多卤代二苯并对二恶英/二苯并呋喃(PXDD/Fs)通常作为燃烧过程的副产物释放到环境中,伴随着烟气。氯化(Cl)和溴化(Br)前体在形成PXDD/Fs中起着至关重要的作用。然而,Cl-前体和Br-前体对PXDD/Fs形成的具体贡献尚未完全阐明。在这里,我们证明了Br-前体的形成可以增加在特定位置取代的多氯二苯并对二恶英/二苯并呋喃(PCDD/Fs)同源物的分数,例如1,2,3,4,6,7,8-HpCDD,OCDD,2,3,4,7,8-PeCDF,和2,3,4,6,7,8-HxCDF。这归因于Br-前体的亲电氯化反应,其中包括Br-to-Cl转化途径,遵循区域选择性原则。从1,2-二溴苯(1,2-DiBBz)作为Br前体观察到的多溴/氯化二苯并对二恶英/苯并呋喃(PBCDD/Fs)的形成提供了直接证据支持拟议的Br到Cl的转化。量子化学计算用于讨论Br到Cl转化中的区域选择性原理,阐明亲电子氯化的优先地位。此外,由1,2-DiBBz形成的PCDD/Fs的浓度为1.6μg/kg,与多溴二苯并对二恶英/二苯并呋喃(PBDD/Fs)(2.4μg/kg)相当,强调溴化有机污染物作为PCDD/Fs形成前体的潜力。这项研究提供了溴前体形成PCDD/Fs的三种潜在途径,为阐明Cl和Br共存下PXDD/Fs的形成机理奠定了理论基础。
Polyhalogenated dibenzo-p-dioxins/dibenzofurans (PXDD/Fs) are commonly released into the environment as byproducts of combustion processes, accompanied by flue gases. Chlorinated (Cl) and brominated (Br) precursors play crucial roles in forming PXDD/Fs. However, the specific contributions of Cl-precursors and Br-precursors to PXDD/Fs formation have not been fully elucidated. Herein, we demonstrate that the formation of Br-precursors can increase the fraction of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) congeners substituted at specific positions, such as 1,2,3,4,6,7,8-HpCDD, OCDD, 2,3,4,7,8-PeCDF, and 2,3,4,6,7,8-HxCDF. This is attributed to the electrophilic chlorination reaction of the Br-precursors, which includes the Br-to-Cl transformation pathway, following the principle of regioselectivity. The observed formation of polybrominated/chlorinated dibenzo-p-dioxins/benzofurans (PBCDD/Fs) from 1,2-dibromobenzene (1,2-DiBBz) as a Br precursor provides direct evidence supporting the proposed Br-to-Cl transformation. Quantum chemical calculations are employed to discuss the principle of regioselectivity in the Br-to-Cl transformation, clarifying the priority of the position for electrophilic chlorination. Additionally, the concentration of PCDD/Fs formed from 1,2-DiBBz is 1.6 μg/kg, comparable to that of polybrominated dibenzo-p-dioxins/dibenzofurans (PBDD/Fs) (2.4 μg/kg), highlighting the potential of brominated organic pollutants as precursors for PCDD/Fs formation. This study provides three potential pathways for PCDD/Fs formation from Br-precursors, establishing a theoretical foundation for elucidating the formation mechanism of PXDD/Fs in the coexistence of Cl and Br.