Experimental Determination of pK a for 10 PFAS, Mono‑, Di‑, and Trifluoroacetic Acid by 19F‑NMR
Accurate pK a values of per- and polyfluoroalkyl substances (PFAS) are urgently needed to improve predictions of their environmental fate, bioaccumulation, and removal, yet reliable experimental data remain scarce. Here, we determined the pK a values of 10 PFAS and three short-chain fluorinated acid...
| Authors: | , , , , , , |
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| Format: | article |
| Status: | Published version |
| Publication Date: | 2025 |
| Country: | España |
| Institution: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repository: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/400494 |
| Online Access: | http://hdl.handle.net/10261/400494 https://api.elsevier.com/content/abstract/scopus_id/105015481032 |
| Access Level: | Open access |
| Keyword: | Per-/polyfluoroalkyl substances COSMO-RS GenX PFOA PFOS Acid dissociation constant Fluorotelomers http://metadata.un.org/sdg/9 http://metadata.un.org/sdg/3 Ensure healthy lives and promote well-being for all at all ages Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation Ensure sustainable consumption and production patterns |
| Summary: | Accurate pK a values of per- and polyfluoroalkyl substances (PFAS) are urgently needed to improve predictions of their environmental fate, bioaccumulation, and removal, yet reliable experimental data remain scarce. Here, we determined the pK a values of 10 PFAS and three short-chain fluorinated acids (MFA: 2.58 ± 0.03; DFA: 1.22 ± 0.03, TFA: 0.03 ± 0.08) using 19F and 1H NMR-based chemical shift perturbation. Results were compared to prior experimental values, OPERA predictions (CompTox), and our COSMO-RS calculations. Measured pK a values include PFPrA (-0.18 to -0.54), PFOA (-0.27 ± 0.18), PFBS and PFOS (< -1.85), 6:2 FTS (<0.0), GenX (-0.20 ± 0.09), NFDHA (-0.32 ± 0.18), PFMPA (-0.26 ± 0.13), and 6:2 FTUCA (2.59 ± 0.11). Across C2, C3, and C8 homologues, PFCAs exhibit pK a values of approximately -0.2 to -0.3. Telomerization markedly reduces acidity: 5:3 FTCA (pK a = 4.05 ± 0.04) is >104-fold less acidic than PFOA, with COSMO-RS predicting similar effects from PFOS to 6:2 FTS. The dominant acidifying influence arises from CF2 groups at C1 and C2 near COOH or SO3H. The unusually low pK a values for TFA, PFOA, and GenX reflect our low-MeOH, sorption-resistant NMR method. COSMO-RS consistently outperformed OPERA, underscoring the need for experimental benchmarks to improve predictive models for emerging PFAS. |
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