Perfluoroalkyl carboxylic acids
Perfluoroalkyl carboxylic acids (PFCAs), or perfluorocarboxylic acids are compounds of the formula CnF(2n+1)CO2H that belong to the class of per- and polyfluoroalkyl substances. 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. Perfluoroalkyl dicarboxylic acids (PFdiCAs) are also known, e.g. C2F4(CO2H)2.[1]
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 perfluoroalkyl carboxylic acids, e.g. with five to nine carbons, are useful fluorosurfactants and emulsifiers used in the production of polytetrafluoroethylene (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
Long-chain PFCAs such as perfluorooctanoic acid (PFOA) are either banned or being under scrutiny because they are extremely persistent and bioaccumulative. Short-chain PFCAs (scPFCAs) are formed from atmospheric oxidation of fluorotelomer compounds and chlorofluorocarbon (CFC) replacements introduced as a result of the Montreal Protocol.[2][3]
Common examples of perfluoroalkyl carboxylic acids
| Name | Abbreviation | Molecular formula | Molecular weight (g/mol) | CAS No. |
|---|---|---|---|---|
| Trifluoroacetic acid | TFA | CF3COOH | 114.02 | 76-05-1 |
| Perfluoropropanoic 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
- ^ a b 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
- ^ Ozone layer: Concern grows over threat from replacement chemicals, BBC News 14 May 2020
- ^ 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.
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External links
- OECD, ed. (2022), "2. Perfluoroalkyl carboxylic (a) and dicarboxylic (b) acids", Fact Cards of Major Groups of Per- and Polyfluoroalkyl Substances (PFASs), OECD Environment, Health and Safety Publications 68 Series on Risk Management, pp. 16–30
- Perfluorocarboxylic Acid Content in 116 Articles of Commerce (PDF)