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 pK_a of 1.48 indicates that it is a strong acid.^[1]

Pentafluorobenzoic acid

Names
Preferred IUPAC name Pentafluorobenzoic acid
Other names perfluorobenzoic acid
Identifiers
CAS Number	602-94-8
3D model (JSmol)	Interactive image
Beilstein Reference	2054395
ChemSpider	11277
ECHA InfoCard	100.009.115
Gmelin Reference	2054395
PubChem CID	11770
UNII	B4JCP8R5GJ Y
CompTox Dashboard (EPA)	DTXSID4060527
InChI InChI=1S/C7HF5O2/c8-2-1(7(13)14)3(9)5(11)6(12)4(2)10/h(H,13,14) Key: YZERDTREOUSUHF-UHFFFAOYSA-N InChI=1/C7HF5O2/c8-2-1(7(13)14)3(9)5(11)6(12)4(2)10/h(H,13,14) Key: YZERDTREOUSUHF-UHFFFAOYAQ
SMILES Fc1c(c(F)c(F)c(F)c1F)C(=O)O
Properties
Chemical formula	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)
Solubility in water	Very soluble
log P	2.06
Acidity (pKa)	1.60
Hazards
NFPA 704 (fire diamond)	2 0 0
Flash point	87 °C (189 °F; 360 K)
Related compounds
Related carboxylic acids	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]