Single-pot mechanochemically-enabled fluorine atom closed-loop economy using PFASs as fluorinating agents

Domain: chemistry
Published: 2026-03-20
Editorial outcome: minor_revision

Abstract
Per- and polyfluoroalkyl substances (PFASs), also known as “forever chemicals”, pose an increasing threat to the environment and human health. Despite recent advancements in PFASs destruction, the recycling processes for such molecules remain limited to methods using high-temperatures or strong reducing agents. Sustainable degradation methods for PFASs, along with the subsequent utilization or recycling of the resulting fluorides, are indeed highly beneficial. In this study, we present a user-friendly, single-pot mechanochemical defluorination approach for fluorine transfer from PFASs to organic molecules. The high efficiency of this mechanochemical system obviates subsequent purification steps, requiring only minimal solvent filtration, even on a decagram scale. Furthermore, this strategy can be extended to the defluorination of everyday fluoroplastic and fluorinated polymers, such as PVDF membranes, pipes, and PTFE, thus addressing a critical challenge in sustainably breaking down persistent and environmentally harmful “forever chemicals”.

Introduction
Per- and polyfluoroalkyl substances (PFASs) have become indispensable within industries such as pharmaceuticals, electronics, energy storage, and materials1. Most notably, the structure of PFASs comprises of multiple strong C–F bonds, which means they have exceptional chemical stability, high-temperature resistance, low surface energy, and corrosion resistance2–5. However, these properties, which make them advantageous in their quotidian use, also mean that effective strategies to recycle PFASs are limited. This has then led to their widespread accumulation in water sources, soil, and within organisms, thus causing PFASs to earn the notorious label of “forever chemicals” (Fig. 1a)6–9. All of this leads to an increased risk to the ecosystems and to human health10–19.

Several strategies have been explored to date for the degradation of PFASs, including photochemical20,21, catalytic22–24, and electrochemical decomposition (Fig. 1b)25–28. Kang29 and Miyake30 recently made significant advances in novel photocatalytic degradations of PFASs to combat this crisis. Both employed photoreductants to efficiently defluorinate and degrade a wide range of PFASs. Although studies have been conducted in this field, significant challenges do indeed persist. This includes the difficulty in defluorinating more inert polymers and the high costs associated with the use of additives, solvents, electrolytes, and, importantly, the inefficient recovery of fluorine sources. Since fluorine is an important resource within organic chemistry, to be able to recycle it is a major driving force to finding ways to do so efficiently and sustainably31–33. Mechanochemical degradation (MCD) has shown great promise for polymer recycling and degradation34–40. However, its application to the defluorination of polymeric PFASs has thus far proven elusive41. We propose using MCD to efficiently cleave C–F bonds42–44 and form new bonds45, while also circumventing the challenges associated with the poor solubility of polymeric PFASs, such as polytetrafluoroethylene (PTFE) and polyvinylidenedifluoride (PVDF).

Herein, we present a user friendly, “one-pot” approach using solely a single base in conjunction with MCD to address fluorine atom closed-loop economy via a defluorination–fluorination process (Fig. 1c). This strategy can transform a range of PFASs, including widely used fluoroplastics such as PTFE, ETFE, and fluorinated ethylenepropylene (FEP), to synthetically valuable sulfonyl fluorides as Sulfur(VI) Fluoride Exchange hubs (SuFEx hubs). These remarkably stable SuFEx hubs have excellent selectivity and are therefore central to the Nobel prize-winning SuFEx click chemistry46,47. This strategy reduces cost, waste, and energy consumption by eliminating the use of high temperatures, expensive catalysts and hazardous fluorinating agents. Additionally, our approach is scalable, allowing for the reaction to be upscaled to a 10 g scale, proving efficient for large-scale waste management. During the preparation of this manuscript, Gouverneur and Shibata published studies on the mechanochemical degradation of PFASs, enabling the isolation of fluorinating agents48,49. Nonetheless, compared to these approaches, our strategy has distinct advantages, as it enables both the PFASs defluorination and subsequent synthesis of high-value SuFEx precursors, in an operationally simple “single-pot” reaction without pre/post-drying of the PFAS or subsequent fluorine mixture, or column separation steps. This compares favorably to the three-step distinct steps required in the prior state-of-the-art.

Results
Reaction development
The aim of this strategy was to degrade and defluorinate PVDF, and to then directly perform nucleophilic fluorination in the same flask. As shown in Table 1, the ball milling was conducted in a 5 mL 304 stainless-steel jar, using a stainless-steel ball with a diameter of 7 mm. PVDF was subjected to ball milling in the presence of tBuOK at 30 Hz for 100 minutes (B1) to defluorinate the polymer. Tosyl chloride (1) was then introduced to this mixture, and the flask was placed back into the ball mill for an additional 100 min (B2). Under these conditions, only a simple filtration using CHCl3 was required to obtain pure product 2 in 95% yield (Table 1, entry 1). To investigate the necessity of the base for the defluorination of PVDF, the reaction was probed without tBuOK, which resulted in no formation of the fluoride product (entry 2). The choice of the base significantly impacted the fluorination reaction. Inorganic bases, such as K3PO4 and Cs2CO3, resulted in moderate yields of product 2 (entries 3 and 4). However, K2HPO4, KOH and Ca(OH)2 gave much lower yields (entries 3, 5 and 6). For the latter two bases, substantial aggregation of the material inside the jar after the initial ball milling was observed. This observation was suggestive of a possible formation of H2O from the base, thus hindering the movement of the stainless-steel ball and limiting the efficacy of the milling process.

Nucleophilic fluorinating reagents are not only limited to inorganic reagents50. Therefore, and to explore whether this method could be extended to organic bases, pyridine was trialed. In this case, the fluorination was ineffective, giving less than 5% yield of product 2 (entry 7). In addition, the reaction proceeded well with a larger 10 mm stainless-steel ball and a ZrO2 ball, giving 94% and 95% yields, respectively (entries 8 and 9). Reducing the ball milling frequency gave inferior results (entry 10), and reducing the milling time for both B1 and B2 to 45 minutes slightly diminished the yield (entry 11). It is noteworthy that using conventional reaction conditions, i.e., in a round-bottomed flask (RBF) in MeCN, only 5% of the fluorination product 2 was generated. This is presumably due to the low solubility of the polymer and fluoride ion in this solvent, highlighting the advantages of MCD (entry 12).

Evaluation of substrate scope
With the optimized conditions for the fluorination of substrate 1 in hand, the robustness of the reaction was explored (Fig. 2). This sequential MCD and fluorination method showed excellent functional group tolerance (Fig. 2a). Starting with phenylsulfonyl chlorides with various substituents, ranging from electron-donating groups such as tert-butyl (4), methoxy (5), and phenyl groups (6) to electron-withdrawing halogens (7–9) and nitro groups (10) at different substitution positions provided excellent to near quantitative yields (90–98%). Furthermore, phenylsulfonyl chlorides containing multiple substituents were examined, including sterically hindered 2,4,6-tri-isopropyl-(11) and 2,4,6-trichloro-phenylsulfonyl chlorides (12), which achieved yields of 92% and 95%, respectively. In addition, naphthylsulfonyl chloride (13) gave a yield of 96%, and (E)-2-phenyl-ethenesulfonyl chloride (14) gave a yield of 90%.

Importantly, this mechanochemical fluorination demonstrated a broad tolerance for heterocyclic sulfonyl chlorides (15–18), with yields ranging from 73% to 91%. Notably, this method was also applicable to simple alkyl sulfonyl chlorides, such as n-dodecyl (19), methyl (20), L-(-)-10-camphorsulfonyl chloride (21), and cyclopropane sulfonyl chloride (22). Next, a variety of PFASs were evaluated. As shown in Fig. 2b, PVDF with different molecular weights were first investigated (23–26) using substrate 1, all of which worked efficiently under otherwise identical conditions. This strategy also proved applicable to copolymers, with poly(vinylidene fluoride-hexafluoropropylene) (27) yielding product 2 with a 96% yield. It is noteworthy that the piezoelectric materials poly(vinylidene fluoride-trifluoroethylene) and poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (28, 29) were also suitable for this reaction. In addition, defluorination of ethylene tetrafluoroethylene (30) gave product 2 with a 90% yield. Interestingly, by changing the material and size of the ball mill flask to a 30 mL ZrO2 flask, and using a slightly bigger 15 mm ZrO2 ball, stubborn fluoroplastics and low molecular weight (Mw) PFASs could be defluorinated. The MCD of fluorinated ethylene propylene (31) generated product 2 with a 78% yield. Gratifyingly, polytetrafluoroethylene (32) (PTFE), which is extremely chemically and biologically inert, could also be defluorinated successfully, achieving a yield of 88% for the desired fluorinated product (Fig. 2c). Finally, with low Mw PFASs, including perfluorinated heptanoic acid (33), sulfonyl fluoride (34), alkyl alcohol (35), olefin (36), and perfluorooctane (37), were all compatible with our mechanochemical fluorination giving yields ranging from 51% to 77% (Fig. 2d).

Investigation of defluorination
Further investigation into the composition of the fluoride mixture after ball milling was also conducted. Using the two bases that were shown to give the high yields with PVDF for the fluorination of substrate 1, the generation of fluoride over time was measured using 19F-NMR, with a control experiment conducted in the absence of a base (Fig. 3a). The control exhibited no fluoride release, confirming the inherent stability of PVDF under neutral conditions. In contrast, both bases facilitated degradation, showing around 10–20% fluorine release after only 5–10 min of ball milling. Notably, the extent of defluorination increased over time, with tBuOK showing the highest fluoride release, suggesting a sustained and progressive defluorination process to a certain point. The differences in defluorination could stem from variations in base strength and nucleophilicity. The 19F-NMR spectrum of the PVDF and PTFE mixture in D2O was measured after ball milling (Fig. 3b). In both cases, aqueous fluoride formation was observed with yields of 35% and 28%, respectively, as confirmed by comparison with KF (Fig. 3b-bottom). This demonstrates that this method indeed generates aqueous fluoride from both proton-containing and non-proton containing PFASs. To confirm the role of tBuOK brand variability, four different commercial sources were tested (Fig. 3c.), revealing no significant differences in fluoride yield of TsF (2) yield. These results further prove the robustness of this strategy. Furthermore, switching from 7 mm to 10 mm stainless steel milling balls and increasing the tBuOK equivalents enabled near-complete PVDF defluorination, achieving a 93% yield of fluoride (Fig. 3e.).

Infrared spectroscopy of the polymer residue after 100 minutes of ball milling provided further evidence for the degradation pathway of PVDF (Fig. 3d). The FTIR spectrum of the residue after ball milling with tBuOK revealed the emergence of a new C=C bond stretching peak at approximately 1600 cm−1. This was consistent with the possible defluorination of PVDF via proton abstraction aided by the base. Notably, there was a significant reduction in intensity of the original PVDF vibrational peaks, which was indicative of a substantial polymer backbone modification. Surprisingly, the formation of a C≡C bond stretch peak was not observed, suggesting that the dehydro-fluorination occurred up to a certain point. With this evidence in hand, the mechanism of defluorination of PVDF could be hypothesized (Fig. 4). This includes the deprotonation of PVDF, which then eliminates F-, generating dehydrofluorinated PVDF (dPVDF) and KF. The further degradation of dPVDF is most likely much harder than the initial elimination, and may not be occurring via the same mechanism, hence why there is a plateau for the generation of fluoride. However, the mechanism of degradation for PTFE is most likely not going through the same path as the proposed mechanism for PVDF due to the lack of protons in the polymeric PFASs.

To gain more insight into the possible degradation pathway of PTFE, NMR studies were performed on the residual powder after ball milling. These were carried out in order to identify any small molecules formed via C–C bond cleavage, which were shown to occur for other methods of PTFE degradation29. Results from the 1H- and 13C-NMR spectra for the polymeric PFASs were inconclusive, due to the formation of an insoluble black residue upon completion. This visual transformation is characteristic of the formation of amorphous carbon (char). To gain further mechanistic insight, the 13C-NMR of the mixture obtained from the ball milling of perfluorooctane with tBuOK was performed. This showed trace formation of oxalate (174.2 ppm), formate (171.7 ppm) and carbonate (169.1 ppm) within the sample (Fig. 3f). This confirms that a portion of the carbon content for perfluorooctane undergoes oxidative mineralization to small, water-soluble anions. This could give an indication of the mechanism of degradation for PFASs with no protons, which could proceed through a radical pathway, whereby there is defluorination and consequent C–C bond cleavage51–53. However, the pathway involving an SN2 type defluorination cannot be ruled out, where there is direct fluoride displacement and base mediated bond scission48.

Transformation and application
PFASs are ubiquitous in daily life and are seen in many everyday products, thus, they are often discarded after a single use, contributing to environmental pollution. To evaluate the practicality of our MCD method, we tested the defluorination reaction on various PFASs-containing waste materials commonly encountered in daily life (Fig. 5a). These included items such as filter membranes (38, 40, 44), tubing (42, 45) and sensor materials (39). Notably, these PFASs substrates achieved nearly quantitative yields in the fluorination of TsCl, generating TsF (2) without requiring chromatographic purification.

Crucially, the method proved highly scalable, maintaining efficiency even at the 10g scale (Fig. 5b). This scale-up was achieved using two parallel jars and required only 1.3 equivalents of PVDF and base, with no compromise in the yield or purity of the TsF product (2). A mixed waste stream containing 1 gram of blended PVDF-derived waste (38–45) was also successfully processed, producing 940 mg of TsF (2) (90% yield). The products from both large-scale reactions were isolated simply via filtration using a minimal amount solvent, highlighting our method’s industrial viability and sustainability. Sulfonyl fluorides constitute the core electrophiles of SuFEx chemistry, one of the next-generation click reactions pioneered by Sharpless and coworkers. Such reactions have been recognized by the 2022 Nobel Prize in Chemistry for its robust, modular, and biocompatible bond-forming potential46,47,54,55. Given the importance of sulfonyl fluorides in SuFEx click chemistry, the reactivity of the synthesized TsF (2) was explored through a series of late-stage SuFEx transformations (Fig. 5c). The formation of an S–C bond was demonstrated by coupling 2 with a fluorescent aromatic substrate, affording compound 46 in excellent yield. Starting from Melatonin, tosylation of the pyrrole nitrogen yielded the N–S bonded product 47 in 85% yield. A range of alcohols were also subjected to SuFEx reactions with TsF (2). The tosylation of the hydroxyl group in diacetone-d-glucose afforded the sulfonate ester 48 in 72% yield. Similarly, the reaction with the antimalarial drug Quinidine afforded compound 49 in 67 % yield. The SuFEx-mediated tosylation of δ-tocopherol (form of vitamin E) afforded the tosylated product 50 in an excellent 91% yield. Finally, the reaction with the natural steroid, Diosgenin, yielded the tosylated product 51 in 62% yield. These transformations showcase the broad synthetic utility of the generated TsF (2) in generating valuable sulfonyl derivatives across multiple classes of compounds. By demonstrating that fluorine atoms can be reclaimed from plastic waste and upcycled into functional SO2F motifs, our method not only addresses a pressing environmental challenge but also provides direct access to click-enabled materials, expanding the synthetic utility of SuFEx chemistry.

To conclude, we have developed a sustainable and operationally simple single-pot mechanochemical defluorination of PFASs, including highly inert fluoropolymers such as PVDF and PTFE. This user-friendly method requires a base and a ball mill, and enables the direct transfer of fluorine atoms from PFASs to synthetically valuable sulfonyl fluorides, without the need for harsh reagents, high temperatures or extensive purification. The reaction is scalable, waste-tolerant and compatible with a wide variety of PFASs ranging from low Mw PFASs to consumer waste materials. Crucially, this method provides direct access to a SuFEx hub in high yields, offering a valuable route towards a closed-loop fluorine economy. This work also addresses the challenge in recycling these “forever chemicals”, thus, bringing together environmental remediation with synthetic utility7.

Methods
General procedure for mechanochemical defluorination of PFASs
Ball milling reactions were performed under air. The reagents were used without pre-purification or drying. To a 5 mL Reich stainless-steel milling jar equipped with a PTFE sealing ring was added a 7 mm stainless-steel ball, PFASs (1.5 equiv.), and tBuOK (1.5 equiv.). The jar was tightly sealed, mounted on the shaker mill, and milled at 30 Hz for a milling cycle (B1). Upon completion of B1, the jar was opened, and sulfonyl chloride (1.0 equiv.) was added to the resulting black mixture. The jar was then resealed and subjected to a second milling cycle (B2). After completion of B2, 3 mL of CHCl3 was added to wash the black solid. The mixture was filtered through a small pad of celite®, and the reaction vessel was subsequently rinsed with an additional 2 × 3 mL of CHCl3, followed by a second filtration. The combined filtrates were concentrated under reduced pressure and dried under vacuum to afford the pure target product without the need for further purification. The substrates were either purchased directly from commercial suppliers or prepared according to previously reported procedures (see supplementary information). All other reagents and solvents used in this study were purchased from commercial sources and used as received.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Long and coworkers describe a mechanochemical strategy employing KOtBu as a base for the defluorination of fluorinated polymers and other PFASs. The method is noteworthy for its capacity to synthesize high-value SuFEx precursors in a single pot with high yield and minimal postprocessing. Nonetheless, several technical and interpretive issues should be addressed prior to publication.\n1.The substrates 31 and 34–36 are labeled with subscript “b.” According to the figure legend, this subscript indicates PVDF. This annotation appears inconsistent with the described chemical structures and should be clarified.\n2.A mechanistic explanation should be provided to rationalize why K₃PO₄ yields superior results compared with tBuOK, despite tBuOK being both a stronger base and nucleophile. Discussion in the context of Gouverneur’s system would improve clarity.\n3.The dosage of the internal standard (HFIP) or the exact formula used for calculating the fluorine yield should be included. The fluorine yield in Figure 3c must be explicitly reported. In Figure S8, if the integral “0.37” corresponds to 0.37 mmol fluoride using 0.3 mmol tBuOK, the source of the additional 0.07 mmol should be clarified. Additionally, the relative peak intensities at 122.4 ppm in Figures S8 and S9 are inconsistent with the stated integrals; this discrepancy should be examined.\n4. The reason for lower yields with low–molecular-weight PFASs (particularly 35 and 37) should be discussed. Possible factors include volatility, low melting point, or inherent difficulty of defluorination.\n5.The brand and quality of tBuOK, should be specified. Since results may vary among suppliers, testing tBuOK from different manufacturers is recommended to ensure reproducibility.\n6.For PFAS-containing waste materials, it should be verified whether additives or dyes (especially in black plastic pipes) affect the purity of TsF when only CHCl₃ extraction is used. 1H NMR spectra should be provided to confirm product identity and purity.\n7.The destination of the remaining fluorinated polymeric residue should be considered. Discussion should include whether such material poses environmental risks.\n8.Since generating TsF from PVDF and KOtBu is costlier than direct methods (e.g., using KF), this limitation should be acknowledged.\n9.It is recommended to report the defluorination yield relative to the total fluorine content of the polymer, rather than only the yield of the small-molecule product. If possible, the authors should provide an example demonstrating complete defluorination, for example using excess potasium base, to illustrate that no partially fluorinated polymeric byproducts are formed, thereby avoiding potential new environmental concerns.", "reviewer_2": "This is an interesting study on the mechanochemical degradation of PFAS polymers. The resulting fluorides are subsequently used for fluorination to obtain sulfonyl fluorides, which are SuFEx precursors. The manuscript should not be published in Nature communications. I suggest publication in a specialized journal.\nRecently, two articles with very similar content were published recently by Shibata and Gouverneur (Ref 48,49). They essentially describe analogous results. In both papers PFAS polymers were defluorinated mechanochemically and the obtained fluorides were used for fluorination. The formation of sulfonyl fluorides and other S(VI) compounds was also described. Additionally, in the paper by Shibata the same strategy was used for defluorination, e.g. addition of tBuOK to the ball milling process to give KF.\nMechanistically the paper by Ackermann and coworkers suggests for the PVDF degradation the same pathways as published before. There are no conclusive mechanistic studies for the PTFE defluorination and the authors suggest “a radical pathway”, which, however, should be further investigated, for instance by trapping experiments. It is not clear what happens to the carbon content of the polymers. The authors mention the formation of “traces of oxalate, formate and carbonate”, but they did not study this further. This should be done."}, "author_response": "Comment 1.: The substrates 31 and 34–36 are labelled with subscript “b.” According to the figure legend, this subscript indicates PVDF. This annotation appears inconsistent with the described chemical structures and should be clarified.\nResponse: We thank the reviewer for the comment and suggestion. The figure legend has now been changed accordingly.\nComment 2.: A mechanistic explanation should be provided to rationalize why K₃PO₄ yields superior results compared with tBuOK, despite tBuOK being both a stronger base and nucleophile. Discussion in the context of Gouverneur’s system would improve clarity.\nResponse: We thank the reviewer for this comment. In our case, tBuOK yields superior results than with K PO . As we envisioned the development of a user-friendly approach to defluorination/fluorination, neither our base nor the PFAS used were pre-treated. The Gouverneur group disclosed that anhydrous K PO was necessary to achieve high defluorination yields, which accounts for why it is not working as well in our system. Additionally, the fluorination using K PO in our strategy yielded 49% of TsF (Table 1 entry 3 in the main text), which we believe is due to the lower nucleophilicity of the PFAS/base mixture generated in B1, in comparison to our tbuOK/PFAS mixture.\nComment 3.: The dosage of the internal standard (HFIP) or the exact formula used for calculating the fluorine yield should be included. The fluorine yield in Figure 3c must be explicitly reported. In Figure S8, if the integral “0.37” corresponds to 0.37 mmol fluoride using 0.3 mmol tBuOK, the source of the additional 0.07 mmol should be clarified. Additionally, the relative peak intensities at 122.4 ppm in Figures S8 and S9 are inconsistent with the stated integrals; this discrepancy should be examined.\nResponse: We thank the reviewer for this comment. For the fluoride yield 10 µL of HFIP is used as an internal standard. The internal standard is always integrated for 1. The formulas used are as follows:\nFor HFIP as an internal standard:\n𝐼𝐼𝐼𝐼𝑐𝑐𝑀𝑀𝐼𝐼𝑝𝑝𝐼𝐼𝑀𝑀 𝑀𝑀𝑜𝑜 𝑃𝑃𝑝𝑝𝑀𝑀𝑝𝑝𝑢𝑢𝑐𝑐𝑐𝑐\n𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 𝑀𝑀𝑜𝑜 𝑝𝑝𝑝𝑝𝑀𝑀𝑝𝑝𝑢𝑢𝑐𝑐𝑐𝑐 =  × 𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 𝑀𝑀𝑜𝑜 𝐼𝐼𝐼𝐼𝑐𝑐𝑀𝑀𝑝𝑝𝐼𝐼𝐼𝐼𝑀𝑀 𝑀𝑀𝑐𝑐𝐼𝐼𝐼𝐼𝑝𝑝𝐼𝐼𝑝𝑝𝑝𝑝\n(𝐼𝐼𝐼𝐼𝑐𝑐𝑀𝑀𝐼𝐼𝑝𝑝𝐼𝐼𝑀𝑀 𝑀𝑀𝑜𝑜 𝐼𝐼𝐼𝐼𝑐𝑐𝑀𝑀𝑝𝑝𝐼𝐼𝐼𝐼𝑀𝑀 𝑀𝑀 𝑐𝑐𝐼𝐼𝐼𝐼𝑝𝑝𝐼𝐼𝑝𝑝𝑝𝑝)/6\n𝑚𝑚𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 𝑀𝑀𝑜𝑜 𝑝𝑝𝑝𝑝𝑀𝑀𝑝𝑝𝑢𝑢𝑐𝑐𝑐𝑐\n × 100\n𝑀𝑀𝑌𝑌𝑚𝑚𝑌𝑌𝑐𝑐𝑌𝑌𝐼𝐼𝐼𝐼 𝑝𝑝𝑀𝑀𝐼𝐼𝐼𝐼𝑀𝑀𝐼𝐼𝑐𝑐 𝑚𝑚𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀\n𝑌𝑌𝑌𝑌𝑀𝑀𝑀𝑀𝑝𝑝 𝑀𝑀𝑜𝑜 𝑜𝑜𝑀𝑀𝑢𝑢𝑀𝑀𝑝𝑝𝑌𝑌𝐼𝐼𝑀𝑀 =\n𝐼𝐼𝑢𝑢𝑚𝑚𝑛𝑛𝑀𝑀𝑝𝑝 𝑀𝑀𝑜𝑜 𝑜𝑜𝑀𝑀𝑢𝑢𝑀𝑀𝑝𝑝𝑌𝑌𝐼𝐼𝑀𝑀𝑀𝑀 𝑌𝑌𝐼𝐼 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃\nFor example, for Figure S8, the moles of product are\n0.37\n𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 𝑀𝑀𝑜𝑜 𝑝𝑝𝑝𝑝𝑀𝑀𝑝𝑝𝑢𝑢𝑐𝑐𝑐𝑐 =  × 0.0095=0.2109 𝑚𝑚𝑚𝑚𝑀𝑀𝑀𝑀\nThus, 1/6\n0.2109\n × 100\n0.3\n𝑌𝑌𝑌𝑌𝑀𝑀𝑀𝑀𝑝𝑝 𝑀𝑀𝑜𝑜 𝑜𝑜𝑀𝑀𝑢𝑢𝑀𝑀𝑝𝑝𝑌𝑌𝐼𝐼𝑀𝑀 = =35.15 %\nThe formula for the fluorine yiel2d determination was added to the revised Supporting Information (page S3). As suggested, a discussion regarding the yield in the now Figure 3b was added to the revised manuscript as follows:\n“The 19F-NMR in D O of the PVDF and PTFE mixture was measured after ball milling (Fig. 3b). In both cases, the formation of aqueous fluoride was observed with a yield of 35 % and 28 %, respectively, and was confirmed by comparison with KF (Fig. 3b-bottom).”\nIn terms of the intensities of the peaks, this is most likely to do with the dilution/concentration of the sample taken for the 19F-NMR.\nComment 4.: The reason for lower yields with low-molecular-weight PFASs (particularly 35 and 37) should be discussed. Possible factors include volatility, low melting point, or inherent difficulty of defluorination.\nResponse: We thank the reviewer for this comment. The diminished efficiency observed for low molecular weight PFASs most likely arises from multiple related factors, including low volatility or low melting points, and the resistance of certain low molecular weight PFAS to defluorination. Additionally, the C-F bonds may be less accessible in comparison to the solid polymeric PFASs. For example, the milling mixture for liquid low molecular weight PFASs (e.g. PFOS, perfluorooctane) not being homogeneous and therefore does not mix as efficiently.\nComment 5.: The brand and quality of tBuOK, should be specified. Since results may vary among suppliers, testing tBuOK from different manufacturers is recommended to ensure reproducibility.\nResponse: We thank the reviewer for this suggestion. The brand of tBuOK used throughout the manuscript is from TCI. We have since trialed the defluorination of PVDF with tBuOK from four different suppliers (Figure 3). There is no significant difference between each brand of bases. The results were as shown:\nEntry tBuOK from different manufacturers/batches Fluoride yield(%)b\n1 97% pure, TCI, P1008 38%\n2 98% pure, Thermo Fisher, 168881000 (25g) 43%\n3 98% pure, Thermo Fisher, 168885000 (500g) 39%\n4 98% pure, Sigma-Aldrich, 156671 43%\nIn addition, ICP-MS analysis of the tBuOK was performed for each brand in order to verify their respective composition. This analysis showed no significant amount of metals in each sample of the base. After ball milling in the stainless steel 5mL jar with a 7mm stainless steel ball for 100 minutes at 30 Hz, there is, as expected, an increase of certain metals, in this case mostly iron. These results have since been added to the Supporting Information (page S12).\nComment 6.: For PFAS-containing waste materials, it should be verified whether additives or dyes (especially in black plastic pipes) affect the purity of TsF when only CHCl₃ extraction is used. 1H NMR spectra should be provided to confirm product identity and purity.\nResponse: We thank the reviewer for this comment. For all PFAS-containing waste materials the purity of the TsF is >95 % when only CHCl is used, where only the tBuOH from the base is seen in the crude NMR, which is removed under vacuum when drying the TsF. The crude NMR spectra for each reaction (Figure 5, 38-45) were added to the revised Supporting Information.\nComment 7.: The destination of the remaining fluorinated polymeric residue should be considered. Discussion should include whether such material poses environmental risks.\nResponse: We thank the reviewer for highlighting this aspect. All remaining fluorinated PFAS residue was disposed of through standard laboratory hazardous waste protocols at our institution, in full compliance with German laboratory safety regulations (TRGS 526) and EU waste handling guidelines. These protocols ensure proper segregation, collection by certified waste services, and thermal treatment to prevent any environmental leaching or waterway contamination. This, therefore, eliminates the environmental risks from residual materials. We have added a statement confirming these procedures to the Experimental Section (Supporting Information page S3).\nComment 8.: Since generating TsF from PVDF and KOtBu is costlier than direct methods (e.g., using KF), this limitation should be acknowledged.\nResponse: We thank the reviewer for this important point. The generation of TsF from PVDF in the presence of tBuOK involves more steps compared to direct fluorination approached using KF, which may make it slightly costlier. However, the primary aim of our developed strategy is to establish the use of waste PFAS materials, which are environmentally persistent and harmful “forever chemicals”, as a sustainable fluorine source. Our approach valorizes problematic PFAS waste by converting it into valuable organic fluorinated compounds, addressing urgent environmental and health concerns by both degrading persistent pollutants and recycling their fluorine content.\nComment 9.: It is recommended to report the defluorination yield relative to the total fluorine content of the polymer, rather than only the yield of the small-molecule product. If possible, the authors should provide an example demonstrating complete defluorination, for example, using excess potassium base, to illustrate that no partially fluorinated polymeric byproducts are formed, thereby avoiding potential new environmental concerns.\nResponse: We thank the reviewer for this comment and suggestion. We explored various reaction conditions to completely defluorinate PVDF. Thus, we were able to show near complete defluorination by running the ball mill firstly with two equivalents of tBuOK for 100 minutes using a larger 10mm stainless steel milling ball, followed by the addition of another 2 equivalents of tBuOK for another 100 minutes of ball milling, yielding 93 % of fluorine. These results were added to the revised Supporting Information (page S15) and manuscript (figure 3).\nIn this context, an updated discussion was added to the revised manuscript as follows:\n“Furthermore, switching from 7 mm to 10 mm stainless steel milling balls and increasing the tBuOK equivalents enabled near-complete PVDF defluorination, achieving a 93% yield of fluoride (Fig 3e.).”\nReviewer #2 This is an interesting study on the mechanochemical degradation of PFAS polymers. The resulting fluorides are subsequently used for fluorination to obtain sulfonyl fluorides, which are SuFEx precursors. The manuscript should not be published in Nature communications. I suggest publication in a specialized journal.\nComment 1: Recently, two articles with very similar content were published recently by Shibata and Gouverneur (Ref 48,49). They essentially describe analogous results. In both papers PFAS polymers were defluorinated mechanochemically and the obtained fluorides were used for fluorination. The formation of sulfonyl fluorides and other S(VI) compounds was also described. Additionally, in the paper by Shibata the same strategy was used for defluorination, e.g. addition of tBuOK to the ball milling process to give KF.\nResponse: We thank the reviewer for highlighting these important recent studies by Shibata and Gouverneur. Our preprint was publicly available on ChemRxiv prior to the Shibata publication (10.26434/chemrxiv-2025-02hh7), establishing the independent development of this approach. Nonetheless, we fully acknowledge both contributions and consider our work complementary. Our developed strategy differs from these reports in operational simplicity, product focus, and mechanistic insights, as summarized in the table below.\nFirst, our approach operates under markedly simpler conditions: both tBuOK and the PFAS substrates are used directly as received, without any pre-drying or pre-purification. Second, our approach uniquely delivers high-value sulfonyl fluorides (SuFEx hubs) in a true one-pot fashion, directly coupling PFAS defluorination with synthetically useful fluorination in a single operational sequence. Finally, our mechanistic analysis supports both an elimination and nucleophilic (S 2-type) pathway under tBuOK-mediated mechanochemical conditions, whereas the Gouverneur study is consistent with a purely S 2 pathway and the Shibata group with a dehydrofluorination-type mechanism. We have clarified these distinctions in the revised manuscript and hope this makes the complementary nature of our contribution more apparent.\nComment 2: Mechanistically the paper by Ackermann and coworkers suggests for the PVDF degradation the same pathways as published before. There are no conclusive mechanistic studies for the PTFE defluorination and the authors suggest “a radical pathway”, which, however, should be further investigated, for instance by trapping experiments.\nResponse: We thank the reviewer for this comment. We have since changed the manuscript regarding the ‘radical pathway’. The evidence for the radical pathway for low molecular weight PFASs is currently still ongoing within the lab. However, we believe that the defluorination of PTFE and perfluorooctane under our conditions ball milling with tBuOK, likely proceeds through either a base-mediated elimination, S 2 pathway combined with possible radical formation. This supports why our strategy presents a broad substrate scope for different types of PFASs.\nS 2 pathway: The Gouverneur group demonstrated that phosphate-mediated PTFE degradation proceeds via an S 2 mechanism, which they calculated via DFT (Nature 2025, 640, 100–106). The strong nucleophilicity and basicity of tBuOK in our system mean that it is equally, or more capable of nucleophilic attack of the C–F bonds in PTFE, perfluorooctane, and other similar PFASs. This can enable direct fluoride displacement, and base mediates C–C bond scission.\nBall milling is well-known to induce C–C bond cleavage in polymers, generating reactive macroradicals (Briš et al., Green Chem. 2025, 27, 11345–11382). Critically, this can be achieved using both stainless-steel and ZrO milling flasks and balls. Furthermore, for our strategy, we were able to identify the formation of carbonates, formates, and oxalates from the ball milling of perfluorooctane, which is similar to the work from Kang (Nature 2024, 635, 610–617) who suggested a similar radical-mediated carbon backbone fragmentation.\nIn this context, we included a discussion in the revised manuscript as follows:\n“To gain more insight into the possible degradation pathway of PTFE, NMR studies were performed on the residual powder after ball milling. This was done to identify any small molecules formed via C–C bond cleavage which has been shown to occur for other methods of PTFE degradation.29 Results from the 1H- and 13C-NMR spectra for the polymeric PFASs were inconclusive, due to the formation of an insoluble black residue upon completion. This visual transformation is characteristic of the formation of amorphous carbon (char). To gain further mechanistic insight, the 13C-NMR of the mixture obtained from the ball milling of perfluorooctane with tBuOK was performed. This showed trace formation of oxalate (174.2 ppm), formate (171.7 ppm), and carbonate (169.1 ppm) within the sample (Fig. 3f). This confirms that a portion of the carbon content for perfluorooctane undergoes oxidative mineralization to small, water-soluble anions. This could give an indication as for the mechanism of degradation for PFASs with no protons, which could proceed through a radical pathway, whereby there is defluorination and consequent C–C bond cleavage.51-53 However, the pathway involving an S 2 type defluorination cannot be ruled out, where there is direct fluoride displacement and base mediated bond scission.48”\nComment 3: It is not clear what happens to the carbon content of the polymers. The authors mention the formation of “traces of oxalate, formate, and carbonate”, but they did not study this further. This should be done.\nResponse: We thank the reviewer for this comment regarding the fate of the carbon content. As discussed in the manuscript (and shown in Figure 3d), the degradation of the model substrate perfluorooctane yields soluble mineralized species, specifically formate, oxalate, and carbonate, which we identified via 13C-NMR.\nFor the polymeric PFASs (PVDF/PTFE), we observed the formation of a significant amount of an insoluble black solid during the reaction. This is characteristic of the formation of amorphous carbon/char, which is frequently observed in mechanochemical and photocatalytic defluorination (e.g., Shibata, Nature 2024, 635, 610; Nature 2025 640, 100–106), and the presence of remaining partially- and completely defluorinated polymers. In this regard, we have now updated the discussion in the \"Investigation of Defluorination\" section as follows:\n“To gain more insight into the possible degradation pathway of PTFE, NMR studies were performed on the residual powder after ball milling. These were carried out in order to identify any small molecules formed via C–C bond cleavage, which were shown to occur for other methods of PTFE degradation.29 Results from the 1H- and 13C-NMR spectra for the polymeric PFASs were inconclusive, due to the formation of an insoluble black residue upon completion.”"}, {"round": 2, "reviewer_comments": {"reviewer_1": "This manuscript has been well revised. Although the authors have made significant efforts to address some of the comments by the authors, there is one improvement necessary for publication.\n- On Page 6, Line 111, the author described that 0.3 mmol of PFAS was applied. However, the amount for some substrates seems incorrect. For example, on Page 29 of the SI, 40 mg of PTFE was used, which corresponds to 0.4 mmol when C₂F₄ is considered as the structural unit. The author should check this carefully. It would be helpful if the author could provide the yield calculation formula for the substrate 30 to 33.", "reviewer_2": "The authors made a good effort to address the questions raised by Reviewer 1. However, I still think that the paper is not at all suitable for Nature Communications. Very related results have been published before by Shibata and Gouverneur. I mentioned this before and like to emphasize gain that “they essentially describe analogous results. In both papers PFAS polymers were defluorinated mechanochemically and the obtained fluorides were used for fluorination. The formation of sulfonyl fluorides and other S(VI) compounds was also described. Additionally, in the paper by Shibata the same strategy was used for defluorination, e.g. addition of tBuOK to the ball milling process to give KF.” KF is also formed in the manuscript by Ackermann.\nThe authors claim in their rebuttal letter that the “developed strategy differs from these reports in operational simplicity, product focus, and mechanistic insights, as summarized in the table below.” Essentially, the Shibata method were simply optimized and altered (see Table on the rebuttal letter) to obtain similar fluorinated products. Mechanistic studies also relate to the Gouverneur paper and a paper by Will Dichtel. The new methods that have been applied/developed are very minor, at least when the results should be published in Nature Communications.\nIn addition, a preprint published online before the Shibata publication does not justify publication in a prestigious journal., as suggested by the authors.\nThe studies requested by the authors concerning the black residue after ball milling were inconclusive. I quote them:\n“Results from the 1H- and 13C-NMR spectra for the polymeric PFASs were inconclusive, due to the formation of an insoluble black residue upon completion.”"}, "author_response": "Reviewer #1 (Remarks to the Author):\nThis manuscript has been well revised. Although the authors have made significant efforts to address some of the comments by the authors, there is one improvement necessary for publication.\nComment: On Page 6, Line 111, the author described that 0.3 mmol of PFAS was applied. However, the amount for some substrates seems incorrect. For example, on Page 29 of the SI, 40 mg of PTFE was used, which corresponds to 0.4 mmol when C₂F₄ is considered as the structural unit. The author should check this carefully. It would be helpful if the author could provide the yield calculation formula for the substrate 30 to 33.\nResponse: We thank the reviewer for this observation. For co-polymers 27-31, an excess of PFAS was used (27-30 = 100 mg, 31 = 40 mg) due to a variation of the ratio of the co-polymer segments. This was carried out to ensure that effective defluorination could be achieved for these polymers. For PTFE (32), a slight excess of 2 equiv. (0.4 mmol) was used. This was rectified in the revised manuscript (Fig. 2 caption) and the revised Supporting Information.\nReviewer #2 (Remarks to the Author):\nComment: The authors made a good effort to address the questions raised by Reviewer 1.\nHowever, I still think that the paper is not at all suitable for Nature Communications. Very related results have been published before by Shibata and Gouverneur. I mentioned this before and like to emphasize gain that “they essentially describe analogous results. In both papers PFAS polymers were defluorinated mechanochemically and the obtained fluorides were used for fluorination. The formation of sulfonyl fluorides and other S(VI) compounds was also described. Additionally, in the paper by Shibata the same strategy was used for defluorination, e.g. addition of tBuOK to the ball milling process to give KF.” KF is also formed in the manuscript by Ackermann. The authors claim in their rebuttal letter that the “developed strategy differs from these reports in operational simplicity, product focus, and mechanistic insights, as summarized in the table below.” Essentially, the Shibata method were simply optimized and altered (see Table on the rebuttal letter) to obtain similar fluorinated products. Mechanistic studies also relate to the Gouverneur paper and a paper by Will Dichtel. The new methods that have been applied/developed are very minor, at least when the results should be published in Nature Communications. In addition, a preprint published online before the Shibata publication does not justify publication in a prestigious journal., as suggested by the authors.\nThe studies requested by the authors concerning the black residue after ball milling were inconclusive. I quote them: “Results from the 1H- and 13C-NMR spectra for the polymeric PFASs were inconclusive, due to the formation of an insoluble black residue upon completion.”\nResponse: Thank you for your continued feedback and for acknowledging our efforts in addressing the prior comments. We appreciate your emphasis on the contributions by Shibata, Gouverneur, which we have indeed cited. We respectfully stand by the differences outlined in our previous reviewer response, which we believe provides support for the publication of our manuscript in Nature Communications. Regarding the preprint, it was mentioned for chronological context and transparency, as our strategy was already developed before the publication of Shibata and coworkers, and remained unchanged. Further studies into the residual PFAS black powder and the exact mechanism for PFASs containing no hydrogens (e.g. PTFE, PFO) are currently ongoing within our research group. We apologize if this wasn’t made clear in the previous reviewer response."}]

Decision letter