Breaking Down Polychlorinated Biphenyls and Aryl Chlorides: A Computational Study of Thermal-, Pressure-, and Shear-Induced Decomposition.

Reactive molecular dynamics (MD) simulations were used to study the decomposition of aryl chlorides, including polychlorinated biphenyls (PCBs), under varying conditions. Using the ReaxFF force field, which models bond breaking and formation, the study focused on PCB 77 (3,3',4,4'-tetrachlorobiphenyl) and compared it to safer alternatives: 1,2-dichlorobenzene (DCB) and 3,4-dichlorotoluene (DCT). Density functional theory (DFT) calculations validated decomposition pathways and enthalpies of C-Cl bond homolytic cleavage, revealing a multistep radical mechanism. Analysis showed that the decomposition rate and product distribution were sensitive to temperature and Cl-binding positions, emphasizing the complexity of PCB breakdown. Decomposition products were analyzed to understand the efficiency and safety of current remediation processes, such as incineration, which can produce hazardous byproducts like dioxins if poorly managed. The results suggested DCT as a promising candidate for further investigation in laboratory experiments due to its decomposition pathways and relevance to PCB analogues. This study advances knowledge of PCB degradation mechanisms, informing safer, sustainable remediation strategies, and highlighting the risks of pyrolysis-based approaches.