Jump to main content
Jump to site search


Reaction of phenol with singlet oxygen

Author affiliations

Abstract

Photo-degradation of organic pollutants plays an important role in their removal from the environment. This study provides an experimental and theoretical account of the reaction of singlet oxygen O2(1Δg) with the biodegradable-resistant species of phenol in an aqueous medium. The experiments combine customised LED-photoreactors, high-performance liquid chromatography (HPLC), and electron paramagnetic resonance (EPR) imaging, employing rose bengal as a sensitiser. Guided by density functional theory (DFT) calculations at the M062X level, we report the mechanism of the reaction and its kinetic model. Addition of O2(1Δg) to the phenol molecule branches into two competitive 1,4-cycloaddition and ortho ene-type routes, yielding 2,3-dioxabicyclo[2.2.2]octa-5,7-dien-1-ol (i.e., 1,4-endoperoxide 1-hydroxy-2,5-cyclohexadiene) and 2-hydroperoxycyclohexa-3,5-dien-1-one, respectively. Unimolecular rearrangements of the 1,4-endoperoxide proceed in a facile exothermic reaction to form the only experimentally detected product, para-benzoquinone. EPR revealed the nature of the oxidation intermediates and corroborated the appearance of O2(1Δg) as the only active radical participating in the photosensitised reaction. Additional experiments excluded the formation of hydroxyl (HO˙), hydroperoxyl (HO2˙), and phenoxy intermediates. We detected for the first time the para-semibenzoquinone anion (PSBQ), supporting the reaction pathway leading to the formation of para-benzoquinone. Our experiments and the water-solvation model result in the overall reaction rates of kr-solvation = 1.21 × 104 M−1 s−1 and kr = 1.14 × 104 M−1 s−1, respectively. These results have practical application to quantify the degradation of phenol in wastewater treatment.

Graphical abstract: Reaction of phenol with singlet oxygen

Back to tab navigation

Supplementary files

Publication details

The article was received on 31 Jul 2018, accepted on 21 Nov 2018 and first published on 21 Nov 2018


Article type: Paper
DOI: 10.1039/C8CP04852E
Citation: Phys. Chem. Chem. Phys., 2019, Advance Article
  •   Request permissions

    Reaction of phenol with singlet oxygen

    J. Al-Nu’airat, B. Z. Dlugogorski, X. Gao, N. Zeinali, J. Skut, P. R. Westmoreland, I. Oluwoye and M. Altarawneh, Phys. Chem. Chem. Phys., 2019, Advance Article , DOI: 10.1039/C8CP04852E

Search articles by author

Spotlight

Advertisements