Environment Research Institute, Shandong University, Jinan 250100, PR China.
Chemosphere. 2013 Sep;93(3):512-20. doi: 10.1016/j.chemosphere.2013.06.024. Epub 2013 Jul 5.
2,4,5-Tribromophenol (2,4,5-TBP) and 3,4-dibromophenol (3,4-DBP) have the minimum number of Br atoms needed to form 2,3,7,8-PBDD/Fs, which are the most toxic among all 210 PBDD/F isomers. A mechanistic understanding of the formation of PBDD/Fs is a prerequisite for minimizing their emissions. In this paper, the homogeneous gas-phase formation of PBDD/Fs from 2,4,5-TBP and 3,4-DBP as precursors was investigated theoretically by using the density functional theory (DFT) method. The mathematical model to predict the formation of PBDD/Fs places a high demand on accurate kinetic parameters. So, the rate constants of key elementary steps involved in the formation of PBDD/Fs were calculated by using canonical variational transition-state (CVT) theory with small curvature tunneling (SCT) contribution over a wide temperature range of 600-1200K. The pre-exponential factors and the activation energies are also reported. This might be the first to investigate the formation of 2,3,7,8-PBDD/Fs. The present study shows that the formation of PBDDs dominates over the formation of PBDFs. The meta bromine facilitates the dimerization of bromophenoxy radicals (BPRs), whereas the para and ortho bromines suppress the dimerization of BPRs.
2,4,5-三溴苯酚（2,4,5-TBP）和 3,4-二溴苯酚（3,4-DBP）是形成 2,3,7,8-四溴二苯并二恶英/呋喃（2,3,7,8-PBDD/Fs）所需的最少溴原子数，而 2,3,7,8-PBDD/Fs 是所有 210 种 PBDD/F 异构体中毒性最大的。对 PBDD/Fs 形成的机理理解是最大限度减少其排放的前提。本文采用密度泛函理论（DFT）方法，从理论上研究了 2,4,5-TBP 和 3,4-DBP 作为前体在均相气相中形成 PBDD/Fs 的过程。预测 PBDD/Fs 形成的数学模型对准确的动力学参数要求很高。因此，在 600-1200K 的宽温度范围内，使用正则变分过渡态（CVT）理论和小曲率隧道（SCT）贡献，计算了形成 PBDD/Fs 过程中关键基元步骤的速率常数。还报道了指前因子和活化能。这可能是首次研究 2,3,7,8-PBDD/Fs 的形成。本研究表明，PBDDs 的形成占主导地位，而 PBDFs 的形成则被抑制。间位溴促进溴苯氧基自由基（BPR）的二聚化，而对位和邻位溴则抑制 BPR 的二聚化。
