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Parabens and salicylates were examined as disinfection byproduct (DBP) precursors to explore the possible influence of ipso substitution (i.e., halogen exchange) on the yield and speciation of trihalomethanes (THMs) formed during water chlorination. Substoichiometric conversion of C–Br bonds into C–Cl bonds was confirmed for several parabens and salicylates. The co-occurrence of (mono)brominated and nonhalogenated precursors in the presence of free chlorine (but in the absence of added Br–) generated polybrominated THMs, implicating ipso substitution. The THM molar yield, bromine incorporation, and bromine recovery from brominated and nonhalogenated precursor mixtures were commensurate with those observed from equimolar additions of NaBr, indicating efficient displacement of aromatic bromine by free chlorine followed by reincorporation of liberated HOBr into DBP precursors. The THM molar yield from brominated precursors was enhanced by a factor of ≤20 relative to that from nonhalogenated precursors. Trends in THM molar yields and bromine incorporation differed between brominated parabens and brominated salicylates, suggesting that the influence of ipso substitution on THM formation varies with the structure of the organic precursor. Collectively, these results provide new evidence of the often-overlooked role ipso substitution can play in promoting halogen exchange and bromine enrichment among DBPs in chlorinated waters. 

Aqueous free bromine species ( e.g. , HOBr, BrCl, Br 2 , BrOCl, Br 2 O, and H 2 OBr + ) can react with activated aromatic compounds via electrophilic aromatic substitution to generate products with industrial applications, environmental consequences, and potentially adverse biological effects. The relative contributions of these brominating agents to overall bromination rates can be calculated via nonlinear regression analyses of kinetic data collected under a variety of solution conditions, including variations in parameters ( e.g. , [Cl − ], [Br − ], and pH) known to influence free bromine speciation. Herein, kinetic experiments conducted in batch reactors were employed to evaluate the contributions of steric and electronic effects on bromination of monosubstituted alkylbenzenes (ethyl, isopropyl, tert -butyl) and alkoxybenzenes (ethoxy, isopropoxy, tert -butoxy) and to elucidate the inherent reactivities of aqueous brominating agents towards these aromatic compounds. For bromination at the para position of alkylbenzenes, overall reactivity increased from tert -butyl < ethyl ≈ isopropyl. For bromination at the para position of alkoxybenzenes, reactivity increased from tert -butoxy < ethoxy < isopropoxy. In going from ethyl to tert -butyl and ethoxy to isopropoxy, unfavorable steric effects attenuated the favorable electronic effects imparted by the substituents. When comparing unsubstituted benzene, alkyl-, and alkoxybenzenes, the structure of the substituent has a significant effect on bromination rates, nucleophile regioselectivity, and electrophile chemoselectivity. Hirshfeld charges were useful predictors of reactivity and regioselectivity. The experimental results were also modeled using Taft equations. Collectively, these findings indicate that steric effects, electronic effects, and brominating agents other than HOBr can influence aromatic compound bromination in solutions of free bromine. 

Parabens are antimicrobial additives found in a wide array of consumer products. However, the halogenated compounds formed from parabens during wastewater disinfection are a potential environmental concern. In order to identify these transformation products and investigate their mechanism of formation, a synthetic route to ethyl parabens labeled with the stable isotope carbon‐13 at specific positions within the benzene ring was developed. This efficient two‐step procedure starts from commercially available¹³C‐labeled phenols and involves (1) initial acylation of the phenol via a Houben–Hoesch reaction with trichloroacetonitrile followed by (2) a modified haloform reaction of the resulting trichloromethyl ketone to afford the corresponding¹³C‐labeled ethyl parabens in 65%–80% overall yield. The scope of the modified haloform reaction was also investigated, allowing for the synthesis of other parabens derived from primary or secondary alcohols, including¹³C‐ and deuterium‐labeled esters. In addition, 4‐hydroxybenzoic acid can be formed directly from the common trichloromethyl ketone intermediate upon treatment with lithium hydroxide. This protocol complements existing methods for preparing¹³C‐labeled paraben derivatives and offers the specific advantages of exhibiting complete regioselectivity in the Houben–Hoesch reaction (to form thepara‐disubstituted product) and avoiding the need for protecting groups in the modified haloform reaction that forms the paraben esters.

 

The toxic effects of herbicides are often incompletely selective and can harm crops. Safeners are “inert” ingredients commonly added to herbicide formulations to protect crops from herbicide-induced injury. Dichloroacetamide safeners have been previously shown to undergo reductive dechlorination in anaerobic abiotic systems containing an iron (hydr)oxide mineral (goethite or hematite) amended with Fe( ii ). Manganese oxides ( e.g. , birnessite) are important redox-active species that frequently co-occur with iron (hydr)oxides, yet studies examining the effects of more than one mineral on transformations of environmental contaminants are rare. Herein, we investigate the reactivity of dichloroacetamide safeners benoxacor, furilazole, and dichlormid in binary-mineral, anaerobic systems containing Fe( ii )-amended hematite and birnessite. As the molar ratio of Fe( ii )-to-Mn( iv ) oxide increased, the transformation rate of benoxacor and furilazole increased. The safener dichlormid did not transform appreciably over the sampling period (6 hours). The concentration of pH buffer ([MOPS] = 10–50 mM), ionic strength ([NaCl] = 10–200 mM), and order of solute addition ( e.g. , safener followed by Fe( ii ) or vice versa ) do not appreciably affect transformation rates of the examined dichloroacetamide safeners in Fe( ii ) + hematite slurries. The presence of agrochemical co-formulants, including the herbicide S -metolachlor and three surfactants, in solutions containing Cr(H 2 O) 6 2+ (as a model homogeneous reductant) also did not substantially influence rates of safener transformation. This study is among the first to examine laboratory systems of intermediate complexity ( e.g. , systems containing mixtures of agrochemical co-formulants or mineral phases) when assessing the environmental fate of emerging contaminants such as dichloroacetamide safeners.