. reaction 48) only slowly if at all.…”

“…ref ). For organic hydroperoxides, two pathways are conceivable, reactions 42 and 43, but only the former route is taken in a one-electron reduction process . The reason for this is the much higher solvation energy of OH - as compared to that of RO -…”

The reaction of superoxide radical anion with dithiothreitol: a chain process

“…This is in keeping with what we know about the decomposition of -butylhydroperoxide by the solvated electron, where the formation of -butoxyl radicals and hydroxide ions is also favored over the formation of f-butoxide ions and an OH radical. 49 From the foregoing, we may further conclude that the RSO* radicals must be rather poor H abstractors and must display a considerable preference of reacting with the thiol rather than the alcohol, the latter being present in 50-fold excess. In fact, an electron transfer from thiolate to RSO* seems more likely than an H-abstraction reaction (reaction 30): this kind of behavior is exhibited by other moderately oxidizing radicals (cf.…”

Free Radical Mechanisms for the Treatment of Methyl tert-Butyl Ether (MTBE) via Advanced Oxidation/Reductive Processes in Aqueous Solutions

“…The reaction of • OH with TBA is largely by H-abstraction of a carbon-bound hydrogen (95.7%) with a small contribution (4.3%) of H-abstraction at the OH-group (Scheme ) . The major TBA-derived radical reacts with O 2 , giving rise to the corresponding peroxyl radical ( J ), while the minor radical, the tert -butoxyl radical, decomposes into acetone and • CH 3 . , …”