Mechanistic Insight into the Catalytic Electroreduction of Tetrabromobisphenol-a at Carbon Cathodes

Abstract

Polyhalogenated phenols are a class of environmental pollutants that serve as precursors to dioxins and behave as endocrine disruptors.1,2 As a result, an efficient route of degradation is needed. Traditional methods of remediation include microbial, thermal, and chemical pathways; however, these typically require large amounts of toxic solvents, excessive amounts of energy, and can be tremendously time-consuming.3 Electrochemistry has become a growing area of research for the remediation of environmentally-harmful compounds, as the electroreductive behavior of carbon–halogen bonds is well understood.Herein, we report the electrochemical reduction of the flame retardant 3,3',5,5'-tetrabromobisphenol-A (TBBPA), at carbon cathodes in the absence and presence of nickel(II) salen. Cyclic voltammograms at varying scan rates, coupled with voltammograms in the presence of a hydrogen-bonding stabilizer, suggest reduction proceeds by cleavage of a carbon–bromine bond, followed by reduction of a short-lived intermediate. Controlled-potential (bulk) electrolysis was performed to determine the extent of reduction that could be achieved; moreover, gas chromatography–mass spectrometry was utilized to separate and identify reduction products. Electrolyses performed in the presence of deuterium oxide and 1,1,1,3,3,3-hexafluoroisopropanol-OD reveal a carbanion intermediate present in the reduction mechanism. References M. Montaño, A. C. Gutleb, and A. J. Murk, Environ. Sci. Technol., 2013, 47, 6071–6081.C. D. Klaassen, Casarett & Doull’s Toxicology the Basic Science of Poisons, McGraw-Hill Education, 2013.E. T. Martin, C. M. McGuire, M. S. Mubarak and D. G. Peters, Chem. Rev., 2016, 116, 15198–15234.