Ipso Substitution of Aromatic Bromine in Chlorinated Waters: Impacts on Trihalomethane Formation

Abstract

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.

Role of Copper in Disinfection Byproduct Formation Derived from Algal Organic Matter: Based on Two-Dimensional Correlation Spectroscopy Analysis

“…Compared to the reaction sequence between EOM and chlorine, aliphatic C–Cl groups and amide CO groups in Cu-EOM (formed by the binding of Cu­(II) and EOM) were preferentially reacted with chlorine to form DBP. Previous researches have shown that aliphatic compounds had higher TCM yield than aliphatic compounds without a chlorine atom . Therefore, the influence of Cu­(II) on DBP formation during chlorination was summarized as that the complexation of Cu­(II) and EOM fractions formed various binding ligands and altered their chloride reactivity, thus increasing the risk of DBP generated by EOM, which was consistent with a previous report that a hydroxyl group in aliphatic organic compounds conversed to a carbonyl group by the catalysis of Cu­(II) .…”

“…Previous researches have shown that aliphatic compounds had higher TCM yield than aliphatic compounds without a chlorine atom. 43 Therefore, the influence of Cu(II) on DBP formation during chlorination was summarized as that the complexation of Cu(II) and EOM fractions formed various binding ligands and altered their chloride reactivity, thus increasing the risk of DBP generated by EOM, which was consistent with a previous report that a hydroxyl group in aliphatic organic compounds conversed to a carbonyl group by the catalysis of Cu(II). 44 These results also confirmed that the TCM yield in EOM increased with increasing Cu(II) concentration (Figure 1c).…”