Investigation on tetrabromobisphenol A-bis(2,3-dibromopropyl ether) thermal decomposition behaviours: Evolutionary mechanisms of main pyrolysis products.

Tetrabromobisphenol A-bis(2,3-dibromopropyl ether) (TBBPA-DBPE), as a new type of flame retardant, is widely used in electronic equipment. During its degradation process, some toxic brominated compounds can be produced and released into the environment, causing great harm to human health and the ecological environment. There are relatively few in-depth theoretical studies on the pyrolysis mechanism of TBBPA-DBPE, therefore, the evolution mechanism of thermal degradation products of TBBPA-DBPE is studied in detail by using the density functional theory method in this paper. The calculation results of bond dissociation energy (BDE) show that, in the initial reaction, the value of BDE required for ether bond cleavage is the lowest, followed by C2-Br bond and C-CH3 bond cleavage, and the required BDEs are 271.2 kJ/mol, 281.0 kJ/mol, and 305.0 kJ/mol, respectively. The unimolecular elimination of hydrogen bromide (HBr) is the main reaction in the concerted reaction, and the breaking of ether bonds is the main competitive reaction, leading to the formations of 3-bromopropene, 2,3-bromopropene, and tetrabromobisphenol-A. The participation reactions of hydrogen radicals mainly involve abstract reactions and substitution reactions, and HBr is mainly derived from the abstraction reaction, which has a lower reaction energy barrier (14.9-29.6 kJ/mol). Substitution reactions are mainly the substitution of bromine radicals by hydrogen radicals, and the activation energy required for substitution reactions on the benzene ring is lower than that on the propyl group. The main pyrolysis brominated products are HBr, 1,2,3-tribromopropane, 2,3-dibromopropane, 3-bromopropene, bromophenol. The results of this study are conducive to deepening the understanding of the evolution mechanism of TBBPA-DBPE during the thermal process and effectively controlling the emissions of harmful pollutants such as bromine-containing products.