Chlorination and bromination of olefins: Kinetic and mechanistic aspects

Juan Li; Jin Jiang; Tarek Manasfi; Urs von Gunten

doi:10.1016/j.watres.2020.116424

Chlorination and bromination of olefins: Kinetic and mechanistic aspects

Water Res. 2020 Dec 15:187:116424. doi: 10.1016/j.watres.2020.116424. Epub 2020 Sep 19.

Authors

Juan Li¹, Jin Jiang², Tarek Manasfi³, Urs von Gunten⁴

Affiliations

¹ Institute of Environmental and Ecological Engineering, Guangdong University of Technology, Guangzhou 510006, China; State Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin 150090, China; School of Architecture, Civil and Environmental Engineering (ENAC), École Polytechnique Fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland.
² Institute of Environmental and Ecological Engineering, Guangdong University of Technology, Guangzhou 510006, China. Electronic address: jiangjin@gdut.edu.cn.
³ Eawag, Swiss Federal Institute of Aquatic Science and Technology, Ueberlandstrasse 133, 8600, Duebendorf, Switzerland.
⁴ School of Architecture, Civil and Environmental Engineering (ENAC), École Polytechnique Fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland; Eawag, Swiss Federal Institute of Aquatic Science and Technology, Ueberlandstrasse 133, 8600, Duebendorf, Switzerland; Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, 8092 Zurich, Switzerland. Electronic address: vongunten@eawag.ch.

PMID: 33038657
DOI: 10.1016/j.watres.2020.116424

Abstract

Hypochlorous acid (HOCl) is typically assumed to be the primary reactive species in free available chlorine (FAC) solutions. Lately, it has been shown that less abundant chlorine species such as chlorine monoxide (Cl₂O) and chlorine (Cl₂) can also influence the kinetics of the abatement of certain organic compounds during chlorination. In this study, the chlorination as well as bromination kinetics and mechanisms of 12 olefins (including 3 aliphatic and 9 aromatic olefins) with different structures were explored. HOCl shows a low reactivity towards the selected olefins with species-specific second-order rate constants <1.0 M^-1s^-1, about 4-6 orders of magnitude lower than those of Cl₂O and Cl₂. HOCl is the dominant chlorine species during chlorination of olefins under typical drinking water conditions, while Cl₂O and Cl₂ are likely to play important roles at high FAC concentration near circum-neutral pH (for Cl₂O) or at high Cl^- concentration under acidic conditions (for Cl₂). Bromination of the 12 olefins suggests that HOBr and Br₂O are the major reactive species at pH 7.5 with species-specific second-order rate constants of Br₂O nearly 3-4 orders of magnitude higher than of HOBr (ranging from <0.01 to >10³ M^-1s^-1). The reactivities of chlorine and bromine species towards olefins follow the order of HOCl < HOBr < Br₂O < Cl₂O ≈ Cl₂. Generally, electron-donating groups (e.g., CH₂OH- and CH₃-) enhances the reactivities of olefins towards chlorine and bromine species by a factor of 3-10², while electron-withdrawing groups (e.g., Cl-, Br-, NO₂-, COOH-, CHO-, -COOR, and CN-) reduce the reactivities by a factor of 3-10⁴. A reasonable linear free energy relationship (LFER) between the species-specific second-order rate constants of Br₂O or Cl₂O reactions with aromatic olefins and their Hammett σ⁺ was established with a more negative ρ value for Br₂O than for Cl₂O, indicating that Br₂O is more sensitive to substitution effects. Chlorinated products including HOCl-adducts and decarboxylated Cl-adduct were identified during chlorination of cinnamic acid by high-performance liquid chromatography/high resolution mass spectrometry (HPLC/HRMS).

Keywords: bromine (HOBr); bromine monoxide (Br(2)O); chlorine (Cl(2)); chlorine monoxide (Cl(2)O); free available chlorine (FAC); olefin.

MeSH terms

Alkenes
Chlorine
Halogenation*
Kinetics
Water Purification*

Substances

Alkenes
Chlorine