A perfluorinated compound (PFC) per- or polyfluoroalkyl chemical is an organofluorine compound containing only carbon-fluorine bonds (no C-H bonds) and C-C bonds but also other heteroatoms. PFCs, also known as perfluorinated chemicals, have properties that represent a blend of fluorocarbons (containing only C-F and C-C bonds) and the parent functionalized organic species. For example, perfluorooctanoic acid functions as a carboxylic acid but with strongly altered surfactant and hydrophobic characteristics. Fluorosurfactants are ubiquitously used in teflon, water resistant textiles and fire-fighting foam.
Perfluorinated compounds are used ubiquitously: For example, fluorosurfactants are widely used in the production of teflon and related fluorinated polymers. They have been used to confer hydrophobicity, stain-resistance to fabrics and as fire-fighting foam. Fluorosurfactants powerfully reduce surface tension by concentrating at the liquid-air interface due to the lipophobicity of fluorocarbons. Chlorofluorocarbons were formerly used as refrigerants until they were implicated in ozone degradation.
Fluorine-containing compounds are derived from the mineral fluorspar, which is the chemical compound CaF2. There are examples of organisms that possess fluorine-containing compounds in their biochemistry and examples where organisms can be used to synthesize fluorinated compounds, but the vast majority are man-made. The synthesis of perfluorinated compounds involves the use of F2 and HF reagents that are derived from natural product CaF2. A common industrial method for synthesizing perflurocompounds involves direct fluorination of organic compounds using F2 gas, where C-H bonds are replaced by C-F bonds accompanied by the formation of HF.
Classes of PFCs by functional groupEdit
Representative members of this large family of compounds are listed below. Also numerous are compounds that contain many fluoride centers but also some hydrogen, e.g., trifluoroethanol.
Perfluorinated alkyl and aryl halidesEdit
- Trifluoroiodomethane, an alkylating agent
- Pentafluoroethyl iodide, an alkylating agent
- Perfluorooctyl bromide (perflubron) is a contrast medium for magnetic resonance imaging, computer tomography and sonography. It has also been used in liquid breathing.
- Dichlorodifluoromethane, refrigerant
Perfluoroethers and epoxidesEdit
- Hexafluoropropylene oxide, precursor to perfluoromethyl vinyl ether (CF2=CFOCF3), a useful monomer
- Krytox, perfluorinated polyether used in special greases
- Pentafluorophenol, a moderately strong acid
Primary and secondary perfluorinated alcohols are unstable with respect to dehydrofluorination.
- Hexafluoroacetone, building block in organofluorine chemistry.
- Trifluoroacetic acid, a moderately strong acid useful in organic chemistry
- Heptafluorobutyric acid, a moderately strong acid that is useful in organic and analytical chemistry
- Pentafluorobenzoic acid, a moderately strong acid of interest in research community
- Perfluorooctanoic acid (PFOA), surfactant used to make fluoropolymers such as Teflon
- Perfluorononanoic acid (PFNA), surfactant in the emulsion polymerization of fluoropolymers, like PFOA.
Perfluoronitriles and isonitrilesEdit
- Trifluoromethylisocyanide, the simplest perfluorinated isonitrile.
- Trifluoromethylacetonitrile, the simplest perfluorinated nitrile
- Triflic acid, a useful strong acid
- perfluorobutanesulfonic acid (PFBS) used as a replacement for PFOS in 3M's reformulated Scotchgard.
- perfluorobutane sulfonamide (FBSA), sulfonamide derivative of PFBS.
- perfluorooctanesulfonyl fluoride (POSF), precursor to PFOS-based compounds.
- perfluorooctanesulfonamide (PFOSA), used in 3M's Scotchgard formulation.
- perfluorooctanesulfonic acid (PFOS), used in the semiconductor industry, 3M's former Scotchgard formulation, and 3M's former fire-fighting foam mixture.
Perfluorinated aryl boratesEdit
- Na[B(C6F5)4], salt of a weakly coordinating anion.
Environmental and health concernsEdit
There are several examples of environmental and health concerns around the industrial production and use of perfluoroalkane compounds. The unique chemical stability of perfluorinated compounds is desirable, and many times required, for many material applications but is also cause for environmental and health concerns.
Low-boiling perfluoroalkanes are potent greenhouse gases, in part due to their very long atmospheric lifetime. The environmental concerns for perflurocompounds are similar to chlorofluorocarbons and other halogenated compounds used as refrigerants and fire suppression materials. The history of use, environmental impact, and recommendations for use are included in the Kyoto Protocol.
The fluorocarbons PFOA (perfluorooctanoic acid) and PFOS (perfluorooctane sulfonate) have both been investigated by the EU and the United States Environmental Protection Agency (EPA) which regards them being harmful to the environment. Specifically, studies found that PFOS caused "unusual and serious effects in animal toxicity tests," that it was present around the world in humans and wildlife, and that it was highly persistent in the environment. (Similar concerns followed for PFOA.)
Fluorosurfactants tend to bioaccumulate, since they are extremely stable and can be stored in the bodies of humans and animals. Examples include PFOA and PFOS, frequently present in water resistant textiles and sprays conferring water resistant properties to textiles and fire-fighting foam. Data from animal studies of PFOA indicate that it can cause several types of tumors and neonatal death and may have toxic effects on the immune, liver, and endocrine systems. As of 2010[update] data on the human health effects of PFOA were sparse.
As of 2015, the U.S. Air Force had been testing 82 former and active US military installations for fluorosurfactants contained in fire fighting foam. In 2015, PFCs were found in groundwater at Naval Air Station Brunswick, Maine and Grissom Air Reserve Base, Indiana, and in well water at Pease Air Force Base, New Hampshire, where 500 people including children had blood tests as part of a bio-monitoring plan through the state Department of Health and Human Services. The U.S. Department of Defense's research programs have been trying to define nature and extent of PFAS contamination at U.S. military sites, especially in groundwater.
A 2016 study found unsafe levels of fluorosurfactants in 194 out of 4,864 water supplies in 33 U.S. states. Covering two-thirds of drinking water supplies in the United States, the study found thirteen states accounted for 75% of the detections. In order of frequency, these were: California, New Jersey, North Carolina, Alabama, Florida, Pennsylvania, Ohio, New York, Georgia, Minnesota, Arizona, Massachusetts, and Illinois. Firefighting foam was singled out as a major contributor.
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The U.S. manufacturer of PFOS voluntarily phased out production of PFOS after reporting substantial risks to the Environmental Protection Agency under requirements of the Toxic Substances Control Act. Following this, the EPA used its "significant new use authority" under TSCA to strictly limit 270 PFOS-related chemicals. Not long after concerns arose around PFOA, after which the EPA launched a voluntary industry program for voluntary reduction of global PFOA emissions (reduced 95% by 2010 and eliminated entirely by 2015), to which eight major companies committed.
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- Strategic Environmental Research and Development Program (SERDP), Environmental Security Technology Certification Program (ESTCP) Per- and Polyfluoroalkyl Substances (PFASs): Analytical and Characterization Frontiers webinarslides, January 28, 2016
- Lustgarten, Abrahm (2018-06-20). "Suppressed Study: The EPA Underestimated Dangers of Widespread Chemicals". ProPublica. Lisa Song, Talia Buford. Retrieved 2018-06-23.
- Associated Press (2017-07-31). "Air Force won't pay for towns' water contamination costs". Air Force Times. Retrieved 2018-06-23.
- Above the minimum reporting levels required by the EPA − 70 parts per trillion (ng/L) for PFOS and PFOA
- Unsafe levels of toxic chemicals found in drinking water for 6 million Americans Science X network, phys.org, August 9, 2016
- Media related to Perfluorinated compounds at Wikimedia Commons