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 inmore »
This content will become publicly available on June 16, 2023
Enhanced Reactivity for Aromatic Bromination via Halogen Bonding with Lactic Acid Derivatives
We report a new method for regioselective aromatic bromination using lactic acid derivatives as halogen bond
acceptors with N-bromosuccinimide (NBS). Several structural analogues of lactic acid affect the efficiency of aromatic brominations,
presumably via Lewis acid/base halogen-bonding interactions. Rate comparisons of aromatic brominations demonstrate the
reactivity enhancement available via catalytic additives capable of halogen bonding. Computational results demonstrate that Lewis
basic additives interact with NBS to increase the electropositive character of bromine prior to electrophilic transfer. An optimized
procedure using catalytic mandelic acid under aqueous conditions at room temperature was developed to promote aromatic
bromination on a variety of arene substrates with complete regioselectivity.
- Publication Date:
- NSF-PAR ID:
- 10335933
- Journal Name:
- The Journal of Organic Chemistry
- ISSN:
- 0022-3263
- Sponsoring Org:
- National Science Foundation
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