Pentafluorobenzoic acid

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 ;
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

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]

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

^ ^a ^b ^c Prakash, G. K. S.; Hu, J. "Pentafluorobenzoic Acid" in e-EROS Encyclopedia of Reagents for Organic Synthesis, 2005. doi:10.1002/047084289X.rn00682
^ Harper, 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.
^ 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.

[Prakash-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] Harper, 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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