Assessing the reactivity of free chlorine constituents Cl₂, Cl₂O, and HOCl toward aromatic ethers.
Cl(2) and Cl(2)O are highly reactive electrophiles capable of influencing rates of disinfection byproduct (DBP) precursor chlorination in solutions of free available chlorine (FAC). The current work examines how organic compound structure influences susceptibility toward chlorination by Cl(2) and Cl(2)O relative to the more abundant (but less reactive) electrophile HOCl. Chlorination rates and products were determined for three aromatic ethers, whose reactivities with FAC increased in the order: 3-methylanisole <1,3-dimethoxybenzene <1,3,5-trimethoxybenzene. Varying solution conditions (pH, [FAC], [Cl(-)]) permitted quantification of regiospecific second-order rate constants for formation of each product by Cl(2), Cl(2)O, and HOCl. Our results indicate that as the reactivity of methoxybenzenes decreases, the importance of Cl(2) and Cl(2)O (relative to HOCl) increases. Accordingly, Cl(2) and Cl(2)O are likely to play important roles in generating DBPs that originate from natural organic matter (NOM) constituents of somewhat moderate reactivity. As [Cl(2)] is proportional to [Cl(-)] and [Cl(2)O] is proportional to [HOCl](2), ramifications for DBP control measures may differ significantly for these precursors compared to more reactive NOM moieties likely to react predominantly with HOCl. In particular, the role of chloride as a chlorination catalyst challenges its traditional classification as an "inert" electrolyte in water treatment processes.
Department of Geography and Environmental Engineering, Johns Hopkins University, 313 Ames Hall, 3400 North Charles Street, Baltimore, Maryland 21218, United States.
John D
JD
Sivey
A Lynn
AL
Roberts
D002713:Chlorine / Q000737:chemistry*; D017606:Chlorine Compounds / Q000737:chemistry*; D004202:Disinfectants / Q000737:chemistry*; D004987:Ethers / Q000737:chemistry*; D054879:Halogenation; D006863:Hydrogen-Ion Concentration; D006997:Hypochlorous Acid / Q000737:chemistry*; D007700:Kinetics; D009994:Osmolar Concentration; D010087:Oxides / Q000737:chemistry*; D018508:Water Purification / Q000379:methods
D017606:Chlorine Compounds; D004202:Disinfectants; D004987:Ethers; D010087:Oxides; D002713:Chlorine; D006997:Hypochlorous Acid; C025109:chlorine dioxide