Room-Temperature Defluorination of PTFE and SF6 by Magnesium(0), Magnesium(I), and Magnesium-Dinitrogen Compounds

Abstract

Abstract

The room temperature reductive defluorination/degradation of the PFAS “forever chemical” PTFE, and the extremely potent greenhouse gas SF 6 , has been achieved by their treatment with either the magnesium(0) [{( tBu BDI TCHP )MgNa} 2 ] ( tBu BDI TCHP = [{(TCHP)NC(tBu)} 2 CH] - , TCHP = 2,4,6-tricyclohexylphenyl), magnesium-dinitrogen [K 2 {( Et NON TCHP )Mg} 2 (m-N 2 )] ( Et NON TCHP = 4,5-bis{(TCHP)N}-2,7-diethyl-9,9-dimethylxanthene) or anionic dimagnesium(I) [K 2 {( tBu NON Trip )Mg} 2 ] ( tBu NON Trip = 4,5-bis{(Trip)N}-2,7-di- tert -butyl-9,9-dimethylxanthene, Trip = 2,4,6-triisopropylphenyl) compounds. In all cases, facile E‒F (E = C or S) bond activations occurred, leading to the formation of dimeric, anionic magnesium(II) fluoride products, [{( tBu BDI TCHP )MgF 2 } 2 (m-Na) 2 ], [{( Et NON TCHP )MgF} 2 (m-K) 2 ] and [{( tBu NON Trip )MgF} 2 (m-K) 2 ], respectively. Treatment of two of these with 18-crown-6 led to their de-aggregation, and formation of monomeric magnesium(II) fluorides, viz. [( tBu BDI TCHP )Mg(m-F) 2 Na(k 2 -18-crown-6)] and [( tBu NON Trip )MgFK(k 6 -18-crown-6)]. Analyses of the dark grey, insoluble products resulting from the reductions of PTFE ( viz. PTFE-R) by FTIR spectroscopy, imply they can be formulated as (F 2 C‒CF 2 ) x (FC=CF) y . The outcome of the sulfur component of SF 6 in its reduction reactions could not be determined. This study highlights the utility that low oxidation state magnesium compounds have for the facile degradation of normally inert PFAS, and related fluorinated, chemicals.