Room Temperature Defluorination of Poly(tetrafluoroethylene) by a Magnesium Reagent

Abstract

Perfluoroalkyl substances (PFAS) are pervasive in the environment. The largest single use material within the PFAS compound class is poly(tetrafluoroethylene) (PTFE), a robust and chemically resistant polymer. Despite their widespread use and serious concerns about their role as pollutants, methods for repurposing PFAS are rare. Here we show that a nucleophilic magnesium reagent reacts with PTFE at room temperature, generating a molecular magnesium fluoride which is easily separated from the surface-modified polymer. The fluoride in turn can be used to transfer the fluorine atoms to a small array of compounds. This proofof-concept study demonstrates that the atomic fluorine content of PTFE can be harvested and reused in chemical synthesis.

Main group metal-mediated strategies for C–H and C–F bond activation and functionalisation of fluoroarenes

“…Interestingly when assessing the reactivity of Ae[N(SiMe 3 ) 2 ] 2 /PhSiH 3 mixtures towards uorobenzene it was found that while the Ba amide can promote the hydro-deuorination reaction aer 6 h at 120 °C (85% conversion), the lighter Sr and Ca amides provided reduced conversions of 54% and 11% respectively under the same conditions (Scheme 13b), evidencing a clear correlation between the metal size and their conversion rates. 55 Related to this work, Okuda and Maron have also reported the ability of dicationic dimeric Ca hydride complex [(Me (43) along with benzene. 57 Forcing reaction conditions are required (two days at 60 °C) to promote this hydro-deuorination process which is proposed to occur via a nucleophilic aromatic substitution mechanism.…”

“…More recently this reactivity has been extended to room temperature deuorination of polyuoroalkyls such as poly(tetrauoroethylene) (PTFE) using [( Mes Nacnac)Mg-Mg( Mes Nacnac)] ( 19) (Mes = 2,4,6-trimethylphenyl) in combination with 4-(dimethylamino)pyridine (DMAP) generating molecular magnesium uoride which can be used as a viable uorinating agent. 43 An 24) with concomitant elimination of NaF. Contrasting with previous studies using Mg(II) complex 20, containing a strongly reducing {C 6 H 6 } 2− anion, which required the use of forcing reaction conditions (5 days, 100 °C), 44 the C-F bond activation of uorobenzene using 23 occurs rapidly at room temperature (10 min, 20 °C), highlighting the enormous difference in reactivity on these two related Mg complexes where Mg displays different oxidation states.…”

“…More recently this reactivity has been extended to room temperature defluorination of polyfluoroalkyls such as poly(tetrafluoroethylene) (PTFE) using [( Mes Nacnac)Mg–Mg( Mes Nacnac)] ( 19 ) (Mes = 2,4,6-trimethylphenyl) in combination with 4-(dimethylamino)pyridine (DMAP) generating molecular magnesium fluoride which can be used as a viable fluorinating agent. 43…”

“…Many other main-group metal mediated protocols, with the exception of the high reactivity shown by Mg(0) complex 23 (Scheme 7), 44 require the use of harsh reaction conditions, irradiation or transition-metal catalysis. 43,51 For example, using [Pd(PCy 3 ) 2 ] as pre-catalyst, efficient and selective C–F alumination of fluorobenzene can be achieved using Roesky's Al( i ) complex 14 in just 5 min while operating at ambient temperature (Scheme 11). 51 c Combining experimental studies with DFT calculations, mechanistic insights have been gained implying the involvement of heterobimetallic species such as {Pd[( Dipp Nacnac)Al] 2 } ( 36 ) as on-cycle intermediates during the catalysis.…”

Trendbericht Anorganik 2024: Hauptgruppen‐ und Molekülchemie

“…Das entstehende Magnesiumfluorid ist gut abzutrennen und eignet sich für Fluorierungsreaktionen (Abbildung 5). 6) Ein Magnesiumhydridcluster von Kretschmer und Team überrascht mit einem Hydridion in nahezu quadratisch-planarer Koordinationsumgebung (Abbildung 6). Die Koordinationszahl 4 ist außerdem die höchste bisher beobachtete Koordinationszahl für Hydride dieser Verbindungsklasse.…”