Researchers at Brandeis University have presented a paper that offers renewed hope in finding commercially viable routes to the successful breakdown of fluorinated compounds such as CFC and some well known surfactant and fluorinated polymers namely perfluorooctanesulfonic acid derivatives (PFOS) (this particular class of compound has shown itself to be toxic and highly persistent), which all lead to global warming [Douvris et al., Science (2008) 321, 1188].
The carbon to fluorine bond is the strongest single bond to carbon, making it one of the most unreactive functionalities in chemistry, their reactivity and performance under various conditions is still poorly realized; organic fluorines also have very poor kinetic properties and act as weak ligands or Lewis bases. Taking these observations further fully fluorinated (perfluoroalkyl) groups are observed to be even more inert than compounds containing a single carbon to fluorine bond. Due to the increase in strength of the carbon to fluorine bond with increasing degrees of fluorination, shortening of the carbon to fluorine bond which results in greater shielding of the carbon atom.
The simplest modification of the carbon to fluorine bond is conversion to the simple carbon to hydrogen bond, this conversion is known as hydrodefluorination or HDF. The methodology usually involves the use of highly reducing metal agents or catalysts to cleave the carbon to fluorine bond. Conversion to carbon carbon bonds is also possible but the research within this field is still in its infancy. Douvris et al decided on a variation to the use of a reducing metal agent and used instead a silylium Lewis acid, which provides a more favorable reaction dynamic.
The researchers are conducting further studies to further understand the reaction dynamics at play. The overall viability of this process will depend on cheaper sources of silane and the ability to remove Lewis-basic impurities from the substrate, if this is possible it could lead to larger scale reactions, in a bid to securing a commercially viable route to hydrodefluorination.