Assessing the Reactivity of Free Chlorine Constituents Cl₂, Cl₂O, and HOCl Toward Aromatic Ethers

Abstract

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.

Photochlorination-induced transformation of graphene oxide: Mechanism and environmental fate

“…Rather, chlorination of GO led to electrophilic additions of chlorine atoms at the unsaturated sites of GO's benzene ring . Higher HClO dosage had additional effects on GO's surface chemistry, such as further oxidation of hydroxyl groups to carboxyl groups (Sivey and Roberts, 2012). However, neither HClO nor aqueous Cl 2 was reactive enough to break GO's carbon platelets and add new oxygen functional groups onto them.…”

Determination of rapid chlorination rate constants by a stopped-flow spectrophotometric competition kinetics method

“…Since Cl 2 O is highly reactive, k Cl2O could approach a rate constant of diffusion control (i.e. 1 Â 10 9 M À1 s À1 ) (Sivey and Roberts, 2012). The k value was measured as (5.03 AE 0.02) Â 10 4 M À1 s À1 at pH 6.75 (Fig.…”

Chlorination of tramadol: Reaction kinetics, mechanism and genotoxicity evaluation

“…The reaction order in [chlorine] at various pH ranged from 1.01 to 1.67, indicating that reactions appearing first-order and second-order in [chlorine] simultaneously existed during the TRA chlorination process. Recent works demonstrated that chlorine monoxide (Cl 2 O) and molecular chlorine (Cl 2 ) could also be identified as active chlorination agents during the chlorination process (Sivey et al, 2010;Sivey and Roberts, 2012). Cl 2 can serve as a chlorination oxidant in the presence of chloride especially under low pH conditions (as Eq.…”

“…Generally, the former studies considered hypochlorous acid (HOCl) and hypochlorite (ClO À ) as the main chlorine species, and the degradation reactions followed second-order kinetics, first order in the concentration of target compound, and first order in the chlorine concentration (Dodd and Huang, 2004;Soufan et al, 2012). Recently, some researchers pointed out that some other active species such as chlorine monoxide (Cl 2 O) and molecular chlorine (Cl 2 ) take part in the chlorination disinfection process as well, in addition to HOCl/ClO À (Sivey et al, 2010;Sivey and Roberts, 2012). Despite their relatively lower concentrations, such species (Cl 2 , Cl 2 O) possess much higher reactive activity with organic products compared with HOCl/ClO À (Sivey et al, 2010;Sivey and Roberts, 2012;Cai et al, 2013).…”

“…Recently, some researchers pointed out that some other active species such as chlorine monoxide (Cl 2 O) and molecular chlorine (Cl 2 ) take part in the chlorination disinfection process as well, in addition to HOCl/ClO À (Sivey et al, 2010;Sivey and Roberts, 2012). Despite their relatively lower concentrations, such species (Cl 2 , Cl 2 O) possess much higher reactive activity with organic products compared with HOCl/ClO À (Sivey et al, 2010;Sivey and Roberts, 2012;Cai et al, 2013). Therefore, the contributions of HOCl/ClO À , Cl 2 and Cl 2 O should all be considered during the PPCPs chlorination process.…”