Commonly known as “forever chemicals,” PFAS are notorious for persisting in the environment and our bodies. Osaka Metropolitan University chemists may end the “forever” life of PFAS with their simple yet innovative technique that converts these harmful substances into valuable compounds.
Scientists have found a new way to change N-heterocyclic carbenes (NHCs), chemicals often used to make reactions happen faster. The new way involves adding fluorine atoms to the NHC, which changes how the chemical behaves and makes it better at helping some reactions happen.
The research group was led by Professor Masato Ohashi and Assistant Professor Kenichi Michigami of the Graduate School of Science at Osaka Metropolitan University. It has successfully synthesized ligands called fluorine-decorated N-heterocyclic carbenes (NHCs) from perfluoroalkenes, a type of PFAS (Perfluoroalkyl and Polyfluoroalkyl Substances). The NHCs developed in this study play significant roles in stabilizing unstable molecules and enhancing the performance of their ligated transition metal complexes.
This is the first time NHCs have been made with many fluorine atoms attached. The new way is based on a reaction between a sodium formamidinate and another chemical called tetrafluoroethylene. The product of this reaction is then mixed with a third chemical called lithium tetrafluoroborate to make a 4,5-difluorinated imidazolium salt. This salt can then be turned into a 4,5-difluorinated NHC.
The scientists also found that they could use the same method to attach other groups of fluorine atoms to the NHC. This led to the creation of two new kinds of NHCs.
Studying PFAS and NHCs
When the scientists studied these new NHCs and their related chemicals, they found that the fluorine atoms made the NHCs act as electron donors, which was unexpected. This is because the fluorine atoms have a positive mesomeric effect, which means they can share electrons with other atoms. However, the rings attached to the NHCs are electron acceptors because they have a negative inductive effect, which means they pull electrons away from other atoms.
The new NHCs were also found to be better catalysts than traditional NHCs in both simple and complex reactions. This is because they can accept more electrons from other chemicals.
Finally, the scientists found that the amount of space that the new NHCs take up is similar to the amount of space that traditional NHCs take up. This means that adding fluorine atoms to the NHCs does not significantly change the size of the molecule.
“Our results enable the easy transformation of harmful PFAS into functional NHCs,” explained Dr. Michigami. “The versatile applications of fluorinated NHCs show potential advantages in various fields such as fluorine chemistry, organometallic chemistry, catalysis chemistry, and materials science.”
Their findings were published in the Journal of the American Chemical Society.
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