Perfluorinated carboxylic acid

Perfluorinated carboxylic acids (PFCAs), or perfluorocarboxylic acids are compounds of the formula CnF(2n+1)CO2H. The simplest example is trifluoroacetic acid. These compounds are organofluorine analogues of ordinary carboxylic acids, but they are stronger by several pKa units and they exhibit great hydrophobic character. Perfluorinated dicarboxylic acids are also known, e.g. C2F4(CO2H)2.[1]

Perfluorononanoic acid, an example of a perfluorinated carboxylic acid (PFCA)

Applications

Trifluoroacetic acid is a widely employed acid, used for example in the synthesis of peptides. Its esters are useful in analytical chemistry.

Longer chain perfluorinated carboxylic acids, e.g. with five to nine carbons, are useful fluorosurfactants and emulsifiers used in the production of Teflon and related fluoropolymers.[1]

Production

These compounds are typically prepared by electrochemical fluorination of the carboxylic acid fluorides followed by hydrolysis:

CnH(2n+1)COF + (2n+1) HF → CnF(2n+1)COF + (2n+1) H2
CnF(2n+1)COF + H2O → CnF(2n+1)CO2H + HF

Environmental Concerns

Larger PFCAs such as perfluorooctanoic acid (PFOA) are under scrutiny because they are extremely persistent and bioaccumulative, although it is unclear whether their presence poses a risk.[2][3] Short-chain PFCAs (scPFCAs) are formed from atmospheric oxidation of fluorotelomer compounds and chlorofluorocarbon (CFC) replacements introduced as a result of the Montreal Protocol.[4][5]

Common Examples of Perfluorinated carboxylic acids
Name Abbreviation Molecular formula Molecular weight (g/mol) CAS No.
Trifluoroacetic acid TFA CF3COOH 114.023 76-05-1
Perfluoropropanic acid PFPrA C2F5COOH 164.03 422-64-0
Perfluorobutanoic acid PFBA C3F7COOH 214.04 375-22-4
Perfluoropentanoic acid PFPeA C4F9COOH 264.05 2706-90-3
Perfluorohexanoic acid PFHxA C5F11COOH 314.05 307-24-4
Perfluoroheptanoic acid PFHpA C6F13COOH 364.06 375-85-9
Perfluorooctanoic acid PFOA C7F15COOH 414.07 335-67-1
Perfluorononanoic acid PFNA C8F17COOH 464.08 375-95-1
Perfluorodecanoic acid PFDA C9F19COOH 514.08 335-76-2
Perfluoroundecanoic acid PFUnDA C10F21COOH 564.09 2058-94-8
Perfluorododecanoic acid PFDoDA C11F23COOH 614.10 307-55-1
Perfluorotridecanoic acid PFTrDA C12F25COOH 664.10 72629-94-8
Perfluorotetradecanoic acid PFTeDA C13F27COOH 714.11 376-06-7

See also

References
  1. Günter Siegemund, Werner Schwertfeger, Andrew Feiring, Bruce Smart, Fred Behr, Herward Vogel, Blaine McKusick "Fluorine Compounds, Organic" Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2002. doi:10.1002/14356007.a11_349
  2. Houde M, Martin JW, Letcher RJ, Solomon KR, Muir DC (June 2006). "Biological monitoring of polyfluoroalkyl substances: A review". Environ. Sci. Technol. 40 (11): 3463–73. Bibcode:2006EnST...40.3463H. doi:10.1021/es052580b. PMID 16786681.
  3. "Water Pollution Continues At Famous Russian Lake". ScienceDaily. 25 March 2008. Retrieved 11 January 2009.
  4. Ozone layer: Concern grows over threat from replacement chemicals, BBC News 14 May 2020
  5. Heidi M. Pickard, Alison S. Criscitiello, Daniel Persaud, Christine Spencer, Derek C. G. Muir, Igor Lehnherr, Martin J. Sharp, Amila O. De Silva, Cora J. Young (2020-05-28). "Ice Core Record of Persistent Short‐Chain Fluorinated Alkyl Acids: Evidence of the Impact From Global Environmental Regulations". Geophysical Research Letters. 47 (10). doi:10.1029/2020GL087535.CS1 maint: multiple names: authors list (link)
  • Perfluorocarboxylic Acid Content in 116 Articles of Commerce (PDF)
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