title: Reaction of bromine and chlorine with phenolic compounds and natural organic matter extracts--Electrophilic aromatic substitution and oxidation.
abstract: Phenolic compounds are known structural moieties of natural organic matter (NOM), and their reactivity is a key parameter for understanding the reactivity of NOM and the disinfection by-product formation during oxidative water treatment. In this study, species-specific and/or apparent second order rate constants and mechanisms for the reactions of bromine and chlorine have been determined for various phenolic compounds (phenol, resorcinol, catechol, hydroquinone, phloroglucinol, bisphenol A, p-hydroxybenzoic acid, gallic acid, hesperetin and tannic acid) and flavone. The reactivity of bromine with phenolic compounds is very high, with apparent second order rate constants at pH 7 in the range of 10(4) to 10(7) M(-1) s(-1). The highest value was recorded for the reaction between HOBr and the fully deprotonated resorcinol (k = 2.1 × 10(9) M(-1) s(-1)). The reactivity of phenolic compounds is enhanced by the activating character of the phenolic substituents, e.g. further hydroxyl groups. With the data set from this study, the ratio between the species-specific rate constants for the reactions of chlorine versus bromine with phenolic compounds was confirmed to be about 3000. Phenolic compounds react with bromine or chlorine either by oxidation (electron transfer, ET) or electrophilic aromatic substitution (EAS) processes. The dominant process mainly depends on the relative position of the hydroxyl substituents and the possibility of quinone formation. While phenol, p-hydroxybenzoic acid and bisphenol A undergo EAS, hydroquinone, catechol, gallic acid and tannic acid, with hydroxyl substituents in ortho or para positions, react with bromine by ET leading to quantitative formation of the corresponding quinones. Some compounds (e.g. phloroglucinol) show both partial oxidation and partial electrophilic aromatic substitution and the ratio observed for the pathways depends on the pH. For the reaction of six NOM extracts with bromine, electrophilic aromatic substitution accounted for only 20% of the reaction, and for one NOM extract (Pony Lake fulvic acid) it accounted for <10%. This shows that for natural organic matter samples, oxidation (ET) is far more important than bromine incorporation (EAS).
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Dübendorf, Switzerland; Curtin Water Quality Research Centre, Curtin University, GPO Box U1987, Perth, WA 6845, Australia; Université Lille 1 Sciences and Technologies, LASIR, UMR CNRS 8516, 59655 Villeneuve d'Ascq, France.
authors.forename: Justine
authors.initials: J
authors.lastname: Criquet
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Dübendorf, Switzerland; Departamento de Ingeniería Química y Química Física, Universidad de Extremadura, Avda. Elvas s/n, 06006 Badajoz, Spain; School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: Eva M
authors.initials: EM
authors.lastname: Rodriguez
authors.affiliation: Curtin Water Quality Research Centre, Curtin University, GPO Box U1987, Perth, WA 6845, Australia.
authors.forename: Sebastien
authors.initials: S
authors.lastname: Allard
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Dübendorf, Switzerland.
authors.forename: Sven
authors.initials: S
authors.lastname: Wellauer
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Dübendorf, Switzerland.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Salhi
authors.affiliation: Curtin Water Quality Research Centre, Curtin University, GPO Box U1987, Perth, WA 6845, Australia.
authors.forename: Cynthia A
authors.initials: CA
authors.lastname: Joll
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Dübendorf, Switzerland; School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland; Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, CH-8092 Zürich, Switzerland. Electronic address: vongunten@eawag.ch.
authors.forename: Urs
authors.initials: U
authors.lastname: von Gunten
mesh_terms: D001966:Bromine / Q000737:chemistry*; D002713:Chlorine / Q000737:chemistry*; D006812:Humic Substances / Q000032:analysis*; D010084:Oxidation-Reduction; D010636:Phenols / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification
chemical_list: D006812:Humic Substances; D010636:Phenols; D014874:Water Pollutants, Chemical; D002713:Chlorine; D001966:Bromine
keywords: Bromine; Chlorine; Electron transfer; Electrophilic aromatic substitution; Hydroxy aromatic compounds; Natural organic matter