Removing fluorines from chemicals = greener CFCs?

Removing stubborn fluorines detoxifies CFCs.

Jun 17, 2010

Douvris, C, CM Nagaraja, C-H Chen, BM Foxman and OV Ozerov. 2010. Hydrodefluorination and other hydrodehalogenation of aliphatic carbon-halogen bonds using silylium catalysis. Journal of the American Chemical Society 132(13):4946-4953.

Synopsis by Adelina Voutchkova
A new method for removing fluorines from fluorinated chemicals offers a promising method to detoxify some types of organohalogen pollutants, such as CFCs.

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A new method to take the fluorine atoms off of fluorinated chemicals may be a promising way to detoxify them, according to an article published in the Journal of the American Chemical Society.

The new method would selectively remove fluorines from chemicals, such as chlorofluorocarbons (CFCs), a class of compounds notorious for causing global warming. Removal of fluorines is considered highly challenging as fluorine atoms are known to bind very strongly to a molecule’s carbon framework.

The method could be more broadly applied to other organofluorines, including perfluorinated compounds (PFCs) such as PFOA and PFOS. PFOA is a chemical used in nonstick cookware and PFOS was used in anti-stain fabrics and water resistant coatings. They do not biodegrade and can only be partially recycled, therefore, defluorination to polyethylene (nylon) would be one strategy to avoid accumulation of PFCs.

Many organofluorine compounds have been banned or removed from manufacturing or industrial use due to their severe potential hazard. CFCs, for instance, were taken out of refrigerants because they can destroy the Earth’s protective ozone layer. Some others that were phased out include polychlorobiphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF). The compunds contaminate the environment and contribute to global problems. CFCs and some of their chemical cousins that replaced them have tremendous global warming potentials. So much so they have been called “super-greenhouse gases.”

In addition, harmful derivatives of these chemicals can persist in the environment where they travel through food chains and accumulate in animals and people. The health effects associated with the compounds are varied but include cancer, reproductive problems and developmental changes.

Removal of fluorines from chemicals – a process called defluorination – has been generally viewed as a way to neutralize existing over stocks of these chemicals.

Researchers from Texas A&M and Brandeis University developed the chemical defluorination technique. They used silicon and boron-containing solids to efficiently defluorinate CFCs under mild conditions.

Although this is an advancement, the technology has some significant drawbacks. The process requires large amounts of a sacrificial chemical to abstract the fluorine. The disposal of this by-product would itself be problematic, and there is no evidence it can be recycled. In addition, the report indicates that tetrafluoromethane, the smallest fluorinated chemical and commonly used in refrigerants, resists defluorination under research conditions.

Future endeavours will undoubtedly be aimed towards developing defluorination processes that overcome these drawbacks.