Degradation of flame retardant tetrachlorobisphenol A by potassium permanganate: Kinetics, oxidation products and reaction pathways

Abstract:

The purpose of this article was to investigate the kinetics, oxidation products and reaction pathways for the degradation of flame retardant tetrachlorobisphenol A (TCBPA) by aqueous potassium permanganate. Experiments were conducted to examine the reaction kinetics of potassium permanganate with TCBPA under the condition with potassium permanganate in excess over a wide pH range, determine the brominated oxidation products and theorize the reaction pathways of TCBPA by aqueous potassium permanganate using liquid chromatography-triple quadrupole mass spectrometry (LC-MS/MS). The results showed that the degradation of TCBPA followed the second-order kinetics and the rate constants (40.1-981.7 L/(mol·s)) increased with the increase of pH and reached the maximum near the pK_a (7.5/8.5) of TCBPA, after which they decreased gradually. Four chlorinated oxidation products were detected by the precursor scan approach of liquid chromatography tandem mass spectrometry (LC-MS/MS-PIS), the oxidation products of m/z 219/221(Ⅰ), 201/203(Ⅱ), 379/381/383/385(Ⅲ&Ⅲ′), 523/525/527/529/531/533(Ⅳ), respectively. Reaction pathways mainly involves the initial one-electron oxidation of TCBPA to phenolic radical and subsequent release and further reactions of 2, 6-dibromo-4-isopropylphenol carbocation intermediate, leading to the formation of 4-(2-hydroxyisopropyl)-2, 6-dibromophenol and 4-isopropylene-2, 6-dibromophenol) as well as two polymeric products(Ⅲ&Ⅲ′and Ⅳ).