electron adducts and reduced forms of HCB or through
hydroxyl radical reactions with surfactant molecules (Route
2) to produce reducing radicals that undergo electron transfer
with HCB.
SCHEME 1. Reaction Mechanism for HCB Degradation in
RA-40a
Acknowledgments
G.A.Z. would like to thank Dr. Suresh Das for his teachings
on all subjects and good company. K.A.G. gratefully ac-
knowledges the support of The Center for Catalysis and
Surface Science at Northwestern University. P.V.K. acknowl-
edges the support of the Office of Basic Energy Sciences of
the Department of Energy. This is Contribution No. NDRL-
4152 from the Notre Dame Radiation Laboratory.
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Later experiments with HFB in solutions at pH 14 by
Shoute and Mittel contradicted the findings of Koster and
Asmus (40). They stated that HFB, following electron capture,
does not undergo fluoride elimination and instead forms
dimers and trimers of HFB. However, Shoute and Mittel failed
to explain the conductivity findings of Koster and Asmus. In
addition, the presence of an electron adduct was not detected
in experiments at lower values of pH (<13). These spectra
were attributed to the presence of a hexafluorocyclodienyl
radical, a result of rapid protonation of the hexafluorobenzyl
radical. In addition, research with pentahalophenols has
shown that the reaction of electrons with pentachlorophe-
noxide ions results in chlorine expulsion and the formation
of hydroxyphenyl radicals (21). In this case, researchers were
unable to detect the presence of an electron adduct due to
rapid protonation of hydroxyphenyl radicals to yield phenoxyl
radicals.
Primarily on the basis of the results of Koster and Asmus,
we conclude that the transient spectra of the intermediate
at 320 nm to be that of the HCB electron adduct which
undergoes subsequent protonation to form cyclohexadienyl
radicals and, ultimately, pentachlorobenzene.
In summary, as shown in Scheme 1, reactions in our
surfactant system may occur either through direct electron
reaction with HCB (Route 1) involving the generation of
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3 4 0 6 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 34, NO. 16, 2000