Reductive Defluorination of Branched Per- and Polyfluoroalkyl Substances with Cobalt Complex Catalysts

Abstract

This study investigates structure−reactivity relationships within branched per-and polyfluoroalkyl substances (PFASs) undergoing cobalt-catalyzed reductive defluorination reactions. Experimental results and theoretical calculations reveal correlations among the extent of PFAS defluorination, the local C−F bonding environment, and calculated bond dissociation energies (BDEs). In general, BDEs increase in the following order: tertiary C−F bonds < secondary C−F bonds < primary C−F bonds. A tertiary C−F bond adjacent to three fluorinated carbons (or two fluorinated carbons and one carboxyl group) has a relatively low BDE that permits an initial defluorination to occur. Both a biogenic cobalt−corrin complex (B 12 ) and an artificial cobalt−porphyrin complex (Co-PP) are found to catalytically defluorinate multiple C−F bonds in selected PFASs. In general, Co-PP exhibits an initial rate of defluorination that is higher than that of B 12 . Neither complex induced significant defluorination in linear perfluorooctanoic acid (PFOA; no tertiary C−F bond) or a perfluoroalkyl ether carboxylic acid (tertiary C−F BDEs too high). These results open new lines of research, including (1) designing branched PFASs and cobalt complexes that promote complete defluorination of PFASs in natural and engineered systems and (2) evaluating potential impacts of branched PFASs in biological systems where B 12 is present.

Real-time degradation dynamics of hydrated per- and polyfluoroalkyl substances (PFASs) in the presence of excess electrons

“…This facile dissociation of secondary C-F bonds is due to their lower bond dissociation energy compared to the primary C-F bonds, as noted in a few earlier studies. 23,24 Contrary to the addition of a single electron, we find that the spin-density can evolve in two different ways with the addition of multiple electrons, as shown in the middle and bottom panels of figure 3. We refer to these different regimes as a trans-type (middle panel) or cis-type elimination (bottom panel) based on how the fluorine atoms have dissociated from the PFAS backbone structure.…”

“…For example, Liu et al have shown that fluorine atoms attached to a C=C bond (i.e., sp 2 carbon atoms) dissociate more readily compared to fluorine atoms attached to a C-C bond (sp 3 carbon atoms). 23 Since most of our simulations with excess electrons resulted in a trans-type elimination with the formation of a C=C bond (which is known to be more susceptible to defluorination), we infer that this trans-type intermediate plays a crucial role in PFAS defluorination, which could explain the PFAS degradation (with excess electrons) observed by Su et al 20 Apart from the trans-type intermediate, we also found that an HF molecule was formed during our simulations (see figure S5 and the Supplementary Information for further details).…”

Microbial Cleavage of C–F Bonds in Two C6 Per- and Polyfluorinated Compounds via Reductive Defluorination

“…where H* represents the enthalpy of formation. 8 DNA Extraction and Quantitative Polymerase Chain Reaction. Biomass from 0.5 mL of the culture was sampled from each biological replicate.…”

Interactive effects of changing stratospheric ozone and climate on tropospheric composition and air quality, and the consequences for human and ecosystem health

“…Reductive defluorination of long-chain perfluorinated compounds can be catalysed by natural and anthropogenic compounds containing cobalt. 190 This study did not report defluorination of TFA but the conditions for these reactions are unlikely to be found in the environment.…”