The pH dependence of azide radical, hydroxyl radical and hydrated electron induced decomposition of 4-chloro- and 4-bromophenol was investigated by pulse radiolysis in airfree solutions under reducing and oxidizing conditions and also in air saturated solutions. Under oxidizing conditions the main intermediate is the phenoxyl radical. In reaction with azide radicals, the phenoxyl radical forms with k = 1.5×108 and 1.4×108 mol-1dm3s-1 in neutral, and with 6.2×109 and 5.9×109 mol-1dm3s-1 in alkaline solutions. The OH radicals add to the ring producing cyclohexadienyl type radicals. The adducts around the pKa decay in pH dependent OH- elimination to phenoxyl radical. In neutral solution the radical under the condition applied (dose/pulse ∼10 Gy) decays in bimolecular self-termination reactions. Under reducing conditions in neutral solution the hydroxyphenyl radicals, formed in dehalogenation following eaq- scavenging, mostly react with tert-butanol added to eliminate OH radicals. In alkaline solutions the hydroxyphenyl radical anion by protonation gives phenoxyl radical. In air saturated solution the decomposition mostly occurs through OH adducts. In alkaline solutions there is a competition between OH- elimination and reaction with O2. In neutral or slightly acidic solutions the radical scavenging by O2 dominates. The scavenging reaction is most probably reversible, and in the complex processes phenoxyl type radicals and benzoquinone radical anion form with relatively high yield.
|Number of pages||23|
|Journal||ACH - Models in Chemistry|
|Publication status||Published - Dec 1 1997|
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