title: Chlorination Revisited: Does Cl-Serve as a Catalyst in the Chlorination of Phenols?
abstract: The aqueous chlorination of (chloro)phenols is one of the best-studied reactions in the environmental literature. Previous researchers have attributed these reactions to two chlorine species: HOCl (at circum-neutral and high pH) and H2OCl+(at low pH). In this study, we seek to examine the roles that two largely overlooked chlorine species, Cl2and Cl2O, may play in the chlorination of (chloro)phenols. Solution pH, chloride concentration, and chlorine dose were systematically varied in order to assess the importance of different chlorine species as chlorinating agents. Our findings indicate that chlorination rates at pH < 6 increase substantially when chloride is present, attributed to the formation of Cl2. At pH 6.0 and a chlorine dose representative of drinking water treatment, Cl2O is predicted to have at best a minor impact on chlorination reactions, whereas Cl2may contribute more than 80% to the overall chlorination rate depending on the (chloro)phenol identity and chloride concentration. While it is not possible to preclude H2OCl+as a chlorinating agent, we were able to model our low-pH data by considering Cl2only. Even traces of chloride can generate sufficient Cl2to influence chlorination kinetics, highlighting the role of chloride as a catalyst in chlorination reactions.
authors.affiliation: Department of Environmental Health and Engineering, Johns Hopkins University , 313 Ames Hall, 3400 North Charles Street, Baltimore, Maryland 21218, United States.
authors.forename: Stephanie S
authors.identifier: 0000-0001-9082-7324
authors.initials: SS
authors.lastname: Lau
authors.affiliation: Department of Environmental Health and Engineering, Johns Hopkins University , 313 Ames Hall, 3400 North Charles Street, Baltimore, Maryland 21218, United States.|Institute of the Environment and Sustainability, University of California, Los Angeles , La Kretz Hall, 619 Charles E. Young Drive East #300, Los Angeles, California 90024, United States.
authors.forename: Sonali M
authors.initials: SM
authors.lastname: Abraham
authors.affiliation: Department of Environmental Health and Engineering, Johns Hopkins University , 313 Ames Hall, 3400 North Charles Street, Baltimore, Maryland 21218, United States.
authors.forename: A Lynn
authors.initials: AL
authors.lastname: Roberts
mesh_terms: D002713:Chlorine; D054879:Halogenation; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010636:Phenols; D018508:Water Purification
chemical_list: D010636:Phenols; D002713:Chlorine