title: Chlorination of phenols: kinetics and formation of chloroform.
abstract: The kinetics of chlorination of several phenolic compounds and the corresponding formation of chloroform were investigated at room temperature. For the chlorination of phenolic compounds, second-order kinetics was observed, first-order in chlorine, and first-order in the phenolic compound. The rate constants of the reactions of HOCl with phenol and phenolate anion and the rate constant of the acid-catalyzed reaction were determined in the pH range 1-11. The second-order rate constants for the reaction HOCl + phenol varied between 0.02 and 0.52 M(-1) s(-1), for the reaction HOCl and phenolate between 8.46 x 10(1) and 2.71 x 10(4) M(-1) s(-1). The rate constant for the acid-catalyzed reaction varied between 0.37 M(-2) s(-1) to 6.4 x 10(3) M(-2) s(-1). Hammett-type correlations were obtained for the reaction of HOCl with phenolate (log(k) = 4.15-3.00 x sigma sigma) and the acid-catalyzed reaction of HOCl with phenol (log(k) = 2.37-4.26 x sigma sigma). The formation of chloroform could be interpreted with a second-order model, first-order in chlorine, and first-order in chloroform precursors. The corresponding rate constants varied between k > 100 M(-1) s(-1) for resorcinol to 0.026 M(-1) s(-1) for p-nitrophenol at pH 8.0. It was found that the rate-limiting step of chloroform formation is the chlorination of the chlorinated ketones. Yields of chloroform formation depend on the type and position of the substituents and varied between 2 and 95% based on the concentration of the phenol.
authors.affiliation: Swiss Federal Institute for Environmental Science and Technology (EAWAG), Dübendorf.
authors.forename: Herve
authors.initials: H
authors.lastname: Gallard
authors.forename: Gunten Urs
authors.initials: GU
authors.lastname: von
mesh_terms: D017606:Chlorine Compounds / Q000737:chemistry*; D002725:Chloroform / Q000737:chemistry*; D007700:Kinetics; D010636:Phenols / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry*; D013696:Temperature; D018508:Water Purification; D014881:Water Supply
chemical_list: D017606:Chlorine Compounds; D010636:Phenols; D012997:Solvents; D002725:Chloroform