A theoretical study on the pyrolysis of perfluorobutanoic acid as a model compound for perfluoroalkyl acids

The potential energy surface is mapped out for all plausible reactions in the self-decomposition of perfluorobutanoic acid (CF3CF2CF2COOH) as a model compound for the notoriously toxic and bio-accumulative perfluoroalkyl acids. Initial decomposition of perfluorobutanoic acid is found to be controlled by HF elimination and the formation of an α-lactone intermediate. The fate of this intermediate is predicted to be dominated by two competing channels, namely formation of pentafluoropropanoyl fluoride (CF3CF2COF) and the closed-shell singlet CF3CF2CF:. Direct elimination of CO2 through decarboxylation is found to be retarded by strong hyperconjugation effects induced by fluorine atoms on the carbon chain. The results presented herein provide insightful information towards a comprehensive understanding of the decomposition of perfluoroalkyl acids in thermal systems.