Perfluorinated compound

A perfluorinated compound (PFC) is an organofluorine compound containing only carbon-fluorine bonds (no C-H bonds) and C-C bonds but also other heteroatoms. PFCs 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.^[1]

Applications

Many perfluorinated compounds are useful. For example, fluorosurfactants powerfully reduce surface tension by concentrating at the liquid-air interface due to the lipophobicity of fluorocarbons, due to the polar functional group added to the fluorocarbon chain. Elements commonly incorporated into fluorocarbon based compounds include oxygen, such as in the carboxyl group present in some flourosurfactants, and chlorine, in chlorofluorocarbons, which were formerly used as refrigerants, and are presently implicated in ozone degradation). Fluorosurfactants are widely used in the production of teflon and related fluorinated polymers. They have also been used to confer hydrophobic, stain-resisting properties to fabrics and fire-fighting foam.^[2]

Classes of PFCs by functional group

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 halides

• 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

Fluorochloroalkenes

• Chlorotrifluoroethylene, monomer
• Dichlorodifluoroethylene (three isomers), monomers

Perfluoroethers and epoxides

• hexafluoropropylene oxide , precursor to perfluoromethyl vinyl ether (CF₂=CFOCF₃), a useful monomer
• Krytox, perfluorinated polyether used in special greases

Perfluoroalcohols

• Pentafluorophenol, a moderately strong acid

Perfluorinated alcohols are unstable with respect to dehydrofluorination.

Perfluoroamines

• Perfluorotripentylamine (and related derivatives) are found in Fluorinert, electronic coolants.

Perfluoroketones

• Hexafluoroacetone, building block in organofluorine chemistry.

Perfluorocarboxylic acids

• 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 isonitriles

• Trifluoromethylisocyanide, the simplest perfluorinated isonitrile.
• Trifluoromethylacetonitrile, the simplest perfluorinated nitrile

Perfluorosulfonic acids and related derivatives

• Triflic acid, a useful strong acid
• perfluorobutanesulfonic acid (PFBS) used as a replacement for PFOS in 3M's reformulated Scotchgard.
• 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 borates

• Na[B(C₆F₅)₄], salt of a weakly coordinating anion.

Environmental and health concerns

Naturally-occurring

While there are some natural fluorocarbons such as tetrafluoromethane, which has been reported in rocks,^[3] the vast majority are man-made.

Greenhouse gases

Low-boiling perfluoroalkanes are potent greenhouse gases, in part due to their very long atmospheric lifetime. Their use is covered by the Kyoto Protocol.

Fluorosurfactants

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.^[4]

Fluorosurfactants tend to bioaccumulate, since they are extremely stable and can be stored in the bodies of both 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.^[4] 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 data on the human health effects of PFOA were sparse.^[5]

A 2016 study covering 2/3 of drinking water supplies in the United States found unsafe levels of fluorosurfactants were detectable at the minimum reporting levels required by the EPA safety limit of 70 parts per trillion (ng/L) for two types of PFASs: perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) in 194 out of 4,864 water supplies in 33 states across the U.S. Drinking water from 13 states accounted for 75% of the detections, including, in order of frequency of detection: California, New Jersey, North Carolina, Alabama, Florida, Pennsylvania, Ohio, New York, Georgia, Minnesota, Arizona, Massachusetts, and Illinois.^[6] The other third were not studied, firefighting foam being singled out as a major contributor.

Since 2015, the Air Force has been testing 82 former and active military installations nationwide for fluorosurfactants contained in fire fighting foam.^[7] 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.

See also

• Fluorosurfactants
• Fluorocarbons

References

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