Trifluoroacetic acid

Trifluoroacetic acid
Names
IUPAC name
2,2,2-Trifluoroethanoic acid
Other names
Perfluoroacetic acid
Trifluoroethanoic acid
TFA
Identifiers
76-05-1 Yes
ChEBI CHEBI:45892 
ChEMBL ChEMBL506259 Yes
ChemSpider 10239201 Yes
Jmol-3D images Image
PubChem 6422
RTECS number AJ9625000
UNII E5R8Z4G708 Yes
Properties
C2HF3O2
Molar mass 114.02 g/mol
Appearance colorless liquid
Density 1.489 g/cm3, 20 °C
Melting point −15.4 °C (4.3 °F; 257.8 K)
Boiling point 72.4 °C (162.3 °F; 345.5 K)
miscible
Acidity (pKa) 0.23 [1]
Hazards
MSDS External MSDS
Main hazards Highly corrosive
R-phrases R20 R35 R52/53
S-phrases S9 S26 S27 S28 S45 S61
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazards (white): no codeNFPA 704 four-colored diamond
1
3
1
Flash point −3 °C (27 °F; 270 K)
Related compounds
Related perfluorinated acids
Perfluorooctanoic acid
Perfluorononanoic acid
Related compounds
 Acetic acid
Trichloroacetic acid
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Trifluoroacetic acid (TFA) is an organofluorine compound with the chemical formula CF3CO2H. It is a colorless liquid with a sharp odor similar to vinegar, but stronger in acidity. TFA is an analogue of acetic acid with the three hydrogen atoms replaced by three fluorine atoms. The acidity of TFA is approximately 34,000 times stronger[2] than that of acetic acid due to the electronegativity of the trifluoromethyl group. TFA is widely used in organic chemistry for various purposes.

Synthesis

TFA is prepared industrially by the electrofluorination of acetyl chloride and acetic anhydride, followed by hydrolysis of the resulting trifluoroacetyl fluoride:[3]

CH
3COCl + 4 HF → CF
3COF + 3 H
2 + HCl
CF
3COF + H
2O → CF
3COOH + HF

Where desired, this compound may be dried by addition of trifluoroacetic anhydride.[4]

An older route to TFA proceeds via the oxidation of 1,1,1-trifluoro-2,3,3-trichloropropene with potassium permanganate. The trifluorotrichloropropene can be prepared by Swarts fluorination of hexachloropropene.

TFA occurs naturally in sea water, but only in small concentrations (<200 ng/L).[5][6]

Uses

TFA is the precursor to many other fluorinated compounds such as trifluoroacetic anhydride and 2,2,2-trifluoroethanol.[3] It is a reagent used in organic synthesis because of a combination of convenient properties: volatility, solubility in organic solvents, and its strength as an acid.[7] TFA is also less oxidizing than sulfuric acid but more readily available in anhydrous form than many other acids. One complication to its use is that TFA forms an azeotrope with water (b. p. 105 °C).

TFA is popularly used as a strong acid in peptide synthesis and other organic synthesis to remove the t-butoxycarbonyl protecting group.[8][9]

At a low concentration, TFA is used as an ion pairing agent in liquid chromatography (HPLC) of organic compounds, particularly peptides and small proteins. TFA is a versatile solvent for NMR spectroscopy (for materials stable in acid). It is also used as a calibrant in mass spectrometry.[10]

TFA is used to produce trifluoroacetate salts.[11]

Safety

Trifluoroacetic acid is a corrosive acid but it does not pose the hazards associated with hydrofluoric acid because the carbon-fluorine bond is not labile. Toxic.

See also

References

  1. ↑ Ref 1 in Milne, J. B.; Parker, T. J. (1981). "Dissociation constant of aqueous trifluoroacetic acid by cryoscopy and conductivity". Journal of Solution Chemistry 10 (7): 479. doi:10.1007/BF00652082.
  2. ↑ Note: Calculated from Ka ratio of TFA and acetic acid
  3. ↑ 3.0 3.1 G. Siegemund, W. Schwertfeger, A. Feiring, B. Smart, F. Behr, H. Vogel, B. McKusick (2005), "Fluorine Compounds, Organic", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a11_349
  4. ↑ Wilfred L.F. Armarego and Christina Li Lin Chai. "Chapter 4 - Purification of Organic Chemicals". Purification of Laboratory Chemicals (6th Ed. ed.). doi:10.1016/B978-1-85617-567-8.50012-3.
  5. ↑ "Trifluoroacetate in ocean waters". Environ. Sci. Technol. 36 (1): 12–5. January 2002. Bibcode:2002EnST...36...12P. doi:10.1021/es0221659. PMID 11811478.
  6. ↑ "Trifluoroacetate profiles in the Arctic, Atlantic, and Pacific Oceans". Environ. Sci. Technol. 39 (17): 6555–60. September 2005. Bibcode:2005EnST...39.6555S. doi:10.1021/es047975u. PMID 16190212.
  7. ↑ Eidman, K. F.; Nichols, P. J. (2004). "Trifluoroacetic Acid". In L. Paquette. Encyclopedia of Reagents for Organic Synthesis. New York: J. Wiley & Sons. doi:10.1002/047084289.
  8. ↑ Lundt, Behrend F.; Johansen, Nils L.; Vølund, Aage; Markussen, Jan (1978). "Removal of t-Butyl and t-Butoxycarbonyl Protecting Groups with Trifluoroacetic acid". International Journal of Peptide and Protein Research 12 (5): 258–268. doi:10.1111/j.1399-3011.1978.tb02896.x. PMID 744685.
  9. ↑ Andrew B. Hughes. "1. Protection Reactions". In Vommina V. Sureshbabu, Narasimhamurthy Narendra. Amino Acids, Peptides and Proteins in Organic Chemistry: Protection Reactions, Medicinal Chemistry, Combinatorial Synthesis 4. doi:10.1002/9783527631827.ch1.
  10. ↑ Stout, Steven J.; Dacunha, Adrian R. (1989). "Tuning and calibration in thermospray liquid chromatography/mass spectrometry using trifluoroacetic acid cluster ions". Analytical Chemistry 61 (18): 2126. doi:10.1021/ac00193a027.
  11. ↑ O. Castano, A. Cavallaro, A. Palau, J. C. Gonzalez, M. Rossell, T. Puig, F. Sandiumenge, N. Mestres, S. Pinol, A. Pomar, and X. Obradors (2003). "High quality YBa2Cu3O7 thin films grown by trifluoroacetates metal-organic deposition". Superconductor Science and Technology 16 (1): 45–53. Bibcode:2003SuScT..16...45C. doi:10.1088/0953-2048/16/1/309.