�Everybody loves the way breakfast egg conveniently slide off of Teflon without leaving whatever pesky pieces of eggs in the pan. Indeed, the carbon-fluorine bond at the heart of Teflon cookware is so helpful we too use it in wear, lubricants, refrigerants, anesthetics, semiconductors, and regular blood substitutes. But the very strength of the C-F chemical bond that makes it useful in so many applications also gives it unnerving greenhouse throttle effects that persist in nature. In a groundbreaking ceremony study in Science, Brandeis scientists report they have identified a catalyst that efficiently breaks the C-F bond and converts it to a carbon-hydrogen bond, rendering it harmless to the environment.
Chlorofluorocarbons (CFCs or freons) are harmful to the ozone layer. Hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs) are generating concern because they are considered super-greenhouse gases, with great potency to warm the surround by trapping solar radiation and remaining virtually undestroyable in the atmosphere.
"The C-F bond is difficult to transform into other bonds under meek conditions because it is inert and unreactive; it's a challenge to chemists," said lead author chemist Oleg Ozerov, who conducted the research with postdoc Christos Douvris. "But we found a way to take a C-F bond certificate that you can do very little with and break it and convert it cleanly into something else at room temperature."
With research support from the Department of Energy, Sloan Foundation, and Research Corporation, Ozerov identified a new catalytic process for a class of carborane-silylium compounds that causes the bonds in representative HFCs to react at room temperature, swapping their carbon-fluorine bonds for carbon-hydrogen bonds. The silylium catalyst performs the critical job of breakage the C-F bond by abstracting the fluoride from the fluorocarbon and attaching it to a atomic number 14 atom. The end product is a compound with a silicon-fluorine bond, which is no longer a greenhouse threat.
This finding could eventually spark advance to large-scale reactions to convert environmental pollutants that contain C-F bonds into products that could be reused or destroyed without special equipment.
"Conversion of PFCs remains a challenge, and our enquiry efforts ar directed at designing even more active catalysts, capable of PFC activation," said Ozerov.
Source: Laura Gardner
Brandeis University
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Wednesday, 3 September 2008
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