Conversion of hydroxyphenyl to phenoxyl radicals: a radiolytic study of the reduction of bromophenols in aqueous solution

Journal Article · Wed Jun 23 04:00:00 EDT 1976 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00429a015· OSTI ID:7345469

Schuler, R H; Neta, P; Zemel, H; Fessenden, R W

Both steady-state ESR and spin trapping experiments demonstrate that hydroxyphenyl radicals are produced in the reaction of hydrated electrons with the bromophenols. Conductometric and optical pulse radiolysis studies show that the anionic forms of the ortho and para hydroxyphenyl radicals protonate rapidly at the radical site to produce phenoxyl radical. At pH 11.5 the protonation periods are respectively 14 and 4.1 ..mu..s. The meta isomer protonates at least an order of magnitude more slowly. Protonation is not observed for the neutral forms of these radicals. The important feature required for protonation appears to be the existence of appreciable negative charge density at the radical site. The rapid protonation of the p-hydroxyphenyl radical anion observed here provides a reference with which to compare other reactions of this radical and it has been possible to estimate a rate constant of 6 x 10/sup 5/ M/sup -1/ s/sup -1/ for its abstraction of H from tert-butyl alcohol and 4 x 10/sup 7/ M/sup -1/ s/sup -1/ for its addition to nitromethane. In the case of p-bromophenol, the phenoxyl radicals resulting from the initial protonation undergo a tertiary electron transfer reaction with p-bromophenoxide with a rate constant of 2.0 x 10/sup 8/ M/sup -1/ s/sup -1/, so that the optical absorption spectra of the three bromophenoxyl radicals produced by OH reactions were also examined and are reported here. Because of this tertiary transfer, phenoxyl radicals cannot be observed in steady-state ESR experiments on these systems. Studies of the dependence of the width of the ESR lines of phenoxyl radical produced from phenol on the phenol concentration show that electron transfer between the radical and the substrate occurs with a rate constant of 1.9 x 10/sup 8/ M/sup -1/ s/sup -1/.

• Research Organization: Carnegie-Mellon Univ., Pittsburgh
• OSTI ID: 7345469
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 98:13; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400104 -- Spectral Procedures-- (-1987)
400301 -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
400600* -- Radiation Chemistry
ABSORPTION SPECTRA
AQUEOUS SOLUTIONS
ARYL RADICALS
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISTRY
DECOMPOSITION
DISPERSIONS
ELECTRON SPIN RESONANCE
ELECTRONS
ELEMENTARY PARTICLES
FERMIONS
HYDRATION
HYDROXY COMPOUNDS
INTERMEDIATE STRUCTURE
KINETICS
LEPTONS
MAGNETIC RESONANCE
MIXTURES
ORGANIC BROMINE COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
RADIATION CHEMISTRY
RADIATION EFFECTS
RADICALS
RADIOLYSIS
REACTION KINETICS
REDUCTION
RESONANCE
SOLUTIONS
SOLVATED ELECTRONS
SOLVATION
SPECTRA