The Origin of Base Catalysis in the •OH Oxidation of Phenols in Water

Autor:	Yali Su, G. N. R. Tripathi
Rok vydání:	2004
Předmět:	chemistry.chemical_classification chemistry.chemical_compound Electron transfer Aqueous solution chemistry Base (chemistry) Intramolecular force Ultrafast laser spectroscopy Substrate (chemistry) Phenols Physical and Theoretical Chemistry Photochemistry Catalysis
Zdroj:	The Journal of Physical Chemistry A. 108:3478-3484
ISSN:	1520-5215 1089-5639
DOI:	10.1021/jp031365j
Popis:	Time-resolved Raman and transient absorption studies on hydroxyl (•OH) radical reactions with aqueous 4-carboxyphenol (-O2C−PhOH), the substrate in p-hydroxybenzoate hydroxylase, have led to the first direct observation of the basic form of a dihydroxycyclohexadienyl (•OH-adduct of phenolate anion) radical and hydration-induced intramolecular electron transfer in this species. The base-catalyzed phenoxyl radical formation in this model system has been quantitatively described in terms of pKa of the phenolic proton (9.05) of the •OH-adduct and the rate of OH- elimination (2.9 × 106 s-1) from its basic form. A small fraction, 12(+2)%, of the phenoxyl radical is formed via water elimination from the •OH-adduct at the ipso position of the hydroxyl group (rate > 107s-1). About 3% •OH addition is seen at the carboxylic ipso position in basic solutions, which produces the p-benzosemiquinone radical anion (rate ∼ 106s-1). This work provides spectroscopic and kinetic evidence of the early chemical steps in the phe...
Databáze:	OpenAIRE
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