On the reaction of 2,4,5-trichlorophenol with hydroxyl radicals: New information on transients and their properties

Marija Bonifačić, Klaus Dieter Asmus, Kimberly A Gray*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

A reinvestigation of the ̇ OH radical reaction with 2,4,5-trichlorophenol (TCP) provided unambiguous direct evidence, in contrast to an earlier study, for the formation of two different ̇ OH-adducts, namely, at the C-6 and C-3 positions. They appear to be formed at about equal yield and exhibit different optical absorption spectra with maxima at 320 and 350 nm for the C-6 adduct and 320 nm for the C-3 adduct. Both are mild reductants as can be deduced from their reaction with Fe(CN) 6 3- . Owing to its relatively low pK a (4.8 ± 1), the C-6-adduct reacts in neutral to slightly acid solutions preferentially through its deprotonated form. Absolute rate constants have been measured for the reduction of Fe(CN) 6 3- by the anion of the 6-hydroxy adduct radical (1.4 ± 0.3) × 10 8 M -1 s -1 and by the neutral form of the 3-hydroxy adduct radical (2.7 ± 0.6) × 10 6 M -1 s -1 . The latter assignment corrects the previous conclusion that attributed the low 10 6 M -1 s -1 order of magnitude rate constant to the reaction of the C-6 adduct radical. Based on the reduction kinetics measurements, the rate constant for the C-6 adduct radical deprotonation process has been estimated to be about 3 × 10 4 s -1 . The C-6-adduct, both in its neutral as well as in its anionic form, gains particular stability through hydrogen bond bridging between the two hydroxyl groups positioned at C-6 and C-1, and this accounts for the elevated rates that we report.

Original languageEnglish (US)
Pages (from-to)1307-1312
Number of pages6
JournalJournal of Physical Chemistry A
Volume107
Issue number9
DOIs
StatePublished - Mar 6 2003

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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