Graduate Student Luc Mauro

Most fluorochemicals originate from hydrogen fluoride (HF), a highly toxic gas produced under harsh conditions through the acid digestion of fluorspar (CaF2), a naturally occurring mineral.1 However, CaF2's inherent insolubility in both water and organic solvents has historically hindered its direct use in fluorination.1 Researchers at Oxford University have reported a groundbreaking approach, poised to revolutionize fluorination. Their method bypasses HF production by utilizing mechanochemical synthesis with CaF2, rendering the fluorination process simpler and safer.1 However, CaF2 is a limited resource as in 2022, 8 million metric tons were mined out of the 260 million metric tons global reserves.2 Fortunately, the fluorine contained within CaF2 is minor compared to that in phosphate rock (apatite) which contains over 90% of the total accessible fluorine.2 Interestingly, the fluorine in apatite is an unwanted impurity that is removed and disposed of during the refining process of apatite to phosphoric acid.3 There is potential for this waste byproduct to be used as an alternative fluorine source if recovery and conversion is optimized.3
Other potential fluorine sources could be derived from recycled fluorochemicals. It would be particularly beneficial to recycle perfluoroalkyl substances (PFAS) as they are prevalent environmental pollutants.4 It remains a challenge to efficiently recycle PFAS due to their inert nature.4 The Crimmin lab recently reported a method to convert polytetrafluoroethylene into a magnesium fluoride complex which has been shown to be capable of transferring the fluorine atom.4 With more research, all of these fluorine sources offer a viable alternative to HF derived from CaF2, thus likely increasing the suitability, safety, profitability, and simplicity of fluorination.

References
[1] Patel, C.; André-Joyaux, E.; Leitch, J. A.; de Irujo-Labalde, X. M.; Ibba, F.; Struijs, J.; Ellwanger, M. A.; Paton, R.; Browne, D. L.; Pupo, G.; Aldridge, S.; Hayward, M. A.; Gouverneur, V. Fluorochemicals from fluorspar via a phosphate-enabled mechanochemical process that bypasses HF. Science 2023, 381, 302-306.
[2] U.S. Geological Survey Mineral Commodity Summaries 2023 Data Release. 2023.
[3] Dahlke, T.; Ruffiner, O.; Cant, R. Production of HF from H2SiF6. Procedia Engineering 2016, 138, 231-239.
[4]Sheldon, D. J.; Parr, J. M.; Crimmin, M. R. Room Temperature Defluorination of Poly(tetrafluoroethylene) by a Magnesium Reagent. J. Am. Chem. Soc. 2023, 145, 10486-10490.