Pentafluorobenzoic acid

Pentafluorobenzoic acid (PFBA) is an organofluorine compound with the formula C6F5CO2H. It is a white crystalline powder that has a high solubility in water. Its pKa of 1.48 indicates that it is a strong acid.[1]

Pentafluorobenzoic acid
Names
IUPAC name
2,3,4,5,6-pentafluorobenzoic acid
Other names
perfluorobenzoic acid
Identifiers
3D model (JSmol)
2054395
ChemSpider
ECHA InfoCard 100.009.115
2054395
Properties
C7HF5O2
Molar mass 212.075 g·mol−1
Appearance White crystalline powder
Density 1.942 g/cm3
Melting point 100–102 °C (212–216 °F; 373–375 K)
Boiling point 220 °C (428 °F; 493 K)
Very soluble
log P 2.06
Acidity (pKa) 1.60
Hazards
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
0
2
0
Flash point 87 °C (189 °F; 360 K)
Related compounds
benzoic acids,
Nitrobenzoic acids
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Preparation

Pentafluorobenzoic acid is prepared by treating pentafluorophenyllithium (or pentafluorophenyl Grignard reagent) with carbon dioxide. These reagents are usually prepared in situ from pentafluorobenzene and bromopentafluorobenzene.[1][2]

It arises via the reaction of perfluorotoluene with trifluoroacetic acid and antimony pentafluoride.[3]

Substitution reactions

Substitution of fluoride occurs typically at the para position. This reaction has been used to anchor the −C6F4CO2H group to surfaces. Magnesium methoxide results in ortho methoxylation. Cleavage of this ether gives tetrafluorosalicylic acid. Via similar ortho-directed reactivity, nickel complexes catalyse the defluoridation of 2 and 5 positions. Without nickel, defluoridation occurs with para-selectivity.[1]

References
  1. Prakash, G. K. S.; Hu, J. "Pentafluorobenzoic Acid" in e-EROS Encyclopedia of Reagents for Organic Synthesis, 2005. doi:10.1002/047084289X.rn00682
  2. Haper, R. J.; Jr; Soloski, E. J.; Tamborski, C. (1964). "Reactions of Organometallics with Fluoroaromatic Compounds". J. Org. Chem. 29 (8): 2385. doi:10.1021/jo01031a067.
  3. Zonov, Yaroslav V.; Karpov, Victor M.; Platonov, Vyacheslav E. (2007). "Transformation of perfluorinated benzocycloalkenes and alkylbenzenes to their carbonyl derivatives under the action of CF3COOH/SbF5". Journal of Fluorine Chemistry. 128 (9): 1058–1064. doi:10.1016/j.jfluchem.2007.05.020.
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