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Sodium sulfite, sodium thiosulfate, and ascorbic acid are commonly used to quench free chlorine and free bromine in studies of disinfection byproducts (DBPs) in drinking water, wastewater, and recreational water. The reducing capabilities of these quenchers, however, can lead to the degradation of some redox-labile analytes. Ammonium chloride, another common quencher, converts free chlorine into monochloramine and is therefore inappropriate for analytes susceptible to chloramination. Herein, we demonstrate the utility of 1,3,5-trimethoxybenzene (TMB) as a quencher of free chlorine and free bromine. The reactivity of TMB toward free chlorine was characterized previously. The reactivity of TMB toward free bromine was quantified herein ( k HOBr,TMB = 3.35 × 10 6 M −1 s −1 ) using competition kinetics. To explore the feasibility of TMB serving as a free halogen quencher for kinetic experiments, chlorination of 2,4-dichlorophenol, bromination of anisole, and chlorination and bromination of dimethenamid-P were examined. Although TMB does not react with free chlorine or free bromine as quickly as do some (but not all) traditional quenchers, there was generally no significant difference in the experimental rate constants with TMB (relative to thiosulfate) as the quencher. By monitoring the chlorination and bromination products of TMB, free halogen residuals in quenched samples were quantified. Furthermore, TMB did not affect the stabilities of DBPs ( e.g. , chloropicrin and bromoacetonitriles) that otherwise degraded in the presence of traditional quenchers. TMB could, therefore, be an appropriate quencher of free chlorine and free bromine in aqueous halogenation experiments involving redox-labile analytes and/or when selective quantification of residual free halogens is desired.
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This content will become publicly available on November 14, 2026
Unexpected Reactivity of Commercially Relevant Phthalates with Free Chlorine
Phthalates are the most prevalent plasticizers in poly(vinyl chloride) (PVC), the most commonly used polymer for drinking water distribution pipes. Though typically considered inert to the free chlorine necessary for drinking water disinfection, we found that certain commercially relevant phthalates leach from PVC and transform in the presence of free chlorine. The extent of aqueous phthalate leaching was alkyl chain length-dependent; the greatest leaching was observed for the most soluble 1-carbon chain phthalate, which was unaffected by free chlorine. In contrast, 2- and 4-carbon chain phthalates leached significantly less, and their concentrations decreased further in the presence of free chlorine. These observations were rationalized by experiments showing increased chlorine consumption with increasing phthalate alkyl chain length, indicative of structure-dependent chemical transformations of the parent phthalate with free chlorine. Using gas and liquid chromatography, high-resolution mass spectrometry, and nuclear magnetic resonance spectroscopy, we identified 13 disinfection byproducts of diisobutyl phthalate, 2 of which were confirmed using reference materials. The presence of both chlorinated and hydroxylated transformation products suggests reactions with both free chlorine and chlorine-derived reactive intermediates. This study underscores the need for consideration of chemical structure in predicting phthalate reactivity and highlights potential exposure risks in drinking water infrastructure.
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- Award ID(s):
- 2001611
- PAR ID:
- 10649771
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- ACS ES&T Water
- Volume:
- 5
- Issue:
- 11
- ISSN:
- 2690-0637
- Page Range / eLocation ID:
- 6842 to 6852
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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