Environmental Science & Studies Program, Towson University, Towson, Maryland 21252, United States.
Department of Chemistry, Towson University, Towson, Maryland 21252, United States.
Environ Sci Technol. 2023 Nov 28;57(47):18801-18810. doi: 10.1021/acs.est.3c00852. Epub 2023 Apr 25.
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.
对防腐剂和水杨酸盐进行了研究，作为消毒副产物 (DBP) 前体，以探讨异丙基取代（即卤素交换）对水中氯化形成的三卤甲烷 (THM) 产率和形态的可能影响。几种防腐剂和水杨酸盐的 C-Br 键被证实发生了亚化学计量的 C-Cl 键转化。在存在游离氯（但没有添加 Br）的情况下，（单）溴化和非卤化前体的共存产生了多溴化 THM，暗示了异丙基取代。从溴化和非卤化前体混合物中获得的 THM 摩尔产率、溴掺入和溴回收与从等摩尔添加 NaBr 观察到的结果相当，表明游离氯有效地取代了芳香族溴，然后将释放的 HOBr 重新掺入到 DBP 前体中。与非卤化前体相比，溴化前体的 THM 摩尔产率提高了 ≤20 倍。溴化防腐剂和溴化水杨酸盐的 THM 摩尔产率和溴掺入趋势不同，表明异丙基取代对 THM 形成的影响因有机前体的结构而异。总的来说，这些结果提供了新的证据，证明异丙基取代在促进氯化水中 DBP 中的卤素交换和溴富集方面的作用常常被忽视。
