Polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) are the potential persistent organic pollutants in the environment. A comprehensive understanding of the formation and evolution mechanisms of PBDD/Fs contributes to better control their emissions. In this paper, the formation mechanisms of PBDD/Fs from 2,6-dibromophenol pyrolysis were investigated, and the kinetic and thermodynamic parameters in all formation pathways were calculated through using density functional theory (DFT) method B3P86 with the 6-311 + G(d,p) basis set. The calculation results show that the 2-bromophenoxy radical is a major decomposition product in initial pyrolysis of 2,6-dibromophenol, and dimerization of bromophenoxy radicals occurs mainly through O-C coupling or C-C coupling. O-C coupling results in the formation of PBDD precursors, and C-C coupling results in the formation of PBDF precursors. The formation of PBDD/Fs proceeds mainly via H-abstraction or H-transfer, cyclization, and debromination or dehydroxylation. The energy barriers of rate-determining steps in the formation of PBDDs are lower than those of PBDFs, so the formations of brominated dibenzo-p-dioxins are superior to the formations of brominated dibenzofurans.

多溴联苯- 二恶英和二苯并呋喃 (PBDD/Fs) 是环境中潜在的持久性有机污染物。全面了解PBDD/Fs的形成和演化机制有助于更好地控制其排放。本文研究了 2,6-二溴苯酚热解 PBDD/Fs 的形成机理，并使用密度泛函理论 (DFT) 方法 B3P86 计算了所有形成途径中的动力学和热力学参数，其中 6-311 + G (d,p) 基组。计算结果表明，2-溴苯氧基自由基是2,6-二溴苯酚初始热解的主要分解产物，溴苯氧基自由基的二聚反应主要通过OC偶联或CC偶联发生。OC偶联导致PBDD前体的形成，和 CC 耦合导致 PBDF 前体的形成。PBDD/Fs 的形成主要通过 H-提取或 H-转移、环化、脱溴或脱羟基作用进行。PBDDs 形成过程中决速步骤的能垒低于 PBDFs，因此溴化二苯并-对二恶英优于溴化二苯并呋喃的形成。