Effects of Atmospheric Water on ·OH-initiated Oxidation of Organophosphate Flame Retardants: A DFT Investigation on TCPP

Abstract

Tris(2-chloroisopropyl) phosphate (TCPP), a widely used organophosphate flame retardant, has been recognized as an important atmospheric pollutant. It is notable that TCPP has potential for long-range atmospheric transport. However, its atmospheric fate is unknown, restricting its environmental risk assessment. Herein we performed quantum chemical calculations to investigate the atmospheric transformation mechanisms and kinetics of TCPP initiated by ·OH in the presence of O/NO/NO, and the effects of ubiquitous water on these reactions. Results show the H-abstraction pathways are the most favorable for the titled reaction. The calculated gaseous rate constant and lifetime at 298 K are 1.7 × 10 cmmolecule s and 1.7 h, respectively. However, when considering atmospheric water, the corresponding lifetime is about 0.5-20.2 days. This study reveals for the first time that water has a negative role in the ·OH-initiated degradation of TCPP by modifying the stabilities of prereactive complexes and transition states via forming hydrogen bonds, which unveils one underlying mechanism for the observed persistence of TCPP in the atmosphere. Water also influences secondary reaction pathways of selected TCPP radicals formed from the primary H-abstraction. These results demonstrate the importance of water in the evaluation of the atmospheric fate of newly synthesized chemicals and emerging pollutants.

Benchmarking of DFT functionals for the kinetics and mechanisms of atmospheric addition reactions of OH radicals with phenyl and substituted phenyl‐based organic pollutants

“…Density functional theory (DFT) methods represent a viable alternative for elucidating the kinetics and mechanisms of atmospheric chemistry processes, due to their excellent performance‐to‐cost ratio . Thus far, many functionals have been developed, each with merits and drawbacks.…”

Theoretical study on the atmospheric degradation mechanism and subsequent products of E,E‐2,4‐hexadienal with hydroxyl radical

“…For the loss pathways of peroxynitrate, it needs mentioning that Bai et al found that the peroxynitrate of CH 3 OC(CH 3 ) 2 CH 2 CH(OONO 2 )OH proceeded via self‐degradation to form CH 3 OC(CH 3 ) 2 CH 2 COOH and HNO 3 with high energy hydrogen transfer in gaseous and aqueous phase [37]. And it is worth noting that similar degradation process of peroxynitrate was observed by Li et al for the Tris(2‐chloroisopropyl) phosphate (TCPP) initiated reaction by ·OH in the presence of O 2 /NO/NO 2 [38].…”

Mechanism of methylphosphonic acid photo-degradation based on phosphate oxygen isotopes and density functional theory

“…It can be proposed that a series of reactions between phosphonate and other substances in the solution were induced by ultraviolet photons, and a nucleophilic substitution occurred with the generated radical O species and phosphonate. 49 The nucleophilic attack could be inuenced by the nature of the group adjacent to the C-P bond in phosphonate. The hydrolysis mechanism and the water incorporation pattern/slope for phosphate released from the phosphonate studied here differ markedly from those reported for the phosphomonoesters hydrolyzed by UVR in similar labeled water in the previous experiments.…”