A new method for utilizing the strongest greenhouse gas

Sulfur hexafluoride (SF6), which is particularly harmful to the environment, has a global warming potential that is 23,900 times higher than that of CO2. Researchers have succeeded in converting this synthesis gas into a reagent and generating compounds with high added value from it.

Sulfur hexafluoride (SF6) is a powerful greenhouse gas. Its global warming potential is 23,900 times that of CO2 and its atmospheric lifetime is 3,200 years. This synthetic gas has been subject to considerable restrictions since the 1997 Kyoto Protocol. Its use in the manufacture of sneakers, for example, has now been banned. However, in the absence of alternative products, it is still used as an electrical insulator for high voltage equipment to prevent arcing. This use accounts for 80% of all SF6 produced. A team from the ICBMS (Institute of Molecular and Supramolecular Chemistry and Biochemistry), in collaboration with the ENS (Ecole Normale Supérieure) of Lyon and the ICR (Institute of Radical Chemistry), has just developed a method to improve SF6 to make compounds with to generate high added value. The results of their research have just been published in the journal International edition of Angewandte Chemie.

Researchers developed a new strategy to activate SF6 by breaking a SF (sulfur-fluorine) bond under mild conditions. Specifically, this gas was brought into contact with an organic molecule in solution, in this case an amine, and then irradiated with blue visible light. This mixture made it possible to obtain an intermediate solid that can be filtered and stored. “While SF6 is a very stable and inert gas, we managed to get it to lose a fluoride and turn it into a reagent: SF5-“ reveals Anis Tlili, researcher at CNRS.

This solid was then used to run two types of reactions. It was first used to introduce fluorine into organic molecules via a deoxyfluorination reaction, with the aim of converting oxygenated products into fluorinated products. This reaction is interesting, for example, for the deoxygenation of biomass products, in particular to convert them into fuel.

Achieve better physicochemical stability

Fluorine greatly alters the properties of the organic compounds that carry it, making it highly sought after. “You should know that about 40% of agrochemicals and 20% of pharmaceuticals contain at least one fluorine, adds the researcher. This incorporation allows certain physico-chemical properties, in particular better stability, to be achieved. For example, when CH (carbon-hydrogen) bonds are replaced by CF (carbon-fluorine) bonds in pharmaceuticals, this change makes them more stable and prevents possible under-reactions in the human body. »

The second reaction developed from this solid is the insertion of the fluorinated group SF5 into organic compounds. This grouping is very popular for the reasons mentioned above, but there are few methods to incorporate it. The advantage of this reaction is therefore to obtain this group starting from a greenhouse gas. “We killed two birds with one stone from this very environmentally harmful inert gas and proved that we can win potentially interesting products in all areas of life science.”says Anis Tlili.

This research work continues, in particular to try to carry out the reactions on a larger scale than that of the laboratory. The scientists also want to try to obtain other intermediate molecules that are even more stable and have other potential applications.

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