Electrochemical Oxidation of 6:2 Polyfluoroalkyl Phosphate Diester-Simulation of Transformation Pathways and Reaction Kinetics with Hydroxyl Radicals

Polyfluoroalkyl phosphate diesters (diPAPs) are widely used for paper and cardboard impregnation and discharged via waste streams from production processes and consumer products. To improve the knowledge about the environmental fate of diPAPs, electrochemical oxidation (EO) was used to characterize the transformation pathways and reaction kinetics. 6:2 diPAP was transformed electrochemically to perfluorocarboxylic acids (C-5-C-7 PFCAs) and two intermediates (6:2 fluorotelomer carboxylic acid, FTCA, and 6:2 fluorotelomer unsaturated carboxylic acid, FTUCA). EO of potential intermediates 6:2 monoPAP and 6:2 fluorotelomer alcohol (FTOH) showed similar transformation products but with different ratios. We show that 6:2 diPAP is initiated by OH radical (center dot OH) reactions, as evidenced by the measured steady-state concentrations of center dot OH with the probe molecule terephthalic acid, quenching experiments, and pH dependency of the reaction. PFHpA was the main product of 6:2 diPAP oxidation, and it was formed in a pseudo-first-order reaction for which a bimolecular rate constant was estimated to be k center dot(from PFHpA)(OH,diPAP) = 9.4(+/- 1.4) x 10(7) M-1 s(-1) by an initial rate approach. This can be utilized to estimate the environmental half-life of 6:2 diPAP for the reaction with center dot OH and the formation kinetics of persistent PFCAs.

Automated summary

The study demonstrates that Polyfluoroalkyl phosphate diesters can be transformed into perfluorocarboxylic acids and intermediates through electrochemical oxidation, mainly initiated by OH radicals, with PFHpA as the main product. This information can be used to estimate the environmental half-life of diPAPs and the formation kinetics of persistent PFCAs.